Module 4: V1 - V5 Flashcards
What are the three functions of lipids?
storage, structure and signalling
What are biological lipids?
a chemically diverse group of compounds that play and equally diverse set of functions in the cell
What are the properties of biological lipids?
generally non-polar (entirely or in part) and therefore have a low solubility in water
What are fatty acids?
a universal form of storage lipid which consist of carboxylic acids and hydrocarbon chains containing between 4 to 36 carbons
What are some examples of storage lipids?
fatty acids, triacylglycerol and waxes
What are some examples of membrane lipids?
phospholipids, glycolipids, cholesterol
What are some examples of signalling and cofactor lipids?
steroid hormones, eicosanoids, lipid soluble vitamins
What is a saturated fatty acid?
no double bonds between carbons in the chain
What is a monounsaturated fatty acid?
one double bond between carbons in the alkyl chain
What is a polyunsaturated fatty acid?
more than one double bond in the alkyl chain
What makes fatty acids ampiphatic?
having both hydrophobic and hydrophilic characteristics
Why are saturated fatty acids able to pack together?
because the fully saturated C backbone is usually in a fully extended conformation and they are stabilised by extensive hydrophobic interactions of the hydrocarbon chain
What are trends of physical properties? Why?
higher melting temperatures in longer carbon chains
longer carbon chains require more energy to disrupt the packing
What is an unsaturated fatty acid?
hydrocarbon chain containing one or more double bonds
Is the double bond usually in the cis or trans configuration?
cis
How is a fatty acid named?
using the X:X Δ^x format
if the fatty acid has 18 carbons and one double bond at C9 then this will give 18:1 Δ^9
Why do unsaturated fatty acids pack less orderly?
due to the kink which leads to less-extensive favourable interactions
Does it take more or less thermal energy to disrupt disordered packing of unsaturated fatty acids?
less thermal energy (lower melting point)
How are trans fatty acids formed? Does this result in a higher or lower melting point than their cis forms?
formed by partial dehydrogenation of unsaturated fatty acids (adopts an extended conformation)
higher melting point
How does solubility in water change in relation to chain length?
decreases as the chain length increases
How does melting point change in relation to chain length and number of double bonds?
decreases as chain length decreases
decreases as the number of double bonds increases
What are omega-3 fatty acids and why do humans need them?
essential nutrients
because humans cannot synthesize them
What does omega mean in relation to fatty acids? What does this have to do with omega-3 fatty acids?
the omega carbon is the last carbon in the fatty acid chain
omega-3 fatty acids have their first double bond on C3 in relation to the omega carbon which is C1 in this context
What is a triacylglycerol?
fatty acid esters of glycerol
What provides the three sites for fatty acid linkage in triacylglycerols?
three OH groups of glycerol
What are simple triacylglycerols?
all three fatty acids are identical
What are mixed triacylglycerols?
fatty acids differ
What are the advantages of triacylglycerols?
- higher energy yield than oxidation of other fuel sources such as glycogen or starch
- not hydrated (less weight)
What is the role of triacylglycerols?
provide stored energy and insulation
What is the structure of adipocytes?
their internal structure is dominated by a large lipid-filled droplet
What are biological membranes and what do they do?
double layer of lipids (lipid bilayer) with a hydrophobic core, acting as a barrier to the passage of polar molecules and ions
What are phospholipids defined by?
defined by the phosphate group within their polar head group
What are glycerophospholipids?
based on the glycerol molecule
What are sphingolipids?
based on sphingosine
What is the most common glycerophospholipid?
phosphatidylcholine
What does the charge on glycerophospholipid range from?
ranges from -4 to 0
What is the role of glycerophospholipids?
structural and signalling roles
What are carbons 1, 2 and 3 of the sphingosine backbone equivalent to?
the 3 carbon glycerol, but in addition the sphingosine contributes 1 of the 2 “tails”
Do sphingolipids always contain a phosphate groups?
no
What is a glycolipid? What can they contribute to?
a lipid that contains a sugar (contain mono or oligosaccharide units in their head groups)
they can contribute to sites of biological recognition
What are sterols composed of? Are they ampipathic?
4 fused carbon rings which constrain their conformation, are almost planar and are relatively rigid
yes because they have both hydrophilic and hydrophobic characteristics
What is the main sterol in animal tissues and what is its purpose?
cholesterol which plays an important role in structure of membranes and signalling, acting as a precursor for steroid hormones
How thick are membranes?
3 nm
What are three features of the fluid mosaic model?
proteins embedded in the bilayer sheet which are held by hydrophobic interactions
the interactions among the components are noncovalent (allowing fluidity)
charges of the lipid head groups contribute to surface properties of membranes
What do fatty acids form and what do phospholipids form?
fatty acids form micelles due to the wedge-shaped cross section of their individual units while phospholipids form sheet-like structures or bilayers due to the cylindrical cross section of their individual units
Why are hydrophobic regions at the edges of the bilayer never exposed? What happens instead?
because this is unstable
instead bilayers fold back on self to form a hollow vesicle (liposome) with aqueous cavity
What does the fluidity of a membrane depend upon?
depends upon the composition of the membrane
e.g. fatty acid composition and cholesterol content
What is the phase transition temperature? Are biological membranes fluid at 37˚C or solid?
temperature at which membrane goes from paracrystalline state to fluid state
fluid
Is the movement of a phospholipid from one bilayer to the next energetically favoured? What happens as a result of this? Can this process be catalysed by enzymes?
no, this process is very slow and as a result two monolayers can have different lipid compositions
yes
Do membranes show “sidedness” i.e. an asymmetry of distributions of proteins and lipids between two membrane leaflets?
yes
What are membrane rafts?
where sterols and sphingolipids cluster together resulting in a region of differing fluidity to the rest of the membrane
How manytriacylglycerolspecies are theoretically possible usingpalmiticacid (16:0) and oleic acid (18:1D9)?
six triacylglycerol species
Do you think you could use the “FRAP” technique to study the movement of lipids that make up the inner leaflet of the plasma membrane of a cell? Explain why or why not?
no, the “FRAP” technique can only be used to study the movement of lipids that make up the outer leaflet of the plasma membrane
this is because the “FRAP” technique works by reacting the outer surface of the cell with a fluorescent probe to label the lipids and then bleaching a small area with an intense laser
this cannot be done to the inner surface of the cell, therefore the “FRAP” technique cannot be used
Often the detection of phosphatidylserine is used as a marker of cell death. What is it about the usual localisation of phosphatidylserine that makes this possible? Why do you think this would change after cell death?
the usual localisation of phosphatidylserine is inside the cell
this would change after cell death because apoptosis results in lysis of the cell resulting in the insides of a cell mixing with the external environment
