Chapter 5 - Flashcards
what is the main structural component in a cell membrane?
phospholipid bilayer
name of the model showing membrane structure?
fluid mosaic model
why is it called fluid mosaic model?
- fluid bc molecules move
- mosaic bc molecules in membrane forma pattern like a mosaic
what do membranes do? (3)
- compartmentalisation
- site of chemical reactions
- cell communication
Compartmentalisation?
- form partially permeable barriers between cytoplasm and cell’s environment
- plasma cell surface membrane
- organelles and cytoplasm - e.g. nuclear envelope, outer mitochondrial membrane
- separating different parts of the same organelles - e.g. inner mitochondrial membrane
site of chemical reactions?
e.g. thylakoid membranes are where the light dependent reactions of photosynthesis happen
cell communication?
receptors bind signal molecules e.g. hormones and neurotransmitters
- antigens indicate whether a cell is self or non self
factors affecting membrane structure: 1 - temperature
(see Beetroot Pag)
- as temp increases, the KE of phospholipid molecules increases and the fluidity of the membrane increases
- temporary gaps appear between phospholipids which increases the permeability of the membrane
- at high temps, intrinsic proteins denature forming large gaps in the membrane which becomes freely permeable
factors affecting membrane structure: organic solvents
E.g ethanol/ other alcohols
Organic solvent molecules get into the hydrophobic core of the membranes, dissolving the fatty acids
Thfr, destroying membrane
2 factors affecting membrane structure are?
- Temperature
- Organic solvents
Ways substances cross membranes depends on which 2 things?
- What the substance is
- Conc gradient (direction)
The 5 ways substances can cross membranes are:
- Simple diffusion
- Facilitated diffusion
- Active transport
- 5, endocytosis, exocytosis
Simple diffusion?
- Requires no energy from ATP hydrolysis, diffusion is always a passive process
- Lipid soluble, non polar particles dissolve in the fatty acids of the membrane and move down the conc gradient across phospholipid bilayer
- E.g. carbon dioxide, oxygen, lipid soluble hormones e.g testosterone
- exception - water can cross via simple diffusion despite being polar - osmosis
Facilitated diffusion?
- Water soluble, polar particles need a channel/ carrier protein to facilitate their diffusion
- DOWN conc gradient
- Carrier protien - conformational change
- Channel protein - specific hydrophilic pore
- E.g. glucose, amino acids
Active transport?
- Any particles can be transported against conc gradient by a carrier protein using ATP hydrolysis
- E.g. the Na(^+) and K(^+) pump
ATP hydrolysis equation?
ATP -> ADP + Pi
Endocytosis, Exocytosis ?
The ‘bulk transport’ of many particles or entire cells in and out of cells
ACTIVE - requires energy from ATP hydrolysis
Repeatability definition?
Every time a replicate is done, it is similar to previous replicates
Precision definition?
How close replicates are to each other
Overlapping standard deviation error bars?
Difference in mean isn’t significant
Error bars don’t overlap?
Difference in mean is significant
What is standard deviatioN?
SD gives a measure of how spread out a set of replicates is about the mean
Small SD=?
Replicates tightly clustered around mean - high repeatability and precision
Large SD =?
Replicates spread widely about the mean - low repeatability & precision
Water potential is a measurement of?
The pressure of water in a solution
Pure water has the?
Highest water potential: 0kPa
Water potential of any solution must be?
Negative
Use a _____ ___ to figure out direction of water movement?
Number line
On the number line?
0 is at the top
Arrow at bottom
Rate of water potential depends on?
Steepness of water potential gradient
OSMOSIS DEFINITION?
The movement of water from a high to low water potential across a selectively permeable membrane
Isotonic solution definition?
Same water potential, same conc of solute
Hypertonic solution ?
- lower water potential, higher conc of solute
Hyper = strong, strong when hype
Hypotonic solution?
Higher water potential, lower conc of solute
Hippoes - weak solution
Plant cell in pure water
Cell becomes TURGID as solution is hypotonic
Plant cell in concentrated salt solution?
Cell becomes PLASMOLYSED as solution is hypertonic
Animal cell in pure water?
Cytolysis as solution is hypotonic (bursts)
Animal cell in conc salt solution?
