chapter 5 - plasma membranes Flashcards
what is the fluid mosaic model a diagram of?
the cell surface membrane / plasma membrane
what is the function of the phospholipid bilayer
separates the cell from the outside
fluid - moves more freely
selective permeability (permeable to small or non-polar molecules but impermeable to large molecules)
what is a phospholipid made up of?
a glycerol, two fatty acids (tails) and a phosphate-linked head group
how is the phospholipid bilayer arranged?
two layers of phospholipids, with their tales pointed inwards.
where are carbohydrate groups present in the plasma membrane ?
what do they form?
only on the outer surface of the membrane and are attached to proteins
forming glycoproteins, or attached to lipids forming glycolipids
which part of the phospholipid is hydrophilic and which part is hydrophobic?
and what does this mean?
the head is hydrophilic - water loving
the fatty acid tail is hydrophobic - water fearing
what are proteins called that extend all the way across the membrane?
transmembrane
integral
intrinsic
what are the top 3 major components in the cell membrane
- phospholipids
- proteins
- carbohydrates
why is it important for carbohydrate to form distinctive cellular markers?
so the immune cells can differentiate between body cells, which they shouldn’t attack and foreign cells or tissue which they should attack
how do saturated and unsaturated fatty acids react differently when temperature drops?
at cooler temperatures the saturated fatty acids pack tightly together, making a dense, fairly rigid membrane
unsaturated fatty acids can not pack together as tightly due to the bent structure of their tales.
because of this, a membrane containing unsaturated fatty acid tails with remain fluid at lower temperatures than a membrane of saturated ones
how does cholesterol minimize the effects of low and high temperatures
keeps phospholipids from packing tightly together.
at high temperatures the cholesterol reduces fluidity, allowing for a wider range of temperatures in which a membrane maintains a functional, healthy fluidity
what is important about the charge of the phospholipids
the head is polar - charged at the top
causing the phospholipid to become amphiphatic (some parts charged, others aren’t)
what are the 6 main functions of the cell surface membrane
- partially permeable (controls what enters and leaves the cell)
- protection from external environment
- surface proteins (antigens) bind and allow binding sites
- compartmentalise the cell
- cell communication & signalling
- hormone, toxin and medicinal drugs binding site
how thick is the surface membrane typically?
7-10nm thick
what is the name for the carbohydrate chain that forms glycoproteins or glycolipids? (sugar)
“saccharide” sugar
mono-saccharide = one sugar
poly-saccharide = many sugars
what are the names of proteins that go all the way through the membrane?
transmembrane
integral
intrinsic
what is the difference between extracellular and cytosolic peripheral proteins?
extra-cellular = on the outside of the cell - act as receptors and normally glycoproteins
cytosolic = on the inner side of the cell surface membrane - for cell signalling or chemical reactions
what are the 2 types of cholesterol apparent in the cell surface membrane?
LDL - low density
HDL - high density
what are the main functions of integral/ transmembrane proteins?
-transport of ions, sugars and amino acids
- some are receptors for hormones, neurotransmitters or enzymes
how does
-temperature
-solvents
and -detergents
affect the permeability of cell surface membranes?
- temperature = increase permeability - more Kinetic energy
at extremely high temperatures enzymes denature increasing fluidity further. - low temperature - ice crystals form, piercing membrane, increasing permeability
- solvents - increase (dissolve phospholipids)
-detergents - increase (strips phospholipid heads away)
what are the two passive processes to move molecules across membranes
diffusion
facilitated diffusion
define net movement
the overall movement
what molecules need facilitated diffusion
b. and what is used to “facilitate” this and how is it done?
- large molecules and charged particles
- channel proteins - form a pore/channel in membrane
carrier proteins - shaped so specific molecule fits into it then changes shape to permit molecule to pass
why do small molecules diffuse quicker
it takes more kinetic energy to get larger molecules moving
define - (in relation to water solutions)
a. isotonic
b. hypertonic
c. hypotonic
a. isotonic - the same water potential inside the cell and outside the cell (no movement of water)
b. hypertonic - (lower water potential) less water molecules outside the cell than inside the cell (water leaves cell)
c. hypotonic - (higher water potential) more water molecules outside the cell than inside the cell (water enters cell)
how to animal and plant cells react to being placed in hypotonic solutions
plant- water enters cell -vacuole swells - contents push against cell wall, - turgid - doesn’t burst due to cell wall exerting an equal and opposite pressure to turgor pressure from the water.
animal - water enters cell - no cell wall so cell bursts or lysis
haemolysis (RBC) (destruction of red blood cells)
how do animal and plant cells react to being placed in hypertonic solutions?
plant - water leaves cell and vacuole
cell membrane pulls away from cell wall
plasmolysis (contraction of plant cell)
flaccid (loose or hanging limply)
animal - water leaves cell
cell shrinks
cell crenation (describing the round-toothed edge and notched or scalloped surface)
what molecules can be moved by regular diffusion?
and why?
