When carrying out the buriet test for proteins. Suggest why scientist would de- ionise water?
1 mark
As a control
What is a amino acid?
A monomer in which proteins are made
What is the structure and function of antibodies?
Two light pp chain (short)
Two heavy pp chain (long)
Bonded together
Found in blood
Immune response.
Have variable regions which bind to antigens invading cells
Two proteins have the same number and type of amino acids but different tertiary structures
Explain why.
2 marks
Different sequence of amino acids
OR
Different primary structure;
If assumed proteins are the same, accept effect of different pH/ temperature
Forms ionic / hydrogen / disulfide bonds in different places;
Describe how a peptide bond is formed between two amino acids to form a dipeptide.
2 marks
Condensation (reaction) / loss of water;
Between amine / NH and carboxyl / COOH;
Accept between amino (group) and carboxylic acid group
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
Similarity
Amino group NH3 (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);
When carrying out chromatography with different amino acid using electrodes
explain why they would be in different positions?
3 marks
Moved to negative (electrode) because positive (ly charged)
Moved positive electrode because negative charged
(Spots move) different distances/rates because (amino acids) different charge/mass;
One spot has 2 amino acids because (amino acids) same charge/mass;
Enzymes are a protein. What is their structure?
Spherical and compact with a tightly folded polypeptide chain
Describe how structure of a protein depends on amino acid it contains.
5 marks
- Structure is determined by (relative) position of amino acid/R
group/interactions;
Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions
- Primary structure is sequence/order of amino acids;
- Secondary structure formed by hydrogen bonding (between amino acids);
Accept alpha helix/ß-pleated sheet for ‘secondary structure’
- Tertiary structure formed by interactions (between R groups);
Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions - Creates active site in enzymes
OR
Creates complementary/specific shapes in antibodies/carrier proteins/receptor (molecules); - Quaternary structure contains >1 polypeptide chain
OR
Quaternary structure formed by interactions/bonds between polypeptides;
Accept for intereactions’, hydrogen bonds/ disulfide bridges/ionic bonds/hydrophobichydrophilic interactions
Accept prosthetic (group)
A change from Glu (negative charge) to Lys at amino acid 300 had no effect on the rate of reaction catalysed by the enzyme.
The same change at amino acid 279 significantly reduced the rate of reaction catalysed by the enzyme.
Use all the information and your knowledge of protein structure to suggest reasons for the differences between the effects of these two changes.
3 marks
- Both) negatively charged to positively charged change in amino acid;
- Change at amino acid 300 does not change the shape of the active site
OR
Change at amino acid 300 does not change the tertiary structure OR
Change at amino acid 300 results in a similar tertiary structure;
Reference to ‘shape’ of active site only needed once. - Amino acid 279 may have been involved in a (ionic, disulfide or
hydrogen) bond and so the shape of the active site changes
Or
Amino acid 279 may have been involved in a (ionic, disulfide or hydrogen) bond and so the tertiary structure changed;
Amino acid 279 may be in the active site and be required for binding the substrate;
Reference to ‘shape’ of active site only needed
Both parts are required for each mark option.
For ‘a bond’ reject peptide bond.
Suggest two variables the biochemist controlled when investigating the effect of temperature on the rate of breakdown of a protein by the protease.
1 mark
Intial/ starting substrate concentration
Enzyme conc
Ph
Describe the primary structure of all proteins.
2 marks
- Sequence / order of amino acids
- (Joined by) peptide bonds
