Biological Membrane Flashcards
1
Q
What do some organelles have and what do these do?
A
Have membranes within them and form barriers too
2
Q
What does permeability refer to?
A
The ability to let substances pass through
3
Q
How do very small molecules get through the cell membrane?
A
Diffuse through cell membrane between structural molecules
4
Q
What do some substances do to get through the membrane?
A
Dissolve in the lipid later and pass through
5
Q
How do other substances pass through cell membrane?
A
Pass through special protein channels it are carried by carrier proteins
6
Q
Why are these membranes described as partially permeable?
A
The membranes don’t let all types of molecules to pass through
7
Q
What determines the cells permeability?
A
The properties if the component molecules of the cell membrane
I.e. Which molecules it allows through
8
Q
What is the plasma membrane sometimes referred to?
A
Cell surface membrane
9
Q
What are some roles of membranes at the surface of cells?
A
Separates cell’s components from its external environment
Regulates transport into and out of cell
May contain enzymes involved in specific metabolic pathways
Has antigens
May release chemicals that signal to other cells
Contains receptors for chemical signals
May be site of chemical reactions
10
Q
How does a membrane separate cells components from external environment in single and multicellular organisms?
A
Single celled organisms environment is external surrounding Multicellular organism (humans) each cell's environment is tissue fluid or cells surrounding it
11
Q
Why does the cell membrane have antigens?
A
So organisms immune system can recognise organisms immune system can recognise cell as self and not attack it
12
Q
What does the membranes around organelles present in eukaryotic cells separate what?
A
Organelle contents from cell cytoplasm
13
Q
Why does it departs the organelles content?
A
Discrete entity
Able to perform its function
14
Q
Where do metabolic processes happen on some organelles?
A
On membranes
15
Q
What do mitochondria folded inner membranes gives?
A
Large surface area for some of the reactions of aerobic respiration and localise some of enzymes needed for respiration to occur
16
Q
What do inner membranes of chloroplasts call themselves?
A
Thylakoid membranes
House chlorophyll
17
Q
What do you find on these membranes?
A
Some of reactions of photosynthesis occurring
18
Q
Where are some digestive enzymes?
A
On plasma membrane of epithelial cells that line small intestine
Enzymes catalyse some final stages in breakdown of certain types of sugars
19
Q
State the year and what singer and nicolson?
A
1972
Proposed model allowed passage of molecules through membrane
20
Q
What did their structure explain and who are they?
A
Singer and Nicolson explained how cell membranes could be more dynamic and interact more with cell’s environment
21
Q
What was singer and Nicolsons 1972 model called?
A
Fluid mosaic model
22
Q
What did fluid mosaic model propose?
A
Fabric of membrane consisted of phospholipid bilayer with proteins floating in it making mosaic pattern
Lipid molecules change places with each other
Some proteins may move giving fluidity
23
Q
What is the fabric of the membrane?
A
Lipid bilayer made of 2 layers of phospholipid molecules
Hydrophilia heads in contact with watery exterior or cytoplasm
Hydrophobic tail regions in centre of membrane away from water
24
Q
How thick is the phospholipid bilayer?
A
About 7nm in width
25
What does a carrier protein have?
Water-filled channel inside channel protein lined with hydrophilic amino acids
26
What makes a glycoprotein?
Glycocalyx attached to protein
| Carbohydrate chain attracted to protein molecules
27
What can a protein not spanning the lipid bilayer act as?
An enzyme
28
Phospholipid info
Fatty acid tails hydrophobic
| Phosphate head has charge and is hydrophobic
29
Cholesterol does what in the cell membrane? What do
Gives mechanical stability and flexibility
30
What's glycocalyx?
Carbohydrates molecules on outside of membrane very hydrophilic and attract water with dissolved solutes helping cells interact with watery environment and obtain substances
31
Glycolipid is?
Carbohydrate chain attached to lipid
32
What do some protein membranes have?
