Cell Structure & Function Lecture 6 Flashcards
What is gene expression?
Transcription and translation
Gene expression stages?
Transcription and RNA processing, nuclear export and translation
Housekeeping proteins?
Regularly transcribed, protein and mRNA present in large quantities, long half life in cells
Signalling proteins?
Produced in response to stimuli
What is transcription?
The synthesis of RNA from a DNA template
What is transcription initiated by?
Basal transcription factors, matching RNA polymerase with appropriate promoter region in DNA, many contain the TATA box
Eukaryotic cells contain how many RNA polymerases and which one transcribes genes that code for proteins to produce mRNA
RNA polymerase II
Eukaryotic transcription has three stages?
Initiation, elongation and termination
In elongation which end do the RNA nucleotides bind to?
The 3’ end
What unwinds the DNA template strand?
RNA polymerase II
For termination what does RNA Pol II add to the end of the RNA strand?
It transcribes a polyadenylation signal 5’ AAUAAA 3’
What does the 5’ cap do?
Modified guanine residue protects the RNA from degrading and aids in stability promoting it to exit the nucleus and move on to translation
What is the poly A tail?
50-250 adenine nucleotides is added to the 3’ end for stability, more As means that it degrades slower
What are exons?
Coding regions that form final mRNA
What are introns?
Non-coding regions
What are spliced out of the mRNA transcript?
Introns
What is the spliceosome?
snRNA sequence is complementary to intron splice sites, and the two bind, the intron is excised and degraded, and the exons are joined, all catalysed by the spliceosome
What is the spliceosome made up of?
Several snRNPs (snRNA + proteins)
What is the adapter molecule?
Holds amino acids in place while interacting directly and specifically with a codon in mRNA, this is called tRNA
How many different codons are there?
61 codons
How many different tRNAs are there?
About 40
What is the Wobble hypothesis?
The anticodon of the tRNA can bind successfully to a codon whose third position requires a non-standard base (only depends on the third base), one tRNA can bind to more than one codon
Where are ribosome subunits assembled?
The nucleolus
Two functional groups of the amino acid?
Amino group and carboxyl group
What two forms can the amino acid have?
Non-ionised and ionised
What changes a proteins properties?
Size of protein (how many amino acids), content of amino acids and their sequence
What is the peptide bond?
Joins amino acids together
What is the N and C terminuses?
N terminus is the amino group end and the C terminus is the carboxyl group end, and the polypeptides are directional
Other features of the peptide bond?
It is flexible and there are side chains that stick out
Difference between a peptide and a protein?
Peptide is less than 50 aminos and a protein is more than 50
Functions of the large and small subunit of the ribosome?
Large: forms peptide bonds, small: holds the mRNA in place
What are the three sites of the ribosome?
A site, P site and the E site
What is the A site?
Acceptor site for an aminoacyl tRNA, binds to mRNA codon
What is the P site?
Peptide bond forms that adds an amino acid to the growing polypeptide chain
What is the E site?
tRNAs no longer bound to an amino acid exit the ribosome
What are the three stages of translation?
Initiation, elongation and termination (same as transcription)
