Cell Membranes Flashcards
What does the world amphipathic mean
It means that the membrane lipid has both hydrophilic and hydrophobic parts
Why do membrane lipids act as a permeability barrier
It is difficult for most solutes to simply diffuse through
How would you describe the general structure of membrane lipids
water hating fatty acyl chains associate with each other and water loving polar head groups interface with the water
What enzyme is involved in the synthesis of fatty acyl chains
Fatty acid synthase
Describe roughly how a fatty acid chain is synthesised
a two carbon unit joins with a three carbon unit, the loss of carbon occurs, you get a 4c unit and this is repeated until you obtain a long fatty acid chain
what is the two carbon molecule involved in fatty acyl synthesis
acetyl coA
what is the three carbon molecule involved in fatty acyl synthesis
malonyl coa
how many carbons does palmitic acid have and how many double bonds
it is fully saturated because it has no double bonds and it has 16 carbons
what is a fatty acid desaturase
A fatty acid desaturase is an enzyme that removes two hydrogen atoms from a fatty acid, creating a carbon/carbon double bond.
what is the carboxyl end of a fatty acid referred to as
carboxyl end
what is the methyl end of a fatty acid referred to as
the omega end
when delta is used to describe a fatty acid chain what does it mean
delta - indicating that the double bond is created at a fixed position from the carboxyl group of a fatty acid (for example, Δ9desaturase creates a double bond at the 9th position from the carboxyl end).
when omega is used to describe a fatty acid chain what does it mean
omega (e.g. ω3desaturase) - indicating the double bond is created between the third and fourth carbon from the methyl end of the fatty acid.
is cis or trans commonly found in nature
cis
if two hydrogen atoms are removed from the same side in a fatty acid how would you describe the fatty acid
it would be cis
if two hydrogen atoms are removed from opposite sides in a fatty acid, it would be referred to as
trans
trans fatty acids have what kind of shape
they are straight
what does polyunsaturated mean
Polyunsaturated fats are lipids in which the constituent hydrocarbon chain possesses two or more carbon–carbon double bonds.
what are the two essential fatty acids
Only two fatty acids are known to be essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).
why must we obtain the two essential fatty acids from our diet
this is because we do not have the desaturase enzymes to remove the hydrogens from omega3 or omega6 carbons
why are essential fatty acids referred to as essential
because we must get them from our diet
what is the actual name for omega-6 fatty acid
linoleic acid
what is the actual name for omega-3 fatty acid
alpha-linolenic acid
what are the essential fatty acids omega3 and omega6 required for
they are important precursors in a pathway to arachidonic acid and eicosapentaenoic acid
what is the function of arachidonic and eicosapentaenoic acid
they are used in paracrines so cell-cell communication
what is the enzyme used to convert arachidoni and eicosapentaenoic acid into paracrines
cyclo-oxygenase 2 (cox-2)
list three paracrines
leukotrienes, prostaglandins and thromboxanes
what is the function of leukotrienes, prostaglandins and thromboxanes
they are mediators of inflammation, pain, fever, immunosuppresion, clotting, blood vessel constriction, airway constriction
which three drugs inhibit cox-2 and therefore do not allow the production of paracrines and therefore don’t allow pain to be felt
aspirin, ibuprofen and indomethicin
what is the enzyme that converts linoleic acid and alpha linolenic acid into the arachidonic acid and the eicosapentraenoic acid
elongases desaturases
elongases desaturase enzymes convert omega6 into what
into arachidonic acid
elongases desaturase enzymes convert omega3 into what
eicosapentaenoic acid
what are fatty acids primarily stored as
triglycerides
why are triglycerides in fat droplets efficient
because 1g of triglyceride is 6x energy store of 1g of glycogen and it occupies less volume
which cell type has loads of triglycerides in fat droplets
adipocytes
why are the fatty acids in phospholipids describes as amphiphillic
due to the polar hydrophillic headgroup and the non polar hydrophobic tail
*label this structure of a fatty acid in a phospholipid
there
what are two of the hydroxyls of the glycerol molecule on a fatty acid coupled to
to two acyl chains
what is the final hydroxyl of the glycerol molecule - excluding the two hydroxyl groups that are coupled to two acyl chains -attached to
the third hydroxyl is coupled to a phosphate
what type of double bond is present in one of the acyl chains attached to one of the hydroxyls of the glycerol
a cis- doulbe bond
what does the cis double bond in one of the fatty acid acyl chains result in
makes the acyl chain more bulky
the amphiphilicity of membrane lipids means what happens when they
the amphiphilicity of membrane lipids means that they readily self associate in water
membrane lipids form a bilayer of two leaflets rather than a micelle, why is this
membrane lipids have a cyclindrical shape therefore they favour a bilayer of two leaflets, rather than a micelle
what do fatty acids form when in water
they would form a lipid micelle
what is a liposome
A liposome is a spherical vesicle having at least one lipid bilayer. The liposome can be used as a vehicle for administration of nutrients and pharmaceutical drugs.
