Lock-and-key model

Lock-and-key model definition example

strong>Lock-and-key model n., [lɑk ænd ki ˈmɑdl̩] Definition: a model for enzyme-substrate interaction

Table of Contents

Lock-and-key model Definition

Lock-and-key model is a model for enzyme-substrate interaction suggesting that the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. In this model, enzymes are depicted as highly specific. They must bind to specific substrates before they catalyze chemical reactions . The term is a pivotal concept in enzymology to elucidate the intricate interaction between enzymes and substrates at the molecular level. In the lock-and-key model, the enzyme-substrate interaction suggests that the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. Like a key  into a  lock , only the correct size and shape of the substrate ( the key ) would fit into the  active site  ( the keyhole ) of the enzyme ( the lock ).

Compare: Induced fit model   See also: enzyme , active site , substrate

Lock-and-key vs. Induced Fit Model

At present, two models attempt to explain enzyme-substrate specificity; one of which is the lock-and-key model , and the other is the Induced fit model . The lock and key model theory was first postulated by  Emil Fischer   in 1894. The lock-and-key enzyme action proposes the high specificity of enzymes. However, it does not explain the stabilization of the transition state that the enzymes achieve. The induced fit model (proposed by Daniel Koshland in 1958) suggests that the active site continues to change until the substrate is completely bound to the active site of the enzyme, at which point the final shape and charge are determined. Unlike the lock-and-key model, the induced fit model shows that enzymes are rather flexible structures. Nevertheless, Fischer’s Lock and Key theory laid an important foundation for subsequent research, such as during the refinement of the enzyme-substrate complex mechanism, as ascribed in the induced fit model. The lock-and-key hypothesis has opened ideas where enzyme action is not merely catalytic but incorporates a rather complex process in how they interact with the correct substrates with precision.

Lock and key model definition and example

Key Components

Components of the lock and key model:

  • Enzyme : the enzyme structure is a three-dimensional protein configuration, with an active site from where the substrate binds.
  • Substrate : often an organic molecule, a substrate possesses a structural feature that complements the geometry of the enzyme’s active site.

In the lock and key model, both the enzymes and the substrates facilitate the formation of a complex that lowers the activation energy needed for a chemical transformation to occur. Such reduction in the activation energy allows the chemical reaction to proceed at a relatively faster rate, making enzymes crucial in various biological and molecular processes.

Lock-and-key Model Examples

Some of the common examples that are often discussed in the context of the Lock and Key Model are as follows:

  • Enzyme lactate dehydrogenase with a specific active site for its substrates, pyruvate and lactate. The complex facilitates the interconversion of pyruvate and lactate during anaerobic respiration
  • Enzyme carbonic anhydrase with a specific active site for the substrates carbon dioxide and water. The complex facilitates the hydration of carbon dioxide, forming bicarbonate
  • Enzyme lysozyme binding with a bacterial cell wall peptidoglycan, which is a vital immune function

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  • Aryal, S. and Karki, P. (2023).  “Lock and Key Model- Mode of Action of Enzymes”. Microbenotes.com. https://microbenotes.com/lock-and-key-model-mode-of-action-of-enzymes/
  • Farhana, A., & Lappin, S. L. (2023, May).  Biochemistry, Lactate Dehydrogenase . Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK557536/

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Last updated on January 11th, 2024

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Leon Trotsky

The moscow “confessions”.

Written: 18 December 1936. First Published: The Red Flag [London], March-April 1937. Translated: The Red Flag Transcription/HTML Markup: Martin Fahlgren Public Domain: Leon Trotsky Internet Archive 2008; This work is completely free. In any reproduction, we ask that you cite this Internet address and the publishing information above.

Despite all obstacles, truth hews out a way. The whole trial rests on confessions that are surprising in their crudeness and teeming with psychological contradictions. In order to understand the value of these standardised “confessions” by the clients of the G.P.U. one must begin by examining the standardised political capitulations, of which the “confessions” are the sequel and the immediate development. The history of the capitulations extends over the last thirteen years, and would, with the “human” documents, furnish matter for many dozens of volumes.

