B4 - TRANSPORT ACROSS CELL MEMBRANES

What makes up a phospholipid?

glycerol, two fatty acids, phosphate group

What molecule is made up of glycerol, two fatty acids and a phosphate group

Which part of a phospholipid is hydrophobic?

fatty acid tails

Which part of a phospholipid is hydrophilic?

phosphate head

Are the fatty acid tails in phospholipids hydrophobic or hydrophilic?

hydrophobic

Are the phosphate heads in phospholipids hydrophobic or hydrophilic?

hydrophilic

Which way do the heads of phospholipids point in the bilayer?

outside

Which way do the tails of phospholipids point in the bilayer?

inside

Why do the heads of phospholipids point outside the bilayer?

they are hydrophilic

Why do the tails of phospholipids point inside the bilayer?

they are hydrophobic

What are the functions of phospholipids in the cell-surface membrane?

allow lipid-soluble substances through, prevent water-soluble substances through, make the membrane flexible, make the membrane self-sealing

Which component of the cell-surface membrane allows lipid-soluble substances through?

phospholipids

Which component of the cell-surface membrane does not allow water-soluble substances through?

phospholipids

Which component of the cell-surface membrane makes the membrane flexible?

phospholipids

Which component of the cell-surface membrane makes the membrane self-sealing?

phospholipids

What do phospholipids arrange themselves into in the cell-surface membrane?

phospholipid bilayer

How thick is a typical phospholipid bilayer?

5-10nm

Where in the cell-surface membrane are proteins?

embedded in the phopholipid bilayer

How many types of protein are embedded in the phospholipid bilayer?

2

Name the 2 types of protein embedded in the phospholipid bilayer:

extrinsic, intrinsic

Which type of protein is located in the surface of the phospholipid bilayer?

extrinsic

Which type of protein spans the whole of the phospholipid bilayer?

intrinsic

Where are extrinsic proteins located in the cell-surface membrane?

the surface of the phospholipid bilayer

Where are intrinsic proteins located in the cell-surface membrane?

spanning the phospholipid bilayer

What are the functions of extrinsic proteins in the cell-surface membrane?

cell receptors, mechanical support, work with glycolipids

What are the functions of intrinsic proteins in the cell-surface membrane?

channel proteins, carrier proteins

Which type of protein acts as cell receptors, mechanical support, and works with glycolipids?

extrinsic

Which type of protein acts as channel or carrier proteins?

intrinsic

Name the functions of proteins in the membrane:

structural support, channel proteins, carrier proteins, receptors, adhesion between cells,

Which component of the cell-surface membrane provides structural support?

proteins

Which component of the cell-surface membrane acts as channels?

proteins

Which component of the cell-surface membrane acts as carriers?

proteins

Which component of the cell-surface membrane acts as receptors?

proteins

Which component of the cell-surface membrane acts to create adhesion between cells?

proteins

What molecules make up glycolipids?

lipids and carbohydrates

What bond is between a lipid and a carbohydrate in a glycolipid?

covalent

Name the functions of glycolipids:

recognition sites, maintains membrane stability, helps cells to attach to each other

Which components of the cell-surface membrane act as a recognition site?

glycolipids and glycoproteins

Which component of the cell-surface membrane maintains membrane stability?

glycolipid

Which components of the cell-surface membrane help cells to attach to each other?

glycolipids and glycoproteins

Is cholesterol hydrophilic or hydrophobic?

hydrophobic

Name the functions of cholesterol in the cell surface membrane:

reduce lateral movement, reduce fluidity, prevent loss of water and ions

What type of molecule is cholesterol?

lipid

Which component of the cell-surface membrane reduces lateral movement?

cholesterol

Which component of the cell-surface membrane reduces membrane fluidity?

cholesterol

Which component of the cell-surface membrane prevents loss of water and ions?

cholesterol

Is cholesterol in bacterial cell membranes?

no

Is cholesterol in animal cell membranes?

yes

What molecules make up glycoproteins?

