1.4 - Proteins Flashcards
Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3)
- Substrate binds to the active site/enzyme / Enzyme-substrate complex forms
- Active site changes shape (slightly) so it is complementary to substrate
- Active site changes shape (slightly) so
distorting/breaking/forming bonds in the substrate - Reduces activation energy
A competitive inhibitor decreases the rate of an enzyme-controlled reaction. Explain how. (3)
- Inhibitor similar shape to substrate
‘accept complementary to active site’ - Fits/binds to active site;
- Prevents/reduces enzyme-substrate complex forming
Describe how the structure of a protein depends on the amino acids it contains. (5)
- Structure is determined by the (relative) position of amino acid/R group/interactions
‘accept for ‘interactions’ for hydrogen bonds/disulfide bridges /ionic bond’ - Primary structure is the sequence/order of amino acids
- Secondary structure formed by hydrogen bonding (between amino acids)
‘accept alpha helix/β-pleated sheet’ - Tertiary structure formed by interactions (between R groups)
‘hydrogen bonds/disulfide bridges/ionic bonds’ - Creates active site in enzymes / Creates complementary/specific shapes in antibodies/carrier
proteins/receptor (molecules) - Quaternary structure contains >1 polypeptide chain
Quaternary structure formed by interactions/bonds between
polypeptides;
Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end. (2)
- One amine/NH2 group joins to a carboxyl/COOH group to form a peptide bond
- (So in the chain) there is a free amine/NH2 group at one end and a free carboxyl/COOH group at the other
/ Each amino acid is orientated in the same direction in the chain
Explain how the active site of an enzyme causes a high rate of reaction. (3)
- Lowers activation energy
- Induced fit causes the active site (of enzyme) to change shape
- (So) enzyme-substrate complex causes bonds to form/break
Describe a biochemical test to confirm the presence of protein in a solution. (2)
- Add biuret (reagent)
- (Positive result) purple/lilac/violet /mauve
A dipeptide consists of two amino acids joined by a peptide bond.
Dipeptides may differ in the type of amino acids they contain. Describe two other ways in which all dipeptides are similar and one way in which they might differ. (3)
Similarities:
- Amine/NH2 (group at end)
- Carboxyl/COOH (group at end)
- Two R groups
- All contain C and H and N and O
Difference:
- Variable/different R group(s);
Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction. (3)
- Attaches to the enzyme at a site other than the active site;
‘attaches to allosteric/inhibitor site’ - Changes (shape of) the active site
/ Changes tertiary structure (of enzyme) - (So active site and substrate) no longer complementary so
less/no substrate can fit/bind
Describe how a peptide bond is formed between two amino acids to form a dipeptide. (2)
- Condensation (reaction) / loss of water
- Between amine (NH2) and carboxyl (COOH)
The secondary structure of a polypeptide is produced by bonds between amino acids. Describe how. (2)
- Hydrogen bonds
- Between NH (group of one amino acid) and C=O (group)
/ Forming β pleated sheets and α helix
Two proteins have the same number and type of amino acids but different tertiary structures. (2)
- Different sequence of amino acids / Different primary structure
- Forms ionic / hydrogen / disulfide bonds in different places
Formation of an enzyme-substrate complex increases the rate of reaction. Explain how. (2)
- Reduces activation energy
‘accept reduces Ea’ - Due to bending bonds
/Without enzyme, very few substrates have sufficient energy for reaction
A decrease in temperature decreases the kinetic energy of molecules in a solution. Explain how a decrease in temperature decreases the rate of an enzyme-controlled reaction. (2)
- Molecules moving less / slower; reduces chance of collision
(between enzyme and substrate) / of enzyme-substrate
complexes being formed
Urea breaks hydrogen bonds. Explain how the addition of urea would affect the rate of an enzyme-controlled reaction. (3)
- These bonds hold/maintain tertiary/ globular structure (of enzyme)
- Enzyme denatured / tertiary structures destroyed / (shape of) active site distorted/changes;
- Substrate no longer fits / enzyme-substrate complex not formed
