ch 3 and 4 memb and transport

Question 1

cell membrane structure

Answer 1

• trilaminar app
  -7 nm width
  the dark layers are phospholipids heads and light are fatty acids tail

Question 2

fluid mosaic (2 marks)

Answer 2

‘Fluid’ refers to the movement of phospholipids while ‘mosaic’ (constant motion) refers to the scattered proteins (and glycoproteins) in the phospholipid bilayer

Question 3

effect of tail length on membrane fluidity

Answer 3

longer the tail, the less fluid the membrane

Question 4

Effect of fatty acid composition on membrane fluidity

Answer 4

the more unsaturated they are, the more fluid the membrane. This is as unsaturated fatty acid tails are bent and fit together more loosely

Question 5

Cholesterol

Answer 5

• Regulates the fluidity of membrane
• At low temperatures, cholesterol increases the fluidity of the membrane preventing it from being too rigid, this is because it prevents close packing of phospholipid tails
• At high temperatures, cholesterol decreases the fluidity of membrane and stabilises the cell

found in animal imp as leakage of ions will slow down nerve impulses

Question 6

glycolipids and glycoproteins

Answer 6

carbohydrate chains projecting out of lipids+proteins-

• Stabilises the membrane structure by forming hydrogen bonds with water molecules surrounding the cell
• Glycocalyx - sugary cell coating formed by carbohydrate chains
• Act as receptor molecules: (Signalling receptors - recognise messenger molecules like hormones and neurotransmitters; Endocytosis - bind to molecule to be engulfed by membrane)
• Act as cell markers/antigens allowing cell-cell recognition

Question 7

channel proteins

Answer 7

• do not require energy
• transport substances through membrane passively, along their concentration gradient
• used for both active transport and facilitated diffusion

Question 8

cell signaling cascade

Answer 8

1. signal arrives at protein receptor in cell membrane
2. the receptor’s shape is complementary to the ligand
3. the signal brings about a change in the receptor’s shape
4. changing the shape of the receptor allows it to interact with the next component of the pathway so the message gets transmitted
5. binding triggers/stimulates reactions within the cell
6. cell signalling results in a response which may be intracellular or extracellular

Question 9

carrier proteins

Answer 9

• require energy
• go against the concentration gradient
• take substances from outside and pumps it inside or vice versa
• used for active transport

Question 10

diffusion

Answer 10

Net movement of non polar molecules or ions from a region of higher concentration to a region of lower concentration down a gradient, as the result of the random movement of particles

Question 11

facilitated diffusion

Answer 11

• Diffusion of a substance (polar mol) through transport proteins in a cell surface membrane
• The proteins provide hydrophilic areas that allow the molecules or ions to pass through the membrane which can fit and bind to it so they change shape this process require no extra energy from resp

Question 12

Osmosis

Answer 12

Net movement of water molecules from a region of higher water potential to a region of lower water molecules (dipolar) potential through a partially permeable membrane as a result of their random motion (most by aquaporins because it has hydrophilic lining)

Question 13

The membrane surrounding the vacuole, called the tonoplast, has a fluid mosaic structure. Describe the structure of this membrane. 4M

Answer 13

1) phospholipid bilayer
2) phospholipids have hydrophilic heads and hydrophobic tails
3) labile nature of bilayer structure is due to phospholipids moving within their monolayer
4) protein molecules, interspersed / scattered / not a complete layer
5) many different protein molecules present
6) idea of most proteins moving / not in fixed position

Question 14

uniport

Answer 14

pump ones kind of ions into or out cell

Question 15

Endocytosis

Answer 15

Bulk movement of liquids (pinocytosis) or solids (phagocytosis) into a cell by the infolding of the cell membrane to form vesicles containing the substance

Question 16

Exocytosis

Answer 16

Bulk movement of liquids or solids out of a cell by the fusion of vesicles containing the substance with the cell surface membrane guided by cytoskeleton using atp

Question 17

phospholipid molecules

Answer 17

phospholipid molecules have hydrophilic heads which face water and hydrogen bond and hydrophobic tails which repel water.by this the phospholipid molecules arrange themselves tail to tail to form a phospholipid bilayer with hydrophobic core

Question 18

why cells need cholesterol

Answer 18

1) for membrane stability
2) regulating fluidity of membrane
3) production of steroid hormones

Question 19

carbohydrates

Answer 19

attached to protein molecule in the cell surface membrane forming glycoproteins,& to lipids forming glycolipids. they point outwards. glycoproteins & glycolipids are also known as glycocalyx

Question 20

Aquaporin

Answer 20

to increase permeability of membrane to water for more abs of water

Question 21

protein function

Answer 21

act as enzyme
anchors the cytoskeleton

Question 22

cotransport

Answer 22

pumps one kind in and another kind out at the same time
pumps two diff mol across memb at same time

Question 23

what increases fluidity of the cell membrane?

Answer 23

-shorter the length of the fatty acid tails the more fluidity
-the Prescence of many unsaturated fatty acid the more fluidity
-the more cholesterol the more fluidity

Question 24

there are 4 ways through which charged practicles can move

Answer 24

-simple diffusion and osmosis
-active transport
-facilitated diffusion
-cytosis

Question 25

explain how CO2 be excreted from the body

Answer 25

CO2 diffuses through phospholipid bilayer of endothelial cell membrane of capillaries and alveolar epithelial cell memb down conc gradient

Question 26

carbohydrates

Answer 26

attached to protein mol in the cell surface membrane forming glycoprotein and lipids forming glycolipids, they point outwards, glycoproteins and glycolipids are also known as glycocalyx

Question 26

active transport

Answer 26

movement of polar mol through specific protein transporters “carriers” with complementary vinding site, fit and bind to them changing it shape “conformational change” to pass across the phospholipid bilayer against concentration gradient using ATP

Question 27

explain what disrupts the permeability cell membrane

Answer 27

alcohol: dissolves the hydrophobic core of the phospholipid bilayer

temp: it increases the KE of phospholipids molecules increasing the fluidity and breaks down the hydrogen and ionic bonds on the protein mol held in the cell surface membrane changing it shape and specificity
acids: changing the PH breaks down the ionic bonds of protein molecules held in the membrane changing it3D shape and specificity
reducing agents: break down the disulfide bonds of protein molecule

Question 28

explain why glucose cant pass through phoph bilayer

Answer 28

large in size
glucose is polar and water soluble and cant pass through hydrophobic core

Question 29

protein structure

Answer 29

-intrinsic (span whole protein)
-extrinsic (partial)
-peripheral

Question 30

role of cell surface membrane

Answer 30

act as barrier between cytoplasm and ext env
cell to cell adhesion
cell recognition
flexibility of the cell
anchors to cytoskeleton
has specific receptors for hormones
sites for enzyme to catalyze rxns
formation of hydrogen bonds with water mol for stability of the memb