ch.8

Question 1

Biological Membrane Structure and Function

Answer 1

Structure: Composed of phospholipid bilayer, proteins, and cholesterol.
Functions:
Acts as a barrier, regulating entry and exit of substances.
Facilitates communication between cells.
Provides structural support and shape to cells.
Plays a role in metabolic reactions and signal transduction.

Question 2

Fluid Mosaic Model of Plasma Membrane

Answer 2

Description: The membrane is fluid with proteins embedded in or attached to a flexible lipid bilayer.

Question 3

Key Experiment fluid mosaic model

Answer 3

Mouse and human cells were fused, and over time, proteins intermixed. This showed lateral movement of proteins and supported the model of fluidity in membranes.

Question 4

Membrane Fluidity and Permeability

Answer 4

Fluidity: Refers to the ability of membrane lipids and proteins to move laterally within the bilayer.
Relation to Permeability: Higher fluidity generally increases permeability, allowing more substances to pass through

Question 5

Factors Affecting Membrane Fluidity

Answer 5

temperature, saturation of fatty acids, fatty acid length, cholesterol

Question 6

Temperature on membrane fluidity

Answer 6

Increase: Increases fluidity as lipid molecules move faster.
Decrease: Reduces fluidity as molecules pack more tightly.

Question 7

Saturation of Fatty Acids and membrane fluidity

Answer 7

Saturated Fats: Decrease fluidity as they pack closely together.
Unsaturated Fats: Increase fluidity due to kinks in their structure, preventing tight packing.

Question 8

Fatty Acid Length and membrane fluidity

Answer 8

Long Chains: Decrease fluidity due to more interactions.
Short Chains: Increase fluidity as there are fewer interactions between chains

Question 9

Cholesterol and membrane fluidity

Answer 9

Fluidity Buffer: Stabilizes fluidity by preventing membrane from becoming too fluid at high temperatures and too rigid at low temperatures.

Question 10

Adaptations in Membrane Composition

Answer 10

Homeoviscous Adaptation: Ability of some organisms to adjust membrane lipid composition in response to environmental changes, maintaining optimal fluidity.

Question 11

Classes of Membrane Proteins

Answer 11

Integral Proteins: Span the membrane; e.g., transport proteins.
Peripheral Proteins: Attach to surface of membrane; e.g., enzymes.

Question 12

Transmembrane Proteins

Answer 12

Structure: Amphipathic with hydrophobic regions within the bilayer and hydrophilic regions exposed to water on both sides.
Function: Facilitate specific transport, cell signaling, and structural support.

Question 13

Asymmetry in Membrane Faces

Answer 13

Distribution: Cytoplasmic (inner) and extracellular (outer) leaflets have distinct lipid and protein compositions, which are essential for specific cellular functions.

Question 14

Selective Permeability of Membranes

Answer 14

Definition: Allows selective passage of certain substances.
Importance: Maintains cell homeostasis.
Roles of Components:
Lipids: Provide a hydrophobic barrier.
Proteins: Act as channels, carriers, and receptors to facilitate movement.

Question 15

Six Functional Classes of Membrane Proteins

Answer 15

Transport: Channels and carriers for substances.
Enzymatic Activity: Catalyze reactions.
Signal Transduction: Receptors for signals.
Cell Recognition: Glycoproteins identify cells.
Intercellular Joining: Junctions between cells.
Attachment: Anchors for cytoskeleton or ECM.

Question 16

Cell Junctions in Eukaryotes

Answer 16

Types:
Tight Junctions: Prevent leakage between cells.
Desmosomes: Provide mechanical stability.
Gap Junctions: Allow direct communication.

Question 17

Plant vs. Animal Cells

Answer 17

Plant Cells: Plasmodesmata link cells.
Animal Cells: Use gap junctions for communication.

Question 18

Membrane Synthesis

Answer 18

Process: Built in the ER and Golgi apparatus.
Glycoproteins and Glycolipids: Carbohydrates are added to the extracellular face in the Golgi, and appear on the outer side when vesicles fuse with the membrane.

