Translation

Ribosome Association and Initiation of Translation

- The initiation stage of translation brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits 1. A small ribosomal subunit binds with mRNA and a special initiator tRNA, then the small subunit moves along the mRNA until it reaches the start codon (AUG) 2. Initiation factors bring in the large subunittranslation initiation complex is complete

tRNA molecule

- a specific amino acid on one end - On the other end-ananticodon(theanticodonbase-pairswitha complementary codon on mRNA)

Point mutations

- chemical changes in just one base pair -The change of a single nucleotide in a DNA template strand can lead to the production of an abnormal protein

Aminoacyl-tRNA synthetase

-20 forms, each one is specific to one amino acid, and attaches the AA to an appropriate tRNA -tRNA with an appropriate AA attached is called an activated amino acid

Polyribosomes

-A number of ribosomes can translate a single mRNA simultaneously, forming a polyribosome (or polysome) -Polyribosomes enable a cell to make many copies of a polypeptide very quickly • Polypeptide chains are modified after translation to become functional by: • Adding sugars, lipids, phosphate, other amino acids, etc. • Polypeptide chain also needs to be folded correctly (3D shape)

Insertions/deletions

-Adding or losing a nucleotide pair in a gene. Generally leads to a frameshift mutation, where insertion or deletion is not a multiple of three, so amino acids added incorrectly. Usually DANGEROUS

Nonsense mutations

-Coding changes to a stop codon and polypeptide prematurely terminated. Almost always bad

Missense mutations

-Coding protein changes to another non-stop codon. Sometimes good, sometimes bad...

Silent mutations

-No effect on coding protein

Substitution

-Replacement of one nucleotide AND its 'partner' with another pair of nucleotides

Ribosomes

-Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis -2 ribosomal subunits (large and small): made of proteins and ribosomal RNA (rRNA) -A ribosome has three binding sites for tRNA • A site. Attaches to next tRNA. • P site. Holds tRNA with growing polypeptide chain. • E site. Releases tRNA.

gene

-can be defined as a region of DNA that can be expressed to produce a final functional product, either a polypeptide or an RNA molecule

Elongation of the Polypeptide Chain

1. During the elongation stage, amino acids are added one by one to the preceding amino acid at the C-terminus of the growing chain 2. Each addition requires elongation factors and occurs in three steps: codon recognition peptide bond formation and translocation 3. Translation proceeds along the mRNA in a 5′ to 3′ direction

Translation

Genetic information flows from mRNA to protein through the process of translation -mRNA - the coded message -mRNA message is translated into protein with the help of transfer RNA (tRNA) -tRNAs transfer amino acids from the cytoplasm to the growing polypeptide in a ribosome -tRNAs: specific to codons and coded as an anti-codon Accurate translation requires two steps - First: a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA synthetase - Second: a correct match between the tRNA anticodon and an mRNA codon

Termination of Translation

Termination: a stop codon in the mRNA reaches the A site of the ribosome. The A site accepts a protein called a release factor - The release factor causes addition of H2O instead of an amino acid - Polypeptide is released and ribosome complex dissasemblies -Formation of a polypeptide takes only about a minute

Mutations

changes in the genetic material of a cell or virus