Proteins and Enzymes Flashcards
Describe the structure of proteins (6)
Polymer of amino acids
Joined by peptide bonds
Formed by condensation reactions
Primary structure is sequence and number of amino acids
Secondary structure is folding of polypeptide chain into alpha helixes and beta pleated sheets due to hydrogen bonding (C=O:H-N)
Tertiary structure is 3D folding due to hydrogen bonds, ionic bonds and disulphide 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 (2)
Condensation reaction
Between amine group and carboxyl group
Q
Describe how an enzyme-substrate complex increases the rate of reaction (2)
Reduces activation energy
Due to bending bonds
Describe how a change in the base sequence of the DNA coding for an enzyme may result in a non-functional protein. (3)
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? (1)
number of different proteins that a cell is able to produce at a given time
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 structure
Antibody binds to antigen because it is complementary
Antigens (on pathogen) bind to antibody to form antibody-antigen complex
Describe how to carry out a test for proteins. (2)
Add equal volume of Biuret reagent
Purple/Violet colour change indicates protein is present
Sucrose doesn’t hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why. (2)
Lactose has a different structure
Doesn’t bind/fit to active site of enzyme/sucrase
Describe the induced fit model of enzyme action (2)
Active site not complementary
Active site is flexible
(Change in enzyme’s shape of active site) allows substrate to bind and form enzyme-substrate complex
Describe one way that the lock and key model is different from the induced fit model. (2)
Active site is rigid/fixed
So substrate fits and is complementary before binding
An enzyme catalyses only one reaction at a time. Explain why. (1)
Enzyme’s active site has a specific shape
So only one substrate binds
Suggest why a protein can be the substrate for two different enzymes. (2)
Different parts of the protein have different amino acid sequences so are a different shape
Each enzyme active site is a specific shape and complementary to a different part of the protein
What is the effect of temperature on the rate of an enzyme controlled reaction? (3 marks)
As temperature increases, there is more kinetic energy so more frequent successful collisions take place
More enzyme substrate complexes formed per second
If temperature increases beyond optimum temperature, the weak Hydrogen bonds, ionic bonds and disulphide bridges break and changes the tertiary structure which alters the shape of the active site and the enzyme can become denatured
Therefore, less enzyme substrate complexes are formed per second
What is the effect of pH on the rate of an enzyme controlled reaction? (3 marks)
a slight change in the pH can denature the enzyme and alter the active site
so less enzyme substrate complexes form per second so rate of reaction decreases
enzyme becomes denatured
What is the effect of substrate concentration on the rate of an enzyme controlled reaction? (3 marks)
- 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;
