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