Biological Membrane Flashcards
What do some organelles have and what do these do?
Have membranes within them and form barriers too
What does permeability refer to?
The ability to let substances pass through
How do very small molecules get through the cell membrane?
Diffuse through cell membrane between structural molecules
What do some substances do to get through the membrane?
Dissolve in the lipid later and pass through
How do other substances pass through cell membrane?
Pass through special protein channels it are carried by carrier proteins
Why are these membranes described as partially permeable?
The membranes don’t let all types of molecules to pass through
What determines the cells permeability?
The properties if the component molecules of the cell membrane
I.e. Which molecules it allows through
What is the plasma membrane sometimes referred to?
Cell surface membrane
What are some roles of membranes at the surface of cells?
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
How does a membrane separate cells components from external environment in single and multicellular organisms?
Single celled organisms environment is external surrounding Multicellular organism (humans) each cell's environment is tissue fluid or cells surrounding it
Why does the cell membrane have antigens?
So organisms immune system can recognise organisms immune system can recognise cell as self and not attack it
What does the membranes around organelles present in eukaryotic cells separate what?
Organelle contents from cell cytoplasm
Why does it departs the organelles content?
Discrete entity
Able to perform its function
Where do metabolic processes happen on some organelles?
On membranes
What do mitochondria folded inner membranes gives?
Large surface area for some of the reactions of aerobic respiration and localise some of enzymes needed for respiration to occur
What do inner membranes of chloroplasts call themselves?
Thylakoid membranes
House chlorophyll
What do you find on these membranes?
Some of reactions of photosynthesis occurring
Where are some digestive enzymes?
On plasma membrane of epithelial cells that line small intestine
Enzymes catalyse some final stages in breakdown of certain types of sugars
State the year and what singer and nicolson?
1972
Proposed model allowed passage of molecules through membrane
What did their structure explain and who are they?
Singer and Nicolson explained how cell membranes could be more dynamic and interact more with cell’s environment
What was singer and Nicolsons 1972 model called?
Fluid mosaic model
What did fluid mosaic model propose?
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
What is the fabric of the membrane?
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
How thick is the phospholipid bilayer?
About 7nm in width
What does a carrier protein have?
Water-filled channel inside channel protein lined with hydrophilic amino acids
What makes a glycoprotein?
Glycocalyx attached to protein
Carbohydrate chain attracted to protein molecules
What can a protein not spanning the lipid bilayer act as?
An enzyme
Phospholipid info
Fatty acid tails hydrophobic
Phosphate head has charge and is hydrophobic
Cholesterol does what in the cell membrane? What do
Gives mechanical stability and flexibility
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
Glycolipid is?
Carbohydrate chain attached to lipid
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
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
What does the meaning Some proteins are carriers by changing shape?
Some proteins are carriers by changing shape, carry specific molecules across the membrane
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
What do eukaryotic cell membrane contain?
Cholesterol
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
What is the width thickness of a cell membrane?
5 to 10 nm
What is outside the membrane?
Glycocalyx
Wha cud glycocalyx Formed from?
Carbohydrates chain attached to either (glycolipids) or proteins (glycoproteins) in the membrane
What may membranes have a particular and to allow what?
Particular distributions of proteins
Enable them to carry out their specific functions
What allows entry and exit of ions?
In neurones, protein channels and carriers in plasma membrane covering long axon
What does this bring?
Conduction of electrical impulse along their length
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
Neurones features?
Myelin sheath formed by flattened cells wrapped around them several times giving several layers of cell membrane
Membrane forming myelin sheath.
What percentage lipid and protein is a neurone?
76% lipid
20% protein
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
When could the white blood cell react?
Invading pathogens
Organ transplant
What do root hair cells have?
Many carrier proteins
What do these carrier proteins do?
Actively transport nitrate ions from soil into cells
What percentage lipid and protein is the mitochondria?
76% protein
24% lipid
Why is this so?
Inner membrane contains many electron carriers made of protein and hydrogen ions channels associated with ATP synthase enzymes
What do cells need to receive?
Raw material or reactants for reactions
What do they respire to make?
ATP
What does ATP provide?
