Module 2.1.5 - plasma membranes Flashcards
What are the general roles of membranes?
- separating cell contents from external environment
- cell recognition and signalling via receptors
- separating cell components from cytoplasm
- holding components of the same metabolic pathways in place
- regulating transport of materials in or out of cells
What is the phospholipid bilayer?
- consists of 2 layers of phospholipids, one being the hydrophobic interior and a hydrophilic exterior
- hydrophilic head group and hydrophobic tails (fatty acid chains) are depicted in the single phospholipid molecule
What molecules can and can’t diffuse through the phospholipid bilayer?
Small and fat soluble molecules can diffuse through
large, charged and fat insoluble molecules can’t diffuse through so require membrane proteins
What are polar molecules?
- partially charged
- fat insoluble
hydrophilic
What are non-polar molecules?
- uncharged
- soluble in fats
- hydrophobic
What is the fluid mosaic model?
States membranes are composed of a phospholipid bilayer with various protein molecules floating around within it
What does the lipid bilayer contain?
lipid molecules which have their hydrophilic heads in contact with the watery exterior
e.g. cytoplasm
What do hydrophilic phosphate heads form?
They form hydrogen bonds with water molecules
Where are hydrophobic tail regions in the fluid mosaic model?
In the centre of the membrane, away from the water
What membrane do intrinsic proteins have?
transmembrane
What are the 2 types of intrinsic proteins?
Channel proteins - act as passageways to allow ions with electrical charges to pass through
Carrier proteins - can change shape to allow specific molecules across
Some proteins (glycoproteins) are attached to carrier proteins and act as enzymes, antigens or receptor sites for chemicals, such as hormones
What are extrinsic proteins?
- serve in transport of molecules and as receptors
- present in one side of the bilayer
What are glycoproteins?
- proteins that contain covalently attached sugar residues
- role in cell adhesion and as receptors for signalling
What does the receptor binding do in glycoproteins?
Triggers a direct response or a cascade of events inside the cell
e.g. receptors for insulin and glucagon are glycoproteins
What are glycolipids?
Lipids with a carbohydrate attached by a glyosidic bond
What is the role of glycolipids?
to maintain stability of the cell membrane n to facilitate cellular recognition (antigens) which is crucial to the immune response and in the connections that allow cells to connect to one another to form tissues
How is glycocalyx formed?
from the carbohydrate chains attached to lipids (glycolipids) or proteins (glycoproteins) in the membrane
What is glycocalyx?
‘sugar coat’
What is cholesterol?
- type of lipid/fat
- has a hydrophilic end and a hydrophobic end
- regulates fluidity and stability of the membrane
- helps the membrane resist temperature changes
What does the folded inner membrane of the mitochondria (cristae) create?
A large surface area for aerobic respiration
Enzymes requires are localised in the cristae
Where do light dependent reactions occur?
Thylakoid membranes in chloroplasts which is part of the inner membrane containing chlorophyll
What do digestive enzymes on the plasma membrane of epithelial cells of the small intestine do?
Catalyse some of the final stages of the breakdown of certain types of sugars
What do membranes control?
The passage of different substances in and out of cells (and organelles)
What is vital to selective permeability?
Membrane integrity
What 4 factors effect membrane permeability?
- temperature
- proportion of cholesterol
- proportion of saturated and unsaturated fats
- presence of solvents
How does temperature effect membrane permeability?
- phospholipid molecules constantly moving
- increase temp means increase in KE of phospholipids so more fluidity
- more fluidity = less membrane integrity
- excessive temp = membrane disintegrates completely
- proteins are less stable than phospholipids
How does cholesterol effect membrane permeability?
- buffers the effect of lowered temperatures to prevent a reduction in the membrane’s fluidity
- prevents phospholipid molecules from packing together too closely
- reduces membrane fluidity at moderate temperatures
- low temperatures, hinders them
How do unsaturated and saturated fats effect membrane permeability?
- unsaturated hydrocarbon tails with kinks are better in cold temperatures = have a double covalent bond
- saturated hydrocarbon tails have no kinks so better in warm temperatures = have single covalent bonds
How do solvents effect membrane permeability?
- dissolve membranes, disrupting cells
- rationale behind ethanol use in antiseptic
- very strong alcohol solution = toxic
- less concentrated alcoholic solutions = don’t dissolve membranes, still cause damage
- ethanol = non polar, diffuses across lipid bilayer and through channel proteins, disrupting membrane structure = increasing permeability
- disrupted neuronal membranes = disrupted nerve impulses = lack of coordination/slower reaction time associated with drunkenness
What buffers to lower the temperature?
Cholesterol
What do unsaturated hydrocarbon tails do?
Have kinks so work better in low temperatures a the tails allow diffusion to happen even though there is low energy levels
What do saturated hydrocarbon tails do?
Have no kinks so diffusion still happens quickly as there is high energy levels from the high temperatures
What is diffusion?
The NET movement of particles from a high concentration to a low concentration, down the concentration gradient
What do molecules posses as they move randomly?
kinetic energy
The steeper the concentration the…
Higher diffusion rate
What are the 2 types of diffusion?
simple and facilitated diffusion
What is simple diffusion?
- Molecules pass through the membrane unassisted
- down the concentration gradient
- no proteins are involved
- some molecules pass straight through the membrane
- molecules are small and soluble in lipids so can pass through lipids in the membrane
- a passive process, no energy required
What are water molecules?
