B2.2- membranes and membrane transport

Question 1

general structure of phospholipid

Answer 1

-is amphipathic
-hydrophilic head is soluble/polar
-hydrophobic tails are insoluble and polar
-have different regions
-when in water, hydrophilic regions are attracted to water and hydrophobic regions are attracted to each other
-tail dont attract strongly, allows membrane to be flexible

Question 2

what can/cant pass through bilayer

Answer 2

large/ polar/ hydrophilic molecules cant pass
small non-polar molcules can pass; glucose, oxygen

Question 3

Simple diffusion

Answer 3

-Movement of Oxygen/CO2 molecules across phospholipid membrane from high conc to low conc -Moves along conc gradient
-Oxygen into cell, CO2 diffuses in opposite direction as it is produced by respiration inside cell and is present in higher conc inside cell

Question 4

Integral/peripheral proteins in membrane

Answer 4

-Integral= shows ampipathic character (hydrophobic mid region and hydrophillic region exposed to water molecules each side of membrane)
-Peripheral proteins= bound to surface of membrane (Hydrophilic)
-Can be found in both inner/outer sides of membrane
-Often anchored to an integral protein

Question 5

Passive transports

Answer 5

-High conc to low conc
-Along conc gradient
-Does not require cellular energy
-Movement comes from kinetic energy of molecules
-Movement will continue until equilibrium

Question 6

Active transport

Answer 6

-Moves against conc gradient
-ATP energy must be present
-Equilibrium not reached
-Allows cell to maintain interior conc of molecules that are different from exterior conc

Question 7

Osmosis

Answer 7

-Passive movement of water molecules across a partially permeable membrane form high conc to low conc (along conc gradient)

Question 8

How water can diffuse through membrane

Answer 8

-1. Simple diffusion=small water molecules in small number can still slip through hydrophobic region
2. Aquaporins=integral channel proteins that selectively transport water

Question 9

Facilitated diffusion

Answer 9

-Type of diffusion that involves 2 types of integral proteins; carrier proteins and channel proteins

Question 10

Carrier proteins

Answer 10

-Change shape in order to carry a specific substance from one side of a membrane to another
-Can carry substance along or against conc gradient
-Can carry water soluable/insoluable molecules

Question 11

Channel proteins

Answer 11

-Proteins with pores through which molecules with appropriate size can pass
-Contains gates that open/close in response to chemical signals
-Do not change shape just open and close a channel that molecules can diffuse through.

Question 12

Active transport steps

Answer 12

-specific particle binds to a binding site on soecific protein pump
-ATP binds to protein pump and hydrolises to become ADP
-Phosphate remains attached to protein pump to change shape
-Particle is moved against conc gradient and released.
-Phosphate is released causing the protein pump to return to original shape

Question 13

overview of types of transport

Answer 13

1. Passive transport=
   -simple diffusion
   -facilitated diffusion (carrier protein/channel protein)
2. Active transport

Question 14

Selective/ non selective transportation

Answer 14

Simple diffusion is non selective as any small/hydrophobic particles can pass
-Large/polar molecules can not pass
-Facilitated diffusion and active transport are selective processes

Question 15

Glycoproteins and glycolipids

Answer 15

Gylcoproteins= membrane proteins with carbohydrate chain
-Attached to membrane proteins
Glycolipds= phospholipids with carbohydrate chains
-Attach to phospholipid

Question 16

Importance of glycoproteins/glycolipids

Answer 16

1. Cell identification=allows body to work out which cell belongs to which
   -has specific shapes
   -act as antigens if carbohydrate chain is not recognised by cells
2. Cell adhesion=direct attachment to neighbouring cells
   -joining of cells creates matrix which provide structural support and formation of tissues
   3) receptors= act as receptors for hormones

Question 17

Role of cholesterol molecules

Answer 17

-Have a role in determining membrane fluidity which changes with temperature
-Interact with tails of phospholipid and act to stablise at higher temperatures and maintain flexibility at lower temp

Question 18

Fatty acid composition and fluidity

Answer 18

• saturated fatty acids (single bonds in hydrocarbon chain) are linear and allow dense arrangement of phospholipids
  -have higher melting point due to increased density and decreased viscosity
  -membrane is stronger and more able to remain effective at higher temps
  2. unsaturated fatty acids (1 plus double bond in hydrocarbon chain) bend resulting in kinks preventing close packaging.
  -Have lower melting point and viscosity increases

Question 19

Temperature and fatty acid composition

Answer 19

Low temps= high conc of unsaturated fatty acids maintains membrane fluidity
High temp=higher conc of saturated fatty acids increases stability of membranes

