Biochem 7 Flashcards

Question

lipid droplets are dynamic

Answer 1

- 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

Answer 2

- 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

Answer 3

- 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)

Answer 4

- 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

Answer 5

- 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

Answer 6

- 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

Answer 7

- 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

Answer 8

- 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

Answer 9

- 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

Answer 10

- 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

Answer 11

- 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)

Answer 12

- 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)

Answer 13

- 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

Answer 14

- 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

Answer 15

- 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

Answer 16

- acetyl-CoA, NADH, FADH2 | - generates ATP

Answer 17

- 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

Answer 18

- 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

Answer 19

- 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

Answer 20

- 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

Answer 21

- 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)

Answer 22

- 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

Answer 23

- 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

Answer 24

- 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

Answer 25

- 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

Answer 26

- 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)

Answer 27

- 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

Answer 28

- 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

Answer 29

- found in alcoholics - high (NADH), depletion of oxaloacetate required for gluconeogenesis - elevated ketone body production - low blood pH - this will kill you if prolonged

Answer 30

- 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

Answer 31

- 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

Answer 32

- 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

Answer 33

- 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

Answer 34

- 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

Answer 35

- acetyl-CoA is transported out of the matrix into the cytosol - in the high energy state -> high abundance of acetyl-CoA - acetyl-CoA cannot diffuse out -> it is converted into citrate -> citrate transporter -> cytosol - acetyl-CoA is the precursor for fatty acid biosynthesis - acetyl-CoA generated in the mitochondrial matrix in the liver - acetyl-CoA is conjugated to oxaloacetate via citrate synthase-> forms citrate - tricarboxylate transport system- transport citrate across the inner mitochondrial membrane - citrate is now the substrate for ATP-citrate lyase in the cytosol - transfer these carbons from the citrate onto a CoA -> generates a cytosolic pool of acetyl-CoA -> precursor of fatty acid biosynthesis - in the cytoplasm oxaloacetate is converted to malate -> pyruvate -> generates a pool of NADH - this NADPH is used for fatty acid biosynthesis

Answer 36

- high concentration of citrate in the cytosol of the liver is a marker of high energy state - increases the rate of fatty acid biosythesis

Answer 37

- occurs primarily in the liver but also in other tissues (adipose tissue) - major precursor of acetyl-CoA in the liver is sugar (glucose) - reverse of beta oxidation - conjugation of 2 carbon units (acetyl-CoA/malonyl-CoA) to produce palmitate (16 carbon fatty acid) - each cycle is adding two carbons to the carbon fatty acid chain until we generate palmitate

Answer 38

- both in the cytoplasm - acetyl-CoA carboxylase (ACC)- converts acetyl-CoA to malonyl-CoA - malonyl-CoA- 3 carbon compound - this conversion is committed step to fatty acid biosynthesis - fatty acid synthase (FAS/FASN)- converts malonyl-CoA to palmitate - an acetyl-CoA + 7 malonyl-CoAs to generate palmitate via FAS

Answer 39

- cytoplasmic - committed step to fatty acid biosynthesis - heavily regulated - entry point of acetyl-CoA - acetyl-CoA carboxylase (ACC) converts acetyl-CoA to malonyl-CoA - biotin cofactor - bicarbonate (CO2) is attached to biotin factor - takes acetyl-CoA and attach bicarbonate to the methyl group of acetyl-CoA -> generate a 3 carbon malonyl-CoA - ATP is used - Acetyl-CoA + HCO3- + ATP -> malonyl-CoA + ADP + Pi

Answer 40

- very large - many domains - domains are far apart - substrate have to be shuttled from one domain to the next - biotin carboxylase side- biotin group comes in and becomes attached CO2 - once this occurs biotin has to swing between 40-80A to the CT (transcarboxylase) site -> acetyl-CoA comes in and CO2 is transferred - large movements - same for FAS

