Genetics Lecture 5 Flashcards
Name three features of the genetic code.
Triplet, continuous, and redundant.
Is the genetic code universal?
Nearly.
What is the start codon, and what does it code for?
AUG - modified methionine.
Name the 3 stop codons, and what they code for.
UAA
UGA
UAG
They dont code for an amino acid.
What structure is tRNA made of?
RNA forming 3 hairpin loops.
Where is the anticodon found in tRNA?
Loop 2.
There are 64 codons, but only 20 amino acids. How can this be? Name the theory name.
Base-pair wobble
First two codons will always be complimentary. The third anticodon is a special nucleotide allowing it to bind to more than one nucleotide.
How many enzymes are there for tRNA? What is the enzymes name? What does it do, and where does it get its energy?
20 amino acyl tRNA synthetases - attaches a tRNA to its appropriate amino acid, using energy from ATP hydrolysis.
What are the two prokaryotic ribosomal subunits? Which rRNA attaches to each?
Large 50S - 23S and 5S rRNA attaches
Small 30S - 16S rRNA attaches
Where are ribosomes made in eukaryotes?
Nucleolus, exported to the cytosol.
Which RNA is the most abundant?
rRNA.
What are the three ribosomal sites?
A site - aminoacyl-tRNA site
P site - peptidyl binding site
E site - exit site
What does translation initiation require?
GTP
What aligns the ribosome with the initiation codon?
Shine-Dalgarno sequence.
Which prokaryotic ribosomal subunit is the Shine-Dalgarno sequence complimentary to?
16S rRNA of the small 30S.
Describe the steps of initiation of translation.
30S binds to the mRNA, with a GTP molecule. Initiator tRNA binds to the AUG sequence on mRNA.
50S hydrolyses GTP, binding it to 30S, forming 70S.
Initiator tRNA binds to the P site.
After translation initiation is over, how are subsequent tRNAs brought to the 70S ribosome?
Elongation Factors Ts and Tu use GTP to do so.
What is peptidyl transferase responsible for?
Breaks the bond between tRNA and the amino acid, and forms a peptide bond between two adjacent amino acids.
How does the ribosome move forward, and what is this called?
Codon translocation
Done by elongation factor G, and uses GTP for energy.
What does the E site typically hold?
An uncharged tRNA (no amino acid).
In prokaryotes, what happens when the termination sequence is reached?
A release factor binds to the mRNA codon, causing the polypeptide and ribosomal units to release.
It has no amino acid.
Can an mRNA be translated by many ribosomes at a time, or one by one?
By many.
Can mRNA be translated as it is being transcribed by RNA polymerase?
Only in prokaryotes - poly-ribosomes.
How are polypeptides needing post-translational modifications moved to the appropriate organelle (name it)?
They bind to signal recognition particles - SRPs.
They carry it to the ER and bind to an SRP receptor.
They are sorted within the cisternal space within the ER.
