Transcription & Translation

Question 1

Define codon

Answer 1

Triplets of mRNA bases that code for an amino acid

Question 2

What are codons? What does this mean

Answer 2

Degenerate
Each amino acid can be coded for by more than one triplet

Question 3

What is the shape of a protein determined by? What is that directed by

Answer 3

It’s amino acid sequence which causes the polypeptide chain to fold up
The assembly of amino acids is directed by the genetic code on the DNA

Question 4

Define genome

Answer 4

The full range of DNA/genes in a cell

Question 5

Define proteome

Answer 5

Full range of proteins that a cell is able to produce

Question 6

Define splicing

Answer 6

The editing of pre-mRNA, where introns are removed and exons are joined together

Question 7

Describe the process of transcription

Answer 7

Hydrogen bonds between bases are broken using DNA helicase causing strands to separate
RNA polymerase moves along the DNA template strand
Complementary RNA nucleotides join together (U-A and C-G)
RNA polymerase joins adjacent nucleotides together by phosphodiester bonds
Pre-mRNA is made and a DNA rejoins
When the ‘stop codon’ is reached, pre mRNA detaches
Pre mRNA is spliced and introns are removed

Question 8

What is step 1 of the process of transcription

Answer 8

Hydrogen bonds between bases are broken using DNA helicase causing strands to separate

Question 9

What is step 2 of the process of transcription

Answer 9

RNA polymerase moves along the DNA template strand

Question 10

What is step 3 of the process of transcription

Answer 10

Complementary RNA nucleotides join together (U-A and C-G)

Question 11

What is step 4 of the process of transcription

Answer 11

RNA polymerase joins adjacent nucleotides together by phosphodiester bonds

Question 12

What is step 5 of the process of transcription

Answer 12

Pre-mRNA is made and a DNA rejoins

Question 13

What is step 6 of the process of transcription

Answer 13

When the ‘stop codon’ is reached, pre mRNA detaches

Question 14

What is step 7 of the process of transcription

Answer 14

Pre mRNA is spliced and introns are removed

Question 15

Define transcription

Answer 15

The production of messenger RNA (mRNA) from DNA, in the nucleus

Question 16

Define translation

Answer 16

Production of polypeptides from the sequence of codons carried by mRNA, at ribosomes

Question 17

What are the similarities between tRNA and mRNA

Answer 17

They are both single polynucleotide strand

Question 18

What are the differences between tRNA and mRNA

Answer 18

tRNA is folded into a clover leaf shape whereas mRNA is linear/straight
tRNA has hydrogen bonds between the paired bases, mRNA doesn’t
tRNA is a shorter, fixed length whereas mRNA is a longer, variable length (more nucleotides)
tRNA has an anticodon, mRNA has codons
tRNA has an amino acid binding site, mRNA doesn’t

Question 19

How is the production of mRNA different in a eukaryotic cell to a prokaryotic cell? Why

Answer 19

Pre-mRNA is produced in eukaryotic cells, whereas in prokaryotic mRNA is produced directly in prokaryotic cells
This is because genes in prokaryotic cells do not contain introns, so no splicing needs to occur in prokaryotic

Question 20

Describe the process of translation

Answer 20

mRNA attaches to a ribosome and the ribosome moves to a start codon
tRNA brings a specific amino acid and the tRNA anticodon binds to the complementary mRNA codon
The ribosome moves along to the next codon and another tRNA binds so that 2 amino acids can be joined in a condensation reaction forming a peptide bond - this uses hydrolysis of ATP
The tRNA is released after its amino acid joins the polypeptide
The ribosome moves along the mRNA to form the polypeptide, until a stop codon is reached

Question 21

What is step 1 of the process of translation

Answer 21

mRNA attaches to a ribosome and the ribosome moves to a start codon

Question 22

What is step 2 of the process of translation

Answer 22

tRNA brings a specific amino acid and the tRNA anticodon binds to the complementary mRNA codon

Question 23

What is step 3 of the process of translation

Answer 23

The ribosome moves along to the next codon and another tRNA binds so that 2 amino acids can be joined in a condensation reaction forming a peptide bond - this uses hydrolysis of ATP

Question 24

What is step 4 of the process of translation

Answer 24

The tRNA is released after its amino acid joins the polypeptide

Question 25

What is step 5 of the process of translation

Answer 25

The ribosome moves along the mRNA to form the polypeptide, until a stop codon is reached

Question 26

Describe the role of ATP in translation

Answer 26

Hydrolysis of ATP to ADP + Pi releases energy so amino acids have the energy to join to tRNAs and form peptide bonds between each other

Question 27

Describe the role of tRNA in translation

Answer 27

It attaches to a specific anticodon in relation to its anticodon, the anticodon will have complementary base pairs to an mRNA codon and will form hydrogen bonds 2 tRNAs bring amino acids together so peptide bonds can form

Question 28

Describe the role of ribosomes in translation

Answer 28

mRNA binds to ribosomes with space for 2 codons which allows tRNA with anticodons to bind The ribosome catalyses the formation of a peptide bond between amino acids The ribosome also moves along the mRNA in order to get the next codons