biological membranes Flashcards
role of membranes within cells
-provide internal transport system
-selectively permeable to regulate passage of molecules into or within organelles
-provide reaction surface
-isolate organelles from cytoplasm for specific metabolic reactions.
Functions of membranes on the surface of cells
Isolates cytoplasm from extracellular environment
Selectively permeable to regulate transport of substances
Involved in cell signalling/cell recognition
Describe the fluid mosaic model of membranes
Phospholipid molecules form a continuous double layer(bilayer). Fluid-phospholipid are constantly moving =membrane has flexible shape
Mosaic= extrinsic and intrinsic proteins of different sizes and shapes are embedded. Some proteins have a carb attached -glycoproteins and some have a lipid attached- glycolipids. It also has cholesterol molecules in the bilayer
Draw the phospholipid bilayer
What’s three factors that affect membrane permeability
Temp
Solvents
Ph
How can substances move across the plasma membrane
Osmosis
Diffusion
Active transport
How do phospholipids form the bilayer
They have a head and tail. The head is hydrophilic so it attracts water the tail is hydrophobic it repels water.
The molecules automatically arrange themselves in a bilayer where the heads face out towards the water on either side of the membrane
The centre of the bilayer is hydrophobic so it doesn’t allow water soluble substances/hydrophilic molcules (ions and polar molecules)to diffuse through it, it acts as a barrier to dissolved substances.
Fat soluble substances/hydrophobic molcules dissolve in bilayer and easily pass through
Why can’t water soluble substances go past the hydrophobic centre
Because of the hydrophobic tails being non polar and water soluble substances being polar
Why can water molcules pass through the cell membrane
Because even though it’s polar it’s extremely small
Function of cholesterol in phospholipid bilayer
Gives the membrane stability.
Cholesterol molecules have a hydrophilic group on one end, this can attract the the polar hydrophilic heads on the phospholipid molecules. The rest of the cholesterol molecule is hydrophobic and non polar which can attract the hydrophobic tails of the phospholipids.
So because it fits between the phospholipids and binds to the tails it packs the molcules more closer together increasing strength of cell surface membrane.
This makes the membranes less fluid more rigid preventing the sideways movement of phosphilipids and other molecules.
And this prevents membrane from being too fluid in warm conditions and too rigid in cool conditions.
Also by packing spaces between phospholipids it reduces movement of water soluble substances across cell surface membrane.
Where is cholesterol molecules found
Lipid found In all cell membranes except bacterial
What’s the functions of proteins in the bilayer
Controls what enters and leaves the cell
Extrinsic proteins - Binding sites/receptors
Antigens
Bind cells together
Involved in cell signalling
Intrinsic proteins - electron carriers(photosynthesis and resp)
Channel proteins (allow small charged particles through with facilitated diffusion)
Carrier proteins(transport larger molcules and charged particles across membranes by facilities diffusion and active transport)
What’s the function of glycoproteins and glycolipids
Stabilise the membrane by forming hydrogen bonds with surrounding water molecules.
Some GP allow cells to attach to each other to form nervous tissue
Act as receptors for messenger molecules in cell signalling and is a binding sites for drugs antibodies and hormones.
They can act as antigens - cell surface molcules involved in self recognition and the immune response
What are glycolipids and glycoproteins
Carbs attached to lipids and carbs attacged to proteins
How does temp affect membrane permeability
It affects how much the phospholipids in the bilayer can move.
Temps below 0= phospholipids don’t have much energy so can’t move much .they’re packed close and rigid but channel and carrier proteins in the membrane denature(losing structure and function) increasing permeability of membrane. I’ve crystals may form and pierce the membrane making highly permeable when it thaws
Temps between 0-45- phospholids can move around and aren’t packed tight tg so the membrane is partially permeable. As the temp increases the phospholipids move more because they have more energy this increases permeability of membrane.
Temps above 45- Pbilayer starts to melt and break down and membrane becomes more permeable. Water inside cell expands putting pressure on membrane. Channel proteins and Carrier proteins denature so they can’t control what enters or leaves the cell- inc permeability of membrane
How to investigate membrane permeability
Colorimetry-
1-cut 5 equally sized pieces of beetroot and rinse the pieces to remove an pigment released
2-add 5 pieces to diff test tubes containing 5cm of water and use a measuring cylinder/Pipette to measure the water
3- placed each test tube in a water bath at diff temps for same length of time
4- remove pieces of beetroot from tubes leaving just coloured liquid
5- turn on colorimeter and leave for 5 mins for it to stabilise and then set it up with a blue filter
6- add distilled water to a cuvette and put it into the colorimeter and calibrate the machine to zero.