Answer 41

- high cytosolic citrate concentration -> high energy state - abundance of energy and acetyl-CoA - cytosolic citrate activates ACC (committed step) - citrate induces polymerization of ACC - forms long polymers -> large increase in activity -> commits

Answer 42

- regulate this with malonyl-CoA - in a high energy state acetyl-CoA is converted to malonyl-CoA (committed) - in the cytosol malonyl-CoA inhibits beta-oxidation of fatty acids by inhibiting the CPT1 enzyme (faces cytosol) - CPT1 converts acyl-CoA into acyl carnitines -> allows fatty acids to be transported into the matrix for beta oxidation

Answer 43

- upregulated in cancer and obesity - acetyl-CoA and malonyl-CoA are used to generate palmitate - multifunctional enzyme that catalyzes fatty acid biosynthesis - acetyl-CoA (malonyl-CoA) -> palmitate (C16:0) - adds 2 carbons to growing fatty acid chain per cycle - has many domains: catalytic - has acyl carrier protein (ACP) - 6 enzymatic activities, 7 cycles of C2 elongation 1. MAT- malonyl/acetyl CoA ACP transferase 2. KS- keto synthase 3. ER- enoyl reductase 4. KR- keto reductase 5. DH- hydroxylacyl dehydrogenase 6. TE- palmitol thioesterase

Answer 44

- acetyl-CoA comes in - 2 acetyl groups are transferred to the enzyme - all the next cycles the malonyl-CoA comes in (3C) - with each cycle the chain grows by 2 carbons and CO2 (from malonyl-CoA) leave - grows in the opposite direction of beta oxidation

Answer 45

- dimeric- symmetry - large - many domains: SD, KR, ER, ER, KR, SD, DH, DH, MAT, KS, KS, MAT - dynamic

Answer 46

- tethered to the growing fatty acid chain - apart of FAS enzyme - transports the fatty acid chain to each domain of fatty acid synthase as it is growing - ensures that the fatty acid chain is never released from the enzyme - structurally similar to CoA - has a sulfhydryl on the end (SH) - ACP is covalently tethered to the enzyme (FAS) -> this is different from CoA (free floating)

Answer 47

- in the first cycle acetyl-CoA will come into the MIT site of FAS - acyl carrier protein will be docked at the MAT site - acetyl group is transferred onto the ACP to generate acetyl-ACP (CoA floats away) - ACP with the acetyl group will migrate over to the KS site and transfer the acetyl group to a cystine on the enzyme - ACP group is liberated and goes back to MAT site to start bringing in malonyl groups - same process happens with malonyl -> malonyl goes to KS site and conjugates with the acetyl group that was attached there previously (from acetyl-CoA) -> forms acetoacetyl group attached to ACP (4C with a beta ketone) - then beta oxidation in reverse (many steps here) -> butyryl-ACP (4C molecule) - this group goes back to the KS site and repeat (keeping adding malonyl-ACP)

Answer 48

- ACP on the acetoacetyl-ACP swing it into the KR site - beta ketone becomes a hydroxyl (reverse beta oxidation) via beta-ketoacyl-ACP reductase (KR) -> forms D-beta-hydroxybutyryl-ACP - KR uses NADPH - ACP swing this into the DH site - beta-hydroxyacyl-ACP dehydrase (DH) removes the hydroxyl and proton -> water leaves -> generates a alpha-beta trans double bond (reverse beta oxidation) - ACP swings this into ER site - enoyl-ACP reductase (ER) reduces the double bond between the alpha and beta carbon -> generates a fully saturated 4C fatty acid -> butyryl-ACP - ER uses NADPH - butyryl will go back to KS site and transfer the 4C fatty acid to the cysteine of KS and the ACP will go back to MAT to bring another malonyl-CoA - repeat until we get 16C unit -> palmitate

Answer 49

- after 7 cycles butyryl-ACP forms palmitoyl-ACP (16C) - ACP docks to TE -> water comes in and attacks -> ACP is released -> goes back to MAT to get acetyl group - palmitoyl thioesterase (TE) converts palmitoyl-ACP to palmitate - only goes to TE once we have a 16C fatty acid chain

