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Membranes Flashcards

1
Q

What is the plasma membrane?

A

A barrier that encloses a cell, controlling substance movement.

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2
Q

What is the plasma membrane made of?

A

A phospholipid bilayer with proteins and other molecules.

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3
Q

What does ‘selectively permeable’ mean?

A

The membrane controls which substances pass through.

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4
Q

What are amphipathic molecules?

A

Molecules with both hydrophilic and hydrophobic parts.

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5
Q

Why must phospholipids form a bilayer in water?

A

Hydrophilic heads face water, hydrophobic tails avoid it.

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6
Q

Why is the bilayer effective as a barrier?

A

The hydrophobic core blocks most hydrophilic molecules.

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7
Q

How do hydrophobic and hydrophilic properties maintain membrane structure?

A

Hydrophilic heads face water; hydrophobic tails repel water.

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8
Q

What is simple diffusion?

A

Passive movement from high to low concentration.

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9
Q

How does simple diffusion differ from facilitated diffusion?

A

Simple diffusion does not require membrane proteins.

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10
Q

What molecules use simple diffusion?

A

Small, nonpolar molecules like oxygen and CO₂.

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11
Q

What factors affect simple diffusion rate?

A

Surface area, membrane thickness, and permeability.

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12
Q

What is facilitated diffusion?

A

Passive transport using membrane proteins.

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13
Q

Why is facilitated diffusion needed for some molecules?

A

Polar and large molecules can’t cross the bilayer easily.

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14
Q

What is osmosis?

A

The passive movement of water across a membrane.

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15
Q

What membrane proteins assist with osmosis?

A

Aquaporins, which help water move faster.

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16
Q

Why does water use facilitated diffusion if it can pass freely?

A

Aquaporins speed up water transport.

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17
Q

What are the six main functions of membrane proteins?

A

Transport, receptors, anchoring, adhesion, identification, enzymes.

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18
Q

How do integral membrane proteins interact with the bilayer?

A

Their hydrophobic regions embed in the membrane core.

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19
Q

What are examples of integral membrane proteins?

A

Ion channels, GPCRs, and transporters.

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20
Q

How do peripheral proteins differ from integral proteins?

A

They attach loosely and can be easily removed.

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21
Q

What happens to cells in an isotonic solution?

A

No net water movement, cells remain the same.

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22
Q

What happens to cells in a hypertonic solution?

A

Water leaves the cell, causing shrinkage.

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23
Q

What happens to cells in a hypotonic solution?

A

Water enters, potentially causing cell lysis.

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24
Q

Why does high solute concentration mean low water concentration?

A

Solute binds water, reducing free water molecules.

