2.1.5 Biological membranes Flashcards
1
Q
what is compartmentalisation
A
- the formation of separate membrane-bound areas in a cell
2
Q
what is the plasma membrane
A
- the cells surface membrane which separates the cell from its external environment
3
Q
what are membranes formed from
A
- a phospholipid bilayer
4
Q
what are some types of membranes a cell can have
A
- plasma membrane
- tonoplast (around vacuole)
- mitochondrial membrane (outer + inner)
- chloroplast membrane (outer + inner)
- nuclear membrane / envelope
5
Q
why is compartmentalisation vital to cells
A
- metabolism includes many different + often incompatible reactions
- containing reactions in separate parts of cells allows specific condition required for cellular reactions
6
Q
describe what makes up the phospholipid (the components)
A
- phosphate group attached to glycerol by one phosphoester bond
- 2 fatty acids attached to glycerol by 2 ester bonds
- consists of hydrophilic head + hydrophobic tail
7
Q
what functions do membranes have
A
- partially permeable, controlling what passes through
- involved in cell signaling (communication between cells)
- provide attachment sites for enzymes + other molecules involved in metabolism
- allow electrical signals to pass along them
- produce different compartments inside cells
8
Q
what is a phospholipid bilayer
A
- polar hydrophilic phosphate group face aqueous solutions
- non-polar hydrophobic fatty acids move away from aqueous environments
- tissue fluid + cytoplasm aqueous so phospholipids form two layers with hydrophobic tails facing inwards + phosphate groups facing outwards
9
Q
what is the fluid mosaic model
A
- phospholipids are free to move within the layer relative to each other (they are fluid)
> gives the membrane flexibility - proteins embedded in bilayer vary in shape, size and position (like tiles of mosaic)
10
Q
what are the two types of membrane proteins on cell surface membrane
A
- intrinsic (integral)
- extrinsic (peripheral)
11
Q
what are intrinsic proteins
A
- transmembrane proteins that are embedded through both layers of a membrane
12
Q
how are intrinsic proteins kept in place
A
- they have amino acids with hydrophobic R-groups on their external surfaces, which interact with hydrophobic core of the membrane and keep them in place
13
Q
what are extrinsic proteins
A
- present in one side of the bilayer
> can be present in either layer and some move between layer
14
Q
what do extrinsic proteins have that allow them to move
A
- hydrophilic R-groups on their outer surfaces and interact with polar heads of phospholipids or intrinsic proteins
15
Q
name the two intrinsic proteins that are involved in transport across the membrane
A
- channel proteins
- carrier proteins
16
Q
what do channel proteins do + have
A
- provide hydrophilic channel allowing passive movement (diffusion) of polar molecules and ions down a conc gradient through membranes
17
Q
what do carrier proteins do
A
- important roles in active and passive transport into cells
> often involves protein shape changing
18
Q
what are glycoproteins example of
A
- intrinsic proteins
19
Q
where are glycoproteins found
A
- embedded in cell surface membrane with attached carbohydrate (sugar) chains of varying lengths and shapes
20
Q
what is the role of glycoproteins
A
- cell adhesion
> (cells joining to form tight junctions in certain tissues) - act as receptors for chemical signals
21
Q
what is cell signaling or cell communication
A
- when chemical binds to receptors, it triggers a response from the cell
- this can set off a series of event inside the cell
22
Q
what are glycolipids
A
- lipids with carbohydrate (sugar) chains
23
Q
what are glycolipids also called
A
- cell markers or antigen
> can be recognised by cells of immune system as self or non-self
24
Q
what is cholesterol
A
- lipid with hydrophilic end + hydrophobic end
- regulates fluidity of membranes
25
where is cholesterol found in plasma membrane
- positioned between phospholipids in a membrane bilayer with hydrophilic end interacting with heads + hydrophobic interacting with tails
> pulls them closer together
26
what is the role of cholesterol in plasma membrane
- prevent membrane becoming too solid
> by stopping phospholipid molecules from grouping too closely + crystallising
27
what are some functions of membrane bound proteins
- receptors
- enzymes
- structural (attached to microtubules)
28
what are the 4 types of cell signalling
- paracrine
- synaptic
- endocrine
- autocrine
29
what is paracrine signalling
- releases chemicals near them (locally)
30
what is synaptic signaling
- nerve signaling near them
> signal goes along nerve cell + transmitted across synapse
31
what is endocrine signalling
- long distance hormonal signaling
32
what is autocrine signaling
- cell releases signals to target itself or cells of the same type
33
what is the stimuli / signal
- the message molecule sent out
34
what is the most common type of signal
- hormones (endocrine)
35
to detect signals what must cells have
- sensors called receptors (often proteins)
36
what happens to polar + non polar signals through plasma membrane
- polar signal binds to membrane bound receptors (intrinsic proteins) on plasma membrane
- non polar signals diffuse directly through membrane (phospholipid bilayer) + bind to intracellular receptors
37
what are the main steps in cell signaling
- stimuli: detects change + what cell responding to
- receptors: on surface of cells + signals bind to it, usually glycoproteins
- transducers: bring signal from outside to inside cell
- amplifiers: increase intensity of signal
- intracellular response: outcome of response to signal
38
what are hormones
- chemical messengers transported in blood
39
what are target cells
- any cell with a receptor for a specific hormone
40
where is insulin released from + why
- released from beta cells in pancreas
- released in response to high blood glucose levels
41
how does insulin lead to increase in glucose uptake in cells
- insulin released + attaches to glycocalyx of cells such as muscle/liver where most glucose stored
- when bind, signal sent through cell + allows vesicle containing glucose channels to fuse with plasma membrane causing them to be released
- now more glucose channels + more glucose can be taken from blood and into cells where they're stored in form of glycogen
> reduces blood glucose levels