Answer 50

8 acetyl-CoA (1 acetyl-CoA + 7 malonyl-CoA) + 14 NADPH + 7 ATP -> palmitate + 14 NADP+ + 8 CoA + 7 ADP + 7 Pi + 6 H2O - NADPH is used by ER and and KR - ATP is used by acetyl-CoA carboxylase -> when we synthesized acetyl-CoA from malonyl-CoA

Answer 51

- cytoplasm - once you have a 16C fatty acid it can be extended to 18C, 20C, so forth - desaturases enzymes -> create double bonds - humans lack desaturase that can extend beyond the 9th carbon - bc of this there are fatty acids that essential to us bc we cant make them (diet) - ex. linoleic acid

Answer 52

- cytosol - glucose provides the major source for the precursors for fatty acid biosynthesis (after we eat) - high glucose is not good for you because it pools a large portion of fatty acid biosynthesis -> obesity - (recall) chylomicron remnants that are taken up by the liver have dietary triglycerides -> broken back down into fatty acids - dietary fatty acids + fatty acids from acetyl-CoA -> used to resynthesize triglycerides - these remade triglycerides + cholesterol and cholesterol esters -> are stored in lipid droplets in liver BUT more importantly they are shipped out into the circulation in the lipoproteins called very low density lipoprotein (VLDL) -> other tissues - tissues are getting dietary fatty acids from chylomicrons and VLDL

Answer 53

- in the liver triglycerides (from acetyl-CoA and from chylomicron remnants) and cholesterol/cholesteryl esters are incorporated into VLDL - lipoproteins that are released into the bloodstream - triglycerides and cholesteryl esters are packed in the hydrophobic lipoprotein interior while cholesterol is confined to the phospholipid monolayer - VLDL is analogous to chylomicrons

Answer 54

- shipped into the bloodstream - just like chylomicrons -> triglycerides will be substrates for lipoprotein lipase - lipoprotein lipase cleaves triglycerides in VLDL to generate fatty acids that can be taken up by adipose or muscle tissue - deliver for storage (adipose tissue) - if return back to a low energy state -> glucagon levels rise -> triglycerides will be cleaved in the adipose tissue -> delivered back to liver to make ketones or muscle tissue for energy - VLDL -> LDL

Answer 55

- malonyl-CoA will inhibit CPT1 (commits to biosynthesis) - regulated by insulin (promotes) and glucagon and epinephrine (inhibits) - majority of regulation is at acetyl-CoA carboxylase step (committed step) - high energy state- insulin rising - low energy state- glucagon levels are rising

Answer 56

- activated by AMP (an low ATP) -> therefore when its in a low energy state - AMPK phosphorylates and inactivates acetyl-CoA carboxylase (ACC) (committed step) - no malonyl-CoA is synthesized -> relieves inhibition of CPT1 -> fatty acid oxidation is activated - fatty acid biosynthesis occurs under high energy states, necessitating the inactivation of AMPK - Low energy state -> high AMP -> inhibit ACC -> decrease malonyl concentration -> relieve inhibition of CPT1 -> increase beta oxidation - many hormones regulate AMPK activity - high energy state- insulin rising -> AMPK inactivated -> fatty acid biosynthesis - low energy state- glucagon levels are rising -> AMPK activated -> beta oxidation

Answer 57

- formation of filaments increases ACC activity >20-fold - in the presence of citrate ACC forms filaments -> activates ACC -> more malonyl-CoA - citrate induces abnormal filament formation when ACC is phosphorylated by AMPK -> even in the presence of citrate ACC is still inhibited by AMPK

Answer 58

- acetyl-CoA carboxylase and cancer - ACC and FAS are important drivers of cancer/tumor growth - cells use fatty acids for energy, to build membranes, and division - ACC expression is elevated in cancer cells - fatty acid promote cancer cell proliferation - cancer cells lacking acetyl-CoA carboxylase (ACC1KO) -> tumors grow smaller - FAS overexpression also promotes prostate cancer metastasis -> tumors are larger - FAS is upregulated in many cancers including prostate cancer

