MTC exam II week I Flashcards
How does dna replication happen in a mitochondrion
begins at Oh (origin of replication for the heavy strand) with binding of mitochondrial RNA primer. we see L strand displacement and clockwise replication. RNA primer is synthesized by mitochondrial RNA pol. we see growth of the D loop. When the H strand replication has proceede dto around 8 o’clock, L strand replication begins with the binding of the 2nd RNA primer in a coungerclockwise direction. topoisomerases allow for recoil of the mitrochndrial DNA
What are the 2 non-coding regions in the control regions of mitochondrial DNA?
hypervariable regions I and II
What are some things that pyruvate can become?
lactate, alanine, acetyl CoA and oxaloacetate. maybe DHAP>
What is an example of a nuclear-based mitochondrial defect that is not autosomal recessive?
most common pyruvate dehydrogenase (to acetyl CoA) is X-linked dominant
Leber’s Hereditary Optic Nueropathy (LHON)
mitochondrial disease
usually complex I mutation
central vision loss due to retinal degradation; most common among men
heteroplasmy rare
MELAS
mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes
progressive neurodegenerative diseases involving chemical stroke, lactic acidosis, and myopathy
tRNA leu gene is missing/defective
heteroplasmy common
MERRF
myoclonic epilepsy with ragged red fibers
myotonic seizures, dementia, ataxia, ragged red fibers
tRNAlys gene
heteroplasmy
KSS and CPEO
diseases seen before 20 yrs of age
opthalmoplegia, ptosis, atypical retinitis pigmentosa, ragged-red fibers. involve contiguous deletion of part of the mitochondrial tRNA
kearns-sayre syndrome and chronic progressive external ophthalmoplegia
NARP and Leigh diseases
ataxias. mutations in the ATP6 gene
Where does fatty acid synthesis occur (organ and organelle)? What five factors are required?
fatty acid synthesis occurs in the cytosol of the hepatocytes. it requires acetyl CoA, ATP, CO2/bicarb, biotin, pantothenic acid, and NADPH
What are happens in the first stage of fatty acid synthesis? What enzyme catalyzes this reaction?
acetyl CoA +CO2 + ATP forms malonyl CoA (which has 3 C). this reaction is catalyzed by acetyl CoA carboxylase and a biotin cofactor
What enzyme is inhibited by malonyl CoA
CPTI (carnitine palmitol transferase I, which is involved in fatty acid degredation)
acetyl CoA carboxylase
catalyzes the first reaction of fatty acid synthesis (CO2 + acetyl CoA yield malonyl CoA). Requires biotin. ping-pong
What happens in the 2nd stage of fatty acid synthesis? What is the enzyme?
you start with acetyl CoA and add 2 carbons from malonyl CoA at a time. Enzyme is fatty acid synthase
fatty acid synthesase
cofactors: 4/phosphopantethein from pantothenic acid. catalyzes 4 different rxns and has two major binding sites.
mechanism of action: fatty acid synthetase
sites A and B alternate as attachemnt sites for growing fatty acid chaine.
- Acetyl group attaches to the sulfhydryl of the A/KS site.
- malonyl attaches to the B/ACP site
- acetyl group attached to KS displaces the terminal carbonyl of the malonyl group and CO2 is released. The 4 C chain on the ACP site is called beta-ketobutyryl ACP
- betaketobutyryl ACP swings around and undergoes reduction (uses NADPH), hydration, and reduction again (another NADPH)
- growing chain is transfered back to the the KS subunit
palmitoyl thioesterase
detaches the palmitic acid from the fatty acid synthase enzyme
What are the energetic costs of palmitate synthesis?
