proteins (k,l,m,n,o) Flashcards
1
Q
What is a peptide?
A
A polymer made up of amino acid molecules
2
Q
What is a protein?
A
Consists of one or more polypeptides arranged as complex macromolecules and have specific biological functions. Contain C,H,O,N,S
3
Q
Structure of an amino acid
A
- same basic structure with variable R-groups
NH₂ (amine)
|
R-group - C - H
|
COOH (carboxyl)
4
Q
Describe the synthesis and breakdown of peptides
A
- the hydroxyl in the carboxylic acid group of one amino acid reacts with a hydrogen in the amine group of another amino acid
- condensation reaction forming a peptide bond and water
- resulting compound is a dipeptide
- polypeptides formed when many amino acids are joined together by peptide bonds
- synthesis catalysed by peptidyl transferase
- breakdown/hydrolysis catalysed by proteases
5
Q
Describe the primary structure of proteins
A
- the sequence in which amino acids are joined
- directed by information in the DNA
- involves peptide bonds only
- influences how the polypeptide forms
6
Q
Describe the secondary structure of proteins
A
- the H, O, N atoms of basic repeating structure interact
- hydrogen bonds may form within the amino acid chain - coiling it into an alpha helix
- hydrogen bonds may join polypeptide chains parallel to each other - forming beta pleated sheets
7
Q
Describe the tertiary structure of the protein
A
- the folding of a protein into its final shape
- brings R-groups of different amino acids together so they are close enough to interact
- hydrogen bonds: weakest bonds formed
- hydrophobic/hydrophilic interactions: weak interactions between polar and non-polar R-groups
- ionic bonds: stronger than hydrogen bonds + form between oppositely charged R-groups
- disulphide bonds/bridges: covalent and strongest of the bonds but only form between R-groups that contain sulphur atoms
8
Q
Describe the quaternary structure of the protein
A
- the associated of 2 or more individual proteins (subunits) - interactions same as tertiary structure but between different protein molecules instead of within one molecule
- protein subunits can be identical or non-identical
- e.g. enzymes - 2 identical etc.
9
Q
Describe globular proteins
A
- compact
- water-soluble
- spherical in shape
- form when proteins fold into their tertiary structures in such a way that the hydrophobic R-groups on the amino acids are kept away from the aqueous environment
- hydrophilic R-groups on outside so the proteins are soluble in water - important for the function
10
Q
Describe insulin
A
- a globular protein
- hormone involved in the regulation of blood glucose concentration
- transported in bloodstream so must be soluble
- must fit into specific receptors on cell-surface membranes so has precise shapes
11
Q
Describe conjugated proteins
A
- globular proteins that contain a prosthetic group - non-protein component
- e.g. lipids or carbs or metal ions can combine to them
12
Q
Describe haemoglobin
A
- red, oxygen-carrying pigment in red blood cells - conjugated
- quaternary structure: 4 polypeptides - 2 alpha and 2 beta subunits
- each subunit contains a prosthetic haem group
- Fe²⁺ ions present in haem groups are each able to combine reversibly with an oxygen molecule
- can pick oxygen up in the lungs and transport it where needed in cells to be released
13
Q
Describe catalase
A
- an enzyme - conjugated protein
- quaternary structure: 4 haem prosthetic groups
- Fe²⁺ presence allow catalase to interact with hydrogen peroxide to speed up its breakdown
- hydrogen peroxide is a common by-product of metabolism, but damaging to cells and cell components if allowed to accumulate
14
Q
Describe fibrous proteins
A
- long
- insoluble
- non-spherical
- strong
- amino acid sequences are quite repetitive so organised structure - high proportion of hydrophobic R-groups
15
Q
Describe collagen
A
- (fibrous) a connective tissue found in skin, tendons, ligaments + the nervous system
- 3 polypeptides wound together in a long + strong rope-like structure
- flexible - minerals can bind to it to increase its rigidity, e.g. in bone