Answer 59

- essential component of membranes: modulates fluidity and permeability (40%) - precursor for bile salts (liver): natural detergents in gut - digest triglycerides - precursor for steroid hormones (estrogen & testosterone) - regulates the activity of proteins - signaling functions - free hydroxyl on one end and hydrophobic on the other end -> hydrophobic molecule but has a polar group - has 27C

Answer 60

- endogenous sources: - liver (majority)- synthesizes 1g of cholesterol daily - accounts 70% of all cholesterol needed by the body - dietary sources: - account for the other 30% of cholesterol - 1 large egg= 190mg of cholesterol - big mac= 80 mg of cholesterol - clinically used drugs reduce cholesterol levels by targeting both of these processes (dietary and endogenous) - endogenous drugs are more effective bc the liver makes majority of cholesterol

Answer 61

- accounts for the only route of cholesterol out of our bodies - through the GI (intestines)

Answer 62

- occurs predominantly in the liver - increased by insulin and reduced glucagon - high energy state - cholesterol biosynthetic enzymes are found in the cytoplasm -> *bc it allows you to spatially segregate energy producing functions in the matrix and biosynthetic rxns in the cytoplasm - utilizes acetyl-CoA as the major carbon donor (same source of fatty acid biosynthesis) - precursor is acetyl-CoA - very similar to fatty acid biosynthesis!

Answer 63

-HMG-CoA reductase

Answer 64

1. acetyl-CoA to HMG-CoA to mevalonate (C5) 2. conversion of mevalonate to 2 activated isoprenes 3. condensation of 6 activated isoprenes to make squalene (30C) 4. cyclization of squalene to make lanosterol and conversion of lanosterol into cholesterol

Answer 65

- acetyl-CoA + oxaloacetate is converted to citrate via citrate synthase - citrate is transported from matrix to the cytoplasm via tricarboxylate transport system - citrate is converted back to oxaloacetate in the cytoplasm -> generates acetyl-CoA - all of this is the same from fatty acid biosynthesis

Answer 66

- acetyl-CoA is converted to isopentenyl-pyrophosphate (isoprene) - 4C chain with a methyl group on 2 -> 5C

Answer 67

- HMG-CoA is made from 3 molecules of acetyl-CoA - all the cytosolic isozymes for making ketone bodies (matrix) are in the cytosol (use the same enzymes) - thiolase (acetyl-CoA acetyltransferase) combines 2 acetyl-CoAs and forms acetoacetyl-CoA (4C) - HMG-CoA synthase brings in another acetyl-CoA (2C) -> forms HMG-CoA (6C) - this product is diverted towards cholesterol biosynthesis (instead of ketone) - HMG-CoA becomes the substrate for HMG-CoA reductase

Answer 68

- HMG-CoA lyase is not found in the cytoplasm - we are left with the product HMG-CoA -> diverted to cholesterol biosynthesis - this also makes sense bc when we are in a high energy state we are synthesizing cholesterol -> we dont want to make ketones (made during low energy)

Answer 69

- rate limiting enzyme in cholesterol biosynthesis - major regulatory site - major drug target to reduce cholesterol levels - HMG-CoA is converted to mevalonate via HMG-CoA reductase - uses 2 NADPH - reduces C=O and releases CoA

Answer 70

- mevalonates is converted to 2 isoprenes - mevalonate is a substrate for mevalonate-5-phosphotransferase -> produces phosphomevalonate - we use ATP -> ADP - transfers the phosphate from ATP to mevalonate - phosphomevalonate kinase then converts phosphomevalonate to 5-pyrophosphomevalonate - adds another phosphate via ATP - there are now 2 phosphate groups attached - pyrophosphomevalonate decarboxylase converts 5-pyrophosphomealonate to isopentenyl pyrophosphate - decarboxylates and dehydrates to produce the isoprene unit - uses ATP - releases CO2 - forms a double bond - 5C unit with 2 phosphates attached

