Biochem 7 Flashcards
1
Q
classes of lipids
A
- free fatty acid (nonsterified fatty acid)- carboxylic acid group and acyl chain
- can have one or more double bond but they are always cis
- triglyceride- 3 fatty acid attached to glycerol (3 carbons) via ester bonds
- cholesterol- hydrophobic and free hydroxyl group that gives it polarity
- if you conjugate the hydroxyl with a fatty acid -> forms a cholesteryl ester
- cholesteryl ester- highly hydrophobic (loses polarity)
2
Q
fatty acid nomenclature
A
- carboxylic acid chain is the first carbon
- alpha carbon- second carbon
- beta carbon- third carbon
- gamma carbon- fourth carbon
- omega carbon- last carbon
- if there is a double bond three carbons away from the omega end -> omega 3 fatty acid
3
Q
adipose tissue
A
- major storage site for lipids:- triglycerides
- adipocytes- major cell type of adipose tissue (lipid storage)
- *endocrine organ- regulate metabolism, inflammation, energy balance
- releases hormones- leptin
- white bc they are filled with fats- lipid droplet
4
Q
fasting state
A
- high glucagon
- high glycogenolysis
- high gluconeogenesis
- high fatty acid oxidation
- low glycolysis in liver
- low glycogenesis
- low fatty acid biosynthesis
5
Q
fed state
A
- high insulin
- high glycolysis
- high glycogenesis
- high fatty acid biosynthesis
- low glycogenolysis
- low gluconeogenesis
- low fatty acid oxidation
6
Q
control of food intake (satiety/hunger)
A
- why are we hungry?
- low blood sugar
- empty stomach
- hormonal control:
- ghrelin
- leptin
7
Q
ghrelin
A
- peptide hormone released by stomach
- travel in the blood to the hypothalamus of the brain to stimulate food intake
- before a meal ghrelin levels rise
- after a meal ghrelin levels fall and then increase
8
Q
leptin
A
- hormone released predominantly by adipose tissue
- acts in the hypothalamus of the brain to reduce feeding
- tell us we are full
- chronically elevated in people who are obese
- theory of leptin resistance- obese become desensitized to effects of leptin due to chronically elevated leptin levels
9
Q
leptin deficiency
A
- obesity
- after being treated with leptin -> body weight returns to normal
10
Q
lipid digestion: small intestine
A
- primarily small intestine
- dietary triglycerides are metabolized to monoglycerides and free fatty acids
- free fatty acids, monoglycerides, and cholesterol is absorbed by intestinal cells
11
Q
triglycerides
A
- highly hydrophobic
- pack into large lipids globules
- acyl chains face out -> hydrophobic
- no polar or charged surfaces
- makes it hard to digest -> bile salts
12
Q
bile salts emulsify lipids
A
- synthesized by liver
- stored in gall bladder
- released into the small intestine
- aids in lipid digestion
- makes triglyceride globules smaller and increases SA -> enzymes act on this
- bile salts are derivatives of cholesterol and have highly charged groups
- amphipathic
13
Q
triglyceride hydrolysis by pancreatic lipase
A
- pancreatic lipase enzyme is secreted by the pancreas
- hydrolyzes triglycerides into 2 fatty acids and 2 monoacylglycerol (MAG) in the small intestine
- cleaves triglyceride at the 1 and 3 position
14
Q
summary of triglyceride metabolism and absorption
A
- consume fats -> globules
- mix will bile salts to form smaller globules -> increase SA
- pancreatic lipase can hydrolyze easier -> releases monoacylglycerols and fatty acids
- absorbed by the intestinal cells
15
Q
what happens if you inhibits pancreatic lipase
A
- you cant absorb triglycerides if you cant cleave them
- drugs have targeted this to induce weight loss -> but if we cant absorbs fats -> oily stools
16
Q
intestinal cells
A
- fatty acids and monoglycerides are resynthesized back into triglycerides after absorption
- triglycerides and cholesterol is packaged into chylomicrons and shipped into blood
17
Q
triglycerides and cholesterol ester synthesis in intestinal cells
A
- monoacylglycerol is converted back to triglyceride by adding fatty acids back to the 1 and 3 position
- cholesterol that was absorbed is converted to cholesteryl esters (hydrophobic!)
