lipid biochemistry: active lipids Flashcards
what is the basic role of phosphoinositides
cell signaling and differentiating
what is the head group of phosphoinositides
inositol
at which positions can inositol be phosphorylated
3, 4, 5
how many phosphates total can there be on a molecule of phosphatidylinositol
4 (PI already has a phosphate, and then 3 more can be added to the inositol head group)
give the abbreviations for all the phosphorylated forms of phosphatidylinositol
PI, PIP, PIP2, PIP3
what is the full name of PIP2
phosphatidylinositol 4,5-bisphosphate
where is PIP2 found + in what orientation
clustered on the inner leaflet of plasma membranes
what cleaves PIP2
phospholipase
what activates the phospholipase that cleaves PIP2
extracellular signals
give the full names + abbreviated names of the products of PIP2 cleavage
inositol 1,4,5-triphosphate (IP3)
diacylglycerol (DAG)
once IP3 and DAG are made via PIP2 cleavage, where do they go
IP3: travels into the cytosol
DAG: stays embedded in the membrane
why does IP3 travel to the cytosol but DAG stays embedded in the membrane once PIP2 is cleaved?
IP3 is water soluble while DAG is not water soluble
which type of pathway is PIP2 cleavage involved in?
GPCRs and trimeric G proteins
describe how PIP2 cleavage is involved in GPCR/trimeric G protein pathways
IP3 causes Ca2+ to exit the ER
DAG and Ca2+ activates protein kinase C
what is the full name of PIP3
phosphatidylinositol-3,4,5-triphosphate
how is PIP3 formed
phosphorylation of PIP2
what phosphorylated PIP2 to create PIP3
phosphoinositide 3-kinase (PI3K)
which carbon of PIP2 is phosphorylated to get PIP3
C3
what is the charge of PIP3? which part of the molecule carries the charge?
negatively charged, inositol head carries the charge
what is the outcome of the PIP3 signaling pathway
growth, proliferation, survival
why is PIP3 a target for cancer treatment
PIP3 signaling pathways are related to growth, meaning it correlates with tumor progression
what is the PIP3 signalling pathway initiated by
receptor tyrosine kinases (RTKs)
describe how PIP3 is part of the cellular response to insulin
it activates glycogen synthesis (lowers blood glucose), brings GLUT4 to the PM so glucose can leave the bloodstream, and the insulin receptor is an RTK
what can PIP3 do with adaptor or scaffold proteins?
it uses those proteins to help cluster together proteins that are involved in the same signaling pathway
give an example of an adaptor protein that PIP3 uses
AKAP5
using AKAP5 as an example, describe how PIP3 interacts with adaptor proteins
AKAP5 has binding sites for PIP3, which localizes the adaptor and its associated proteins into lipid rafts
what is a conjugated lipid
one with alternating double and single bonds
describe how conjugated dienes produce specific colors
the delocalized electrons (due to conjugation) can be excited by certain wavelengths of visible light, and so they will reflect a different wavelength = color
how do birds acquire different colors
by ingesting conjugated dienes via their diet
how do birds acquire sex-specific feather colors?
either by different diets between males and females, or by different metabolic processing of the conjugated dienes
what is the general function of eicosanoids
they are signalling hormones
what type of signalling do eicosanoids do
paracrine signalling
what is paracrine signalling
signalling over short distances
how many carbons are eicosanoids composed of
20
which fatty acid are all the eicosanoids derived from? give the shorthand name and the common name
20:4Δ(5,8,11,14)
arachidonate
list the 3 eicosanoids we cover in this course
prostaglandin, thromboxane, leukotriene
what structural characteristic defines a prostaglandin
5C ring
where were prostaglandins originally discovered
prostate gland
T or F: prostaglandins can be released by most tissues
true
when are prostaglandins released
when there is a site of injury or inflammation
list the roles of prostaglandin at a site of injury/inflammation
promote either vasodilation or vasoconstriction, promote tissue inflammation and pain, promote fever
describe how prostaglandins regulate the female reproduction system
they’re required for ovarian follicle to rupture and release eggs during ovulation. They stimulate smooth muscle contraction in uterus during menstruation and childbirth
when are synthetic prostaglandins used
can be used to induce labour
what structural characteristic defines thromboxanes
a 6C ring
what produces thromboxanes
platelets (thrombocytes)
where in the body are thromboxanes released
released near damaged blood vessels
describe the roles of thromboxanes at damaged blood vessles
they promote local platelet aggregation to help form blood clots, promote formation of new platelets, vasoconstriction, and increases in blood pressure
what structural characteristics define leukotrienes
they have 3 conjugated double bonds in a row. They do not have any rings like the other eicosanoids do
which of the eicosanoids have rings in their structure? which doesn’t?
