Bio

Central Ideas

• Cell division must be controlled: Unregulated cell division can lead to cancer. The cell cycle is regulated by checkpoints, cyclins, and other proteins.

• Cellular and subcellular structures and functions: Cells contain organelles, each with specialized functions essential for maintaining homeostasis.

• Cell size and magnification calculations: The formula M = I/A (magnification = image size / actual size) is used to determine cellular dimensions in microscopy.

• Membrane fluidity and dynamic processes: The fluid mosaic model describes how phospholipids and proteins move within the membrane to allow flexibility and function.

• Methods of transport (active and passive): Cells transport materials via passive transport (diffusion, osmosis, facilitated diffusion) and active transport (endocytosis, exocytosis, protein pumps).

• Stem cells and therapeutic use: Stem cells can differentiate into specialized cell types and are used in regenerative medicine (e.g., bone marrow transplants, treating spinal cord injuries).

• Cellular evolution: The endosymbiotic theory explains the origin of eukaryotic cells from prokaryotic ancestors.

Key Terms

• Amphipathic: A molecule with both hydrophobic and hydrophilic regions (e.g., phospholipids).

• Asexual reproduction: The production of offspring without the involvement of gametes, resulting in genetically identical clones.

• Binary fission: A form of asexual reproduction in prokaryotic cells where the cell divides into two identical daughter cells.

• Cell: The basic unit of life that carries out essential biological processes.

• Cyclins: Proteins that regulate the cell cycle by activating cyclin-dependent kinases (CDKs).

• Cytokinesis: The process of dividing the cytoplasm to form two daughter cells after mitosis or meiosis.

• Diffusion: The passive movement of molecules from an area of higher concentration to lower concentration.

• Eukaryotic cell: A cell containing membrane-bound organelles, including a nucleus (e.g., animal and plant cells).

• Homeostasis: The maintenance of a stable internal environment within a cell or organism.

• Magnification: The ratio of an image’s size to the actual size of the object being observed.

• Metabolism: The sum of all chemical reactions occurring within an organism, including catabolic and anabolic reactions.

• Mitosis: The process of cell division that results in two genetically identical daughter cells.

• Multicellular: An organism made up of many cells that perform specialized functions.

• Organelle: A specialized structure within a cell that carries out a specific function (e.g., mitochondria, ribosomes).

• Osmosis: The passive movement of water molecules across a selectively permeable membrane from a region of lower solute concentration to higher solute concentration.

• Prokaryotic cell: A simple cell without membrane-bound organelles or a nucleus (e.g., bacteria and archaea).

• Sexual reproduction: The process of producing offspring through the combination of gametes (sperm and egg), leading to genetic diversity.

• Stem cell: An undifferentiated cell capable of self-renewal and differentiation into specialized cell types.

• Unicellular: An organism composed of only one cell, performing all functions of life (e.g., bacteria, amoeba).

Cell Biology Review

Cell Theory

• What makes it a theory?

  • The cell theory is supported by extensive evidence and observation.

  • It is widely accepted but remains open to refinement as new discoveries emerge.

• Examples that challenge cell theory:

  • Striated muscle fibers: Long, multinucleated cells challenge the idea that cells are the basic unit of structure.

  • Aseptate fungal hyphae: Continuous cytoplasm with multiple nuclei, contradicting the idea of cells as discrete units.

  • Giant algae (Acetabularia): Large, unicellular organisms challenge the idea that all cells are small.

• Spontaneous Generation (Abiogenesis) – Pasteur’s Broth Experiment

  • Louis Pasteur’s experiment disproved spontaneous generation by demonstrating that sterilized broth remained free of microorganisms unless exposed to contaminants.

• Origin of Eukaryotes – Endosymbiotic Theory

  • Mitochondria and chloroplasts evolved from prokaryotic cells that were engulfed by larger cells.

  • Evidence: Double membranes, their own DNA, and ribosomes similar to bacteria.

Functions of Life

• Metabolism: Chemical reactions within cells (e.g., respiration, enzyme activity).

• Growth: Increase in size and cell number.

• Reproduction: Production of offspring (asexual or sexual).

• Response: Ability to react to environmental stimuli.

• Homeostasis: Maintaining stable internal conditions.

• Nutrition: Obtaining nutrients for energy and growth.

• Excretion: Removal of metabolic waste.

• Paramecium and Chlorella Experiments

  • Paramecium: A heterotrophic unicellular organism that moves using cilia and consumes food via phagocytosis.

  • Chlorella: A unicellular autotroph that performs photosynthesis.

Cell Types

• Similarities:

  • Both prokaryotic and eukaryotic cells have a plasma membrane, cytoplasm, DNA, and ribosomes.

• Differences:

  • Prokaryotes lack membrane-bound organelles, whereas eukaryotes have them.

Cell Membrane Models

• Davson-Danielli Model vs. Singer-Nicholson Model

  • The Davson-Danielli model proposed a static, protein-layered membrane.

  • The Singer-Nicholson model (fluid mosaic model) showed proteins embedded within a dynamic, fluid phospholipid bilayer.

• Membrane Transport

  • Active Transport (requires energy)

    • Phagocytosis: Engulfing solid particles (e.g., white blood cells engulfing bacteria).

    • Pinocytosis: Engulfing liquid droplets.

  • Passive Transport (no energy required)

    • Diffusion: Movement of molecules from high to low concentration.

    • Osmosis: Movement of water across a membrane.

    • Facilitated Diffusion: Transport of molecules via channel or carrier proteins.

Cell Cycle

• Mitosis Phases

  • Prophase, Metaphase, Anaphase, Telophase.

• Mitotic Rate: High rates can indicate cancerous activity.

• Cancer: Uncontrolled cell division due to mutations in oncogenes or tumor suppressor genes.

• Control of the Cell Cycle: Cyclins regulate progression through checkpoints.

• Stages

  • G1 phase: Cell grows.

  • S phase: DNA replication occurs.

  • G2 phase: Cell prepares for division.

  • M phase: Mitosis (nuclear division) and cytokinesis (cytoplasm division).

• Cell Size Limitations

  • Limited by surface area-to-volume ratio. Large cells struggle with transport efficiency.

Stem Cells

• Types and examples

  • Totipotent: Can become any cell type (e.g., zygote).

  • Pluripotent: Can become most cell types (e.g., embryonic stem cells).

  • Multipotent: Limited differentiation (e.g., bone marrow stem cells).

• Therapeutic Uses

  • Leukemia treatment: Bone marrow transplants replace diseased blood cells.

  • Parkinson’s disease: Stem cells used to regenerate damaged neurons.

  • Skin grafts: Used for burn victims.