Biol 1500: ch. 7

What is the plasma membrane made of?

The plasma membrane is built from amphipathic lipids and proteins arranged as a fluid mosaic.

What is an amphipathic molecule?

A molecule that has both hydrophilic and hydrophobic regions.

What are the two parts of a phospholipid?

A hydrophilic head and hydrophobic tails.

What does hydrophilic mean?

Water-loving; attracted to or compatible with water.

What does hydrophobic mean?

Water-fearing; avoids or is not compatible with water.

Why do phospholipids form a bilayer in water?

Their hydrophilic heads face water while their hydrophobic tails avoid water and face inward.

What is the hydrophobic interior of the membrane?

The interior region formed by the phospholipid tails that avoids contact with water.

How does the phospholipid bilayer create a stable boundary?

The hydrophobic interior separates the cell from its watery surroundings.

What property does the phospholipid bilayer give the membrane?

Selective permeability.

What is selective permeability?

The ability of a membrane to allow some substances to cross more easily than others.

What is the fluid mosaic model?

A model describing the membrane as a dynamic structure made of lipids, proteins, and carbohydrates arranged as a functional patchwork.

What does "fluid" mean in the fluid mosaic model?

Many lipids and some proteins can move laterally within the bilayer.

What does "mosaic" mean in the fluid mosaic model?

Proteins, lipids, and carbohydrates form a patchwork of different functions.

Are membrane proteins randomly scattered?

Not necessarily; proteins are often organized into functional clusters.

What can change membrane organization?

Cell type, organelle type, and environmental conditions.

What did the Frye and Edidin experiment demonstrate?

It provided evidence that membrane proteins can move laterally within the membrane.

How did the Frye and Edidin experiment test membrane protein movement?

Mouse and human membrane proteins were labeled with different markers, the cells were fused, and the labeled proteins mixed over time.

What did the mixing of labeled proteins in the Frye and Edidin experiment indicate?

Membrane proteins can move laterally within the plane of the membrane.

Do all membrane proteins move freely?

No. Some membrane proteins are anchored.

How do unsaturated fatty acid tails affect membrane fluidity?

They introduce kinks and increase fluidity.

Why do unsaturated fatty acid tails increase fluidity?

Their kinks prevent phospholipids from packing tightly.

How do saturated fatty acid tails affect membrane fluidity?

They pack tightly and decrease fluidity.

What happens to membrane fluidity when saturated fatty acid content increases?

Fluidity decreases because the tails pack more tightly.

What does cholesterol do to membrane fluidity at high temperatures?

It restrains phospholipid movement.

What does cholesterol do to membrane fluidity at low temperatures?

It prevents tight packing and helps maintain fluidity.

Why is membrane fluidity important?

Membranes must avoid becoming too rigid or too leaky so they can remain functional.

What type of membrane lipids do cold-adapted organisms often have?

More unsaturated membrane lipids.

Why do cold-adapted organisms often have more unsaturated lipids?

More unsaturated tails help maintain membrane fluidity in cold conditions.

How can organisms adapt their membrane composition to seasonal temperature changes?

They can alter their lipid composition as temperatures shift.

What happens if a membrane becomes too rigid?

Transport and protein movement can be impaired.

What happens if a membrane becomes too fluid?

Protein function and permeability control can be disrupted.

What happens to membrane fluidity in cold conditions?

More unsaturated tails help maintain fluidity.

What role does cholesterol play in warm conditions?

It provides restraint against excessive phospholipid movement.

What is the goal of membrane lipid regulation?

To maintain functional membrane fluidity.

What are peripheral membrane proteins?

Proteins that attach to the surfaces of membranes.

What are integral membrane proteins?

Proteins that penetrate the hydrophobic core of the membrane.

What are transmembrane proteins?

Integral proteins that span the entire phospholipid bilayer.

How are membrane-spanning regions of proteins anchored in the membrane?

Hydrophobic amino acids anchor the membrane-spanning regions inside the bilayer.

Why are hydrophobic amino acids found in membrane-spanning regions?

They interact favorably with the hydrophobic interior of the membrane.

What are the six major functions of membrane proteins?

Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment.

What is the transport function of membrane proteins?

Transport proteins move specific solutes across the membrane.

What is the enzymatic function of membrane proteins?

Membrane proteins can catalyze reactions at the membrane surface.

What is signal transduction?

The process in which membrane proteins receive and relay messages.

What is cell-cell recognition?

The ability of cells to identify other cells based on molecular markers.

What is the function of membrane proteins in intercellular joining?

They help stabilize tissues and connect cells to the cytoskeleton or extracellular matrix.

How do carbohydrates function on the cell membrane?

They act as molecular identification tags.

What is a glycolipid?

A carbohydrate attached to a lipid.

