L4 - Protein Synthesis

Question 1

Genetic code def & features

Answer 1

Relationship between base sequence of DNA (nucleotides ) ie mRNA transcripts & sequence of AA in a protein

Features

• Contains codons : 3 nucleotides
• 3 stop codons
• some AA are coded by more than 1 codon
• genetic code is read by tRNA ( thus they know what AA to transp0rt to the ribosome ? )

Question 2

Amino acyl tRNA transferase

Answer 2

Attaches AA & tRNA

tRNA molecule that has AA attaches is ACTIVATED & called amino acyl tRNA

Question 3

3 sites where tRNA molecule with AA attaches to the ribosomes :

Answer 3

Amino acyl site
Peptidyl site
Exit site

Question 4

Components required for protein synthesis (translation)

Answer 4

• Ribosome sub units
• mRNA
• amino acyl tRNA ( activated tRNA molecule )
• Protein factors
• GTP

Question 5

Protein synthesis - translation little more technical

Answer 5

INITIATION :
- formation of ribosome from ribosome sub units
- AA & tRNA molecule attach (amino acyl tRNA
- this then attaches time ribosome : 3 binding sites :
Amino acyl , peptidyl , exit site

ÉLONGATION :

• 2nd tRNA molecule arrives @ ribosome
• peptide bond forms (2 AA)
• tRNA molecule moves to the E site & leaves

TERMINATION

• release factor ( a protein ) recognises stop codon on mRNA molecule & stops translation
• ribosome splits into subunits ready to repeat the process again

Question 6

Translocation

Answer 6

Exchange of DNA form NON - HOMOLOGOUS chromosome

Question 7

Homologous vs non homologous chromosomes

Answer 7

H : contain alleles for the same type of gene

NH : contain alleles for different type of genes

Question 8

Lots of ribosomes are called ?

Answer 8

Polysomes or polyribosomes

Question 9

Modification of DNA post translational :

Answer 9

Adding chem groups eg

• Phosphorylation
• glycosylation - adding Carbohydrates

Proteolytic processing
- where enzymes called proteasomes break down or cleave 1 or more bonds

All these mods either activate , deactivate or change the original function etc

Question 10

Inhibitors of protein synthesis

Answer 10

Do I need to know???