Transcription/Translation Flashcards
(22 cards)
What occurs during transcription?
Formation of one mRNA strand from a DNA strand. mRNA is synthesised 5’-3’ so the DNA is read 3’-5’.
What are some differences between Transcription and DNA replication (4)?
- DNA replication copies whole chromosome, transcription just copies a gene(s)in response to signals
- DNA two strands are forms, transcription just 1 mRNA
- DNA polymerase vs RNA polymerase
- DNA the lagging strand is replicated in Okazaki fragments, RNA is just the leading strand in one length
(Both synthesised 5’-3’)
What occurs during Translation?
On the ribosomes, mRNA attaches, tRNA brings a codon (amino acid) and translates it into a protein, peptide bonds form between amino acids to form the proteins. tRNA is reused and brings another codon. Proteins released into RER lumen or remain in cytoplasm if on free ribosomes.
What are the substrates for DNA replication/Transcription/Translation comparatively
dNTPs, NTPs, amino acids
Talk through Transcription:
Initiation (3)
Elongation (2)
Termination (3)
Initiation 1) TATAA box promotor region binds in sequence specific place
2) Transcription sequences bind where TATAA box is
3) RNA polymerase bind where the transcription factors are
Elongation 1) RNA polymerase unwinds DNA
2) RNA polymerase reads 3’-5’ and transcribes 5’-3’
Termination 1) 5’-5’ cap of phosphates
2) PolyA tail - Endonucleases cleave sequence specific region
PolyA Polymerase adds As (up to 200)
3) Splicing - removes introns
What benefits do the 5’-5’ cap and poly A tail have respectively?
What can happen when splicing is altered/inomplete (2)
5’-5’ cap and poly A tail prevent degradation. 5’-5’ cap also has role in translation.
If splicing is altered/incomplete it can cause disease or it can also help regulate transcription.
Talk through translation
Initiation (5)
Elongation (4)
Termination (3)
Initiation
1) Aminoacetyl tRNA (Met) recognised 5’-5’ tail.
2) Initiation factors bind
3) 40S subunit binds (GTP)
4) 1,2,3 bind to RNA cap and move along until AUG
5) 60S binds (GTP)
Elongation
1) 2 codons can bind to ribosome P&A site. Met in P, new AA in A site.
2) Peptidyl Transferase forms peptide bond between Met and AA, puts P AA on A AA.
3) Remove tRNA
4) Translocation (GTP) - frees up A site for new AA
Termination
1) Stop codon
2) Free both tRNA and peptide using water to break bond.
Do ribosomes choose the AA sequence?
no mRNA brings it
What are the 2 prokaryotic Ribosomal subunits and together? and 2 eukaryotic ribosomal subunit and together?
Pro - 70 = 30, 50
Eu - 80 = 40, 60
What is a polyribosome?
A cluster of ribosomes that are bound with mRNA undergoing translation
Why is the DNA code degenerate?
64 codons for 20 amino acids
What are 3 facts about the way in which codons read
Non overlapping
No gaps
Make protein N-C
Three types of RNA and the RNA polymerases they use?
r - 1
m - 2
t - 3
How much of each r,m,tRNA % is in the body. Are there many types of each?
r - 80% of RNA, few types many copies
m - 2% of RNA, many types few copies
t - 15%, ~100 types, many copies
Does Met (AUG) initiation codon always stay on protein?
No it can and often is cleaved off.
What is tRNA structure roughly
3 stem loops one with anticodon on that is recognised by mRNA
How are amino acids attached to tRNA? How are they activated?
Attached to corresponding tRNA via ester bonds, catalysed by aminoacyl-synthetase
What is the enzyme to activate amino acids on tRNA?
Aminoactyl-synthetase
How is the codon of mRNA recognised by tRNA? What may the anticodon contain? What does this do?
tRNA containing an amino acid has an anticodon that recognises the corresponding mRNA. tRNA may contain a wobble base on the 5’ end (3rd position), this allows for tRNA to read >1 codon.
What is a wobble base pair? How many are there? What are they? Why is this useful?
5' end of anticodon of tRNA and 3' end of mRNA codon that doesn't follow normal base pairing rules. There are 4 wobble base pairs. I-U I-A I-C G-U
Because inosine can recognise many bases, putting it on the 5’ end means it can recognise many codons. Means only need ~100 types tRNA.
Does translation require energy?
Yes
Which direction is DNA, mRNA read? Which direction are proteins made?
DNA - 3’-5’
mRNA- 5’-3’
Protein - N to C terminus
