protein synthesis

Question 1

What happens during transcription

Answer 1

• the section of DNA which codes for the protein so the gene unwinds
• DNA helices causes hydrogen bonds to break
• complementary RNA nucleotides attach to the exposed DNA nucleotides
• instead of thymine base, it is uracil base
• hydrogen bonds from
• RNA polymerase catalyses formation of phosphodiester bonds forming phosphate backbone
• pre-mRNA is formed

Question 2

How do we change from pre-mRNA to mRNA?

Answer 2

• splicing
• pre-mRNA contains introns(non-coding regions of RNA0 and extrons(coding regions of RNA)
• spicing removes introns

Question 3

What happens to the mRNA after transcription?

Answer 3

• it is small enough to move out of the nucleus via the nuclear pores and attach itself to the mRNA binding site on the small subunit of the ribosome
• ribosome holds mRNA in place ready for translation

Question 4

What happens during translation?

Answer 4

• ribosome reads mRNA in codons
• each codon codes for an amino acid
• each codon attract a tRNA which hold a complementary anticodon on one side and the amino acid for that codon on the other
• it attaches to the large subunit
• maximum of two tRNAs on ribosome at any time
• peptidyl transferase which is part of the rRNA component catalyses the formation of peptide bonds between the amino acids
• like this, a sequence of amino acids gives us the primary structure of amino acids
• translation continues until a stop codon is reached

Question 5

What are the features of the genetic code?

Answer 5

• universal.. all organisms follow the same code
• degenerate…. many codons can code for the same amino acids because there are 64 possible codons but only 20 amino acids
• non overlapping.. one start codon to ensure that it is read from base 1/ read in frame

Question 6

In what direction is mRNA synthesised?

Answer 6

• 5’ to 3’