Cell Bio Exam 2 (copy)

What is the main function of the plasma membrane?

Acts as a selective barrier controlling what enters and leaves the cell.

What is the plasma membrane made of?

A lipid bilayer composed mainly of phospholipids and proteins.

What makes phospholipids amphipathic?

They have a hydrophilic head and hydrophobic tails.

How do phospholipids arrange in water?

Hydrophobic tails face inward, hydrophilic heads face outward toward water.

What are the three major types of membrane lipids?

Phospholipids, cholesterol, and glycolipids.

What is the role of cholesterol in the membrane?

Reduces fluidity and permeability by filling gaps between fatty acid tails.

How does temperature affect membrane fluidity?

Higher temperature increases fluidity; lower temperature decreases fluidity.

How do unsaturated fatty acids affect fluidity?

Increase fluidity due to double bonds causing kinks.

How do saturated fatty acids affect fluidity?

Decrease fluidity because tails pack tightly.

What happens when fatty acid tails are shorter?

Membrane becomes more fluid.

Where are new phospholipids made in the cell?

In the smooth endoplasmic reticulum (ER).

What enzyme randomly flips phospholipids in the ER membrane?

Scramblase

What enzymes maintain specific lipid orientation in the Golgi and plasma membrane?

Flippase and floppase.

Which membrane face are glycolipids found on?

The non-cytosolic (extracellular) side.

What is the glycocalyx?

The carbohydrate-rich "sugar coat" on the cell surface used for protection and cell recognition.

What are integral membrane proteins?

Proteins that are embedded in the lipid bilayer.

What are peripheral membrane proteins?

Proteins attached to membrane surfaces through noncovalent interactions.

Why are transmembrane proteins amphipathic?

Hydrophobic regions span the bilayer; hydrophilic regions face water.

What structures allow transmembrane proteins to span membranes?

Alpha helices or beta barrels.

What type of protein spans the membrane once?

Single-pass transmembrane protein.

What type of protein spans the membrane multiple times?

Multi-pass transmembrane protein.

How do alpha-helices orient their R-groups in the membrane?

Hydrophobic R-groups face the lipid tails; hydrophilic face inside the channel.

What do beta-barrel membrane proteins form?

Hydrophilic pores that allow passage of polar molecules.

How are integral membrane proteins isolated in the lab?

Using detergents like SDS to dissolve the lipid bilayer.

What is the function of SDS detergent?

Disrupts membranes and unfolds proteins by binding hydrophobic regions.

What is the difference between a micelle and a liposome?

Micelle has one fatty acid tail; liposome has two forming a bilayer.

What experiment measures protein mobility in the membrane?

FRAP (Fluorescence Recovery After Photobleaching).

What does FRAP test show?

How quickly fluorescent membrane proteins move back into a bleached area—indicating fluidity.

What factors reduce membrane protein movement?

Anchoring to the cytoskeleton, extracellular matrix, or tight junctions.

What is the cytoskeleton network beneath the plasma membrane called?

The cell cortex.

What protein forms the cell cortex in red blood cells?

Spectrin.

What are tight junctions?

Barriers that restrict movement of membrane proteins to specific regions.

What is the cytosolic side of the membrane?

The inner layer of the membrane that faces the cell's cytoplasm.

What is the non-cytosolic side of the membrane?

The outer layer of the membrane that faces the extracellular space or organelle lumen.

What does membrane permeability mean?

Permeability is how easily molecules can pass through the membrane.

What determines if a molecule can diffuse through a lipid bilayer?

Size, charge, and polarity

Which types of molecules cross membranes easily?

Small nonpolar molecules like O₂ and CO₂.

Which molecules cross slowly?

Small uncharged polar molecules like water and urea.

Which molecules cannot cross without help?

Ions and large polar molecules.

What is simple diffusion?

Movement of small uncharged molecules directly through the bilayer from high to low concentration.

What are the two main types of membrane transport proteins?

Transporters and channels.

How do transporters and channels differ?

Transporters bind specific molecules and change shape; channels allow passive flow of ions based on size and charge.

What is passive transport?

Movement down a concentration gradient without energy use.

What is active transport?

Movement against a gradient that requires energy.

What does "down the concentration gradient" mean?

Moving from high concentration to low concentration.

What does "against the concentration gradient" mean?

Moving from low concentration to high concentration.

What drives passive transport of uncharged molecules?

Concentration gradient only.

What drives passive transport of charged molecules?

The electrochemical gradient (concentration + electrical forces).

