2.3 Transport across cell membranes

Question 1

what is diffusion:

Answer 1

the net movement of a substance down a concentration gradient

Question 2

DNA in prokaryotes vs eukaryotes

Answer 2

PRO
* circular w/ no free ends
* relatively short
* not bound to histones, doesnt exist as chromos
* no introns, only exons

EU
* linear DNA w/ 2 ends
* much longer
* tightly wrapped around histones, to form chromos
* has introns and exons

Question 3

Function of cholesterol:

Answer 3

• cholesterol increases stability
• by reducing movement of other molecules in membrane

Question 4

function of Extrinsic proteins

Answer 4

• receptor sites for hormones
• detect chemicals released from other cells
• cell recog.

Question 5

Function of Glycolipid:

Answer 5

• for cell recog.
• carb chain can be metabolised to provide energy

Question 6

Function of Glycoprotein?

Answer 6

• recognise type of cell
  Cell signalling
• act as receptors for hormones
• triggering changes in cell

Question 7

Function of Intrinsic proteins:

Answer 7

• allows water soluble, large, charged molecules to pass through memb
• by facilitated diffusion or active transport

Question 8

molecules that can only go through carrier or channel proteins?

Answer 8

polar, water soluble, large
* allows cell to control what goes in and out so there can be different concentrations on either side of membrane

Question 9

Why is plasma mebrane described as Fluid Mosaic?

Answer 9

fluid - molecules within membrane able to move
mosaic - mixture of phospho. and proteins/ arrangement of proteins

Question 10

describe homogenisation

Answer 10

• sample of tissue place in cold, isotonic, buffer solution
• solution homegenised using homogeniser (grinds up cells
• breaks plasma membrane of cells and releases organelles into homogenate

Question 11

why does solution tissue is put in have to be ice cold?

Answer 11

ice cold to stop enzyme activity to prevent digestion of organelles.

Question 12

why does solution tissue is put in have to be buffered?

Answer 12

so that pH is kept constant, so that proteins, enzymes are not denatured

Question 13

describe filtration

Answer 13

• homogenate filtered through gauze
• to seperate large cell debris or tissue debris that wasn’t broken up
• leaving filtarte containing mixture of organelles

Question 14

Describe centrifugation: (4)

(Just the actual centrifugation part)

Answer 14

• filtrate placed in tube into centrifuge and spun at low speed
• causes heaviest organelle to sink to botton and form pellet (nuclei)
• supernatatant drained, put in new tube and spun at higher speed
• new pellet forms (eg mitochondria)

Question 15

order of mass of organelles

Answer 15

1. nuclei
2. chloroplast (if plant)
3. mitochondria
4. lysosomes
5. endoplasmic reticulum
6. ribosomes

Question 16

examples of artefacts:

Answer 16

• dust
• fingerprints

Question 17

explain how movement of substances across molecules is affected by membrane structure (5)

Answer 17

• phos. bilayer allows diffusion of non-polar, lipid soluble substances
• carrier/channel allow polar substances to cross bilayer
• no. of carrier/channel determines how much movement
• channel/carrier allow facilitated diffusion
• shape of carrier determines which substances move
• membrane SA determines how much movement
• cholesterol affects fluidity/permeability

Question 18

centrifugation.

Why does solution have to be isotonic?

Answer 18

To prevent osmosis so that the organelles do not shrivel or burst.

Question 19

What is ultracentrifugation? Describe what happens?

Answer 19

• used to separate very small things such as different lengths of DNA.
• sample put into tube.
• spun at a lower speed.
• the most dense organelle forms a pellet, at bottom of test tube.
• other organelles remain suspended in supernatant.
• supernatant removed and put into clean test tube and spun at higher speed.
• second most dense organelle forms sediment at bottom.

Question 20

how do you find the sodium chloride solution with the same water potential as the potato using a graph

Answer 20

• plot a graph of concentration against ratio
• find the concentration where ratio is 1 (there is no mass change)

Question 21

carrier proteins…

Answer 21

require energy

Question 22

Compare and contrast the processes by which water and inorganic ions enter the cell. (3)

Answer 22

Compare
* Both move down concentration gradient.
* Both move through protein channels in membrane.

Contrast
* Ions can move against a concentration gradient by active transport.