2.5 - E - Biological Membranes Flashcards
Explain what a phospholipid consists of
1 phosphate head
2 fatty acid tails
Define hydrophilic
Water-loving
Define hydrophobic
Water-hating
Why are phosphate heads hydrophilic?
The charges on the head are unevenly distributed (polar)
This lets it interact with the water molecules easily
Why are fatty acid tails hydrophobic?
The charges on them are evenly distributed (non-polar)
This means they won’t mix with water and will repel the molecules
When in water, why can phospholipids slide around one another?
Because the lack of bonds causes fluidity
What is the average thickness of a phospholipid bilayer?
7-10nm
What should you always refer to the cell membrane as and never refer to it as?
Refer to it as: the plasma membrane or the cell surface membrane
Never refer to it as: the cell membrane
What do some phospholipid bilayers contain and how does this affect them?
Aquaporins (protein channels which allow water through) which make them much more permeable to water.
What is a liposome?
An artificially prepared vesicle made of a lipid bilayer
List 7 roles of the plasma membrane
Separating cell contents from outside environments and cell components from cytoplasms
Regulating transport of materials in and out of cells
Holding components of some metabolic pathways in place
May contain enzymes involved in specific metabolic pathways
Has antigens, so the immune system doesn’t attack it
May release chemicals for other cells (cell signalling), contains receptors for chemicals, site for cell communication/signalling
May be the site of chemical reactions
What does delta mean and what is the sign?
Like an 8 without the top right but yaknow
Delta - a little bit
What is the difference between polar and non-polar
Polar - uneven charge
Non-polar - even charge
Explain the charge of a water molecule
2 delta + hydrogen ions
1 delta - oxygen ion
Overall, + polar
Who proposed the fluid mosaic model?
Singer and Nicolson
1972
What is a glycoprotein?
A carbohydrate chain attached to a protein molecule
What is a glycolipid?
A carbohydrate chain attached to a lipid
What is the function of cholesterol and where is it found?
Gives mechanical stability and flexibility
It fits between fatty acid tails and ‘plugs gaps’ ‐ makes the membrane less permeable to water molecules and to ions
It restricts too much movement within the phospholipid layer
What do carbohydrate molecules do around the membrane and what is another name for them?
Glycocalyx
They are hydrophilic and attract water with dissolved solutes, helping the cell interact with its watery environment and obtain dissolved substances
What is the difference between an intrinsic protein and an extrinsic protein? Give an example of each
Intrinsic protein - goes through the entire membrane (channel protein)
Extrinsic protein - partially embedded inside or outside the membrane (carrier protein)
What is the purpose of glycoproteins and glycolipids?
They are involved in cell signalling - they are “self “to allow recognition by the immune system.
They are receptors for hormones/drugs
On the surface of pathogens they are antigens ‐ immune system can
recognise them as ‘foreign’
Glycoproteins can bind cells together in tissues
Are intrinsic proteins hydrophobic or hydrophilic and why?
Hydrophobic - due to passing through the hydrophobic region as they span the whole membrane
What are channel proteins?
They have pores for small ions or small water soluble molecules to diffuse through the membrane - intrinsic
What are carrier proteins?
They help larger molecules to diffuse through the membrane, or can be used for active transport across the membrane - extrinsic
How is the cytoskeleton related to the fluid mosaic model?
Actin microfilaments and its proteins help anchor membranes and stop them moving around too much.
List the 3 factors that affect membrane permeability
Temperature
Cholesterol
Saturation
Explain how an increase in temperature affect membrane permeability (4)
The phospholipids acquire more kinetic energy and move around more. This increases fluidity and therefore permeability.
It also affects the way membrane-embedded proteins are positioned and may function. If they move, rate of reactions change.
Temp may affect the infolding of membranes during phagocytosis.