Pores and act as channels
Some proteins are carriers by changing shape
Other proteins may be attached to carrier proteins
33
What does Pores and act as channels mean?
Some membranes have pores and act as channels to allow ions, have electrical charge surrounded by water molecules to pass through
34
What does the meaning Some proteins are carriers by changing shape?
Some proteins are carriers by changing shape, carry specific molecules across the membrane
35
What is the meaning of Other proteins may be attached to carrier proteins?
Other proteins may be attached to carrier proteins and functions as enzymes, antigens or receptor sites for complementary-shaped signalling chemicals such as hormones
36
What do eukaryotic cell membrane contain?
Cholesterol
37
What is the importance of this?
Helping to regulate fluidity of the membrane
| Maintain mechanical stability and resist effects of temperature changes on structure of the membrane
38
What is the width thickness of a cell membrane?
5 to 10 nm
39
What is outside the membrane?
Glycocalyx
40
Wha cud glycocalyx Formed from?
Carbohydrates chain attached to either (glycolipids) or proteins (glycoproteins) in the membrane
41
What may membranes have a particular and to allow what?
Particular distributions of proteins
| Enable them to carry out their specific functions
42
What allows entry and exit of ions?
In neurones, protein channels and carriers in plasma membrane covering long axon
43
What does this bring?
Conduction of electrical impulse along their length
44
Why does the cell membrane need to allow some molecules through, into it out of the cell?
Cell membranes form barriers and separate cell content from cell's exterior environment
45
Neurones features?
Myelin sheath formed by flattened cells wrapped around them several times giving several layers of cell membrane
Membrane forming myelin sheath.
46
What percentage lipid and protein is a neurone?
76% lipid
| 20% protein
47
What's the plasma membrane of a white blood cell like?
Contains special protein receptors that ape recognition antigens on foreign cells usually from invading pathogens
48
When could the white blood cell react?
Invading pathogens
| Organ transplant
49
What do root hair cells have?
Many carrier proteins
50
What do these carrier proteins do?
Actively transport nitrate ions from soil into cells
51
What percentage lipid and protein is the mitochondria?
76% protein
| 24% lipid
52
Why is this so?
Inner membrane contains many electron carriers made of protein and hydrogen ions channels associated with ATP synthase enzymes
53
What do cells need to receive?
Raw material or reactants for reactions
54
What do they respire to make?
ATP
55
What does ATP provide?
Cellular energy to drive biochemical reactions
| They need oxygen and glucose to do this
56
What do they also need to do?
Remove toxic metabolic waste products e.g. Carbon dioxide
| Need to export some molecules that they make like enzymes m, hormones and other signalling molecules
57
How can some substances cross the cell membrane?
Without using ATP
| Passive processes as use kinetic energy
58
What's simple diffusion?
GCSE diffusion
59
What does simple diffusion rely on?
All molecules have kinetic energy that can move freely and randomly within gas or liquid media
Will happen without being shaken/stirred
60
What causes diffusion?
High concentration bump into each other as randomly move
Eventually will spread further from each other
More will move to lower concentration until dispersed
61
What happens when molecules have to move down their concentration gradient?
Still moving randomly
Remain evenly dispersed so net diffusion
Reached equilibrium
62
How can some molecules like oxygen and carbon dioxide pass through?
Simple diffusion because they are small
63
How can larger fat-soluble molecules get through?
Things like steroid hormones can diffuse through cell membranes as dissolve in lipid bilayer
Still move down concentration gradient
64
Why is water a special case?
Polar and insoluble in lipid
Phospholipid layer would seem to be an impermeable barrier
Water in such great concentration significant direct diffusion occurs
65
What do molecules where high water movement required have?
Aquaporins to allow water molecules to cross membrane without challenge of moving lipid environment
66
What maintains the concentration gradient?
Many molecules entering cells pass into organelles used for metabolic reactions
67
What does it also do?
