Transcription Flashcards
Definition of transcription
The process of copying genetic information stored in DNA into a complementary RNA molecule.
& The synthesis of mRNA from a DNA template which occurs in 5’ - 3’ direction.
Definition of translation
A process in which the formation of polypeptide (protein) by decoding mRNA produced in transcription.
This occurs in the ribosomes within the cytoplasm.
Protein construction
Proteins are made from chains of amino acids, which fold into unique 3 dimensional shapes. The bonds within this will help to stabilise their structure and the final folded forms of the proteins to be well adapted for their functions.
Post-Translational modifications in protein construction
- Cleavage - removal of signal peptides or other sections of the protein
- Phosphorylation - addition of phosphate groups to regulate activity
- Glycosylation - addition of carbohydrate chains for structural or functional purposes
- Lipidation - attachment of lipids for membrane association
Definition of peptides
A short chain of amino acids that contains between 2 to 50 amino acids.
What are oligopeptides ?
Peptides with fewer than 20 amino acids
What are polypeptides ?
Peptides with 20 to 50 amino acids
What are proteins ?
Chains of 50+ amino acids which are made up of one or more polypeptides
Amino acid structure
General structure = Central carbon, to which is linked:
- An amino acid group (-NH2)
- An carboxyl (acid) group (-COOH)
- A hydrogen atom (H)
- A variable chemical group (R), R group (side chain)
The 20 standard amino acids
- Glycine
- Alanine
- Valine
- Leucine
- Methionine
- Isoleucine
- Serine
- Threonine
- Cysteine
- Proline
- Asparagine
- Glutamine
- Aspartate
- Glutamate
- Lysine
- Arginine
- Histidine
- Phenylaline
- Tyrosine
- Tryptophan
Classification of amino acids - Structure
- Alpha (a-) amino acids: the amino and carboxyl groups are attached to the same carbon atom (a- carbon)
- Beta (B-) amino acids: B- amino acids have an amino group attached to the B beta carbon, which is bonded to the an alpha carbon.
Classification of amino acids - Side chain properties
- Non-polar = hydrophobic e.g, alanine
- Polar = uncharged e.g, serine
- Acidic = negatively charged e.g, glutamate
- Basic = positively charged e.g, lysine
Classification of amino acids - Polarity
- Polar molecules - amino acids with a side chain insole e.g, tryptophan
- Non-polar molecules - amino acids with a non-reactive methyl side chain e.g, alanine
Classification of amino acids - Side chain group type
- Aliphatic - amino acids with a side chain that is not linear e.g, leucine
- Aromatic - amino acids with a non-polar aromatic beta carbon substituent e.g, tryptophan
Peptide Bond Formation
A covalent between the carboxyl group of one amino acids which and the amino group of another.
Primary structure of protein
The linear sequence of amino acids held by peptide bonds.
- Determines higher level structures
- Corresponds to the amino acid sequence according the mRNA gene
- E.g, insulin sequence
Secondary structure of proteins
The folding of the amino acids held chain into sub structures such as the alpha helix and beta sheet. Held by hydrogen, disulphide and ionic bonds.
Tertiary structure of proteins
The 3D folding of a polypeptide chain. Held by hydrogen, ionic bonds and disulphide bonds. E.g, myoglobin
Quaternary protein structure
The assembly of multiple polypeptide chains. E.g, haemoglobin
What are (molecular) chaperones ?
The proteins that help other proteins fold correctly and so prevents aggregation.
