plasma membrane (cell membrane)
a partially permeable membrane consisting of a fluid phospholipid bilayer and proteins
what is the size of a
... [Show More] plasma membrane
7nm
fluid mosaic model of membrane structure
states that a membrane is a fluid structure with a "mosaic" of various proteins embedded in it.
phospholipid bilayer
A double layer of phospholipids consisting of phosphate and lipids
Structure of phospholipid bilayer
their hydrophilic heads are in contact with the watery exterior or interior (cytoplasm). Their hydrophobic tail is in the center away from water.
structure of cholesterol
Cholesterol molecules are made up of four rings of hydrogen and carbon atoms. They are hydrophobic and are found among the hydrophobic tails in the lipid bilayer.
what does the hydrophobic tail consist of in a phospholipid?
wo strings of hydrogen and carbon atoms called fatty acid chains
function of cholesterol
important for maintaining the level of fluidity of the membrane, and because it is hydrophobic and hydrophilic portion, it allows it to bind to the phospholipids, so preventing them to become too fluid.
also prevents fatty acids to crystallise.
examples of intrinsic proteins?
channel proteins and carrier proteins
what are peripheral proteins? examples?
proteins attached to the surface of lipid bilayer. glycoproteins and glycolipids.
3 functions of proteins in general in the plasma membrane?
enzymes to speed up chemical reactions, receptors for specific molecules, or transport materials across the cell membrane.
function of transmembrane proteins
to transport water soluble or charged particles through the membrane
what is the size of a transmembrane channel?
0.8 nm in diameter
what is the glycolax?
glycoprotein and glycolipid covering that surrounds the cell membranes of some bacteria, epithelia, and other cells.
as the temperature increases, what component becomes more fluid?
phospholipid bilayer
what occurs in detail when the temperature increases in a phospholipid bilayer? 5
1.the phospholipids vibrate more
2. there is an increase in gaps in membrane
3. bilayer becomes more fluid
4. at 40 degrees, proteins are denatured
5.this disrupts the membrane structure
function of the glycolax?
1. provides protection for plasma membrane. 2. form surface antigens by which the immune system can identify the cell
5 functions of cell membranes within cells?
1. it can form vesicles for transport 2. seperates organelles from cytoplasm 3. it is the site of reactions 4.it provides surface for attachment of enzymes or ribosomes 5. controls what substances enter/leave
what is cell signalling?
communication between cells
how do cell surface membranes contribute to the process of cell signalling?
signal molecules are released by exocytosis and glycoproteins (or glycolipids) have receptors that are specific to signal as they have a complementary shape. the attachment of signal molecule causes changes inside cells. the cell surface membrane allows entry of some signal molecules
structure of glycoproteins
Protein with a chain of carbohydrates attached.
function of glycoprotein?
carbohydrate chains can form hydrogen bonds with water, stabilising the membrane structure. can act as receptors for hormones in cell signalling.
Glycolipids
phospholipid with a chain of carbohydrate molecules attached.
Glycocalyx functions
in cell adhesion, recognition and immunity.
carrier proteins
a protein that transports substances from a low concentration to a high concentration across a cell membrane.
aquaproins
channel protein that allows water to pass through membrane
Enzyme
allows reactions to take place on the membrane surface.
what can pass through the phospholipid bilayer?
small, non-polar molecules can pass (O2, CO2)
what cannot pass through the phospholipid bilayer?
large, polar molecules cannot pass (glucose,amino acids and water)
how do receptors change cells? 3
1. release a secondary messenger inside the cell, which can initiate a variety of effects
2. opening or closing of a protein channel
3.activate an enzyme
Diffusion
Movement of molecules from an area of higher concentration to an area of lower concentration (it is passive, it doesn't require ATP).
facillitated diffusion
movement of molecules from an area of high concentration to low concentration across a partially permeable membrane via protein channels or carrier proteins (it is passive, it doesn't require ATP).
factors affecting simple diffusion
Temperature, surface area, concentration gradient, diffusion gradient and molecule size.
temperature
as the temperature increases so does kinetic energy therefore increasing the rate of diffusion.
surface area
the larger the surface area to volume ratio the faster the rate of diffusion.
concentration gradient
the steeper the gradient the faster the rate of diffusion.
diffusion distance
the greater the distance over which diffusion must occur, the longer it takes.
Molecule size
the smaller the molecule the faster the rate of diffusion.
factors affecting facilitated diffusion (in addition to simple diffusion)
the number of channels/carriers in the membrane and whether the channel/carrier is open/closed.
Osmosis
passage of water molecules down their water potential gradient across a partially permeable membrane.
water potential
The measure of the relative tendency of water to move from one area to another
Solute
the substance that is dissolved
Solvent
the substance in which the solute dissolves in
Solution
a liquid containing dissolved solids
what unit do we measure water potential in?
KPa (kilopascals)
What lowers water potential?
addition of solute molecules
What is the water potential of pure water?
0 kPa
Cytolysis
Bursting of an animal cell caused by the intake of too much water.
Turgid / turgidity
the pressure created by water pushing up against the cell wall in a plant cell.
why do animal cells burst and not plant cells?
because plant cells have a cellulose cell wall that prevents bursting and gives a stable cell structure.
Crenation
in animal cells, shriveling of the cell due to water leaving the cell when the environment is hypertonic.
Plasmolysis
This happens when a cell shrinks inside its cell wall while the cell wall remains intact (in plant cells only).
Heamolysis
when red blood cells burst.
active transport
Energy-requiring process that moves material across a cell membrane against a concentration gradient, using ATP and carrier proteins.
Endocytosis
bulk transport of molecules too large to pass through a cell membrane via channel/carrier proteins, using ATP, into a cell.
Exocytosis
bulk transport of molecules too large to pass though a cell membrane via channel/carrier proteins, using ATP, out of a cell.
How is active transport different from passive transport?
faster than diffusion, one way passage, uses ATP. often of molecules that the cells need more of than what can be provided by diffusion.
carrier protein in active transport
1) molecule binds with a specific/complementary carrier protein.
2) ATP IS USED.
3)causes a conformation change.
4)molecule moved across the membrane from low to high concentration.
bulk transport
1) plasma membrane bends around the material.
2) membrane pinches off.
3) puts material into a vesicle.
phagocytosis (endo/exo)
the intake/excretion of solid material through endo/exocytosis.
Pinocytosis (endo/exo)
the intake/excretion of l [Show Less]