quiz 2 Flashcards
essential fatty acids
linoleate (w-6) and linolenate (w-3)
mammals lack the enzymes to introduce double bonds at carbon atoms beyond C9 in the hydrocarbon chain
these are precursors for other needed fatty acids
fatty acid synthesis
occurs in cell cytoplasm
when high rates of intramitochondrial generation of acetyl co-A and citrate, citrate is transported out of mitochondria
enzymes (malic enzyme, ACL, ACC, FAS) then make saturated FA (palmitic acid (C16))
requires substantial investment of ATP and NADPH so pathway operates at maximum rates when glucose is readily available
happen predominantly in liver and lactating mammary gland
fatty acid oxidation
mostly in liver and in muscle (but in all tissues except for the brain and RBCs)
requires presence of functioning mitochondria and readily available oxygen
called beta oxidation because the oxidation begins at the beta carbon in the hydrophobic chain
occurs within the mitochondria
ketogenesis
only in the liver
partial oxidation of FA creating water soluble fuels (ketone bodies) from water-insoluble compound
requires mitochondria
ATP citrate lyase
citrate + ATP + CoA + H2O = acetyl CoA + ADP + Pi + oxaloacetate
ATP investment to get the pathway started
step 1 in FA synthesis
acetyl-coA carboxylase (ACC)
converts acetyl CoA to malonyl CoA by adding carboxyl group
contains biotin (vitamin B7)
rate-limiting, highly regulated step
also requires ATP
has two isozymes - first ACC-alpha - in the liver and mammary gland - in cytosol
second = ACC-beta - in muscle and liver - attached to outside of mitochondria and creates inhibitory processes
process has two steps:
first: e-biotin + ATP + HCO3 = E-N-carboxybiotin + ATP + Pi
second: E-N-carboxybiotin + acetyl-CoA = malonyl CoA + E-biotin
Fatty acid synthase (FAS)
dimeric enzyme with multiple catalytic centers
uses the vitamin pantothenic acid as part of ACP domain - this acid immobilizes reaction intermediates
adds two cycles of carbon addition to malonyl coA
creates double bonds in the process that require reduction by NADPH
only expressed in lipogenic tissues
has 8 catalytic domains and exists as a dimer
ACP domain uses vitamin B5 (coenzyme A)
malonyl attaches to serine on B5
the acetyl group attaches to the other dimer
the enzyme transfers 2 carbons from the malonyl to the acetyl group, making butyryl and then loads another malonyl group and transfers another two carbons - continues until 16 carbons long resulting in palmitic acid
malic enzyme
only expressed in FA synthesizing tissue
its activity links OAA formation by ACL to NADPH synthesis
source of NADPH needed to reduce FA made by FAS
converts malate to pyruvate so the pyruvate can go to making more NADPH - results in 8 moles of NADPH (get the other 6 needed for FA synthesis from the pentose phosphate pathway)
isocitrate dehydrogenase (IDH)
when high activity in mitochondria because high glucose levels the high activity will inhibit IDH - this results in a backup in the cycle and extra citrate which is then exported from the mitochondria to be converted into FA
malate dehydrogenase
makes oxaloacetate into malate with NADH (part of FA synthesis)
transport of FA
from liver to adipose tissue in VLDL
stored as TG in adipose tissue
in ingested it’s transported as chylomicrons
lipoprotein lipase allows for its transportation
fructose versus glucose
when glucose metabolized, high ATP levels inhibit phosphofructokinase I which limits the downstream products which limits the synthesis of FA
fructose metabolism is upstream of fructokinase so its inhibition doesn’t inhibit fructose metabolism so get much larger cytoplasmic pool of acetyl coA from fructose than from glucose
fructose also induces transcription of genes for FA synthesis in liver to greater extent than glucose does - get more ACC, FAS
fructose also binds with greater affinity to sweet receptors
lipoprotein lipase (LPL)
