AP Bio Unit 2 Review

Cell Theory and Cell Types

Cell Theory

• All living organisms are composed of one or more cells, emphasizing cells as the fundamental building blocks of life.

• The cell is the basic unit of life, capable of carrying out all life processes like metabolism and reproduction.

• Rudolf Virchow's concept states that all cells arise from pre-existing cells, highlighting the continuity of life.

• Endosymbiotic Theory: The theory that eukaryotic organelles like mitochondria and chloroplasts were once free living prokaryotes that were ingested by a larger prokaryotic host cell.

Cellular Organelles and Functions

Nucleus

• Function: Stores genetic material (DNA) and regulates cellular activities through gene expression.

• Structure: Surrounded by a double membrane (nuclear envelope) with nuclear pores for selective transport.

Ribosomes

• Function: Sites of protein synthesis, translating mRNA into polypeptide chains.

• Location: Free-floating in the cytosol or attached to the rough endoplasmic reticulum (ER).

Endoplasmic Reticulum (ER)

• Rough ER: Synthesizes and transports proteins, studded with ribosomes.

• Smooth ER: Involved in lipid synthesis, detoxification, and calcium ion storage.

Golgi Apparatus

• Function: Modifies, sorts, and ships proteins and lipids received from the ER.

• Structure: Composed of flattened membrane-bound sacs (cisternae) for processing cellular products.

Mitochondria

• Function: Generates ATP through cellular respiration, known as the powerhouse of the cell.

• Structure: Double membrane with inner membrane folds (cristae) for increased ATP production.

Plant Cells vs. Animals Cells

• Plant cells have a cell wall made of cellulose

• Plant cells have chloroplasts

• most of the cytoplasm within a plant cell is usually taken up by a large vacuole (the central vacuole)

Prokaryotic vs. Eukaryotic Cells

• AP likes to test this a lot

• Prokaryotic Cells:

  • Lack a nucleus and membrane-bound organelles.

  • Found in bacteria and archaea.

  • Ribosomes are smaller and called “70S“ ribosomes

  • Components:

    • plasma membrane

    • flagella and cilia

    • cell wall

    • nucleoid region

    • ribosomes

    • circular chromosomes

    • cytoplasm

• Eukaryotic Cells:

  • Contain a nucleus and various organelles, allowing for specialized cellular functions.

  • Ribosomes are larger and called “80S“ ribosomes

  • Components:

    • nucleus

    • nucleolus

    • rough endoplasmic reticulum

    • smoother endoplasmic reticulum

    • Golgi body

    • ribosomes

    • mitochondria

    • vacuole

    • lysosome

    • peroxisomes

    • centrioles (animals only)

    • cytoplasm

    • plasma membrane

    • cytoskeleton (microtubules, microfilaments)

    • central vacuole (plants only)

    • cell wall (plants, fungi, and some protists)

Membrane Structure and Transport

Fluid Mosaic Model

• Describes the cell membrane (plasma membrane) as a dynamic phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Phospholipids: Form a semi-permeable barrier with hydrophilic heads outward and hydrophobic tails inward.

• The hydrophobic nature of the inside of the membrane is responsible for its selective permeability

Membrane Proteins

• Transport Proteins: Facilitate substance movement across the membrane for selective permeability.

• Receptors: Bind signaling molecules to initiate cellular responses.

• Ex: aquaporins - water specific channels that allow water to traverse the membrane despite the membrane being nonpolar

• Glucose and ions such as Na+ and K+ are also transported across plasma membranes through membrane proteins

  • membranes may become polarized as these ions move across them

Selective Permeability

• Definition: Allows certain substances to cross more easily, maintaining homeostasis.

• Examples: Diffusion, osmosis, and facilitated diffusion based on molecule characteristics.

• They do this because substances want to move down a concentration gradient, going from high concentration to low concentration (diffusion)

• Transport through the membrane depends on size and polarity of the molecules and concentration gradients

• Facilitated diffusion - When diffusion required the help of a channel protein

• Osmosis - When water is diffusing

  • Water is usually present as a solution

  • The solvent (water) can move toward equilibrium in order to make the concentration the same across the membrane

    • Water moves to “dilute“ a solution

    • Can be tricky because one side may look like it “gains“ water even though it has a higher concentration already, however that concentration is the solute and water as the solvent moves to dilute the solute

      

Transport Across the Membrane

• Passive Transport: Includes diffusion, osmosis, and facilitated diffusion.

• Active Transport: Requires ATP to move molecules against their concentration gradient.

  • Ex: Sodium-potassium pump

  • Shoots out three sodium ions and brings in two potassium ions across the cell membrane

  • This pump depends on ATP to get ions across that would otherwise remain in regions of higher concentration

Types of Cellular transport

• Simple diffusion

  • Ex: Steroids such as testosterone are hydrophobic lipids. Therefore, testosterone can cross the inner region of the phospholipid bilayer

• Facilitated transport

• Active Transport

• Bulk Flow

• Dialysis

• Endocytosis

• Exocytosis

Surface Area to volume ratio

• Higher surface area to volume ratio is more efficient to diffuse more

• When there is insufficient surface area to support a cell's increasing volume, a cell will either divide or die

Water Potential Equations

Solute Potential of a Solution

Energy Conversion and Communication

Mitochondria and Cellular Respiration

• Aerobic Respiration: Converts glucose and oxygen into ATP through Glycolysis, Krebs Cycle, and Electron Transport Chain.

