Cell Biology Lecture 1 Flashcards
Cell Membrane (Plasma Membrane)
Functions
Functions:
* Provides a continuous barrier.
* Separates the cell from the external environment.
* Creates selectively permeable membrane.
* Provides a unique internal environment.
Cell Membrane Structure
Composition
Composition:
* Majority: Phospholipids (75%).
* Amphipathic nature.
* Polar phosphate head, non-polar fatty acid tails.
* Forms a phospholipid bilayer in aqueous solution.
Selective Permeability
Definition, Permeable to, Impermeable to
Definition:
* Allows specific substances to pass.
Permeable to:
* Non-polar, hydrophobic, uncharged substances.
Impermeable to:
* Polar, hydrophilic, and charged substances.
* Requires carriers or channels.
Lipids in Cell Membrane
Other Lipids:
* Phospholipids (75%), Cholesterol (20%), Glycolipids (5%).
* Cholesterol functions in structural integrity and fluidity.
* Glycolipids contribute to cell recognition and signaling.
Membrane Proteins
Types, Functions
Types:
* Integral (firmly embedded).
* Peripheral (distributed on the surface).
Functions:
* Transporters, Ion channels, Receptors, Enzymes, Linkers, Markers.
Membrane Proteins Functions
6 total
- Transporters: Move polar substances through impermeable membrane.
- Ion Channels: Selectively transport ions.
- Receptors: “Lock and key” recognition for specific ligands.
- Enzymes: Dissolve/breakdown extracellular material.
- Linkers: Attach and link other proteins, providing structural stability.
- Markers: Cell identity markers, aiding recognition by other body cells.
Fluid Mosaic Model
Definition, Variability
Definition:
* Describes the cell membrane’s high fluidity.
* Recognizes constant movement.
Variability:
* Shape and function vary based on cell specialty.
Types of Transport
Two types
Passive Transport:
* Requires no energy (ATP).
* Uses electrical or concentration gradients.
Active Transport:
* Requires energy (ATP).
Passive Transport Overview
Characteristics, Gradients Defined
Characteristics:
* Does not require ATP.
* Utilizes electrical or concentration gradients.
Gradients Defined:
* Electrical: Difference in charges between regions.
* Concentration: Difference in substance concentration between regions.
Passive Transport Mechanisms
Selective Permeability, Membrane Potential
Selective Permeability:
* Creates a chemical difference between cell interior and exterior.
* Results in a membrane gradient.
Membrane Potential:
* Resting membrane potential present in all cells.
* Crucial for biological processes like nerve impulses.
Types of Passive Transport
2 Types
1. Diffusion:
* Movement of solutes from higher to lower concentration.
2. Osmosis:
* Movement of water from higher to lower concentration.
Diffusion
Definition, Factors Affecting Rate
Definition:
* Movement of solutes from higher to lower concentration.
Factors Affecting Rate:
* Temperature, steepness of gradient, mass/size, distance (thickness of membrane), surface area.
Types of Diffusion
Two types
1. Simple Diffusion:
* Substances move through the membrane.
* No energy required.
2. Facilitated Diffusion:
* Substances move with the help of transmembrane proteins.
* Still a passive process.
Facilitated Diffusion Channels
2 Types
Channel-Mediated:
* Involves gated channels.
* Responds to ligands, voltage, or pressure.
Carrier-Mediated:
* Carrier proteins undergo conformational changes.
* Examples: Glucose, fructose, vitamins.
Osmosis
Definition, Direction
Definition:
* Movement of water through a selectively permeable membrane.
Direction:
* From an area of high to low water concentration.
Osmosis Pressure
Definition, Oncotic Pressure
Definition:
* Pressure exerted on the solute side of the membrane.
* Directly proportional to solute concentration.
Oncotic Pressure:
* Exerted by blood plasma proteins (e.g., albumin).
* Aids in pulling water back into circulation.
Hydrostatic Pressure
Definition
Definition:
* Pressure exerted by the solvent on its surroundings.
