1. Unit 1 Cell and Molecular Biology Section 6 Catalysis

2. Chemical Reactions (Revision) Synthesis (anabolic) Condensation reactions Removal of water to form a bond Degradation (catabolic) Hydrolysis reactions Addition of water to break a bond

3. Enzymes Proteases Hydrolyse peptide bonds break down proteins into amino acids Nucleases Hydrolyse phosphodiester bonds Break down nucleic acids into nucleotides ATPases Hydrolyse ATP Break ATP into ADP and P i with the release of energy Kinases Catalyse the transfer of a phosphate group onto a molecule such as a carbohydrate or a protein

4. Specificity of enzymes

5. Induced-fit model When substrate combines with the enzyme it causes a change in shape of the active site The change in shape results in an optimal fit for the substrate-enzyme interaction Once the product diffuses away, the enzyme returns to its original shape

6. Cyanide Cyanide is found is a gas (sometimes liquid) Used / found in House fires Apricot stones Suicide pills Gas chambers (both US and Nazi Germany) Stock piled by US and Soviet Union in 50’s and 60’s Mining Photography Electroplating

7. Binds to iron atom in the enzyme cytochrome C oxidase This changes the shape of the enzyme Knowing how this works has important applications for Detection of poisoning Treatment

8. Control of enzyme activity Competitive Inhibitors Decrease the rate of reaction Inhibitor is similar in structure and electrical charge to substrate It binds to the active site An increase in the substrate can result in an increase of product formation (inhibitor is out competed) Competitive inhibition can be reversible or irreversible (depending on mechanism of binding)

10. Non-competitive inhibitors Decrease the rate of reaction Inhibitors have no similarity to the substrate Inhibitor binds to part of the enzyme (other than the active site) distorting the shape of the enzyme Increase in substrate concentration does not increase product formation Can also be reversible

11. Control of enzymes – Enzyme modulators Allosteric enzymes Allosteric enzymes have at least one other binding site than the active site (called an allosteric site) Allosteric enzymes have 2 forms – active and inactive When a substance binds to an allosteric site it changes the shape of the active site.

12. Positive modulation The modulator changes the active site so the enzyme becomes active (substrate fits) Positive modulators are activators Negative modulation The modulator changes the active site so the enzyme becomes inactive Negative modulators are inhibitors

14. Control of enzymes – Covalent modifications Addition, modification or removal of a variety of chemical groups Changes the shape of the enzyme Phosphorylation and dephosphorylation Kinase enzymes add phosphate Phosphatase enzymes remove phosphate Some enzymes are activated by phosphorylation, others are inactivated (and vice versa for dephosphorylation)

15. Proteolytic cleavage Conversion of an inactive enzyme to an active one Example Trypsinogen – Trypsin Trypsinogen is synthesised in the Pancreas Activation occurs when trypsinogen has amino acids removed in the duodenum by another protease enzyme This changes the trypsinogen into the active form trypsin Trypsin then helps to activate more trypsinogen molecules

16. Control of metabolic pathways End product inhibition Chemical reactions are normally organised into metabolic pathways with enzymes controlling each chemical reaction The end-product can act as a negative modulator, binding to the first enzyme preventing the metabolic pathway from proceeding because intermediary substrates are not produced This is a process of negative feedback

17. Activity Read and take notes from DART pg 61-68 Scholar 6.3 and 6.4 Check out http://highered.mcgraw- hill.com/sites/0072437316/student_view0/chap ter8/animations.html#http://highered.mcgraw- hill.com/sites/0072437316/student_view0/chap ter8/animations.html# Find examples for each type of enzyme control