lecture 2 (30/09/24)

Question 1

The Pulse-Chase Experiment (scientists, dates, general idea)

Answer 1

Paul Zamecnik and Sydney Brenner
early 1950s
cells were exposed to radioactive uracil (a component of RNA)
RNA moved from nucleus to the cytoplasm
first clue RNA was a messenger

Question 2

Where are proteins made?

Answer 2

in the ribosomes

Question 3

What is the central dogma?

Answer 3

DNA –> RNA –> protein

Question 4

Who discovered the enzymes responsible for synthesizing RNA and DNA?

Answer 4

Severo Ochoa and Arthur Kornberg
Nobel prize in 1959

Question 5

What are some key differences between DNA and RNA?

Answer 5

DNA has deoxyribose (one less O than ribose), RNA has ribose
DNA has T, RNA has U
DNA is double stranded, RNA is single stranded

Question 6

What are some consequences for the differences at the levels of sugar in DNA and RNA?

Answer 6

RNA is chemically more reactive than DNA - ribose has 2’ OH group
DNA is accurate and can be used as long-term storage, RNA can’t due to chemical activity
RNA is transient

Question 7

describe the structure of RNA

Answer 7

RNA is largely single stranded
can form a variety of 3D shapes
can pair with other nucleic acids

Question 8

What is the function of mRNAs?

Answer 8

code for proteins

Question 9

What is the function of rRNAs?

Answer 9

form the core of the ribosome’s structure and catalyse protein synthesis

Question 10

What is the function of miRNAs?

Answer 10

regulate gene expression

Question 11

What is the function of tRNAs?

Answer 11

serve as adaptors between mRNA and amino acids during protein synthesis

Question 12

What is the function of other non coding RNAs?

Answer 12

used in RNA splicing, gene regulation, telomere, maintenance, and other processes

Question 13

What is the role of RNA polymerase I?

Answer 13

transcribes rRNAs

Question 14

What is the role of RNA polymerase II?

Answer 14

transcribes mRNAs

Question 15

What is the role of RNA polymerase III?

Answer 15

transcribes tRNAs

Question 16

What is the direction of transcription?

Answer 16

5’ –> 3’

Question 17

what is an NTP?

Answer 17

nucleoside containing nitrogenous base
ribose/ deoxyribose
3 phosphate groups bound to the sugar

Question 18

What is needed for RNA synthesis?

Answer 18

enzyme (RNA polymerase)
DNA locally single stranded - one strand is template
NTPs (ATP, CTP, GTP, UTP)
pyrophosphate lost
5’ –> 3’ direction

Question 19

Complementary base pairing pairs

Answer 19

DNA RNA
A ——> U
C ——> G
T ——> A
G ——> C

Question 20

summarize RNA synthesis

Answer 20

complementary base pairing
5’ –> 3’ direction
breakage of phosphoanhydride bond of NTP releases energy
phosphodiester bonds are formed
(strands are antiparallel)

Question 21

summarise mRNA processing idea

Answer 21

eukaryotic mRNA is processed before it leaves the nucleus
Pre mRNA –> mature mRNA
processing the ends of mRNAs is essential for stability

Question 22

mRNA processing step by step

Answer 22

1. 5’ cap w/ atypical nucleotide
2. 3’ tail of poly-A-nucleotides
3. introns removed

Question 23

What are introns?

Answer 23

non-coding sequences
not in bacterial genes
removed in the spliceosome

Question 24

What do the 5’, 3’ splice sites and branch point do?

Answer 24

help in the removal of introns

Question 25

What are snRNAs?

Answer 25

small nuclear RNA molecules that perform splicing

Question 26

What are snRNPs?

Answer 26

small nuclear ribonucleoprotein particles
snRNAs + proteins = core of the spliceosome

Question 27

What is a ribonucleoprotein?

Answer 27

a complex of ribonucleic acid and RNA-binding protein

Question 28

What is alternative splicing?

Answer 28

more than one protein expressed from a single gene
can form different isoforms of mRNA depending on splicing

Question 29

What % of genes in humans exhibit alternative splicing?

Answer 29

~95%

Question 30

What are RNA binding proteins?

Answer 30

mark a mature and intact mRNA for export from the nucleus

Question 31

What does the exon junction complex do?

Answer 31

it shows the introns have been removed and that the mRNA is ‘ready to go out’

Question 32

What does the nuclear pore complex do?

Answer 32

it checks the mRNA

Question 33

What happens to the incorrectly synthesised mRNAs?

Answer 33

they are broken down and the nucleotides are reused and go back into the nucleus

Question 34

mRNAs are degraded by the cell

Answer 34

mRNAs can be translated many times
stability of an mRNA determines home much protein is translated in the cell
the sequence of a mRNA affects its half-life