Cell becomes crenated as solution is hypertonic
Pressure potential
Same water potential inside and outside of cell as cell contains solute particles
This is explained by the pressure the cell wall is exerting on the cytoplasm, preventing water movement - this is pres pot
Water potential =
Water potential of cell = solute potential + pressure potential
Water p = 0 or -
Solute p = always -
Prssure p = 0 or _+
Pressure potential counteracts?
Solute potential
Phospholipid?
2 hydrophobic fatty acid tails joined with ester bonds to glycerol which is also bound to a phosphate group, forming a hydrophilic phosphate group
Carrier protein?
A intrinsic protien capable of undergoing conformational change. Can active transport particles across the membrane using energy from ATP hydrolysis, or allow particles to cross the membrane by facilitated diffusion
Channel protein?
An intrinsic protein with a hydrophilic pore, allowing a specific water soluble particle (e.g. glucose) to cross the membrane by facilitated diffusion
How are channel proteins held in place?
Inteactions between the hydrophobnicbcore of the membrane and the hydrophobic R groups on the outside of proteins
Cholesterol?
s
Regulates the fluidity of membrane by stabilising the phospholipids at high temps, and preventing them from crytraslising at low temp
Receptor protein?
An instrinic protein with a binding site on the extracellular surface complementarty to a signal molecule, like a hormone. When a signal molecule binds to a receptor, a response is triggered inside the cell - cell signalling
E.g. receptors for neurotransmitters
Signal molecule?
A molecule like a hormone or neurotransmitter that binds to a receptor, triggering a response
Glycoprotein?
A chain of carbohydrates attarhed to a protein. Can act as an antigen if extrinsic and extracellular, identifying a cell as self or non self.
If instrinic, can act as a receptor in the same way as a receptor protein
Glycolipid?
A chain of carbs attached to the fatty acids in the core of the membrane. Can act as antigens, identifying the cell as self or non self
Phospholipid bilayer?
- Hydrophobic core forms a barrier impermeable to water soluble particles separating the cytoplasm from the extracellular envir.
- Hydrophilic phosphate heads interact with the water either side of the membrane
Intracellular extrinsic membrane proteins could be?
Enzyme
What is particular to each type of cell?
the type and number of proteins and lipids
all cells contain?
plasma membrane
cell membranes act as ?
barriers to control what passes in/ out of cells and organelles
functions of the phospholipid bilayer in cell membrane?
- creates partially permeable barrier - controls envir of cell
- keeps membrane fluid but stable
2 types of membrane proteins?
integral
peripheral
integral are ?
based in centre
peripheral are?
outside
integral/ intrinsic proteins?
- firmly embedded into cell membrane
- the region of the protein that is inside the CM is hydrophobic which keeps it anchored in place
transmembrane proteins - what are they?
some integral proteins can span both layers of the cell membrane
peripheral/ extrinstic proteins?
- found ONLY ON 1 SIDE of CM and are not embedded into membrane
- loosely held in place by electrostatic forces such as ionic bonds
types of transmembrane protiens?
channel & carrier
how do channel proteins work?
they form hydrophilic channels that allow specific water soluble molecules to pass through the membrane
how do carrier proteins work?
transport specific molecules across M by changing shape when the mols bind to the protein
what is a glycoprotein?
proteins with a chain of carbohydrate molecules attached
what is a glycolipid?
- lipids or phospholipids with a chain or carb molecules attached
like phospholipids, cholesterol also has?
a hydrophilic end and a hydrophobic end
how does cholesterol regulate membrane fluidity?
may sit inbetween the phospholipd mols
how does cholesterol prevent the CM from becoming too sitff?
it prevents the phospholipids from grouping too close together
how does cholesterol prevent the CM from becoming too fluid?
by interacting with the fatty acid tails of the phospholipids
if CMs become too fluid?
water nd small soluble mol can more easily pass thru
the fact that the CM acts as a partially permeable barrier allows?
the maintenance of diff conditions both inside and outside of cells
why is compartmentalisation important for cells?