prostaglandins and thromboxanes have rings, leukotrienes do not
what produces leukotrienes
leukocytes
when do leukocytes release leukotrienes
during allergies or asthma attacks
describe the roles of leukotrienes during allergies or asthma attacks
they promote inflammation, increase mucus production, and they can cause contraction of smooth muscle in bronchioles
how do some anti-asthma medications work? what do they target?
they target leukotriene synthesis
other than allergies and asthma, what else do leukotrienes play a role in
arthritis and inflammatory bowel disease
what is the full name for NSAIDs
nonsteroidal anti-inflammatory drugs
what do NSAIDs do
inhibit the enzymes that help from prostaglandins and thromboxanes from their precursor molecule (arachindonate)
give 3 examples of nonsteroidal anti-inflammatory drugs
aspirin, ibuprofen, motrin
how many rings do sterols have
4
describe the structure of the 4 sterol rings
three 6C rings and one 5C ring
are sterols rigid or fluid
rigid
are sterols planar or not planar
planar
describe C-C rotation in sterols
there is little rotation around C-C bonds in sterols, as they’re rigid and planar
what are bile acids formed from
polar derivatives of cholesterol
where are bile acids secreted from
liver
where are bile acids stored
gall bladder
where are bile acids moved to from the gall bladder
moved into the small intestine
role of bile acids in the small intestine?
helps emulsify fats to allow digestion of fats by lipases
what are steroid hormones formed from
oxidized derivatives of cholesterol
describe the basic structure of steroid hormones
they have the sterol nucleus but lack the alkyl chain
where are sex (steroid) hormones synthesized
testes and ovaries
where are adrenocortical (steroid) hormones synthesized
in the adrenal gland
where do steroid hormones go once they’re synthesized
they travel to target tissues in the blood bound by hydrophilic carriers
where do steroid hormones go once they’re synthesized
they travel to target tissues in the blood bound by hydrophilic carriers
what do steroid hormones do once they reach their target tissue
they can trigger changes in gene expression
why might lipid signalling molecules in plants be fragranced
to attract pollinators or to repel herbivores
list 3 functions of lipid signalling molecules in plants (other than fragrance), and give examples
bending a shoot towards light (auxin), repairing insect damage (jasmonate), or ripening fruit (ethylene)
which plant lipid is responsible for bending shoots towards light
auxin
which plant lipid is responsible for repairing insect damage
jasmonate
which plant lipid is responsible for ripening fruit
ethylene
what are plant lipids often made from
fatty acids or sterol derivatives
most fragrant plant signalling molecules are generated from ____ units
isoprene
what are isoprenes? what is their basic structure?
isoprenes are lipids. 5C molecules joined via condensation reactions to build 10-40C molecules
isoprene units contribute to many other active lipids too, such as _________________
fat soluble vitamins
which isoprene-unit molecule produces geranium smell
geraniol
which isoprene-unit molecule produces pine smell
b-pinene
which isoprene-unit molecule produces lime smell
limonene
which isoprene-unit molecule produces mint smell
menthol
which isoprene-unit molecule produces spearmint smell
carvone
are vitamins essential?
yes
can vitamins be synthesized by the body?
no
describe the origins of the word “vitamin”
originally every vitamin was believed to have amine in it
vital + amine = vitamin
what are the two categories of vitamins?
water soluble and fat soluble
list the fat soluble vitamins
A, D, E, K
how are the fat soluble vitamins synthesized?
by isoprene condensation
what is the name of vitamin A1
retinol
list the main structural characteristics of vitamin A1
lipid with trans double bonds and a hydroxyl group
from which foods do we acquire vitamin A1
fish oils or dairy, or it can be formed from B-carotene precursor that’s prevalent in carrots/sweet potatoes
what characteristics does vit A have due to the conjugated double bonds
it can absorb light
what two things are formed from retinol when it’s oxidized
retinal or retinoic acid
by which process are retinal and retinoic acid formed from retinol
oxidation
T or F: B-carotene is comprised of isoprene units
true
what functional group does retinal have
aldehyde
what is the initial structure of retinal after the oxidation of retinol
a cis double bond on carbon 11
T or F: 11-cis-retinal is the final form of retinal
false; it undergoes a change
what happens to 11-cis-retinal (because this isn’t its final form)
it binds to a protein (opsin) in rod cells of the retina to form rhodopsin pigment. Rhodopsin is excited by visible light and changes 11-cis-retinal to all-trans-retinal
what is the result of 11-cis-retinal changing to all-trans-retinal
a signal cascade that results in vision
what protein does 11-cis-retinal bind to on the way to converting to its new form
opsin
where do 11-cis-retinal and opsin bind
in rod cells of the retina
11-cis-retinal + opsin = ?
