Lecture Notes: Protein Synthesis (D1.2)

Overview

• Theme: Continuity and change
• Level: Molecules
• Guide Time:
  • SL: 3 hours
  • AHL: 3 hours

Guiding Questions

1. How does a cell produce a sequence of amino acids from a sequence of DNA bases?
2. How is the reliability of protein synthesis ensured?

Key Points

SL and HL Content

Transcription

• D1.2.1:
  • Transcription is the synthesis of RNA from a DNA template.
  • Role of RNA polymerase:
    • Untwists and separates DNA strands
    • Builds complementary RNA strand
• D1.2.2:
  • Hydrogen bonding and complementary base pairing in transcription:
    • G-C and T-A pairing
    • Adenine (A) on DNA pairs with uracil (U) on RNA
• D1.2.3:
  • DNA's stability allows it to serve as a template for transcription without changing its sequence.
  • Conservation of DNA sequences is crucial in non-dividing somatic cells.
• D1.2.4:
  • Transcription is crucial for gene expression.
  • Not all genes are expressed simultaneously; transcription can switch gene expression on/off.

Translation

• D1.2.5:
  • Translation synthesizes polypeptides from mRNA.
  • mRNA base sequence is translated into amino acid sequence.
• D1.2.6:
  • Roles of mRNA, ribosomes, and tRNA:
    • mRNA binds to ribosome's small subunit
    • Two tRNAs bind to the large subunit
• D1.2.7:
  • Complementary base pairing between tRNA anticodon and mRNA codon.

Genetic Code

• D1.2.8:
  • The genetic code is degenerate and universal.
  • Triplet code is necessary due to the 20 amino acids needing more combinations than two RNA bases provide.
• D1.2.9:
  • Using genetic code tables to deduce amino acid sequences from mRNA.
• D1.2.10:
  • Ribosome movement along mRNA and peptide bond formation during polypeptide elongation.

Mutations

• D1.2.11:
  • Mutations can affect protein structure.
  • Example: Point mutations.

Additional Higher Level Content

Transcription and Translation Directionality

• D1.2.12:
  • Understanding 5' to 3' transcription and translation.

Transcription Initiation

• D1.2.13:
  • Transcription initiated by transcription factors binding to the promoter.

Non-Coding DNA Sequences

• D1.2.14:
  • Examples include gene expression regulators, introns, telomeres, rRNA, and tRNA genes.

Post-Transcriptional Modifications

• D1.2.15:
  • Includes intron removal, exon splicing, and 5' cap and 3' polyA tail additions.

Alternative Splicing

• D1.2.16:
  • Allows a single gene to code for different proteins.

Translation Initiation

• D1.2.17:
  • Involves ribosomal subunit binding to mRNA, moving to start codon, tRNA binding, and large subunit attachment.
  • Three tRNA binding sites: A (acceptor), P (peptidyl), E (exit)

Polypeptide Modification

• D1.2.18:
  • Many polypeptides require modification to become functional. Example: Proinsulin to insulin.

Protein Recycling

• D1.2.19:
  • Proteasomes recycle amino acids, maintaining a functional proteome.

Linking Questions

• How does protein diversity contribute to cellular function?
• What biological processes depend on hydrogen bonding?