why is a sealed compartment formed by the phospholipid bilayer when making liposomes more energetically favourable compared to a planar phospholipid bilayer with edges exposed to the water
The closed structure is stable because it avoids the exposure of the hydrophobic hydrocarbon tails to water, which would be energetically unfavorable.
list two uses of liposomes, in terms of future study and cures
they can be used to study the behaviour of lipid membranes and because they are readily taken up by cells they have also been used to deliver drugs and dna to patients
what is special about the membrane surrounding a fat droplet
it is surrounded by a membrane lipid monolayer
why does the membrane surrounding a fat droplet have a monolayer
because the contents are hydrophobic
what do fat droplets form from
They are thought to form from discrete regions of the endoplasmic reticulum membrane where many enzymes of lipid metabolism are concentrated.
how would you describe how fat droplets are formed from the er
Neutral lipids are deposited between the two monolayers of the endoplasmic reticulum membrane. There, they aggregate into a three-dimensional droplet, which buds and pinches off from the endoplasmic reticulum membrane as
a unique organelle, surrounded by a single monolayer of phospholipids and associated proteins.
*label this diagram of the rough er
there
the fluid mosaic model describes the phospholipids being able to move in three ways within the bilayer, what are these three types of movements
phospholipids can rotate within the bilayer, they can diffuse laterally within the leaflet, flip-flop
describe the flip flop motion in the fluid mosaic model
the movement of phospholipid from one leaflet to the other - this is rate but can occur rapidly in certain cell types under certain conditions
*label this diagram of the movements occuring in the fluid mosaic model
there
finish off the sentence, membranes separate the cell contents from the
outside
finish off the sentence, membranes separate the contents of different organelles from the
rest of the cell
finish off the sentence, membranes form a permeability barrier to many
biologically important molecules
are gases such as co2, n2 and o2 permeable or impermeable through the cell membrane
they are permeable
are large uncharged polar molecules such as glucose and fructose permeable or impermeable through the cell membrane
impermeable
are ions such as k+, mg2+ permeable or impermeable through the cell membrane
impermeable
are charger polar molecules such as amino acids, atp, proteins and nucleic acids permeable or impermeable through the cell membrane
impermeable
what are the three major lipids present in the cell membrane
phosphoglycerides, sphingolipids and sterols
what is the sterol present in the cell membranes of animal cells
cholestrol
list the five phospholipids and what makes them fit under this category
- phosphatidylinositol 2. phosphatidylethanolamine 3. phosphatidylserine 4. phosphatidylcholine 5. sphingomylein - they fit under this category because they all have a phosphate group present
what is the only lipid component in the cell membrane which has an overall negative charge
phosphatidylserine
name the two amino phospholipids
phosphatidylethanolamine and phosphatidylserine
name the two choline phospholipids
phosphatidylcholine and sphingomyelin
name the two glycolipids
cerebrosidase and gm1-ganglioside
name the three sphingolipids
sphingomyelin, cerebrosidase and gm1-ganglioside
what is the difference between sphingolipids and glycerophospholipids
sphingolipids are built from sphingosine rather than with glycerol as the ‘back-bone’
how are the major lipid components of most biological membranes arranged between the two leaflets of the bilayer
asymmetrically
*describe the structure of a cholesterol molecule
a polar head group at the top, a rigid steroid ring structure and a nonpolar hydrocarbon tail
how does the absence of cholesterol molecules in the cell membrane impact the cell membrane
it makes it more fluid. the more cholesterol molecules in the cell membrane, the more gel-like/ rigid the cell membrane becomes
focusing in on the membrane structure, the head group of a cholesterol molecules associates with what part of the neighbouring glycerophospholipid
the head group of the glycerophospholipid
what part of the cholesterol molecule intercalates with the acyl chains of the glycerophospholipids
the steroid ring and the acyl chain of the cholesterol molecule
describe the structure of the membrane when there is more cholesterol - 3 points
the membrane is more densely packed, less fluid and less permeable
what affect does cholesterol have on membranes made of sphingolipid
cholesterol intercalation reducing the packing density of sphingolipids and keeps the membrane more fluid
what is a lipid raft
the self association of sphingomyelin and cholesterol to form ‘rafts’ - OR Lipid rafts are subdomains of the plasma membrane that contain high concentrations of cholesterol and glycosphingolipids. They exist as distinct liquid-ordered regions of the membrane that are resistant to extraction with nonionic detergents.
