Biological Membranes Flashcards
1
Q
what is a plasma membrane?
A
a membrane at the cell surface
2
Q
what is the function of a plasma membrane?
A
- they create a barrier between the cell and its environment
- they control which substances enter and leave the cell by being partially permeable (only letting some molecules through)
- they allow substances to move across via diffusion, osmosis or active transport
- they allow recognition by other cells and cell communication/signaling
3
Q
what is an intracellular membrane?
A
internal membranes within cells
4
Q
what is the function of an intracellular membranes?
A
- they divide the cell into different compartments
- they act as a barrier between the organelle and the cytoplasm
- they can form vesicles to transport substances (e.g. proteins) between different areas of the cell
- they control which substances enter and leave the organelle by being partially permeable
- they can be the sight of chemical reactions
5
Q
what is an advantage of intracellular membranes dividing cells into different compartments?
A
it makes different functions of the cell more efficient (e.g. the substances needed for respiration, like enzymes, are kept inside mitochondria by its outer membrane)
6
Q
what feature of an intracellular membrane can make chemical reactions more efficient?
A
if it is folded - this increases its surface area, increasing the efficiency of chemical reactions
(e.g. the inner membrane of a mitochondria is folded to make respiration more efficient)
7
Q
what is the function of membranes within organelles?
A
they act as barriers between the membrane contents and the rest of the organelle
(e.g. thylakoid membranes within chloroplasts keep the components needed for photosynthesis together)
8
Q
what is model used to describe the arrangement of molecules in a membrane?
A
fluid mosaic model of membranes
9
Q
why is it called the fluid mosaic model?
A
- ‘fluid’ - the phospholipids are constantly moving (mainly sideways within their own layer)
- ‘mosaic’ - the scattered proteins through the bilayer are like tiles in a mosaic
10
Q
what is the structure of the fluid mosaic model?
A
- it is a continuous double layer (bilayer) of phospholipid molecules
- some proteins have a carbohydrate attached (glycoproteins)
- some lipids have a carbohydrate attached (glycolipids)
- cholesterol molecules are also present within the bilayer
11
Q
draw a diagram of the fluid mosaic model
A
p117
12
Q
draw a diagram of the phospholipid bilayer
A
(include head and tail of phospholipid)
13
Q
what are the 5 main components of most membranes?
A
- phospholipids
- cholesterol
- proteins
- glycolipids
- glycoproteins
14
Q
what is the structure of a phospholipid?
A
each phospholipid is made up of a:
- non-polar, hydrophobic tail that faces inwards
- polar, hydrophilic head that faces outwards
therefore, they automatically arrange themselves into a bilayer
15
Q
what does hydrophobic mean?
A
repels water
16
Q
what does hydrophilic mean?
A
attracts water
17
Q
what is the role of a phospholipid?
A
- they form a barrier to dissolved (water-soluble) substances due to the hydrophobic tails preventing polar molecules or ions from passing across the membrane
- this ensures water soluble molecules (e.g. sugars, amino acids, proteins) cannot leak of the cell
- it allows fat-soluble substances (e.g. fat-soluble vitamins) to dissolve in the bilayer and pass directly through the membrane
18
Q
what is cholesterol?
A
a type of lipid that is present in all cell membranes (expect bacteria’s)
19
Q
where is cholesterol within the phospholipid bilayer?
A
- cholesterol molecules fit between the phospholipids
- they do this by binding to their hydrophobic tails
- this causes them to pack more closely
20
Q
what is the role of cholesterol?
A
- it gives the membrane stability
- it can create a further barrier to polar substances moving through the membrane due to it having hydrophobic regions
- it helps the cells survive through temperature changes by adjusting how fluid/rigid the membrane is by altering how closely packed together the phospholipids are (fluidity increases at lower temperatures)
21
Q
how does cholesterol give the membrane stability?
A
- cholesterol molecules fit between the phospholipids by binding to their hydrophobic tails
- this causes them to pack more closely, making the membrane less fluid and more rigid
22
Q
what is the role of a protein?
