What can you remember about enzymes? Mr W

Transcription

1 What can you remember about enzymes? Mr W

2 Human Cells (f) Enzymes and Metabolism

3 Learning Intentions Describe metabolism, synthetic (energy requiring) and breakdown (energy releasing) pathways

4 Cell Metabolism All the biochemical reactions that occur in a living cell are called cell metabolism Most of these reactions are catalysed by enzymes

5 Cell Metabolism Metabolic pathways involve biosynthetic processes (anabolism) and the breakdown of molecules (catabolism) to provide energy and building blocks.

6 Anabolic Reactions They make complex molecules from simpler ones They usually require energy What reactions can you think of that are synthesis reactions?

7 Catabolic Reactions Complex molecules are broken down into simpler ones. These reactions release energy and provide building blocks for anabolic reactions. What reactions can you think of that are break down reactions?

8 Learning Intentions State that metabolic pathways are controlled by the presence or absence of particular enzymes State that metabolic pathways rate of reaction are regulated by key enzymes within the pathway

9 Metabolic Pathways Metabolic pathways are regulated by enzymes that catalyse specific reactions A pathway often has reversible and irreversible steps that help with this control

10 Alternative Routes Metabolic pathways can also take alternative routes that allow steps to be bypassed. The example shown occurs when a cell has a plentiful supply of glucose.

11 Summary Metabolism is the integrated and controlled pathways of enzyme catalysed reactions within a cell. Metabolic pathways involve biosynthetic pathways (anabolic, require the input of energy) and pathways that break down molecules (catabolic, usually release energy). Metabolic pathways can have reversible and irreversible steps. they can also have alternative routes that can bypass steps in a pathway.

12 Group Task Using the enzyme co op cards, create a poster that includes information on the following: The effect of an enzyme on the activation energy of a reaction What is induced fit means The role of the enzyme active site including shape, substrate and product affinity

13 Learning Intentions Describe the effect of an enzyme on the activation energy of a reaction

14 Lesson starter 1. What is the difference between anabolism and catabolism? 2. What words did we use instead of these to describe these reactions, in enzymes? 3. Name one anabolic reaction and one catabolic reaction? 4. In what three ways can we prove enzymes are catalysts? 5. Come up with a way to remember q1

15 Activation Energy Every biochemical reaction is catalysed by an enzyme and enzymes speed up biochemical reactions. Biochemical reactions may involve joining molecules together or splitting complex molecules in each case energy is needed to break chemical bonds and start the reaction. This is called the activation energy

16 Activation Energy Energy input needed to break chemical bonds and start a chemical reaction (activation energy) is reduced when an enzyme is used When the bonds break they become unstable and are now in the transition state - the reaction can start

17

18 Learning Intentions Describe what induced fit means

19 Induced Fit The shape of an active site is specific to the shape of a substrate However, the active site is flexible. The shape of the active site can change slightly when it comes into contact with a substrate molecule so that the active site fits it better.

20 Induced Fit It can be described as being like a slightly too small rubber glove forming a very tight fit round a hand Induced fit means that the active site comes into very close contact with the molecules of substrate and increases the chance of a reaction taking place. This lowers the activation energy required for the reaction to occur

21 Learning Intentions Explain the role of the enzyme active site including shape and substrate affinity

22 Specificity At some point on the surface of an enzyme molecule, there is an active site. Only one substrate will fit into the enzymes active site. The enzyme is specific to its substrate and the substrates shape is complementary to the enzymes active site.

23 Enzyme A Perfect fit Active site Substrate A

24 Enzyme B Won t fit.. Wrong shape! Substrate A

25 Substrate Affinity When there are two or more reactants, the shape of the active site determines the orientation of the reactants (how they line up) This ensures that they are held together in such a way that the reaction between them can take place. This lowers the activation energy required for the reaction to occur

26 Product Affinity The active site holds the two reactants closely together in an induced fit. Once the reaction has taken place the, products have a low affinity for the active site and are released.

27 Active Site Summary The substrate attaches to the active site on the enzyme The active site orientates (lines up) the molecules. This causes an induced fit - the enzyme changes shape slightly so that the active site fits better This lowers the activation energy required for the reaction to occur Products are released as they have a low affinity for the active site

28 Quick questions 1. What is meant by metabolism? 2. What is meant by activation energy? 3. What is meant by induced fit?