18
Q
chylomicron synthesis
A
- chylomicrons allow large quantities of hydrophobics like cholesteryl esters and triglycerides in intestinal cells to be transported through blood
- triglycerides are packaged alongside cholesterol and cholesteryl esters into chylomicrons
- densely packed core of triglycerides and cholesteryl esters (highly hydrophobic) -> these are then surrounded by a phospholipid monolayer
- phospholipid monolayer- one layer of phospholipid with the head groups (charged, soluble) are on the outside and the tail (hydrophobic) are in the inside
- shields from the aqueous environment -> solubilized
- allows hydrophobics to be soluble in water
- free cholesterol is embedded in the phospholipid monolayer -> free cholesterol has a free charged hydroxyl group that allows this
- proteins coating the surface of the chylomicrons
19
Q
two fates of chylomicrons
A
- chylomicrons have two fates in the blood: use energy immediately or store it
- within the blood stream chylomicrons will be acted upon by a lipoprotein lipase protein
- lipoprotein lipase is embedded in capillaries that are surrounded adipose, fat or muscle tissue
- lipoprotein lipase will cleave triglycerides within the chylomicron back into monoglycerides and fatty acids -> taken up my muscle tissue for energy use or lipocytes for energy storage
20
Q
lipoprotein lipase (LPL)
A
- enzyme that lines the endothelium (lumen) of capillaries surrounding adipose and muscle tissue
- enzyme is never free floating -> its is localized and tethered to walls
- cleaves the triglycerides within the chylomicrons in the blood
- cleaves triglycerides within chylomicrons at the 1 and 3 positions to generate free fatty acids (FFA) and 2-monoacylglycerols
- free fatty acids and monoglycerides are taken up my muscle tissue for energy or by adipose tissue for storage
21
Q
GPIHBP1 anchors lipoprotein lipase
A
- GPIHBP1 is a binding partner for lipoprotein lipase
- it is tethered to the capillary wall
- has an acidic domain that interacts with lipoprotein lipase and the chylomicron
- the chylomicron and the LPL dock next to each other -> starts to cleave the triglycerides of the chylomicron
- GPIHBP1 anchors lipoprotein lipase to the endothelium of capillaries surrounding adipose and muscle tissue
- enzyme is never free floating -> it is localized
22
Q
chylomicron remnants are taken up by the liver
A
- chylomicrons are filled with triglycerides and cholesteryl esters -> LPL cleaves triglycerides -> monoglycerides and fatty acids
- adipose tissue take up for storage
- muscle tissue takes up for energy use
- LPL doesnt cleave cholesteryl esters -> make up the chylomicron remnants (some triglycerides too)
- liver takes up chylomicron remnants (cholesteryl esters)
23
Q
what would you expect to occur in individuals deficient in lipoprotein lipase
A
- chylomicrons build up
- lipoprotein lipase deficiency
- rare- 1-2 cases/million
- elevated chylomicrons -> elevated triglycerides and cholesterol
- causes abdominal pain (colic in infancy), loss of appetite, nausea, vomiting
- glyberia treatment
24
Q
fatty acids and cholesterol are stored in intracellular lipid droplets
A
- triglycerides are rebuilt again and stored in lipid droplets in adipose tissue
- lipid droplets are in every cell but are prominent in adipose tissue
- *lipid droplets are similar structurally to chylomicrons -> inner core of cholesteryl esters and triglycerides, surrounded by phospholipid monolayer with acyl chains facing inward and charged heads outward, free cholesterol and proteins are embedded in the monolayer
- they are different in that the lipid droplets are inside cells (intracellular) and are a storage site for excess fat
- storage depots for cellular lipids (triglycerides and cholesteryl esters)
- during times of energy need triglycerides are hydrolyzed back into free fatty acids for tissue
25
Q
lipid droplets are dynamic
A
