Proteins and Enzymes Flashcards
what are the monomers of proteins
-amino acids
what do amino acids consist of and how do they bind
- all have an amine (-HNH-) and carboxylic acid (-COOH-) group but have different R groups
-Joined by peptide bonds (-CONH-) to create a polypeptide
Primary Structure of protein
Sequence of amino acids in a polypeptide chain which determines the shape of the protein
Secondary Structure of protein
Chain folds due to hydrogen bonds between amino acids into structures like α-helix and β-pleated sheet
Tertiary Structure of protein
-Further folding due to Hydrogen, Ionic and Disulphide bonds between R groups
- Tertiary Structures determines the shape of the active site and its function
Quaternary Structure of protein
> 1 polypeptide chain
-Multiple chains held together by Hydrogen Ionic and Disulphide bonds
How are proteins hydrolysed
Proteins can hydrolysed either by heating with acid or by using enzymes (proteases)
How are proteins denatured and what bonds are broken by what?
- Caused by Hydrogen (Heat) and Ionic (pH) bonds breaking
-Disulphide bonds are stronger than both Ionic and Hydrogen bonds
Protein Test
- Add Biuret Reagent
- Positive = Purple/Lilac
- Negative = Blue
What are enzymes
Biological catalysts that speed up the rate of reaction without being used up by lowering the activation energy
Describe the Induced Fit model
- Substrate enters the active site of the enzyme
- Active site slightly changes shape to fit the substrate perfectly
- An enzyme-substrate complex is formed
- Products leave and active site returns to original shape
Describe the Induced Fit model in Hydrolysis Reactions
- Enzyme puts a strain on the substrate molecule
- Strain distorts the particular bond
- Lowers the activation energy needed to break the bond
Describe the Induced Fit model in Condensation Reactions
- Pulls molecules closer together
- Makes sure they are the right orientation making them more likely to react
Describe the effect of substate concentration on an enzyme controlled reaction
- Rate of reaction initially increases as more particles means more collisions
- Rate of reaction then levels out as all the enzyme actives sites are saturated (occupied)
- Enzyme concentration is now the limiting factor
Describe the effect of Temperature on enzyme activity
- As temperature increases the rate of reaction also increases due to the molecules moving at a higher speed and therefore more collisions
- This continues until the optimum temperature where the rate of reaction is at its fastest
- After the optimum temperature the enzymes start to denature and less enzyme-substrate complexes form decreasing the rate of reaction
Describe the effect of enzyme concentration
When the concentration of substrate is in excess:
- More enzyme molecules means there are more active site available
- Increased number of collisions means more enzyme-substrate complexes formed
Describe the effect of pH on enzyme activity
All enzymes work best at optimal pH. above and below the optimal pH the rate of reaction decreases. Extreme pH changes can denature the enzyme.
What are Enzyme Inhibitors
A number of chemicals can act as enzyme inhibitors, slowing down the rate of enzyme catalysed reactions
Describe how Competitive Inhibition works
- the inhibitor has a similar structure to the normal substrate molecule and competes with it for attachment to the active site
- the rate of reaction is reduced as substrate cannot bind to active site when inhibitor molecule is occupying it
- competitive inhibition can be reduced by increasing the concentration of the substrate
Describe how Non competitive inhibition works
- non competitive inhibitor is not similar in structure to substrate
- it combines away from the active site to form an enzyme-inhibitor complex altering the tertiary structure and shape of the active site of an enzyme
- substrate cannot attach as it is no longer complimentary to active site
- a high concentration of substrate will not reduce non-competitive inhibition
