Lesson 2 ESC and Specificity

Starter • Hand in your t-test questions to be marked • Hand in your standard deviation questions if you did not hand in on Monday • Complete the recap questions in your protein structure booklet

Denaturation of protein • Breaking of hydrogen and ionic bonds.

Questions 1.

2.

3.

4.

Answers

1. Secondary, tertiary and quaternary 2. It will change the specific shape of In which stages of protein the proteinstructure are these bonds present? 3. Breaking of the hydrogen and ionic bonds Why will this prevent theaprotein 4. Because change in temperature or pH will break the hydrogen and functioning? ionic bonds changing the specific What causes proteins to denature? shape of the enzyme so it can no Why do enzymes need optimum temp longerthe catalyse the specific reaction.

and pH?

Which structures are represented?

Recap questions.

• 1. What is the monomer of a protein?

• 2. Draw an amino acid and label the amino group, carboxylic acid group and the R group?

• 3. There are twenty naturally occurring amino acids, how do they differ from each other?

• 4. Which bond holds together two amino acids and what is this molecule now called?

• 5. What is the primary structure of a protein and which bonds are present?

Recap questions.

• 6. What is the secondary structure, which bonds are present and can you give examples?

• 7. What is the tertiary structure, which bonds are present?

• 8. Describe a globular protein, giving examples.

• 9. How would you test for the presence of a protein?

Enzymes Catalysing life

Enzymes are vital to our health and change the rate at which chemical reactions happen

Enzymes are proteins • enzymes are globular proteins with a specific tertiary structure. • enzymes catalyse metabolic reactions in living organisms.

You need to be able to discuss protein structure in relation to enzyme function.

GCSE recap • Label

A = substrate

c = enzyme

B = active site

d = product

Enzyme substrate complex (ESC)

Define the following terms: 1.

Anabolic reactions: Reactions that build up molecules

2.

Catabolic reactions: Reactions that break down molecules

3.

Metabolism:

Combination of anabolic and catabolic reactions

4.

Catalyst:

A substance that speeds up reactions without changing the produced substances

5.

Metabolic pathway: Sequence of enzyme controlled reactions

6.

Specificity:

7.

Substrate:

8.

Product:

Only able to catalyse specific reactions The molecule(s) the enzyme works on Molecule(s) produced by enzymes

• Intracellular enzymes Work inside cells eg.DNA polymerase • Extracellular enzymes Secreted by cells and work outside cells eg. pepsin, amylase

•

Enzymes are Specific!

• All enzymes are globular proteins → spherical in shape • Enzymes are large molecules (100’s of amino acids) most of which are involved in maintaining the specific shape of the enzyme • Very few (often fewer than 10) amino acids form the actual active site.

• Each enzyme has a very specific, individual active site shape, maintained by a very specific overall tertiary structure.

Remember with all proteins‌ shape matters!

Lock-and-key • Only one substrate (key) can fit into the enzyme's active site (lock) • Both structures have a unique shape

Induced fit • When the enzyme and substrate form a complex, structural changes occur so that the active site fits precisely around the substrate (the substrate induces the active site to change shape). • The reaction will take place and the product, being a different shape to the substrate, moves away from the active site. The active site then returns to its original shape.

Induced fit • Substrate binds to the enzyme's active site

 The shape of the active site changes and moves the substrate closer to the enzyme  Amino acids are moulded into a precise form  Enzyme wraps around substrate to distort it

• This lowers the activation energy • An enzyme-substrate complex forms → fast reaction

▫ E + S → ES → P + E ▫ Enzyme is not used up in the reaction (unlike substrates)

Flexibility is key the enzyme ‘bends’ to fit!

Induced fit

Induced fit – 3 dimensional

• Compare and contrast the ideas of induced fit and lock and key. • Make a table of the similarities and differences between the two theories.

Energy levels of molecules

Enzymes lower the activation energy of a reaction

Initial energy state of substrates

Activation energy of enzyme catalysed reaction

Activation energy of uncatalysed reactions

Final energy state of products Progress of reaction (time)

Why do enzymes increase the rate?

Activation energy • Enzymes are catalysts → speed up chemical reactions ▫ Reduce activation energy required to start a reaction between molecules ▫ Substrates (reactants) are converted into products ▫ Reaction may not take place in absence of enzymes (each enzyme has a specific catalytic action) ▫ Enzymes catalyse a reaction at max. rate at an optimum state

Exam questions – 11 minutes