- very small molecules - will fit between phospholipids
- lipid based molecules - fat= soluble
what are the two active processes involved in movement across membranes and what do they require
active transport - energy in the form of ATP and a carrier protein
bulk transport - uses membranes to transport large amounts of material - needs ATP
why do active processes require energy
moving against the concentration gradient
why do passive processes not require ATP
because they move molecules down a concentration gradient
how do active processes differ to facilitated diffusion ?
uses ATP
moves specific molecules one way across a membrane
must faster than FD
opposite direction of the concentration gradient
what are the two types of bulk transport and what do they mean?
endocytosis - enter the cell
exocytosis - exit/leave the cell
define phago and pino
phago - solid
pino - liquid
what is a plasmolysed cell
a cell that’s lost water through osmosis causing it’s cell membrane to shrink away from the cell wall
why don’t plant cells undergo lysis
because the cell wall contains an equal and opposite pressure to TURGOR pressure (expelled by the water), stopping too much water from entering the cells
when carrying out an experiment to test the affect of temperature on membrane permeability, why would the absorption eventually stop increasing?
when the pigment is in equal concentration, inside and outside the cells
what happens at the isotonic point of movement across membranes?
the movement of water into cells is equal to the movement of water out of cells
does cholesterol bond to the phospholipid head or the fatty acid tail?
fatty acid tail
what is the difference between pinocytosis and phagocytosis
pinocytosis = liquid into a cell
phagocytosis = solid into or out of cell
what are the 3 different parts of ATP
adenine - base
ribose - sugar
3 phosphate groups
in active transport, how does ATP release energy?
ATP is dephosphorylated, (dephosphorylation) releasing a phosphate group and the energy stored, activating the enzymes
ATP changes to ADP + P
ADP+P is then phosphorylated as the reaction is reversible, deactivating the enzymes
what is the highest water potential achievable?
0kPa (distilled/pure water)
define water potential
a measure of the ability of water molecules to move freely in a solution
define osmosis
the NET movement of water molecules
from a region of HIGHER water potential to a region of LOWER water potential
DOWN a water potential gradient
ACROSS a partially permeable membrane
why might some cells not bind to the stain, even at low temperatures?
if the cells are dead or not respiring.
no metabolic energy, ATP to take up stain
7 functions of glycoproteins
- acting as antigens
- identification/ recognition of cells as self or foreign
- cell signalling eg communication between cells
- receptors/ binding site for hormones/ chemical signals/ medicinal drugs
- binding site/ receptor on transport proteins
- cell adhesion, hold cells together in a tissue
- attach to water molecules to stabilise membrane/cell
how can glycoproteins act as receptors
they have a tertiary structure complimentary to the shape of the trigger molecule. trigger molecule binds to receptor/ glycoprotein
define cell signalling
the communication of cells, to trigger a response/ reaction inside the cell
define reliability
how can you improve it in an experiment?
the variation between the data
take more samples/ readings
define accuracy
how can you improve it in an experiment?
how close your data is to the true value
use higher resolution equipment, more significant figures
keep equipment calibrated
what is ATP made up of?
adenine
ribose
3 phosphates
what is the equation that represents how factors effect diffusion rate
temperature x surface area x concentration difference
/ diffusion distance x size of particle
if two sucrose solutions are separated by a partially permeable membrane. what change will occur to the less concentrated solution?
less concentrated solution will decrease in volume because it has a higher water potential, therefore water molecules will move via osmosis to a lower water potential
if four 10 g L-1 solutions were made out of
1. sucrose
2. glucose
3. DNA
4. haemoglobin
which would have the lowest water potential
B. glucose
all of the molecules are polar and therefore soluble in water. the more OH groups forming hydrogen bonds with water the lower the water potential, glucose has more OH groups
what is not an acceptable description of the permeability of the plasma membrane?
“semi”
Which part of the membrane restricts movement of small, lipid insoluble molecules
The fatty acid tails (in the bilayer)
