Proteins & Enzymes Flashcards
Describe the structure of proteins.
- Polymer of amino acids
- Joined by peptide bonds
- Formed by condensation reactions
- Primary structure is number and order of amino acids
- Secondary structure is folding of polypeptide into Alpha-helix and Beta-pleated sheets due to hydrogen bonding
- Tertiary structure is 3D folding due to hydrogen bonding, ionic bonding and disulphide bridges
- Quaternary structure is 2 or more polypeptide chains joined together
Describe how a peptide bond is formed between two amino acids to form a dipeptide
- Condensation reaction/loss of water
2. Between amine (NH2) and carboxyl (COOH)
Describe how an enzyme-substrate complex increases the rate of reaction
- Reduces activation energy
2. Due to bending bonds OR without the enzyme, very few substrates have sufficient energy for the reaction
Describe how a change in the base sequence of the DNA coding for an enzyme may result in a non-functional protein.
- Change in primary structure changes sequence of amino acids
- Hydrogen bonds, ionic bonds and disulphide bridges form in different positions
- Alters the tertiary structure of the enzyme/active site
- No enzyme-substrate complexes can be formed
What is the proteome of a cell?
-The proteome is the full range of/number of different proteins that a cell is able to produce (at a given time)
OR
-The proteome is the full range of/number of different proteins the genome/DNA is able to code for
When a pathogen causes an infection, plasma cells secrete antibodies which destroy this pathogen.
Explain why these antibodies are only effective against a specific pathogen.(2)
-Antigens (on pathogen) are a specific shape/have specific tertiary/3D structure
-Antibody fits/binds/is complementary to antigen/antibody-antigen complex forms
OR
Antibodies are a specific shape/have specific tertiary/3D structure
-Antigens (on pathogen) bind/are complementary to antibody/antibody-antigen complex forms;
Describe and explain how you could use the biuret test to distinguish a solution of enzyme, lactase, from a solution of lactose. (2)
- Add Biuret reagent to both solutions – no mark
- Lactase/enzyme will give purple/lilac/mauve
OR - Lactose/reducing sugar will not give purple/lilac/mauve/will remain blue
- Because lactase is a protein
Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why. (3)
- Lactose has a different shape/structure
- Does not bind to active site of enzyme/sucrase
OR - Active site of enzyme/sucrase has a specific shape/structure
- Does not fit/bind to lactose so no enzyme-substrate complexes formed.
Describe the induced fit model of enzyme action. (2)
- Active site not complementary
- Active site changes shape
- Change in enzyme allows substrate to able to fit/ enzyme-substrate complex to form
Describe one way that the lock and key model is different from the induced fit model. (2)
- Active site does not change (shape)/is fixed (shape)
- Already fits the substrate/is
complementary before binding
An enzyme catalyses only one reaction. Explain why.
- (Enzyme has) active site is a specific shape
2. Only one substrate fits/binds (the active site)
Diabetes mellitus is a disease that can lead to an increase in blood glucose concentration. Some diabetics need insulin injections. Insulin is a protein so it cannot be taken orally. Suggest why insulin cannot be taken orally. (2)
- Broken down by enzymes/digested/denatured (by pH)/too large to be absorbed;
- Insulin no longer functional
What is the effect of substrate concentration on the rate of an enzyme controlled reaction. (3)
- Increases then plateaus/rate does not change
- It plateaus as all active sites occupied/saturated
- (rate of reaction)/maximum number of enzyme-substrate complexes per second
Explain how a competitive inhibitor works.
- Inhibitor is a similar shape to substrate
- Inhibitor enters active site/competes with substrate
- Less substrate binds/fewer enzyme-substrate complexes form per second.
Describe how a non-competitive inhibitor works.
- Attaches to the enzyme at a site other than the active site (allosteric site)
- Changes (shape of) the active site
OR
Changes tertiary structure (of enzyme) - (So active site and substrate) no longer complementary so less/no substrate can fit/bind, less/no enzyme-substrate complexes form
