Module 4 Flashcards
Lipids are incorporated into . . .
triacylglycerols + waxes + phospholipids
Monounsaturated fatty acids are usually in the ___ config
CIS
Define fatty acids
carboxylic acids w a hydrocarbon chain b/w 4 to 36 carbons long
Are double bonds normally conjugated in unsat fatty acids?
NO
As the HC chain gets longer, the fatty acids melting point gets. . .
HIGHER
- sat fat acids can pack into stable aggregates
- nearly crystalline array
- stabilized by extensive hydrophobic interactions on the HC chain
Cis fatty acids pack less orderly due to the. . .
kink
- less thermal energy needed to disrupt disordered packing
How are trans fatty acids made?
partial dehydrogenation of unsaturated fatty acids
higher melting point
How to count when naming fatty acids?
start counting from carboxyl group when trying to work out where the bonds are
unless you’re talking about omega, start from other side
3 structural properties of triacylglycerols
1) composed of glycerol backbone
2) the 3 OH of glycerol provide the 3 sites for fatty acid linkage (ester linkages)
3) all are hydrophobic
3 functional features of triacylglycerols
1) when broken down into constituent fatty acids, can go onto oxidation to produce energy
2) provide stored energy + insulation
3) not hydrated (less weight) - so carry no water
Wat are the 2 types of phospholipids?
- glycerophospholipids
- sphingolipids
What is the most common glycerophospholipid?
phosphatidylcholine
What does the charge on each glycerophospholipid depend on?
the charge on each will depend on IDENTITY of head group (ranges from -4 to 0)
simplest example is phosphatidic acid, where X=H
What are some features of sphingolipids?
carbons 1, 2, & 3 of the sphingosine backbone can be considered equivalent to the 3-C glycerol, but in addition the sphingosine contributes 1 of the 2 tails
simplest example is CERAMIDE
sphingolipids don’t ALWAYS contain a phosphate group, but CAN also fall into a glycolipid grouping
What are some features of glycolipids?
contain mono or oligosaccharide units in their HEAD groups
are components of the outer membrane leaflet
What is lateral diffusion?
- when the lipid moves from one end of a bilayer to another area in the same layer
- FRAP can be used to demonstrate lateral diffusion
What is FRAP?
- react cell w fluorescent probe to label lipids
- view surface with fluorescence microscope
- intense laser beam bleaches small area
- with time, unbleached phospholipids diffuse into bleached region
- measure rate of fluorescence return
Flip-flop transverse diffusion requires. . .
catalysis (enzyme) bc it is highly energetically unfavourable
3 types of transbilayer translocations
1) Flippase (out to in)
2) floppase (in to out)
3) scramblase
As temp increases in membrane, heat produces. . .
thermal motion of acyl side chains (from paracrystalline state / solid to fluid state)
What are membrane rafts?
slightly thicker, more ordered and harder to dissolve non-ionic detergents than the surrounding regions
allows for efficient signalling IN and OUTSIDE of cel
Properties of peripheral membrane proteins
associated w membranes by IONIC INTERACTIONS & H bonding with
1) polar head groups of lipids
2) integral membrane proteins
Properties of integral membrane proteins
associated w membranes by HYDROPHOBIC INTERACTIONS w:
1) acyl chains of membrane lipids
2) integral proteins are all oriented in same way within bilayer
3) protease sensitivity of protein from intact cells –> CHOPPING UP PROTEINS
How are peripheral membrane proteins experimentally released from biological membranes?
1) high salt
2) change in pH
3) chelating agent (binds metals more tightly)
- all of these factors disrupt ionic interactions and separate proteins from the membranes
Why is a hydropathy plot useful?
helps us determine which proteins are transmembrane
helps us predict numbers of typical membrane helices
Can we predict which proteins are membrane proteins just based on their amino acid sequence?
i. Sequence will consist of hydrophobic amino acids
ii. Conformation will be an a-helix
iii. Span (segment of protein) equal to width of membrane
Provide an example of an passive transporter.
GLUT 1
- facilitates passage of glucose DOWN a concentration gradient
- glucose transporter exists in 2 conformations
- binding of glucose (from blood plasma) may induce a change from T1 to T2
Provide an example of an active transporter.
P-type ATPases
- ATP powered pumps
- the hydrolysis of ATP to ADP produces energy which drives the conformational change that allows the molecules to be transported across the membrane
- phosphorylation also stabilises the conformation of that enzyme to release the molecules
IN A HYDROPATHY PLOT, what is the charge of the HYDROPHOBIC region?
Hydrophobic = +
Hydrophilic = -
How are integral membrane proteins released from membranes and studied?
released from membrane by reagents that disrupt hydrophobic interactions, e.g. detergents (such as SDS – sodium dodecyl sulphate)
i. They interact with membrane, specifically the hydrophobic regions
ii. They solubilize chunks of lipid into the solution
iii. Same thing happens with the protein
What are monosaccharides?
aldehyde or ketones that have 2 or more hydroxyl (OH) groups (CH2O)n
What’s the difference between a ketose and aldose?
ketose contains ketones, aldose contains aldehyde
in aldehydes, the presence of a tetrahedral carbon w. 4 dif substituents gives rise to chirality
Fructose is a _____ while glucose and ribose are _____
ketose
aldoses
Most natural sugars belong to . . .
the D series; they’re all structurally related to D-glyceraldegtde
- OH projects to the RIGHT in D when CHO is on top
- of the asymmetric carbon furthest away from the aldehyde group
(aldehyde group carbon is carbon-1)
What is special about Fischer projections?
provide a clear and simple view of the stereochemistry at each carbon centre
horizontal lines = out of plance
Monosaccharides have. . .