rhodopsin pigment
how does rhodopsin convert 11-cis-retinal to all-trans-retinal
it’s excited by visible light
what are rods and cones
photoreceptors
where are rods and cones located
in the inner layer of the eyeball (retina)
what is the retina
the inner layer of the eyeball where rod and cone cell photoreceptors are located
what is a photoreceptor
a modified neuron
visual information captured by ____ is relayed by ____ to the ____ towards the brain
photoreceptors, neurons, optic nerve
in order for vision to occur, what must rods release
neurotransmitters
what do rods release neurotransmitters to
neurons
rods –> release NTs to neurons –> ? –> ?
optic nerve, brain
what type of vision do we get from rods
light (greyscale)
what type of vision do we get from cones
colors
describe the structures of rod and cone photoreceptors
the outer segment has many membranous disks filled with visual pigments
what is the visual pigment of rods
rhodopsin
retinal lipid + opsin protein = ?
rhodopsin pigment
? + ? = rhodopsin pigment
retinal lipid + opsin protein
what type of protein is opsin
a GPCR
how do the conformational changes of retinal affect vision
conformational changes of cis retinal to trans retinal = conformational changes in the opsin protein (a GPCR)
T or F: the trans state of retinal is permanent
false; it is not permanent and will eventually convert back to its cis form
what gets activated once light (photons) activate the visual pigment
transducin
what is transducin (what type of protein)
a G protein
once activated, what does transducin do
it activates phosphodiesterase (PDE)
what does PDE stand for
phosphodiesterase
what does PDE do once it’s activated by transducin
it converts cGMP –> GMP (causing cGMP levels to fall)
as PDE forms GMP, what is the effect of cGMP levels falling
cGMP-gated cation channels close = hyperpolarization
how do Na+ channels close during the visual cascade
closed via light-induced signal transduction
what happens to the rod’s membrane potential when a Na+ channel closes
Na is no longer coming in = membrane potential gets more negative = hyperpolarization
describe the behavior of hyperpolarized neurons
they’re less likely to release neurotransmitters, so they’re turned “off” when hyperpolarized
T or F: a rod is “off” in the presence of light
TRUE
when will rod cells be depolarized
in the DARK
T or F: the absence of a neurotransmitter release from the rod is what triggers vision
TRUE!!!
which neurotransmitter do rods release
glutamate
describe how the visual signal is ceased
when light isomerizes cis retinal to trans retinal, it causes opsin to expose its C-terminal. Because of this, rhodopsin kinase will phosphorylate residues on the C-term of opsin. Arrestin then binds to phosphorylated opsin and stops the GPCR from activating its G protein
during the cease of the visual signal, which enzyme phosphorylated opsin
rhodopsin kinase
during the cease of the visual signal, which part of opsin gets phosphorylated
C-terminal
during the cease of the visual signal, which protein binds to phosphorylated opsin to prevent it from activating its G protein
Arrestin
how is retinoic acid formed
via the oxidation of retinal
what functional group does retinoic acid have
carboxylic acid
what type of molecule is retinoic acid
a hormone
which form of retinoic acid is a hormone
all-trans
role of retinoic acid? (3)
it regulates gene activity in the early embryo to determine anterior/posterior axis patterning, cell differentiation, and organogenesis
T or F: excess or deficiency in vitamin A during pregnancy has no negative effects
false; it’s correlated with increased risks of birth defects in many mammals
vitamin A deficiency is the leading cause of ___ ___ in children
preventable blindness
what is golden rice and why is it beneficial
rice that’s enriched with beta carotene. Useful because it decreases the risk of childhood blindness (B-carotene is a precursor of retinol, which is involved with the visual signal)
exposure to __ __ causes a compound in the skin to be converted to vitamin D3
UV light
what disease does vit D prevent
rickets
what is rickets
a disease where bones soften in children
where is/was rickets common
in cold climates where heavy clothing blocked UV light
which form of vit D is produced in yeast and added to our milk and butter
D2
why is vit D2 added to our milk and butter
to mimic vit D3
T or F: vit D3 is biologically active
false; it needs to be converted to an active form
what is D3 converted to to become active? where does this take place?
D3 is converted to calcitriol (a hormone) via reactions in the kidney and liver
what type of molecule is calcitriol
a hormone
what does calcitriol do
it increases absorption of calcium from foods and deposits it into bones
describe the basic structure of vit E and K
aromatic rings with a long side chain formed from isoprenoids
T or F: humans are rarely deficient in vit E and vit K
true
what does vit E do
helps prevent oxidative damage to membranes
what does vit K do
assists with blood clotting
what does the drug Warfarin do? what vitamin does it mimic, but what sets it apart from this vitamin
Warfarin is a blood thinner that mimics vitamin K, but it actually prevents excess blood clotting (unlike K)
