12.2 Proteins and Enzymes Flashcards
Structure of amino acid
- Amine group
- R group
- Carboxylic acid group
- Hydrogen
What is a dipeptide?
- Two amino acids joined
- Via a condensation reaction
- Joined by a peptide bond
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;
Test for proteins
- Place the sample in a test tube
- Add equal volumes of Biuret solution
- Colour change to purple shows protein is present
Enzyme
- Globular proteins which act as biological catalysts
- Increase the rate of reaction
- Lowering the activation energy
- Done by stressing AND distorting the bonds during the formation of the ESC
Lock & Key model
- Active site is rigid and does not change shape
- Substrate binds to enzymes active site
- Substrate fits exactly to the complementary active site
- Products are formed so are released as no longer fit the active site
- Enzyme free to take part in another reaction
Induced fit model
- Active site not complementary
- Active site changes shape as the substrate binds
- So stressed the substrate bonds to lower the Ea of the reaction
- Active site returns to its original shape
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;
Describe the induced fit model of enzyme action.(2)
- 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(2)
- 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
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.
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;
Factors effecting enzyme action
Temperature
pH
Substrate conc
Enzyme conc
Effect of temperature on ROR
- Increase in temp
- Increase in kinetic energy
- More successful collisions
- More ESC form per second
- Denaturation: past the optimum the hydrogen/ionic bonds will break causing a change in tertiary structure causing a change in the active site
- Active site is no longer complementary so less ESC
Effect of pH on ROR
- Enzymes have an optimal pH
- If made more acidic or more basic
- Charge on R groups are changed
- Ionic bonds are broken
- Tertiary structure is changed
- Active site changes shape
- No longer complementary
- Less ESC formed
Effect of substrate conc. on graph
- Increases
- Then plateaus
- As enzyme becomes the limiting factor
Effect of enzyme conc. on graph
- Increases
- Then plateaus
- As substrate becomes the limiting factor
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’);
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;
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;
