Protein Synthesis

Question 1

What is transcription?

Answer 1

Transcription is the first stage of protein synthesis. During transcription an mRNA copy of a gene is made in the nucleus.

Question 2

Why is mRNA in eukaryotic DNA edited?

Answer 2

Genes in eukaryotic DNA contain introns that don’t code for amino acids

Question 3

What are introns?

Answer 3

Sections of DNA that don’t code for amino acids

Question 4

What are extrons?

Answer 4

Sections of DNA that code for amino acids

Question 5

What is pre-mRNA?

Answer 5

mRNA strands containing introns and extrons

Question 6

What happens during splicing?

Answer 6

Introns are removed from pre-mRNA and extrons joined together to form an mRNA strand

Question 7

What is translation? Where does it take place?

Answer 7

It is the second stage of protein synthesis

It takes place in the ribosomes in the cytoplasm

Question 8

What happens during translation?

Answer 8

Amino acids are joined together by a ribosome to make a polypeptide chain following the sequence of codons carried by the mRNA

Question 9

Name the cell organelle involved in translation.

Answer 9

Ribosome

Question 10

What is the role of RNA polymerase in transcription?

Answer 10

Join nucleotides, to form a strand/along backbone

Question 11

Explain how a change in the base sequence of the mRNA could lead to a change in the tertiary structure of the toxin.

Answer 11

Different primary structure / amino acid sequence / amino acid coded for.

Question 12

Give two differences between the structure of mRNA and the structure of tRNA.

Answer 12

mRNA has no base-pairing & tRNA has base-pairing
mRNA linear & tRNA cloverleaf shape
mRNA has no binding site for amino acids & tRNA

Question 13

Explain how DNA replicates

Answer 13

Hydrogen bonds broken
Semi-conservative replication 
Nucleotides line up
Complementary / specific base pairing / A and T / C and G
DNA polymerase

Question 14

Starting with mRNA in the nucleus of a cell, describe how a molecule of protein is synthesised.

Answer 14

1. mRNA leaves (nucleus) through nuclear pore;
2. To ribosome;
3. tRNA molecules bring amino acids (to ribosome);
4. Specific tRNA molecule for specific amino acid;
5. Anticodon of tRNA corresponds / complementary to codon on mRNA; 6. Peptide bonds form between amino acids;
6. tRNA detaches and collects another amino acid;
7. Ribosome moves along mRNA;

Question 15

Starting with mRNA, describe how the process of translation leads to the production of a polypeptide.

Answer 15

mRNA attaches to ribosome.
Codon on mRNA.
Binds to an anti-codon on tRNA.
Each tRNA brings a specific amino acid.
Sequence of codons determines order of amino acids. Formation of peptide bonds/amino acids joined by condensation reactions.

Question 16

Describe the role of RNA polymerase in transcription.

Answer 16

Moves along template DNA strand, causing the bases on this strand to join with the individual complementary nucleotides from the pool that is present in the nucleus.
Until a stop codon is reached.

Question 17

Why is splicing of pre mRNA necessary?

Answer 17

Splicing is necessary because pre mRNA has nucleotide sequences derived from from introns in DNA.
These introns are non functional and, if left on mRNA, would lead to non functional polypeptides.
So they’re removed.

Question 18

Describe the role of DNA helicase in transcription.

Answer 18

This acts on a specific region of the DNA molecule to break the hydrogen bonds between the bases, causing the two strands to separate and expose the nucleotide bases.

Question 19

Transcription

Answer 19

Enzyme DNA helicase acts on a specific region of DNA to break h bonds between bases causing strands to separate.
Enzyme RNA polymerase moves along template strand causing nucleotides to join with complementary nucleotides.
DNA strands form behind it and pre-mRNA is made.
When RNA polymerase meets a stop codon it detaches.

Question 20

Translation

Answer 20

The ribosome binds to mRNA at a specific area.
The ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence.
Each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain as a result of an enzyme + ATP.
Stops once a stop codon is reached.