- now insulin reduces causing membrane to pinch of vesicle so glucose channels decrease as blood sugar levels back to normal
42
how does increase in temperature affect membrane structure
- temp inc leads to phospholipids to have more kinetic energy + move more
- membrane now more fluid + begin to lose structure
- if temp continues to inc, the cell will eventually break down completely
43
how does increase in temperature affect membrane permeability
- loss of structure inc permeability of membrane
> easier for particles to cross
44
what happens to carrier + channel proteins as temp increases
- denature at higher temps
> these proteins involved in transport across membrane so as they denature, the membrane permeability will be affected
45
how do polar solvents affect the structure of membranes
- they dissolve the membranes, as polar solvents interact with charged phosphate heads
> e.g. strong con of alcohol destroy cells in body
46
how do non-polar solvents affect the structure + permeability of membranes
- non-polar molecules enter cell membrane + presence of these between phospholipids disrupts membrane
- when membrane disrupted, it becomes more fluid and permeable
47
what is diffusion
- the net movement of particles from a region of higher conc to a region of lower conc
48
what type of process is diffusion
- passive
49
why does diffusion happen
- particles have kinetic energy + random movement + unequal distribution of particles will eventually spread to become equal
50
what factors affect diffusion
- temp (higher = faster rate)
- conc difference (greater conc diff = faster rate)
> overall movement from high to low conc is larger
51
when can diffusion across membranes happen
- if membrane is permeable to particle
> non-polar molecules diffuse freely through down con gradient
52
can charged particles diffuse through membrane
- very small charged particles like water + small ions can diffuse through but at very slow rate
53
how does SA affect rate of diffusion across membrane
- larger area of exchange surface = higher rate
54
how does thickness of membrane affect diffusion
- thinner the exchange surface = higher rate
55
what is facilitated diffusion
- diffusion across a membrane through protein channels
56
what does it mean that membranes with protein channels are selectively permeable
- most of the protein channels are specific to one molecule or ion
> so only let them through
57
facilitated diffusion can also involve carrier proteins, how does this work
- carrier proteins change shape when a specific molecule binds
> movement of molecules down conc gradient
> no ATP required to change shape of protein, the collision of the molecule to the protein causes the shape to change
58
when does net diffusion stop
- when there is a concentration equilibrium between both regions
59
list the key factors affecting rate of diffusion
- temp
- conc gradient
- SA
- thickness
- number of protein channels
60
what is active transport
- movement of molecules or ions into/out of a cell from a region of lower conc to higher conc
61
what type of process is active transport
- active
> requires energy and carrier proteins
62
why does active transport need energy
- particles are being moved up a conc gradient
63
what is the role of carrier proteins in active transport
- they span the membrane + act as pumps
64
describe the steps in active transport
- molecule/ion to transport binds to receptors in channel of carrier protein on outside of cell
- inside cell the ATP binds to carrier protein causing protein to change shape - opens up inside of cell
- molecule/ion released to inside of cell
- phosphate molecule released from carrier protein + recombines with ADP to from ATP
- carrier proteins return to its original shape
65
what is bulk transport
- its a form of active transport
- large molecules are too big to move through channel or carrier proteins so they are moved in/out of cell by bulk transport
66
what is endocytosis
- bulk transport of material into cells
67
what are the two types of endocytosis
- phagocytosis: cell engulfing solid matter
- pinocytosis: cell ingesting liquids
68
describe the process / steps of endocytosis
- cell surface membrane invaginates (bends inward) when comes into contact with material to be transported
- membrane enfolds the material until membrane fuses, forming vesicle
- vesicle pinches off + moves into cytoplasm to transfer material for further processing within cell
69
what is exocytosis
- vesicles, formed by Golgi apparatus, move towards + fuse with cell surface membrane
- contents of vesicle are then released outside of cell
70
why is energy needed for bulk transport
- energy used to form vesicle + to move them along the cytoskeleton
71
why do cells performing active transport contain many mitochondria
- they release energy in form of ATP during aerobic respiration
72
what is osmosis
- net movement of water molecules from an area of high water potential to an area of low water potential, across a partially permeable membrane
73
what is a solute
- substance dissolved in a solvent (e.g. water), forming a solution
74
what is water potential
- the pressure exerted by water molecules as they collide with a membrane of container
> measured in units of pressure pascals (Pa) or kilopascals (kPa)
75
what is the water potential of pure water
- 0 kPa (at standard temp -25C and atmospheric pressure 100kPa
76
how does water potential change as solute conc changes
- the more conc the solution, the more negative the water potential
77
what is hydrostatic pressure
- if a solution of high volume is in a closed system, it results in inc pressure + expansion
> this pressure is called hydrostatic pressure
78
what is cell lysis
- when cell placed in solution of higher wp + water molecules move in by osmosis, so inc hydrostatic pressure too much
> cell bursts when too much pressure + no cell wall
79
what is the effect on an animal cell when it is placed in higher wp
- cytolysis
80
what is the effect on an animal cell when it is placed in lower wp
- crenation
81
what is the effect on a plant cell when it is placed in higher wp
- turgor
82
what is the effect on a plant cell called when it is placed in lower wp
- plasmolysis
83
what is osmotic pressure
- when water moves from high to low wp, water is pulled into it by osmosis
> the pull is referred to as osmotic pressure - pulling pressure
84
what is incipient plasmolysis
- the point at which a plant cell membrane begins to move away from the cell wall
