Plasma Membrane Flashcards
Meaning of amphipathic
molecule containing both polar and non-polar parts
what components make up the plasma membrane?
Proteins- integral, peripheral,
lipid anchored
lipids- Cholesterol, glycolipid,
phospholipid
Carbohydrates- glycoprotein+
glycolipid
what are phospholipids made of and their structure?
-2 FA (can be sat/unsat or mixed)
- Phosphorylated Alcohol (choline/serine)
-phosphoglycerate (glycerol+ phosphate)
what are glycolipids made of?
- carbohydrate (sugar)
- Glycerol
- FA
Where is cholesterol located?
-B/W phospholipids
-Amphipathic- polar and non polar parts
What is meant by membranes being self sealing?
they repair themselves if damaged forming the original pattern
How the phospholipids are arranged in the membrane
Arranged in a Bilayer-
polar heads point outwards towards the aqueous environment on both sides and non-polar tails point away from the aqueous environment towards center of bilayer.
what are integral proteins/ how are they arranged
-completely span across the bilayer
- some partially span (halfway across the bilayer)
-non covalent bonded
Where are peripheral membrane proteins located?
can be Located on internal/external of PM so inside or outside of the cell
- non covalent bonding
How do Lipid anchored membrane proteins work?
Lipid of the mem protein anchors the protein to the membrane by covalently bonding it to the bilayer
so the protein itself is not embedded only lipid is
Example of Lipid Anchored mem protein give 2 examples of each of the mem proteins
GPI
what are the membrane carbohydrates attached to?
protein- Glycoprotein
Lipid- Glycolipid
where are carbohydrates located?
present on extracellular side of PM not inside of cell so cause PM asymmetry
Why is it called Fluid Mosaic Structure?
Fluid- Phospholipids and proteins are flexible they move side to side
Mosaic- Pattern produced by the scattering of lipids, carbs and proteins
Experiment that proves phospholipids move around
Fluorescently label lipids of phospholipid
Example of Flippase clinical use
blood clot
What Factors determine the Fluidity of the Plasma membrane?
-Length and type of Hydrocarbon tail
- Cholesterol
- Lipids and proteins movement within the membrane
Do saturated FA tails make membrane more/less fluid Why?
Saturated hydrocarbons make the phospholipids more linear so have ordered arrangement = less fluid
Do Unsaturated FA tails make membrane more/less fluid Why?
unsaturated= irregular arrangement so more Fluid
How length of hydrocarbon tail determines membrane fluidity?
short= more fluid
long = less fluid example: extremophile bacteria have membrane with long hydrocarbon chain so membrane is not damaged by heat
What is the Role of Cholesterol?
Control Fluidity of the PM by adjusting the movement of phospholipids.
prevent the membrane becoming less fluid at low temperature and too fluid at high temperature.
How cholesterol maintains fluidity at low temperature
Makes phospholipids more flexible so move more and fluidity increases
How cholesterol maintains fluidity at high temperature?
Restricts movement of phospholipids+ prevents membrane becoming too fluid
other roles of cholesterol such as sterols
sterols control movement of oxygen into cells so act as o2 sensors
What experiment proves that proteins can move within the membrane
Fluorescence recovery after photobleaching(FRAP)
Details of the FRAP experiment
tag proteins with GFP(Green Fluorescent protein)
kill fluorescent with laser (photobleaching)
if mobile= killed spot should recover
Not mobile: killed spot missing proteins stays the same
How do we look at protein movement nowadays?
Advances in microscopy look at protein molecules individually- use fluorescent microscopy to see proteins move under the microscope.
What are the forms of Transport across the membrane
active- active transport
passive- simple/ facilitated diffusion
Features of Simple diffusion
-no energy needed- comes from inbuilt chemical energy of molecules
- high to low conc.
