2.3.32 · Biological Molecules
Protein Shape — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
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Lesson summary
2.3.3 Protein Shape — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe the four types of R-group interaction that determine tertiary structure.Folding — a polypeptide folds because of interactions between R groups.Variety — each of the 20 amino acids has a uni…
- Peptide bond
- Hydrogen bonds
- Disulfide bond
- Ionic bond
- Hydrophobic interaction
- Haemoglobin
Section 1 of 8How R groups determine shape
How R groups determine shape
Folding
- Folding a polypeptide folds because of interactions between R groups.
Variety
- Variety each of the 20 amino acids has a unique R group, giving a vast range of shapes and functions.
Tertiary structure
- Tertiary structure the resulting three-dimensional configuration.
Section 2 of 8Disulfide bonds
Formation
- Formation strong covalent bonds between the sulfur atoms of two cysteine R groups.
Strength
- Strength the strongest bonds in a protein, but they are less common.
Role
- Role they stabilise proteins and are common in secreted proteins such as insulin.
Breakage
- Breakage they can be broken by reduction.
Section 3 of 8Ionic bonds
Formation
- Formation between positively charged R groups (–NH3+) and negatively charged R groups (–COO-).
Strength
- Strength stronger than hydrogen bonds but not common.
Breakage
- Breakage pH changes break them.
Section 4 of 8Hydrogen bonds
Formation
- Formation between strongly polar R groups.
Strength
- Strength the weakest bonds, but the most common because many R groups can form them.
Section 5 of 8Hydrophobic interactions
Formation
- Formation between non-polar R groups in the interior of the protein.
Nature
- Nature an interaction is a low-energy attraction, unlike a bond, which is high energy.
Section 6 of 8More from the specification
1
Primary structure
- The sequence of amino acids in a polypeptide.
2
Quaternary structure
- Arrangement of multiple polypeptide subunits.
3
Amine group
- The –NH2 functional group.
4
Triple helix
- Three polypeptides wound together.
5
Collagen
- A protein in skin, gums and bones that needs vitamin C to form.
6
Haemoglobin
- Protein in red blood cells that binds oxygen.
7
Hydrophobic
- Water-hating; non-polar and unable to dissolve in water.
8
Sequence
- The order of bases in DNA or amino acids in a protein.
9
Specific
- Able to act on only one type of substrate.
10
Globular protein
- A rounded, usually soluble protein, such as an enzyme or insulin.
11
Fibrous protein
- A long, insoluble structural protein, such as collagen.
12
Prosthetic group
- A non-protein component, such as haem in haemoglobin.
13
Peptide bond
- Peptide bond the C–N link where the carbon is double-bonded to oxygen; the R group takes no part in it.
14
Hydrogen bonds
- Hydrogen bonds in secondary structure they join backbone amino and carboxyl groups, whereas in tertiary structure they join R groups.
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Tertiary structure | The 3D shape formed by interactions between R groups. |
| Disulfide bond | A strong covalent bond between two cysteine R groups. |
| Ionic bond | An attraction between oppositely charged R groups. |
| Hydrogen bond | A weak attraction between polar R groups. |
| Hydrophobic interaction | A weak attraction between non-polar R groups. |
| Cysteine | The amino acid with a sulfur atom in its R group. |
Section 8 of 8Exam technique
1
Treating an interaction as a bond — an interaction is a low-energy attraction.
2
Saying hydrogen bonds are the strongest — disulfide bonds are the strongest.
3
Saying disulfide bonds form from any R groups — they require cysteine.
4
Saying ionic bonds are unaffected by pH — pH changes break them.
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