SA

Int. Bio Unit 1

Structure-Function Relationships

  • Phenotype: Any physical observable trait.
    • Result of genes and the environment.
    • Examples: behavior, color, resistance to disease, lifespan.
    • Both structure and function are phenotypes.
    • Example: How birds hear song, how birds make song, how birds learn to sing.
  • Proximate causation: Explanations focusing on the molecular and cellular mechanisms responsible for a function.
  • Ultimate causation: Explanations focusing on why structures and processes exist in terms of evolutionary history and impact on fitness (big picture).

Central Dogma

  • Describes the flow of genetic information: DNA to RNA, and RNA to proteins.
  • Includes both transcription and translation.
  • Transcription:
    • Begins in the nucleus.
    • mRNA leaves the nucleus to cytoplasm for translation by ribosomes.

Eukaryotic Transcription

  • Occurs in the nucleus.
  • Requires transcription factors + promoter region for eukaryotic transcription to occur.
  • RNA polymerase reads the template (non-coding) DNA strand in the 3’ to 5’ direction.
  • RNA polymerase adds bases to the 3’ end of the growing mRNA strand.
  • mRNA is transported from nucleus to the cytoplasm for translation.

Eukaryotic Translation

  • Occurs in the cytoplasm.
  • mRNA binds to ribosome once in the cytoplasm.
  • The (L) & (S) ribosome subunits attach to the mRNA to initiate translation.
  • A tRNA contains an anticodon that is complementary to the mRNA codon that it binds (usually start AUG).
  • The corresponding amino acid is attached to the tRNA at the A site, transferred to the next tRNA at the P site, and will exit at the E site.
  • Peptide will continue to grow until reaching stop codon.
  • The A site is where amino acid-carrying tRNAs enter the ribosome.
  • The P site is where peptide bond formation takes place between the new amino acid and the chain of already added ones.
  • The E site is where tRNAs sit once the amino acid they were carrying has been added to the growing protein; the now-uncharged tRNA exits the ribosome from this site.

DNA and RNA

  • Purines: guanine, adenine (two rings).
  • Pyrimidines: cytosine, thymine, uracil (only one ring).
  • A and T have two hydrogen bonds.
  • G and C have three hydrogen bonds.
  • Polarity of DNA: Opposite sides of the molecule are different.
  • RNA structure: More reactive than DNA, can fold back on itself and perform various jobs in the cell because it has an extra oxygen on the 2’ carbon.

Heritability vs. Plasticity

  • Heritability: The proportion of phenotypic variation attributable to genetic variation.
    • HERITABILITY = 1: All variation in trait is due to variation in genotype.
    • HERITABILITY = 0: All variation in trait is due to variation in environment (fully plastic).
  • Examples:
    • Huntington's Disease
    • Cholesterol
    • Skin cancer
    • Sprint speed
    • Human language
  • Heritability is not the same as inheritance.
    • Inheritance is just passing on an allele to your offspring.

Mutations

  • Point mutations:
    • Silent: No change in amino acid sequence.
    • Nonsense: Results in a stop codon.
    • Missense:
    • Conservative: New amino acid similar to the original.
    • Non-conservative: New amino acid is different from the original.
  • Example:
    • DNA: TTC, TTT, ATC, TCC, TGC
    • mRNA: AAG, AAA, UAG, AGG, ACG
    • Amino Acid: Lys, Lys, STOP, Arg, Thr

Graphs

  • Discrete variable: A quantity that can only take certain, discrete values (e.g., the number of people).
  • Continuous variable: A quantity that can take a continuous range of values (e.g., blood pressure).

Commonly Asked about Topics

  • Directionality of DNA/mRNA during transcription and translation