The content of the confessions in no way corresponds with the characteristics of a “crime,” whether carried out or not; rather it corresponds with the diverse needs of the Government. That is why the public confessions have a purely ritualistic, standardised character. Their sole political significance is to teach everyone to think, or at least to express himself, uniformly. But precisely for this reason no one among the persons in question has taken these “repentances” seriously. These confessions are not real confessions but a contract signed with the bureaucracy. The proof of this is that even I. N. Smirnov, one of the most sincere and honourable of men, in 1929 drew up in the space of a few weeks several different texts of confessions which were in flagrant contradiction with one another. (These texts were published at the time in the Bulletin de l’Opposition .) I must add that nearly all the confessions (tens of thousands of them) belonging to the thermidorean period had but one single object, namely, to attack me personally. In order to be received back into the bosom of the great family of the bureaucracy, or to assure himself at least the right to a morsel of bread, each oppositionist, semi-oppositionist, or even mere citizen, was compelled on all occasions to denounce Trotskyism and condemn Trotsky. The more startling the manner of these denunciations the more success they had. Confessions and renunciations have become for them very like the rituals of the church. Thus political confessions have paved the way for judicial confessions which are their inevitable consequence.

I repeat, these lines are being written in the claws of the Norwegian “Socialist” government. I am forced to confine myself to the most important facts. We must throw into relief particularly the following points:

1. It is false that “all 16 accused” have admitted their crime. There were not 16 accused who participated in a crime of the same nature or who were even suspected of a like crime. In actual fact the sixteen men in the dock had been meticulously chosen from among many hundreds, many thousands of “candidates.” Only those who had proved their aptitude for publicly fulfilling the role which had been assigned to them were in the first instance made to appear before the tribunal. (On this subject see the Livre Rouge .)

2. Did the G.P.U. use medical or chemical methods of compulsion? I do not know. But such a hypothesis is not necessary. It is enough to know the facts, the persons, and the circumstances in order to understand how the accused could have been forced to put the rope around their own necks. Among the accused there was not a single oppositionist or Trotskyist. They were all capitulators, persons who had confessed on many occasions, accusing themselves in their confessions of the most shameful actions and the lowest instincts; persons who had renounced all political conceptions, all reason for living, all personal dignity. (Of course, I am not speaking of real provocateurs , lost in the clutches of the G.P.U..) For years these ex-revolutionaries, demoralised and morally broken, had flitted hither and yon between life and death. Were narcotics still necessary? The very idea (which Rosenmark takes responsibility for) that these people had been spurred on by a thirst for power is absurd. They had renounced it long since. The idea that these people, who had renounced their programme, their banner, their personal dignity, who had many a time publicly covered themselves with mortification and calumny, could hope to attain power by political assassinations would seem an idiotic political conception.

“G.P.U. has Revolvers”

No, at the trial the accused gave themselves the lie as they had done before in their innumerable confessions. The G.P.U. took plenty of time to extort from its victims increasingly complete “confessions.” Today “A” admitted a little “fact.” If “B” does not admit the same thing it implies that all his past confessions and humiliations were “lies” (Stalin’s favourite word, Stalin the champion of “sincerity”). “B” hastens to admit what “A” has admitted, and even a little more. And now it’s “C’s” turn again. To avoid any overly crude contradictions, they are given the opportunity, if they wish, to elaborate their theme in common. If “D” refuses to associate himself with this he risks losing all hope of saving himself. So he outdoes the others in order to prove his goodwill (reread the stammering and hysterical confessions of Reingold). And now all the others must align their lies with those of “E.” ... The infernal game continues. The accused are under lock and key. The G.P.U. is in no hurry. The G.P.U. has Mauser revolvers. Jules Romains shows (in his Les Creatures ) how it is possible without having any “idea” or “theme” to write a truly poetical work by taking as a point of departure a play on words. The G.P.U. works thus. These gentlemen, having at their disposal neither facts nor a completed plan, construct their amalgam by a play on “confessions.” If one or another of the confessions appears inconvenient in the end, it is quite simply omitted as an unnecessary hypothesis. These “creatures” are free of all ties.

From time to time they give their victims a provisional liberty in order to allow the rebirth of vague hopes. At the first opportunity those who have been freed are arrested once more. Thus ceaselessly tossed between hope and despair these men become little by little the shadow of their former selves.

Nervous Collapse

But still this is not the end. For each one of them there comes a moment when they begin to resist. No, they cannot go to such lengths in denial of themselves. At this point the G.P.U. shoots the most obstinate.

