better chapter 5 flashcards

What is selective permeability?

A property of the plasma membrane that allows some substances to cross more easily than others.

What does amphipathic mean?

A molecule has both a hydrophilic (water-loving) region and a hydrophobic (water-fearing) region.

Why are phospholipids amphipathic?

They have a hydrophilic phosphate head and hydrophobic hydrocarbon tails.

What is the fluid mosaic model?

The membrane is a fluid phospholipid bilayer with proteins embedded in or associated with it, forming a mosaic.

What are the two main components of the plasma membrane?

Phospholipids and proteins.

What happens to membrane fluidity as temperature decreases?

Phospholipids move less and pack more closely; at sufficiently low temperatures, the membrane can solidify.

How do unsaturated hydrocarbon tails affect membrane fluidity?

Their kinks prevent close packing, helping the membrane remain fluid at lower temperatures.

Why do unsaturated tails have kinks?

Double bonds in the hydrocarbon tails create bends.

How does cholesterol affect membrane fluidity at high temperatures?

It restrains phospholipid movement, making the membrane less fluid.

How does cholesterol affect membrane fluidity at low temperatures?

It disrupts regular phospholipid packing, helping prevent the membrane from solidifying.

What is cholesterol's overall role in membrane fluidity?

It acts as a fluidity buffer, helping moderate changes in fluidity as temperature changes.

What are integral membrane proteins?

Proteins that penetrate the hydrophobic interior of the lipid bilayer; some span the entire membrane.

What are transmembrane proteins?

Integral proteins that span the entire phospholipid bilayer.

What are peripheral membrane proteins?

Proteins loosely associated with the membrane surface that are not embedded in the lipid bilayer.

What are the six major functions of membrane proteins?

Transport; enzymatic activity; signal transduction; cell-cell recognition; intercellular joining; attachment to the cytoskeleton and extracellular matrix.

How do membrane proteins perform transport?

They form selective hydrophilic channels or change shape to move substances across the membrane; some use ATP.

How do membrane proteins perform enzymatic activity?

They act as enzymes with exposed active sites or work together to carry out sequential steps of a metabolic pathway.

How do membrane proteins perform signal transduction?

A specific chemical messenger binds to the protein, causing a shape change that relays a message into the cell.

How do membrane proteins help with cell-cell recognition?

Glycoproteins act as identification tags recognized by proteins on other cells.

How do membrane proteins help with intercellular joining?

They connect adjacent cells through long-lasting junctions, such as tight junctions or gap junctions.

How do membrane proteins attach to the cytoskeleton and extracellular matrix (ECM)?

They bind to microfilaments or ECM molecules, helping maintain cell shape, stabilize protein locations, and coordinate changes inside and outside the cell.

What are membrane carbohydrates?

Carbohydrates attached to membrane lipids or proteins, forming glycolipids or glycoproteins.

What are the functions of membrane carbohydrates?

Cell identification and recognition, embryonic tissue sorting, immune defense, and determining human blood types.

What is a glycoprotein?

A protein with an attached carbohydrate chain.

What is a glycolipid?

A lipid with an attached carbohydrate chain.

What is a channel protein?

A membrane protein that provides a hydrophilic passageway for specific molecules or ions.

What is a carrier protein?

A membrane protein that binds a substance and changes shape to move it across the membrane.

What is the key difference between channel and carrier proteins?

Channel proteins provide a passageway; carrier proteins bind a substance and change shape to transport it.

What are aquaporins?

Channel proteins that greatly increase the speed of water movement across membranes.

How does carbon dioxide (CO2) cross the membrane?

By simple diffusion directly through the phospholipid bilayer.

How does oxygen (O2) cross the membrane?

By simple diffusion directly through the phospholipid bilayer.

How does glucose cross the membrane?

By facilitated diffusion through specific carrier proteins, when moving down its concentration gradient.

How can hydrogen ions (H+) cross the membrane?

Through ion channels or via active transport, such as proton pumps.

How does water cross the membrane?

Water can diffuse slowly through the lipid bilayer, but aquaporins greatly facilitate its movement by osmosis.

Why can CO2 and O2 cross the lipid bilayer easily?

They are small, nonpolar molecules that dissolve in the hydrophobic interior of the membrane.

Why can charged ions not easily cross the lipid bilayer directly?

The hydrophobic interior of the membrane resists charged and highly polar substances.

What is diffusion?

The net spreading of particles from higher to lower concentration into available space.

What is a concentration gradient?

A region along which the concentration of a substance increases or decreases.

What is passive transport?

Movement of a substance across a biological membrane without energy investment by the cell.

What drives passive transport?

The substance's concentration gradient; particles move down the gradient.

What is osmosis?

The diffusion of free water across a selectively permeable membrane.

What is an isotonic solution?

A solution with an equal concentration of nonpenetrating solutes relative to the cell, causing no net movement of water.

What is a hypertonic solution?

A solution with a higher concentration of nonpenetrating solutes than the cell, causing the cell to lose water.

What is a hypotonic solution?

A solution with a lower concentration of nonpenetrating solutes than the cell, causing the cell to gain water.

What happens to an animal cell in an isotonic solution?

There is no net movement of water, so the cell generally maintains its size.

What happens to an animal cell in a hypertonic solution?

Water leaves the cell, causing it to shrink.

What happens to an animal cell in a hypotonic solution?

