Cell Structure and Function

• This note covers the topics of Microscopes and Studying Cells, Prokaryotic vs. Eukaryotic Cells, Nucleus and Ribosomes, Endomembrane System, Mitochondria & Chloroplasts, Cytoskeleton, Cell Walls & ECM and Membranes

Microscopes and Studying Cells

• Magnification makes objects appear larger.
• Resolution enhances the clarity of an image.
• Electron microscopes kill cells, precluding observation of living specimens.
• SEM provides 3D surface images.
• TEM offers detailed internal views of cells.

Prokaryotic vs. Eukaryotic Cells

• The domains Bacteria and Archaea are prokaryotic.
• Prokaryotic DNA resides in the nucleoid, lacking a membrane.
• Eukaryotic DNA is housed within the membrane-bound nucleus.
• Prokaryotic components include cell wall, plasma membrane, chromosome, nucleoid, cytoplasm, and flagella.
• The cell wall protects the cell.
• The plasma membrane regulates substance entry and exit.
• Chromosomes contain DNA.
• The nucleoid is the DNA-containing region (not a nucleus).
• Cytoplasm is the jelly-like substance inside cells.
• Flagella aid in cell movement.
• Small cells have a high surface area-to-volume ratio, facilitating efficient material exchange.

Nucleus and Ribosomes

• Nuclear envelope consists of a double layer with pores for material transit.
• Chromatin comprises DNA and proteins, condensing into chromosomes during cell division.
• The nucleolus, visible in resting cells, synthesizes ribosomes.
• Ribosomes, made of rRNA and protein, are responsible for protein synthesis.

Endomembrane System

• The endomembrane system includes the nuclear envelope, ER, Golgi, lysosomes, vacuoles, vesicles, and plasma membrane.
• The ER lumen is the internal space of the ER.
• Transport vesicles facilitate substance movement.
• Smooth ER synthesizes lipids, detoxifies, and stores calcium.
• Rough ER, studded with ribosomes, produces proteins.
• Secretory proteins are packaged into vesicles for Golgi transport.
• Rough ER also produces membranes.
• The Golgi apparatus modifies and sorts proteins.
• The cis face of the Golgi receives proteins; the trans face ships them out.
• Lysosomes contain digestive enzymes for waste breakdown and function at a low (acidic) pH.
• Phagocytosis involves the cell engulfing food or bacteria, exemplified by white blood cells.
• Autophagy is where lysosomes break down old cell parts.
• Tay-Sachs disease results from lysosomes' inability to break down fats, causing brain buildup.
• Food vacuoles store food.
• Contractile vacuoles pump out excess water.
• Central vacuoles (in plants) store water, nutrients, and waste.

Mitochondria & Chloroplasts

• Mitochondria are the cell's powerhouses, producing ATP (energy).
• Chloroplasts use sunlight for photosynthesis.
• Folded inner membranes in mitochondria and chloroplasts increase surface area for energy production.
• Peroxisomes break down fatty acids and detoxify harmful substances.

Cytoskeleton

• The cytoskeleton provides cells with shape, support, and facilitates movement.
• The cytoskeleton provides structural support.
• The cytoskeleton moves organelles within the cell.
• The cytoskeleton aids in cell movement via cilia and flagella.
• Microtubules are hollow tubes essential for transport and movement.
• Microfilaments, thin rods, contribute to cell shape and movement.
• Intermediate filaments provide strong support.
• Dyneins are motor proteins that use ATP to move cilia and flagella.

Cell Walls & ECM

• The cell wall protects, supports, and regulates water intake.
• Plant cell walls are made of cellulose.
• Fungi cell walls are made of chitin.
• Bacteria cell walls are made of peptidoglycan.
• Plasmodesmata are channels connecting plant cells.
• Animal Cell Junctions

Membranes are Fluid Mosaics

• Four main classes of large molecules: Carbohydrates, lipids, proteins, and nucleic acids
• Amphipathic molecules possess both hydrophobic (water-repelling) and hydrophilic (water-attracting) regions.
• Decreasing temperature reduces membrane fluidity, potentially causing solidification.
• Unsaturated hydrocarbon chains maintain membrane fluidity due to kinks in fatty acids.
• Cholesterol helps maintain fluidity by preventing solidification at low temperatures.
• Integral proteins are embedded within the membrane.
• Peripheral proteins attach to the membrane surface.
• Membrane proteins transport substances.
• Membrane proteins catalyze chemical reactions.
• Membrane proteins transmit signals.
• Membrane proteins enable cell-cell recognition.
• Membrane proteins join cells together.
• Membrane proteins attach to the cytoskeleton and ECM to maintain cell shape.
• Cell-cell recognition examples include immune system recognition and blood type determination.
• Glycolipids are carbohydrates attached to lipids.
• Glycoproteins are carbohydrates attached to proteins.

Selective Permeability

• Channel proteins form tunnels for molecule passage.
• Carrier proteins change shape to transport molecules.
• CO2 crosses the membrane via simple diffusion.
• Glucose crosses the membrane via carrier proteins (facilitated diffusion).
• H+ (hydrogen ions) uses active transport.
• O2 crosses the membrane via simple diffusion.
• H2O crosses the membrane via osmosis (sometimes through aquaporins).

Passive Transport

• Diffusion is the movement of molecules from high to low concentration.
• A concentration gradient is the concentration difference between two areas.
• Passive transport moves molecules without energy.
• Osmosis is water diffusion across a membrane.
• Isotonic solutions have equal concentrations inside and outside the cell.
• Hypertonic solutions have more solutes outside, causing water to exit the cell.
• Hypotonic solutions have fewer solutes outside, causing water to enter the cell.
• Turgid plant cells are firm in a hypotonic solution.
• Flaccid plant cells are limp in an isotonic solution.
• Plasmolysis occurs when the cell membrane pulls away from the wall in a hypertonic solution.
• A limp carrot results from water loss due to osmosis in a hypertonic environment (plasmolysis).
• Facilitated diffusion is protein-assisted passive transport, such as glucose transport and ion channels.
• Plant cells resist bursting due to their cell walls.

Active Transport

• Active transport uses ATP energy to move molecules against their concentration gradient, aided by carrier proteins.
• The sodium-potassium pump moves 3 Na+ out and 2 K+ in, using ATP.
• It helps maintain nerve cell function.
• Membrane potential is the voltage across the membrane, with the outside being positive.
• Ion movement is driven by concentration gradients and electrical charge.
• Combined forces create an electrochemical gradient.
• Cotransport involves one substance's movement aiding another, used in diarrhea treatment to enhance glucose absorption.

Bulk Transport

• Endocytosis takes in large molecules.
• Phagocytosis involves "cell eating".
• Pinocytosis involves "cell drinking".
• Exocytosis releases materials.
• Receptor-mediated endocytosis involves specific molecules binding to receptors for uptake.
• A ligand is a molecule that binds a receptor to trigger events.
• Bulk transport is active, requiring ATP energy.

Exploration of cell structures, functions, and differences between prokaryotic and eukaryotic cells. Topics covered include microscopes, cell components, and membranes. Key organelles such as the nucleus, ribosomes, mitochondria, and chloroplasts are discussed.