- protection - e.g. fragile DNA in nucleus
- the ability to maintain diff conditions for diff metabolic reactions
cell membranes are also involved in
the uptake and secretion of larger molecules
e.g. at synapse
cell membranes as sites of chemical reactions?
membranes also contain prtns that are involved in chemical reactions e.g. respiration requires the presence of electron carriers & ATPase to be located on the inner mitochondrial membrane
what happens if the membrane is too fluid?
can break apart
why is temp an imprtnt factor affecting membrane fluidity?
many organisms cannot regulate their body temp
at a very high temps what can happen to membrane fluidity?
the increased fluidity can cause the membrane to completely lose its structure
apart from denaturation, what else can happen to membrane proteins at high temps?
can drift sideways which reduced their ability to function
reducing the effect of low temp on CM fluidity- sat, unsat?
- compression of phospholipids can be reduced by changing proportion of sat and unsat tails
- unsat phslips have kiks which push them further apart
- many organisms in cold envirs ar able to change proportion
reducing the effect of low temp on CM fluidity- cholesterol?
cholesterol prevents compression of phslips
reducing effects of high temp - cholesterol?
cholestrol pulls the phslips together by intercating with the tails
effect of organic solvents - low and high conc?
low - makes CM more permeable to charged or larger mols
high - can destroy cells
diffusion definition?
the net movement of particles from an area of high conc to an area of lower conc
(diffusion) equilibrium is reached when?
- conc of particles is equal on both sides of the CM so there is no net movement
simple diffusion - what is able to slowly diffuse across the bilayer?
small polar mols with small diffs in charge e..g. water
facilitated diffusion definition?
the net movement of particles from an area of high conc to an area of low conc across a partially permeable membrane via channel or carrier proteins
what are aquaporins?
special channels proteins for water movement
kidney has lots
both channel and carrier proteins are ?
specific to 1 type of particle
channel vs carrier proteins
channel: transport small, polar, charged particles
carrier: larger or charged
factors affecting diffusion?
temp conc gradient surface area diffusion distance no of channel and carrier protiens size of molecule
factors affecting diffusion- temp?
when temp inc, KE of particles inc, so move and collide at faster rate
factors affecting diffusion- conc gradient?
steeper conc gradient = faster rate
factors affecting diffusion- diffusion distance?
how far particles hav to move
takes longer to move further, so larger diffusion distance = slower rate
so organsims have specialised exchange surfaces
factors affecting diffusion- SA?
rate can be increased by incrasing SA of CM
greater SA = greater no. of particles that can diffuse across CM in a given amount of time
factors affecting diffusion- no of transport proteins?
- rate of diffusion can be increased by increasing no of transport proteins in a given area of CM
more channel & carrier prtns = more particles can cross CM in given amnt of time
osmosis is a ? process
PASSIVE
osmosis stops when?
equilibrium is reached
as no cell wall to prevent bursting, its imporant to ?
carefully regulate water potential of blood and other extracelllular fluids at all times in animal cells
why do plant cells have cell walls?
they prevent from bursting as they arb’t always able to regulate the water potential of the fluid outside cell
active transport definition?
the movement of particles from an area of low conc to an area of higher conc using ATP and protein carriers
endocytosis definition?
the bulk transport of ;arhe molecules into a cell
exocytosis definition?
the bulk transport of large molecules out of a cell
endocytosis: phagocytosis and pinocytosis?
phagocytosis: bulk transport of solid material into a cell
pinocytosis: bulk transport of liquids into a cell
steps of endocytosis?
- invagination of cell surface membrane around material that will be taken in
- membrane fuses, enclosing material in vesicle
- vesicle pinches off from CSM and moves towards interior of cell
steps of exocytosis?
- secretory vesicle moves towards CSM
- vesicle fuses with CSM
- which results in release of material to outside of cell
where is ATP used in bulk transport?
- fusion of cell membranes to create/destroy vesicles
- movement of vesicles along cytoskeleton
process of active transport?
- particle must bind to specific site in carrier prtn
- on inside of cell, ATP also binds to carrier prtn
- ATP is hydrolysed into ADP & Pi which releases energy and causes conformational change in carrier
- carrier prtn is now open to other side of membrane and particle is released
- phosphate mol is then released from carrier prtn, causing prtn to retrurn to orginl shape
equilibrium doesn’t mean that the particles stop moing just that
the movements are equal in both directions
what is hydrostatic pressure?
increased volume of solution. if solution is in a close system, such as a cell, this resulsts in an increase in pressure
intrinsic and extrinsic proteins functions:
- acting as recptors for drugs and hormones to bind to
- acting as recognition sites for immune system
helping cells adhere toegther to form tissues