enzyme that breaks down triglycerides to FA to allow the FA to enter the adipose store - they are reassembled back into TG once inside the adipose cell
enzymes needed to get FA out of adipose tissue
TG can't be transported out of the adipose cell so it has to broken down into FA chains first ATG-L - takes off the first FA chain HSL - takes off the second FA chain MGL - takes off the third ATG-L and HSL are highly regulated
perlipin
enzyme involved in getting TG stores out of adipose cells
positions the ATG-L and HSL enzymes
needed to create the vacuoles for glycolysis
one of the ways the transport/breakdown of TG is regulated
albumin
FA are detergents and so can’t circulate freely or they would cause cell damage
they’re bound to albumin when circulating so that they don’t lyse cell membranes
these are free FA (even though they’re bound to something)
CD36
cell channel that takes up FA after they dissociate from albumin
low density lipoprotein (LDL)
have much less triacylglycerol than VLDL
high concentration of cholesterol and CE
primary function = provide cholesterol to peripheral tissues
bind to cell-surface membrane LDL receptors (apo-B-100/apo-e receptors) that recognize apo B-100 (and also apo-e)
steps of uptake and degradation:
1: LDL receptors negatively charged glycoproteins - clustered in pits on cell membranes - intracellular side of pit coated with clathrins
2: LDL binds and LDL-receptor complex internalized via endocytosis (binding encouraged by T3 hormone)
3: vesicle loses clathrin coat and fuses with other similar vesicles - makes endosomes
4: pH of endosome falls - allows for separation of LDL from receptor
5: receptors migrate to one side of endosome and LDLs stay in lumen (structure called CURL at this point)
6: receptor recycled - lipoprotein degraded in lysosomes, releasing free cholesterol, AA, FA and phospholipids
pancreatic lipase
enzyme responsible for the hydrolysis of ingested TG in the small intestine
adipocyte triglyceride lipase (APL)
in adipocyte
removes first fatty acid chain from triglyceride
hormone-sensitive lipase (HSL)
in adipocyte
removes second FA chain from what was originally TG (but is no diglyceride because ATGL must act before HSL)
monoglyceride lipase (MGL)
in adipocyte
takes last FA chain off of what was once TG (is now monoglyceride - can only act after ATGL and HSL have already removed the first two FA chains)
non-esterified fatty acids (NEFA)
also known as free fatty acids
FA circulating in the plasma bound to albumin
can be converted to ketone bodies in the liver
glycerol
what the FA are bound to to make TG
when TG are broken down, the TG is also released into the plasma and can be used by the liver and kidney as a gluconeogenic precursor
fatty acyl-CoA synthases
step one of FA oxidation
when FA are taken up into cells, these enzymes catalyze the formation of the fatty acyl thioester conjugate with coenzyme A
requires ATP
accelerated by pyrophosphatase enzyme
occurs on the outer mitochondrial membrane
pyrophosphatase
enzyme that breaks down PPi created by the acyl CoA synthases in the first step of FA oxidation
breaking down the PPi makes the reaction essentially reservable and speeds up the reaction because it’s removing one of the products, pushing the reaction equilibrium towards the products
carnitine acyltransferase I (CAT-1) aka carnitine parlmitoyl transferase (CPT-1)
step two of FA oxidation
the fatty acyl-CoA can’t enter the mitochondria
this enzyme conjugates the FA with carnitine (derived from lysine) via a transesterification reaction (removes the CoA and replaces it with carnitine)
this is inhibited by malonyl CoA - when there’s lots of FA synthesis there’s lots of malonyl CoA and so FA synthesis is inhibited - allosteric inhibition - this allows for the rate of FA synthesis to be tied to levels of glucose present (lots of malonyl-CoA when glycolytic rates high)
reversible
only occurs in the presence of O2
occurs on the outer membrane of mitochondria
CAT-II
step 4 of FA oxidation