- they grow and shrink depending upon the rate of lipid turnover
- as you consume/store more fat lipid droplet grow and diffuse with each other -> form large lipid globules
- this happens are you gain weight
- as you use the lipid they will shrink
26
Q
fasting state: dipping into the fat/energy storage in adipose tissue: lipolysis
A
- highly regulated
- we dont want to be using stored fats right after a meal
- process of hydrolyzing lipid droplets stored in adipose tissue into free fatty acids -> released into blood -> used by muscles
- glucagon (fasting) and epinephrine/adrenaline (fight or flight) stimulate this
27
Q
enzymatic conversion of triglycerides into fatty acids
A
- triglyceride in lipid droplets is cleaved by adipocyte triglyceride lipase (ATGL, specific to triglyceride)
- ATGL cleaves at the 1 position and generates a diglyceride
- then hormone sensitive lipase (HSL) cleaves the diglyceride into a monoacylglyceride
- monoacylglycerol lipase then cleaves
- 3 fatty acid and glycerol product
- occurs during times of energy need (from storage)
28
Q
regulation of lipolysis
A
- protein kinase A (PKA) phosphorylates proteins involved in lipolysis
- glucagon (or epinephrine) is released from pancreas when you are hungry -> activates a receptor that is present on the adipocyte
- when glucagon activates -> it activates protein kinase A (PKA)
- PKA is a major regulator of lipolysis
- PKA phosphorylates to 2 proteins: perilipin-1 and ABHD5 (and hormone sensitive lipase)
- perilipin-1 and ABHD5 are tethered to each other are in a complex on a lipid droplet surface
- when they are phosphorylated by PKA they dissociate -> ABHD5 can then fully dock onto the lipid droplet surface
- ABHD5 recruits adipocyte triglyceride lipase (ATGL) to the lipid droplet (when phosphorylated) -> ATGL initiates lipolysis
- phosphorylation of hormone sensitive lipase allows it to be recruited to lipid droplet surface -> increase activity
- ATGL and HSL are highly regulated while MAGL isnt
29
Q
chanarin-dorfman syndrome
A
- rare autosomal recessive neutral lipid storage disease
- mutation resulting in nonfunctional ABHD5
- ABHD5 deficiency
- means you cannot recruit ATGL to lipid droplets -> store too many fats
- cannot cleave triglycerides in lipid droplets
- patients have hepatomegaly
- hepatocyte triglyceride lipase, hormone sensitive lipase, monoacylglyceride lipase are also in the liver with similar function -> liver can store some lipids
- patients accumulate fats
30
Q
glycerol is converted into glycolytic intermediates
A
- glycerol is released from adipose tissue
- glycerol is taken up by liver and used for gluconeogenesis
- free fatty acids (released by adipose tissue) are in blood and taken up by other tissue to be used for beta-oxidation
- beta-oxidation- fatty acids are converted to acetyl CoA and NADH, FADH
31
Q
beta-oxidation
A
- mechanism through which cells utilize energy stored in fatty acids (carbons of fatty acyl chains)
- series of enzymatic rxns within the mitochondrial matrix:
- fatty acids -> acetyl CoA
- palmitate (fatty acid)- 16 carbon fatty acid -> 8 acetyl CoA
- acyl-CoA -> acetyl-CoA
32
Q
acyl-CoA synthetase enzyme (ACS)
A
- convert fatty acids into acyl-CoAs
- molecule of Coenzyme A is attached to fatty acid molecule
- these enzymes are in the cytoplasm (membrane enzymes that are cytoplasmically oriented)
- activate fatty acids
- forms a acyladenylate intermediate
- 2 ATP equivalents used (breakage of 2 high energy bonds)
- requires ATP for activation of the fatty acid
- rate limiting
33
Q
activation of fatty acids mechanism
A
- fatty acid -> acyl CoA
- fatty acid comes in the active site of acyl-CoA synthetase and attacks the alpha phosphate of ATP
- breaks the phosphodiester bond
- produces pyrophosphate and fatty acid is attached to alpha phosphate of the adenosine monophosphate (AMP)