Question 19

Diffusion and Concentration Gradient

Answer 19

Definition: Passive movement of molecules from high to low concentration.
Driving Force: Concentration gradient; occurs spontaneously until equilibrium.

Question 20

Net Diffusion and Dynamic Equilibrium

Answer 20

Net Diffusion: Movement of molecules with a net direction until equilibrium.
Dynamic Equilibrium: Molecule movement continues with no net change in concentration.

Question 21

Factors Influencing Diffusion Rate

Answer 21

Molecule Size: Smaller molecules diffuse faster.
Temperature: Higher temperature increases rate.
Concentration Gradient: Larger gradients increase rate.

Question 22

Simple vs. Facilitated Diffusion

Answer 22

Simple Diffusion: Passive movement of small, nonpolar molecules.
Facilitated Diffusion: Uses channels/carriers for larger or polar molecules.

Question 23

Transporters in Membranes

Answer 23

Function: Proteins that assist in moving substances across membranes.
Mechanisms:
Channels: Provide a pathway for ions.
Carriers: Bind substances and undergo shape changes.

Question 24

Gated Channels

Answer 24

Description: Open in response to stimuli.
Types:
Voltage-Gated: Respond to electrical signals.
Ligand-Gated: Open with specific molecule binding.
Function: Control ion flow and cell signaling.

Question 25

Osmosis and Osmotic Gradient

Answer 25

Definition: Water diffusion across a membrane. Driving Force: Osmotic gradient, moving water to balance solute concentrations.

Question 26

Osmotic Pressure:

Answer 26

Pressure needed to stop water flow.

Question 27

Osmolarity:

Answer 27

Total solute concentration.

Question 28

Tonicity:

Answer 28

Effect of a solution on cell volume (isotonic, hypotonic, hypertonic).

Question 29

Predicting Water Movement

Answer 29

Animal Cells: Swell in hypotonic, shrink in hypertonic Plant Cells: Turgor pressure supports structure; plasmolysis in hypertonic.

Question 30

Active Transport

Answer 30

Process: Moves substances against gradient using energy. Difference from Facilitated Diffusion: Active transport requires ATP; facilitated diffusion does not.

Question 31

Pump Mechanisms

Answer 31

Example: Na+/K+ pump moves ions against gradient, maintaining cellular ion balance. Electrogenic Pumps: Create voltage difference; Na+/K+ in animals, proton pumps in plants.

Question 32

Electrochemical Gradients and Membrane Potential

Answer 32

Gradient: Combination of electrical and chemical potential across a membrane. Membrane Potential: Voltage difference maintained by ion distribution.

Question 33

Secondary Active Transport

Answer 33

Process: Uses energy from gradients created by primary pumps. Example: H+/sucrose symporter in plants; Na+/glucose in animals.

Question 34

Types of Bulk Transport

Answer 34

exocytosis, endocytosis

Question 35

Exocytosis:

Answer 35

Exocytosis is the process by which cells move large molecules or particles, like proteins or waste, from the inside of the cell to the outside.

Question 36

Endocytosis

Answer 36

Endocytosis is the process by which cells take in large particles, such as nutrients or debris, by engulfing them in a section of the plasma membrane that pinches off into the cell.

Question 37

Isotonic Solution

Answer 37

Definition: The concentration of solutes outside the cell is equal to the concentration inside the cell. Animal Cells: No net movement of water; cell volume remains stable. Plant Cells: Cells maintain shape but are not as firm as in a hypotonic environment since turgor pressure is minimal. Example: Physiological saline (0.9% NaCl) is isotonic to human cells, so cells retain their normal shape and function.

Question 38

Hypotonic Solution

Answer 38

Definition: The concentration of solutes is lower outside the cell than inside. Animal Cells: Water enters the cell, causing it to swell. Cells may burst (lyse) if too much water enters. Plant Cells: Water enters, increasing turgor pressure, which supports the cell wall and gives structure to the plant. Cells become turgid (firm). Example: Distilled water is hypotonic to cells; it causes animal cells to swell and plant cells to become firm.

