3.10- Protein Synthesis

Question 1

What is transcription?

Answer 1

The process of copying sections of DNA base sequences to produce smaller molecules of mRNA.
This happens because DNA molecules are too large to leave the nucleus.

Question 2

Explain the stages of transcription.

Answer 2

1. Section of DNA containing gene unwinds and unzips by DNA helicase, beginning at a start codon. Involves breaking of hydrogen bonds between bases.
2. The antisense strand acts as a template strand, so that the complimentaryRNA strand formed carries the same base sequence as the sense strand.
3. Free RNA nucleotides will base pair with complimentary bases exposed on the anti sense strand when the DNA unzips.
4. Phosphodiester bonds are formed between the RNA nucleotides by enzyme RNA polymerase.
5. Transcription stops at the end of the gene and mRNA is formed. It detaches from the DNA template and leaves the nucleus through a nuclear pore.
6. DNA double helix reforms and mRNA travels to a ribosome.

Question 3

What is the sense and antisense strand? (Transcription)

Answer 3

Only one of the two strands of DNA contains the code for the protein to be synthesised.

• This is the sense strand- it runs from 5’ to 3’.
• The other strand is the antisense strand- runs 3’ to 5’. It is a complimentary copy of the sense strand and does not code for a protein but instead acts as a template during transcription.

Question 4

What is translation?

Answer 4

The process by which the complimentary code carried by mRNA is decoded by tRNA into a sequence of amino acids.

Question 5

What is ribosomal RNA?

Answer 5

• the subunits that make up a ribosome.
• maintains the structural stability of the protein synthesis sequence.
• plays a biochemical role in catalysing the reaction.

Question 6

What is transfer RNA?

Answer 6

A form of RNA that carries an amino acid specific to its anticodon to the correct position along mRNA in translation.
-composed of a strand of RNA folded in a way that three bases (anticodon), are at one end of the molecule.
The tRNA molecules carry an amino acid corresponding to that codon.
-when the tRNA anticodons bind to the complimentary codons along the mRNA, the amino acids are brought together in the correct sequence to form the primary structure of the protein coded for by the mRNA.
-the amino acids are added one at a time and the polypeptide chain grows as this happens.
-ribosomes act as the binding site for mRNA and tRNA and catalyse the assembly of the protein.

Question 7

Explain the stages of translation.

Answer 7

1. mRNA binds to the small subunit of the ribosome at its start codon (AUG)
2. A tRNA with the complimentary anticodon (UAC) binds to the mrna start codon. (This trna carries the amino acid methionine)
3. Another tRN
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