Week 3 Skildum Flashcards
TH4 and Cobalamin glycogen synthesis Purine/ pyrimidine metabolism Cholesterol metabolism
What are the 3 ways single methyl groups are transferred in cells?
folate metabolism
vitamin B12 (cobalamin)
S-adenosyl methionine
What 5 substrates are used to donate into one-carbon pool?
Serine, Glycine, Histidine, choline, Formate
Which substrate is the most important source of since C groups for biosynthetic reactions?
Serine, single C is first bound to FH4 (tetrahydrofolate)
Where is folate found in the diet?
green leafy vegetables, liver, legumes, yeast, and fortified flour
What is digested by gut when folate enters the body that must be remade in liver?
poly glutamate tail
What is hereditary folate malabsorption?
inherited mutation in protein coupled folate transporter (PCFT)
-causes a functional folate deficiency despite adequate folate in diet
What causes spina bifida?
What is it?
folate deficiency before and during pregnancy
-defects in neural tube
What enzyme changes folate to dihydrofolate then to its active form tetrahydrofolate?
dihydrofolate reductase (DHFR) -uses 2 NADPH to activate to FH4
What drugs target DHFR?
methotrexate (cancer, rheumatoid arthritis), trimethoprim (antibacterial), pyrimethamine (antimalarial)
What does FH4 + formate create?
N10-formyl FH4 (can be used to make other oxidation states)
What is the Methyl trap?
Once 5-Methyl THF is made it can’t be reverted into other forms. ONLY can be used with cobalamin to make methylcobalamin
What does FH4 + histidine create?
FIGLU which releases NH4+ to make 5,10-Methenyl THF
What cofactor and enzyme are involved in serine to glycine reaction?
PLP is cofactor, enzyme is serine hydroxymethyl transferase
-methyl goes to FH4 to make N5-Nth-CH2-FH4 (5,10-methylenetetrahydrofolate) used with TS reaction to make dTTP)
What does FH4 + serine make?
N5N10-methylene FH4 (3rd possible product)
What 3 sources can make methylene-THF?
serine, glycine (reversible), and choline
What products can be made with methylene-THF?
- serine
- can regenerate glycine,
- methyl-THF (then converted to methionine)
- TMP + dihydrofolate –> DNA
What creates methenyl-TFH?
histidine + THF, to formimino-THF –> methenyl-TFH
What is formyl-THF used to make?
formyl-methionine
Purines
CO2
What are the 4 main products of one carbon donations?
thymidine nucleotide, purine bases, methionine, and S-adenosyl methionine
Which 3 forms of FH4 can be converted between?
10-Formyl THF, 5,10-Methenyl THF, and 5,10-Methylene TFH
What enzyme reduces a methylene FH4 carbon to methyl during its transfer to dTMP to make dTMP?
Thymidylate synthase (TS) -then must regenerate TH4 (reaction oxidizes it to TH2)
What type of anemia is caused by dietary folate deficiency? Why?
megaloblastic anemia, since dTMP can’t be made, DNA is not made. Few RBCs and ones left can’t divide
Where do the drugs 5-fluorouracil and methotrexate target?
5-flourouracil- stops thymidylate synthase (can’t form dTMP)
Methotrexate- targets dihydrofolate reductase
SAM does what?
Donates methyl groups to numerous substrates, including precursors to amino acids
Norepinephrine + SAM –>
Epinephrine
Guanidoacetate + SAM –>
Creatine
Nucleotides + SAM –>
Methylated nucleotides
Phosphatidylethanolamine + SAM –>
phosphatidylcholine
acetylserotonin + SAM –>
melatonin
What are the 2 types of cobalamin that can be formed?
methyl cobalain
adenosine cobalamin
In what reaction does N5-methyl TH4 donate its carbon?
to form methylcobalamin
What does methylcobalamin donate its C to? and what is the product
donates to homocysteine to make methionine
What does adenosylcobalamin donate its C to? and what is the product?
to methylmalonyl CoA to make succinyl CoA
What dietary sources can cobalamin (vitamin B12) be found?
meats, eggs, diary (either free or protein bound)
Where does the methyl group or adenosine bind cobalamin?
at the cobalt in the center of the ring
What binds cobalamin first in stomach and is then digested away?
R-Binder, secreted from gastric mucosa of stomach
What binds cobalamin after R-binder has been digested away?
intrinsic factor, produced in parietal cells
Where is cobalamin bound to intrinsic factor taken up?
by intestinal epithelial cells and transported in blood as a complex with transcobalamin 2 protein
What does B12 deficiency cause?
pernicious anemia (megaloblastic anemia plus neuropathy)
What can cause vitamin B12 deficiency?
- dietary deficiency
- loss of function of intrinsic factor, transcobalamin 2, or cubillin
what is cubillin?
most intrinsic factor is stored in liver in complex with culillin
What enzyme converts methylmalonyl CoA to succinyl CoA using B12 Adenosyl cobalamin?
methylmalonyl CoA mutase (succinyl CoA enters TCA cycle to produce 1 GTP 1 NADH and 1 FADH2)
Which enzyme converts homocysteine to methionine using methylcobalamin?
methionine synthase, methylcobalamin must be remade after each reaction (by accepting methyl from N5-methyl TH4)
What is hyperhomocysteinemia?
result from mutations in methionine synthase, linked to cardiovascular and neurological problems (can’t convert it to methionine)
What are the 3 possibilities hyperhomocysteinemia can result from?
