2.1.2 - Proteins Flashcards
Structure of proteins
- Proteins are polymers
- Monomer : Amino acid
- Made up of C,H,O,N and could contain S,P
Function of proteins
- Structural roles - Muscles or tendons
- Metabolic roles - Enzymes or hormones
- Transport roles - Haemoglobin
Amino acids
- Amine group: NH2
- Central Carbon
- H
- R group
- Carboxyl group : COOH
Synthesis of dipeptides
- Two amino acids are joined together by a condensation reaction to form a dipeptide
- A peptide bond is the covalent bond formed when two amino acids are joined together
- Water is removed
Breakdown of dipeptides
- Hydrolysis reaction
- Water added
- Peptide bond broken
Primary structure
The specific sequence of amino acids in a polypeptide chain
Secondary structure
The folding of the polypeptide chain into alpha helix or beta pleated sheet due to the formation of hydrogen bonds
Alpha helix
In an alpha helix, the polypeptide chain coils, H bonds form between amino acids and keep the coil stable
Beta pleated sheet
Chains form a zigzag and fold over themselves, H bonds stabilise the structure
Tertiary structure
- The overall specific 3D shape determined by interactions between R groups
- Bonds form between R groups : Hydrogen bonds, ionic bonds, disulphide bonds and hydrophobic and hydrophilic interactions
Hydrogen bonds
These form between polar R-groups
Ionic bonds
These form between positively and negatively charged R groups
Disulphide bonds
These form between sulphur atoms in R groups
Quaternary structure
The specific 3D shape of a protein that is determined by the multiple polypeptide chains bonded together
Haemoglobin structure
- Globular protein
- Made up of four polypeptide chains
- Quaternary structure
- Two alpha chains and two beta chains
- Each polypeptide chain has an iron ion prosthetic group, so it is a conjugated protein
- The four prosthetic groups are called haem groups and contain a Fe2+ ion
Haemoglobin function
- Found in red blood cells
- Transports oxygen around the body
- The haem group allows haemoglobin to combine reversibly with oxygen
Conjugated protein
Non- protein component
Haem group
Insulin structure
- Globular protein
- Two polypeptide chains
- Chain A starts with an alpha helix and chain B ends with a beta pleated sheet
- Both are folded into tertiary structures which are then joined by disulphide bonds
- Hydrophilic parts outside and hydrophobic parts on the inside
Insulin function
- Secreted by the pancreas
- Important role in maintaining blood glucose concentration
- The shape of insulin allows it to specifically bind to receptors in cell membranes to help lower blood glucose concentration.
- Insulin also has hydrophilic R groups on the outside making it soluble in water. This allows insulin to dissolve in the blood and be easily transported around the body.
Catalase structure
- Enzyme
- 4 polypeptide chains
- 4 haem prosthetic groups(Fe2+ ions)
- Has a specific active site
Catalase function
- Catalysed a reaction, so it increases the rate of reaction
- Breaks down hydrogen peroxide
- Hydrogen peroxide can be damaging to cells.
- It is a byproduct of metabolism so catalyse prevents hydrogen peroxide accumulating in the body.
Globular proteins (Properties)
- Spherical shape
- Soluble
- Complementary to another molecule
- Contain prosthetic group
- Temp/pH sensitive
Fibrous proteins (Properties)
- Elongated strands
- Insoluble
- Strong/tough
- Flexible
Keratin
- Fibrous protein
- Hard and strong
- High amounts of cysteine results in disulphide bonds
- This gives it a lot of strength
Collagen
- Fibrous protein
- Forms very strong fibres, so it is used to provide strength to many parts of the body
- Artery walls : Prevents vessels from bursting
- Tendons : Connect muscles for bone
- Connective tissue
Elastin
- Fibrous protein
- Elastic properties
- Can stretch and recoil
- Found in walls of blood vessels and the alveoli
- Expand and contract
Fibrous protein functions
- Structure: Collagen is a connective tissue
- Protection : Keratin provides strength to hair and nails
- Elasticity : Elastin allows blood vessels to expand and contract
Globular protein functions
- Enzymes : Catalyse reaction by reducing activation energy. E.g. Catalase catalyses the breakdown of hydrogen peroxide
- Hormones :Insulin control blood sugar concentration
- Transportation : Haemoglobin transports oxygen around the body
