3.1.4 Proteins Flashcards
Monomers of proteins
Amino acid -> polypeptide -> protein
How many amino acids are there?
100
How many amino acids occur in living organisms?
20
What does each amino acid differ by?
The R group
Components of an amino acid
- R group
- Carboxyl group
- Amino group
Amino acid: R group
- Side chain
- Variety of different chemical groups different for each amino acid
Amino acid: Carboxyl (COOH) group
an acidic group which gives the amino acid the acid part of its name
Amino acid: amino (NH2) group
basic group where the amino part of the name amino acid comes from
Formation of proteins
- Condensation reaction between 2 amino acids forms a peptide bond (between the -OH of the carboxyl group and the -H of the amino group of another amino acid)
- NH2 joins to COOH
- There is a free NH2 at one end and a free COOH group at another end
Dipeptide
Formed by the condensation of 2 amino acids
Polypeptides
Formed by the condensation of many amino acids
4 structure stages of proteins
- Primary
- Secondary
- Tertiary
- Quaternary
Primary structure of proteins
- The order and number of amino acids in a protein
- Contains initial sequence of amino acids + so determines the protein’s function and 3d shape
- Specific for each protein (small alteration can affect protein function
Secondary structure of proteins
- The shape of the amino acid chain
- Hydrogen bonds form between the H of the -NH (overall positive charge) and the O of the C=O (overall negative charge)
- This causes the polypeptide chain to be twisted into a 3D shape (either alpha helix or beta pleated)
Tertiary structure of proteins
- Interactions between R groups
- 3D shape of the protein (makes each protein distinct and recognisable)
- Further twisting + folding
- Disulfide bridges, ionic bonds and hydrogen bonds form
Tertiary structure: Disulfide bridges
Fairly strong, not easily broken
Tertiary structure: Ionic bonds
Formed between any carboxyl and amino groups that are not involved in forming peptide bonds
Tertiary structure: Hydrogen bonds
Numerous, but easily broken
Tertiary bonds in terms of strength
- Disulfide bridges
- Ionic bonds
- Hydrogen bonds
Quaternary structure of proteins
Present in proteins with more than 1 polypeptide chain
Test for proteins
- To a test tube add equal amounts of liquid sample and sodium hydroxide (to make it alkaline)
- Add biuret reagant
- If protein is present, colour change: blue -> purple
Biuret reagent
Add few drops of dilute copper (II) sulfate solution
Types of proteins
- Globular proteins (have metabolic functions)
- Fibrous proteins (have structural functions)
How many polypeptides does a simple protein contain?
1
How many polypeptides does a functional protein contain
1 or more polypeptides
Fibrous proteins
- Long polypeptide chains which run parallel to each other, and have cross-linkages between them -> stable
Examples of fibrous proteins
- Collagen
- Keratin
Globular proteins
Compact, roughly spherical shape
Examples of globular proteins
- Haemoglobin and enzymes (these are conjugated proteins because they also contain a non-protein chemical group)
What is the structure of a protein determined by?
position of amino acid, therefore the primary structure
Similarities between amino acids
- NH2
- COOH
Difference between amino acids
different R groups
