Week 5 - DNA Replication, Transcription and Translation

Question 1

What are the subunits of DNA and RNA?

Answer 1

nucleotides

Question 2

What does each nucleotide contain?

Answer 2

a five carbon sugar, a nitrogenous, base, a phophate group

Question 3

What is five carbon sugar in DNA?

Answer 3

deoxyribose

Question 4

What is a nucleoside?

Answer 4

base + sugar (no phosphate group)

eg adenosine, guanosine

Question 5

How are sugars in nucleic acids linked to one another?

Answer 5

by phosphodiester bridges

Question 6

What is a nucleosome?

Answer 6

a particle made of histone proteins with approximately two turns of DNA wrapped around them

Question 7

How many hydorgen bonds hold together G and C?

Answer 7

3, A and T linked by 2

Question 8

What is needed for DNA replication?

Answer 8

single stranded template

DNA polymerase enzyme

deoxynucleoside triphosphates (dATP, dCTP ect)

a primer

Question 9

What is a primer?

Answer 9

a short piece of nucleic acid base-paired to the template, acts as a start point, a 3’ -OH group

Question 10

What enzyme catalyses the formation of the primer?

Answer 10

primase - an RNA polymerase that synthesises a short stretch of RNA complementary to the DNA strand

Question 11

What enzyme partially unwinds the DNA replication fork?

Answer 11

DNA helicase

Question 12

In what direction does DNA synthesis occur?

Answer 12

5’ to 3’

Question 13

Which strand is synthesised continously?

Answer 13

the leading strand

Question 14

How is the lagging strand synthesised?

Answer 14

as short fragments called Okazaki fragments

RNA primer is degraded ands replaced with upstream Okazaki fragment acting as primer

Question 15

What enzyme extends the ends of chromosones?

In what cells does this occur?

Answer 15

telomerase

germ-line cells and to a lesser degree stem cells

telomerase is also found in cancer cells

Question 16

What is the end replication problem?

Answer 16

On the lagging strand there is an incomplete 5’ end after removal of the RNA primer which cannot be filled because there is no upstream Okazaki fragment

chromosones shorten each time they replicate

Question 17

What is an intron?

Answer 17

a non-coding portion of DNA

DNA sequences that are present in the gene but not in the corresponding RNA

Question 18

What is an exon?

Answer 18

a coding portion of DNA

Question 19

What is a promotor?

Answer 19

a DNA sequence that signals the start of a gene

a binding site for RNA polymerase

Question 20

What is a codon?

Answer 20

a triplet of nucleotides representing an amino acid

eg UUU - Phe, AGU - Ser

Question 21

What does the term degenerate mean in reference to the genetic code?

Answer 21

same amino acid may be represented by more than one codon

eg Asn - AAU and AAC

Question 22

What is the initiation codon?

Answer 22

AUG

Question 23

What are the three termination codons?

Answer 23

UGA, UAG, UAA

Question 24

What is translation?

Answer 24

synthesis of a protein from mRNA

second step in gene expression

Question 25

To what part of the tRNA molecule does mRNA bind?

Answer 25

the anticodon

Question 26

What is an aminoacyl tRNA?

Answer 26

a tRNA attached to their amino acid an amino acid is 'activated' by attaching to tRNA

Question 27

How many different types of aminoacyl-tRNA synthetases are there?

Answer 27

20 they are the enymes that link tRNAs to their aminoacids and there most be 20 different types for each type of amino acid ATP is required for the reaction

Question 28

What is the overall size of the human ribosome?

Answer 28

**80S** large subunit - 60S small subunit 40S DO NOT add them together to make 100

Question 29

What size are mitochondrial ribosomes?

Answer 29

55S

Question 30

What are the three tRNA binding sites on the ribosome?

Answer 30

P (peptidyl) site, the A (aminoacyl) site and the E (exit site)

Question 31

What does the translation cycle involve?

Answer 31

binding of aminoacyl-tRNA (requires GTP) the peptidyl transferase reaction (peptide bond synthesis) translocation (movement of the ribosome one codon along the mRNA - needs GTP)

Question 32

What site does the first aminoacyl-tRNA (Met) bind to on the ribosome?

Answer 32

P site

Question 33

What is the mechanism of action of the antibiotics ethryomycin and clarithromycin?

Answer 33

inhibits bacterial protein synthesis by inhibiting the peptidyl transferase reaction and translocation

Question 34

What is purpose of the peptidyl-transferase reaction?

Answer 34

to form peptide bonds between adjacent amino acids during translocation

Question 35

What enzyme carries out transcription?

Answer 35

RNA polymerase

Question 36

What is the process of removing introns called?

Answer 36

splicing

Question 37

What DNA bases are purines?

Answer 37

adenine and guanine 2 ring structure