Question 39

Hypertonic Solution

Answer 39

Definition: The concentration of solutes is higher outside the cell than inside. Animal Cells: Water leaves the cell, causing it to shrink (crenate). Plant Cells: Water leaves the cell, and the cell membrane pulls away from the cell wall (plasmolysis), leading to wilting. Example: A solution with high salt concentration (like seawater) is hypertonic to human cells, causing them to shrink as water exits.

Question 40

Mechanism for exocytosis

Answer 40

Vesicle Formation: Molecules that need to be exported are packaged into membrane-bound vesicles, usually in the Golgi apparatus. Vesicle Transport: The vesicle moves toward the plasma membrane, typically along cytoskeletal structures (microtubules). Vesicle Fusion: The vesicle membrane fuses with the plasma membrane. This fusion requires energy (usually from ATP) and specific proteins called SNAREs to facilitate the merging of the two membranes. Release of Contents: Once the vesicle membrane has fused, its contents are released into the extracellular environment. Membrane Recycling: The vesicle membrane becomes part of the plasma membrane, helping to maintain membrane surface area.

Question 41

Functions of exocytosis

Answer 41

Secretion of Proteins and Hormones: Many cells use exocytosis to release proteins (e.g., antibodies by immune cells) and hormones (e.g., insulin from pancreatic cells). Waste Removal: Cells expel waste products that cannot be broken down internally. Membrane Expansion: Adds phospholipids and proteins to the plasma membrane, aiding in cell growth and repair.

Question 42

Types of exocytosis

Answer 42

Constitutive Exocytosis: A continuous process where vesicles fuse with the membrane without regulation, typically for membrane repair and general secretion. Regulated Exocytosis: Triggered by specific signals, such as a neural impulse or hormone binding, as seen in neurotransmitter release at synapses.

Question 43

Mechanism of endocytosis

Answer 43

Membrane Invagination: The cell membrane folds inward to form a pocket around the targeted material. Vesicle Formation: The pocket deepens and eventually pinches off, forming a vesicle within the cell, enclosing the material from the extracellular environment. Internalization and Transport: The vesicle can then be transported to different cellular compartments for processing, degradation, or use.

Question 44

Types of Endocytosis

Answer 44

1. phagocytosis 2. pinocytosis 3. receptor-mediated endocytosis

Question 45

Phagocytosis ("Cell Eating"):

Answer 45

Description: Large particles like bacteria, dead cells, or food particles are engulfed by the cell. Mechanism: The plasma membrane extends around the particle, forming a phagosome that enters the cell. The phagosome then typically fuses with a lysosome, where digestive enzymes break down the particle. Example: White blood cells (macrophages) use phagocytosis to engulf pathogens and debris as part of the immune response.

Question 46

Pinocytosis ("Cell Drinking"):

Answer 46

Description: The cell takes in extracellular fluid and dissolved solutes in small vesicles. Mechanism: The cell membrane forms small, fluid-filled vesicles that contain molecules from outside the cell. Example: Common in cells of the digestive system and kidney tubules, where fluids and solutes need to be absorbed continuously.

Question 47

Receptor-Mediated Endocytosis:

Answer 47

Description: Allows the cell to take in specific molecules with the help of cell surface receptors that recognize and bind to particular ligands (molecules like hormones, vitamins, or lipoproteins). Mechanism: Binding: Target molecules in the extracellular fluid bind to specific receptors on the cell surface. Vesicle Formation: Once bound, the receptor-ligand complexes cluster together, and a vesicle forms around them. Internalization: The vesicle enters the cell and is processed in endosomes, where ligands may be released and transported to other parts of the cell or delivered to lysosomes for degradation. Example: Uptake of cholesterol by cells using low-density lipoprotein (LDL) receptors.