29 Answers 1. Metabolism is the term for all the enzyme controlled biochemical reactions that occur in a living cell 2. Activation energy is the energy is needed to break chemical bonds and start the reaction 3. Induced fit is the changing of the shape of the active site so that it fits the substrate better

30 Extra Questions 1. What is meant by the affinity of substrate molecules for an enzyme s active site? 2. Rewrite the following sentences choosing he correct answer from each underlined choice: The shape of the active site ensures that the reactants are correctly orientated/denatured so that the reaction can take place. This is made possible by the fact that the enzyme increases/decrease the activation energy needed by the reactants to reach the transitory/transition state

31 Extra Questions Answers 1. The chemical attraction between them 2. The shape of the active site ensures that the reactants are correctly orientated so that the reaction can take place. This is made possible by the fact that the enzyme decrease the activation energy needed by the reactants to reach the transition state

32 HW table Word Definition Genomics Bioinformatics Systematics Pharmacogenetics The study of human genome. Involves determining the sequence of nucleotide bases along DNA strands. Use of computer technology to identify DNA sequences. The study of a group of living things with respect to their diversity, relatedness and classification. The study of and individual s genetic makeup and how this affects response to certain drugs.

33 Lesson starter Explain the role of the active site in enzyme-catalysed reactions (3 marks)

34 Answer 1. The substrate attaches to the active site (on the enzyme). 2. The active site orientates / lines up the molecules. 3. This causes an induced fit/the enzyme to change shape slightly so that the active site fits better. 4. This lowers the activation energy (required for the reaction to occur). 5. Products are released as they have a low affinity for /attraction to the active site.

35 Learning Intention State the effects of substrate concentration on the direction and rate of enzyme reactions

36 Factors Affecting Enzyme Action The direction and rate of enzyme reactions can be affected by temperature, ph and: substrate concentration end product concentration (feedback inhibition we ll come back to this!)

37 Effect of Substrate Concentration on Enzyme Activity Into each boiling tube add 10 ml of hydrogen peroxide each should have a different concentration. Drop the piece of liver into the first boiling tube and time for time for 1 minute then measure the height of the oxygen foam. Repeat this for each concentration of hydrogen peroxide

38 Substrate Concentration The reaction rate increases as substrate concentration increases. This will continue until a point where enzyme concentration becomes a limiting factor all the active sites are used up. Substrate concentration a limiting factor Enzyme concentration a limiting factor all active sites involved in the reaction Change your graph on p9 and give it the title Effect of substrate concentration

39

40 Substrate Concentration Summary The reaction rate increases as substrate concentration increases. This will continue until a point where enzyme concentration becomes a limiting factor all the active sites are used up.

41 Control Reaction A Reaction B Describe the effect of increasing substrate concentration on the rate of reaction in the control. Increasing the substrate concentration increases the rate of reaction until approximately 40mg/l when the rate of reaction then remains constant

42 Learning Intention Describe the control of enzymes in metabolic pathways by gene action and signal molecules

43 Metabolic Pathways A metabolic pathway is a sequence of enzyme controlled reactions that convert one metabolite to another enzyme 1 enzyme 2 enzyme 3 enzyme 4 A B C D E Some examples of metabolic pathways include Glycolysis, Kreb cycle and photosynthesis.

44 Control of Metabolic Pathways Enzyme action in a metabolic pathway can be controlled at 2 levels. Either by: gene expression (which genes are switched on and off) enzyme action or

45 Control of Metabolic Pathways enzyme 1 enzyme 2 enzyme 3 enzyme 4 A B C D E If the pathway is interrupted by the lack of a particular enzyme, the pathway comes to a stop. Intermediate metabolites will accumulate in the pathway.

46 Complete questions on page 85

47 Control by Gene Action Some metabolic pathways are only required to operate under certain circumstances. To prevent resources being wasted, genes that code for the enzymes controlling each of their stages are switched on or switched off as required

48 Lactose Lactose is a sugar found in milk It is made up of a molecule of glucose attached to a molecule of galactose glucose Galactose The enzyme b - galactocidase breaks down lactose to glucose and galactose Lactose B- galactocidase Glucose + Galactose

49 Lactose B- galactocidase Glucose + Galactose Lactose is not present all of the time It would be very wasteful of energy and resources to produce b - galactocidase when there was no substrate for it to act on So organisms can switch the gene to make the enzyme off when it is not needed

50 Lesson starter 1. What is an enzyme? 2. What is meant by induced fit? 3. What is meant by specific? 4. Where do the enzyme and substrate meet? 5. What is meant by enzyme affinity? 6. What is another word for a degradation reaction? 7. Give an example

51 Jacob and Monod E.coli has a gene which codes for b-galactosidase the enzyme is only found only when the substrate lactose is found in a cell. Jacob and Monod formulated a model of how the gene to make the enzyme b- galactocidase is switched off and on in the bacteria E. coli.