- allows passage of only small, non polar, hydrophobic molecules
What is facilitated diffusion and features of it
Passive- with the help of transporter proteins
speed up movement of molecules until the no of proteins is the limiting factor
these transport proteins make the membrane selective
types of transporter proteins and examples
-channel proteins(aquaporins+ ion channels)
-carrier proteins
Define osmosis
Movement of water molecules from an area of high wp(low solute conc) to low wp(Higher solute conc) through selectively permeable membrane
is osmosis passive/ active
passive
hypotonic meaning
what happens to animal cells
solute conc. outside cell< inside so water enters cell and animal cells burst(lysed) as no cell wall is present
Hypertonic meaning
what happens to animal cells?
Solute conc outside> inside
animal cells lose h20 and shrivel
isotonic meaning
what happens in animal cells
same solute conc inside and outside cell
no net movement of water
Features of Active transport
Energy required (ATP)
Substances move from low to high conc against conc gradient
allows cells to maintain their conc gradient e.g sodium gradient is created so glucose can enter the cell
Example of clinical importance of ion channels-
what conditions can defects in ion channels lead to?
cystic fibrosis-
How defects in the cystic fibrosis transmembrane receptors leads to cystic fibrosis?
defects in the CFTR means cl- unable to move out of the lung cells through CFTR so no water moves out to hydrate the mucus- mucus stays thick and sticky clogging lungs.
what ion passes through CFTR?
where are they located?
These are cl- channels
defects in these channels in epithelial cells leads to lung congestion
- What does the word plasma membrane mean? where does it come from?
plasma: comes from cytoplasm or plasm for short is the membrane that surrounds the cytoplasm, its around the cell.
are there any membranes around organelles?
which organelles are surrounded by membrane?
1) yes
2) lysosome, nucleus (nuclear envelope), Mitochondria (double membrane), Golgi,
what is special about nuclear membrane/ envelope?
contains pores (junctions b/w) to allow passage of small molecules (mRNA)
What is different in membranes around different organelles?
they have different composition of protein/ lipid/ carbohydrates
for example: mitochondria membrane has higher proportion of proteins as these are enzymes involved in aerobic respiration.
axon membranes have higher proportion of lipid compared with lysosome membrane as lipid insulates the axon speeding up nervous impulse
what are the common features of all plasma membranes?
1) PM is fluid-
2) Self sealing-
3) Electrically polarised
4) non- covalently bonded
5) PM is asymmetric
What is meant by membrane being asymmetric?
composition of lipids and proteins vary in the extracellular side compared to intracellular side
e.g glycolipids only occur on extracellular side of PM
Why is the membrane electrically polarised?
the membrane has an electrical charge due to unequal conc. of ions across a membrane e.g axon membrane
what type of bonding holds the phospholipids of the bilayer together?
non-covalent interactions
H bond, vdw these bonds stabilise the membrane
what biological molecules make up the PM?
proteins- peripheral, integral
lipids- glycolipid, phospholipid, cholesterol
carbohydrates- glycolipid, glycoprotein
what is the structure+ different components of phospholipids?
Draw a PHOSPHOLIPID
– 2 FA chains(hydrophobic) can be saturated/ unsaturated or mixed
– phosphorylated alcohol(choline/ serine)
– phosphoglycerate
Phospholipids and cholesterol are amphipathic what does this mean?
they have polar and non-polar parts
what are the components of glycolipids?
carbohydrate (oligo or monosaccharide)
- FA(one/2)
-Glycerol
What are the components of cholesterol? where are they located
are present b/w phospholipids
- hydroxyl group attached to long hydrocarbon chain
How are phospholipids arranged on the membrane?
arranged in a bilayer.
Hydrophilic(polar) heads point towards the aqueous environment on both sides
hydrophobic tails point away from the aqueous environment towards the center of bilayer
what are glycolipids and glycoproteins?
carbohydrate chain + Glycerol attached to protein
carbohydrate+ glycerol attached to lipid
why glycoprotein/ lipids cause membrane asymmetry?
they are only present on extracellular side of PM not inside the cell
3 types of proteins that make up PM
Integral
peripheral
lipid anchored
what are integral proteins and give 3 examples
span across the bilayer completely or partially embedded by non covalent bonds
GPCR, CFTR, insulin receptor
what are the 3 types of integral membrane proteins? explain each with examples
- Monotopic: embedded in only one layer of phospholipids of the bilayer(prostaglandin E synthase)
- single span transmembrane protein: span the membrane completely once
- multi-span membrane protein: span the membrane more than once GPCR spans 7 times
where are peripheral proteins located?
