Biological membranes Flashcards
(114 cards)
1
Q
membrane function
A
-separate contents of cells from their environment
- separate organelles from each other and cytosol
2
Q
compartmentalisation
A
formation of separate membrane bound areas in a cell
3
Q
why is compartmentalisation important
A
- metabolism
- containing reactions
4
Q
why is compartmentalisation needed for metabolism
A
as there are many different and often incompatible reactions happening in a cell
5
Q
why is compartmentalisation needed for containing reactions
A
- some reactions are only needed in some parts of the cell
- cell components need to be protected
- chemical gradients need to be contained
6
Q
plasma membrane
A
cell surface membrane which separates the cell from its external environment
7
Q
structure of plasma membrane
A
- membranes are formed from a phospholipid bilayer
8
Q
how does the phospholipid bilayer work in cell membranes
A
- hydrophilic phosphate heads form the inner and outer surface of a membrane
- this sandwiches the hydrophobic fatty acid tails that form a hydrophobic core inside the membrane
9
Q
why is only hydrophilic heads contacting water suitable for plasma membranes
A
- cells are usually in an aqueous environment and the inside of cells and organelles are usually aqueous so membranes are suited
10
Q
fluid mosaic model
A
phospholipids are free to move within the layer relative to each other giving membrane flexibility and because proteins embedded in the bilayer vary in shape size and position
11
Q
cell membrane components
A
- contain various proteins and lipids
12
Q
glycoprotien
A
branching carbohydrate protein
13
Q
glycoprotein function
A
regulates site for chemical reactions
14
Q
glycolipid function
A
acts as recognition site
15
Q
cholesterol function
A
for stability/flexibility
16
Q
types of protein in cell membranes
A
extrinsic protein
intrinsic protein
17
Q
extrinsic protein
A
partly embedded
18
Q
intrinsic protein
A
spans the whole phospholipid bilayer
19
Q
which direction to hydrophobic tails point
A
inwards
20
Q
what direction to hydrophilic heads point
A
outwards
21
Q
intrinsic protein structure
A
transmembrane proteins
embedded through both layers of membrane
have amino acids with hydrophobic R groups on their external surfaces which interact with hydrophobic core of membrane keeping them in place
22
Q
channel proteins
A
- provide a hydrophilic channel
- allows passive movement of polar molecules and ions down a concentration gradient through membranes
23
Q
how are channel proteins held in position
A
by interactions between hydrophobic core 0f membrane and hydrophobic R groups on outside of proteins
24
Q
carrier proteins
A
play role in passive and active transport
often involves protein shape changing
25
what type of protein is a glycoprotien
intrinsic
26
glycoprotein structure
embedded in cell surface membrane with attached carbohydrate chains
27
glycoprotein function
plays role in cell adhesion as receptors for chemical signals
28
chemical signalling
when a chemical binds to a receptor it elicits a response from the cell causing events inside the cell
29
e.g receptor for neurotransmitters
acetycholine at nerve cells
30
e.g receptor for peptide hormone
insulin
31
glycolipid strucure
lipids with an attached carbohydrate chains
32
glycolipid function
cell markers/antigens can be recognised by the cells immune system as self ( of the organisms) or non self (cells belonging to another organism)
33
extrinsic proteins structure
present on one side of the bilayer
normally have hydrophilic R group on their outer surface and interact with polar heads of phospholipids or with intrinsic proteins
34
cholesterol structure
lipid with hydrophilic and hydrophobic end
- positioned between phospholipids in a membrane bilayer :
- hydrophilic end interacts with heads
- hydrophobic end interacts with tail
this pulls them together
35
cholesterol function
regulates membrane fluidity
adds stability to membranes without making them rigid
prevent membranes being too solid by stopping phospholipid molecules grouping too closely
36
how could cell processes be disrupted in relation to membranes
- if membranes lose their structure they lose control of letting substances in and out of cells
37
what happens if temperature increases
- phospholipids have more kinetic energy
- move more
- membrane is more fluid and loses its structure
38
what happens if temperature continues to increase
cell will completely break down
39
what happens when a membrane loses its structure and becomes more permeable
it is easier for particles to cross it so carrier and channel proteins will denature so membrane permeability will be affected
40
what happens when organic solvents e.g alcohol mix with membranes
- they dissolve membranes disrupting cells
- this is why alcohol is used in antiseptic wipes
41
passive transport
utilises energy from natural movemnt particles instead of energy from another source
42
diffusion
net movement of particles from a high concentration to a low concentration
43
explain how diffusion is a passive process
- it continues until there is equilibrium and no concentration difference between the 2 areas
44
describe features of diffusion
- happens in a gas/liquid
- random movement
- over short distances diffusion is faster
45
why are cells ideal for diffusion
they are small
46
how does temperature affect diffusion
increased temperature
particles have more kinetic energy
more diffusion
47
how does concentration difference affect diffusion
greater concentration difference = steeper concentration gradient = more diffusion
48
simple diffusion
diffusion without a membrane/barrier
49
what does diffusion across membranes involve
passing through a phospholipid bilayer
if membrane is permeable to particles
50
can substances with a +/- charge easily pass through a membrane
no, as the hydrophobic interior of membranes repels these
51
can polar molecules with a partial +/- easily pass through
they can, but slowly and smaller polar molecules pass through more easily than big ones
52
what are membranes in term of permeability
only partially permeable
53
what is the rate at which molecules/ions diffuse across membranes affected by
- surface area (increased sa, increased diffusion
- membrane thickness (thicker membrane, less diffusion)
54
facilitated diffusion
diffusion across a membrane through a protein channel
55
how permeable are membranes with protein channels
they are selectively permeable
56
why are membranes with protein channels selectively permeable
they are often specific to 1 ion or molecule
57
how does facilitated diffusion also involve carrier proteins
they change shape when other molecules bind so external energy isn't required
58
what does diffusion of water into a solution do to the volume of that solution
increase its volume
59
if a solution is in a closed sytem and water has entered increasing its volume, what happens to pressure
it increases, this is hydrostatic pressure
60
if an animal cell is placed into a solution with a higher water potential than the cytoplasm what happens
water will move into the cell by osmosis and hydrostatic pressure increases
61
what happens if too much water moves into the animal cell via osmosis
cell bursts
62
what is cytosis
cell bursting
63
why does cytosis occur
cells have thin surfaces membranes and no cell walls so the membrane can't stretch and withstand the pressure
64
what happens if an animal cell is placed into a solution which has lower water potential than cytoplasm
it loses water to the solution via osmosis
65
what happens if cell loses too much water
crenation - cell surface membrane puckers
66
how do animal cells prevent cytosis/crenation
they have control mechanisms to make sure cells are continuously surrounded by aqueous solutions with equal water potential
67
can plants control water potential of fluid around them
no
68
what do cells help to support them
cellulose walls
69
when water enters plant cells by osmosis what does the increased hydrostatic pressure do ?