7- use a pippete to transfer a sample of liquid from first test tube to clean cuvette
8-put cuvette in colorimeter and read and record absorbable
9- repeat 7-8 for the other 4 liquids
The higher the absorbable reading the more pigment released so the higher the permeability of membrane
What is diffusion
The net movement of particles from an area of higher conc to an area of low conc.
How does diffusion work
Particles will diffuse down a concentration gradient until particles are evenly distributed between both concentration where equilibriums reached and there is no overral net movement.
Does diffusion need energy?
No it’s a passive process no metabolic energy needed. It can easily diffuse across plasma membrane as long as particles in membrane can move freely.
Factors that affect rate of diffusion
Conc-gradient-the greater this is the greater the rate of diffusion
Particle charge/size-because of the cell membranes hydrophobic core charged particles will not be able to diffuse through but some molecules like water can because of its size. The smaller the molecule the faster the rate of diffusion
Temp-in warmer conditions particles have more Ke and diffuse faster
SA-larger the Sa the faster ROD as there’s more space for molecules to diffuse across a membrane
Distance - greater distance the slower ROD. Particles have to travel more
Hydrophilic substances are needed for many processes in the cell so how do they get by the cell membrane?
Through facilitated diffusion
What happens in facilitated diffusion
In facilitated diffusion hydrophilic substances diffuse across cell membrane via carrier proteins or channel without interacting with the hydrophobic core of the bilayer
Carrier proteins move large molcules into or out the cell down the conc gradient. First a large molecule attached to carrier protein in membrane
Then the tertiary structure of protein changes shape.
This change on shape brings the chemical across membrane where it’s now released.
Channel proteins- form pores in membrane for smaller ions and polar molcules to diffuse though down conc gradient.The pore is lined with hydrophilic AA and contains water. Hydrophilic substances can pass through channel. These are very specific to the chemical that passes through so only certain ones can pass though each type of PC.They may not always be open and may need to get triggered, either by a chemical binding to the channel or a change in voltage across membrane.
Similarities between facilitated diffusion and diffusion
Both have particles moving from a high concentration to a low concentration down a conc gradient
They’re both passive as well
How to investigate diffusion (conc gradient)
With agar jelly- same consistency to cytoplasm of real cell- and phenolphthalein (ph indicator) it’s pink in alkali solutions and colourless in acidic. So if you place cubes of agar jelly in phenolphthalein and an alkali(NaOH) it will turn colourless as the acid diffuses into agar jelly neutralising NaOH.
1) make up some agar jelly with Phnelohtlanr and dilute NaOH.
2)prepare 5 test tubes containing Hcl in inc conc
3)cut out 5 equal sized cubes from agar jelly
4) put one of the cubes in test tube and time how long it take to turn colourless
5) do the same for rest
The cube in highest conc of HCL to go go colourless fastest as it has highest concentration gradient
How to investigate diffusion based on SA and temp
Cut the agar jelly into different sized cubes this times and work out SA:V ratio. And time how long it takes to go colourless. Cube w the highest Sa:V will.
Temp-prepare agar jelly and cut into equal sized cubes and prepare several boiling tubes w same conc of HCl and put it into water baths of diff temps. Then put agar jelly into each and time how long it takes to go colourless. Highest temp would go fastest
What is osmosis
The net movement of water molecules form an area of high water potential to an area of low water potential across a partially permeable membrane.
What’s the highest water potential and what can adding solutes do to it
0 KPa(pure water)
dilute the water potential into negatives so the more negative a solution the stronger the concentration of solutes
When does the net movement of water become zero
When the water potential between both concentrations are equal and water molecules are evenly spread out and have reached equilibrium.
Why does the cytoplasm of all animal cells have a negative alter potential
Contains a number of solutes dissolved in water these solutes could be mineral ions and glucose
What is the same as the water potential of cytoplasm and whats this mean
The water potential of blood plasma in RBC
Osmosis isn’t taking place as water potential is same outside and inside but water molcules are still moving across membrane but rate of movement inwards and outwards is the same so no net movement of molcules.
If two solutions have same water potential then they’re isotonic.
What happens when we put an animal and plant cell into pure water and what does that make the solution
Water potential outside cell is higher than inside so water molcules will move inside cell, this movement of water molcules causes pressure inside the cell to increase rupture and burst.