carbohydrates and proteins

Name the functions of glycoproteins in the cell surface membrane:

act as recognition sites, help cells to attach to each other, allows cells to recognise each other

Which component of the cell-surface membrane allows cells to recognise each other?

glycoproteins

What specifically do glycoproteins act as receptors for?

hormones and neurotransmitters

What type of molecules can not diffuse through the cell surface membrane?

not lipid-soluble, large, same charge as protein channels, electrically charged

What type of molecules can diffuse through the cell surface membrane?

lipid-soluble, small, different charge to protein channels, electrically uncharged

Why must molecules be lipid-soluble to pass through the cell surface membrane?

to go through the phospholipid bilayer

Why must molecules be small to pass through the cell surface membrane?

to fit through channels

Why must molecules be differently charged to protein channels to pass through the cell surface membrane?

to not be repelled by them

Why must molecules be electrically uncharged to pass through the cell surface membrane?

to go through the non-polar hydrophobic tails in the phospholipid bilayer

What factors affect permeability of the cell surface membrane?

temperature, solvent concentration, pH

Why does temperature affect cell surface membrane permeability?

increased temperature → increased fluidity → increased permeability

How does solvent concentration affect cell surface membrane permeability?

more easily dissolved phospholipid bilayer →increased permeability

How does pH affect cell surface membrane permeability?

increased temperature →denatured proteins

Define 'diffusion':

the net movement of particles down a concentration gradient

Define 'concentration gradient':

the difference in concentration between two areas

What is the word for a liquid or gas?

fluid

What is defined as: 'the difference in concentration between two areas'?

concentration gradient

What is defined as: 'the net movement of particles down a concentration gradient'?

diffusion

Which way do molecules move in diffusion?

down the concentration gradient

Name three substances which move in and out of the cell by simple diffusion:

carbon dioxide, oxygen, urea

Which type of molecules move in and out of the cell by simple diffusion?

small, uncharged, lipid-soluble

What is facilitated diffusion?

the net movement of particles via transport proteins down a concentration gradient, without requiring extra energy from respiration

What types of proteins are used in facilitated diffusion?

channel or carrier

What type of molecules would be unable to move through the cell membrane so might need to be transported by facilitated diffusion?

large or polar

What process might large or polar molecules need to be transported by?

facilitated diffusion

Is facilitated diffusion active or passive?

passive

Does facilitate diffusion require extra energy?

no

What, effectively, is a channel protein?

water-filled pore

What type of molecules do channel proteins allow to diffuse through the membrane?

polar

Which type of transport protein is effectively a water-filled pore?

channel

Which type of transport protein has a fixed shape?

channel

Which type of transport protein does not have a fixed shape?

carrier

What does a carrier protein do to transport molecules?

undergo a conformational change

Which type of transport protein undergoes a conformational change to transport molecules?

carrier

Do molecules diffuse along or against the concentration gradient in facilitated diffusion?

along

What is the net movement of particles via transport proteins down a concentration gradient, without requiring extra energy from respiration?

facilitated diffusion

Name the five factors that affect rate of diffusion:

concentration gradient, temperature, surface area, thickness, channel/carrier proteins

What is concentration gradient?

difference in concentration gradient between two areas

If concentration gradient increases, how does the rate of diffusion change?

increases

If concentration gradient decreases, how does the rate of diffusion change?

decreases

If temperature increases, how does the rate of diffusion change?

increases

If temperature decreases, how does the rate of diffusion change?

decreases

If the membrane surface area increases, how does the rate of diffusion change?

increases

If the membrane surface area decreases, how does the rate of diffusion change?

decreases

If the membrane thickness increases, how does the rate of diffusion change?

decreases

If the membrane thickness decreases, how does the rate of diffusion change?

increases

If the number of channel/carrier proteins increases how does the rate of diffusion change?

increases until equilibrium

If the number of channel/carrier proteins decreases how does the rate of diffusion change?

decreases

Define 'osmosis':

the diffusion of water across a partially permeable membrane from a dilute to a concentrated solution

What is the water potential of pure water?

0

What has a water potential of 0?

pure water