BIOLOGICAL MEMBRANES Flashcards
What are the roles of cell membrane
- separates cell contents from environment
- selectively permeable, allows certain molecules through
- cell to cell attachment- forms tissue
What are the roles of membranes inside cells
Isolated enzymes (might damage cell eg. Lysosomes)
Isolated DNA in eukaryotes
Internal transport system provided
COMPARTMENTALISATION (isolate organelles)
What is the function of phospholipids?
Gives membrane fluidity
Barrier to large water soluble molecules and ions
Unsaturated fatty acids=kinks in tail=prevention of close packaging=movement
What is the structure of proteins?
Alpha helix proteins (coils)
Intrinsic (all way through membrane)
Extrinsic (one side of membrane)
What is the function of proteins?
Structural support
Transport- channel proteins, carrier proteins
What is the function of cholesterol?
Fits between fatty acid tails, making the barrier complete (without would be too permeable)
What’s a glycolipid?
Carbohydrate chains attached to phospholipids
What is a glycoproteins?
Carbohydrate chains attached to proteins
Function of glycocalyx?
Helps cells adhere to one another, forming tissues
Forms hydrogen bonds with water to stabilise the membrane
Max magnification of light and electron microscope
X2000 nm
X200,000 nm
Max resolution of light and electron microscope
200nm
TEM 0.2nm
SEM 2nm
How does temperature change the membrane?
Increase in temp=increase in KE
Increase in movement=increase in permeability, as membrane has more fluidity
Phospholipids vibrate causing them to move further apart=larger gaps allowing larger molecules to pass through=increases permeability
Very high temps=phospholipid completely moves apart causing membrane to break down
What are the effects of organic solvents on membrane permeability?
Organic solvent are less polar than water and can dissolve lipids
Ethanol dissolves lipids in the cell membrane=membrane loses structure
-very strong alcohol solution, will destroy cells
Increase the conc. of the solvent will increase permeability of membrane
Definition of diffusion (passive process)
NET movement of molecules or ions from a region of high concentrations to a region of lower concentration-down a concentration gradient
What are factors affecting the rate of diffusion?
Temperature-increase temp=increase in KE-molecules move faster
Surface area-when increased, more molecules or ions move across the membrane so diffusion is faster
Type of molecule-larger=slower as energy needed to break it down first. Non polar molecules diffuse quicker over phospholipid bilayer
What is simple diffusion?
Movement directly to the phospholipid bilayer between phospholipids Examples: Small molecules: -CO2 -H2O -O2
What is the definition of facilitated diffusion?
Passive movement of molecules or ions through a channel or carrier protein from high to low concentration
Description of channel proteins and examples
Specific to certain ions, certain shape and size (polar molecules) Examples: -sodium ion channels -calcium ion channels Channel proteins have hydrophilic lining Sometimes gated=open or closed
Description of carrier proteins and examples
For specific large polar molecules (eg: glucose)
Examples:
-glucose
-amino acids
When the specific molecules bind to the protein, it changes shape and allows it to cross the membrane
Definition of osmosis (passive process)
Special form of diffusion involving water
NET movement of water molecules from high to low water potential (down a water potential gradient) across a partially permeable membrane
What is a solute?
Substance that dissolves in a liquid to form a solution
What is a solvent?
Liquid in which a solute dissolves
What is a solution?
The ,mixture formed when a solute has dissolved in a solvent
What is the water potential of pure water?
0
What is water potential measured in?
kPa
In animal cells, what’s the effect on the cell with a low water potential?
(concentrated sugar solution)
- reduction in cell volume
- cytoplasm becomes concentrated
- cell dies if too much water lost
In animal cells, what’s the effect on the cell with a high water potential?
(pure water)
- pressure inside cell will increase
- no cell wall to prevent lysis (cell bursting)
In plant cells, what’s the effect on the cell if there’s a low water potential (concentrated sugar solution)?
Full plasmolysis=cytoplasm tears away from cell wall, cell dies if membrane rips
Volume of cells will decrease
In plant cells, what’s the effect on the cell if there’s high water potential (pure water)?
- turgid (important in photosynthesis as if leaves wilt, surface area is lost)
- cell wall stops cell bursting
Definition of active transport
Movement of molecules or ions through carrier proteins across ,membranes against their concentration gradient, using energy from ATP
What are examples of active transport?
Roots-magnesium ions taken in for chlorophyll
Intestine (villi)-removal of glucose from gut into blood
Kidney-useful molecules reabsorbed (eg: glucose)
How is active transport different to facilitated diffusion?
- moves against concentration gradient
- uses energy (ATP)
- specific molecules are passed one way
What is active transport affected by?
- temperature (more KE)
- oxygen concentration (needed for aerobic respiration=ATP)
- poison (stops/kills cells=no respiration)
- lots of mitochondria (aerobic respiration)
What are examples of bulk transport?
Hormones-pancreatic cells make insulin. Processed and packaged into vesicles in Golgi-vesicles fuse with outer membrane to release insulin into blood
Plant cells-materials required to build the cell wall are carried outside in vesicles
Phagocytes-engulf invading microorganisms forming vesicles around them. Vesicles fuse with lysosomes, contain hydrolytic enzymes that can break down and digest microorganisms
What is endocytosis?
The bulk movement of material into a cell
What is exocytosis?
Bulk movement out of a cell
What is phagocytosis?
‘cell eating’ solid material
- bacteria bins to receptors on membrane
- membrane folds engulfing bacteria
- membrane fuses with itself, forming a vesicle
- vesicle moves through cytoplasm along microfilaments (ATP required)
- vesicle fuses with a lysosome
What is pinocytosis?
‘cell drinking’ liquid material
What is bulk transport needed for?
Moving large molecules
What happens during bulk transport?
Whole membrane changes and moves, vesicle membrane becomes part of the cell surface membrane
How is active transport different to facilitated diffusion?
- moves against the concentration gradient
- uses energy (ATP)
- specific molecules are passed one way
What are the stages to cell signalling?
- first message (eg: hormone)
- second messenger (eg: cyclic AMP)
- activation of energy (cascade effect)