Cellular energy to drive biochemical reactions
They need oxygen and glucose to do this
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
How can some substances cross the cell membrane?
Without using ATP
Passive processes as use kinetic energy
What’s simple diffusion?
GCSE diffusion
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
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
What happens when molecules have to move down their concentration gradient?
Still moving randomly
Remain evenly dispersed so net diffusion
Reached equilibrium
How can some molecules like oxygen and carbon dioxide pass through?
Simple diffusion because they are small
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
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
What do molecules where high water movement required have?
Aquaporins to allow water molecules to cross membrane without challenge of moving lipid environment
What maintains the concentration gradient?
Many molecules entering cells pass into organelles used for metabolic reactions
What does it also do?
Keeps more molecules entering the cell
What does oxygen do here?
Diffuses into cytoplasm of respiring cells
Diffuses into microchrondria used for aerobic respiration
What does carbon dioxide do?
Diffuse into palisade mesophyll cells of plant leaf will then diffuse into chloroplasts and be used for photosynthesis
What factors affect simple diffusion?
Temperature Diffusion distance Surface area Size of diffusing molecule Concentration gradient
Temperature affects rate of diffusion how?
Hotter temperature more molecule movement rate of diffusion increases
Colder temperature less molecule movement rate of diffusion decreases
How does diffusion distance affect rate of diffusion?
Thicker membrane across which molecules have to diffuse the slower the rate of diffusion
Size of diffusing molecules affect simple diffusion?
Smaller ions or molecules diffuse more rapidly than larger molecules
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
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
What did that mean?
Diffuse through water filled protein channels (pores) embedded in membrane
Channels around 0.8 nm in diameter
What do the cholesterol do here?
Reduce permeability of membrane to water-soluble molecules
Can glucose diffuse through?
No they are too large through water-filled protein channel in a membrane
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
What do different cell types have?
Differing proportions of transmembrane protein channel and transmembrane protein carriers.
What does this allow?
Cells to control types of molecules that pass in or out
What do Neurone plasma membrane have?
Many channel specific to either sodium ions/ potassium ions
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.
What are at the synapses?
Calcium ion channels
Many have chloride ion channels
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
What is the liquid in a solution that solute molecule are dissolved in?
Solvent.
What is the solvent in an aqueous solution?
Water
What can water do with a phosolipid bilayer?
Pass directly through
What do some membranes also have?
Aquaporins which allow water molecules to cross more rapidly
What do water molecules have?
Kinetic energy
What does this cause them to do?
Move randomly thus spreading out
Define osmosis
Net diffusion from a region of relatively more water molecules to an area of fewer water molecules
What happens when solute molecules are added to water?
The relative number of water molecules in the solution changes.
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.
Why?
Sodium chloride molecules dissociate into sodium ions and chloride ions, number of particles in solution doubles
Water potential is?
Measure of tendency of water molecules to diffuse from one region to another
What has the highest water potential and what is it?
Pure water 0
What happens when solute molecules are added?
Lower water potential of solution. The more solute molecules in solution the lower the water potential
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
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.
What is water potential measured in?
kPa
Which is lower the water potential inside the cell or in pure water?
The water potential inside the cell
Why is this?
Solutes in solutions in cytoplasm and inside large vacuole of plant cells
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.
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.
What do plant cells have to prevent bursting?
A rigid and strong cellulose cell wall
What will plant cells do with high water potential?
Cell will swell to certain size when contents pushed against cell wall resisting further swelling.
What is the swollen cell called?
Turgid.
What does turgidity do?
Helps support plants especially non-woody ones
What happens when cells are placed in solution of lower water potential?
Water leaves cells by osmosis across partially permeable membrane
When is the word crenated used here?
Animal cell shrivel
What do plant cells do?
Cytoplasm of plant cell shrinks. Membrane pulls away from cellulose cell wall. (Plasmolysis).
What are plant tissue with plasmolysis cells described as?
Flaccid.
What do plasmolysed cells suffer from?
Degree of dehydration. Metabolism can’t proceed as enzyme-catalyst reactions need to be in solution.
What does increasing the temperature do to the kinetic energy?
