2.5 biological membranes Flashcards
What are the 5 purposes of cell membranes?
Form a barrier between the contents of a cell and it’s environment.
Also regulates transport of material in and out of cell
May contain enzymes involved in metabolic pathways
Has antigens
May be the site of chemical reactions
What is the plasma membrane composed of?
A phospholipid bilayer with a hydrophilic phosphate head and hydrophobic fatty acid tails causing them to form a bilayer when in water.
What is the fluid mosaic
1972 Proposed that the phospholipid bilayer had proteins floating in it and that lipid molecules can change places with each other and some of the proteins may move giving it fluidity allowing it to interact with its environment e.g. phagocytic cells.
What spans the cell membrane.
proteins
carrier proteins
cholesterol
glycocalyx
carbohydrates
What is the purpose of proteins spanning the membrane?
Some proteins have pores and act as channels for polar ions
Carrier proteins
Proteins that act as enzymes, antigens, receptor site.
What is the purpose of cholesterol in the membrane?
regulates fluidity and resists the effects of temperature change.
What are the glycocalyx spanning the membrane?
Formed from the carbohydrate chains to either proteins or lipids
What is the purpose of carbohydrate in the membrane
Hydrophilic molecules and they attract water with dissolved solutes
Define simple diffusion.
If there is a high concentration of molecules will bump into each other randomly and spread out further.
Small molecules can diffuse through the membrane or fat soluble molecules can dissolve through the membrane
However, polar molecules such as water diffuse through channels called aquaporins.
What can affect simple diffusion?
Temperature
concentration gradient
diffusion distance
surface area
size of molecule
Define facilitated diffusion.
Movement of molecules down a concentration gradient via protein channels or carrier proteins and doesn’t require ATP
Define osmosis
Net diffusion from an area of high water potential to an area of low water potential
Define water potential.
measure of tendency of water molecules to diffuse from one region to another
What is the highest water potential?
Pure water (0kPa) and when solutes are added the water potential is lowered
Define cytolysis
animal cell swells and burst due too much water
Define turgid.
The cell will swell and the membrane pushes against the cell wall and the strong cellulose cell wall prevents bursting
Define crenation
animal cell shrinks due to water loss and appears wrinkled
Define plasmolysis/flaccid
Plant cell membrane pulls away from cell wall as water leaves
How does a drop in temperature affect the membrane
Unsaturated fatty acids as they become compressed the kinks in their tails push adjacent phospholipid molecules away, maintaining fluidity
Cholesterol also prevents phospholipid molecules from packing together too closely
saturated fatty acids become compressed
What happens to the membrane when temperature increases?
Phospholipids acquire more kinetic energy and move more increasing fluidity
Embedded proteins may also drift
Increased fluidity affects the infolding of the plasma membrane during phagocytosis
It can cause some proteins to denature creating gaps and if both the membrane embedded and cytoskeleton threads begin to denature then the plasma membrane will begin to fall apart.
What happens to the membrane when in solvents?
Organic solvents such as acetone will damage the membrane ad the dissolve lipids
Define active transport
The movement of substances against a concentration gradient using ATP and carrier proteins
For example, mineral ions to root hair cells and potassium ions to guard cells
Describe the process of active transport
Carrier proteins act similarly to enzymes and bind reversibly with certain solute molecules and they also have a site that binds and allows hydrolysis of ATP
What are the 3 types of bulk transport?
Endocytosis
pinocytosis
exocytosis
Define endocytosis
A segment of the plasma membrane surrounds and encloses the particle and brings it into the cell enclosed in a vesicle e.g phagocytosis
define pinocytosis
Intake of liquid.
ATP is needed to produce energy to form the vesicle and move them using cytoskeleton threads and motor proteins
Define exocytosis
A membrane bound vesicle containing the substance to be secreted is moved towards the cell surface membrane. The cell surface membrane and vesicle fuse together and the fused site opens releasing the contents of the secretory vesicle
How is ATP turned into energy.
ATP is hydrolysed into ADP+Pi