A
- they control what enters and leaves the cell
- they act as receptors for molecules (e.g. hormones) in cell signaling (when a molecule binds to the protein, a chemical reaction is triggered inside the cell)
23
Q
what are the 2 types of proteins within membranes?
A
- channel proteins
- carrier proteins
24
Q
what is a glycolipids?
A
a lipid with a carbohydrate attached
25
what is a glycoprotein?
a protein with a carbohydrate attached
26
what is the role of glycolipids and glycoproteins?
- they stabilize the membrane by forming hydrogen bonds with surrounding water molecules
- they act as receptors for messenger molecules in cell signaling
- they are sites where drugs, hormones and antibodies bind
- they are antigens (cell surface molecules involved in self-recognition and the immune response)
27
what are the 2 factors that affect membrane permeability?
- temperature
- solvent concentration
28
draw a graph showing membrane permeability against temperature
p119
29
from the graph, what happens at temperatures below 0?
- the phospholipids don't have much energy so cant move very much
- therefore, they are packed closely and the membrane is rigid
- channel and carrier proteins in the membrane denature, increasing the permeability of the membrane
- ice crystals may also form, piercing the membrane, making it highly permeable when it thaws (defrosts)
30
from the graph, what happens between temperatures of 0-45?
- the phospholipids can move around and aren't packed as closely together
- therefore, the membrane is partially permeable
- as temperature increases between these values, the phospholipids gain more energy and move more, increasing membrane permeability
31
from the graph, what happens at temperatures above 45?
- the phospholipid bilayer starts to melt and break down, increasing membrane permeability
- water inside the cell expands, putting pressure on the membrane
- channel and carrier proteins in the membrane denature, meaning they can no longer control what enters and leaves the cell, increasing membrane permeability
32
how does solvent concentration affect membrane permeability?
- the permeability of a cell membrane depends on the solvent surrounding them
- some solvents (e.g. ethanol) dissolve the lipids in the cell membrane, meaning it loses its structure, increasing permeability
- some solvents (e.g. ethanol) increase membrane permeability more than others (e.g. methanol)
- increasing the concentration of these solvents will increase membrane permeability
33
draw a graph showing membrane permeability against alcohol concentration
p119
34
investigating cell membrane permeability - beetroot PAG
p120
35
why do cells need to communicate with eachother?
- to control processes inside the body
- to respond to changes in the environment
36
what is cell signaling?
- a way for cells to communicate with each other
- it uses messenger molecules
37
summarize how cell signaling works
- it starts when one cell releases a messenger molecule (e.g. a hormone)
- this molecule travels to another cell (e.g. in the blood)
- the messenger molecule is then detected by the cell because it binds to a receptor on its cell membrane
- the binding then triggers a change in the cell (e.g. setting off chemical signals)
38
what is are membrane-bound receptors?
proteins in the cell membrane that act as receptors for messenger molecules
39
what are a feature of these receptor proteins?
-they have specific shapes, meaning only messenger molecules with a complementary shape can bind to them
40
what is a target cell?
- different cells have different types of receptors that respond to different messenger molecules
- the cell that responds to a particular messenger molecule is called a target cell
41
show hoe messenger molecules bind to target cells, but NOT non-target cells
p122
42
how do hormones work as messenger molecules?
they bind to receptors in cell membranes, triggering a response in the cell
43
how does the hormone glucagon work as a messenger molecule?
- glucagon is released when there isn't enough glucose in the blood
- it binds to receptors on liver cells
- this causes the liver cells to break down stores of glycogen to glucose
44
how does the hormone FSH work as a messenger molecule?
- FSH is released by the pituitary gland during the menstrual cycle
- it bind to receptors on cells in the ovaries, causing an egg to mature ready for ovulation
45
what is the role of drugs in membrane receptors?
- many drugs work by binding to receptors in cell membranes
- they either trigger a response in the cell or block the receptor and prevent it from working
46
how does the drug morphine work alongside membrane receptors?
