B2.1 Membranes

Question 1

what are cell membranes made of

Answer 1

phospholipids in a bilayer

Question 2

what is the structure of phospholipids and how do they react to water

Answer 2

they have a hydrophilic head that points outwards, and a hydrophobic tail( made of fatty acids) which move away from water

Question 3

why is the plasma membrane fluid

Answer 3

because the phospholipids dont have bonds and are held together through attraction

Question 4

what is the function of the phospholipid bilayer

Answer 4

they create a strong, stable barrier between aqueous solutions that allow substances to leave or enter the cell

Question 5

what is diffusion

Answer 5

the passive movement of particles from a higher to lower concentration, down a concentration gradient, using kinetic energy of the molecules

Question 6

when does diffusion across the cell membrane occur

Answer 6

the plasma membrane is fully permeable to the solute.
The lipid bilayer is permeable to non polar substances

Question 7

what are peripheral proteins

Answer 7

proteins attached to the outer surface of the bilayer or the inner surface

Question 8

functions of peripheral proteins

Answer 8

shuttles between integral proteins
scaffold proteins that hold shape
receptors for extra cellular signals

Question 9

what are integral proteins

Answer 9

proteins embedded in one or both layers of the membrane.
They can act as channels, receptors or antigens

Question 10

what is osmosis

Answer 10

the diffusion of water molecules across a membrane that is permeable to water(partially permeable) down a concentration gradient

Question 11

what happens to dissolved substances in water

Answer 11

they attract a group of polar water molecules around it

Question 12

what happens when the solution is more concentrated( in terms of water potential)

Answer 12

the greater the number of water molecules that are held almost stationary

Question 13

what are aquaporins

Answer 13

a water channel pore in a membrane that allow water to diffuse through the plasma membrane
is a protein

Question 14

what is facilitated diffusion

Answer 14

particles of a substance that cannot diffuse across the plasma membrane are helped across the membrane by integral proteins that span the membrane

Question 15

is facilitated diffusion passive or active

Answer 15

passive diffusion

Question 16

what do channel proteins transport

Answer 16

through facilitated diffusion, they provide hydrophilic channels for polar and charged molecules to pass through,
only specific charged particles

Question 17

what is active transport

Answer 17

movement of particles from lower to higher concentration, using energy from ATP that has been created during respiration

Question 18

How is active transport facilitated

Answer 18

through carrier proteins

Question 19

what are pump proteins

Answer 19

used for active transport across membranes that is used selectively to move one or two specific substances across

Question 20

characteristic features of active transport

Answer 20

occurs against a concentration gradient
active uptake is highly selective
involves pump molecules

Question 21

How is permeability determined in the case of simple diffusion

Answer 21

not selective and depends only on the size and hydrophilic or hydrophobic properties

Question 22

what creates selective permeability in membranes

Answer 22

facilitated diffusion and active transport

Question 23

what cannot pass through the hydrophobic interior of membranes

Answer 23

Large polar molecules or charged molecules

Question 24

What are glycoproteins and glycolipids

Answer 24

carbohydrates that are on the surface of the plasma membrane which are attached to proteins or lipids

Question 25

what is the glycocalyx

Answer 25

glycoproteins and glycolipids together

Question 26

what do carbohydrates do in membranes

Answer 26

help with cell recognition and cell adhesion highly hydrophilic and attracts large amounts of watedr

Question 27

Explain fluid mosaic model of membrane structure

Answer 27

described as fluid because the components are on the move mosaic because the proteins are scattered about in patterns

Question 28

what is the effect of unsaturated fatty acids on the phospholipid bilayer

Answer 28

because unsaturated fatty acids have lower melting points, an excess makes the membrane more fluid

Question 29

what do saturated fatty acids do to the phospholipid bilayer

Answer 29

they make the membrane stronger at higher temperatures

Question 30

why must membranes be sufficiently fluid

Answer 30

they must be fluid for proteins to move around and function

Question 31

what does a decrease in temperature lead to in the membrane

Answer 31

temperature falling leads to less fluidity and the membrane can even solidify

Question 32

what is homeo-viscous adaptation

Answer 32

adaptation that allows some organisms to vary the balance between saturated and unsaturated fatty acids in response to ambient temperatures