- molecule of CoA comes in -> the sulfur of CoA attacks the fatty acid carbon of the acyladenylate mixed anhydride intermediate
- breaks the bond -> fatty acid becomes transferred to Coenzyme A
- yields Acyl-CoA and AMP
- what drives this rxn forward is the cleavage of the high energy bond between the beta and gamma phosphate during hydrolysis of the pyrophosphate
- this rxn breaks 2 high energy bonds: between alpha and beta phosphate and beta and gamma phosphate -> uses 2 ATP equivalents
34
Q
transport of long chain fatty acids into mitochondria
A
- inner mitochondria membrane is not permeable to long chain acyl-CoA
- carnitine palmitoytransferase (CPT) AKA carnitine acyltransferase
- carnitine is a rate limiting carrier
- there are 2 CPT’s: CPT1
- CPT1- enzyme on the outer mitochondrial membrane facing the cytosol
- CPT1 takes the activated acyl-CoA and transfers the fatty acid group to a molecule of carnitine in the cytoplasm -> converts carnitine into acyl carnitine (permeable)
- transporter can transport acyl carnitine in to the matrix of mitochondria (translocase)
- coenzyme A is liberated and returned to cytosol
- CPT2- enzyme on the inner mitochondrial membrane facing the matrix
- CPT2 catalyzes the reverse rxn -> transfer the fatty acid from the acyl carnitine back to the CoA -> regenerates acyl CoA in the matrix
- carnitine is transported back to cytosol
- rate limiting
35
Q
beta oxidation: acyl CoA is converted into acetyl CoA, NADH, FADH2
A
- energy in the carbon bonds are used for energy
- 1 NADH, 1 FADH2, 1 acetyl-CoA with each cycle (2 carbons at a time and repeat)
36
Q
step 1: beta oxidation
A
- aceyl-CoA dehydrogenase (AD)
- formation of trans-alpha-beta double bond through dehydrogenase by acyl-CoA dehydrogenase
- glutamate extracts proton from alpha carbon
- hydride ion (H+) from beta carbon is transferred to FAD -> FADH2
- mitochondria possess 4 acyl-CoA dehydrogenases with different chain link specificities:
- VLCAD- very long chain acyl-CoA DH (12-20C)
- LCAD- long chain acyl-CoA DH (8-20C)
- MCAD- medium chain acyl-CoA DH (6-10C)
- SCAD- short chain acyl-CoA DH (4C)
37
Q
step 2: beta oxidation
A
- enoyl-CoA hydratase
- hydrates the alpha-beta-trans double bond by adding water to the beta carbon
- water is coordinated by 2 glu
- double bond is reduced
- multiple forms for different chain lengths
- beta carbon takes OH and alpha carbon takes 1 H
- no energy generated
38
Q
step 3: beta oxidation
A
- NAD+-dependent dehydrogenation
- 3-L-hydroxyacyl-CoA dehydrogenase (HAD)
- oxidizes a 2ndary alcohol using NAD+
- creates a ketone on the beta carbon
- transfer electrons onto NAD -> NADH
39
Q
step 4: beta oxidation
A
- alpha carbon - beta carbon cleavage in a thiolysis rxn
- thiolase (KT)
- generates acetyl-CoA and a acyl-CoA the is 2C shorter
- cleaves the bond between alpha and beta carbon
- molecule of coenzyme A comes in and sulfur attacks -> attacked to beta carbon
- yields acetyl-CoA and fatty acyl-CoA (2C shorter)
- new fatty acyl-CoA can go back into the cycle
- 8 carbons -> 3 rounds
- 4 carbons -> 1 round
40
Q
products of beta-oxidation are shuttled to the citric acid cycle and oxidative phosphorylation
A
- acetyl-CoA, NADH, FADH2
- generates ATP
41
Q
palmitate (16:0) requires 7 rounds of beta-oxidation
A
- 16C fatty acid
- 7 rounds of beta oxidation
- generates 8 acetyl CoA, 7 FADH2, 7 NADH
- 1 FADH2 generates about 1.5 ATP -> 10.5 ATP
- 1 NADH generates about 2.5 ATP -> 17.5 ATP
- 8 acetyl-CoA generates 10 ATP -> 80 ATP
- 108 ATP molecules per palmitate
- however 2 ATP are used to activate the fatty acid (convert to acyl-CoA)
- net of 106 ATP per palmitate
42
Q
genetic disorders of beta oxidation
A
- new borns
- acyl-CoA dehydrognase:
- VLCAD- cardiomyopathy and muscle weakness
- LCAD- pulmonary surfactant dysfunction
- MCAD- most common beta-oxidation defect (1:15000) -> hypoketotic hypoglycemia with lethargy that develop into coma
