Membrane or Membrane transport

What is the main structural component of the cell membrane?

The phospholipid bilayer.

Why is the phospholipid bilayer described as amphipathic?

Because it has a hydrophilic (polar) head and two hydrophobic (non-polar) tails.

Which part of a phospholipid is hydrophobic?

The fatty acid tails.

Which part of a phospholipid is hydrophilic?

The phosphate head.

How are phospholipids arranged in the membrane?

They form a bilayer with hydrophobic tails facing inward and hydrophilic heads facing the cytosol and extracellular fluid.

What type of interaction holds the phospholipid tails together?

Weak hydrophobic interactions.

What is the function of cholesterol in the membrane?

It regulates membrane fluidity and maintains stability.

Is cholesterol found in plant cell membranes?

No, it is only found in animal cell membranes.

What are glycoproteins responsible for?

Cell-to-cell recognition.

What are glycolipids responsible for?

Cell recognition and distinguishing between self and non-self in the immune system.

What is the glycocalyx?

A carbohydrate-rich outer layer formed by glycoproteins and glycolipids that helps bind cells together and protect the cell surface.

What are integral proteins?

Proteins permanently embedded within the membrane, often spanning it (transmembrane proteins).

What are peripheral proteins?

Proteins temporarily attached to one side of the membrane by non-covalent interactions.

Junctions

join cells together

Enzymes

catalyze reactions on membrane surface

Transport

move molecules across membrane

Recognition

act as cellular ID markers

Anchorage

attach cytoskeleton or extracellular matrix

Transduction

act as hormone or signal receptors

What is the fluid mosaic model?

It describes the membrane as a fluid structure with moving lipids and proteins forming a mosaic pattern.

What does “semi-permeable” mean?

The membrane allows only certain molecules to pass through while blocking others.

What is diffusion?

The passive movement of particles from a region of high concentration to low concentration.

Four factors that affect the rate of diffusion.

Temperature, membrane surface area, particle size, and concentration gradient.

What is facilitated diffusion?

Passive transport that uses channel or carrier proteins to move substances across the membrane.

Does facilitated diffusion require energy (ATP)?

No, it is a passive process.

What is osmosis?

The passive movement of water molecules from a region of low solute concentration to high solute concentration across a partially permeable membrane.

What determines the direction of water movement in osmosis?

The solute concentration, water moves toward higher solute concentration.

What happens to a cell in a hypertonic solution?

Water moves out of the cell, causing it to shrink.

What happens to a cell in a hypotonic solution?

Water moves into the cell, causing it to swell.

What happens to a cell in an isotonic solution?

Water moves in and out equally, no net change.

What are aquaporins?

Channel proteins that increase the membrane’s permeability to water.

What is active transport?

The movement of molecules against their concentration gradient using energy (ATP).

What is the sodium-potassium pump?

A membrane protein that pumps 3 sodium ions out and 2 potassium ions in, maintaining a negative charge inside the cell.

What is indirect active transport (co-transport)?

Transport that uses energy released from one molecule moving down its gradient to move another molecule against its gradient.

What do gated ion channels do?

They allow ions to pass through membranes under specific conditions, such as voltage or chemical signals.

What triggers voltage-gated ion channels to open?

Changes in membrane polarity (electrical potential).

What triggers neurotransmitter-gated channels to open?

The binding of neurotransmitters to receptor sites.

What neurotransmitter is used at the junction between a neuron and a muscle cell?

Acetylcholine.

Why do sodium and potassium channels open and close during nerve impulses?

To allow ion movement that changes the membrane potential, enabling electrical signaling.

What is endocytosis?

The process of taking substances into the cell by engulfing them with the cell membrane.

What is pinocytosis?

A type of endocytosis where the cell takes in liquids.

What is phagocytosis?

A type of endocytosis where the cell engulfs solid particles.

What is exocytosis?

The process of releasing materials (such as waste or hormones) out of the cell via vesicles.

What are the two types of exocytosis?

Excretion (Removal of waste or undigested materials)            Secretion (Release of useful products like enzymes or hormones.)

How do unsaturated fatty acids affect membrane fluidity?

They increase fluidity and flexibility.

How do saturated fatty acids affect the membrane?

They make it thicker and less fluid.

How does temperature affect the ratio of saturated and unsaturated fatty acids?

Cold environments - more saturated fatty acids (stability)

Warm environments - more unsaturated fatty acids (fluidity)

Why is membrane fluidity important?

It allows membranes to move, break, and reform during endocytosis and exocytosis.

What are cell adhesion molecules (CAMs)?

Proteins that help cells stick together to form tissues.

What is the function of desmosomes?

To connect animal cells, providing flexibility and strength to tissues.

What is the function of plasmodesmata?

To connect plant cells by forming tubes between their cytoplasms.

What is the role of the extracellular matrix (ECM)?

Provides structural support and anchors cells via membrane proteins.

What two properties characterize cell membranes?

They are semi-permeable and selective.

What happens when a membrane is too rigid?

Transport and flexibility decrease, affecting cell function.

What ensures that waste is excreted and useful substances are secreted properly?

Controlled membrane transport and exocytosis.

Which of the following molecules can easily pass through the lipid bilayer?

Small non-polar molecules

What is the “bias” of cell membranes in terms of permeability?

They are more permeable to small, non-polar molecules and less permeable to ions or large polar molecules.

What happens to the membrane potential when sodium channels open during a nerve impulse?

Sodium rushes in, making the inside of the cell more positive (depolarization).

What happens immediately after sodium channels close in a nerve impulse?

Potassium channels open, allowing K⁺ to leave, restoring the negative charge (repolarization).

Why are phospholipids able to form bilayers spontaneously in water?

Because of their amphipathic nature, hydrophobic tails avoid water, hydrophilic heads face it.