Cell Biology: Mitosis, Viruses, and Cellular Structures

Posted on Feb 17, 2025 in Biology

Mitosis and Cell Division

Mitosis is the process of cell division that creates two identical daughter cells. It has 4 stages (PMAT):

  1. Prophase: Chromosomes form, nuclear membrane breaks down.
  2. Metaphase: Chromosomes line up in the middle.
  3. Anaphase: Sister chromatids are pulled apart to opposite sides.
  4. Telophase: Nuclear membranes reform, chromosomes loosen.

Cytokinesis follows, splitting the cytoplasm into two cells.

Key Cell Biology Concepts

Here’s a concise summary of key cell biology concepts:

  • Viruses: Non-living, need a host to replicate.
  • Protists: Unicellular, eukaryotic.
  • Osmosis: Water moves across a membrane; hypotonic (water in), hypertonic (water out).
  • Cell membrane: Controls entry/exit of substances.
  • Mitochondria: Powerhouse, ATP production.
  • Photosynthesis: Process by which plants convert light energy into chemical energy.
  • Cell cycle: Interphase, mitosis (PMAT), cytokinesis.
  • DNA: Double helix, genetic information.
  • Prokaryotes: No nucleus, circular DNA.
  • Eukaryotes: Nucleus, linear DNA.

Cellular Structures: Unit 1

  1. What are the structure and function of biomolecules and the cell membrane?

    Biomolecules include proteins, lipids, carbohydrates, and nucleic acids. The cell membrane regulates what enters and exits the cell.

  2. What is the role of enzymes and substrates?

    Enzymes speed up reactions. Substrates bind to enzymes and are changed, while enzymes remain unchanged.

  3. What are the effects of temperature on enzymes?

    High temperatures can denature enzymes (change their shape), making them nonfunctional.

  4. What is the difference between prokaryotes and eukaryotes?

    Prokaryotes have free-floating DNA, no nucleus, and no membrane-bound organelles. Eukaryotes have a nucleus and organelles.

  5. How do viruses compare to cells? What is the structure of viruses?

    Viruses are non-living, need a host to reproduce, and have a capsid (protein coat) protecting their genetic material.

DNA and mRNA

  1. How do you determine amino acids using a codon chart?

    Use the codons (3-base sequences) to find the matching amino acid.

  2. How do you write a complementary mRNA strand?

    Replace DNA bases with their RNA complements:

    • A → U
    • T → A
    • G → C
    • C → G

  3. How does the sequence of DNA bases determine traits?

    The order of DNA bases determines the amino acid sequence, which builds proteins for traits.

Prokaryotes and Eukaryotes: Shared Features

Prokaryotes and eukaryotes both have:

  1. Cell membrane: Controls what enters and exits the cell.
  2. Cytoplasm: Jelly-like substance where cellular activities occur.
  3. Ribosomes: Make proteins.
  4. DNA: Genetic material that carries instructions for life.

Cell Membrane Functions

The cell membrane has several important functions:

  1. Controls entry and exit: Acts as a selective barrier (semi-permeable).
  2. Provides protection: Surrounds and protects the cell’s contents.
  3. Maintains homeostasis: Regulates the internal environment.
  4. Facilitates communication: Contains receptors for signaling molecules.
  5. Supports the cell’s structure: Provides shape and anchors the cytoskeleton.

Virus Composition

Viruses are made of:

  1. Genetic material: Either DNA or RNA that carries instructions for replication.
  2. Capsid: A protein coat that protects the genetic material.
  3. Optional envelope: Some viruses have a lipid envelope around the capsid, derived from the host cell membrane.

Viruses are simple structures but require a host cell to reproduce.

Understanding Viruses

Viruses are non-living infectious agents made up of genetic material (DNA or RNA), a protein coat (capsid), and sometimes a lipid envelope. They can only replicate inside a living host cell by taking over the host’s machinery to produce new viruses.

  • Structure: Genetic material, capsid, and optional envelope.
  • Replication: Viruses attach to a host, enter the cell, use the host’s machinery to make new viruses, and then release them to infect other cells.
  • Host specificity: Viruses are specific to certain hosts (animals, plants, or bacteria).
  • Diseases: Viruses cause diseases like the flu, COVID-19, and HIV.