Meanwhile the press unanimously continues to yell against the “traitors,” the “counterrevolutionaries,” the “agents of imperialism,” and so forth. The prisoners have no other press at their disposal than that of Stalin. Physical torture? I think not. The torture of calumny, of uncertainty, and of terror destroys the nervous system of the accused just as surely as physical torture. And one must add the fact of the incessant allusion to the dangers of war. Are you for the fatherland (that is, for Stalin), or against the fatherland? Pravda calls even André Gide’s book an “anti-Soviet witness.” A foreigner of less renown would have been treated long since as an agent of Hitler. What is to be said of the soviet oppositionists? Gide shows how they extorted from him a telegram of praise for Stalin and how the celebrated author was reduced to impotence and ... to capitulation. What shall we say then of the methods of the G.P.U.? Are you for the U.S.S.R. (that is, for Stalin), or against the U.S.S.R.? You have repented of course long ago; you are not dangerous to us as you yourself know; we don’t wish you ill. But Trotsky continues his poisonous work abroad. He continues his sapping exploits against the U.S.S.R. (that is, against the omnipotence of the bureaucracy). His influence is growing. Trotsky must be discredited once and for all. Thus your question resolves itself. If you are for the U.S.S.R. you will help us. If not, all your repentance was a lie. In view of the approaching war we shall be forced to consider you as agents of Trotsky, as foreign enemies of the country. You must admit that Trotsky has pushed you on to the path of terror. But no one will believe it!—Oh! we will undertake this aspect of the question. We have our Duclos and our Thorez, our Pritts and our Rosenmarks. Has Trotsky pushed you onto the path of terror, yes or no? He who replied “Yes” is ready to allow himself to be used further.

By repeating the questions endlessly, the replies can be made increasingly concrete. Smirnov and Goltzman tried to stop themselves in mid-road, between “terror in general” and the assassination of Kirov.

Others (but not all) went further. Whoever resisted was liquidated in the course of the “technical” preparation of the trial. The man against whom violence was successful was led on the scene to be presented to the eyes of Pritt in the capacity of an impartial expert.

Is it possible to talk to any honourable person about these “confessions” and neglect the fact that for years the G.P.U. has prepared and “questioned” the accused with the help of periodic capitulations, humiliations, self-degradation, calumnies, and also by means of reprisals? Only complete fools can shut their eyes to these facts. [1]

The story of this unfortunate sailor is but a tiny episode taken from the book of the confessions of the accused—and of their accusers and their judges. From being the instrument of the revolution, the G.P.U. has become the instrument of the soviet aristocracy, the personal instrument of Stalin, about whom Lenin warned in 1922: “This cook will prepare only peppery dishes.”

The statement that the accused admitted the facts which incriminated them independently of one another is a triple lie. There is no material proof of the confessions. The accused abandoned themselves to self-accusations and summary denunciations. They were utterly terrified that these accusations should be made more precise. It is not by chance that each time one of the accused, in order to support the logic of his own confessions, tried to make the times and places definite, the G.P.U. fell into contradictions that were only too crying. As far as the concrete elements of their own confessions are concerned, the accused contradicted themselves and each other. Only a fraction of these contradictions is brought to light in the Livre Rouge , about which Pritt and Rosenmark grit their teeth.

Sedov’s Meeting

Must we return again to Goltzman’s confessions? Among the accused of the older generation Goltzman alone “personally saw” me and was said to have received from me “terrorist” instructions. My son, Leon Sedov, is said to have been the intermediary and organiser of the meeting. His meeting with Goltzman is alleged to have taken place at the Hotel Bristol. This is the chief point in the confession.

Alas! My son has never been to Copenhagen. The fact that he did not go there in 1932 can be incontestably proved by means of visas, telegrams, and statements coming from more than thirty persons of different nationalities and different political tendencies. The Hotel Bristol, where the meeting is supposed to have taken place, has not been in existence since 1917. What then does Goltzman’s confession mean?

The declarations of Berman-Yurin, Fritz David and Olberg are full of similar absurdities and nonsense. Nevertheless, on the basis of these confessions, the defenders of the Rights of Man (and of the interests of the G.P.U.) consider me worthy of the death penalty. How far can human baseness go?

But however scandalous the confessions of Goltzman and others may be, their contradictions and their crude inventions seem to be merely decorations designed to adorn the walls of this strange monument of lies and errors.

The whole indictment and all the confessions center around the assassination of Kirov. The organisation of this murder, however, was a chain in the struggle against the Opposition. The plot against Kirov was organised by the G.P.U. for the purpose of striking a blow at the Leningrad organisation of Zinovievists. Stalin, Yagoda, Kirov himself, were in close touch with the conspiracy. This fact is proved beyond any shadow of a doubt by the trial of Medved, the former chief of the Leningrad G.P.U.. The plot against Kirov was to have had a fictitious character; it was essentially directed against the Opposition.

