Biology Essentials: Genetics, Evolution, and Cell Division

Genetics

Protein Synthesis

• Step 1: Transcription (Nucleus)
  • The DNA double helix unzips down the middle.
  • An enzyme called RNA polymerase reads one strand of the DNA.
  • It builds a matching strand of mRNA by pairing complementary bases.
  • Note: Wherever DNA has T, mRNA uses U instead.
  • The mRNA strand peels off and leaves the nucleus.
• Step 2: Translation (Ribosome)
  • The mRNA travels to a ribosome.
  • The ribosome reads the mRNA 3 bases at a time; each group of 3 is called a codon.
  • Each codon matches to a specific amino acid (use the codon chart to identify).
  • A special RNA called tRNA carries the correct amino acid and drops it off.
  • The amino acids link together one by one into a chain.
  • That chain folds up into a protein.

Punnett Square Basics

• Genotype: TT : Tt : tt
• Phenotype: 3 pink : 2 white

Cancer and Cell Division

• Metastasis: Cancer cells break away and spread to other body parts.
• Stages of Mitosis (PMAT):
  • Prophase: Chromosomes condense, spindle forms.
  • Metaphase: Chromosomes line up at the center.
  • Anaphase: Sister chromatids pulled to opposite ends.
  • Telophase: Nuclear envelopes reform, chromosomes relax.
  • Cytokinesis: Cytoplasm splits → 2 identical diploid cells.

Viruses and Bacteria

• Bacteria: Prokaryote (living), has cell membrane, cytoplasm, ribosomes, and DNA (no nucleus).
• Viruses: Non-cellular, genetic material in a protein coat (capsid), not considered alive.
• Antibiotics: Target bacterial structures (cell wall, ribosomes) and do not work on viruses.

Evolution

Evidence for Evolution

• Fossil record: Shows species change over time and transitional forms.
• Homologous structures: Same bones, different function (e.g., human arm, whale flipper, bat wing) indicating a common ancestor.
• Analogous structures: Same function, different structure (e.g., bird wing vs. insect wing).
• Embryology: Many animals look nearly identical as embryos, suggesting shared ancestry.
• Molecular biology: More shared DNA indicates a closer relationship.
• Biogeography: Species locations align with evolutionary history.

Natural Selection: The Formula

1. Genetic variation exists in the population.
2. Environment creates selection pressure (predator, disease, climate).
3. Individuals with favorable traits survive more.
4. Survivors reproduce and pass on favorable traits.
5. Over generations, the population shifts (evolution).

Types of Selection

• Stabilizing: Average favored, extremes eliminated (e.g., human birth weight).
• Directional: One extreme favored, population shifts (e.g., giraffe necks, antibiotic resistance).
• Disruptive: Both extremes favored, middle eliminated (e.g., birds with two food sources).

Vestigial Structures

• Body parts that lost their original function through evolution.
• Examples: Human tailbone, whale pelvis, wisdom teeth, goosebumps, snake leg bones.

Adaptations

• Heritable traits that increase fitness (survival and reproduction) in a given environment.
• Arise through natural selection over many generations.