2.1.5- biological membranes Flashcards
what are the roles of the cell surface membrane?
To isolate the cell from it’s surroundings (compartmentalisation).
To control the passage of substances into and out of a cell.
To have receptors for hormones or neurotransmitters.
Cell recognition.
So lipid-soluble substances can diffuse across
what are the functions of the organelle membrane?
To control the entry and exit of substances into organelles like the mitochondria.
To isolate organelles so specific metabolic reactions can occur within them.
To isolate enzymes that might damage other regions.
To provide surfaces for reactions to occur- protein synthesis on the ER
explain the structure of a phospholipid
a hydrophilic phosphate head with two hydrophobic fatty acid tails.
how do phospholipids arrange themselves in a bilayer?
hydrophilic phosphate heads on outside, hydrophobic fatty acid tails on the inside in a bilayer.
describe the fluid mosaic model
proteins can move within this phospholipid bilayer, they fit together like a mosaic.
what is the impact of too much cholesterol in a bilayer?
reduced fluidity as phospholipids group together too closely and crystallise
what are intrinsic proteins?
transmembrane proteins embedded through both sides of the bilayer- they have amino acids with hydrophobic R-groups on their external surfaces which interact with the hydrophobic core of the membrane.
what is the function and structure of a channel protein?
they provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a conc. gradient through membranes. The structure is essentially like a pore
what is the structure and function of a carrier protein?
an important role in both active and passive transport, the movement involves changing the shape of the protein as it binds to the substance. the structure has an indent in it to carry the molecule depending on it’s shape
what are glycoproteins, what is their function?
proteins with attached carb groups embedded in the membrane, attached to intrinsic proteins,
function: cell adhesion, receptors for chemical signals, cell signalling (when a chemical binds to a receptor to elicit a cellular response)
what is the structure and function of extrinsic proteins?
peripheral proteins present on one side of the bilayer, they have hydrophobic R-groups on their outer surfaces and interact with the polar heads of phospholipids.
what are the functions of glycolipids?
cell markers or antigens which can be recognised by the cells of the immune system (cellular recognition), stability
what is cholesterol? function and structure
a lipid in the bilayer, has a hydrophilic end and a hydrophobic head. Plays a role in the regulation of membrane fluidity- molecules are positioned between phospholipids. the hydrophilic end interacts with the heads and hydrophobic end interacts with the tails. therefore it adds stability
describe a triglyceride
contains C H O, is insoluble in water, contains glycerol, contains ester bonds, contains fatty acids
describe a phospholipid
insoluble in water, contains glycerol, contains ester bonds, important in membrane structure, contains fatty acids
describe cholesterol
contains C H O, insoluble in water, important in membrane structure.
define diffusion
the net movement of particles from a region of high concentration to a region of low concentration, down a concentration gradient. a net movement until equilibrium is reached.
why does diffusion occur?
because of the natural energy possessed by molecules or ions which makes them move randomly- the process is passive.
what is simple diffusion?
membranes are freely permeable to the respiratory gases, water, uncharged molecules, and lipid-soluble molecules. Passive transport across the membrane without the use of transmembrane proteins.
what is facilitated diffusion?
the membrane is selectively permeable, carrier proteins which change shape to bind to the molecule or ion carry the molecule across. Carries molecules that are large, ions, or polar.
factors affecting diffusion
Steepness of gradient.
Temperature.
Surface area.
Diffusion distance.
how does the rate of diffusion change with steepness of gradient?
the steeper the gradient, the faster the rate of diffusion as the imbalance of equilibrium is greater
how is the rate of diffusion affected by temperature?
the molecules have more kinetic energy so they diffuse across the membrane faster
how is the rate of diffusion affected by surface area?
if there is a greater area for molecules to diffuse across , i.e. more channel proteins to aid diffusion, the rate will increase
