Translation and Mutations

Physiology I Worksheet: Lecture 13 – Translation (Expression of Genetic Material: Part II of Protein Synthesis)

Genetic Code

  • Definition: The sequence of nucleotides in DNA specifies the sequence of amino acids in protein.

Codon

  • Definition: Triplet of nucleotide bases that code for a particular amino acid.

Redundancy

  • Definition: More than one codon can code for one amino acid.
  • Example: UCU, UCC, UCA, UCG, AGU, and AGC all code for serine.
  • Application: A single nucleotide substitution mutation may not affect the protein’s function due to redundancy.

Unambiguity

  • Definition: Each codon codes for only one amino acid.
  • Example: UCU only codes for serine and not another amino acid.

Phases of Translation

  • Three Phases: Initiation, elongation, and termination.
    • Location: Cytoplasm or RER (not the nucleus).
    • Final Product: Primary structure of a protein.

Components Used in Translation

  • mRNA (the gene)
  • Ribosomes
  • tRNAs carrying amino acids
  • Initiation factor proteins

Initiation Complex Elements

  • mRNA
  • Small ribosomal subunit
  • tRNA carrying methionine
  • Initiation factor proteins

Start and Stop Codons

  • Start Codon: AUG
  • Stop Codons: UAA, UAG, or UGA

Post-Translational Modifications

  • Glycosylation
  • Phosphorylation
  • Methylation
  • Acetylation
  • Folding
  • Ubiquitination
  • Hydroxylation

Mutation

  • Definition: Alterations of the DNA nucleotide sequence that may be passed on to daughter cells.

Induced vs. Spontaneous Mutation

  • Spontaneous Mutations: Permanent changes to DNA that occur without outside influence, due to errors in replication or cell division.
  • Induced Mutations: Permanent changes to DNA caused by some outside agent, such as mutagenic chemicals and/or radiation.

Germ Cell vs. Somatic Mutation

  • Germ Cell Mutations: Affect gametes (egg and sperm) and may be passed down to offspring.
  • Somatic Mutations: Affect body cells (epithelial cells, etc.) and may be passed down to daughter cells during division.
    • Germ cell mutations have the potential to affect offspring.

Types of Mutations

Point Mutations
  • Mutations of a single nucleotide.
Frame Shift Mutations
*   Addition or subtraction of a nucleotide.
*   Changes the reading frame, producing non-functional proteins.
Substitution Mutations
*   Substituting one nucleotide for another (e.g., substituting an A instead of a C).
    *   **Silent:** Has no effect on amino acid produced.
    *   **Missense:** Changes the amino acid; may or may not affect protein function. The sickle cell mutation is an example of a missense mutation.
    *   **Nonsense:** Causes a stop codon to be produced, resulting in a shortened, non-functional protein.
Trinucleotide Repeat Expansions
  • Repeats of nucleotide sequences that occur during DNA replication.
Splice Site Mutations
  • Mutations at the start or end of an intron.
  • Can affect splicing, leading to extra codons and therefore larger, non-functional proteins.
Chromosomal Mutations
  • More extensive mutations.
  • May change the position or orientation of a DNA segment without removing any genetic information, or they may cause a segment of DNA to be lost or duplicated.