7 ATP in the first step
14 NADPH in the second step
8 acetyl CoA
you only get 108 ATP from palmitate, even though it costs about 200 ATP to make
glycerol kinase
found in the liver only. converts glycerol and ATP into glycerol 3 phosphate
glycerol-3-phosphate dehydrogenase
found in adipose and periphery. converts DHAP and NADH into glycerol 3 p for triacylclycerol synthesis in the periphery
acyl CoA synthase
turns fatty acids and ATP into activated fatty acids fro triacylglyceride synthesis
acyl transferase
adds activated fatty acids to glycerol-3-phosphate at C1 and C2 positions. if we stop there, we have phospholipids)
phsphatidic acid phosphatase
removes the P at the C3 position during triacylglycerol synthesis
what enzyme is regulated to control fatty acid synthesis? How?
acetyl CoA carboxylase. regulated via reversible polymerization. polymerized form is active; depolymerized form is inactive. deopolymerization facilitated by phosphorylation. Mn++ prevents inactivation
draw the cycle that allows for cofactors to reach the cytosol in fatty acid synthesis
see attached
hormone sensitive lipase
the hormone that promotes triacylglycerol breakdown in adipose tissue following glucugon or epinephrine stimulation of PKA.
carnitine shuffle
required for fatty acids bigger than 12C into the mitochondria for beta oxidation
- fatty acid + CoA + ATP –> fatty acyl CoA + AMP
- CPT1 in the outer membrane converts fatty acyl CoA to fatty acylcarnitine complex and helps it cross the outer mitochondrial membrane. fatty acyl carnitine complex enters the matrix via the acylcarnitine/carnitine transporter of the inner mitochondrial membrane.
- CPT2 on the inner mitochondrial membrane converts fatty acylcarnitine back to fatty acyl CoA and free arnitine. see picture.
4 enzymes of beta oxidation. important energy use.
acyl CoA dehydrogenase, enoyl hydratase, hydroxyacyl CoA dehydrogenase, acyl CoA thiolase
- double bond formation and FAD to FADH conversion
- O added to double bond
- dehydration. NAD to NADH conversion
- another oxygenation.
Describe the difference between very long chain fatty acids, long chain fatty acids, medium chain fatty acids, and short chain fatty acids
VLCFA: 14-20 C
LCFA: 12-18
MCFA: 4-12
SCFA: 4-6
acyl coA dehydrogenase
catalyzes the formation of a double bond, which is the first step in beta oxidation. converts FAD to FADH. makes an enoyl CoA
hydroxyacyl CoA dehydrogenase
catalyzes the third step in beta oxidation of fatty acids. NAD to NADH. makes a betaketoacyl-CoA
yield of beta oxidation of palmitic acid
131, but 1 atp used in activation of fatty acid so 130 total
4 important things about omega-oxidation
oxidized with mixed function oxidase
requires moleculare O2 and NADPH dehydrogenase
takes place in the ER
important for pts with genetic defects in beta oxidation
what are the 3 metabolites characterized as ketones/ketone bodies?
acetoacetate, beta-hydroxybutyrate, and acetone
4 steps in ketone body synthesis
- condensation of 2 acetyl CoAs to make acetoacetyl CoA and CoA. thiolase is the enzyme.
- acetoacetyl CoA +acetyl CoA + H2O yields HMG CoA. Enzyme is HMG CoA synthase
- HMG-CoA to acetoacetate and acetyl coA. enzyme is HMG CoA lyase
- we can either finish here with acetoacetate, or go to either acetone or beta hydroxybutyrate.
to get to acetone, we lose CO2 in a rxn catalyzed by acetoacetate decarboxylase.
OR
to get to betahydroybuterae, we use the enzyme named for the reverse rxn: beta hydroxybutyrate dehydrogenase. uses an NADH.
What are some symptoms of fatty acid oxidation defects?
profound hypoglycemia, hyperammonemia, acidosis, aketosis or hypoketosis, increased anion gap. rhabdomylysis in ptatines with very long chain or long chain fatty acid disorders (high CK, pain, myoglobinuria)
what is HELLP?
a syndrome that many moms have when they are pregnant with kids with fatty acid disorders. hemolysis, elevated liver enzymes, low platelets or acute fatty liver during pregnancy
MCADD
medium chain acyl dehydrogenase deficiency
hypoglycemia, hyperammonemia, dicarboxylic aciduria
don’t let kids fast; treat with carbs and cornstarch
VLCADD
very long chain acyl dehydrogenase deficiency
catalyzes C12-22 metabolism. more severe than MCADD. dicarboxylica aciduria, increased acylcarnitine increased CK
where does desaturation synthesis occur? what enzyme? other things that are needed?