Answer 71

- isopentenyl pyrophosphate is converted to dimethylallyl pyrophosphate via isopentenyl pyrophosphate isomerase - double bond is shifted - resonance stabilization - 5C units with 2 phosphates attached

Answer 72

- condensation of 6 activated isoprenes to make squalene (30C) - dimethylallyl pyrophosphate and isopentenyl pyrophosphate -> conjugated to each other -> forms 10C unit -> geranyl pyrophosphate - pyrophosphate leaves - geranyl pyrophosphate (10C) is coupled to another 5C -> forms farnesyl pyrophosphate (15C) - conjugate 2 farnesyl pyrophosphates and form -> 30C squalene

Answer 73

- cyclization of squalene to make lanosterol and conversion of lanosterol into cholesterol - ring formations

Answer 74

- lanosterol (30C) is the ultimate precursor to cholesterol - step before (in reality its about 19 steps) - we lose 3 carbons in the process (removal of 3 methyl groups) - one reduction - 27C cholesterol

Answer 75

- two regulation pathways - both are regulated at HMG-CoA reductase - rapid and long-term - drug target of statins

Answer 76

- phosphorylation by AMP-activated protein kinase (AMPK) inactivates HMG-CoA reductase - AMPK is activated in low energy states -> inhibits HMG-CoA -> cholesterol is not produced - this is controlled by energy state: high AMP -> high AMPK -> general biosynthetic pathways decrease - regulates rate limiting step

Answer 77

- regulation of HMG-CoA reductase transcription (mRNA) - regulates rate limiting step - this is the major pathway for regulation - decreased cholesterol induces transcription of mRNA for HMG-CoA reductase - when there is excess cholesterol the liver knows not to make more - 3 proteins (complex) in the liver: SREBP, SCAP, INSIG - these proteins are in the ER - when cholesterol is high the complex remains - when cholesterol drops -> SREBP and SCAP complex dissociates from INSIG - SREBP and SCAP move from the ER to the Golgi apparatus - site 1 protease (S1P) and site 2 protease (S2P) in the Golgi - S1P recognizes SREBP and clips it into 2 -> these pieces become substrate for S2P - S2P clips it ag and the head floats away into the cytosol - the head group is a transcription factor -> translocates into the nucleus -> binds to promoter for HMG-CoA reductase -> increase mRNA levels of HMG-CoA reductase - more HMG-CoA reductase protein to make cholesterol - same process controls to the expression of the LDL receptor

Answer 78

-sterol regulatory element binding protein

Answer 79

- SREBP cleavage-activating protein | - contains sterol-sensing domain

Answer 80

- liver packs dietary and endogenously synthesized cholesterol/cholesterol ester and triglycerides from chylomicron remnants into lipoproteins: VLDL - shipped out from liver into circulation - triglycerides that stayed in the liver are deposited into adipose tissue for storage - triglycerides in the VLDL are substrates for lipoprotein lipase -> stored in adipose tissue - this VLDL becomes triglycerides poor (they are cleaved and taken up) and cholesterol rich -> LDL - lipoprotein lipase cleaves triglycerides in VLDL (very low density lipoprotein) to generate LDL (low density lipoprotein) - LDL is taken up by other tissues and uses the cholesterol

Answer 81

- rich in triglycerides, cholesterols, cholesteryl esters | - very low density lipoprotein

Answer 82

- triglyceride poor - rich in cholesterols and cholesteryl esters - low density lipoprotein - has a protein B100 on its surface - B100 allows your cells to take up LDL from the blood and internalize it - not permeable to blood brain barrier like fatty acids -> cholesterol produced in the liver doesnt enter the brain - brain has its own machinery to make its own cholesterol (very low rate) - turnover of brain cholesterol is very slow - bad cholesterol