In plant it will increase pressure inside and cause cell to become turgid but not burst due to the inelastic cell wall
This makes the solutions hyportonic ( higher water potential than inside)
When an animal cell and plant cell is placed In a solution with a lower water potential then what happens
Water will move out of cell by osmosis. Solutions with lower water potentials are hypertonic. If animal cell placed in hypertonic solutions it’s gna shrink.
If plant cell placed in a hypertonic solution it’s Gna become flaccid. It w experience plasmolysis ( cytoplasm and plasma membrane will eventually pull away from cell wall)
How to Investigate the effect of water potential on plant cells
1-prepare sucrose solutions of 0.0,0.2,0.4,0.6,0.8,1.00
2-use cork bored to cut potatoes into identically sized cylinders 1cm in diameter and measure the mass of each
3-place the cylinders into each solution and leave for 20 mins for each
4- remove cylinders and pat it dry and weigh mass again
5- calc % change
Potato cylinders will gain water with solutions with a higher water potential and lose water in solutions with a lower water potential
How to investigate the effect of water potential on animal cells
1- make up NaCl solution of diff conc 0.2,0.4,0.6,08,1.0
2- take your deshelled eggs and carefully pat them with absorbent paper to remove excess moisture
3-weigh each eggs w mass balance
4-place each egg in diff beaker covered with Nacl and leave eggs for same amount of time
5-remove eggs dry and weigh again.
6-Calc % change
What’s active transport and how’s it work
It uses energy to move molcules and ions across plasma membranes against a concentration gradient.
molecule attaching to the receptor site of carrier protein and then an ATP molecule binds to carrier protein and ATP undergoes hydrolysis making phosphate and a molecule of ADP the phosphate attaches to carrier protein causing it to change shape. this moves the molecule across the membrane from a region of lower concentration to a region of higher concentration releasing it on the other side.phosphate now leaves carrier protein causing it to return to its original shape and ADP and phosphate will reform atp during resp
It’s an active process so this metabolic energy is used from ATP to move solute against its concentration gradient
What happens in endocytosis
A cell can surround a substance with a section of its plasma membrane then the membrane pinched off to form a vesicle inside the cell containing the ingested substance - and this substance has been taken in by endocytosis
This is active so it uses atp for energy
When do molcules under go endocytosis
When molecules are too large to be taken into a cell or when cells want to take larger substances into the cell eg WBC bring in dead organisms and microorganisms by endocytosis to destroy them
What happens in expcytosis
Substances made by cell( hormones,digestive enzymes, lipids) need to be released and this is done by exocytosis.
Vesicles containing these substances pinch off from the sacs of Golgi and move towards plasma membrane. The vesicles fuse with the cell surface plasma membrane and release contents outside the cell ( some substances like membrane proteins in steered straight into plasma membrane).
This is an active process and requires atp for energy
What goes through passive process
Diffusion
Facilitated diffusion
Osmosis pop
Examples of active transport
Uptake of glucose and amino acids in small intestine
Absorption of mineral ions by plant roots
Excretion of hydrogen ions and urea by kidneys
Exchange of sodium and potassium ions in neurons and muscle cells
Why do cells that undertake active trainiert have alot of mitochondria
As it goes through aerobic respiration which makes atp
What’s bulk transport and the two types of bulk transport
When extremely large substances need to be moved across a cell membrane bulk transport used
Endocytosis and exocytosis
Endocytosis can be split into phagocytosis ,pinocytosis and receptor mediated endocytosis
How does atp release energy
Energy released when bonds broken
This is a hydrolysis reaction
A small amount of energy required to break the bond
More then released from breaking it and net energy is released
Atp is resynthesized in condensation reactions by atp synthase
What’s the energy released from atp stored as
Fats and carbs and during cellular respiration these are broken down to make atp
What’s atp made of
And what happens when it’s hydrolysed
Ribose sugar
Adenine base
And three phosphate groups
It forms adp and inorganic phosphate 30.5Kj of energy released. The inorganic phosphate can be used to phosporylate other compounds making them more reactive.
Effect of solvents on membrane permeability
Polar substances like water is important in creating membrane stability with the phospholipids but less polar molecules like alachols can move into bilayer and disrupt structure.
Ethanol is non polar so it can dissolve non polar substances . So if u place a cell in ethanol its membrane will become permeable and allow substances to leak in and out of the cell . As ethanol concentration increases, membrane permeability will increase .
