CHAPTER 7 CELL MEMBRANES

What are the main components of cellular membranes?

Lipids and proteins, with carbohydrates also being important.

What type of molecules primarily compose membranes?

Phospholipids.

What is the structure of phospholipids?

Amphipathic molecules with hydrophobic and hydrophilic regions.

How do phospholipids arrange themselves in a membrane?

They form a bilayer with hydrophobic tails inside and hydrophilic heads exposed to water.

What is the fluid mosaic model?

It depicts the membrane as a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids.

What interactions primarily hold membranes together?

Weak hydrophobic interactions.

How do temperature changes affect membrane fluidity?

As temperatures cool, membranes switch from a fluid state to a solid state.

What type of fatty acids contribute to membrane fluidity?

Unsaturated fatty acids make membranes more fluid than saturated fatty acids.

What role does cholesterol play in animal cell membranes?

Cholesterol restrains phospholipid movement at warm temperatures and maintains fluidity at cool temperatures.

What are the two major types of membrane proteins?

Peripheral proteins and integral proteins.

How can peripheral proteins be removed from the membrane?

They can be removed without destroying the membrane, often by changing pH or ionic concentration.

What distinguishes integral proteins from peripheral proteins?

Integral proteins penetrate the hydrophobic core and usually destroy the membrane if removed.

What are transmembrane proteins?

Integral proteins that span the membrane.

What functions do cell-surface membrane proteins serve?

Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to the cytoskeleton and ECM.

What does selective permeability mean in the context of membranes?

The plasma membrane controls the exchange of materials, allowing some substances to cross more easily than others.

What types of molecules can pass through the lipid bilayer rapidly?

Hydrophobic (nonpolar) molecules like hydrocarbons, CO2, and O2.

What is passive transport?

The diffusion of a substance across a membrane without energy investment by the cell.

What is osmosis?

The diffusion of free water across a selectively permeable membrane.

How do transport proteins assist in membrane transport?

They facilitate the passage of hydrophilic substances across membranes by passing through transport proteins.

What are channel proteins?

Proteins that have a hydrophilic channel for certain molecules or ions to pass through.

What are carrier proteins?

Proteins that bind to molecules and change shape to shuttle them across the membrane.

What is the significance of the concentration gradient in diffusion?

Substances diffuse down their concentration gradient from high to low concentration.

What is dynamic equilibrium in the context of diffusion?

A state where as many molecules cross the membrane in one direction as in the other.

What is the role of membrane fluidity in cellular function?

Fluidity affects permeability and the movement of transport proteins, essential for proper function.

What adaptations do organisms in extreme temperatures have regarding membranes?

They have differences in membrane lipid composition to maintain functionality.

What is the process called when free water molecules diffuse across a membrane?

Osmosis

What is tonicity?

The ability of a surrounding solution to cause a cell to gain or lose water.

What happens in an isotonic solution?

The solute concentration is the same as that inside the cell, leading to no net movement of water and volume of cell is stable.

What is a hypertonic solution?

A solution with a greater solute concentration than that inside the cell, causing water to leave the cell to the surrounding solution and likely die

What is a hypotonic solution?

A solution with a lower solute concentration than that inside the cell, causing water to enter the cell from surrounding cell and burst (lyse).

What is osmoregulation?

The control of solute concentration and water balance in organisms that live in such enviroments.

What role do aquaporins play in facilitated diffusion?

They facilitate the diffusion of water across the plasma membrane.

What are gated channels?

Ion channels that open or close in response to a stimulus.

What is the function of carrier proteins in facilitated diffusion?

They undergo shape changes to move solutes across the membrane without energy input and move substances down the concentration gradient.

What is active transport?

The movement of substances against their concentration gradient, using energy.

What is the sodium-potassium pump?

An electrogenic pump that transports K+ into the cell and Na+ out of the cell using ATP.

What is cotransport?

When the active transport of one solute drives the transport of another substance against its gradient.

What is exocytosis?

The process where transport vesicles fuse with the membrane to release contents outside the cell.

What is endocytosis?

The process of taking macromolecules into the cell by forming vesicles.

What is phagocytosis?

A type of endocytosis where a cell engulfs a particle by extending pseudopodia (cellular eating).

What is pinocytosis?

A type of endocytosis where extracellular fluid is taken up into tiny vesicles (cellular drinking).

What is receptor-mediated endocytosis?

vesicle formation triggered by the binding of solutes to receptors on the cell membrane.

Describe Cellular membranes?

They are fluid mosaics of lipids and proteins

What are the hydrophilic regions of the protein?

They are oriented toward the cytosol and extracellular fluid inside and outside the membrane

What hydrophobic regions are embedded in?

In the bilayer

What is the major structural feature of all membranes?