- SCAD- relatively mild -> leads to elevated levels of butyrate
- HAD:
- lethal cardiomyopathy -> infant form (lethargy) or peripheral neuropathy
- 10% of sudden infant death
- infants feed on milk from mother which has fatty acids -> if they dont have HAD then the heart will die
- there are screening tests for these disorders
43
Q
beta oxidation of unsaturated fatty acids
A
- oleic acid (oils)
- linoleic acid
- presence of double bonds can be problematic for the second enzyme (enoyl-CoA hydratase (EH))
- if there is double bond at the beta and gamma position -> not a substrate for the EH enzyme
- enoyl-CoA isomerase shifts the double bond from the beta gamma position to the alpha beta trans position -> EH proceeds
- there is another problem bc EH cannot react if there is double bond at 4,5 position as well
- 2,4-dienoyl CoA reductase reduces the 2 double bonds into a single double bond in the trans position BUT it puts it in the beta gamma position (problem again!)
- enoyl-CoA isomerase reacts again and takes the beta gamma double bond and puts it between alpha beta position
44
Q
beta-oxidation of odd chain fatty acids
A
- 15C fatty acid (for example)
- goes through 6 rounds of beta-oxidation
- at the end we generate a 3 carbon fatty acyl-CoA -> propionyl-CoA
- propionyl-CoA is not a substrate for AD
- cells convert propionyl-CoA into succinyl-CoA
- succinyl-CoA can enter the citric acid cycle as an intermediate
45
Q
fatty acids and the brain
A
- fatty acids do not readily diffuse into the brain
- during fasting, the brain cannot use fatty acids released by adipose tissue as source of energy
- alternate source is needed to transfer energy stored in fatty acids (i.e. in adipose tissue or liver) to the brain
- during starvation glucagon levels rise -> fatty acids are released from adipose tissue -> muscle tissue -> converted to acetyl-CoA
- blood brain barrier- cells lining the blood vessels forming tight junctions which causes many molecules to be unable to enter (fatty acids)
46
Q
ketone bodies
A
- 4C molecules -> result from condensation of 2 acetyl-CoAs
- ketone on beta carbon
- 2 ketone bodies:
- D-beta-hydroxybutyrate and acetoacetate
- acetone is breakdown product of these ketone bodies (no energy)
- generated from acetyl-CoA in the liver
- only in liver mitochondria
- released into blood stream by liver
- used for energy during fasting/low blood glucose
- can diffuse into brain
- during starvation the liver will take up a significant portion of fatty acids as well and converts them into acetyl-CoA
- build up of acetyl-CoA is funneled into synthesis of ketone bodies by the liver -> released into circulation and taken up by the brain -> converted back to acetyl-CoA
- ketone bodies are produced from acetyl-CoA
- produced at low levels under normal conditions
- ketone bodies increase when blood fatty acid concentration is high -> high fat diet, starvation conditions, intreated diabetes
47
Q
why do untreated diabetics have high ketone levels
A
- insulin response -> insufficient
- glucose isnt taken up by cells
- cells are starving
- blood sugar is elevated but the cells cant take it up
- mobilizing fatty acids bc it thinks it starving -> converted to ketones
48
Q
energy use by the brain
A
- brain comprises 2% of body weight but uses 20% of glucose
- brain (neurons) is heavily reliant on glucose metabolism (supplemented by ketone bodies during starvation)
- during prolonged fasting/starvation, it is imperative that the brain continues to receive glucose as an energy source -> liver and muscle shift to fatty acid metabolism to preserve glucose
- glucose is preserved for brain
49
Q
products of beta oxidation inhibit glycolysis in liver and muscle
A
- liver and muscle shift to fatty acid metabolism to preserve
- fats are taken up from the circulation from adipose tissue -> liver converts to acetyl-CoA
- build up of acetyl-CoA and NADH -> inhibit pyruvate dehydrogenase