What is an electrochemical gradient?

The combined effect of a molecule's concentration and the membrane's voltage difference.

What is osmosis?

Diffusion of water from low solute to high solute concentration.

What are aquaporins?

Channel proteins that allow water to move rapidly across membranes.

What happens to a cell in a hypertonic solution?

Water leaves the cell; it shrinks.

What happens to a cell in a hypotonic solution?

Water enters the cell; it swells.

What happens in an isotonic solution?

No net water movement.

What do plant cells become in a hypotonic environment?

Turgid (firm).

What do animal cells do in a hypotonic environment?

Swell and may burst.

What type of transport moves glucose down its gradient?

Facilitated diffusion using a glucose transporter.

What type of transport moves glucose into a cell against its gradient?

Active transport using a Na⁺/glucose coupled pump.

What are the three main types of active transport proteins?

Coupled carriers, ATP-driven pumps, and light-driven pumps.

What is a uniport?

Transports one molecule in one direction (passive).

What is a symport?

Moves two molecules in the same direction.

What is an antiport?

Moves two molecules in opposite directions.

What does the Na⁺/K⁺ pump do?

Pumps 3 Na⁺ out and 2 K⁺ in using ATP

Why is the Na⁺/K⁺ pump important?

Maintains ion gradients and the resting membrane potential.

Where is Na⁺ concentration highest?

Outside the cell.

Where is K⁺ concentration highest?

Inside the cell.

What is the main function of the Ca²⁺ pump?

Keeps Ca²⁺ levels low in the cytosol by pumping it out or into organelles.

What is a coupled pump?

Uses energy from one molecule moving down its gradient to drive another uphill.

What gradient do animal cells mostly use for coupled transport?

Na⁺ gradient

What gradient do plants, fungi, and bacteria use for coupled transport?

H⁺ gradient.

What are ion channels?

Pores that allow specific ions to move rapidly across membranes.

What determines ion channel selectivity?

Size and charge of the ion.

How do ion channels differ from transporters?

Channels are faster and don't require conformational changes.

What are leaky channels?

Channels that are usually open, allowing ions to move freely.

What do K⁺ leak channels do?

Help set the resting membrane potential by letting K⁺ move out.

What is membrane potential?

The voltage difference across the membrane due to uneven ion distribution.

What is the resting membrane potential of most cells?

Around -70 mV (inside is negative)

What two structures maintain the resting potential?

Na⁺/K⁺ pump and K⁺ leak channels

What is depolarization?

When the inside of the cell becomes less negative due to Na⁺ entering

What is repolarization?

When the membrane potential returns to negative as K⁺ leaves the cell.

What is hyperpolarization?

When the inside becomes more negative than the resting potential.

What is an action potential?

A rapid rise and fall in membrane potential that travels along a neuron.

What triggers voltage-gated Na⁺ channels to open?

A stimulus that depolarizes the membrane to the threshold potential.

What happens when voltage-gated Na⁺ channels open?

Na⁺ rushes into the cell, causing depolarization.

What happens after Na⁺ channels inactivate?

Voltage-gated K⁺ channels open and K⁺ leaves the cell.

What causes the membrane to return to resting potential?

K⁺ efflux and the Na⁺/K⁺ pump

Why does the action potential only move in one direction?

Na⁺ channels become temporarily inactivated after opening.

What is the role of voltage-gated Ca²⁺ channels in neurons?

Allow Ca²⁺ to enter the presynaptic terminal, triggering neurotransmitter release.

What happens when Ca²⁺ enters the axon terminal?

Causes vesicles to fuse with the membrane and release neurotransmitters.

What happens at a chemical synapse?

Neurotransmitters cross the synaptic cleft to bind receptors on the next cell

What do excitatory neurotransmitters do?

Open Na⁺ channels to depolarize the postsynaptic cell.

What do inhibitory neurotransmitters do?

Open Cl⁻ channels to hyperpolarize the postsynaptic cell.

What are the three main types of gated ion channels?

Voltage-gated, ligand-gated, and mechanically gated channels.

What opens mechanically gated channels?

Physical stress or pressure on the membrane.

What opens ligand-gated channels?

Binding of a neurotransmitter or other ligand.

What opens voltage-gated channels?

Changes in membrane potential

What technique is used to study ion channel activity?

Patch clamp recording

What is the purpose of patch clamping?

Measures ion flow through individual channels.

What is the central dogma of biology?

DNA → RNA → Protein.

What enzyme makes RNA from DNA?

RNA polymerase.