Stalin did not wish to kill Kirov; Kirov himself did not wish to be killed; but Nikolaiev, although surrounded on all sides by agents provocateurs , himself took his role too seriously. He escaped from their control and fired before the G.P.U. had succeeded in finishing its amalgam (see my pamphlet, The Stalinist Bureaucracy and the Assassination of Kirov , 1934). What is written there about the preparation of the Moscow trials (both the first and those which have followed) is the result of logical deduction. I have unveiled the plans of the G.P.U. month by month, year by year, stage by stage, especially since the beginning of 1929. The indelible traces of the methodical preparation of articles in the Soviet press, by the interviews of Stalin and Molotov, by various “antiterrorist” declarations of Litvinov at Geneva (apropos of the assassination of King Alexander and Barthou), and by a whole series of other documents, declarations, and suggestions which at the time seemed incomprehensible but which, at the present moment, clearly reveal their criminal meaning.

Turns Without Tears!

In summing up one may say: the trials of the terrorists have been arranged, not because Kirov was murdered, but the assassination of Kirov took place “by accident” during the feverish preparation of the trials against the terrorists.

Sycophants a la Pritt and Rosenmark consider it out of the question that Stalin’s infallible G.P.U. could organise trials which were merely criminal mises en scéne in which the roles had been fixed in advance. On the other hand they find it quite natural that the Opposition—which is a Communist tendency with a long tradition, with experienced cadres, with an elaborated programme and an abundant political literature, should suddenly make a volte face , quite unexpectedly, toward individual terrorism, which it has always condemned as adventurism without results. This tendency, which comprises many thousands of sympathisers, accomplishes this incredible volte face in complete silence, without any previous discussion, without any declarations, without any criticism, without any internal struggle, without any terrorist propaganda, without any literature.

But even this is not enough. This tendency, which has shown itself capable of the greatest sacrifices in struggle for its programme, enters into relations with the Gestapo! And moved to this by the “thirst for power”! As if power in the U.S.S.R. could be obtained with the aid of the Gestapo! And how can one attribute this “thirst for power” to tens of thousands of rank-and-file oppositionists, workers, members of young Communist organisations, who experience unheard of repressions and privations. Only a narrow and over-fed bourgeois who knows nothing of revolutionary struggle, and who, at the same time, is always ready to lick the boots of any government in power, could believe so vile a lie.

Let us, however, admit the impossible. Let us admit precisely that the Trotskyists, in contradiction to their doctrine, their programme, their present writings, and their private correspondence (which is at the disposal of any honest commission of inquiry), have become terrorists—without internal struggles or splits, without the inevitable defections and denunciations. Let us admit that terrorism was necessary for them to restore capitalism; why was this new programme accepted in silence by everyone, without reprobation, without criticism, without opposition? Let us admit further—a few absurdities more or less are of no importance—that in order to ensure the restoration of capitalism and the victory of fascism (yes, yes, even fascism), the Trotskyists signed a pact with the Gestapo, and that they have been pursuing their terrorist activity at least from 1931 to the middle of 1936. Where? How? But this matters little. It all took place in the fourth dimension. They were continually trying to assassinate all the “leaders,” to disorganise the economy, to prepare victory for Hitler and the Mikado.

Can we take all these base absurdities for legal tender? But what do we see in the end? In the middle of 1936, the leaders of this strange tendency, accused of having taken part in these crimes, suddenly repent, all at the same time, and admit to the crimes they had committed (that is, had not committed). Each one rushes to cover himself with as much mud as he can, and each tries to drown the voice of the others in singing the praises of Stalin, whom yesterday he wanted to kill. How can we explain this miracle of Saint Yagoda? Counter-revolutionaries, terrorists, mad fascists, transformed into hysterical flagellants. Let the Pritts and Rosenmarks explain this mystery.

Finally let us suppose that the idea of terrorism was in fact accepted at some time by this group of capitulators and by others, and that in their confessions before the tribunal an echo of the truth was heard (alleged plots of the type: “To hell with Stalin! “) But why bring the Trotskyists and Trotsky himself onto the scene? These people do not conceal their aim: to bring to an end the absolutism of the Stalinist clique, not by individual terrorist adventures, but by the methods of the revolutionary class struggle. In these circumstances, would it not be natural for an “objective” jurist to ask himself: did not the government promise these dishonest capitulators that it would soften their fate if they would consent somehow to implicate Trotsky, Enemy No. 1 of the Stalinist clique?