- as you develop higher energy state from the liver it can feedback and inhibit the breakdown of glucose (glycolysis) in the liver
- acetyl-CoA is stimulating pyruvate carboxylase at the same time -> increase gluconeogenesis in the liver
- as you metabolize fatty acids in the liver -> inhibit glycolysis, activate gluconeogenesis, and excess sugar is released to the brain for energy
50
Q
ketogenesis
A
- in the liver mitochondrial matrix
- reverse beta-oxidation
- input of 3 acetyl-CoA and 1 is regenerated
- 2 acetyl-CoAs are conjugated to each other
- reversal of beta oxidation
- 2 acetyl CoAs
- thiolase (acetyl-CoA acetyltransferase) conjugates 2 carbons from an acetyl-CoA to another acetyl-CoA to generates -> 4 carbon acetoacetyl-CoA
- another acetyl-CoA comes in and attacks -> generates beta-hydroxy-beta-methylglutaryl-CoA (HMG-CoA) (6 carbons fused to CoA)
- hydroxymethylgutaryl-CoA lyase (HMG-CoA lyase)- liver enzyme* and also expressed in the liver mitochondrial matrix*
- only in the matrix of the mitochondria will HMG-CoA lyase enzyme cleave and regenerate an acetyl-CoA and acetoacetate (ketone)
51
Q
ketones
A
- released into the blood stream
- taken up by other tissues (brain, heart, sometimes muscle)
- converted back to acetyl-CoA to use for energy
- ketone bodies provide energy to other tissues -> provide a way to transport acetyl-CoA between tissues
- lower demand for glucose by brain during starvation
- reduce amount of protein (i.e. amino acids) that must be broken down for gluconeogenesis
- liver is shifting towards fatty acid metabolism and away from glucose
52
Q
excess of ketone bodies: diabetic ketoacidosis
A
- tissues unable to take up and utilize glucose
- excess ketone body production
- acetone can be smelled in breath
- ketones are acids -> low blood pH
- this will kill you if prolonged
53
Q
excess of ketone bodies: alcoholic ketoacidosis
A
- found in alcoholics
- high (NADH), depletion of oxaloacetate required for gluconeogenesis
- elevated ketone body production
- low blood pH
- this will kill you if prolonged
54
Q
Glut1 deficiency and the ketogenic diet
A
- consume low levels of sugar and high levels of fat
- shift glucose metabolism to fat metabolism
- Glut1 is a glucose transporter at the blood brain barrier
- mutation in Glut1 reduce glucose uptake by the brain
- children with Glut1 deficiency (heterozygous) frequently develop seizures that are poorly controlled by anti-epileptic medications
- seizures bc low glucose to the brain -> and brain is highly reliant on glucose
- ketogenic diet reduces seizures in these patients
- amount of ketones produced are sufficient to use as excess energy to brain if glucose transporter is at 50% compacity -> Reduce seizures
- fatty acid oxidation- important for generation energy
55
Q
lipids
A
- excess energy is stored in the form of lipids (fatty acids) -> converted to triglycerides
- vast majority for the carbon source of fatty acids -> glucose
- under high energy states the carbon from acetyl-CoA comes out of the matrix to convert to citrate -> citrate is converted back to acetyl-CoA -> used for fatty acid biosynthesis
56
Q
fatty acid synthesis and beta oxidation
A
- beta oxidation is the mitochondrial matrix and help generate energy
- fatty acid biosynthesis requires energy -> cytosol
- these rxns will therefore be spatially separated
- regulated separately
57
Q
fatty acid biosynthesis shares chemical similarities to beta-oxidation
A
- however fatty acid biosynthesis is in the cytoplasm
- input of energy for fatty acid biosynthesis and NADPH
- biosynthesis occurs in a high energy state
- oxidation under a lower energy state
58
Q
Fed state
A
- store energy for energy use
- high energy state
- increased insulin
- increase glycolysis
- increased glycogenesis
- increase fatty acid biosynthesis
- decrease glycogenolysis
- decrease gluconeogenesis
- decrease fatty acid oxidation