Keeps more molecules entering the cell
68
What does oxygen do here?
Diffuses into cytoplasm of respiring cells
| Diffuses into microchrondria used for aerobic respiration
69
What does carbon dioxide do?
Diffuse into palisade mesophyll cells of plant leaf will then diffuse into chloroplasts and be used for photosynthesis
70
What factors affect simple diffusion?
```
Temperature
Diffusion distance
Surface area
Size of diffusing molecule
Concentration gradient
```
71
Temperature affects rate of diffusion how?
Hotter temperature more molecule movement rate of diffusion increases
Colder temperature less molecule movement rate of diffusion decreases
72
How does diffusion distance affect rate of diffusion?
Thicker membrane across which molecules have to diffuse the slower the rate of diffusion
73
Size of diffusing molecules affect simple diffusion?
Smaller ions or molecules diffuse more rapidly than larger molecules
74
How does concentration gradient affect the rate of diffusion?
Steeper gradient (more molecules on one side of membrane compared with other side) the faster diffusion to the side where there are fewer molecules down the gradient
75
Facilitated diffusion depends on?
Small molecules have polarity such as ions that have electrical charge are insoluble in lipids because they can't interact with hydrophobic tails of lipid bilayer
76
What did that mean?
Diffuse through water filled protein channels (pores) embedded in membrane
Channels around 0.8 nm in diameter
77
What do the cholesterol do here?
Reduce permeability of membrane to water-soluble molecules
78
Can glucose diffuse through?
No they are too large through water-filled protein channel in a membrane
79
So how does glucose get in?
They can bind to transmembrane carrier proteins which opens allows glucose to pass out on outer side of membrane, there are specific carrier proteins for different types of molecules
80
What do different cell types have?
Differing proportions of transmembrane protein channel and transmembrane protein carriers.
81
What does this allow?
Cells to control types of molecules that pass in or out
82
What do Neurone plasma membrane have?
Many channel specific to either sodium ions/ potassium ions
83
What is the diffusion of ions into and out of the neurone axon crucial for?
Diffusion of ions into and out of neurones axon crucial for conduction of nerve impulses.
84
What are at the synapses?
Calcium ion channels
| Many have chloride ion channels
85
What plays a crucial role in regulating composition of mucus to trap particles and pathogens?
Plasma membrane of epithelial cells that line your airways have chloride ions channels
86
What is the liquid in a solution that solute molecule are dissolved in?
Solvent.
87
What is the solvent in an aqueous solution?
Water
88
What can water do with a phosolipid bilayer?
Pass directly through
89
What do some membranes also have?
Aquaporins which allow water molecules to cross more rapidly
90
What do water molecules have?
Kinetic energy
91
What does this cause them to do?
Move randomly thus spreading out
92
Define osmosis
Net diffusion from a region of relatively more water molecules to an area of fewer water molecules
93
What happens when solute molecules are added to water?
The relative number of water molecules in the solution changes.
94
What happens if solute molecules dissociate into charged ions?
They exert more effect on relative number of water molecules than larger non-polar molecules like glucose.
95
Why?
Sodium chloride molecules dissociate into sodium ions and chloride ions, number of particles in solution doubles
96
Water potential is?
Measure of tendency of water molecules to diffuse from one region to another
97
What has the highest water potential and what is it?
Pure water 0
98
What happens when solute molecules are added?
Lower water potential of solution. The more solute molecules in solution the lower the water potential
99
What will happen if two aqueous solutions are separated by a partially permeable membrane?
Water molecules will move from solution with high water potential to solution with lower water potential
100
What happens if the water potential both sides of the membrane become equal?
There will be no net osmosis although water molecules will continue to move randomly.
101
What is water potential measured in?
kPa
102
Which is lower the water potential inside the cell or in pure water?
The water potential inside the cell
103
Why is this?
Solutes in solutions in cytoplasm and inside large vacuole of plant cells
104
What happens when cells are placed in a solution of higher water potential?
