4) Cell membranes and Transport

Question 1

how thin is the cell surface membrane ?

Answer 1

7 nm

Question 2

what is the phospholipid structure ?

Answer 2

• polar phosphate head (hydrophilic)
• hydrophobic fatty acid (lipid) tails

Question 3

what does hydrophobic mean ?

Answer 3

no electrical charge, so not attracted to water molecules

Question 4

what does hydrophilic mean ?

Answer 4

has an electrical charge, and is attracted to water molecules

Question 4

what is a glycoprotein ?

Answer 4

carbohydrate attached to a protein

Question 5

difference between placement of integral and peripheral proteins ?

Answer 5

• peripheral : on the edge or outside (do not cross middle line)
• integral : cross the middle line

Question 6

state the roles of a phosphate head

Answer 6

• stability
• hydrophilic/attracted to water
• attracted to extracellular water/ water in cytoplasm

Question 7

state the roles of a fatty acid tail

Answer 7

• fluidity = unsaturated
• stability = hydrophobic interactions between tails
• barriers to hydrophilic substances (eg. glucose/ions)

Question 8

state the roles of cholesterol

Answer 8

• stability between fatty acid tails
• prevents passage between tails
• decreases fluidity

Question 9

state the roles of glycolipids

Answer 9

• stability (hydrophobic)
• receptor for signal molecule
• cell recognition (can be an antigen)

Question 10

state the roles of peripheral proteins

Answer 10

• cell recognition/ antigen
• cell adhesion (cells stick together)
• eg: glycoproteins

Question 11

state the roles of integral proteins

Answer 11

• moves polar substances/ions through membrane
• transport proteins (channel/carrier)
• pumps (active transport)
• membrane bound enzymes

Question 12

state the roles of glycoproteins

Answer 12

• cell recognition (antigen)
• cell signalling
• receptor for hormones (neurotransmitters)

Question 13

the main stages of cell signalling

Answer 13

• ligands (cell signalling molecules) are secreted from a cell (the sending cell) into the extracellular space.
• They are then transported through the extracellular space to the target cell.
• The ligands bind to the surface receptors (specific to that ligand) on the target cell. : These receptors are formed from glycolipids & glycoproteins.
• The message carried by the ligand is relayed through a chain of chemical messengers inside the cell = triggering a response.

Question 14

2 differences between active and passive transport

Answer 14

• Active : uses ATP
  : goes against concentration gradient. (low –> high)
• Passive : does not use ATP
  : goes down the concentration gradient. (high –> low)

Question 15

What are the 2 types of active transport and also their types?

Answer 15

• Active transport : pumps & carrier
• Bulk transport : endocytosis & exocytosis

Question 16

what are the 3 types of passive transport?

Answer 16

• Simple diffusion
• Osmosis
• Facilitated diffusion : channel & carrier

Question 17

what is diffusion ?

Answer 17

net movement of molecules from a region of high concentration to low concentration, using energy from the random movement of particles.

Question 18

what are some factors affecting diffusion ?

Answer 18

• concentration gradient (greater the diff in concentration between 2 regions, greater amount diffuses)
• distance (shorter the distance, greater the diffusion)
• area (larger the area, greater the diffusion)
• size/type of diffusing molecules (smaller / soluble will diffuse faster)

Question 19

what can go through the lipid bilayer, and what cannot ?

Answer 19

• can go through : hydrophobic & small uncharged molecules (H20)
• cannot : large uncharged molecules & ions (Na+)

Question 20

what is facilitated diffusion ?

Answer 20

the transport of polar molecules and ions into and out of a cell. It involves the use of carrier and channel proteins.

Question 21

state 5 differences between channel & carrier proteins

Answer 21

channel proteins (position fixed)
- transport ions
- soluble molecules diffuse thru the pores
- high transport rates
- do not bind with solute molecules it transports
- only transport water soluble molecules

carrier proteins (flip between 2 conformations)
- transport molecules
- solute molecules bound to one side, released from other side
- low transport rates
- consist of alternative solute-bound conformations
- transport both water soluble and insoluble molecules.

Question 22

what is osmosis ?

Answer 22

diffusion of water molecules from high water potential to low water potential through a partially permeable mebrane

Question 23

what is the highest water potential ? (and unit)

Answer 23

0 kPa = water

Question 24

define hypotonic, isotonic, and hypertonic

Answer 24

• hypotonic : higher water potential than the cell (turgid)
• isotonic : same water potential as cell.
• hypertonic : lower water potential than cell (flaccid/plasmolysed)

Question 25

state basic stages of active transport

Answer 25

• particle enters the pump
• binds to a specific site
• uses ATP to change shape of pump
• particle released on the side w higher concentration
• pump then returns to its original shape

Question 26

describe endocytosis

Answer 26

(into cells)
- part of plasma membrane pulled inwards
- a droplet of fluid becomes enclosed when a vesicle is pinched off
- vesicles can then move through the cytoplasm carrying contents

Question 27

describe exocytosis

Answer 27

(out of cells)
- vesicles FUSE w plasma membrane
- contents of vesicle expelled
- membrane then flattens out again

Question 28

differentiate between phagocytosis & pinocytosis

Answer 28

• Phagocytosis : bulk uptake of SOLID material + cell EATING.
  (eg: engulfing of bacteria by white blood cells)
• Pinocytosis : bulk uptake of LIQUID + cell DRINKING.
  (eg: absorb nutrients from food)

Question 29

Summary of differences between passive and active transport

Answer 29

(pg. 16 of 31 from chapter 4 notes )

Question 30

relationship between surface area and diffusion

Answer 30

greater the surface area, faster the diffusion

Question 31

describe turgid plant cell

Answer 31

• hypotonic solution
• higher water potential than the cell, so water moves into the cell
• protoplast swells and presses against cell wall

Question 32

describe plasmolysis (flaccid)

Answer 32

• hypertonic solution
• lower water potential than the cell, so water moves out of the cell
• protoplast pulled away from cell wall

Question 33

explain why phospholipds are able to form bilayer

Answer 33

• polar hydrophilic phosphate groups on the outside.
• so heads face watery env & tails face away / each other

Question 34

explain how the structure of phospholipid molecule makes it suitable for its function

Answer 34

• polar hydrophilic phosphate heads face outwards into water.
• alternatively 2 layered structures called bilayers can form in sheets.
• forms hydrogen bond with water & stabilises membrane.

Question 35

how does inner membrane differ from outer membrane

Answer 35

• fewer channel proteins
• less unsaturated fats
• reduced gaps between membrane molecules

Question 36

2 similarities between active transport and faciliated diffusion

Answer 36

• both use carrier proteins
• both are specific/ have specific binding site.