Protein synthesis (g)

Question 1

What is transcription?

Answer 1

The process of copying sections of DNA base sequence to produce smaller molecules of mRNA, which can be transported out of the nucleus via the nuclear pores to the site of protein synthesis.

Question 2

transcription - unzipping

Answer 2

The section of DNA that contains the gene unwinds and unzips under the control of a DNA helicase, beginning at a start codon - involving the breaking of hydrogen bonds between the bases.

Question 3

transcription - what are the sense and antisense strands?

Answer 3

• the sense strand contains the code for the protein to be synthesised - runs from 5’ to 3’
• the antisense strand (3’ to 5’) is a complementary copy of the sense strand and does not code for a protein. acts as the template strand

Question 4

transcription - pairing

Answer 4

Free RNA nucleotides will base pair with complementary bases exposed on the antisense strand when the DNA unzips.

Question 5

transcription - bonds

Answer 5

Phosphodiester bonds are formed between the RNA nucleotides by the enzyme RNA polymerase.

Question 6

what is produced by transcription and what happens next?

Answer 6

messenger RNA (mRNA) - has the same sequence of bases making up the gene on the DNA (except for U). it detaches from the DNA template and leaves the nucleus through a nuclear pore. the double helix then reforms. mRNA travels to a ribosome.

Question 7

what are ribosomes made up of?

Answer 7

2 subunits - one large and one small. composed of ribosomal RNA (rRNA).

Question 8

importance of rRNA

Answer 8

important in maintaining the structural stability of the protein synthesis sequence and plays a biochemical role in catalysing the reaction.

Question 9

what is translation?

Answer 9

the process by which the complementary code carried by the mRNA is decoded by tRNA into a sequence of amino acids at a ribosome.

Question 10

what is tRNA?

Answer 10

Transfer RNA is composed of a strand of RNA folded in such a way that 3 bases, called the anticodon, are at one end of the molecule.

Question 11

role of tRNA

Answer 11

• the anticodon will bind to a complementary codon on mRNA following normal base pairing rules.
• the tRNA molecules carry an amino acid corresponding to that codon
• when the tRNA anticodons bind to complementary 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.