when the carnitine-FA moiety is transported into the cell, it is then converted back into FA-acyl CoA by this enzyme
this is the rate limiting step
carnitine acylcarnitine translocase (CACT)
step 3 of FA oxidation
transports the carnitine FA across the inner mitochondrial membrane and transfers carnitine out of mitochondria to be used in earlier steps
beta-oxidation pathway
step 5 in FA oxidation
occurs once FA are in the mitochondrial membrane
each step releases a 2-carbon fragment in the form of acetyl-CoA
each palmitoyl CoA (16 carbons) undergoes 7 oxidation cycles yielding 8 acetyl CoAs
acetyl CoA goes into Kreb cycle if there’s enough oxaloacetate present (need some continuous oxidation of glucose for this)
the initial dehydrogenase reaction results in FADH2 and the second one results in NADH - these are used by electron transport chain for ATP synthesis
energy yields from beta oxidation of FA
palmitoyl CoA + 7 FAD + 7 NAD+ + H2O + CoA => 8 Acetyl-CoA + 7 FADH2 + 7 NADH + 7 H+
metabolism of 8 mol acetyl CoA in Krebs cycle = + 80 mol ATP
oxidation of 7 mol FADH2 = + 10.5 mol ATP
oxidation of 7 mol NADH = + 17.5 mol ATP
ATP utilization in fatty acyl-CoA ligase = - 2 mol ATP
= 106 mol ATP per mol palmitat
take away point: about 3x as much ATP produced from one mol FA as from one mol glucose
ketogenesis
conversion of FA to ketones
ketones are water soluble and are used by muscle and brain (can get through BBB whereas FA can’t)
occurs only in the liver!
regulation of ketogenesis
when oxaloacetate levels are low because glucose isn’t available there won’t be much conversion of acetyl CoA to citrate
acetyl CoA will be disposed of via an alternate pathway that only occurs in the liver that genearte acetoacetate and B-hydroxybutyrate (the ketone bodies) and some acetone (eliminated through lungs, hence fruity breath of those in ketosis)
ketone bodies
generated in liver by ketogenesis
acetoacetate and beta-hydroxybutarate
both are organic acids and so when in high concentrations result in acidosis
ketone oxidation
largely in brain and muscle
need mitochondria, oxygen, oxaloacetate and succinyl-CoA
because need succinyl-CoA must have some glucose as well
energy yield for ketones exceeds that of glucose
why can’t we make glucose from FA?
the PDH reaction is essentially irreversible so pyruvate can’t be used to form acetyl-CoA
there’s never any net synthesis of oxaloacetate during FA oxidation - mammals can’t form oxaloacetate de novo from acetyl-CoA and so that component of making glucose would be missing
glucose availability
liver and kidney are principal organs of gluconeogenesis - use AA, glycerol and lactate as precursors
limited amount of glycogen and even less that can support blood glucose because the glycogen stored in the skeletal muscle can’t be released because skeletal muscle lacks glucose-6-phosphatase
when glycogen is depleated gluconeogenesis is used to make the glucose needed for the brain and RBCs and make the oxaloacetate needed for FA/ketone oxidation
gluconeogenesis requires lots of ATP - energy derived from oxidation of FA in the liver
metabolic cycle
ensures the ready supply of immediate energy and the constant replenishment of depleted energy
has two phases:
1: anabolic = period that begins with the ingestion of food and continues until the ingested nutrients are assimilated, utilized or stored as reserve energy
2: catabolic = between termination of anabolic phase and next meal - reserve stores are utilized for energy
levels of insulin glucagon and epinephrine control phases
short-term regulation of metabolism
seconds-minutes
accomplished by changes in catalytic activity of performed enzymes/proteins with no change in the enzyme content of the cell
mechanisms: allosteric regulation and covalent modification of enzymes
long-term regulation of metabolism
changes in enzyme/protein content of cell but also may include changes in specific activity
