DNA and protein synthesis

Question 1

What is transcription?

Answer 1

The production of mRNA from DNA. First stage of protein synthesis.

Question 2

What are the transcription stages? (DNA to protein)

Answer 2

• DNA helicase unwinds the double helix of DNA, breaking the hydrogen bonds between the base pairs
• The two strands of DNA are separated so free RNA nucleotides can fit in.
• Free RNA nucleotide bases hydrogen bond to the template DNA by their complementary base pair rule
• RNA polymerase attaches the RNA nucleotides together to form a molecule of pre-mRNA.
• The single pre-mRNA strand moves away from the DNA helix and another enzyme zips the two strands of DNA back together .
• The pre-mRNA strand undergoes splicing to remove the introns to form mRNA. The mRNA leaves the nucleus and enters the cytoplasm.

Question 3

In eukaryotes, what does transcription result in?

Answer 3

The production of pre-mRNA which is then spliced to form mRNA.(can then be used for translation)

Question 4

In prokaryotes, what does transcription result in?

Answer 4

The production of mRNA from DNA.

Question 5

What is translation?

Answer 5

The production of polypeptides from the sequence of codons carried by mRNA. Second stage of protein synthesis.

Question 6

Name two molecule types that make up ribosomes

Answer 6

RNA, Protein

Question 7

Describe the stages of translation

Answer 7

1. A ribosome attaches to the start codon at one end of the mRNA.
2. A tRNA molecule with an anticodon complementary to the first codon on the mRNA attaches itself to the mRNA by complementary base pairing.
3. A second tRNA molecule attaches itself to the next codon in the same way
4. The two amino acids attached to the tRNA molecules are joined by a peptide bond using an enzyme and ATP
5. The ribosome moves along the mRNA and another codon is now available for the next tRNA to bind, carrying a third amino acid. The first tRNA dissociates leaving its amino acid behind.
6. The amino acid on the 3rd tRNA is added to the dipeptide and the ribosome moves along, the second tRNA dissociates.
7. This process is repeated and amino acids are added at a time to form a polypeptide.
8. When the ribosomes reach a stop codon the ribosome, mRNA and last tRNA separate.

Question 8

What are some of the differences between the structures of mRNA and tRNA

Answer 8

mRNA has more nucleotides than tRNA.

mRNA is a straight molecule, but tRNA is folded.

mRNA has no paired bases/hydrogen bonds but tRNA does have some paired bases.

Question 9

How can 2 amino acids differ from one another?

Answer 9

They can have different R groups.