proteins & 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 (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
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’)
Describe how to carry out a test for proteins. (2)
Add equal volume of Biuret reagent
Purple/Violet colour change indicates protein is presen
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;
What is the effect of substrate concentration on the rate of an enzyme controlled reaction? (3 marks)
Increases then plateaus
It plateaus as all active sites occupied /
Saturated
maximum number of Enzyme-Substrate complexes per second;
The secondary structure of a polypeptide is produced by bonds between amino acids.
Describe how. (2 marks)
Hydrogen bonds
Between N-H and C=0 OR forming beta-pleated sheets and alpha helixes
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 bonds, hydrogen bonds and disulphide bridges in different places
Explain how the shape of an enzyme is related to its function
(3 marks)
Enzyme has specific 3D tertiary structure
Substrate complementary to enzyme’s active site
Substrate binds to active site
What are amino acids
SPEC - the monomers from which proteins are made
What is the general structure of an amino acid
https://static.aqa.org.uk/assets/image/0019/235441/00055366-DA00046398-DB.png
https://static.aqa.org.uk/assets/image/0019/235441/00055366-DA00046398-DB.png
What does each part represent
SPEC -
The NH2 represents an amine group
COOH represents a carbonyl group
R represents a side chain
How do the 20 amino acids common in organism differ
SPEC - In their side group
What does a condensation reaction between two amino acids form
A peptide bond
What does a functional protein contain
One or more polypeptides
What does each enzyme lower
The activation energy of the reaction it catalyses