ER. done by fatty acyl-CoA desaturase. NADPH and O2 are also needed
what molecules help with the release of arachidoic acid from the membrane?
phospholipase A2 (prostaglandins) or phospholipase C
What are the three main pathways for eicosinoid synthesis from arachidonic acid?
cyclooxygenase ( for prostaglandin and TX)
lipoxygenase for LT, HETE, and lipoxin
cytochrome 450 for epoxide and HETE
basic structure of a prostaglandin
20C. cyclopentane ring with 9 and 11 substituted. C15 is hydroxylated and there is a trnas double bond between 13 and 14
structure of thromboxane
6 membered ring with an oxygen atom; also looks kind of like a kite
prostaglandin synthesis
- moblilize arachidonic acid from membrane lipid using phospholipase A2
- use COX for cylooxygenation
- use COX for peroxidase function to make PGH2 (precursor for TX and PGs)
What is the difference between COX1 and COX2
COX1 is constitutively active, COX2 is induced, especially in response to inflammation or infection
what is the difference between how NDSAIDs work and how aspirin works wrt PG synthesis?
aspirin is an uncompetitive irreversible inhibitor, while NSAIDs are competitive inhibitors
explain how aspirin lows risk of MI
PGs andd thromboxanes synthesized from PGH2 in a tissue specific manner. PGI2 causes vasodilation and platelet inhbition in endothelialcells, where as TXA2 causes vasoconstriction and platelet activation in platelets. aspirin inhibits COX, and endothelial cells are more able to make new COX faster than platelet cells
What does lipooxygenase do?
it oxidizes the double bonds at C5, C12, and C15. makes HPETEs, with are reduced to HETEs. in leukocytes, 5-HPETE is converted to LTA4 and mediates inflammatory responses
lipoxins come from LTA5 or 5-HPETE
name four important functions of peroxisomes
- catabolic beta-oxidation of VLCFA and branched chain fatty acids, dicarboxylic acids and PUFA
- anabolic synthesis of ether linked phospholipids called plasmolagen
- bile acid intermediates synthesis
- detox and metabolism of xenobiotics
how to proteins get to the peroxisome?
proteins are syntheisized on free ribosomes
integral membrane proteins have an SKF tag
matrix proteins have a PTS tag (peroxisome targeting sequence). PTS is bound by a receptor protein PEX. this complex binds to a docking complex and imports peroxisomal proteins to the matrix without protein unfolding
Describe VLCFA beta oxidation
starts in peroxisomes until the VLCFA have been oxidized into something smaller that can be dealt with by the mitochondria
differences
1. desaturation with FADH2 used to generate H2O2
2. acetyl CoA and NADH are fed to mitochondria for further metabolism
3. betaoxidation products transported to the mitochondria mediated by CAT and COT (carnitine acetyl transferase and carnitine octanoyl transferase)
Describe branched chain fatty acid oxidation
occurs exclusively in peroxisome
terminal carboxyl group is removed as CO2 such that the methyl is now attached to an alpha carbon. this is alpha oxidation. occasionally generates propinyl CoA insead of acetyl CoA
Zellweger Spectrum Disorders
NALD
infantile refsum disease
caused by mutations in the PEX genes which lead to lack of peroxisomes. you see hypotonia, abnormal reflexes, sensory impairment, growth delay, hepatomegaly, regression, and death
biochemically: high VLCFA buildup, bile acid precursors, phyantic annd pristanic acid buildup
X-linked Adenoleukodystrophy
affects adrenal glands and white matter of CNS
mutations are on the ABCD-1 gene. these patients can’t import VLFCA into peroxisomes, so they can’t perform VLCFA beta oxidation. VLCFA, espcially of saturated VLCFAs, build up leads to demylination, and decreased membrane stability
onset: 4-8 years
visuao spatial defects, behavioral changes, adrenal insufficiency, early death
How many ATP are generated from one turn of the beta oxidation?
- 12 from acetyl CoA, 3 from NADH and 2 from FADH2
