A Level Biology - Enzymes notes PDF

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Summary

Notes summarising the sub-topic 'Enzymes' in the module 'Biological Molecules' in A Level Biology. Very detailed notes that are clear and perfect for on the go revision to consolidate knowledge. ...

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Enzymes Intracellular rxns  amylase and trypsin catalyse the breakdown of carbs and proteins.

Structure:

 

Globular proteins. Extracellular rxns  catalase catalyses Catalysts  lower activation energy. the breakdown of hydrogen peroxide into Measure enzyme activity by: water and oxygen. 1. How fast product is made. 2. How fast the substrate breaks down. Catabolic enzyme  break big molecules by splitting. Anabolic enzyme  builds more complex molecules from small ones.

Models: 1. Lock and key - Every enzyme has a SPECIFIC active site due to tertiary structure. 2. Induced Fit - Active site (tertiary structure) changes slightly to mould around the substrate. - Substrate is still complementary. - Exerting pressure  distorts bonds  lowers activation energy.

Factors that affect enzyme activity:

1. Temperature   

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Kinetic energy increases = RATE increases. Denaturation  molecules vibrate violently, bonds break, substrate not complementary. Bonds responsible for maintaining the enzyme’s tertiary structure become broken and the active site changes shape Enzymes in biological washing powders  60 degrees.

2. pH

   

A measure of H+ concentration. Most human enzymes = Ph7. Pepsin = Ph2 = stomach. H+ and OH- ions in acids and alkalis  disrupt ionic and hydrogen bonds  changes tertiary  changes active site.

3. Substrate concentration  

More substrate = collisions more likely = RATE increases. Saturation point = all active sites are full, increasing substrate concentration has no effect on rate.

4. Enzyme concentration:  More enzymes = collisions more likely = RATE increases.  If substrates start to run out, the enzymes have no further effect.

Competitive Inhibitors: Similar shape to substrate. No reaction. Competes with substrate for active site. Same amount of product, takes longer. High inhibitor concentration = take up all active sites.  High substrate concentration = reduces effect of inhibitor.     

Non-competitive Inhibitors: Different shape. Binds to allosteric site. Don’t compete with substrate. Alters shape of active site  substrate can’t fit.  High substrate concentration = no difference, activity still inhibited.    ...