If ethanol conc is too high phospholipid will dissolve to cause plasma membrane to disintegrate and kill the cell.
Effect of cholesterol on temp and fluidity
Temp high more cholesterol decreases the fluidity of membrane. When the temp is low more cholesterol increases membrane fluidity
What is cell signalling
Why is cell signalling important
When one cell releases a messenger molecule (eg a hormone) this molecule travels to another cell (in the blood)
The messenger molecule is detected by the cell cuz its binds to a receptor in its cell membrane.binding then triggers a change in the cell eg a series of chemical signals is set off.
Important as cells need to communicate w each other to control processes inside body and respond to changes in envronment
What would cells designed to respond to a hormone likely have?
specific receptors for that hormone
What is a primary messenger?
A primary messenger is a signaling molecule, such as a hormone or neurotransmitter, that binds to a receptor on a target cell and initiates a cellular response. Primary messengers are the first step in cell signaling pathways.
What is a secondary messenger?
And eg of a common secondary messenger
Ans why are they necessary
a molecule inside a cell that relays signals from an extracellular primary messenger ) to trigger a cellular response. Secondary messengers amplify the signal and activate intracellular pathways.
Ca2+
They initiate a fast response to stimuli and enhance response when triggered
Why don’t some primary messengers, such as steroid hormones, need secondary messengers or cell receptors?
because they are lipid-soluble. This allows them to diffuse directly through the cell membrane and bind to intracellular receptors in the cytoplasm or nucleus.
What are reactions caused by a secondary messenger called?
signal transduction pathways
What do alcaholic drinks do to cells
While they do not dissolve plasma membranes like strong or pure alcohols, they still damage them because non-polar alcohol molecules get between the phospholipids, disrupting the membrane and making it more fluid and permeable.
Why do organic solvents dissolve membranes
Why alcahol used in antiseptics
Many are less polar than water (i.e alcohols) and some are completely non-polar (i.e benzene). This means that phospholipid bilayer is disrupted and cell membrane dissolves
Its less polar than water so it dissolves plasma membranes of bacteria
Why’s water essential in structure of plasma membranes
To keep heads n tails of phospholids arranged correctly
Are extrinsic n intrinsic proteins hydrophobic or hydrophilic
Ex-philic
In-phobic
how does hydrostatic pressure occur?
N what happens when it increases in animal cells
occurs due to the force exerted by a fluid (such as water) against the walls. Causes cell to rupture n burst it can happen when placed in a HYPOTONIC solution
How is cell membrane used in cell signalling process
Proteins in cell membrane act as receptors for messenger molecules(membrane bound receptors)
How do receptor proteins work
They have specific shapes- only messenger molecule w a complementary shape can bind to them. Diff cells have diff types of receptors -respond to diff messenger molecules- these are non target cells.
Difference between target cell and non target cell
Target cell -messenger molecule binds to receptor on target cell
Non target cell-messenger molecule can’t bind to receptor on non target cells
How do hormones work as messenger molecules and what are the diff types
They bind to receptors in cell membranes triggering a response in the cell.
Eg glucagon hormone released when there isn’t enough in the blood. It binds to receptors on liver cells causing liver cells to break down stores of glycogen to glucose
Fsh is a hormone released by pituitary gland during menstrual cycle. It binds to receptors on cells in the ovaries causing an egg to mature ready for ovulation
Role of drugs as hormones and give some examples
drugs work by binding to receptors in cell membranes. They either trigger a response in the cell, or block receptor + prevent it from working.
how cells communicate using membrane-bound receptors is important in the development of medicinal drugs — receptors can be used as sites for targeted action.
Morphine -
body produces chemicals called endorphins to relieve pain. Endorphins bind to opiod receptors in brain n reduce transmission of pain signals.
Morphines a drug to relieve pain and works by binding to same opioid receptors as endorphins also triggering a reduction in pain signals
2)antihistamines-cell damage=releases chemical histamine.it binds to receptors on surface of other cells and causes inflammation. Antihistamines work by blocking histamine receptors on cell surfaces. This prevents histamine from binding to cell n stops inflammation
Suggest why messenger molecules is only able to produce a response in liver cells
The messenger molecule (e.g., glucagon binds only to cells that have the correct complementary receptor proteins on their plasma membrane.
Liver cells contain specific receptors for these hormones, allowing them to detect and respond.other cells lack this receptor