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25
Why is the bilayer self-sealing?
Hydrophobic tails avoid water, reforming gaps.
26
How do channel proteins ensure selectivity?
They allow passage based on size, shape, charge, and chemical properties.
27
What determines a channel protein's specificity?
Its interior structure, which interacts with specific molecules while excluding others.
28
What do aquaporins transport?
Water molecules.
29
What do ion channels transport?
Ions like Na⁺, K⁺, Ca²⁺, and Cl⁻.
30
What do gap junction proteins (connexins) do?
Facilitate the passage of small molecules and ions between adjacent cells.
31
What factors regulate channel proteins?
Voltage (voltage-gated), ligand binding (ligand-gated), and mechanical stress.
32
How do these factors influence channel proteins?
They control the opening and closing of the channels.
33
How does active transport differ from passive transport?
Active transport moves molecules against their gradient and requires ATP.
34
What are examples of passive transport?
Diffusion and facilitated diffusion.
35
What does the sodium-potassium pump (Na⁺/K⁺ pump) do?
Pumps Na⁺ out and K⁺ into the cell.
36
What does the proton pump (H⁺-ATPase) do?
Moves H⁺ across membranes, aiding stomach acid secretion and ATP synthesis.
37
Why is the Na⁺/K⁺ pump important for neurons and muscles?
It maintains the resting membrane potential, essential for nerve signaling and muscle contraction.
38
What are the functions of glycolipids?
Cell recognition, adhesion, membrane stability, signaling, lubrication, immune response.
39
What are the functions of glycoproteins?
Cell recognition, receptors, adhesion, protection, protein modulation, blood group determination.
40
What are key features of the fluid mosaic model?
• Lipid bilayer • Fluidity • Protein diversity • Selective permeability • Recognition and signaling
41
How does the model describe membrane structure?
As a fluid bilayer with embedded proteins that move dynamically.
42
Why is membrane fluidity important?
It affects protein mobility, permeability, and adaptation to temperature changes.
43
How does fatty acid saturation affect fluidity?
• Unsaturated = More fluid (prevents tight packing). • Saturated = Less fluid (tightly packed).
44
How do cells adapt membrane composition in extreme environments?
• Cold: More unsaturated fats to increase fluidity. • Hot: More saturated fats to reduce fluidity.
45
What type of lipid is cholesterol?
A steroid.
46
Where is cholesterol found in the membrane?
Within the hydrophobic core.
47
How does cholesterol affect membrane fluidity?
• Decreases fluidity at high temperatures. • Increases fluidity at low temperatures.
48
How does cholesterol impact membrane properties?
It regulates permeability, solubility, melting temperature, fluidity, and thickness.
49
How does the fluidity of the lipid bilayer impact its function?
It influences membrane protein mobility, permeability, and the ability to adapt to temperature and environmental changes.
50
How does the degree of saturation of fatty acids affect membrane fluidity?
Unsaturated fatty acids increase fluidity by preventing tight packing, while saturated fatty acids decrease fluidity by allowing tighter packing.
51
Why is membrane fluidity important for temperature adaptation?
It prevents rigidity in cold temperatures and excessive permeability in high temperatures.
52
How do organisms in extreme environments adjust their membrane composition?
They incorporate unsaturated fatty acids in cold environments and saturated fatty acids in hot environments to maintain optimal fluidity.
53
What lipid group does cholesterol belong to?
Cholesterol is a steroid.
54
Where is cholesterol found in the plasma membrane?
It is interspersed within the lipid bilayer, specifically in the hydrophobic core.
55
What properties position cholesterol in the lipid bilayer?
Its amphipathic nature (hydrophilic hydroxyl group + hydrophobic steroid ring) allows interaction with phospholipids.
56
How does cholesterol affect membrane fluidity?
It decreases fluidity at high temperatures and increases fluidity at low temperatures.
57
How does cholesterol impact membrane permeability?
It reduces membrane permeability by restricting phospholipid movement.
58
What chemical properties of membranes does cholesterol affect?
Permeability, solubility, melting temperature, fluidity, and thickness.
59
What is the difference between pinocytosis and phagocytosis?
Pinocytosis ('cell drinking') involves small molecules and fluids, while phagocytosis engulfs large particles like bacteria.
60
How does membrane fluidity allow exocytosis and endocytosis?
It enables membrane flexibility, allowing vesicle fusion and shape changes for material transport.
61
What are gated ion channels?
Membrane proteins that regulate ion flow in response to signals, crucial for neuronal signaling.
62
Why is ion selectivity important in gated ion channels?
It ensures only specific ions pass through, maintaining precise neuronal signaling.
63
Give an example of a neurotransmitter-gated ion channel.
Nicotinic acetylcholine receptors (nAChRs), which open to sodium (Na+) influx upon acetylcholine binding.
64
What is the sodium-potassium pump?
A membrane protein that actively transports Na+ out and K+ in to maintain ion gradients.
65
How do voltage-gated sodium channels contribute to action potentials?
They open upon depolarization, allowing Na+ influx and triggering the action potential.
66
What is the role of voltage-gated potassium channels in action potentials?
They allow K+ efflux, repolarizing and sometimes hyperpolarizing the membrane.
67
Why is the sodium-potassium pump important for resting membrane potential?
It maintains ion gradients needed for electrical signaling.
68
What are sodium-dependent glucose cotransporters (SGLTs)?
Membrane proteins that use Na+ gradients to transport glucose in the small intestine and kidney.
69
How do SGLTs use indirect active transport?
They use the Na+ gradient (from the Na+/K+ pump) to move glucose against its concentration gradient.
70
Why are SGLTs important in glucose absorption?
They enable glucose uptake into enterocytes, ensuring energy availability.
71
Why are SGLTs important in glucose reabsorption in the nephron?
They prevent glucose loss in urine, maintaining blood glucose levels.
72
What is cell adhesion, and why is it essential?
It allows cells to bind, forming tissues and maintaining integrity, crucial for development and healing.
73
What are cell-adhesion molecules (CAMs)?
Proteins on the cell surface that mediate cell-cell and cell-matrix adhesion.

Biology (12 decks)

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