Biological Membranes Flashcards
Examples of where we find biological membranes
Plasma membrane
Mitochondrion
Endoplasmic reticulum
Nucleolus
Partially permeable
Only certain substances can pass through
Components of plasma membrane (could be labelled diagram)
Phospholipid
Phospholipid bilayer
Channel protein
Carrier protein
Glycoprotein
Cholesterol within tails
Hydrophilic head
Hydrophobic tails
Intrinsic protein
Extrinsic protein
What is the role of the plasma membrane
Separates cells components from external environment
Regulate transport of materials into and out of the cell
May contain enzymes
Has antigens for recognition of self cells
May release chemical signals to communicate between cells
What is the role of membranes within cells
Separate organelle from cytoplasm
Provide surfaces for metabolic reactions
May contain enzymes that catalyse metabolic reactions
Membranes within cells can form vesicles to transport substances to different areas in the cell
What substances can pass through the phospholipids in the bilayer
Small and non polar molecules eg O2, CO2
Water is polar but is so small it can also pass through
Large polar substances cannot pass through
Plasma membrane described as what
Fluid mosaic model
Phospholipids free to move relative to each other
Proteins are embedded in bilayer varying in size and shape
channel proteins
provide pores for molecules to move through to enter/exit the cell
allows charged/polar molecules eg. ions through.
shaped only to allow certain molecules to pass through
used for facilitated diffusion
carrier proteins
shaped only to allow certain molecules to bind to them eg. large molecules such as glucose, amino acids
once the molecule has bound, carrier molecule changes shape to transfer it across the membrane
used for facilitated diffusion or active transport
cholesterol
lipid
regulates fluidity of plasma membrane
found between fatty acid tails
low temps - maintain fluidity
high temps - reduces fluidity
glycoproteins
carb chain attached to a protein
cell signalling, cell recognition (antigens) and binding cells together
glycolipids
carb chain attached to a lipid
cell signalling and cell recognition
factors affecting plasma membrane structure
- temperature - as temps increase membrane gets more fluid and permeable. at very high temps proteins denature so membrane loses its structure and becomes more permeable. too low - can form ice crystals which pierce membrane making it highly permeable when it thaws.
- cholesterol - more cholesterol the more fluid
- solvents - some solvents dissolve the lipids in a cell membrane so the membrane loses its structure. less polar solvents may disrupt the membrane and increase permeability.
how does saturation affect plasma membrane structure
more saturated fatty acids - membrane fluidity reduced at low temps as phospholipids can compress
more unsaturated - fluidity maintained at low temps. Don’t pack closely together
simple diffusion
movement of a substance down its concentration gradient from a high to low concentration
factors affecting rate of diffusion
- temperature
- surface area
- concentration gradient
- size of diffusing molecule - smaller=faster rate
- diffusion distance - thinner=faster rate
facilitated diffusion
movement of substances down their conc gradient from high to low conc using channel/carrier proteins
carrier- large molecules (inc ions + polar)
channel - small ions + polar
active transport
movement of molecules from a region of lower conc to a region of higher conc against conc gradient.
so requires energy from ATP
uses carrier proteins that act as pumps
role of ATP in active transport
molecule being transported binds to carrier protein
ATP binds to carrier protein
ATP is hydrolysed, releasing energy
the energy changes the shape of the carrier protein
molecule is transported across to other side of membrane
factors affecting rate of active transport
- number of carrier proteins present
- ability to produce ATP - more ATP = faster rate of active transport
bulk transport
moves substances that are too large eg. enzymes
endocytosis - bulk transport into cell
exocytosis - bulk transport out of cell
endocytosis
- substance to be taken in binds to a receptor on plasma membrane
- plasma membrane folds in and surrounds substance
- substance is brought into cell enclosed in a vesicle
phagocytosis
bulk transport of solid matter into a cell
exocytosis
- substance to be transported is enclosed in a secretory vesicle
- vesicle travels to plasma membrane
- plasma membrane and vesicle fuse together and the contents of vesicle are secreted