It may also change the ability of cell signalling by releasing chemicals (exocytosis)
Explain how a decrease in temperature affects membrane permeability
Phospholipids cluster - crystallised state
Explain how cholesterol affects membrane permeability
Less cholesterol - lower temp
They sometimes insert themselves between phospholipids
Membranes vary in their amount of cholesterol
Less cholesterol increases distance between phospholipids. This increases fluidity
More cholesterol - higher temp
Inserting cholesterol means the phospholipids are already distant, and the cholesterol pulls them together, decreasing fluidity
Explain the saturation of fats and how it affects membrane permeability
Saturated - longer and thinner fatty tails
This means less distance between phospholipids so less fluidity
Unsaturated - shorter, double bonds create kinks/gaps
More distance between phospholipids so more fluidity
List the features of Mrs Gren
What are they all together?
Movement Respiration Sensitivity Growth Reproduction Excretion Nutrition The 7 life processes ‐ all living things do ALL of them [viruses don't ‐ technically not living!]
Define cell signalling
When cells communicate with one another by signals to help them work together and coordinate their actions.
Give 2 examples of cell signals secreted by cells
Cytokines and hormones
What are target cells?
Cells with specific receptors for the hormones
When and where is insulin made?
Beta‐cells in islets of Langerhans in pancreas
When blood glucose is too high
What are the target cells and the effect insulin has on them?
Insulin receptors on many cells inc. muscle and liver cells
Cells take up more glucose from blood = reduces blood glucose level
List the 7 functions of glycoproteins
Cell signalling ‐ communication between cells to help them work together/
They coordinate actions
They act as antigens for cell recognition ‐ recognition as self/non‐self, allows the immune system to not attack it
They are receptors found on target cells… for hormones/cytokines to trigger reactions/responses in cells
They cause cell adhesion ‐ hold cells together in tissues
They form bonds with water molecules to stabilise membrane
They are receptors on transport proteins
Define diffusion
The net movement of molecules from a region of high concentration to a region of low concentration of that molecule, down a concentration gradient. This is a passive process.
Define osmosis
The net movement of water molecules from a region of high concentration of water molecules to a region of low concentration of water molecules down the concentration gradient, across a partially permeable membrane. This is a passive process.
Define active transport
The movement of molecules or ions across membranes from a region of low concentration to a region of higher concentration of that molecule against the concentration gradient. It requires energy in the form of ATP.
A quicker rate of diffusion is caused by…
A steeper concentration gradient
List and explain the 5 factors that affect the rate of diffusion
Temperature ‐ higher temp = more kinetic energy for molecules = higher rate of random movement = higher rate of diffusion
Stirring/moving ‐ stirring increases movement of molecules = higher rate of diffusion
Surface area ‐ diffusion across membranes is faster if there is a larger SA to diffuse across. e.g. alveoli
Distance/thickness ‐ thinner membrane = faster diffusion e.g. alveoli
Size of molecule = smaller molecules = faster diffusion
List and explain the 2 substances that can diffuse directly across the bilayer
Lipid‐based molecules ‐ are fat soluble so dissolve and diffuse readily across the bilayer e.g. steroid hormones
Very small molecules ‐ oxygen and carbon dioxide are small enough to pass between phospholipid molecules. Water and urea molecules are very small but because they are polar (charged) they pass across the bilayer much slower
What features of a molecule cause a quicker rate of diffusion?
The smaller and less polar a molecule, the quicker it will diffuse
across a membrane.
Define facilitated diffusion
The net movement of molecules from a region of high concentration to a region of lower concentration of that molecule, down the concentration gradient, across a partially permeable membrane via carrier or channel proteins. It is a passive process
Explain how channel proteins are a part of facilitated diffusion
They form pores in membranes.
There are hydrophilic conditions inside pore
They are specific to certain small‐water soluble molecules or ions e.g. sodium and calcium ions
They allow diffusion in or out of cell/organelle
How does a channel protein being gated impact the membrane
They can be opened or closed by a signal or change in voltage across the membrane - they can choose what to let in and out of the cell
Explain how carrier proteins are a part of facilitated diffusion
They carry larger molecules e.g. glucose & amino acids ‐ shaped for specific molecules to bind to
The molecule binding changes the shape of the carrier protein
This causes the molecule to be carried to and released on the other side of the membrane
Defin water potential
The measure of the tendency of water molecules to diffuse from one region to another
What is the highest water potential?
