biological membranes

Question 1

roles of membranes

Answer 1

-partially permeable barrier
-compartmentalisation
-site of chemical reactions
-sites of cell communication
-controls entry + exit of substances

Question 2

what does the plasma membrane consist of?

Answer 2

-phospholipid bilayer
-glycoproteins
-glycolipids
-cholesterol
-intrinsic proteins
-extrinsic proteins

Question 3

why is it called the fluid mosaic model?

Answer 3

-fluid because phospholipids are constantly moving
-looks mosaic due to different sizes and shapes of proteins embedded in it

Question 4

role of phospholipids in the plasma membrane

Answer 4

-form a bilayer (hydrophilic head, hydrophobic tail) providing selective permeability, flexibility and acts as a barrier

Question 5

role of cholesterol in the plasma membrane

Answer 5

-lipid w/ hydrophilic and hydrophobic end
-regulates cell membrane / fluidity
-positioned between phospholipids pulling its hydrophilic end and the hydrophobic tail together, adding stability
-prevents membranes becoming too solid by stopping phospholipid molecules from grouping too closely and crystallising

Question 6

what is a glycoprotein and whats its role

Answer 6

-the branched carbohydrate attached to a protein
-acts as a receptor for chemicals, eg hormones
-play a role in cell adhesion

Question 7

how does cell signalling work and give examples

Answer 7

-a chemical (hormones or drugs) binds to a receptor, eliciting a response from the cell
eg) - receptors for neurotransmitters at nerve cell synapses, triggering/preventing an impulse in the next neurone
-receptors for peptide hormones, eg insulin/glucagon, affecting the uptake and storage of glucose by cells

Question 8

what are intrinsic/integral proteins

Answer 8

-transmembrane proteins embedded through both layers of the membrane.
-have amino acids w/ hydrophobic R groups on their external surfaces which interact with the hydrophobic core of the membrane, keeping them in place

Question 9

what are channel proteins

Answer 9

-an intrinsic protein
-provide a hydrophilic channel allowing passive movement of polar molecules+ions through membranes down concentration gradient
-held in place by interactions between hydrophobic R groups on the outside of proteins and hydrophobic core of membrane

Question 10

what are carrier proteins

Answer 10

-an intrinsic protein
-play a role in passive + active transport into cells
-often involves shape of the protein changing

Question 11

what is a glycolipid and whats its role

Answer 11

-the branched carbohydrate attached to a lipid molecule
-acts as a recognition site (cell markers or antigens)
-can be recognised by the cell immune system as self or non-self

Question 12

what are extrinsic/peripheral proteins

Answer 12

-present in one side of the bilayer
-normally have hydrophilic R-groups on outer surface + interact with polar heads of phospholipids or with intrinsic proteins
-can be present in each layer, some even move between the two

Question 13

what are the 2 main factors affecting membrane structure

Answer 13

-temperature
-solvents

Question 14

explain the effect of temperature on the plasma membrane

Answer 14

1- membrane is pierced, very permeable due to poking covalent bonds
2- increase in energy provides channel and carrier proteins to transport molecules faster so permeability increases

Question 15

explain the effect of solvents on the plasma membrane

Answer 15

-phospholipids dissolve in solvent, causing membrane to become more fluid
-this disrupts the structure of the cell membrane to make it more permeable
-increasing concentration of solvent will increase permeability of membrane

Question 16

what is simple diffusion

Answer 16

some molecules diffusing directly through the cell membrane because theyre small and non polar. passive process along concentration gradient

Question 17

what is facilitated diffusion

Answer 17

passive process where large / polar molecules cross the cell membrane via highly specific channel or carrier proteins

Question 18

factors affecting rate of diffusion

Answer 18

-temperature
-thickness of membrane
-concentration gradient
-surface area
-number of molecules

Question 19

what is active transport

Answer 19

an active process of molecules moving across the membrane against the concentration gradient requiring energy in the form of ATP

Question 20

how does ATP facilitate active transport

Answer 20

-ATP binds to carrier protein
-hydrolyses into ADP and Pi
-carrier protein changes shape and released molecule
-Pi released from carrier protein so returns to its original shape

Question 21

factors affecting rate of active transport

Answer 21

1-temperature
2-thickness of membrane
3-number of carrier proteins
4-rate of respiration

Question 22

what is bulk transport

Answer 22

large molecules like enzymes or hormones cant fit into channel or carrier proteins so undergo bulk transport, eg endocytosis or exocytosis (active processes)

Question 23

give examples of exocytosis and endocytosis

Answer 23

exocytosis - vesicles fusing to membrane
endocytosis - phagocytosis or pinocytosis

Question 24

define phagocytosis and pinocytosis

Answer 24

phagocytosis is the uptake of solid material
pinocytosis is the uptake of liquid material

Question 25

what is osmosis

Answer 25

the passive movement of water particles from an area of high water potential to low water potential up the concentration gradient across a partially permeable membrane

Question 26

define a hypotonic, isotonic and hypertonic solution

Answer 26

hypotonic - higher water potential in the solution than the cell isotonic - equal water potential in solution and cell hypertonic - lower water potential in the solution than the cell

Question 27

what happens to an animal cell in hypotonic solution

Answer 27

- water moves into cell - cell swells and bursts ( osmotic lysis )

Question 28

what happens to animal and plant cells in isotonic solution

Answer 28

- no water movement - cell stays the same size

Question 29

what happens to an animal cell in hypertonic solution

Answer 29

- water moves out the cell - cell shrinks

Question 30

what happens to a plant cell in hypotonic solution

Answer 30

- water moves into cell - cell swells and becomes turgid

Question 31

what happens to plant cells in hypertonic solution

Answer 31

- water moves out of cell - cell shrinks and becomes plasmolysed

Question 32

factors affecting rate of osmosis

Answer 32

1- temperature 2- water potential gradient 3- thickness of membrane 4- surface area

Question 33

what is water potential measured in and what is it of water

Answer 33

kPA waters is 0