What more natural than the hypothesis that the confessions may contain a morsel of the truth? But no, you see, our jurists consider it impossible that the accused hoped to be reprieved. They asked for death themselves, then. They “freely” renounced counsel for the defense. What sinister hypocrisy! What shame!

These wretched men, humiliated and broken, asked death for themselves so that they might better fulfill their odious role, and thus attempt to save their lives. It was prearranged in the contract. At any price, the government required the illusion of men wretched and foundering.

The correspondent of the Daily Herald , the organ of the very party to which the dishonest Pritt belongs, wrote after the verdict: “The report is widely current that a decree, published only five days before, which gave them the right to appeal, had been specially designed to spare their lives.” (Retranslated from the French)

I do not know to what decree it is referring. It may be that they did nothing more than spread rumours of such a decree. In any case Stalin did everything to deceive the accused.

18th December, 1936

[1] Dr. Ciliga, a Yugoslav revolutionary who, as an oppositionist spent several years in the G.P.U.’s prisons and places of deportation, testifies: “I saw a sailor who, on many occasions, was told, on being taken out of his cell in the evening, that he was going to be shot. He was led into the courtyard, and then brought back to his cell. ’Since you are a worker we don’t want to shoot you like some White Guard. As a worker, you must confess sincerely....’ The sailor confessed nothing, but after these tortures he became half mad. Then at last they left him in peace. But they still ask him for confessions on the subject of his conspiracy against Stalin.”

Enzymes & Metabolism ( AQA GCSE Biology: Combined Science )

Revision note.


Biology Lead

Enzymes & metabolism

  • Digestive enzymes work outside of cells ; they digest large, insoluble food molecules into smaller, soluble molecules which can be absorbed into the bloodstream
  • Metabolism is the sum of all the reactions happening in a cell or organism, in which molecules are synthesised (made) or broken down
  • Enzymes speed up chemical reactions in cells, allowing reactions to occur at much faster speeds than they would without enzymes at relatively low temperatures (such as human body temperature)
  • Substrates temporarily bind to the active site of an enzyme, which leads to a chemical reaction and the formation of a product(s) which are released
  • Some enzymes can process 100s or 1000s of substrates per second

Enzyme specificity diagram


Enzymes are biological catalysts that work in cells, so they randomly move about wherever they are in the cell. They don’t ‘choose’ to collide with a substrate – collisions occur because all molecules are in motion in a liquid

How do enzymes work?

  • Enzymes catalyse specific chemical reactions in living organisms – usually one enzyme catalyses one particular reaction:

Enzyme specificity of catalase to hydrogen peroxide diagram


The enzyme catalase can bind to its substrate hydrogen peroxide as they are complementary in shape, whereas DNA polymerase is not

  • The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s)
  • Proteins are formed from chains of amino acids held together by bonds
  • The order of amino acids determines the shape of an enzyme
  • If the order is altered, the resulting three-dimensional shape changes

The lock & key model

  • The ‘ lock and key theory ’ is one simplified model that is used to explain enzyme action
  • The enzyme is like a lock, with the substrate(s) the keys that can fit into the active site of the enzyme with the two being a perfect fit


Diagram showing the lock and key model

  • Enzymes and substrates move about randomly  in solution
  • When an enzyme and its complementary substrate randomly collide – with the substrate fitting into the active site of the enzyme – an enzyme-substrate complex forms, and the reaction occurs
  • A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions

The effect of temperature and pH on enzyme activity

The effect of temperature.

  • The specific shape of an enzyme is determined by the amino acids that make the enzyme
  • The three-dimensional shape of an enzyme is especially important around the active site area; this ensures that the enzyme’s substrate will fit into the active site enabling the reaction to proceed
  • Enzymes work fastest at their ‘ optimum temperature ’ – in the human body, the optimum temperature is around 37°C
  • Heating to high temperatures (beyond the optimum) will start to break the bonds that hold the enzyme together – the enzyme will start to distort and lose its shape – this reduces the effectiveness of substrate binding to the active site reducing the activity of the enzyme
  • Substrates cannot fit into denatured enzymes as the specific shape of their active site has been lost

Enzyme denaturation diagram

Enzymes denature at high temperatures

Denaturation is largely irreversible – once enzymes are denatured they cannot regain their proper shape and activity will stop

