S12 Gene Expression Flashcards
Which direction does transcription occur in?
5’ to 3’
What initiates transcription?
Promoter recognition initiation factors e.g. TATA promotor sequence.
An activator can be elsewhere on the sequence though.
What are the three post-transcription modifications (pre-mRNA to mRNA)?
- Splicing
- Polyadenylation
- Capping
What is splicing?
Removing introns (non-coding DNA)
What is polyadenylation? How does it occur?
Adding many adenosine to the 3’ end.
To prevent degradation.
AAUAA sequence recognised, causes sequence cleavage from RNA polymerase. polyA polymerase adds many As.
What is capping?
A 5’ cap (5’-5’ linkage)
Prevents degradation
Which direction is upstream?
Which direction is downstream?
3’ to 5’
5’ to 3’
Where does transcription occur?
In the nucleus
Which strand of DNA is used to make complementary mRNA?
Template strand (not the coding strand)
What is the initiation codon and which amino acid does it code for?
AUG
Methionine
What are the termination codons?
UAA
UAG
UGA
Describe the genetic code:
- Degenerate
- Non-overlapping (and no gaps)
- Universal
What is wobble base position?
Binding in the 3rd nucleotide of a mRNA codon to the tRNA anticodon is weaker allowing no-Watson-Crick base pairing to occur in the 3rd position.
What are the 4 wobble base pairings?
- Guanine - Uracil
- Hypoxanthine (I) - Uracil
- Hypoxanthine - Adenine
- Hypoxanthine - Cytosine
Which direction is the mRNA read in?
5’ to 3’
Which direction is the protein formed in?
N-terminal to C-terminal
What two subunits is the eukaryotic 70s ribosome made up of?
40s and 60s subunits
What is the name given to a tRNA molecule with an amino acid attached?
Amino acyl tRNA
E.g. methionyl tRNA
How do the amino acid and tRNA molecule bind?
- The amino acid and an ATP molecule binds to the enzyme, aminoacyl-tRNA synthetase
- The amino acid is phosphorylated (ATP hydrolysed)
- tRNA molecule binds to the enzyme which then binds to the amino acid and AMP is released
- The amino acyl tRNA molecule unbinds from the enzyme
What are the two sites in translation called?
P and A sites
Describe the structure of a tRNA molecule:
‘Clover’ shaped, one strand that folds back on itself (forming hydrogen bonds between complementary bases). Anticodon at the base of the molecule. Amino acids attaches to the top of the molecule (to -OH).
What are the types of RNA?
- rRNA
- mRNA
- tRNA
- miRNA
- Non-coding RNA
From rRNA, mRNA and tRNA order based on the number of kinds of each and how many copies of each (high to low)…
Number of kinds of each - mRNA, tRNA, rRNA
Copies of each - rRNA, tRNA, mRNA