mechanisms: changes in rate of gene transcription, mRNA turnover, mRNA translation and protein degradation
glucose (as regulator of metabolism)
stimulates its own storage by enhancing net glycogen and fatty acid synthesis
fatty acids (as regulators of metabolism)
diminish rates of FA synthesis and increase FA oxidation
regulation of metabolism by cellular energy status
ATP and AMP can regulate metabolism
5’-AMP activates AMPK (AMP-activated protein kinase) which inactivates enzymes in several synthetic pathways that use ATP and activates other pathways that increase ATP generation
this is regulated by the energy levels because when ATP becomes depleted adenylate kinase converts 2 ADP to ATP + AMP and the AMP activates AMPK allosterically
ATP will inhibit AMPK if there’s high levels of energy production
glucagon and epinephrine
increased levels do the following:
1: activate net hepatic glycogen breakdown in the liver
2: in liver, activate gluconeogenesis
3: in adipose tissue activates lypolysis
4: in skeletal muscle activates FA utilization - Beta-oxidation of FA so they can be liberated from the adipose tissue
5: in liver activates ketone synthesis
insulin receptor activation
receptor has two outer alpha subunits and two inner beta subunits
insulin binds to the alpha subunit and changes the shape of the receptor
the beta subunits are a tyrosine kinase - activation results in autophosphorylation
insulin receptor subunit (IRS) and shc can now dock on the receptor
this pulls in other proteins
ultimately activates AKT
insulin actions
inhibits all of the things glucagon and epinephrine by activating AKT which phosphroylates PDE, resulting in the breakdown of cAMP to 5'AMP - this decreases PKA activity favors FA and glycogen storage 1: stimulates glucose transport 2: inhibits gluconeogenesis 3: stimulates FA synthesis (see other cards for more detail)
insulin stimulation of glucose transport
in skeletal muscle, heart tissue, and adipose tissue
via AKT action
AKT targests vessicle containing GLUT4
vessel fuses with cell membrane and allows glucose to enter cell
when we exercise AMP also activates AMPK which also traffics GLUT 4
as a result, if we exercise right after taking glucose we could get hyperglycemic cause have both mechanisms at once so diabetics have to anticipate exercise
in starvation: glucose falls, insulin falls but no change in the amount of glucose transport to brain and RBCs because they have glucose receptors that are always on the cell membranes
insulin inhibition of gluconeogenesis
ATK phosphorylates FOX01
FOX01 normally stimulates the transcription of PEPCK
when phosporylated FOX01 can’t go into the nucleus to increase the transcription of PEPCK
PEPCK is needed for gluconeogenesis
insulin stimulation of FA synthesis pathway
insulin turns on SREBP
SREBP is a transcription factor for ACC and FAS which are involved in FA synthesis
autophagy
when fasting no insulin so skeletal muscle mass decreases
AKT activity results in decreased protein synthesis and increased autophagy = normal way of removing damaged cells but in extreme situation will canabilize healthy cells
glucagon and epi activation of gluconeogenesis
when levels are high, get more glycerol and AA acids - precursors for gluconeogenesis
PKA turns on set of pathways in gluconeogenesis that encourage gluconeogenesis over glycolysis
low insulin regulation of FA use
when PKA activated because insulin levels are low HSL and ATGL are turned on
droplets of lipid in adipose tissue are surrounded by perilipin
perilipin can now more readily bind to the HSL and ATGL and helps them position on the lipid droplet
malonyl-CoA regulation of FA cycle
in skeletal muscle
if enough malonyl-CoA CAT-1 is inhibited and FA can’t get into the mitochondria
AMPK or PKA phosphroylates ACC
this decreases malonyl CoA levels and now the caratine system is not inhibited so the FA cycle can begin
in liver: phosphorylated ACC (alpha and beta) are inactivated
glucagon and epi both inactivate ACC