what is the overall function of lipid rafts
they bring together proteins that work together, for example proteins for endocytosis or signalling may be bought together
which part of the cell membrane is enriched with cholesterol along with spingholipids
membrane invaginations (caveolae and clathrin coated pits) important for endocytosis
cholesterol is not just a membrane lipid, list four other places it is found
precursor for bile salts, vitamin d, steroids, sex hormones
what are bile salts for
solubilisation of dietary fat and lipophilic vitamins
name two steroids cholesterol acts as a substrate for
cortisol and aldosterone
name three hormones cholesterol acts as a steroid for
progesterone, oestrogen and testosterone
what is the main structural component that glycolipids are based on
ceramide
what type of head groups do glycolipids contain
sugar head groups
name a glycolipid which carries a negative charge
NANA - sialic acid
gm1 ganglioside is a glycolipid found in the cell membrane, what is it a receptor for
the cholera toxin
what is the overall function of glycolipids, list three
protection from hostile environment, important in cell-cell contact, localise to and may be important in lipid raft generation
different organisms/cells/organelles have different lipid composition, why is this
because of differing functions
explain why hepatocyes are enriched in phosphatidylcholine
because they secrete phosphatidylcholine into bile
explain why the er is low in cholesterol and its lipids are asymmetric
in order to make the er more fluid for membrane protein insertion
explain why e.coli lacks cholestrol
because gram negative bacteria already have a double membrane, with peptidoglycan to provide stability
why is myelin enriched in glycolipids
to insulate the nerve axons for nerve impulse conductivity
what does the fluid mean when describing the fluid mosaic model
fluid describes the motions of the lipids and the proteins
what does the world mosaicity describe when discussing the fluid mosaic model
mosaicity describes the membrane proteins embedded in the bilayer
label/describe the following membrane protein, 1 and 2
there
label/describe the following membrane protein, 3
there
label/describe the following membrane protein, 4
there
label/describe the following membrane protein, 5 and 6
there
label/describe the following membrane protein, 7&8
there
what are lipid anchors
they are long chain fatty acids
what can lipid anchors be used for
can be used to recruit proteins to or detach proteins from the membrane
lipid anchors are reversible by what process
de-esterification
what enzyme is involved in the detachment of lipid anchros
lipid transferase
why are transmembrane a helices enriched in hydrophobic amino acids
because they pass through the hydrophobic core of the membrane
give three examples of hydrophobic amino acids which would be found in the transmembrane a helices
any three - glycine (Gly), alanine (Ala), valine (Val), leucine (Leu), isoleucine (Ile), proline (Pro), phenylalanine (Phe), methionine (Met), and tryptophan (Trp).
can lipid anchored membrane proteins associate and dissociate from the membrane
yes
can lipid anchored membrane proteins diffuse laterally
yes
can lipid anchored membrane proteins change conformation
yes
can integral membrane proteins associate and dissociate from the membrane
no
can intergral membrane proteins diffuse laterally
yes
can integral membrane proteins change conformation
yes