Polar and lipid insoluble
When can direct diffusion happen?
If there’s high levels of water molecules
What do some membranes use?
Aquaporin channels (special water channel proteins to allow water molecules to move across the membrane. This is a form of facilitated diffusion)
What happens in the alveoli?
oxygen diffuses into the blood from an area of high to low concentration
What is pumped away to the cell in the blood capillaries?
Oxygen, which maintains the concentration gradient
What happens in the cells?
Oxygen diffuses into the cytoplasm and then into the mitochondria for aerobic respiration, constantly lowering the oxygen conc inside the cell, maintaining conc gradient
What is facilitated diffusion?
- specific proteins carriers or protein channels in the cell membrane are needed to transport molecules
- ions are insoluble in the lipid bilayer due to hydrophobic tails
- these molecules diffuse through protein channels or pores in the membrane down the conc gradient
- doesn’t require energy
What are carrier proteins?
- transmembrane proteins in the membrane called carrier proteins bind with specific molecules, which opens the protein to allow molecules to cross the membrane
- have a specific shape, normally carrying 1 specific shaped molecule
What factors effect diffusion?
- temperature
- diffusion distance
- surface area
- size of diffusing molecule
- concentration gradient
Why does temperature effect diffusion?
high temp - quicker diffusion as more diffusion
low temp - slower diffusion as less energy
Why does diffusion distance effect diffusion?
bigger distance - slower diffusion
small diffusion - quicker diffusion
Why does surface area effect diffusion?
large SA - quicker diffusion
small SA - slower diffusion
Why does size of diffusing molecule effect diffusion?
bigger molecules take longer to diffuse
smaller molecules are quicker to diffuse
Why does concentration gradient effect diffusion?
steep concentration - faster diffusion
not steep - slower diffusion
What is active transport?
The net movement of particles from an area of low concentration to high concentration, against the concentration gradient
What does active transport require?
- Energy/ATP
- carrier proteins
Why do cells need a large amount of ATP in active transport?
kinetic energy isn’t enough
What is often transported by active transport?
Ions
Why are carrier proteins required in active transport?
To transport a substance with a specific shape to the carrier protein against the concentration gradient
What do root hair cells use to absorb minerals from the soil?
Active transport
What doe root hair cells absorb through active transport?
Minerals from the soil
What is the equation for active transport?
ATP + H2O -> ADP +P + energy
What are the 2 types of cytosis?
- exocytosis
- endocytosis
How is cytosis possible?
The fluid nature of the cell surface membrane
What is the process of endocytosis?
- takes substance into cell
- cell surface membrane infolds (invaginates) round the substance outside the cell to form a vesicle
- vesicle enters the cell and membrane reforms
- ATP provides energy to form vesicles and move them using motor proteins along the cytoskeleton microtubules
What is the process of exocytosis?
- solids or liquids leave the cell when vesicles fuse with the cell membrane
- contain isolated substances in vesicles
- vesicles move towards the cell surface membrane and fuses with it, enabling the contents of the vesicle to leave the cell
- the membrane then reforms
What are the 2 types of endocytosis?
- Phagocytosis
- Pinocytosis
What is phagocytosis?
cell eating, vesicle traps solids or food substances to be taken into cell
What is pinocytosis?
Cell drinking, vesicles traps liquid to go into the cell
What is osmosis?
The movement of water molecules across a partially permeable membrane from a region of high water potential to a region of lower water potential, with the water potential gradient
What is the water potential of a solution a measure of?
How much water the solution contains in relation to other substances and how much pressure it exerts on the membrane/container
What does a solution containing a lot of water have?
A higher water potential, exerting some pressure
What does a solution containing a lot of dissolved solutes have?
A lower water potential, exerting less pressure
What is the units and symbol for water potential?
Units = Pa/ KPa
Symbol = ψ (Psi)
What does water potential quantify?
The tendency of water to diffuse from one area to another sue to osmosis
What is the highest water potential you can have?
0 Pa
What type of water has the highest water potential?
Pure/distilled as it contains no dissolves solutes
What is a isotonic solution?
Contains the same amount of solutes and and has the same water potential as a cell suspended in the solution
What does hyper mean?
High, over, excess
What does hypo mean?
Low, under, beneath
What does a hypertonic solution contain?
More solutes
What does a hypotonic solution contain?
Less solutes
What type of water potential do hypertonic solutions have?
Lower water potential than a cell suspended in the solution
What type of water potential do hypotonic solutions have?
Higher water potential than a cell suspended in the solution
What does crenation mean?
Cell shrinkage
What does plasmolysis mean?
Membrane pulls away from cell wall as cytoplasm shrinking due to plant cell being in a hypertonic solution
What does placing an animal cell in a solution of low water potential mean?
An osmotic water potential gradient is established (high inside cell and low outside cell), water moves down the water potential gradient
What does cytolysis mean?
Cell swells and bursts as the membrane breaks when in a hypotonic solution
What does haemolysis mean?
Red blood cell bursts in a hypotonic solution
What does turgid mean?
Plant cell swells but doesn’t burst in a hypotonic solution, increasing turgid pressure
What’s the difference between plant and animal cells when they are in a hypotonic solution?
Plant cells swell/become turgid due to having a cell surface membrane and cell wall
Animal cells burst as they only have a cell surface membrane
