Protein synthesis

Question 1

mRNA

Answer 1

• made during transcription + is a single polynucleotide strand.
• carries genetic code from DNA to ribosomes, where it is used to make a protein during translation.

Question 2

tRNA

Answer 2

• involved in translation + a single polynucleotide strand thats folded into a clover shape - hydrogen bonds between specific base pairs hold the molecule in this shape, every tRNA has a specific sequence of 3 bases - its anticodon at one end and an amino acid binding site at the other end.
• carries amino acids to the ribosomes to make proteins.

Question 3

First stage of protein synthesis

Answer 3

• Transcription - an mRNA copy of a gene is made from DNA.
• eurkaryotes = takes place in nucleus
• prokaryotes = cytoplasm
• starts by RNA polymerase - attaches to start of gene + breaks hydrogen bonds between DNA strands/helix = uncoil = one strand used as a template to make mRNA copy.
• RNA polymerase lines free RNA nucleotides along exposed bases on DNA template strand.
• specific complementary base pairing = RNA nucleotides pair/bind with specific bases - binded by RNA polymerase = forming mRNA (a complementary copy of the template strand)
• hydrogen bonds between DNA strands reform once RNA polymerase has passed (coil back into double helix)
• a particular sequence of DNA - a stop signal = stops making mRNA + detaches from DNA.
• in eurkaryotes - mRNA moves out of the nucleus via a nuclear pore + attaches to ribosome.

Question 4

What happens before mRNA leaves nucleus in eukaryotes?

Answer 4

• introns and exons are both copied into mRNA - this is called pre-mRNA - splicing occurs - introns removed and exons join together - forming mRNA
• prokaryotes dont need to splice as there are no introns in prokaryotic DNA.

Question 5

2nd stage of protein synthesis

Answer 5

Translation - amino acids are joined together to make a polypeptide chain (protein) following the sequence of codons (triplets) carried by the mRNA.

• mRNA attached to ribosomes + tRNA carries amino acids to it (ATP provides energy for bond between amino acid and tRNA to form)
• tRNA carrying amino acid, has an anticodon which is complementary to the 1st codon on mRNA = attaches to mRNA by specific base pairing.
• 2nd tRNA does same thing
• 2 amino acids attached to tRNA join by peptide bond + 1st tRNA moves away leaving amino acid.
• next tRNA binds to next codon on the mRNA + process repeats + creates a polypeptide chain of amino acids until stop signal on the mRNA molecule.
• polypeptide chain moves away from ribosome = complete