Answer 83

- endocytosis - cells have LDL receptor on the plasma membrane - LDL receptor will recognize B100 protein on the surface of the LDL - LDL receptors recognize and bind to apolipoprotein B100 on LDL - all the proteins become hydrolyzed within the cell by lysosomes

Answer 84

- cholesterol is sent back to the liver via HDL (high density lipoprotein) - reduce high levels of cholesterol in the tissue by increasing reverse transport to liver -> excreted through bile salts

Answer 85

- transports cholesterol from peripheral tissues to the liver for excretion - uses protein ABCA1 to transport the excess cholesterol out of the peripheral cell - cholesterol is assembled together into HDL - more HDL you have the more ability you have to transport cholesterol back to liver to excrete as bile salts -> lowers cholesterol - good cholesterol

Answer 86

- caused by deposition of lipid (cholesterol) within arteries - results in hardening and thickening of arteries and restricted blood flow - leading cause of death in the US - greater risk with increasing blood cholesterol (LDL) levels - deposition of cholesterol -> narrower lumen of arteries

Answer 87

- high LDL levels - initiated by deposition of LDL in walls of large blood vessels (typically arteries) - LDL is oxidized -> induces infiltration of macrophages (immune cells), which take up oxidized LDL and become lipid rich foam cells (fat immune cells) - foam cells release proteases and factors that damage artery walls - damage to endothelial lining and cell death results in the formation of necrotic core, calcification (hardening) and thickening of arteries, and reduced blood flow - plaque rupture exposes necrotic core to blood, resulting in the formation of a thrombus (platelet clot) that significantly restricts blood flow as it grows - reduced blood flow causes ischemia (death) of tissue (myocardium) and heart attack - thrombus can detach and lodge in smaller vessels and obstruct blood flow, also leading to heart attack

Answer 88

- diet -> reduce intake of sugar and cholesterol - drugs -> this is better bc most cholesterol is made endogenously - HMG-CoA reductase inhibitors: statins are used

Answer 89

- statins inhibit HMG-CoA reductase (rate limiting) - structurally similar to the substrate HMG-CoA - as cholesterols level drop from statins -> SREBP system upregulates the expression AND the expression of the LDL receptor* -> more LDL is taken up by cells and taken out of blood stream - this reduces the chance of cholesterol embedding into the arteries

Answer 90

- inhibits intestinal cholesterol absorption - cholesterol passes through you - less effective than statins bc its targeting dietary cholesterol (less percentage)

Answer 91

- PCSK9 is secreted by the liver - binds to the LDL receptor and enhances its degradation by lysosome within cells - PCSK9 inhibitors (reptha) block PCKS9 function -> reduce LDL receptor degradation -> allows it to be recycled to the plasma membrane to take up additional LDL

Answer 92

- lipids are derivative of lipids that have biological activity - you want these to be low when your healthy - in addition to providing energy for cellular metabolic needs, some fatty acids are also converted into potent signaling molecules - there are many classes: - prostaglandins - prostacyclin - endocannabinoids - leukotrienes - resolvins - sphingolipids - etc.

Answer 93

- acute inflammation is a protective response to tissue injury and infection - pain - fever -> infection - swelling - many features of inflammation are regulated by signaling lipids

Answer 94

- precursors to numerous signaling lipids - this one fatty acid (inert) can be converted to dozens of specialized signaling lipids - normally inert -> can be converted to many classes of signaling lipids - 20C fatty acid - 4 double bonds

Answer 95

- AA (arachidonic acid) -> PGE2 (prostaglandin E2) - intermediate PGH2 (prostaglandin H2) - COX-1 and COX-2 (cyclooxygenase-1 and 2) convert AA to PGH2 - PGES1 (prostaglandin E synthase 1) converts PGH2 to PGE2 - PGE2 is a major mediator of pain, inflammation, fever -> you dont want this to be elevated if youre not sick - these enzymes (COX-2 and PGES1) will increase during sickness