- the body produces chemicals called endorphins to relieve pain
- endorphins bind to opioid receptors in the brain and reduce the transmission of pain signals
- morphine is used to relieve pain
- it works by binding to the same opioid receptors, triggering the same reduction of pain signals
47
how does the drug antihistamine work alongside membrane receptors?
- cell damage causes the release of a chemical called histamine
- histamine binds to receptors on the surface of other cells and causes inflammation
- antihistamines work by blocking histamine receptors on cell surfaces
- this prevents histamine from binding and stops inflammation
48
what is the definition of diffusion?
the net movement of particles from an area of high concentration to an area of lower concentration (down a concentration gradient)
49
what is classed as a particle?
molecules or ions
50
what does net movement mean?
particles will move both ways but the net movement is calculated by the majority - the overall movement
51
when does diffusion end?
when all the particles are evenly distributed throughout the liquid or gas - its reached equilibrium
52
diffusion is a _______ process
passive - it requires no energy (particles can diffuse across as long as they can move freely)
53
what are the 4 factors that affect the rate of diffusion?
- concentration gradient
- diffusion distance/thickness of exchange surface
- surface area
- temperature
54
how does the concentration gradient affect diffusion rate?
- increased concentration gradient = increased rate of diffusion
- decreased concentration gradient = decreased rate of diffusion
55
how does the diffusion distance/thickness of exchange surface affect diffusion rate?
- increased diffusion distance = decreased rate of diffusion
- decreased diffusion distance = increased rate of diffusion
56
how does the surface area affect diffusion rate?
- increased surface area = increased rate of diffusion
- decreased surface area = decreased rate of diffusion
57
how does the temperature affect diffusion rate?
- increased temperature = increased rate of diffusion
- decreased temperature = decreased rate of diffusion
58
investigating diffusion
p125
59
what is the definition of osmosis?
the net movement of water molecules from an area of high water potential to an area of lower water potential, across a partially permeable membrane (down a water potential gradient)
60
what is the definition of water potential?
the tendency/potential of water molecules to diffuse into or out of a solution
IT IS ALWAYS A NEGATIVE VALUE
61
what is the symbol of water potential?
Ψ
62
what are the units of water potential?
kPa
63
what is the water potential of pure water?
0kPa
64
how do you calculate water potential?
pressure potential + solute potential
65
how do you lower a solutions water potential?
- adding solutes
- this gives a more negative water potential
- therefore, the more negative the value, the stronger the concentration of solutes in the solution
66
what is an isotonic solution?
- its when two solutions have the same water potential
- this means the cells in an isotonic solution wont lose or gain any water due to there being no water potential gradient
67
what happens to animal cells in an isotonic solution?
they stay the same
68
what happens to plant cells in an isotonic solution?
they stay the same
69
what is a hypotonic solution?
- when the solution has a higher water potential compared to the inside of the cell
- this means water will move into the cell by osmosis
70
what happens to animal cells in a hypotonic solution?
they swell and could potentially burst (hemolyzed/lysis?)
71
what happens to plant cells in a- hypotonic solution?
- the vacuole will swell
- the contents of the vacuole and cytoplasm will push up against the cell wall
- this will cause the cell to become TURGID (swollen)
- however, it wont burst as the inelastic cell wall is able to withstand the pressure increase
- this provides support for the plant
72
what is a hypertonic solution?
- when the solution has a lower water potential compared to the inside of the cell
- this means water will move out of the cell by osmosis
73
what happens to animal cells in a hypertonic solution?
it will shrink (crenation?)
74
what happens to plant cells in a hypertonic solution?
- it will become FLACCID (limp)
- the cytoplasm and plasma membrane will eventually pull away from the cell wall - this is called PLASMOLYSIS
75
what is plasmolysis?
when the cytoplasm and plasma membrane pull away from the cell wall
76
investigating the effect of water potential on plant cells
p128
77
investigating the effect of water potential on animal cells
p129
78
what is facilitated diffusion?
the diffusion of larger molecules or charged particles from an area of high concentration to an area of lower concentration through carrier proteins and channel proteins
79
where does facilitated diffusion take place?
in the cell membrane
80
why do we need facilitated diffusion?
