Amino acid and proteins Flashcards
What are the functions of proteins?
Structural support, enzymes (amylase and digestive enzymes), transcription factors, translation factors, hormones (e.g. insulin) and Intracellular signalling
GDNF used to cure Parkinson’s disease.
used to produce dopaminergic neuron from embryonic
& inducible stem cells for cell therapy (experimental)
What is the isoelectric point?
It is the pH at which the amino acid has no net charge. It does not migrate in an electric field, and it exists predominantly as zwitterions.
It is the midpoint concentration between the 2 pKa values of the amino acid.
What gives rise to the different protein structures?
alternative splicing & post-translational modifications.
Which amino acid stereoisomer exists predominantly in cells?
L-amino acid
What is condensation?
A process whereby two molecules/groups (e.g. COOH and NH2 groups of two amino acids) forms a covalent bond, resulting in the elimination of one water molecule.
Why are non-polar amino acids still able to dissolve in water?
It may have R groups that are able to be ionised
How are amino acids classified?
Non-polar (aliphatic and aromatic) and polar (acidic, basic and uncharged)
Examples of non-polar amino acids
Leucine, Proline, Alanine, Valine, Methionine, Phenylalanine, Isoleucine, Tryptophan
Only Tryptophan and Phenylalanine are aromatic
Examples of acidic amino acids
Aspartic acid, Glutamic acid
Examples of basic amino acids.
Histidine, Lysine and Arginine
Examples of polar uncharged amino acids
Glycine, Serine, Asparagine, Glutamine, Tyrosine, Cysteine, Threonine
Which amino acid can act as a neurotransmitter?
Glycine
What is Hydroxyproline and what is the function?
- Hydroxylated form of proline
- It provides stability to collagen fibres
- Insufficient hydroxylation will lead to scurvy - lack of vitamin c resulting in bleeding gums - due to weak collagen
How do cells convey signals from external to internal?
by exploiting reversible changes in some amino acids (e.g. phosphorylation)
-cell signalling involves the relay of information from protein to protein
What is one unit of amino acid called?
Residue
Different types/groups of proteins
Fibrous/Globular/Membrane
What are integral proteins?
Receptors and transporters
What are lipid anchored proteins?
Proteins linked via lipids to the membrane
What are peripheral proteins?
Proteins associated with the membrane
Properties of globular protein
- Soluble in aqueous medium
- Diffuse readily
- tightly folded into a compact globular shape with hydrophobic parts on the inside and hydrophilic parts on the outside
- e.g. enzymes, transport proteins and antibodies
Properties of fibrous protein
- Insoluble in aqueous medium. Hydrophobic parts on the exterior
- Structural or protective role
- e.g. Collagen and a-keratin
Non-covalent forces that stabilise protein structure
- Hydrogen bonds
- Hydrophobic interactions (clathrate)
- Electrostatic interactions (ionic)
- Van der Waal’s forces
Secondary structure of proteins
alpha-helix and beta-pleated sheets
Commonly found in globular proteins
Beta-pleated sheets
- intermolecular H bonds
- Favour amino acids with compact R groups
Why is proline only found at the start/end of helices but not usually found in the middle?
It disrupts a-helix formation because of its backward twist which destabilise the kink
What is a domain?
Discreet and independently folded globular units which consists about 100-200 amino acid residues. Each module has a specific function
Quaternary structure of a protein
Stabilised by non-covalent interactions between subunits
Advantages of quaternary structure
Lower error of synthesised when smaller subunits are held together by non-covalent interactions rather than synthesising a long/large protein chain
What is denaturation of protein
Loss of biological activity due to altered conformations/structure as a result of heat/pH/organic solvents/urea. It destroys the secondary,tertiary and quaternary structures of the protein but the primary structure remains intact.
Intracellular control of protein folding
Break down the protein or exported to the lysosome to help it to fold
When cell is stressful – nucleus will receive a signal to produce more chaperones to help the protein to fold correctly
Cell dies if protein is unable to fold correctly
Diseases associated with protein misfolding
Alzheimer’s disease, Parkinson’s disease
How does urea/Organic solvents/pH/Temp alter the shape of protein?
Urea: planar uncharged and highly soluble in water. Bonds to polarised areas of charge, which destroys the secondary and tertiary structure. Urea can bind to the surface of the protein and disrupts its structure.
pH: change the conformation of the protein, disrupts the hydrogen bond and other IMF. Disrupts the secondary and tertiary and quaternary structure of the protein.
High temperature disrupts the interactions between h bond and other IMF. Disrupts secondary and tertiary structure of proteins.
Detergents: Have hydrophilic and hydrophobic ends, same as detergent. The detergents also have hydrophilic and hydrophobic ends. The detergent is attracted to these ends, forcing the protein apart.