2 or more carbons
How many chiral centers do aldohexoses have?
4
therefore 16 steroisomers
How do D-glucose and D-mannose differ?
only in config at C-2
What are epimers?
sugars that differ only in the config around one carbon atom
How does the pyranose ring form?
Pyranose is a chemical structure that is comprised of a ring. The ring is made up of six members that contain 5 Carbon and 1 Oxygen atom.
- the OH on C-5 attacks the carbonyl of the aldehyde group & form a HEMIACETYL linkage
- when the system cyclizes, a new tetrahedral carbon forms with an OH on it
LURD
What are 2 modifications of monosaccharides?
GalNAc and GlcNAc
How are disaccharides defined?
by the MONOSACCHARIDES and NATURE OF LINKAGES
What are polysaccharides?
- large polymeric structures
- unbranched homopolysaccharides include structural elements on plant cell walls (cellulose) & chitin
- storage fuels include the branched starch (plants) & glycogen (animals)
Aldehydes are capable of. . .
REDUCING other groups by becoming itself oxidized to a carboxylic acid
How can sugar concentrations be determined by measuring Cu2O?
- as increase in concentration of glucose in sample, there’s an increase in conversion of Cu2+ to Cu+
- so, the colour changes from blue to red
Which sugar in the chain can open up?
ONLY 1, that is the reducing sugar (usually shown to the right)
What are some features of chitin?
- is a linear homopolymer of N-acetylglucosamine residues
- similar to cellulose, only different is the presence of an acetylated amino group at C-2
There is less H bonding in. . .
glycogen and starch
have an open helix structure
Why are glycoproteins important?
carbohydrate groups are COVALENTLY attached to many proteins called GLYCOPROTEINS
cell-cell adhesion / recognition
What are the 2 ways in which carbohydrates can be linked to proteins?
1) via the AMIDE side chain of asparagine (GlcNAc - N- Asn)
2) via serine or threonine residues at hydroxyl side chains (O-glycans)
GalNAc- O- Ser
What do glycosyltransferases do?
catalyzes the transfer of sugar (responsible for oligosaccharide assembly)
the hydrolysis of the (nucleotide-monosaccharide) bond with drive the reaction
monosaccharide is transferred from nucleotide sugar to non-reducing end of carbohydrate acceptor
ABO blood group antigens are . . .
GLYCOSPHINGOLIPIDS
- A & B blood group antigens differ from O antigen by one extra monosaccharide
carbohydrates are attached to glycoproteins (& glycolipids) on surfaces of red blood cells
A vs B antigen
A has GalNAc
B has Gal
ABO blood group genes encode a . . .
glycosyltransferase (enzyme)
eg. GalNAc transferase for A
O allele product is a . ..
DEAD enzyme (no active transferase)
How is B allele diff to A allele?
allele has some amino acid substitutions; it cannot bind GalNAc, only Gal
the O allel ehas a premature STOP codon so we can only translate 1 to 118 amino acids
Are there antibodies to the O antigens?
NOO
What happens when antibodies come into contact with antigens?
antibodies will cross link the ‘foreign’ red blood cells (AGGLUTINATION)
incompatibility leads to HEMOLYSIS and can be deadly
What is the universal donor?
O blood
What are some features of the GLUT transporters?
composed of 12 alpha helices containing amino acids
- model with 4 amphipathic helices (1, 4, 7, and 10)
- central polar region allowing the glucose interactions
heptad is reversed, we now have hydrophilic residues at a and d
both N ter and C ter inside
What are lectins?
broad family of proteins which recognize carbohydrates
one large class of them known as C type lectins
How do C-type lectins recognize carbohydrates?
- C-type for calcium binding
- calcium acts as a bridge between the protein & the sugar through direct interaction with sugar hydroxyl groups
What are some features of C type lectins?
- calcium forms an octahedral coordination complex
- different C-type lectins have diff carbohydrate binding specificities
- changes in residues that interact with the sugar alter the carbohydrate binding specificity of the lectin
What are selectins?
- involved in cell-cell adhesion
- class of C-type lectins
- bind white blood cells to sites of injury & allow movement of cells from blood stream to site of infection
How do leukocytes interact with P-selectins?
- site of infection
- causes the expression / activation of P selectins around site of infection
- leukocyte binds to selectin via carbohydrates on gylcoproteins
- moves down from one selectin to the next until is reaches site of infection
- can move through endothelium to attack the virus / bacterium etc.
How do sugars on cell surface interact with the influenza virus & how has that been used to interact with a drug?
- infected host cell gets taken over by influenaz virus
- synthesizing more influenza virus that will bud off and infect other cells
- virion is the new virus
- it is still associated on the surface of the original cell via a receptor containing sialic acid
- hemagglutinin is what binds to sialic acid
- it can use neuraminidase on its surface (of virion) to separate from the host cell
- neuraminidase inhibitors (relenza) binds to all the copies of neuraminidase on the surface of virion and stops it being able to cleave off the host cell - virus remains stuck
- it doesn’t STOP the initial infection; it simply stalls it
