2.3 transport across the cell membrane

Question 1

which points out and is hydrophilic

Answer 1

the hydrophilic head

Question 2

what are 3 of the functions of phospholipids in the membrane

Answer 2

1. allows lipid-soluble substances to enter and leave the cell
2. prevent water-soluble substances entering and leaving the cell
3. make the membrane flexible and self-sealing

Question 3

6 functions of proteins on the cell membranes

Answer 3

1. provide structural support
2. act as channels transporting water-soluble substances across the membrane
3. allow active transport across the membrane through carrier proteins
4. form cell-surface receptors for identifying cells
5. help cells adhere (stick) together
6. act as receptors like hormones

Question 4

what is the integral transport membrane

Answer 4

these pass through the bilayer, channels for transport of substances in and out of cell, serve as receptors as hormones and contain binding sites.

Question 5

what are the extrinsic proteins

Answer 5

on the outer layer of the bilayer, involved in cell signalling

Question 6

glycoproteins and glycolipids function

Answer 6

proteins or lipids that have a carbohydrate attached to them, form part of the glycocalyx, involved in cell adhesion. found of the outside of the cell

Question 7

what is cholesterol

Answer 7

sits between the tails of phospholipids, keeps the membrane fluid and prevents it freezing at low temperatures

Question 8

4 reasons why its called the fluid mosaic model

Answer 8

1. the phospholipids and proteins move around
2. not a fixed structure
3. some proteins can flip into.out of the cell
4. appears mosaic from the surface - all separate components

Question 9

what do channel proteins do

Answer 9

provide a hydrophilic passageway

Question 10

what do carrier proteins do

Answer 10

bind with a large substance and physically move it one side of the membrane to the other

Question 11

define diffusion

Answer 11

the net movement of molecules or ions from a region of high concentration to a region of low concentration

Question 12

define facilitated diffusion

Answer 12

is a passive process and relies on the kinetic energy of the diffusing molecules

there is no input of ATP and still occurs down a concentration gradient, just that it involves proteins at specific points on the plasma membrane

Question 13

describe the proteins channels

Answer 13

allows specific solutes through, the movement is faster than carrier proteins

Question 14

describe carrier proteins

Answer 14

small globular proteins that move in the membrane carrying molecules to either side of the membrane, important more large molecules like glucose which will always go down a concentration gradient

Question 15

define osmosis

Answer 15

the net movement of water particles from a region of high water potential to a region of low water potential

Question 16

define ψ (water potential)

Answer 16

the pressure exerted but moving water molecules

Question 17

is more water potential closer to 0 or further

Answer 17

more ψ = less negative
water will move by osmosis from a region of higher (less negative) ψ such as -20kPa to one of lower (more negative) ψ such as -30kPa

Question 18

define hypotonic

Answer 18

surrounding solution has a higher water potential (less negative) so water moves in

Question 19

define isotonic

Answer 19

surrounding solution has the same water potential so no net movement

Question 20

define hypertonic

Answer 20

surrounding solution has a lower water potential (more negative) so water moves out.

Question 21

do plant cells burst

Answer 21

no - they become tugged when absorb water

Question 22

define active transport

Answer 22

using energy to import and export substances against a concentration gradient in the form of ATP

Question 23

define antiport

Answer 23

cotransporters that transport substances in opposite directions

Question 24

define symports

Answer 24

cotansporters that transport substances in the same direction

Question 25

how does an anti port work

Answer 25

sodium wants out of the cell
potassium wants into the cell

1. three sodium ions want to pass through the membrane so they bind to the sodium-potassium pump with ATP
2. this causes a confirmation change allowing it passage through the membrane
3. two potassium ions from the extracellular fluid outside the cell bind to the transport protein
4. this bind causes another conformational change allowing passage through the membrane
5. the phosphate is removed and the protein returns to its original shape releasing the potassium ions inside the cell

Question 26

how does a symport work

Answer 26

1. sodium ions are actively transported out of epithelial cells into the blood
2. there is now a much higher concentration of sodium in the lumen of the small intestine that inside the epithelial cells
3. sodium ions can now diffuse into the epithelial cells down its concentration gradient through a co-transport proteins in the cell surface membrane
4. these sodium couple with glucose which are carried into the cell with them
5. glucose then passes into he blood by facilitated diffusion using another type of carrier