Flashcards in cell membrane structure and function Deck (35):
what is a plasma membrane?
all membranes around and within cells (including those surrounding organelles)
what do we call the plasma membrane that surrounds cells?
what is the function of a cell surface membrane?
1. to separate the internal and external environments of the cell.
2. to control the movement of substances in and out of the cell.
3. to allow cellular compartments to have different conditions.
name the components of a cell surface membrane
Proteins (intrinsic and extrinsic)
what is a polar molecule?
a molecule that does not have an even distribution of electrons making some regions more negative than others.
what is a non-polar molecule?
a molecule that has an even distribution of electrons, meaning it does not have areas that are more negative than other areas.
phospholipids are made form which 3 molecules?
fatty acid 'tails' x 2
why do phospholipids form a bilayer?
1. phospholipids are amphipathic:
2. polar phosphate head - hydrophilic - will orientate towards aqueous environments.
3. non-polar fatty acid 'tails' - hydrophobic - will orientate away from aqueous environments.
4. as both inside and outside the cell is aqueous, phospholipids form two layers
5. bilayer with hydrophobic tails facing inwards and hydrophilic heads facing outwards (interacting with aqueous environment).
what is the function of the phospholipid membrane?
1. allows lipid soluble (non-polar) molecules to enter and leave.
2. barrier to water soluble (polar) molecules - prevents them from entering and leaving.
3. makes the membrane flexible and self-healing
substances able to cross plasma membrane?
lipid soluble/ small non-polar molecules e.g. carbon dioxide, oxygen and lipid based hormones e.g. steroids.
substances NOT able to cross plasma membrane?
water soluble/large polar molecules e.g. glucose, ions, proteins, urea, amino acids of the same charge as the charge on the protein channels - repelled.
proteins in a cell membrane can either be __________ or _________.
Intrinsic or extrinsic
what's an intrinsic protein?
span the full membrane. Could be protein channel or protein carrier.
what's a protein channel?
water filled tubes to diffuse/transport water soluble molecules/proteins/ions across membrane.
what's a protein carrier?
bind to large/charged water soluble molecules/proteins/ions (glucose/amino acids) and change shape to actively transport/diffuse molecules across membrane.
what's an extrinsic protein?
located on the surface and partially embedded. Don't fully span across membrane and serve in transport of molecules and as receptors.
what is facilitated diffusion?
the passive movement of particles from an area of high concentration to an area of low concentration via transmembrane transport proteins until there is no net movement and equilibrium has been reached.
what are the functions of protein?
1. provide structural support.
2. act as channels and allow the facilitated water-soluble/ large polar substances across the membrane.
3. allow active transport across the membrane through carrier proteins.
4. form cell surface receptors for identifying cells so immune system doesn't attack.
5. help cells adhere together.
6. act as receptors for example hormones.
explain the fluid mosaic model
1. phospholipid molecules can move laterally/freely and makes the membrane fluid/flexible.
2. proteins are distributed throughout the membrane unevenly and vary is shape, size and pattern - like a mosaic.
3. agreed structure based upon experimental + chemical evidence and so is called a model.
cholesterol molecules occur within the...
phospholipid bilayer of the cell-surface membrane.
cholesterol molecules are very...
hydrophobic - preventing loss of water and dissolved ions from the cell. Also, pull together fatty acid 'tails' , limiting their own and other molecules movement without making membrane too rigid.
what are the functions of cholesterol?
1. reduce lateral movement of other molecules including phospholipids.
2. makes the membrane less fluid at high temperatures.
3. prevent leakage of water + dissolved ions from the cell.
what are glycolipids?
carbohydrates covalently bonded to lipids.
the carbohydrate portion extends from the phospholipid bilayer into the...
aqueous environment outside of cell where it acts as a self surface receptor for specific chemicals.
what are the functions of glycolipids?
1. act as recognition sites.
2. help maintain the stability of the membrane.
3. help cells attach to one another and to form tissues.
carbohydrate chains are attached to many...
extrinsic proteins on the outer surface of the cell membrane Glycoproteins also act as cell surface receptors more specifically for hormones and neurotransmitters.
what are the functions of glycoproteins?
1. act as recognition sites.
2. help cells to attach to one another and form tissues.
3. allow cells to recognise one another.
In an investigation about diffusion and plasma membranes (beetroot discs) why would you ensure the temperature remained constant?
so that rate of diffusion remains constant
no change in fluidity of phospholipids
no denaturation of membrane proteins
In an investigation about diffusion and plasma membranes (beetroot discs) why would you ensure the the beetroot discs where shaken?
To ensure all the discs exposed to water/ all discs fully submerged
maintain concentration/diffusion gradient
name the type of molecules that can diffuse through the membrane
during cell fractionation a detergent can be used - why?
cell membranes made of phospholipids
detergent dissolves membranes
releasing cell contents
How does ultracentrifugation work to separate cell organelles?
spin supernatant at low speed initially
then gradually increase the speed
separating organelles out based on their size/density