Gives all molecules more energy to move
What does an increase in kinetic energy in molecules cause?
These molecules to move faster
What does decreasing the temperature do to the kinetic energy?
Lowers the kinetic energy
What does a lower of kinetic energy do to the molecules?
Slows them down
What don’t cold blooded animals do?
Generate heat to maintain their body temperature so their temperate varies with their environment
What do saturated fatty acids become when temperature drops?
Compressed
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
What does the proportion of saturated and unsaturated fatty acids within a cell membrane determine?
The membrane’s fluidity at cold temperature
What does cholesterol in the membrane do when the temperature drops in a cell?
Buffer the effect of lowered temperature
What is the point of cholesterol buffering in the cell membrane when the temperature drops?
Prevent reduction in membranes fluidity
How does cholesterol Prevent reduction in membranes fluidity?
By preventing the phosolipid molecules from packing too closely by being between groups of phospholipid molecules
What can fish and microorganisms change the composition of in their cell membrane?
The composition of fatty acids in response to lowered temperatures
What else can change its composition of fatty acids?
Some plants
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
What happens as a result of the membrane fluidity increasing?
Permeability increases
What does this change also affect?
The way membrane embedded proteins are positioned and may function.
What happens if some of the enzymes in a membrane drift sideways?
It could alter the rate of reactions they catalyse
What may an increase in membrane fluidity affect?
The unfolding of the plasma membrane during phagocytosis
What may an increase in membrane fluidity change?
The ability of cells to signal to other cells by releasing chemicals by exocytosis
What does the presence of a cholesterol molecule buffer?
The effects of increasing heat as it reduces the increase in membrane fluidity
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.
Are proteins as stable as these lipids?
No proteins are not as stable as lipids
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.
What happens to denature proteins?
Tertiary structure change and can’t change back again when they cool
What are just underneath plasma membrane?
Cytoplasm threads
What are cytoplasm made of?
Protein
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.
Will the membrane embedded enzyme continue to work if it’s denatured?
No
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
Give two examples of organic solvents?
Acetone and ethanol
What will organic solvents do the cell membrane and why?
Organic solvents will damage the cell membrane as they dissolve lipids
What does active transport mean?
Movement of substances against concentration gradient of that substance across a cell membrane using ATP protein carriers
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.
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.
Sometimes cell to move substances in or out across their plasma membrane (ATP required) gradient
Against each substances concentration gradient
Why is doing this like swimming against the tide?
Requires more energy than kinetic energy of the molecules
How is the energy provided?
Hydrolysis of ATP
How can cells or organelles accumulate a particular ion?
Simple diffusion
Facilitated diffusion
How can cells or organelles accumulate more of a particular ion?
Root hair cells use active transport to absorb ions from soil
What do membrane have specific?
Regions or sites
What do these membrane protein sites do?
Combine reversibly with only certain solute molecules or ions
What do membrane also have a region for?
Binds to
Allows hydrolysis Of molecule of ATP to release energy and act as an enzyme
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.
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
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
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
What does bulk transport require?
ATP energy
How are large molecules brought into the cell?
Endocytosis
What happens in endocytosis?
Segment of plasma membrane surrounds and enclosed the particle and bring it into the cell enclosed in a vesicle
What is phagocytosis?
Type of endocytosis
Refers to intake of solid matter
What is pino(endo)cytosis
Type of endocytosis
Refers to intake of liquid
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
Exocytosis is?
How large molecules can be exported out of cells
How does exocytosis happen?
Doesn’t pass through plasma membrane
Vesicle containing them is moved towards and then fuses with plasma membrane
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.
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
What is the first stage of exocytosis?
Membrane-bound vesicle containing substance secreted moved towards cell surface membrane
What is the second stage of exocytosis?
Cell surface membrane and membrane of vesicle fuse together
What is step 3 of exocytosis?
Fused site opens releasing contents of secretory vesicle
Isotonic
Solution in which solute and solvent equally distributed
Hypertonic
a solution which contains more solvent than solute
Hypotonic
a solution which contains more solute than solvent
Function of glycoprotein?
Plays important role in hormones.
Function of glycolipid?
A recognition site in the body for cell-cell interactions
