proteins and 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 chain into Alpha-helix and Beta-pleated sheets due to hydrogen bonding;
. Tertiary structure is 3-D folding due to hydrogen bonding and ionic bonding and disulfide bridges;
. Quaternary structure is two 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;
. Between amine / NH2 and carboxyl / COOH;
Describe how an enzyme-substrate complex increases the rate of reaction
. Reduces activation energy
. 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 and Ionic bonds and Disulphide bonds form in different positions;
. Alters the tertiary structure of the enzyme / alters shape of 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) fit/ bind/ are complementary to antibody / antibody-antigen complex forms;
Describe & 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 fit/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 (3)
. Active site not complementary;
. Active site changes (shape) / is flexible;
. (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 (3)
. Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around
. substrate / (already) fits the substrate / is
. complementary (before binding);
An enzyme catalyses only one reaction. Explain why.
. (Enzyme has) active site is a specific shape;
. 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 / constant / steady / 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 (‘no longer complementary so less/no enzyme-substrate complexes form’);