  • Increasing temperature from 0°C to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction
  • This means that low temperatures do not denature enzymes, but at lower temperatures with less kinetic energy both enzymes and their substrates collide at a lower rate

The effect of temperature on enzyme activity diagram


This graph shows the effect of temperature on the rate of activity of an enzyme

The effect of pH

  • The optimum pH for most enzymes is 7 but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2) and some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)
  • If the pH is too high or too low , the bonds that hold the amino acid chain together to make up the protein can be destroyed
  • This will change the shape of the active site , so the substrate can no longer fit into it, reducing the rate of activity
  • Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop


If pH is increased or decreased away from the optimum, then the shape of the enzyme is altered

The effect of pH on enzyme activity diagram


This graph shows the effect of pH on the rate of activity of an enzyme from the duodenum

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Prague Spring, 1968

  • ❖ Since 1957, Czechoslovakia had been led by Antonin Novotný, who was very unpopular because he was a hard-line communist.
  • ❖ Novotný did not bring in reforms , despite Khrushchev's de-Stalinisation policy.
  • ❖ By the 1960s, the Czech economy was struggling and the standard of living was dropping.
  • ❖ When the leader of the USSR , Brezhnev, visited Czechoslovakia in December 1967, he withdrew his support for Novotný because he was so unpopular.
  • ❖ Novotný was replaced by Dubček as the leader of Czechoslovakia on 5th January, 1968, in the hope that this would reduce discontent.
  • ❖ Dubček wanted to reform communism to create ' socialism with a human face'. This would enable the public to be more involved in the government and, hopefully, increase support for communism.
  • ❖ Censorship was relaxed in April 1968, which allowed more criticism of communism.
  • ❖ Free speech was allowed.
  • ❖ Political parties other than the Communist Party were allowed to exist.
  • ❖ Work councils were set up to represent workers and improve working conditions.
  • ❖ The secret police had their powers restricted, so their ability to arrest and detain people without trial was reduced.
  • ❖ Some capitalist elements were even allowed, to create a form of 'market socialism ' economy.
  • ❖ Travel restrictions were lifted, so Czechs could travel abroad.
  • ❖ Dubček publicly declared that Czechoslovakia would not leave the Warsaw Pact .
  • ❖ Dubček declared that Czechoslovakia would keep its alliance with the USSR .
  • ❖ Dubček declared that Czechoslovakia would not change its foreign policy.
  • ❖ Many were horrified at Dubček's reforms , believing they were a threat to communism.
  • ❖ On 3rd August, 1968, 5 leading opponents of the Prague Spring reforms sent a letter to Brezhnev outlining their concerns and asking him to intervene.
  • ❖ Romania would not attend Warsaw Pact meetings.
  • ❖ Tito, the leader of Yugoslavia, did not want the USSR to control his country.
  • ❖ They feared the Prague Spring would lead to calls for reform elsewhere in the Soviet Union's sphere of influence.
  • ❖ In July 1968, the USSR claimed to know of plans by West Germany to invade the Sudetenland, and asked to send Soviet troops to protect Czechoslovakia. Dubček refused.
  • ❖ The USSR considered economic sanctions for Czechoslovakia, but didn't want the country to seek help from the West.
  • ❖ In July, the entire Soviet Politburo ( cabinet ) visited Czechoslovakia to put pressure on Dubček to reverse the reforms.
  • ❖ Warsaw Pact troops from the USSR , Poland and East Germany completed manoeuvres in Czechoslovakia in the summer, to put more pressure on Dubček.
  • ❖ On 15th July members of the Warsaw Pact sent a letter to Dubček, warning him the reforms were dangerous to the Eastern Bloc.
  • ❖ On 20th-21st August, 1968, 500,000 Soviet-led Warsaw Pact troops entered Prague to arrest the reformers.
  • ❖ Nobody in Czechoslovakia was expecting an invasion, especially the armed troops who were completely unprepared.
  • ❖ Dubček and other leaders were arrested. They were taken to Moscow to meet Brezhnev.
  • ❖ Dubček was forced to sign the Moscow Protocol, which stated that Czechoslovakia would protect communism and the reforms would be reversed.
  • ❖ All the reforms were reversed when Dubček returned to Czechoslovakia.
  • ❖ In August 1968, the Brezhnev Doctrine was created. The USSR had the right to invade any country in its sphere of influence which threatened the stability of eastern Europe.
  • ❖ The USSR wanted to ensure it had full control over Czechoslovakia. In 1969, therefore, it replaced Dubček with Husak, a hard-line and reliable communist.
  • ❖ Soviet troops invaded Czechoslovakia on 20th August, 1968.
  • ❖ There was little resistance, but the Czech public refused to cooperate with Soviet troops.
  • ❖ Dubček and other communist leaders were arrested and taken to Brezhnev in Moscow.
  • ❖ All the reforms of the Prague Spring were reversed.
  • ❖ All reforms of the Prague Spring were reversed, and life in Czechoslovakia returned to the way it had been before.
  • ❖ Dubček was demoted and ended up working as a clerk in a lumber yard for 20 years.
  • ❖ The mood in Czechoslovakia, which had previously been optimistic, became more resentful of the USSR .
  • ❖ Several Czech students, including Jan Palach, committed suicide by publicly setting fire to themselves in protest.
  • ❖ The UN wanted to condemn the invasion of Czechoslovakia by Warsaw Pact troops, but the USSR vetoed this.
  • ❖ The USA and the West condemned the invasion.
  • ❖ However, the USA did nothing because it was distracted by Vietnam, there was a US presidential election , and it was the beginning of détente.
  • ❖ Communists in western countries condemned the invasion and created their own version of communism , called Eurocommunism.
  • ❖ In France and Italy, the Communist Party condemned the USSR's actions.
  • ❖ Yugoslavia and Romania spoke out against the USSR's invasion, which worsened their relationship with the Soviet Union.
  • ❖ Poland and East Germany were very supportive of the invasion, as they were trying to control reformers in their own countries.
  • ❖ Communist China condemned the USSR invasion of Czechoslovakia, and the relationship between the two countries greatly deteriorated.
  • ❖ They led to the creation of the Brezhnev Doctrine , which increased USSR control over eastern Europe.
  • ❖ It split the communist world, as communist parties in western Europe became independent of USSR control and communist China condemned the invasion.
  • ❖ It highlighted that, while the USA would condemn the USSR's actions, it wouldn't take any steps to stop them.

