Proteins Flashcards
1
Q
What is a protein
A
- Macromolecules that are polymers
- Large number of amino acids joined together by peptide bonds in a condensation reaction
- To form chains
2
Q
Name 7 examples of proteins and give an example of each
A
- Enzymes (eg DNA helicase)
- Cell membrane proteins (eg carrier)
- Hormones (ONLY SOME) (eg adrenaline)
- Immunoproteins (eg antibodies)
- Transport proteins (eg haemoglobin)
- Structural proteins (eg keratin, collagen)
- Contractile proteins (eg myosin)
3
Q
Describe how a peptide bond forms
A
- OH lost from COOH of one amino acid
- H lost from NH2 of the next
- Forms CONH
- 1 H2O molecule for every peptide bond formed
- Example of a condensation reaction
- The reverse of this happens during hydrolysis
4
Q
Primary structure
A
- Sequence of amino acids
- Peptide bonds
5
Q
Secondary structure
A
- Hydrogen bonds form
- Between -C=O (d-) of one amino acid
- and -N-H (d+) of another
- to form a-helices or b-pleated sheets
- highest level of structure in some structural proteins eg keratin/fibrin
6
Q
Explain the structure of an a-helix
A
- Hydrogen bond forms every 4th peptide bond
- Giving it a helix shape
7
Q
Explain the structure of a b-pleated sheet
A
- Protein folds so that the 2 parts of the polypeptide chain are parallel to each other
- So H bonds form between the folded layers
8
Q
Tertiary structure
A
- Hydrogen, Ionic, Disulfide, Weak hydrophobic interactions and covalent bonds between R groups (common in globular proteins)
9
Q
Quaternary structure
A
- Multiple polypeptide chains (subunits) joined together by disulfide bridges
- Working together as a functional molecule
- Also prosthetic (non-protein) groups may be present
10
Q
Disulfide bridges
A
- Strong covalent bonds (strongest type of bond within a protein)
- Form between 2 cysteine R groups
- Don’t occur frequently
- Help to stabilise proteins and join polypeptide chains together if protein has quaternary structure
- Can be broken by reduction
- Common in proteins secreted by cells
11
Q
Ionic Bonds
A
- Occur between fully charged R groups eg (-NH3+ and COO-)
- Broken by pH changes
- Not common but very strong
12
Q
A
13
Q
Hydrogen bonds
A
- Form between strongly polar R groups
- Weakest bonds but most frequent
- Can be broken easily by pH changes and high temperatures
- Can form between a very wide variety of R groups
14
Q
Describe the Buirets test for Proteins
A
- Add 2cm3 of sample
- Add 2cm3 of Biurets reagent (alkaline solution containing Copper II Sulfate)
- +ve result = colour change from blue to lilac
- But this test is qualitative
15
Q
Globular Proteins
A
- Compact
- Roughly spherical in shape
- High proportion of hydrophilic R groups so they are water soluble
- Play an important part in physiological processes
- Each one has a unique shape, therefore a unique role eg enzymes catalyse specific reactions and immunoglobulins respond to specific antigens
16
Q
Why are globular proteins spherical?
A
- Non-polar/hydrophobic R groups point towards the centre of the protein, away from the surrounding aqueous environment
- Polar/hydrophilic R groups point outwards so water molecules can surround the polar hydrophilic R groups - this makes them soluble
17
Q
Why is it an advantage for globular proteins to be soluble?
A
- They can play important physiological roles
- And easily transported around an organism
- And involved in metabolic reactions
18
Q
What type of structure would a globular proteins have?
A
- Tertiary or Quaternary (it may also be conjugated and have a prosthetic group)
19
Q
Fibrous Proteins
A
- Long strands of PP chains
- Little or no tertiary structure
- Have cross linkages due to hydrogen bonds
- Have a higher proportion of hydrophobic R groups so insoluble in water
- Highly limited and repetitive amino acid sequence
- This creates strong, insoluble, highly organised structures
- Therefore fibrous proteins are very suitable for structural roles
- Eg keratin = nails, horns, hair, feathers
- Eg collagen = connective tissue found in skin, ligaments and tendons
- Eg myosin, actin, fibrin
