Cell Structure & Function Lecture 6

Question 1

What is gene expression?

Answer 1

Transcription and translation

Question 2

Gene expression stages?

Answer 2

Transcription and RNA processing, nuclear export and translation

Question 3

Housekeeping proteins?

Answer 3

Regularly transcribed, protein and mRNA present in large quantities, long half life in cells

Question 4

Signalling proteins?

Answer 4

Produced in response to stimuli

Question 5

What is transcription?

Answer 5

The synthesis of RNA from a DNA template

Question 6

What is transcription initiated by?

Answer 6

Basal transcription factors, matching RNA polymerase with appropriate promoter region in DNA, many contain the TATA box

Question 7

Eukaryotic cells contain how many RNA polymerases and which one transcribes genes that code for proteins to produce mRNA

Answer 7

RNA polymerase II

Question 8

Eukaryotic transcription has three stages?

Answer 8

Initiation, elongation and termination

Question 9

In elongation which end do the RNA nucleotides bind to?

Answer 9

The 3’ end

Question 10

What unwinds the DNA template strand?

Answer 10

RNA polymerase II

Question 11

For termination what does RNA Pol II add to the end of the RNA strand?

Answer 11

It transcribes a polyadenylation signal 5’ AAUAAA 3’

Question 12

What does the 5’ cap do?

Answer 12

Modified guanine residue protects the RNA from degrading and aids in stability promoting it to exit the nucleus and move on to translation

Question 13

What is the poly A tail?

Answer 13

50-250 adenine nucleotides is added to the 3’ end for stability, more As means that it degrades slower

Question 14

What are exons?

Answer 14

Coding regions that form final mRNA

Question 15

What are introns?

Answer 15

Non-coding regions

Question 16

What are spliced out of the mRNA transcript?

Answer 16

Introns

Question 17

What is the spliceosome?

Answer 17

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

Question 18

What is the spliceosome made up of?

Answer 18

Several snRNPs (snRNA + proteins)

Question 19

What is the adapter molecule?

Answer 19

Holds amino acids in place while interacting directly and specifically with a codon in mRNA, this is called tRNA

Question 20

How many different codons are there?

Answer 20

61 codons

Question 21

How many different tRNAs are there?

Answer 21

About 40

Question 22

What is the Wobble hypothesis?

Answer 22

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

Question 23

Where are ribosome subunits assembled?

Answer 23

The nucleolus

Question 24

Two functional groups of the amino acid?

Answer 24

Amino group and carboxyl group

Question 25

What two forms can the amino acid have?

Answer 25

Non-ionised and ionised

Question 26

What changes a proteins properties?

Answer 26

Size of protein (how many amino acids), content of amino acids and their sequence

Question 27

What is the peptide bond?

Answer 27

Joins amino acids together

Question 28

What is the N and C terminuses?

Answer 28

N terminus is the amino group end and the C terminus is the carboxyl group end, and the polypeptides are directional

Question 29

Other features of the peptide bond?

Answer 29

It is flexible and there are side chains that stick out

Question 30

Difference between a peptide and a protein?

Answer 30

Peptide is less than 50 aminos and a protein is more than 50

Question 31

Functions of the large and small subunit of the ribosome?

Answer 31

Large: forms peptide bonds, small: holds the mRNA in place

Question 32

What are the three sites of the ribosome?

Answer 32

A site, P site and the E site

Question 33

What is the A site?

Answer 33

Acceptor site for an aminoacyl tRNA, binds to mRNA codon

Question 34

What is the P site?

Answer 34

Peptide bond forms that adds an amino acid to the growing polypeptide chain

Question 35

What is the E site?

Answer 35

tRNAs no longer bound to an amino acid exit the ribosome

Question 36

What are the three stages of translation?

Answer 36

Initiation, elongation and termination (same as transcription)