0 KPa
What is a solute?
A solid that dissolves
What is a solvent?
A liquid that dissolves solids
What is a solution?
The liquid containing dissolved solids
What does it mean if a cell is haemolysed/cytolysed?
When animal cell surface membranes burst
What happens to cells in higher water potential?
Water moves into the cell by osmosis and the cell swells.
Animal cells burst (become haemolysed/cytolysed)
Plant cells become turgid
What does it mean if a plant cell is turgid?
In a higher water potential the cells swell as water moves in.
It is then ready to burst but the cell wall restricts it from doing so.
The cell is now turgid and osmosis into the cell stops
What does it mean if an animal cell is crenated?
Osmosis out of the cell takes place and the cell begins to shrink and wrinkle
What does it mean if a plant cell is plasmolysed?
In a lower water potential the cells shrink as water moves out.
The cytoplasm then pulls away from the cell wall.
The cell is now plasmolysed
What is incipient plasmolysis?
The point when the cell membrane is about to pull away from the cell wall
What happens to cells in low water potential?
Water moves out of the cell by osmosis and the cell shrinks.
Animal cells wrinkle (become crenated)
Plant cells become plasmolysed
Explain the process of active transport using carrier proteins
Carrier proteins work as pumps.
Specific and complementary shaped molecule binds
Molecules can’t diffuse (due to gradient)
ATP provides the energy needed for the protein to change shape and transport the molecule across the membrane.
Shape change only allows the molecule to fit in the protein on one side
of the membrane ‐ it will not fit on the other side ‐ stops transport in
the wrong direction.
Much faster than diffusion
Can go inside cells/organelles or outside cells ‐ dependant on gradient.
What are the 2 types of bulk transport?
Endocytosis and exocytosis
Define endocytosis
Moving in
Define exocytosis
Moving out
Phago means…
Solids
Pino means…
Liquids
Define exophagocytosis, endopinocytosis, endophagocytosis and exopinocytosis
Solids moving out
Liquids moving in
Solids moving in
Liquids moving out
Explain the process of exocytosis
Vesicle moves towards the cell surface membrane on microtubles using ATP.
The vesicle fuses with the cell surface membrane ‐ requires ATP
The molecules are ejected from the cell
Explain the process of endocytosis
A molecule binds to a receptor and this causes the cell surface membrane to fold in ‐ invaginates
This requires ATP
The cell surface membrane fuses with itself to form a vesicle
What is invaginating?
When a cell surface membrane folds in on itself
What’s the difference between the process of carrier proteins in facilitated diffusion and active transport?
In both processes the carrier protein needs to change shape for the molecule. However, due to the negative concentration gradient in active transport, ATP changes to ADP and releases energy which the protein uses to change its conformation (shape) and in doing so carries the ion from one side to the other.
What does phagocytosis mean?
“Eating by cells”
When is ATP hydrolysed?
A molecule of ATP is hydrolysed for every step that a motor protein takes along the cytoskeleton thread as it drags the vesicles
(Exocytosis)
What does integral mean?
A membrane protein that is permanently attached to the plasma membrane
Describe and explain the role of cholesterol in the plasma membrane
It partially immobilises nearby phospholipids in plasma membranes. This decreases the permeability and maintains the mechanical stability of the plasma membrane.
Define hypertonic, isotonic and hypotonic
Hypertonic - water potential outside the cell is lower than inside
Isotonic - water potential is equal inside and outside the cell
Hypotonic - water potential is higher outside the cell than inside
What is the difference between cytolysis and heamolysis?
Cytolysis happens to any animal cell
Heamolysis happens to red blood cells only
