BM - Proteins and Enzymes Flashcards
Describe the four levels of protein structure and explain how the structure of a protein is related to its function.
- Primary Structure: Sequence of amino acids. Determines protein folding and function.
- Secondary Structure: Folding into alpha helices or beta-pleated sheets (hydrogen bonds).
- Tertiary Structure: 3D shape from R-group interactions (hydrogen bonds, ionic bonds, etc.).
- Quaternary Structure: Multiple polypeptides interact to form functional protein (e.g., hemoglobin).
Give an example of different types of proteins and their roles
- Hemoglobin (quaternary structure, oxygen binding)
- Amylase (tertiary structure, catalyzes starch breakdown).
Explain the mechanism of enzyme action, including the lock-and-key and induced fit models.
- Lock-and-Key: Substrate fits perfectly into the enzyme’s active site.
- Induced Fit: Enzyme shape changes upon substrate binding to better fit substrate.
Discuss how temperature, pH, and substrate concentration affect enzyme activity.
- Temperature: Higher temperature increases activity (up to optimal), high temps denature enzyme.
- pH: Enzymes have an optimal pH; deviations cause denaturation or decreased activity.
- Substrate concentration: Increased concentration increases reaction rate (until enzyme saturation).
Describe the two main types of enzyme inhibition: competitive and non-competitive inhibition. Explain how each type affects enzyme activity.
- Competitive Inhibition: Inhibitor competes with substrate for active site. Can be overcome by increasing substrate concentration
- Non-competetive inhibitors bind to a different part of the enzyme, changing the shape of the active site. this prevents binding of the substrate to the active site. therefore, it doesnt matter how much more substrate you add, the rate of reaction will never be the same as without substrate.
Discuss the role of enzymes as biological catalysts.
Enzymes as Catalysts: Speed up reactions by lowering activation energy and providing an alternate reaction pathway
Explain how enzymes affect activation energy and provide examples of enzyme-catalyzed reactions.
- Amylase: Breaks down starch into glucose.
- DNA Polymerase: Synthesizes DNA during replication.
- Catalase: Breaks down hydrogen peroxide into water and oxygen.
Define denaturation in the context of proteins and enzymes. Describe the causes and consequences of denaturation, particularly how environmental conditions alter enzyme activity.
5 Marks
- Denaturation: Loss of 3D structure, causing loss of function.
- Causes: Extreme temperature, pH changes, or chemicals.
- Consequences:
- Disrupts enzyme active site, preventing substrate binding.
- Example: Heat or extreme pH can denature enzymes, stopping reactions.
Describe the induced-fit model of enzyme action and how an enzyme acts
as a catalyst
3 marker
- Substrate binds to the active site/enzyme
- Active site changes shape (slightly) so it is complementary to substrate
- enzym act as a catalyst by reducing activation energy;
A competitive inhibitor decreases the rate of an enzyme-controlled reaction.
Explain how.
3 marks
- Inhibitor similar shape to substrate therefore complementary to the 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 Marks
- Primary structure is the order of amino acids
- Secondary structure formed by hydrogen bonding (between amino
acids) to form alpha helix/β-pleated sheet - Tertiary structure formed by hydrogen bonds / disulfide
bridges / ionic bonds that form the 3D structure which creates the active site in enzymes - Quaternary structure contains 1 or more polypeptide chain
Explain how the active site of an enzyme causes a high rate of reaction.
3 marks
- Lowers activation energy;
- Induced fit causes 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 marks
- add biuret reagent
- positive results turns from blue to lilac
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 marks
Similarities
- Amine/NH2 (group at end);
- Carboxyl/COOH (group at end);
- Two R groups;
- All contain C and H and N and O;
Difference
5. Variable/different R group(s);
Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction
3 marks
- Attaches to the enzyme at a site other than the active site - allosteric
- Changes (shape of) the active site
- (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 marks
1.Condensation (reaction) / loss of water;
2. Between amine and carboxyl
The secondary structure of a polypeptide is produced by bonds between amino acids.
Describe how.
2 marks
- Hydrogen bonds;
- Between NH (group of one amino acid) and C=O (group);
Forming β pleated sheets / α helix;
Two proteins have the same number and type of amino acids but different tertiary structures.
Explain why
2 marks
- Different sequence of amino acids
- Forms ionic / hydrogen / disulfide bonds in different places;
Formation of an enzyme-substrate complex increases the rate of reaction.
Explain how
2 marks
- Reduces activation energy
- Due to bending bonds
Draw the general structure of an amino acid.
R
]
H2N-C-COOH
]
H
Maltose is hydrolysed by the enzyme maltase.
Explain why maltase catalyses only this reaction.
3 marks
- Active site (of enzyme) has (specific) shape / tertiary structure / active
site complementary to substrate / maltose; - (Only) maltose can bind / fit;
- To form enzyme substrate complex.
A principle of homeostasis is the maintenance of a constant internal environment. An increase in the concentration of carbon dioxide would change the internal environment and blood pH.
Explain the importance of maintaining a constant blood pH.
3 marks
include example
- It’s important to maintain pH to avoid protein / enzyme (in blood) to be affected by change in pH;
- This will result in the change of charge / shape / tertiary structure- denature
- for example less oxygen binds with haemoglobin / less transport across membranes