Answer 96

- COX-1 is expressed in most tissues (constant) - COX-2 expression increases during inflammation - COX-2 upregulation during inflammation* - convert arachidonic acid into prostaglandin H2 (PGH2) - PGH2 has no biological activity as an intermediate (but its converted to many different prostaglandins) - PGH2 is subsequently converted into multiple prostaglandins

Answer 97

- membrane protein - has no transmembrane domains - has 2 regions (alpha helices) that anchor it to the phospholipid bilayer - embedded in the bilayer - arachidonic acid enters the enzymes active site from the lipid bilayer - dimeric - converts AA to prostaglandin H2 (PGH2) - upregulated during inflammation

Answer 98

- nature has evolved COX-2 - COX-1 is normally expressed at constant level - has a 20 amino acid cassette (COX-1 doesnt) -> ensures COX-2 has a very short half life - stable for only short amount of time -> makes the prostaglandin needed -> degraded - limits upregulated so were not always inflamed

Answer 99

- synthesized by the enzyme prostaglandin E synthase (PGES1) from PGH2 - multiple functions during inflammation/sickness: - increase pain - increase swelling/edema (increase vascular permeability) - fever (major and one of the only ones) - appetite suppression

Answer 100

- just like COX-2 | - upregulation

Answer 101

- PGE2 activates 4 receptors: EP1, EP2*, EP4*, EP3 - EP1-4 are highly specific for PGE2 - EP2 and EP4 activate protein kinase A -> activates the cell - when PGE2 activate EP3 receptor is reduces PKA -> inhibit the target cell - PGE2 binds to EP3 within the protein itself (not on top or bottom) -> conformational change

Answer 102

- flu has fever and chills, aches and pains, weakness and fatigue, low appetite - PGE2 regulates this

Answer 103

- specialized nerves that project to skin and muscles (normally not active) -> nociceptors - nociceptors are specialized nerves that transmit painful stimuli from site of inflammation to spinal cord - inflammation sensitizes nociceptors and enhances pain -> activate nociceptors - inflammation will sensitize nociceptors and activate them -> send message to spinal cord -> brain -> pain - high levels of PGE2 activate EP2/EP4 -> activates target cell (increase activity of pain sensing neurons) -> sensitizes nociceptors

Answer 104

- central* mediator of fever (the only one) - cytokines (IL-1, IL-6, TNFalpha) increase the expression of COX-2 and PGES1 in endothelium lining the brain (hypothalamus) - PGE2 increase thermostat in the hypothalamus of the brain by activating the EP3 receptor

Answer 105

- specialized neurons in the spinal cord promote shivering and vasoconstriction (constantly want to produce fever) but are inhibited by specialized neurons from the hypothalamus that express the EP3 receptor - EP3 is expressed in adipocytes - EP3 receptor is the inhibitory receptor -> inhibits the inhibitory cells in the hypothalamus - activation of EP3 by PGE2 inhibits the neurons in the hypothalamus -> reduces their inhibition of spinal cord neurons -> fever

Answer 106

- PGE2 reduces ghrelin (stimulates feeding) secretion in the stomach - PGE2 activate EP4 receptor in the hypothalamus - EP4 is excitatory -> stimulates POMC neurons that suppress feeding - PGE2 activates POMC neurons to reduce the hunger drive

Answer 107

- COX inhibitors - COX-2 inhibitors - reduce pains, inflammation, appetite, fever

Answer 108

- prostaglandins are synthesized by COX-1 and COX-2* during inflammation/sickness - prostaglandins contribute to: pain, fever - inhibition of COX enzymes reduces pain, inflammation, and fever - aspirin (acetylsalicylic acid) - ibuprofen- nonsteroidal anti-inflammatory drug (advil)

Answer 109

- chronic use of COX inhibitor drugs -> develop gastrointestinal ulcers - COX-1 (constant) -> produces prostaglandins that protect the gastric mucosa (stomach and intestine) from gastric acid - when you inhibit COX-1 and 2 -> you inhibit fever, inflammation, pain but you also inhibit protection of gastric mucosa by COX-1 - we can avoid this by designing inhibitors that only target COX-2 and not COX-1 - volume of COX-2 active site is larger and its smaller in COX-1 -> to make drug specific to COX-2 -> make larger drugs