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  1. PPT

    lock and key hypothesis gcse

  2. Illustrate the lock and key hypothesis of enzyme action.

    lock and key hypothesis gcse

  3. PPT

    lock and key hypothesis gcse

  4. Lock And Key Model

    lock and key hypothesis gcse

  5. Enzymes Lock And Key Animation

    lock and key hypothesis gcse

  6. Biology: Lock and key theory Diagram

    lock and key hypothesis gcse



  2. Exam Application Tutorial for B2 Enzymes: The Lock & Key Hypothesis and Temperature Graphs

  3. A-level biology lesson 6: Enzymes and cellular reaction by Dr. Bbosa Science

  4. Mode of Enzymes action

  5. Enzyme (L-2) Mechanism Of Action



  1. What are enzymes?

    In the lock and key hypothesis close lock and key hypothesis Model which compares the specificity of enzymes with a key and its lock., the shape of the active site matches the shape of its ...

  2. 2.1.4 Enzymes & Metabolism

    The lock & key model. The 'lock and key theory' is one simplified model that is used to explain enzyme action; The enzyme is like a lock, with the substrate(s) the keys that can fit into the active site of the enzyme with the two being a perfect fit; Diagram showing the lock and key model. Enzymes and substrates move about randomly in solution

  3. Enzymes and digestion

    GCSE; CCEA; Enzymes and digestion (CCEA) ... This theory is known as the 'lock and key model'. It explains why each enzyme will only work on one substrate. For example, ...

  4. Enzymes

    Unlock the mysteries of the lock and key theory with this comprehensive and viral video! We cover the fundamental concepts of the lock and key theory, includ...

  5. Enzymes

    Revise the molecules of life and the human digestive system for GCSE Combined Science, AQA. ... This theory for the way in which enzymes work is called the lock and key theory close lock and key ...


    Today we're looking at enzymes! You can Studyalong with this video and others the Organisation topic with my workbook available on www.emmatheteachie.co.uk!W...

  7. Explain the lock and key model of enzyme action, including ...

    The lock and key model refers to an analogy used to describe the specific action of an enzyme with a substrate . During this process, the enzyme is acting as the lock and has a section called the active site which is where the reaction will take place, and the substrate, for instance a protein, is the key. In the same way that a key is paired ...