- large molecules would be extremely slow at diffusing through the phospholipid bilayer due to their size
- charged particles would also diffuse slowly due to them being water soluble and the phospholipid bilayer being hydrophobic
81
what are some examples of large molecules that need to use facilitated diffusion?
- amino acids
- glucose
82
what are some examples of charged particles that need to use facilitated diffusion?
- polar molecules
- ions (e.g. sodium, chloride)
83
facilitated diffusion is a _______ process
passive - requires no energy
84
what is the key difference between diffusion and facilitated diffusion?
facilitated diffusion uses membrane proteins - carrier and channel
85
what is the role of carrier proteins?
- they move large or charged molecules into or out of a cell, down a concentration gradient
- different carrier proteins facilitate the diffusion of different molecules
86
what is an example of a carrier protein?
GLUT1 found in all animal cells to transport glucose across the plasma membrane
87
how do carrier proteins work?
1. a large molecule attaches to a carrier protein in the membrane
2. the protein changes shape
3. this releases the molecule on the opposite side of the membrane
SEE DIAGRAM P131
88
what is the role of a channel protein?
- they form (water filled?) pores in the membrane for smaller charged particles (ions and polar molecules) to diffuse through, down a concentration gradient
- these pores are gated (can open and close)
- different channel proteins facilitate the diffusion of different charged particles
89
how do channel proteins work?
- they form a pore
SEE DIAGRAM P132
90
what is a key difference between carrier and channel proteins?
- carrier proteins can switch between 2 shapes
- channel proteins are a fixed shape
91
what is the definition of active transport?
the movement of molecules and ions across a plasma membrane from a region of low concentration to an area of higher concentration (against/up a concentration gradient) through carrier proteins and using ATP
SEE DIAGRAM P132
92
how are carrier proteins used in active transport?
in the same way as facilitated diffusion!
1. a molecule attaches to a carrier protein in the membrane
2. the protein changes shape
3. this releases the molecule on the opposite side of the membrane
SEE DIAGRAM P131
93
active transport is an _____ process
active - it uses the ATP from respiration to move the solute against its concentration gradient
94
what is the difference between active transport and facilitated diffusion?
- active transport is and active process (uses energy)
- facilitated diffusion is a passive process (does not)
95
what is endocytosis?
the movement of large molecules or objects INTO the cell
96
why do we need endocytosis?
- some molecules are too large to be taken into a cell by carrier proteins
- therefore, in order to travel across the plasma membrane, it needs to be taken in by endocytosis
97
what are some examples of molecules that are taken in by endocytosis?
- proteins
- lipids
- some carbohydrates
some cells (e.g. white blood cells - mainly phagocytes) take in much larger objects (e.g. micro organisms and dead cells) through endocytosis in order to destroy them
98
what is the process of taking a cell in by endocytosis?
- a cell surrounds a substance with a section of its plasma membrane
- the membrane then pinches off to form a vesicle inside the cell containing the ingested substance
- this substance has now been taken in by endocytosis
SEE DIAGRAM P132
99
endocytosis is an ______ process
active - it requires ATP for energy
100
what is exocytosis?
the movement of molecules OUT OF the cell
101
why do we need exocytosis?
- some substances produced by the cell need to be released from it
- therefore, this is done through exocytosis
102
what are some examples of substances released by exocytosis?
- digestive enzymes
- hormones
- lipids
103
what is the process of exocytosis?
- vesicles containing the substances pinch off from the sacs of the golgi apparatus
- they then move towards the plasma membrane
- the vesicles fuse with the plasma membrane and release their contents outside of the cell
- however, some substances (e.g. membrane proteins) are inserted straight into the plasma membrane instead
SEE DIAGRAM P133
104
endocytosis is an _____ process
active - it requires ATP for energy
105
summary of transport mechanisms
p134
(all info already in flashcards)
