Transport Across Cell Membranes

Question 1

Fluid Mosaic model of membrane structure

Answer 1

Molecules within member and can move laterally (fluid) e.g. phospholipids

Mixture of phospholipids, proteins, glycoproteins and glycolipids

Question 2

Phospholipid bilayer components

Answer 2

Hydrophilic phosphate heads - attracted to water (orientate to aqueous environment either side of membrane

Hydrophobic fatty acid tails - repel water (orientate to interior of membrane)

Question 3

Embedded proteins (intrinsic or extrinsic)

Answer 3

Channel and carrier proteins (intrinsic)

Question 4

Glycolipids

Glycoproteins

Answer 4

Glycolipid - (lipids with polysaccharide chain attached)

Glycoproteins - (proteins with polysaccharide chain attached)

Question 5

Cholesterol

Answer 5

Binds to phospholipid hydrophobic fatty acid tails

Question 6

Components of the cell membrane (4)

Answer 6

Phospholipid bilayer

Inverted proteins

Glycoproteins and glycolipids

Cholesterol

Question 7

What does the fluid Mosaic model of membrane structure explain?

Answer 7

How molecules can enter and leave a cell

Question 8

How does the phospholipid bilayer allow molecules to enter or leave a cell?

Answer 8

Allows simple diffusion of nonpolar small/lipid soluble molecules (e.g. water oxygen)

Restricts movement of larger/polar molecules

Question 9

How do you channel proteins allow molecules to enter or leave a cell?

Answer 9

Allow movement of water soluble/polar molecules/ions down a concentration gradient (facilitated diffusion)

Question 10

How do you carrier proteins allow molecules to enter or leave a cell?

Answer 10

Allow the movement of molecules against a concentration gradient using ATP (active transport)

Question 11

Features of the plasma membrane that adapt for its other functions (4)

Answer 11

Phospholipid bilayer

Phospholipid bilayer is fluid

Surface proteins

Cholesterol

Question 12

How does the cell membrane being a phospholipid bilayer adapt for another function?

Answer 12

Maintains a different environment on each side of the cell (compartmentalisation of the cell)

Question 13

How does the phospholipid bilayer being fluid adapt it for another function?

Answer 13

Can bend into different shapes for phagocytosis/to form vesicles

Question 14

How do the surface proteins (extrinsic glycoproteins/glycolipids) adapt the cell membrane for another function?

Answer 14

Cell recognition

Act as antigens/receptors

Question 15

How does cholesterol adapt the phospholipid bilayer for another function?

Answer 15

Regulates fluidity

Increases stability

Question 16

What is cholesterol not present in?

Answer 16

Bacterial cell membranes

Question 17

What is the role of cholesterol?

Answer 17

Makes the membrane more rigid/stable/less flexible

By restricting lateral movement of molecules making up the membrane (e.g. phospholipids)

Binds to fatty acid tails of phospholipids causing them to pack more closely together

Question 18

Simple diffusion across the membrane

Answer 18

Net movement of small, nonpolar molecules (e.g. oxygen and carbon dioxide) across a selectively permeable membrane comment down a concentration gradient

Passive, no ATP required

Question 19

Factors affecting rate of simple diffusion

SCD

Answer 19

Surface area

Concentration gradient

Diffusion distance (thickness of surface)

Question 20

Facilitated diffusion across cell membranes

Answer 20

Net movement of larger/polar molecules (e.g. glucose) across a selectively permeable membrane, down a concentration gradient

Through a channel or carrier protein

Passive, no ATP required

Question 21

Factors affecting rate of facilitated diffusion

Answer 21

Surface area

Concentration gradient (until the number of proteins is the limiting factor as all are and use/saturated)

Number of channel or carrier proteins

Question 22

Carrier proteins transport…

Answer 22

Transport large molecules, protein changes shape when the molecule attaches

Question 23

Channel proteins transport…

Answer 23

Large/polar molecules through its pore

Some are gates (open and close) eg. Voltage gated sodium ion channels

Question 24

Specificity associated with channel and carrier proteins

Answer 24

Different carrier on channel proteins facilitate the diffusion of different specific molecules

Question 25

Active transport across cell membranes

Answer 25

Net movement of molecules/ions against a concentration gradient Using carrier proteins Using energy from the hydrolysis of ATP to change the shape of the tertiary structure and push the substances through

Question 26

Factors affecting the rate of active transport

Answer 26

PH, Temperature (affect tertiary structure of carrier protein) Speed of carrier protein Number of carrier proteins Rate of respiration (affects ATP production)

Question 27

Classic example of co-transport

Answer 27

Absorption of sodium ions and glucose by cells lining the mammalian ileum

Question 28

Explain the cotransport of sodium ions and glucose

Answer 28

1. Sodium ions are actively transported out of epithelial cells lining the ileum, into the blood, by the sodium potassium pump. Creating a concentration gradient of sodium (high concentration of sodium in lumen than epithelial cell) 2. Sodium ions and glucose move by facilitated diffusion into the epithelial cell from the lumen, via a co-transporter protein 3. Creating a concentration gradient of glucose – high concentration of glucose in epithelial cell then blood 4. Glucose moves out of the cell into the blood by facilitated diffusion through a protein channel

Question 29

Movement across membranes by osmosis

Answer 29

Net movement of water molecules across a selectively permeable membrane down in water potential gradient Passive

Question 30

Factors affecting rate of osmosis

Answer 30

Surface area Water potential gradient Thickness of exchange surface (diffusion distance)

Question 31

How much cells be adapted for transport across that internal or external membranes?

Answer 31

Increase in surface Sarah Increase the number of channel proteins or carrier proteins

Question 32

Water potential

Answer 32

Potential of water molecules to diffuse out of or into a solution Pure water has highest water potential Adding solutes to a solution low as water potential (becomes more negative)