  8. Explain the lock and key hypothesis of enzyme function

    Explain the lock and key hypothesis of enzyme function. To start, it is important to have a clear understanding of what an enzyme is. An enzyme is a biological molecule which speeds up the rate of a reaction without being changed or used up in the process. Each enzyme can only catalyse a certain reaction and this is determined by what is known ...

  9. Lock-and-key model Definition and Examples

    Lock-and-key vs. Induced Fit Model. At present, two models attempt to explain enzyme-substrate specificity; one of which is the lock-and-key model, and the other is the Induced fit model.The lock and key model theory was first postulated by Emil Fischer in 1894.The lock-and-key enzyme action proposes the high specificity of enzymes.

  10. 1.2.4 The Mechanism of Enzyme Action

    The 'lock and key hypothesis' is one simplified model that is used to explain enzyme action; The enzyme is like a lock and the substrate is the key that fits into the active site (like a keyhole) . For an enzyme to work the substrate has to fit in the active site; If the substrate is not the correct shape it will not fit into the active site ; Then the reaction will not be catalysed

  11. Lock & Key Theory of Enzymes

    In this video you will learn all the science for this topic to get a grade 9 or A* in your science exams! Lock & Key Theory of Enzymes - GCSE Biology | Kaysc...

  12. Enzymes

    Seren is having some difficulty getting into her house with her lock and key. Her helpful science app, Alfred, takes the opportunity to describe the 'lock and key' model. Open Transcript

  13. What is the 'lock and key' hypothesis?

    What is the 'lock and key' hypothesis? A reaction can only be catalysed (sped up) if an enzyme's active site matches the shape of its substrate molecules- the substrate fits into the active site like a key into a lock. This shape is highly specific, meaning one type of enzyme can usually only match with one type of substrate to catalyse a ...

  14. PDF Edexcel Biology GCSE

    Describe the 'lock and key' model 1. Substrate collides with the active site of an enzyme 2. Substrate binds, enzyme-substrate complex forms 3. Substrate converted to products 4. Products released from the active site which is now free to bind to another substrate httpsbit.lypm t-cc httpsbit.lypm t-cc httpsbit.lypmt-edu

  15. Edexcel GCSE. Biology 1. Enzymes. Flashcards

    2. Place a beaker of water on the gauze and adjust the flame to keep the water at about 35°C. 3. Now put two drops of iodine solution into each spot of a spotting tile. 4. Add 2 cm3 of amylase enzyme solution to a test tube. 5. Place 2 cm3 of starch solution into the same tube. 6.

  16. Leon Trotsky: The Moscow "Confessions" (1936)

    But such a hypothesis is not necessary. It is enough to know the facts, the persons, and the circumstances in order to understand how the accused could have been forced to put the rope around their own necks. Among the accused there was not a single oppositionist or Trotskyist. ... The accused are under lock and key. The G.P.U. is in no hurry ...

  17. What is an enzyme? Explain the 'Lock and Key' Hypothesis

    The idea of the substrate fitting 'just right' to the active site of the right enzyme is called the 'Lock and Key' hypothesis.If the active site is altered by exptremes of teperature or changes in pH then the substrate won't fit into it as well and will lead to a decrease in the activity of the enzyme. Hope this was helpful!

  18. Washington Summit, 1987

    At the Washington Summit, Reagan and Gorbachev discussed arms reductions and limitations. Gorbachev finally agreed to disarmament even though Reagan would not abandon SDI .

  19. Lock and key model

    Description. Seren is attempting to get into her house but is having some difficulty as her key won't fit in the lock. In anger, she questions what is wrong with her lock and key. Alfred, the ...

  20. Moscow Summit, 1988

    What was discussed at Moscow? At the Moscow Summit, Reagan and Gorbachev had further discussions about limiting nuclear arms and conventional arms. They also discussed some details of the Intermediate-Range Nuclear Forces ( INF) Treaty .

  21. 2.1.3 Enzymes & Metabolism

    The lock & key model. The 'lock and key theory' is one simplified model that is used to explain enzyme action; The enzyme is like a lock, with the substrate(s) the keys that can fit into the active site of the enzyme with the two being a perfect fit; Diagram showing the lock and key model. Enzymes and substrates move about randomly in solution

  22. Prague Spring, 1968

    The response from the leaders of the Czechoslovakian Communist Party was not enthusiastic. Many were horrified at Dubček's reforms, believing they were a threat to communism. On 3rd August, 1968, 5 leading opponents of the Prague Spring reforms sent a letter to Brezhnev outlining their concerns and asking him to intervene.