Cell Biology Lecture 1

Question 1

Cell Membrane (Plasma Membrane)

Functions

Answer 1

Functions:
* Provides a continuous barrier.
* Separates the cell from the external environment.
* Creates selectively permeable membrane.
* Provides a unique internal environment.

Question 2

Cell Membrane Structure

Composition

Answer 2

Composition:
* Majority: Phospholipids (75%).
* Amphipathic nature.
* Polar phosphate head, non-polar fatty acid tails.
* Forms a phospholipid bilayer in aqueous solution.

Question 3

Selective Permeability

Definition, Permeable to, Impermeable to

Answer 3

Definition:
* Allows specific substances to pass.
Permeable to:
* Non-polar, hydrophobic, uncharged substances.
Impermeable to:
* Polar, hydrophilic, and charged substances.
* Requires carriers or channels.

Question 4

Lipids in Cell Membrane

Answer 4

Other Lipids:
* Phospholipids (75%), Cholesterol (20%), Glycolipids (5%).
* Cholesterol functions in structural integrity and fluidity.
* Glycolipids contribute to cell recognition and signaling.

Question 5

Membrane Proteins

Types, Functions

Answer 5

Types:
* Integral (firmly embedded).
* Peripheral (distributed on the surface).
Functions:
* Transporters, Ion channels, Receptors, Enzymes, Linkers, Markers.

Question 6

Membrane Proteins Functions

6 total

Answer 6

1. Transporters: Move polar substances through impermeable membrane.
2. Ion Channels: Selectively transport ions.
3. Receptors: “Lock and key” recognition for specific ligands.
4. Enzymes: Dissolve/breakdown extracellular material.
5. Linkers: Attach and link other proteins, providing structural stability.
6. Markers: Cell identity markers, aiding recognition by other body cells.

Question 7

Fluid Mosaic Model

Definition, Variability

Answer 7

Definition:
* Describes the cell membrane’s high fluidity.
* Recognizes constant movement.
Variability:
* Shape and function vary based on cell specialty.

Question 8

Types of Transport

Two types

Answer 8

Passive Transport:
* Requires no energy (ATP).
* Uses electrical or concentration gradients.
Active Transport:
* Requires energy (ATP).

Question 9

Passive Transport Overview

Characteristics, Gradients Defined

Answer 9

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.

Question 10

Passive Transport Mechanisms

Selective Permeability, Membrane Potential

Answer 10

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.

Question 11

Types of Passive Transport

2 Types

Answer 11

1. Diffusion:
* Movement of solutes from higher to lower concentration.
2. Osmosis:
* Movement of water from higher to lower concentration.

Question 12

Diffusion

Definition, Factors Affecting Rate

Answer 12

Definition:
* Movement of solutes from higher to lower concentration.
Factors Affecting Rate:
* Temperature, steepness of gradient, mass/size, distance (thickness of membrane), surface area.

Question 13

Types of Diffusion

Two types

Answer 13

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.

Question 14

Facilitated Diffusion Channels

2 Types

Answer 14

Channel-Mediated:
* Involves gated channels.
* Responds to ligands, voltage, or pressure.
Carrier-Mediated:
* Carrier proteins undergo conformational changes.
* Examples: Glucose, fructose, vitamins.

Question 15

Osmosis

Definition, Direction

Answer 15

Definition:
* Movement of water through a selectively permeable membrane.
Direction:
* From an area of high to low water concentration.

Question 16

Osmosis Pressure

Definition, Oncotic Pressure

Answer 16

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.

Question 17

Hydrostatic Pressure

Definition

Answer 17

Definition:
* Pressure exerted by the solvent on its surroundings.
* Equilibrium reached when osmosis equals hydrostatic pressure.

Question 18

Tonicity

Definition

Answer 18

Definition:
* Refers to solute concentration in a solution.
* Measures a solution’s ability to alter cell volume through osmosis.

Question 19

Types of Solutions

3 types

Answer 19

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).

Question 20

Comparison of Tonic Solutions

3 types

Answer 20

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).

Question 21

Active Transport Overview

Characteristics - 3 points

Answer 21

Characteristics:
* Substances transported against their gradients.
* Requires energy (usually ATP).
* Similar to rowing a boat upstream.

Question 22

Sodium-Potassium Pump

Function - 4 points

Answer 22

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.

Question 23

Sodium-Potassium Pump Mechanism

Setting up Gradients - 3 points

Answer 23

Setting up Gradients:
* Creates concentration and electrical gradients.
* Higher [Na+] outside, higher [K+] inside.
* Establishes resting membrane potential.

Question 24

Resting Membrane Potential

Definition, Contributers

Answer 24

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.

Question 25

Types of Active Transport

2 types

Answer 25

1. Primary Active Transport:
* Uses ATP to move solutes against concentration gradient.
2. Secondary Active Transport:
* Uses energy from concentration gradients of other solutes.

Question 26

Primary Active Transport

Example

Answer 26

Example:
* Sodium-Potassium Pump.
* ATP used to move substances against concentration gradient.

Question 27

Secondary Active Transport

Energy Utilization

Answer 27

Energy Utilization:
* Utilizes energy from primary transport (e.g., Na+ concentration gradient).
* Sodium ions store potential energy, which is used to transport other substances.

Question 28

Types of Secondary Active Transporters

Two types

Answer 28

1. Symporters:
* Move 2 substances in the same direction simultaneously.
2. Antiporters:
* Move 2 substances in opposite directions simultaneously.

Question 29

Vesicular Transport Overview

Definition, Classification

Answer 29

Definition:
* Involves small, spherical sacs (vesicles) for controlled release and absorption.
* Active process requiring ATP.
Classification:
* Exocytosis (out of cell).
* Endocytosis (into cell).

Question 30

Exocytosis

Purpose, Examples

Answer 30

Purpose:
* Release of substances useful or waste products.
Examples:
* Secretion (e.g., hormones like insulin).
* Excretion (e.g., release of urea in the kidneys).

Question 31

Endocytosis

Definition, Types

Answer 31

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).

Question 32

Phagocytosis

Definition, Examples

Answer 32

Definition:
* “To eat.”
* Cells engulf large solid particles (e.g., bacteria, viruses).
Examples:
* Immune cells (e.g., white blood cells).

Question 33

Pinocytosis

Definition, Functions

Answer 33

Definition:
* Bulk-phase endocytosis.
* Intake of fluid and solutes from surroundings.
Functions:
* Controls cell volume, transports micromolecules, provides essential nutrients.

Question 34

Receptor-Mediated Endocytosis

Definition

Answer 34

Definition:
* Highly selective endocytosis.
* Cells ingest specific ligands (ions or molecules).

Question 35

Transcytosis

Definition

Answer 35

Definition:
* Combination of endocytosis and exocytosis.
* Example: Antibodies crossing the placenta.