3.4.2

Question 1

Genome

Answer 1

Complete set of genes in the cell

Question 2

Proteome

Answer 2

Complete range of proteins the cell is able to make

Question 3

Describe the structure of mRNA

Answer 3

Long single helix strand
Possesses information in the form of codons
Only contains exons (introns have been spliced)
Chemically unstable

Question 4

Describe the difference between pre mRNA and mRNA

Answer 4

Pre mRNA contains introns and exons whereas mRNA contains only exons

Question 5

What are codons?

Answer 5

A series of 3 bases on mRNA

Question 6

Describe the structure of tRNA

Answer 6

Small
Single stranded- folded into clover shape, held by hydrogen bonds/ complementary base pairing
Around 60 different tRNAs, each with a specific anticodon that attaches to a specific amino acid recognised by different enzymes
3 bases form the anticodon

Question 7

Double or single stranded (DNA, mRNA, tRNA)

Answer 7

DNA- double polynucleotide chain
mRNA- single polynucleotide chain
tRNA- single polynucleotide chain

Question 8

Size (DNA, mRNA, tRNA)

Answer 8

DNA- largest
mRNA- smaller
tRNA- smallest

Question 9

Shape (DNA, mRNA, tRNA)

Answer 9

DNA- double helix
mRNA- single helix
tRNA- clover shaped

Question 10

Pentose sugar (DNA, mRNA, tRNA)

Answer 10

DNA- deoxyribose
mRNA- ribose
tRNA- ribose

Question 11

Bases (DNA, mRNA, tRNA)

Answer 11

DNA- T A G C
mRNA- U A G C
tRNA- U A G C

Question 12

Where is it found (DNA, mRNA, tRNA)

Answer 12

DNA- mostly nucleus, some mitochondria+chloroplast
mRNA and tRNA- made in nucleus, moves into cytoplasm

Question 13

How does quantity vary in different cells of same species (DNA, mRNA, tRNA)

Answer 13

DNA- same in all diploid cells, gametes have half amount
mRNA and tRNA- quantity varies from cell to cell, depending on metabolic rate and protein synthesis demands

Question 14

Chemical stability and why (DNA, mRNA, tRNA)

Answer 14

DNA- chemically very stable, made to persist through generations
mRNA- least stable, broken down quickly to ensure polypeptide synthesis doesn’t continue indefinitely
tRNA- more stable than mRNA but less than DNA, can be used multiple times

Question 15

Name the 2 processes in protein synthesis

Answer 15

Transcription
Translation

Question 16

Describe transcription

Answer 16

DNA helicase enzyme unzips a short section of DNA exposing the bases- one strand becomes template strand
Free RNA nucleotides in nucleoplasm are attracted to complemementary exposed bases
RNA polymerase joins nucleotides by phosphodiester bonds (DNA strands rejoin at same time) until it reaches a stop codon when it detaches
Pre mRNA undergoes splicing (in eukaryotes) to remove introns and leaves nucleus through a nuclear pore

Question 17

Why does pre mRNA undergo splicing?

Answer 17

To remove introns

Question 18

Why do prokaryotes not undergo splicing?

Answer 18

Splicing is the removal of introns
Prokaryotes do not contain introns

Question 19

Summarise translation

Answer 19

Code on mRNA used to assemble a polypeptide
Takes place on ribosomes

Question 20

Describe translation

Answer 20

mRNA leaves nucleus and is attracted to ribosomes
Ribosome attaches to first two codons
tRNA molecule with complementary anticodon carrying specific amino acid pairs with code on mRNA
Repeats for next codon
The two amino acids are joined by a peptide bond using an enzyme to catalyse and ATP to supply energy
Ribosome moves along by one codon
First tRNA is released
Continues until it reaches stop codon