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