* Equilibrium reached when osmosis equals hydrostatic pressure.
Tonicity
Definition
Definition:
* Refers to solute concentration in a solution.
* Measures a solution’s ability to alter cell volume through osmosis.
Types of Solutions
3 types
1. Isotonic:
* Same concentration inside and outside the cell.
* No net water flow; cell shape unchanged.
2. Hypertonic:
* Higher solute concentration outside; water leaves, causing cell shrinkage (crenation).
3. Hypotonic:
* Lower solute concentration outside; water enters, causing cell growth or bulging.
* Excessive water entry may lead to cell explosion and death (lysis).
Comparison of Tonic Solutions
3 types
Isotonic Solution:
* Same strength inside and outside the cell.
Hypertonic Solution:
* Greater strength outside, causing cell shrinkage (crenation).
Hypotonic Solution:
* Lower strength outside, causing cell growth or bulging.
* Excessive entry may lead to cell explosion (lysis).
Active Transport Overview
Characteristics - 3 points
Characteristics:
* Substances transported against their gradients.
* Requires energy (usually ATP).
* Similar to rowing a boat upstream.
Sodium-Potassium Pump
Function - 4 points
Function:
* Important active transporter found in almost every cell (except red blood cells).
* Helps maintain resting membrane potential.
* Pumps out 3 Na+ and brings in 2 K+.
* Requires ATP for energy.
Sodium-Potassium Pump Mechanism
Setting up Gradients - 3 points
Setting up Gradients:
* Creates concentration and electrical gradients.
* Higher [Na+] outside, higher [K+] inside.
* Establishes resting membrane potential.
Resting Membrane Potential
Definition, Contributers
Definition:
* Difference in charge between cell exterior and interior.
* Present in all cells; crucial in neurons and muscle cells.
Contributors:
* Sodium-Potassium Pump, higher K+ permeability, negatively charged organic molecules.
Types of Active Transport
2 types
1. Primary Active Transport:
* Uses ATP to move solutes against concentration gradient.
2. Secondary Active Transport:
* Uses energy from concentration gradients of other solutes.
Primary Active Transport
Example
Example:
* Sodium-Potassium Pump.
* ATP used to move substances against concentration gradient.
Secondary Active Transport
Energy Utilization
Energy Utilization:
* Utilizes energy from primary transport (e.g., Na+ concentration gradient).
* Sodium ions store potential energy, which is used to transport other substances.
Types of Secondary Active Transporters
Two types
1. Symporters:
* Move 2 substances in the same direction simultaneously.
2. Antiporters:
* Move 2 substances in opposite directions simultaneously.
Vesicular Transport Overview
Definition, Classification
Definition:
* Involves small, spherical sacs (vesicles) for controlled release and absorption.
* Active process requiring ATP.
Classification:
* Exocytosis (out of cell).
* Endocytosis (into cell).
Exocytosis
Purpose, Examples
Purpose:
* Release of substances useful or waste products.
Examples:
* Secretion (e.g., hormones like insulin).
* Excretion (e.g., release of urea in the kidneys).
Endocytosis
Definition, Types
Definition:
* Process of taking substances into the cell.
Types:
1. Phagocytosis (engulfing large particles).
2. Pinocytosis (bulk-phase endocytosis).
3. Receptor-Mediated Endocytosis (highly selective).
Phagocytosis
Definition, Examples
Definition:
* “To eat.”
* Cells engulf large solid particles (e.g., bacteria, viruses).
Examples:
* Immune cells (e.g., white blood cells).
Pinocytosis
Definition, Functions
Definition:
* Bulk-phase endocytosis.
* Intake of fluid and solutes from surroundings.
Functions:
* Controls cell volume, transports micromolecules, provides essential nutrients.
Receptor-Mediated Endocytosis
Definition
Definition:
* Highly selective endocytosis.
* Cells ingest specific ligands (ions or molecules).
Transcytosis
Definition
Definition:
* Combination of endocytosis and exocytosis.
* Example: Antibodies crossing the placenta.