push the membrane against the cell wall - turgor
70
how does turgor pressure increase
as it resists entry of further water
71
when plants are placed in a solution with lower water potential what happens
water is lost from the cells by osmosis
72
what happens when plant cells lose water by osmosis
a reduction of volume in the cells cytoplasm which pulls the membrane away from the cell wall - plasmolysed
73
what does plasmolysis mean
the cell membrane pulls away from the cell wall
74
osmosis
diffusion of water from an area of high water potential to an area of low water potential across a semi permeable membrane
75
water potential
the pressure exerted by water molecules as they collide with a membrane or container
76
what is water potential measured in
pascals/kilopascals
77
what is the water potential of pure water
0 kpa
78
what is the highest possible water potential
0 kpa
79
what happens to the water potential value as the concentration of a solution increases
it becomes more negative
80
when will osmosis stop
when equilibrium is reached
81
active transport
movement of ions/molecules into or out of a cell from a region of lower concentration to a region of higher concentration
82
what does active transport require
energy
carrier proteins
83
why does active transport need energy
particles are going against the concentration gradient
84
how is the energy supplied for active transport
metabolic energy supplied by ATP
85
why are carrier proteins needed for active transport
they act as pumps
86
describe the process of active transport
1- molecule/ion being transported binds to receptors in channel of carrier proteins on the outside of the cell
2- on inside of cell ATP binds to carrier protein and is hydrolysed into ADP and phosphate
3- binding of the phosphate molecule to the carrier protein causes protein to open up the cell/ change shape
4- molecule/ion is released to inside of cell
5- phosphate molecule is released from carrier protein and recombines with ADP to form ATP
6- carrier protein returns to original shape
87
how is active transport selective
specific substances are transported by specific carrier proteins
88
bulk transport
form of active transport where large molecules are too big to travel through carrier / channel proteins
89
types of bulk transport
endocytosis
exocytosis
90
endocytosis
bulk transport of material into cell
91
what are the 2 types of endocytosis
phagocytosis
pinocytosis
92
what is phagocytosis for
solids
93
what is pinocytosis for
liquids
94
except for states, are there any differences between phagocytosis and pinocytosis
no
95
process bulk transport
- cell surface membrane invaginates when it comes into contact with the material to be transported
- membrane enfolds the material until membrane fuses forming a vesicle
- vesicle pinches off and moves into the cytoplasm to transfer the material for further processing within the cell
96
exocytosis
opposite of endocytosis
vesicles formed by golgi apparatus fuse with the cell surface membrane and the contents of the vesicle is released outside of the cell
97
what is needed to move the vesicles along the cytoskeleton to change cell shape, engulf materials e.t.c
ATP (energy)
98
why do people's behaviour change after drinking alcohol
- alcohol disrupts the membrane
- membrane becomes more permeable
- affects cells that need intact membranes
- when nerves are transmitted neural membranes are disrupted so nerve impulses don't transmit normally
99
how is glucose adapted to suit its function
- soluble/polar
- has chemical energy in its bonds/respiratory substrate
100
how does cholesterol bind to the cell surface membrane to complete its function
- it binds to the phospholipid fatty acid tails
- increasing the packing of the membrane
- reducing its fluidity
101
how are glucose and oxygen transported across the membrane
diffusion
102
does a membrane provide cell support - true or false
false
103
do water soluble or fat soluble molecules pass through the membrane by facilitated diffusion
water soluble
104
glucose can be reabsorebd by an active process which needs metabolic energy - what is this immediate source of energy
ATP
105
why can’t glucose pass through a cell membrane by simple diffusion
- phospholipids act as barrier
- glucose is too large
106
explain the role of the membrane in the rough endoplasmic reticulum
- compartmentalization
- separating proteins from cell cytoplasm
107
what 2 substances are needed to break down glycosidic bond in lactose
water
lactase
108
why may low pH affect membrane permeability
- changes tertiary structure of proteins
- membrane permeability increases
109
what molecules is ATP made up of
adenine
ribose
phosphate groups
110
fluid mosaic model - structure of membranes
- phospholipid bilayer
- hydrophilic heads face outwards
- fatty acid tails face inwards
- proteins are free to move within membrane
111
structure - rough er
- ribosomes attached to it
- phospholipid bilayer
- membrane is continuous with nuclear envelope
112
which macromolecule does a plant need nitrogen and phosphorus
dna
113
flooding of seawater damages crops, how would it affect water potential if soil
it would become more negative
114