are they covalently bonded to membrane?
example
they are on the interna/ external side of PM can be located on inside/ outside a cell
- non covalent bonding
example cytochrom c
How do lipid anchored proteins work?
lipid of the mem protein is anchoring the protein to the membrane by covalently bonding to bilayer.
protein itself is not embedded only lipid is.
why is it called fluid mosaic model?
fluid- phospholipids and proteins are flexible move side to side
Mosaic- pattern produced by proteins, lipids and carbs which are scattered through the bilayer like tiles in a mosaic
How can you prove that phospholipids move around?
fluorescently label lipids of the phospholipids
laser kill the lipids
phospholipids flip from one side of the bilayer to another
membrane is recovered and phospholipids are replaced
enzyme flippase is used to speed up the flipping process of phospholipids
which factors determine the fluidity of the PM
- length of the FA tail
- type of FA(sat/ unsat)
- cholesterol
-lipid and proteins movement
How type of hydrocarbon tail effects fluidity
are saturated ones more or less fluid?
saturated= less fluid
saturated hydrocarbon tails makes them more linear so they have ordered arrangement , many H bonds form so stick together stronger
how does length of hydrocarbon chain effect fluidity?
long hydrocarbon chain= less fluid membrane
short tail= more fluid
bacteria living in high temperatures their phospholipids have long tail so membrane is not damaged by heat
role of cholesterol in PM
controls fluidity of pm
prevents membrane becoming too fluid at high temperature
how does cholesterol maintain fluidity at low temp?
cholesterol makes phospholipids more flexible so increasing mem fluidity
How does cholesterol maintain fluidity at high temperature?
restricts movement of phospholipids so prevents membrane becoming too fluid
sterol is a cholesterol what role does it play in the membrane
sterol controls movement of o2 into the cell so acts as o2 sensor
may have evolved in eukaryotes as a result of rise in terrestrial o2
Experiment that proves lipids and proteins can move within the membrane
FRAP(fluorescent recovery after photobleaching)
Fluorescentely label proteins with GFP
kill the fluorescence with laser
if mobile= killed spot should recover
not mobile = spot missing stays there
Give an example of clinical importance of protein ION channels
CFTR cystic fibrosis transmembrane receptor carries cl- ions
if inactivated it leads to cystic fibrosis
is CFTR integral or peripheral?
where is it located?
present on epithelial cell membrane of every organ that makes mucus (lungs, pancreas, liver)
integral
located on epithelial cell membrane of every organ that produces mucus
what causes cystic fibrosis?
inherited genetic disorder caused by mutation in CFTR gene located on ch7
what is the role of CFTR?
Acts as channel protein allowing the passage of cl- across epithelial cell membrane
so CFTR regulates salt and water balance
CF patients have saltier sweat
normal functioning of CFTR
CFTR transports cl- from epithelial cell to lumen of airway(lung), this lowers wp so water enters lumen of airway hydrating mucus, thinning it.
what effect does mutation of CFTR have
CFTR is absent on epithelial cell
cl- doesnt move out of epithelial cell
water isnt transported to lumen
thick, sticky mucus cloggs the aIRWAY restricting it
what is wilsons disease?
Autosomal recessive genetic disorder
mutation in the ATP7B gene
what protein does ATP7B gene code for
copper transporting ATPase
what are the effects of inactive ATP7B Protein?
no Cu2+ enters golgi
so cant be packed into vesicles to leave the cell and get excreted
CU2+ is floats free in the cell
Cu2+ has toxic effects
what happens if Cu2+ levels get too high as they cant be metabolised?
enters blood very toxic effect
brain cells cen absorb cu from blood damaging nerve cells leading to dementia and speech problems
How many times does GPCR span the membrane?
7 times
what is the role of GPCR?
allow cells respond to hormones and neurotransmitters
