Biology Keystone Review

Cell Cycle Overview

  • Cell Cycle Definition: The complete life cycle of a cell, involves growth, DNA duplication, and division.
  • Phases:
    • Interphase: Longest phase involving cell growth and DNA replication.
    • G1 Phase: Cell grows and synthesizes proteins.
    • S Phase: DNA replicates, resulting in two full sets of chromosomes.
    • G2 Phase: Further growth and preparation for cell division.
    • M Phase: Includes mitosis and cytokinesis.

Mitosis

  • Stages of Mitosis:
    1. Prophase: Chromatin condenses into chromosomes, spindle fibers form, and the nuclear membrane dissolves.
    2. Metaphase: Chromosomes align at the equatorial plate; spindle fibers attach to centromeres.
    3. Anaphase: Sister chromatids are pulled apart toward the poles.
    4. Telophase: New nuclear envelopes form around each set of chromosomes, nucleolus reappears, and spindle fibers disassemble.
  • Cytokinesis: Division of the cytoplasm, resulting in two identical diploid daughter cells.

Meiosis

  • Comparison of Mitosis and Meiosis:
    • Mitosis:
    • Produces somatic cells
    • One division, yielding 2 identical diploid cells (46 chromosomes in humans)
    • Meiosis:
    • Produces gametes
    • Two divisions, yielding 4 unique haploid cells (23 chromosomes in humans)
  • Key Features of Meiosis:
    • Crossing Over: Homologous chromosomes exchange genetic info during Prophase I, increasing genetic diversity.
    • Nondisjunction: Failure of homologous chromosomes to separate, leading to gametes with abnormal chromosome numbers.

DNA Replication

  • Process: Occurs during the S phase of interphase, leading to two identical DNA molecules via semi-conservative replication.
  • Key Enzymes:
    • DNA Polymerase: Synthesizes new DNA strands.
    • Helicase: Unwinds the DNA double helix.
    • Ligase: Joins Okazaki fragments on the lagging strand.
    • RNA Primase: Prepares the DNA strand for replication.

DNA and Genetics

  • Definitions:
    • Genes: Segments of DNA coding for proteins.
    • Alleles: Variants of a gene (e.g., D for dimples, d for no dimples).
    • Chromatin: Uncondensed form of DNA in the nucleus; becomes chromosomes during cell division.
  • Protein Synthesis (Central Dogma):
    1. Transcription: DNA is transcribed into mRNA in the nucleus.
    2. Translation: mRNA is translated into amino acids at ribosomes in the cytoplasm.

Patterns of Inheritance

  • Definitions:
    • Dominant Alleles: Represented by capital letters, they mask recessive alleles.
    • Recessive Alleles: Represented by lowercase letters, shown only in homozygous recessive forms.
    • Codominance & Incomplete Dominance: Forms of inheritance where phenotypes blend or coexist.
    • Sex-linked Traits: Traits tied to sex chromosomes, affecting males and females differently.
  • Polygenic Traits: Traits controlled by multiple genes.
  • Multiple Alleles: More than two alleles can exist for a trait (e.g., blood type).

Mutations and Genetic Variability

  • Types of Mutations:
    • Point Mutations: Changes in one nucleotide base (silent, nonsense, missense).
    • Frameshift Mutations: Insertions or deletions that disrupt the reading frame.
  • Impact on Phenotype: Mutations can lead to beneficial, harmful, or neutral outcomes.

Biotechnology

  • Genetic Engineering Applications:
    • Selective Breeding: Producing offspring with desired traits.
    • Gene Splicing & Recombinant DNA: Combining genes from different organisms.
    • Gene Therapy: Modifying genes in individual cells for treatment.
  • Forensics: Utilization of DNA fingerprinting and PCR for identification purposes.

Evolution

  • Evidence for Evolution:
    • Fossil Record: Tracks changes in species over time, supporting descent with modification.
    • Anatomical & Physiological Evidence: Includes homologous, analogous, and vestigial structures.
    • Biochemical Evidence: Analyzing DNA and protein similarities among species.
    • Natural Selection: Mechanism leading to evolution.

Ecosystems and Energy Flow

  • Levels of Organization:
    • Organisms to Biosphere: From individual organisms → populations → communities → ecosystems → biomes → biosphere.
  • Energy Flow:
    • Autotrophs vs Heterotrophs: Producers create energy (plants) while consumers derive energy (animals).
    • Food Chains & Webs: Network of energy flow and trophic levels in ecosystems.
    • Energy Pyramid: Illustrates energy transfer through trophic levels.

Climate and Ecosystem Dynamics

  • Natural and Human-Induced Changes: Understand how ecosystems adapt to disturbance.
  • Cycles in Ecosystems: Water, carbon, nitrogen cycles describe matter recycling.

Observation and Hypothesis in Science

  • Definitions of Key Terms:
    • Observation: Data recorded through senses or instruments.
    • Hypothesis: Testable explanation for observations.
    • Theory vs Law: Theory explains phenomena with data, while a law describes consistent observations.

Conclusion

  • Understanding these concepts prepares for the key topics in biology pertaining to cell processes, genetics, evolution, ecosystems, and scientific methodology.