Cell Biology Flashcards

Cell Biology: Structure and Function

Introduction to Cells

• Cells are the fundamental units of life.
• The body consists of a couple hundred different cell types, each with a particular function.
• Cells can be harvested and grown in the lab with the right nutrition and environmental factors.
• Tissues are composed of cells and cell products.

Cell Shapes

• Squamous Epithelium: Thin, single-layered cells.
• Polygonal Cells: Multiple sides.
• Cuboidal Cells: Cube-shaped.
• Columnar Cells: Column-shaped.
• Spherical Cells: E.g., White blood cells.
• Discoid Cells: E.g., Red blood cells.
• Stellate Cells: Star-shaped, e.g., Neurons.
• Fusiform Cells: Spindle-shaped, thick in the middle, tapered on the ends (muscle fibers).
• Fibrous: Muscle fibers.

Microscopy

Light Microscopy

• Utilizes two magnifying lenses to increase zoom.
• Plasma Membrane: Light pink ring around the periphery of cells.
• Nucleus: Large, purple, prominent intracellular organelle.
• Cytoplasm: Space between the plasma membrane and the nucleus.

Electron Microscopy

• Applies a much greater level of magnification, giving greater resolution.
• Plasma Membrane: Outer edge.
• Nucleus: Contains DNA.
• Organelles: Mitochondria, Golgi apparatus, Ribosomes.
• Cytoskeleton: Protein fibers that provide a scaffold for the cell, maintaining its shape.
• Cytosol: Gel-like substance where organelles are embedded.

Cell Structure

• Apical Surface: Top of the cell.
• Basement Membrane: Underlying structure to which most cells are anchored.
• Basal Cell Surface: The bottom surface where the cell is adhered, with the exception of blood cells.
• The cell contains the plasma membrane, nucleus, and intracellular organelles such as the endoplasmic reticulum, mitochondria, golgi, and ribosomes.

Plasma Membrane

• Defines cell boundaries.
• Regulates the uptake of components from outside and the release/secretion of materials.
• Intercellular Space: Space between two plasma membranes of adjacent cells where transport occurs.

Constituents

• Phospholipid Bilayer: The basis of the plasma membrane.
  • Consists of phospholipids with a phosphate head and two fatty acid tails.
  • Phosphate heads project to the extracellular or intracellular regions, while fatty acid tails face one another.
• Channel Proteins: Large proteins.
• Cholesterol: Wedged in between phospholipids.
  • It is made of a four-carbon ring structure.
  • Interrupts the packing of phospholipid molecules, lending to membrane fluidity, and preserves membrane integrity.
• Carbohydrate Tails: Sugar chains extending off phospholipids (glycolipids) or proteins (glycoproteins) on the extracellular surface.

Phospholipids

• Similar to triglycerides, but with one fatty acid tail replaced by a phosphate group.
• Amphiphilic: Contains both hydrophobic (fatty acid tails) and hydrophilic (phosphate head) regions.
• In extracellular and intracellular fluids (water-based), hydrophilic parts interface with the fluid, while hydrophobic parts are protected and face one another.
• The amphiphilic nature drives the confirmation of the bilayer, forcing constituents to line up in the same orientation.
• The hydrophilic part is the most likely part to interface with the aqueous fluid (both intracellular and extracellular).

Membrane Composition

• 98% of membrane molecules are lipids.
  • 75% are phospholipids.
  • 20% is cholesterol, contributing to membrane fluidity by interrupting phospholipid packing.
  • 5% are glycolipids, with carbohydrate chains (sugar chains) extending off the extracellular side, forming the glycocalyx.

Glycocalyx

• A sugar coating on the outside of the cell, composed of carbohydrate chains of glycoproteins and glycolipids.

Functions

• Protection: Provides a physical barrier.
• Immunity to Infection: Allows immune system cells to recognize self vs. foreign cells.
• Transplantation Compatibility: Basis of analysis for compatibility between donor and recipient, including blood transfusions and tissue grafts.
• Cell Adhesion: Makes cells sticky.
• Embryonic Development: Guides embryonic development to mature tissue types.
• Unique: Except for identical twins.

Surface Extensions

• Microvilli: Enhance absorption through actin filaments, which shorten for a milking action.
• Cilia:
  • Nonmotile forms have a largely unknown purpose.
  • Motile forms provide sensory input (taste, odors, hearing).
  • Line the nasal cavity, beat in waves (power stroke followed by recovery stroke) and move mucus to protect from inhaled particles/debris.
• Flagella: Longest surface extension; the only functional flagella in humans are sperm.

Endoplasmic Reticulum (ER)

• A network within the cytoplasm.
• The human genome contains meters of DNA isolated in the cell nucleus.
• Rough ER: Covered with ribosomes, site of synthesis of packaged proteins, phospholipids, and proteins of the plasma membrane.
• Smooth ER: Lacks ribosomes; synthesizes membranes, fats, and steroids (e.g., sex hormones estrogen and testosterone), detoxifies drugs and alcohol, and stores calcium in skeletal muscle.
• Drug tolerance is related to the amount of smoothie r in cells.