Question 33

what is the structure of cholesterol

Answer 33

a steroid, made of hydrophilic hydroxyl and hydrophobic hydrocarbon on either side of a carbon ring

Question 34

what is the role of cholesterol in the phospholipid bilayer

Answer 34

stabilises the membrane at higher temperatures and prevents stiffening at lower temperatures has the effect of disturbing the packing of the phospholipids, increasing the flexibility of the membrane

Question 35

what does cholesterol do to the bilayer in low temperatures

Answer 35

maintains the fluidity of the membrane by forcing apart the phospholipids and maintaining distance between them

Question 36

what does cholesterol do to the bilayer in high temperatures

Answer 36

bonds between the cholesterol and phospholipids maintain the structural integrity of the membrane and prevent them from becoming too fluid

Question 37

what is uptake into a cell called

Answer 37

endocytosis

Question 38

what is export out of a cell called

Answer 38

exocytosis

Question 39

How is endocytosis done

Answer 39

through the formation of vesicles as the plasma membrane pinches inwards, taking material into cell

Question 40

how is exocytosis done

Answer 40

vesicles fuse with the membrane and material is exported

Question 41

what is phagocytosis

Answer 41

bulk transport of solid matter being taken in

Question 42

what is pinocytosis

Answer 42

the bulk transport of fluids

Question 43

how are nerve impulses transmitted along the axon of a nerve cell

Answer 43

through momentary reversal in electric potential difference in the membrane , brought by rapid movements of sodium and potassium ions

Question 44

what are voltage gated channels/gated ion channels

Answer 44

channel proteins that are exclusively permeable for one type of ion

Question 45

what is a neurotransmitter gated ion channel

Answer 45

opens temporarily when a specific neurotransmitter bonds with it

Question 46

steps of a voltage gated channel

Answer 46

When theres a stimulus, sodium channels open and let sodium in The interior of axon depolarises, nerve pulse initiated more positive charge leads to more potassium channels open, sodium channels close potassium ions exit down the axon down an electrochemical gradient interior becomes less positive, so potassium channels close through 'ball and chain' protein when there is more positive charge outside, the channel returns to fully closed

Question 47

what are exchange transporters

Answer 47

used in active transport of sodium and potassium ions used to help generate membrane potentials

Question 48

what are the steps in exchange transporters

Answer 48

3 sodium ions loaded into binding sities ATP reactions cause pump proteins to close to the interior and open to the exterior 3 sodium ions released and 2 potassium ions loaded reversal of shape of pump protein and potassium ions are released

Question 49

what is indirect active transport

Answer 49

cotransporters move sodium in one direction and move glucose as well

Question 50

example of indirect active transport( glucose and sodium)

Answer 50

2 sodium ions moved for each glucose

Question 51

what is movement of sodium in terms of cotransporter protein

Answer 51

build up of concentration gradient allowing sodium to enter cotransporter protein down its concentration gradient

Question 52

what is the result of indirect active transport in terms of glucose

Answer 52

allows glucose to be transferred against it concentration gradient

Question 53

what are Cell Adhesion molecules and where are they located

Answer 53

they help maintain tissue structure/function, and help glue cells together located on the cell surface

Question 54

What is the Extra-Cellular Matrix

Answer 54

a network of proteins and molecules that surround, support and give structure to cells and tissues

Question 55

How are CAM's related to ECM

Answer 55

some are used to bind cells to the ECM, forming a cohesive unit

Question 56

what proteins are used for cell-cell junction

Answer 56

cadherin proteins

Question 57

what proteins are used for cell-ECM junctions

Answer 57

done through integrin proteins

Question 58

what are the 4 types of cell junctions

Answer 58

anchoring junctions( strengthens contact) tight junctions (seal gaps between cells) gap junctions (links cytoplasm) signal relaying junctions ( synapses)