insulin activates ACC
effects of lack of insulin
get high hepatic gluconeogenesis => decreased skeletal muscle disposal, high blood glucose, once blood glucose is over 180 the kidneys won’t retain all of it and there will be glucose in the urine and water follows it resulting in dehydration and weight loss
high lipolytic rate in adipose tissue, liver makes ketones from these but these are acids so blood pH will decrease, acetoacetate is broken down to acetone and makes the breath smell fruity
high lipolytic rate so loss of TG and less creation of new TG - get depletion in adipose mass
breakdown of protein so AA release, increases lipolytic rate, increase glycerol release, also lose volume of adipose tissue and muscle
PKA activation pathway
g-protein coupled receptor activated activates G protein subunit subunit activates adenylate cyclase adenylate cyclase makes cAMP from ATP cAMP activates PKA
cAMP phosphodiesterase (PDE) breaks down cAMP (PDE is activated by insulin)
sources for glycerol phosphate
glycerol phosphate is the initial acceptor of FA during TAG synthesis
in liver and adipose can be produced from glucose
using reactions of glycolytic pathway to make DHAP
DHAP is reduced by glycerol phosphate dehydrogenase to glycerol phosphate
in liver glycerol kinase can convert free glycerol to glycerol phosphate
synthesis of TAG
from glycerol phosphate and fatty acyl CoA
4 reactions that sequentially add 2 FA from FA coA, removes phosphate, adds third FA
Fatty Acyl CoA
activated form of fatty acid
biosynthesized by fatty acyl CoA synthetases using FA, coenzyme A and ATP
fate of TAG in different tissues
in adipose: TAG stored in cytosol of cells in nearly anhydrous form
in liver: little TAG stored - most exported in VLDL into blood
in intestine mucosal cells: TAG major lipid cargo for chylomycrons
very low density lipoproteins (VLDLs)
have apolipoprotein B-100, cholesteryl esters, cholesterol, phospholipid, and TAG
how TAG is exported from liver to rest of body and transported through blood
made in liver
mostly triacylglycerol
job to carry this from liver to peripheral tissues where its degraded by lipoprotein lipase in same manner as chylomicrons
get apo C-II and apo E from HDL
like chylomicrons, decrease in size as circulate as triacylglycerol is degraded and C and E apoproteins are returned to HDL - retain apo B-100
eventually triacylglycerols transferred from VLDL to HDL in exchange for CE by cholesteryl ester transfer protein (CETP) - becomes LDL
glycerophospholipids
phospholipids that contain a glycerol
formed from phosphatidic acid and an alcohol
serine + PA = phosphatidylserine
ethanolamine + PA = phosphatidylethanolamine (cephalin)
choline + PA = phosphatidylcholine (lecithin)
inositol + PA = phosphatidylinositol
glycerol + PA = phosphatidylglycerol
cardiolipin
synthesized in mitochondria from phosphatidylglycerol
consists of two molecules of phosphatidic acid esterified through their phosphate groups to an additional molecule of glycerol
only antigenic glycerophospholipid (with syphillis)
important component of inner mitochondrial membrane and bacterial membranes
sphingophospholipids
have backbone of sphingosine rather than glycerol
synthesis:
1: long-chain FA attached to amino group of sphingosine through amide linkage = ceramide (can also be precursor for glycolipids)
2: alcohol group of carbon 1 of sphingosine esterified to phosphorylcholine = sphingomyelin
phospholipid synthesis
way 1: donation of phosphatidic acid from CDP-diacylglycerol to an alcohol
way 2: donation of the phosphomonoester of the alcohol from CDP-alcohol to 1,2-diacyglycerol
(CDP is the nucleotide cytidine diphosphate)
both ways make an activated intermediate and release CMP
both require activation of the diacylglycerol or alcohol to be added by a linkage with CDP
happens in the smooth ER and are then transported to the golgi where they’re sorted and transported to cell membranes or secreted via exocytosis