In living organisms is a bilayer of phospholipid

What do most of the lipids and some proteins do in membrane?

Can move sideways within the membrane or rotate

What do lipibds or proteins rarely do in membrane?

Rarely, a lipid or protein may flip-flop across the membrane, from one phospholipid layer to the other

What solidifies the membrane?

The temperature at which a membrane solidifies depends on the types of lipids

How do membranes work?

Membranes must be fluid to work properly

What movement does cholesterol restrain?

At warm temperatures (such as 37ºC), cholesterol restrains movement of phospholipids

What does cholesterol do at cool temperatures?

It maintains fluidity by preventing tight packing

What steroids do plants use?

Plants use different but related steroid lipids to buffer membrane fluidity. Plant membranes do not contain cholesterol

How does fluidity affect membrants?

Fluidity affects both permeability and movement of transport proteins

What happens if membranes is too fluid? Too fluid cannot support protein function

How are organisms living in extreme temperatures affected?

Organisms have adaptive differences in membrane lipid composition

What is a membrane a collage of?

Different proteins, often clustered in groups, embedded in the fluid matrix of the lipid bilayer

What do Phospholipids form?

The main structure of the membrane, but proteins determine most of the membrane's functions

What is the protein composition of membranes?

The compositions varies among cells within an organism, and among intracellular membranes within a cell

What do hydrophobic regions consists of?

an integral protein consist of nonpolar amino acids, often coiled into α helices associated with the fatty acid chains

How can you removed peripheral proteins?

You can usually remove peripheral proteins from the membrane by changing the pH, ionic concentration without destroying the membrane.

Can you remove integral protein?

You cannot usually remove integral protein except by destroying the membrane

What are membrane protein functions?

In regulating what gets into and out of the cell

Where do Hydrophobic (nonpolar) molecules dissolve in?

the lipid bilayer and pass through the membrane rapidly by diffusion through the lipid bilayer

What does the hydrophobic interior of the membrane do?

It impedes the passage of hydrophilic (polar) molecules

What is the selective permeability of a membrane dependent on?

It is dependent on both the lipid bilayer and the specific transport proteins it contains

What is Diffusion?

It is the movement of particles of any substance so that they spread out evenly into the available space

What does the concentration gradient represent?

It represents potential energy that drives diffusion

What is the concentration of free water molecules?

Free water moleculesdiffuse across a membrane from the region of lower solute concentration to the region of higher solute concentration.

What is the concentration of water?

Water keeps moving until the solute concentration is equal on both sides, at that point we are at equilibrium

What is Tonicity dependent on?

It depends on the concentration of solutes in the solution that cannot cross the membrane, relative to that inside the cell

What if the solution has a higher concentration of these solutes?

If the solution has a higher concentration than the inside of the cell, water will tend to leave the cell, and vice versa

What problems do Hypotonic or hypertonic environments cause?

Problems for cells without walls because they cannot tolerate excessive water loss or uptake

What is facilitated diffusion?

transport proteins speed the passive movement of molecules across the plasma membrane

What role do Ions play in facilitated diffusion?

Ion channels facilitate the transport of ions

How can carrier proteins change in shape be triggered?

It can be triggered by the binding and release of the transported molecule

Are channels active or passive?

All channels are passive

Are Carriers active or passive?

It can be active or passive depending on whether they require energy expenditure from the cell to do their function

What happens during facilitated diffusion? protein carriers passively carry solutes down their concentration gradient, and the transport requires no energy

What is active transport?

Some transport proteins use energy to move solutes against their concentration gradients, net flow from low concentration to high concentration.

What does active transport enable?

It enables cells to maintain solute concentrations that differ from the environment.

What is the concentration of cotransport?

The "downhill" diffusion of solute is coupled to the "uphill" transport of a second substance against its own concentration gradient

What is a plant cells gradient?

Plant cells use proton pumps to generate an H+ gradient across the cell membrane

What is a co-transporter gradient?

A cotransporter couples the movement of H+ back down its concentration gradient to the active transport of sucrose into the cell

How do hydrogen ions move through gradients? Hydrogen ions are moving through the membrane down a concentration gradient,

How do Animal cells use cotransporter? a cotransporter to couple the active transport of glucose to the diffusion of Na+ into cells lining the intestine

How do small molecules and water transport?

They enter or leave the cell through the lipid bilayer or via transport proteins

How does large molecule transport?

Such as polysaccharides and proteins, cross the membrane in bulk inside vesicles

What does Pinocytosis do?

It is nonspecific for the substances it transports; any and all solutes are taken into the cell

How are receptor proteins bound?

They are bound to specific solutes from the extracellular fluid are clustered in coated pits that form coated vesicles