52 DNA S Structural gene (makes the enzyme) O S Operator gene (controls the structural gene) R O S Regulator gene (makes the repressor protein )

53 NO LACTOSE PRESENT R O S Repressor binds with the operator and blocks it Repressor protein molecule No enzyme ( b galactocidase) made Structural Gene is OFF

54 LACTOSE PRESENT Operator switches structural gene on R O S Lactose blocks repressor Structural gene makes enzyme Repressor molecule ** enzyme digests lactose until supply runs out then repressor combines with operator to switch it back off. enzyme ( b galactocidase made) Structural Gene is ON

55 Lesson Starter 1. What is lactose? 2. What enzyme breaks lactose down? 3. What are the products? 4. What is the function of the structural gene? 5. What is the function of the operator gene? 6. What is the function of the repressor? 7. A)What blocks the operator? B) When does this occur? C) Is the enzyme produced? D) Is the gen switch on/off? 8. Describe what happens when lactose is present.

56 Lesson starter 1. Describe the catabolic reaction that can occur at the lac operon 2. State the difference in molecules during a catabolic and anabolic reaction 3. Describe what is meant by affinity and induced fit in the one sentence 4. If the pathway is interrupted by the lack of a particular enzyme, the pathway comes to a stop. What result does this have with regards to metabolites? 5. State 4 factors that can affect enzyme activity 6. State what is meant by specific 7. What is the substrate for : a) catalase b) amylase c) phosphorylase

57 Control by Signal Molecules In the lac operon sytem, a gene is switched off in response to a signal molecule in the cell s environment lactose. This signal molecule was produced outside the cell so is called an extracellular signal A signal molecule produced within the cell is said to be an intracellular signal

58 Summary of Gene Control Some metabolic pathways are only required on certain occasions. To prevent resources being wasted, the genes that code for their enzymes are switched on or off in response to signals from either within the cell (intracellular) or outwith the cell (extracellular).

59 Enzymes in Metabolic Pathways As metabolite A becomes available enzyme 1 becomes active Enzyme 1 converts metabolite A into metabolite B As metabolite B becomes available enzyme 2 becomes active Enzyme 2 converts metabolite into metabolite As metabolite C becomes available enzyme 3 becomes active Enzyme 3 converts metabolite into metabolite A continuous supply of metabolite A drives the direction of the pathway from A to D B C C D

60 Learning Intention Describe the control of enzymes in metabolic pathways by enzyme action through competitive and non-competitive inhibition

61 Control by Enzyme Action Genes for some enzymes are continuously expressed. These enzymes are always present in the cell and their control involves regulation of their rate of reaction.

62 Non Competitive Inhibition Non competitive inhibition involves the binding of molecules that change the shape of the active site.

63 Competitive Inhibition Competitive inhibition involves molecules that resemble the substrate binding to the active site so it can t bind with the correct substrate

64 Lesson starter 1. Draw the 3 genes present in the lac operon and state their functions 2. State what happens when lactose is absent 3. State what happens when lactose is present 4. Name two enzymes and state their substrates and products, also state whether anabolic or catabolic 5. Draw a diagram to describe a catabolic reaction 6. What is the difference between bioinformatics and systematics?

65 Show me boards

66 Show me boards

67 Show me boards

68 Show me boards

69 Show me boards

70 What name is given to process X? A. Gene expression C. Post transitional modification B. RNA splicing D. Polymerase chain reaction

71

72

73

74

75 Competitive Inhibition Competitive inhibition can be reversed by increasing substrate concentration

76 Competitive Inhibition Example As well as lactose, the chemical ONPG also acts as substrate for the enzyme - galactosidase. Galactose acts as a competitive inhibitor of the enzyme, competing with ONPG for the active site.

77 Competitive Inhibition Example At high concentrations galactose will inhibit the reaction by preventing ONPG forming a complex with the active site. This inhibition can be overcome if the ONPG concentration is sufficiently increased.

78 Competitive and Non Competitive Inhibition Summary Genes for some enzymes are continuously expressed. These enzymes are always present in the cell and their control involves regulation of their rate of reaction. Non competitive inhibition involves the binding of molecules that change the shape of the active site. Competitive inhibition involves the binding of molecules to the active site that resemble the substrate. This can be reversed by increasing substrate concentration.

79 Learning Intention Describe the control of enzymes in metabolic pathways by enzyme action through feedback inhibition

80 Feedback Inhibition In a metabolic pathway, an enzyme early in the pathway can be inhibited by high levels of the final product of the whole pathway. A high level of end product means it is not being used and it is wasteful to make.

81 To overcome this, the end product binds to an early enzyme and reduces it s activity - this is known as end product inhibition Feedback Inhibition

82 Feedback Inhibition Summary Feedback inhibition occurs when an end product binds to an enzyme that catalyses a reaction early in the pathway. This binding causes the enzyme activity to reduce and reduces the amount of product being formed.