Question 20

cholesterol and temperature

Answer 20

higher temp= cholesterol reduced fluidity, increases melting point of phospholipid, resulting in stable membrane

low temps= cholesterol maintains fluidity of membrane and prevents crystallization of phospholipids

Question 21

what are vesicles

Answer 21

small membrane bound structures involved with transporting materials within a cell

Question 23

exocytosis

Answer 23

=the release of a large molecule from a cell
involves the fusion of a vesicle with the plasma membrane, releasing content outside of cell
-requires ATP

Question 24

endocytosis

Answer 24

=process my which large molecule enters cell

portion of plasma membrane is pinched off to enclose macromolecule within a vesicle in the cell
-pinching off involves a change in shape of membrane and vesicle enters cell
-end of membrane reattaches

Question 25

steps of protein exocytosis

Answer 25

1= protein produced by ribosomes of the rough ER enters lumen (inner space of RER) and packaged into vesicle
2= vesicle fuses with cis side of golgi apparatus
3=protein moves through golgi apparatus, modifies, exists on trans side
4=vesicle with protein inside moves and fuses with plasma membrane resulting in secretion of contents from cell

Question 26

gated ion channels

Answer 26

integral proteins which allow specific ions to pass through facilitated diffusion
-pore in ion channel is hyrdophobic
-two examples;
1) neurotransmitter gated ion channel
2) voltage gated ion channel

Question 27

nicotinic Ach receptors

Answer 27

example of neutrotransmitter gated ion channel

=integral proteins on neuron receiving message (acts as receptor and channel protein)

Question 28

steps of secretion of Ach in neurons

Answer 28

1) Ach formed in cytoplasm from acetyl and choline molecules
2) Ach packed into vesicles
3)when action potential arrives, presynaptic membrane depolarizes
3) voltage gates ca2 ion channels open during depolarization
4) ca2+ vesicle fuses with presynaptic membrane
5) Ach released into synaptic cleft where it diffuses across
6)Ach binds to Ach receptor (ligand gated sodium channel) with opens protein and lets ions in
7) sodium ions in causing depolarization
8) when Ach detaches, shape is changes
8) enzyme breaks down Ach and reabsorbed into presynapse

Question 29

voltage gated channels

Answer 29

open and close in response to changes in voltage across a membrane
example: sodium potassium channel

Question 30

sodium potassium channel

Answer 30

sodium channel opens, sodium ions move from outside to inside neuron. This depolarizes the membrane. Sodium channels close and potassium channels open. Potassium ions move from inside cell to outside cell and membrane return to normal potential.

Question 31

what do sodium-potassium pumps do

Answer 31

-actively transport sodium ions out of cell and potassium ions into cell, across conc. gradient
-maintains resting potential in neurons

Question 32

what is neurons resting potential

Answer 32

-70mV, when nerve impulse is not being transmitted

-maintained by sodium ions being outside of neuron and potassium neurons inside neuron

Question 33

septs of sodium-potassium pumps

Answer 33

1) three sodium ions attach to binding site of pump protein
2) ATP attached to the sodium potassium pump
3)ATP is hydrolyzed with phosphate group remaining attached to protein pump, ADP released
4)phosphate causes pump to change shape, moving sodium across axon membrane and releasing sodium outside axon
5)two potassium attach to potassium binding sited of pump protein
6)phosphate is released from pump
7) pump returns to original chape, moving potassium into axon

Question 34

what is indirect active transport

Answer 34

uses energy produced by movement of one molecule down a conc gradient to transport another molecule against conc gradient

Question 35

how glucose is transported from small intestine into epithelial cells

Answer 35

1) facilitated diffusion= glucose passively transported through glucose channels from small intestine into epithelial cells
2) sodium dependent glucose transporters= cotransport links the movement of ion down its conc gradient with the movement of glucose against its conc gradient

Question 36

steps in sodium-dependent glucose cotransporters

Answer 36

1) there are more sodium ions outside then inside intestinal cell
2) sodium ions and glucose molecules bind to transport protein
3)sodium ions pass through the carrier to the inside of the cell down a conc gradient, with the carrier capturing the energy released by movement
4)captured energy used to transport glucose molecules through the same protein into cell.

Question 37

cell adhesion

Answer 37

process in which cell uses extracellular matrix and cell adhesion molecules (CAM’s) to adhere to other cells. required for maintenance of tissues

Question 38

different types of cell junctions that CAM’s are used for

Answer 38

1) tight junction= forming seal between cells, preventing leaking
2) gap junctions= channels between cells that allow molecules to pass
3)adherens junctions=use protein complexed to adhere cells
4)desmosomes=use protein complexes to form strong connections between cells providing tissues with structure