Protein synthesis (BIOL5)

Question 1

Describe transcription

Answer 1

1. ​Helicase attach to DNA double-helix, break H bonds b/w strands - DNA uncoils
2. One strand use as template to make mRNA; polymerase lines up free RNA nucleotides along template strand w/ spec. base pairing (T replaced by U)
3. Nucleotides join by H bonds, forming mRNA
4. H bonds b/w uncoiled strands reform, coil into double-helix
5. When stop signal reached, polymerase detaches from DNA
6. mRNA moves out of nucleus through nuclear pores, attaches to ribosome in cytoplasm

Question 2

Describe splicing

Answer 2

• Genes in eukaryotic DNA contain non-coding sections - introns
• Exons - sections coding for amino acids
• During transcription, introns/exons are copied into mRNA - strands w/ introns/exons are called pre-mRNA
• Introns removed from pre-mRNA by splicing
  
  • Introns are removed, exons join forming mRNA
  • mRNA leaves nucleus for translation

Question 3

Describe translation

Answer 3

1. mRNA attaches to ribosome and tRNA carry amino acids to ribosome
2. tRNA w/ anticodon complementary to first codon, attaches to mRNA by spec. base pairing
3. Second tRNA attaches to next codon on mRNA in same way
4. 2 amino acids attached to tRNA are joined by peptide bond; first tRNA molecule moves away, leaving its amino acid behind
5. Third tRNA binds to next codon on mRNA; amino acid binds to first 2 - second tRNA moves away; continues until stop signal
6. Polypeptide chain (protein) moves away from ribosome