L18 - Mutations Flashcards
(18 cards)
What are the major molecules that take part in translation?
Aminoacylated tRNA, mRNA, Ribosomes
What is a ribosome and what type of molecules is it made up of?
Ribonucleoprotein (65% RNA, 35% protein) made of a smaller subunit which binds to a larger subunit and the mRNA pattern, and a larger subunit (50S) which binds to the tRNA, the amino acids, and the smaller subunit (30S).
What two molecules bind to the mRNA to initiate translation?
Aminoacylated tRNA and small ribosomal subunit
What attaches the amino acid to the tRNA? Is there one for each amino acid, or is there one that does all of them?
Aminoacyl-tRNA synthetases. There are 2 classes, one monomeric and the other dimeric.
Describe the tRNA gene
- 3 areas of double stranded hairpin loops
- Amino acid arm (tRNA covalently bonded to AA)
- Anticodon arm (binds to mRNA)
What is Inosine?
RNA nucleotide that can base pair with AUC, acting as UAG, allowing for the ‘wobble’ in the 3rd base
What type of bond is there between the tRNA and the amino acid
Covalent
RNA or protein carrying out catalytic reactions?
RNA
What is a silent mutation? What is a missense mutation? What is a nonsense mutation? What might a frameshift (insertion or deletion) cause?
- Silent (change in codon has no effect on AA sequence)
- Missense (codon encodes for a different AA)
- Nonsense (STOP codon encoded, if at the end then may not matter much)
- Frame shift (shifts reading frame, where START codon initiates the reading)
How does a prokaryotic ribosome identify the initiation codon in an mRNA? What part of the eukaryotic mRNA is initially recognised and bound by the ribosome?
Pro -Shine-Dalgarno sequence for ribosome binding. It pairs with 16S rRNA, interacts with ribosome so it can find the next START codon
Euka – Ribosome binds the 5’ cap & finds an AUG (using Kozak consensus sequence)
The three sites in the ribosome are E, P and A. What each site named for?
A site: Amino-acyl tRNA
P site: peptidyl tRNA
E site: exit
*usually 2 tRNA in at once
Which end of the growing polypeptide protrudes out of the ribosome?
N terminal end
When does a tRNA move from the A site to the P site? When does it move to the E site?
When a peptide bond is formed between the 2 corresponding AA and the large subunit of the ribosome shifts to the right, then the small subunit shifts along as well.
True or False: The polypeptide and the empty tRNAs both exit from the E site.
False, polypeptide exits from P site.
What needs to bind to terminate transcription, and what does it recognise to bind?
Release factor that recognises a stop codon (e.g. UAG), breaking covalent bond so polypeptide can dissociate.
What are two different cellular locations in which ribosomes might be found (not including mitochondria)? Why would they be in two different locations?
Cytoplasm and Rough ER.
Modifications occur in ER.
What is a signal peptide?
A short (5-30 amino acids long) peptide present at the N-terminus of the majority of newly synthesized proteins that are destined towards the secretory pathway.
Polycistronic mRNA
Cistron, multiple genes but 1 promoter - makes different polypeptides as it has multiple ribosome binding sites