What is a glycoprotein?

A carbohydrate attached to a protein.

Why is carbohydrate diversity on the cell surface important?

It helps cells recognize one another.

What does it mean that membranes have sidedness?

The two faces of a membrane are not interchangeable.

How are membrane components distributed between the two sides of the membrane?

Lipids, proteins, and carbohydrates are distributed asymmetrically.

What helps establish membrane orientation?

ER and Golgi processing.

What happens to membrane orientation when a vesicle fuses with another membrane?

Vesicle fusion preserves which side faces the cytoplasm and which side faces outside.

Where are carbohydrate chains usually located on a membrane?

On the extracellular face.

What would happen if a cold-water fish lost unsaturated fatty acids from its membrane?

Its membrane would become less fluid in cold conditions.

Why would losing unsaturated fatty acids affect a cold-water fish membrane?

Saturated tails pack more tightly and decrease fluidity.

What would happen if a transport protein's hydrophobic membrane-spanning region mutated to charged amino acids?

The protein's ability to remain properly associated with the hydrophobic membrane core would be disrupted.

What could happen if a cell displayed the wrong carbohydrate markers?

Cell recognition could be disrupted because surface carbohydrates act as molecular ID tags.

What happens to membrane orientation when a vesicle fuses with the plasma membrane after leaving the Golgi?

The membrane orientation is preserved, maintaining which side faces the cytoplasm and which side faces outside.

What determines whether a molecule can cross the membrane easily?

Factors including its size, polarity, charge, and compatibility with the lipid bilayer.

What type of molecules cross the lipid bilayer most easily?

Small nonpolar molecules.

Why can small nonpolar molecules cross the membrane easily?

They can pass through the hydrophobic interior of the bilayer.

What happens to small polar molecules crossing the membrane?

They cross slowly; water often uses channels.

What types of molecules generally require transport proteins?

Large polar molecules and ions.

Which molecules can cross the membrane easily according to the lecture?

Oxygen, carbon dioxide, and steroids.

Which molecule often uses channels to cross the membrane?

Water.

Which molecules require transport proteins according to the lecture?

Glucose, amino acids, Na+, K+, and Cl−.

How does polarity affect membrane transport?

The more polar or charged a solute is, the more it depends on proteins to cross the membrane.

What are transport proteins?

Membrane proteins that provide controlled routes for hydrophilic molecules or ions to cross the membrane.

What is a channel protein?

A protein that creates a hydrophilic tunnel for specific ions or molecules.

What is a carrier protein?

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

What is an aquaporin?

A water channel that greatly speeds osmosis.

Why are transport proteins specific?

Their structures allow them to transport particular molecules or ions.

Can a glucose carrier automatically carry fructose?

No. Transport proteins have specificity for particular solutes.

What is diffusion?

The movement of molecules down a concentration gradient.

Why does net diffusion occur?

Random molecular motion causes populations of molecules to spread from areas of high concentration toward areas of low concentration.

Do individual molecules move randomly during diffusion?

Yes.

In what direction does the population show net movement during diffusion?

From high concentration to low concentration.

Does each solute diffuse down its own concentration gradient?

Yes.

What is a concentration gradient?

A difference in solute concentration across space.

What is dynamic equilibrium?

A state in which molecules continue moving randomly but there is no net change in concentration.

Is molecular movement stopped at dynamic equilibrium?

No. Molecules still move, but there is no net movement.

What makes diffusion across a membrane passive?

The cell does not spend energy on the movement.

What is passive transport?

Transport down a gradient without cellular energy input.

What is the direction of passive transport?

Down the concentration or electrochemical gradient.

Do molecules require ATP to move down a concentration gradient?

No.

What is the potential energy stored in a concentration gradient?

The gradient represents stored potential energy that can drive passive transport.

Can cells create concentration gradients?

Yes. Cells can build gradients using active transport.

Why are concentration gradients useful to cells?

The gradients can later be used to perform work.

What determines the direction of net movement across a membrane?

The gradient and the membrane's permeability.

What is osmosis?

The passive movement of water across a selectively permeable membrane.

In which direction does water move during osmosis?

Toward the side with more nonpenetrating solute.

Why does water move toward higher solute concentration?

Free water concentration is lower where solute concentration is higher.

What happens to free water concentration when solute concentration increases?

Free water concentration decreases.

Is osmosis passive or active?

Passive.

Does osmosis require ATP from the cell?

No.

What can make osmosis much faster?

Aquaporins.

When does water movement stop during osmosis?

When solute concentration is balanced or when pressure stops net movement.

What is tonicity?

A measure used to predict how a solution affects a cell's water balance based on nonpenetrating solutes.

What determines tonicity?

The concentration of nonpenetrating solutes around the cell.