• Function: Essential for converting stored glucose energy into usable ATP.

Chloroplasts and Photosynthesis

• Equation: CO₂ + H₂O + Light → Glucose + O₂.

• Process: Occurs in chloroplasts, with light reactions and Calvin cycle in different compartments.

Cell Communication

• Signaling Pathways: Cells communicate through chemical signals and signal transduction for specific responses.

• Types of Signaling: Autocrine, Paracrine, and Endocrine signaling pathways.

Key Terms

• Endocytosis - The process by which cells internalize substances from their external environment by engulfing them in a membrane-bound vesicle.

• Exocytosis - The process through which a cell expels materials by packaging them into vesicles that fuse with the cell membrane and release their contents outside the cell.

• Bulk Flow - The movement of fluids (liquids or gases) driven by pressure differences, facilitating the transport of substances over long distances within a biological system.

• Dialysis - diffusion of solutes across a selectively permeable membrane

  • Ex: Kidney Dialysis is a specialized process where blood is filtered by using machines and concentration gradients

  • Gives substances present at high levels an opportunity to diffuse out of the blood

• Light Microscopes: Microscopes that use visible light and lenses to magnify objects, typically up to 1,000 times.

  • Can visualize plant, animal, and bacterial cells

• Electron Microscopes: Microscopes that use electron beams instead of light for higher magnifications (up to 2 million times).

  • Can visualize cell organelle structures such as the nuclear membrane

• Nucleoid: Region in prokaryotic cells where DNA is located, not surrounded by a membrane.

• Flagella: Long, whip-like appendages used by some cells (e.g., bacteria, sperm) for movement.

• Capsule: Protective outer layer in some prokaryotic cells made of polysaccharides.

• Phospholipid Bilayer: Double layer of phospholipids forming the cell membrane, with hydrophilic heads and hydrophobic tails.

• Peripheral Proteins: Proteins temporarily attached to the surface of the cell membrane.

• Integral Proteins: Proteins embedded within the phospholipid bilayer, may span the entire membrane.

• Transmembrane Proteins: A type of integral protein that spans the entire phospholipid bilayer.

• Adhesion Proteins: Membrane proteins that help cells adhere to each other or the extracellular matrix.

• Receptor Proteins: Membrane proteins that bind to signaling molecules (e.g., hormones) to initiate a cellular response.

• Transport Proteins: Membrane proteins that help move substances across the cell membrane.

• Channel Proteins: Transport proteins that form channels or pores in the membrane to allow specific molecules to pass.

• Cell Surface Markers: Glycoproteins or glycolipids on the outer surface of the cell membrane that aid in cell recognition.

• Carbohydrate Side Chains: Chains of sugars attached to proteins or lipids on the cell membrane for recognition and signaling.

• Cristae: Folds within the inner membrane of mitochondria that increase surface area for ATP synthesis.

• Centrioles: Cylindrical structures involved in organizing microtubules during cell division.

• Microtubule Organizing Centers (MTOCs): Structures (like centrioles) that organize microtubules, especially during cell division.

• Peroxisomes: Organelles involved in fatty acid breakdown and detoxification, producing hydrogen peroxide.

• Microtubules: Tubular structures made of tubulin, providing structural support and helping with cell division and transport.

• Microfilaments: Thin actin fibers that provide mechanical support and assist in cell movement and muscle contraction.

• Tubulin: Protein subunits that make up microtubules.

• Cilia: Short, hair-like projections on cells used for movement or moving substances around the cell.

• Euglena: A genus of flagellated protists that can perform photosynthesis.

• Paramecium: A genus of ciliated protozoa that live in water and use cilia for movement and feeding.

• Chitin: A polysaccharide found in fungal cell walls and arthropod exoskeletons.

• Tonicity: The relative solute concentration in a solution affecting water movement across cell membranes.

• Isotonic: Solution with the same solute concentration as the cell, resulting in no net water movement.

• Hypertonic: Solution with higher solute concentration than the cell, causing water to move out of the cell.

• Hypotonic: Solution with lower solute concentration than the cell, causing water to move into the cell.

• Pinocytosis: Endocytosis where the cell engulfs extracellular fluid and its solutes.

• Phagocytosis: Endocytosis where the cell engulfs large particles (e.g., debris or microorganisms).

• Receptor-Mediated Endocytosis: Endocytosis where specific molecules are taken in by binding to cell surface receptors.

• Clathrin: Protein that helps form coated pits during receptor-mediated endocytosis.

• Bulk Flow: Movement of large amounts of fluid or substances within a system, often driven by pressure differences.