Ribosomes

• Assemble amino acids into proteins.
• Produced within the nucleolus.
• Found within the nucleolus, in the cytosol, covering the rough endoplasmic reticulum.
• They act as protein-making factories.

Golgi Complex

• Acts as a post office and is not continuous with anybody else's membrane.
• Finishes proteins (adds carbohydrates), packages, and distributes them.
• Products are moved to outer edges and break off into Golgi vesicles.
• Some vesicles remain in the cell (become lysosomes), others are incorporated into the plasma membrane, and others are secreted (exocytosis).

Lysosomes

• Contain digestive enzymes (break down substrates).
• Important in autophagy (digesting old organelles) and apoptosis (healthy cell death).

Peroxisomes

• Produce hydrogen peroxide (H2O2) to neutralize free radicals, detoxifying the cell.

Mitochondria

• Powerhouse of the cell.
• Has a double membrane (outer and inner).
• Electron Transport Chain location.
• Cristae: Internal folds with ATP-producing hardware.
• Matrix: Space between membranes, containing ribosomes and mitochondrial DNA (maternal inheritance).

Centrioles

• Not membrane-bound.
• Consist of microtubules (hollow cylinders).
• Important for cell division (separating DNA copies) and are found at the base of sperm flagella.

Cytoskeleton

• Provides support, maintains cell shape, and enables organization and movement.
• Allows cells to respond to stimuli mechanically.
• Internal parts are like ziplining where an organelle or protein is moved from one end of the cell to the other.

Transport Mechanisms

• The plasma membrane is selectively permeable: Regulates what is transported in and out.

Passive Transport

• No ATP is required; substances move down their concentration gradient (from high to low concentration).
• Examples: Filtration, Simple and facilitated diffusion, Osmosis (water-specific diffusion).

Active Transport

• Requires energy (ATP) to move substances against their concentration gradient (from low to high concentration).

• Examples: Active and vesicular transport.

• Some transport mechanisms require chaperones (helper proteins), while others do not.

Passive Transport: Filtration

• Particles are moved through a selectively permeable membrane.
• The driving force is hydrostatic pressure (pressure of body fluids against the plasma membrane).
• Example: Making coffee (water flow and gravity pull water through the filter).
• In the body, occurs at the kidney (blood pressure creates renal filtrate) and capillaries (controls fluid movement in/out of blood).

Passive Transport: Simple Diffusion

• Does not require energy (non ATP consuming).
• Involves moving a substrate from an area of higher concentration to an area of lower concentration.
• Equilibrates distribution of molecules equally through the space.
• Driven by the constant and random motion of substances.
• Also involves the uptake of water and distribution of smaller ions.

Rate Factors

1. Temperature: Increased temp will increase diffusion rate.
2. Molecular Weight: Increased molecular weight will decrease diffusion rate.
3. Steepness of concentration gradient: Increased steepness will increase diffusion rate.
4. Surface area:
5. Membrane permeability.

Passive Transport: Osmosis

• Water-specific diffusion, facilitated by aquaporins (specialized protein channels).
• Can also occur through simple diffusion.
• Water molecules are drawn smaller and are able to move across the membrane.
• Where there is substrate, there is less free water.
• The volume of fluid on the side with no solutes will diminish while the volume will increase where there is more solutes.

Tonicity

• The concentration of these solutions controls osmosis.
  • Isotonic: The concentration is the same inside and out of the cell.
    • No change occurs as the cell maintains its shape.
  • Hypotonic: There is less concentration outside of the cells compared to in it.
    • Cell uptake of water causes the cell to enlarge (lysis) and risk bursting.
  • Hypertonic: There is a higher concentrated solution that the cell is placed in.
    • It will have more free water in it compared to the solution, therefore water diffuses out of the cell and the cell shrivels causing (crenation).

Carrier-Mediated Transport

• Requires a helper or chaperone protein- a car ferry.
• Either facilitated diffusion or active transport.
• It is a highly specific mechanism.
  • Some carriers are uniporters, which carry one solute at a time. Others are called symporters, which can carry two or more at the same time in the same direction. Antiporters carry two or more solutes but in opposite directions.

Facilitated Diffusion

• Involves large protein carrying channels.
• Transports solute down their concentration gradient.
• It is a passive mechanism due to movement down the concentration gradient even with the channel or chaperone.
• The solute combines to the carrier with a lock and key mechanism. If there is a right fit, then we will see a confirmation.

Active Transport

• Moves a substrate against its gradient, from the side of the plasma membrane where it is found already at higher concentrations.
• These are ATP consuming.
• Examples are sodium potassium ATPase or the sodium potassium pump.
• Movement of amino acids into the cells.