Water molecules move by osmosis down the water potential gradient across the plasma membrane into the cell.
105
What is cytolysis?
In animals cell when lots of water molecules enter the cell causing it to swell and burst as the plasma membrane breaks.
106
What do plant cells have to prevent bursting?
A rigid and strong cellulose cell wall
107
What will plant cells do with high water potential?
Cell will swell to certain size when contents pushed against cell wall resisting further swelling.
108
What is the swollen cell called?
Turgid.
109
What does turgidity do?
Helps support plants especially non-woody ones
110
What happens when cells are placed in solution of lower water potential?
Water leaves cells by osmosis across partially permeable membrane
111
When is the word crenated used here?
Animal cell shrivel
112
What do plant cells do?
Cytoplasm of plant cell shrinks. Membrane pulls away from cellulose cell wall. (Plasmolysis).
113
What are plant tissue with plasmolysis cells described as?
Flaccid.
114
What do plasmolysed cells suffer from?
Degree of dehydration. Metabolism can't proceed as enzyme-catalyst reactions need to be in solution.
115
What does increasing the temperature do to the kinetic energy?
Gives all molecules more energy to move
116
What does an increase in kinetic energy in molecules cause?
These molecules to move faster
117
What does decreasing the temperature do to the kinetic energy?
Lowers the kinetic energy
118
What does a lower of kinetic energy do to the molecules?
Slows them down
119
What don't cold blooded animals do?
Generate heat to maintain their body temperature so their temperate varies with their environment
120
What do saturated fatty acids become when temperature drops?
Compressed
121
What do many unsaturated fatty acids making up the cell membrane phosolipid layer do when the temperature drops?
Become compressed
| But their kinks in their tails push adjacent phosolipid molecules away. Maintaining membrane fluidity
122
What does the proportion of saturated and unsaturated fatty acids within a cell membrane determine?
The membrane's fluidity at cold temperature
123
What does cholesterol in the membrane do when the temperature drops in a cell?
Buffer the effect of lowered temperature
124
What is the point of cholesterol buffering in the cell membrane when the temperature drops?
Prevent reduction in membranes fluidity
125
How does cholesterol Prevent reduction in membranes fluidity?
By preventing the phosolipid molecules from packing too closely by being between groups of phospholipid molecules
126
What can fish and microorganisms change the composition of in their cell membrane?
The composition of fatty acids in response to lowered temperatures
127
What else can change its composition of fatty acids?
Some plants
128
What happens to the phosolipid as as the temperature increases?
They acquire more kinetic energy and move more in a random way increasing membrane fluidity
129
What happens as a result of the membrane fluidity increasing?
Permeability increases
130
What does this change also affect?
The way membrane embedded proteins are positioned and may function.
131
What happens if some of the enzymes in a membrane drift sideways?
It could alter the rate of reactions they catalyse
132
What may an increase in membrane fluidity affect?
The unfolding of the plasma membrane during phagocytosis
133
What may an increase in membrane fluidity change?
The ability of cells to signal to other cells by releasing chemicals by exocytosis
134
What does the presence of a cholesterol molecule buffer?
The effects of increasing heat as it reduces the increase in membrane fluidity
135
What can and can't be altered by the movement of phosolipids by changing temperature?
Movement can be altered but integral molecular structure can't be.
136
Are proteins as stable as these lipids?
No proteins are not as stable as lipids
137
What can high temperature therefore cause the atoms in a large protein molecule do?
Causes atoms within large molecule to vibrate which breaks hydrogen bonds and ionic bonds that hold their structure they unfold.
138
What happens to denature proteins?
Tertiary structure change and can't change back again when they cool
139
What are just underneath plasma membrane?
Cytoplasm threads
140
What are cytoplasm made of?
Protein
141
What happens if the membrane embedded proteins and the cytoskeleton threads become denatured?
The plasma membrane will begin to fall apart becoming more permeable as holes appear in it.