Answer 110

- rofecoxib (vioxx) - celecoxib (celebrex) - vioxx taken off market in 2004 due to unexpected side effects (heart attacks) - super drug but heart attack side effect - celebrex is used sparingly still - COX-2 produces prostacyclin (PGI2) in lining endothelial cells of vasculature (blood vessels) -> potent vasodilator and inhibitor of platelet aggregation - COX-1 produces thromboxane A2 (TXA2) in platelets -> vasoconstrictor and stimulates platelet aggregation - inhibition of COX-2 causes a decrease in PGI2 and allows TXA2 produced by COX-1 to predominate -> thrombus (platelet plugs) form - clots occludes blood flow -> tissues die -> heart stops

Answer 111

- selective inhibition of PGES1 reduces PGE2 levels without affecting prostacyclin biosynthesis - currently working on this

Answer 112

- marijuana and a derivative of arachidonic acid (AA) - humans express 2 cannabinoid receptors (CB1 and CB2) - CB1 and CB2 are activated by THC and 2-AG and anadamide (AA derivatives/endocannabinoid) - CB1/CB2 are inhibitory -> their activation inhibits the target cell - cannabinoid receptors are activated by: - delta-tetrahydrocannabinol (THC), the major psychoactive constituent of marijuana - 2-arachidonoylglycerol (2-AG), an endocannabinoid - anadamide, an endocannabinoid

Answer 113

- 2-AG -> 2-arachidonoylglycerol - anadamide - arachidonic derivatives - produced by the body - activation of CB1/CB2 receptors modulates: - pain - reduce anxiety/stress responses - increase appetite - reproduction/fertility - cognition - development - major interest in developing drugs targeting the endocannabinoid system

Answer 114

- arachidonic acid is attached at the 2 position - glycerol - 2-monoacyl glycerol

Answer 115

- you dont want 2-AG to be constantly activating cannabinoid receptors - you want it to be made when needed and then degraded - monoacylglycerol lipase (MAGL)- cleaves the ester bonds of monoglycerides at the 2 position -> generates glycerol and a fatty acid (arachidonic acid) - MAGL terminates the signaling of 2-AG - MAGL inhibition elevates 2-AG levels -> increased activation of cannabinoid receptors

Answer 116

- MAGL inhibition -> same effect as marijuana - elevate 2-AG levels by inhibiting MAGL -> activate cannabinoid receptors -> inhibit pain neurons - same cells are regulated by PGE2 to increase pain

Answer 117

- 2-AG is broken down by MAGL -> generates arachidonic acid - if you inhibit MAGL -> it increase 2-AG levels and reduce arachidonic acid levels -> therefore reduces prostaglandins - now arachidonic acid is the intermediate - arachidonic acid controls levels of prostaglandins - MAGL is the same enzyme that is used in adipose tissue, brain, etc. to control activity of this potent signaling molecule

Answer 118

- arachidonic acid is a precursor to numerous bioactive lipids including prostaglandins - prostaglandins play prominent roles in the modulation of pain and inflammation - endocannabinoids are derivatives of arachidonic acid that activate cannabinoid receptors - modulation of bioactive lipid signaling holds therapeutic promise for the treatment of diverse disorders

Answer 119

-multiple isoforms for different lengths

Answer 120

- low glucose - acetyl-CoA -> ketone bodies - liver -> brain - glycogen is used first and when that is low we use ketones - beta-oxidation products inhibit pyruvate dehydrogenase -> glycolysis (inhibits fatty acid biosynthesis and cholesterol synthesis) - beta-oxidation increases ketones - mutation in acyl-CoA dehydrogenase -> no acetyl-CoA -> no ketones

Answer 121

-shifting OH of D-beta-hydroxybutyrate to the left

Biochem 7 Flashcards

(145 cards)