Water enters the cell, causing it to swell and potentially burst (lyse).

What does turgid mean?

Very firm and healthy; a plant cell becomes turgid when water enters in a hypotonic environment and turgor pressure develops.

What is turgor pressure?

The pressure of the cell contents against the cell wall as water enters a plant cell.

What does flaccid mean?

Limp; a plant cell becomes flaccid when it loses turgor pressure, commonly in an isotonic environment.

What is plasmolysis?

When a plant cell loses water in a hypertonic environment and its plasma membrane pulls away from the cell wall.

What can plasmolysis cause in plants?

Wilting and, if severe, cell death.

What happens to a plant cell in a hypotonic solution?

Water enters, the vacuole expands, and the cell becomes turgid; the cell wall resists further expansion.

What happens to a plant cell in an isotonic solution?

There is no net water movement, so the cell becomes flaccid rather than fully turgid.

What happens to a plant cell in a hypertonic solution?

Water leaves the cell, potentially causing plasmolysis.

Why can a red blood cell burst in a hypotonic solution while a plant cell usually does not?

Animal cells lack a rigid cell wall; plant cell walls resist expansion and generate counteracting turgor pressure.

What is facilitated diffusion?

Passive movement of polar molecules or ions down their concentration gradient through channel or carrier proteins.

Is facilitated diffusion active or passive transport?

Passive transport; it does not require the cell to expend energy to move the substance down its gradient.

Does facilitated diffusion move substances against their concentration gradient?

No. It moves substances down their concentration gradient.

Why is facilitated diffusion needed?

Polar molecules and ions cannot easily pass through the hydrophobic interior of the lipid bilayer on their own.

What is active transport?

Movement of solutes against their concentration gradients using energy and transport proteins.

What type of proteins carries out active transport?

Transport proteins such as pumps and carrier proteins.

What is the role of ATP in active transport?

ATP supplies energy; its terminal phosphate group may be transferred to a transport protein, causing a shape change that moves a solute.

What is phosphorylation?

The addition or transfer of a phosphate group to a molecule or protein.

How does ATP-powered phosphorylation help a transport protein?

It changes the protein's shape and can alter its affinity for a substance, allowing transport against a gradient.

What is the sodium-potassium pump?

An active transport protein that uses ATP to pump 3 Na+ ions out of the cell for every 2 K+ ions pumped into the cell.

What is the first step of the sodium-potassium pump cycle?

Three Na+ ions from the cytoplasm bind to the pump, stimulating phosphorylation by ATP.

What happens when the sodium-potassium pump is phosphorylated?

The pump changes shape, lowers its affinity for Na+, and releases the 3 Na+ ions outside the cell.

What happens after Na+ is released by the sodium-potassium pump?

The outward-facing pump binds 2 K+ ions from outside the cell.

What triggers the release of phosphate from the sodium-potassium pump?

Binding of K+ on the extracellular side triggers dephosphorylation.

What happens when the sodium-potassium pump loses its phosphate group?

It returns to its original shape, lowers its affinity for K+, and releases K+ into the cytoplasm.

What is the sodium-potassium pump's transport ratio?

3 Na+ out of the cell for every 2 K+ into the cell per ATP-driven cycle.

Does the sodium-potassium pump use active or passive transport?

Active transport, because it uses ATP to move ions against their gradients.

What is membrane potential?

The voltage across a plasma membrane caused by a separation of electrical charges.

What membrane potential range is given in the notes?

Approximately −50 to −200 mV.

Which side of the membrane is positive relative to the cytoplasm?

The extracellular side is positive relative to the cytoplasmic side.

What is vesicle transport?

Transport in which membrane-bound vesicles move materials into or out of the cell.

What is exocytosis?

The cell secretes materials when transport vesicles fuse with the plasma membrane and release their contents outside.

What is endocytosis?

The cell takes in molecules or particles by forming vesicles from inward-folding pockets of the plasma membrane.

What is the key difference between endocytosis and exocytosis?

Endocytosis brings materials into the cell; exocytosis releases materials outside the cell.

What is phagocytosis?

Cellular eating: the cell engulfs a large particle by extending pseudopodia around it, forming a food vacuole for digestion.

What are pseudopodia?

Temporary extensions of the cell membrane and cytoplasm that can surround and engulf particles during phagocytosis.

What is pinocytosis?

Cellular drinking: the cell takes in droplets of extracellular fluid and their dissolved solutes in small vesicles.

Does pinocytosis selectively take in specific dissolved solutes?

Usually no. It takes in extracellular fluid and its dissolved solutes nonspecifically.

What is receptor-mediated endocytosis?

A selective type of endocytosis in which specific extracellular substances bind to membrane receptors that cluster in coated pits, forming vesicles.

Why is receptor-mediated endocytosis selective?

Only substances that bind to the appropriate membrane receptors are specifically concentrated for uptake.

How does receptor-mediated endocytosis work?

Specific substances bind to receptors; the receptors cluster in coated pits, which invaginate and form vesicles containing those substances.

What is the key difference between phagocytosis and pinocytosis?

Phagocytosis engulfs large particles; pinocytosis takes in droplets of extracellular fluid and dissolved solutes.

What is the key difference between pinocytosis and receptor-mediated endocytosis?

Pinocytosis takes in fluid nonspecifically; receptor-mediated endocytosis selectively concentrates substances that bind to specific receptors.