142
Will the membrane embedded enzyme continue to work if it's denatured?
No
143
What will happen if the shape of their active sites changes slightly or the enzymes move within the membrane?
The rate of reactions that they catalysed will be slowed
144
Give two examples of organic solvents?
Acetone and ethanol
145
What will organic solvents do the cell membrane and why?
Organic solvents will damage the cell membrane as they dissolve lipids
146
What does active transport mean?
Movement of substances against concentration gradient of that substance across a cell membrane using ATP protein carriers
147
What does endocytosis mean?
Bulk transport of molecules too large to pass through a cell membrane even via channel or carrier proteins into a cell.
148
What does exocytosis mean?
Bulk transport of molecules too large to pass through a cell membrane even via a channel or carrier proteins out of a cell.
149
Sometimes cell to move substances in or out across their plasma membrane (ATP required) gradient
Against each substances concentration gradient
150
Why is doing this like swimming against the tide?
Requires more energy than kinetic energy of the molecules
151
How is the energy provided?
Hydrolysis of ATP
152
How can cells or organelles accumulate a particular ion?
Simple diffusion
| Facilitated diffusion
153
How can cells or organelles accumulate more of a particular ion?
Root hair cells use active transport to absorb ions from soil
154
What do membrane have specific?
Regions or sites
155
What do these membrane protein sites do?
Combine reversibly with only certain solute molecules or ions
156
What do membrane also have a region for?
Binds to
| Allows hydrolysis Of molecule of ATP to release energy and act as an enzyme
157
What this energy help carrier proteins to change?
It's conformation (shape) and doing so carries ions from one side of the cell to other.
158
Give an example of carrier protein.
Guard cells ATP made by chloroplast provides energy to actively transport potassium ions from surrounding cells into guard cells
159
What does this influx of ions do?
Lowers the water potential in guard cells so water enters from surrounding cells by osmosis as guard cells swell their tips bulge opening the stoma between them
160
When is bulk transport used?
When cells need to transport large molecules and particles that are too large to pass through plasma membrane in or out
161
What does bulk transport require?
ATP energy
162
How are large molecules brought into the cell?
Endocytosis
163
What happens in endocytosis?
Segment of plasma membrane surrounds and enclosed the particle and bring it into the cell enclosed in a vesicle
164
What is phagocytosis?
Type of endocytosis
| Refers to intake of solid matter
165
What is pino(endo)cytosis
Type of endocytosis
| Refers to intake of liquid
166
What is ATP needed for in endocytosis?
To provide energy to form vesicles and move them using molecular motor proteins along cytoskeleton threads Ito cell interior
167
Exocytosis is?
How large molecules can be exported out of cells
168
How does exocytosis happen?
Doesn't pass through plasma membrane
| Vesicle containing them is moved towards and then fuses with plasma membrane
169
Give an example of exocytosis
Synapses where chemicals on vesicles are moved by motor proteins moving along cytoskeleton threads to presynaptic membrane. Vesicle membranes and plasma membranes fuse and neurotransmitter chemical are released into synaptic cleft.
170
What is needed in all cases for exocytosis?
ATP to fuse membranes together as well as moving the vesicles
Molecule of ATP hydrolysed for every step that a motor protein takes along cytoskeleton thread as it drags the vesicle
171
What is the first stage of exocytosis?
Membrane-bound vesicle containing substance secreted moved towards cell surface membrane
172
What is the second stage of exocytosis?
Cell surface membrane and membrane of vesicle fuse together
173
What is step 3 of exocytosis?
Fused site opens releasing contents of secretory vesicle
174
Isotonic
Solution in which solute and solvent equally distributed
175
Hypertonic
a solution which contains more solvent than solute
176
Hypotonic
a solution which contains more solute than solvent
177
Function of glycoprotein?
Plays important role in hormones.
178
Function of glycolipid?
A recognition site in the body for cell-cell interactions