1) B12 (cobalamin) deficiency
2) methionine synthase deficiency
3) vitamin B6 (pyroxidal phosphate) deficiency
How is S-adenosylmethionine (SAM) formed? And what does it do?
methionine binds an adenosine nucleoside
-donates methyl groups to numerous substrates including precursors to neurotransmitters
Why does B12 deficiency result in functional folate deficiency?
irreversible formation of 5-Methyl THF (methyl trap) so it builds up and has no where to go without cobalamin to create methylcobalamin
Why are neurological problems associated with B12 deficiency?
neurotransmitter precursors (epinephrine, creatine, methylated NTs, phosphatidyl choline, melatonin)
What do defects in glycogen metabolism present as?
fasting hypoglycemia and muscle pain during exercise
What are the 2 types of C-C bonds in glycogen?
1: 4 - linear chains
1: 6 - make branch points
The addition of what molecule (and what enzyme) activate glucose 6P to make glycogen?
UTP, enzyme UDP glucose pyrophosphorylase. creates UDP-glucose
What protein is the 1 C of UDP glucose attached to?
OH on glycogenin
How long will chain grow until it will branch?
about 11 units long
What enzyme catalyzes branching of glycogen?
glycosyl 4–>6 transferase
What are the 2 key enzymes in glycogen synthesis?
glycogen synthase- adds on UDP glucose in 1:4 linkage
4:6 transferase- branching enzyme
Why does glycogen form branched structure?
More active ends to cut off glucose and add onto
-increases solubility with more OH groups exposed
What are the key enzymes in glycogen degradation?
glycogen phosphorylase- cleaves units of glucose 1 P from glycogen chain
-Debranching enzyme has 2 activities: 4:4 transferase (cleaves 1:4 glycosidic bond and transfers 3 glucose units to end of another chain) and alpha 1,6 glucosidase (hydrolyzes the remaining glucose’s 1:6 bond to release glucose
Is glycogen phosphorylase A or B a more active enzyme? (Lineweaver- Burke plot)
A- more gradual slope so Km is smaller, and lower 1/Vm so Vmax is higher
What are the states of glycogen phosphorylase B and glycogen synthase 1 (A) in fed state?
phosphorylated or not?
glycogen phophorlyase b = inactive
glycogen synthase 1 (a) = active
-neither phosphorylated
What are the states of glycogen phosphorylase B and glycogen synthase 1 (A) in fasted state? phosphorylated or not?
glycogen phosphorylase b = active
glycogen synthase D (a) = inactive
-both are phosphorylated
Is glycogen phosphorylase active or inactive when phosphorylated?
active.
What is more prevalent in fed and fasted states? phosphatases or kinases
Fed = phosphatases Fasted = PKA and PKC kinase
What is the main pathway for hepatocytes in fed state?
insulin binds, activates PDK –> PKB which phosphorylates protein phosphatase 1 (active)and glycogen synthase kinase 3 (inactive)
-active glycogen synthase, inactive glycogen phosphorylase kinase and no glycogenolysis
What enzyme, only found in liver cells, allows glucose to leave?
glucose 6-phosphatase removes phosphate so unbound glucose can leave
What is the extra indicator of fasted state in skeletal cells?
work generates AMP which activates AMP-K which also phosphorylates glycogen phosphorylase
What is the process in skeletal muscle during fed state for glycogen metabolism?
insulin binds receptor –> PDK –> PKB which phosphorylates protein phosphatase (active) and glycogen synthase kinase 3 (inactive)
What is GSD 0?
glycogen synthase deficiency
- normal glucose tolerance, variable clinical presentation of exercise intolerance, cardiac and muscle hypertrophy
- muscle specific
What is GSD 1?
deficiency in glucose 6-phosphatase
-fasting hypoglycemia, lactic acidosis, hepatomegaly due to glycogen accumulation, hyperuricemia and hyperlipidemia (increased FA as starvation response)
Treatment: avoid fasting, frequent eating
What is GSD 3?
deficiency of 1,6-glucosidase activity of debranching enzyme
-fasting hypoglycemia and ketoacidosis, hyperlipidemia, hepatomegaly with elevated AST/ ALT
What are the 2 types of GSD 3 and what cells do they affect?
GSD 3a = affects liver and muscle
GSD 3b = affects only the liver
What is GSV 4?
Deficiency of branching enzyme 4:6- transferase
- failure to thrive, hepatomegaly, liver failure.
- fatal (long chains of glycogen, not enough stores
What is GSD 5?
deficiency of muscle glycogen phosphorylase
- late childhood onset of exercise intolerance, myoglobinuria after exercising
- starved cells break down themselves
- lots of NH4+ after exercising
How do bactericidal and bacteriostatic drugs differ?
bactericidal drugs reduce amount of bacteria (use if patient is immunocompromised) and bacteriostatic drugs limit growth to allow immune system to catch up
What patient factors affect drug absorption, distribution, metabolism, and exretion?
- absorption- movement of drug into vascular system
- distribution- transfer of drug from intravascular to extravascular, blood brain barrier is challenge
- Metabolism- irreversible transformation of parent compound into daughter metabolites, often in liver
- excretion- elimination of the drug fro the body by urine or feces
What is prophylactic therapy?
treat infection that has not developed yet in individuals at a high risk for becoming infected
What is pre-emptive therapy?
have lab test indicating infection but no symptoms
-advantage = decreases amount antibiotics used
What is empiric therapy?
take cultures, patients have an infection with serious potential consequences BUT organism has not been identified yet
What is suppressive therapy?
after initial disease is controlled therapy, continued at a lower dose
What is definitive therapy?
when pathogen is identified, monotherapy, narrow spectrum)
What properties limit usefulness of a drug class and drugs within the class (toxicity)?
- antibiotics need to injure invading organism wile causing minimal adverse affects to host
- hard to make drugs for fungi, parasites, and eukaryotes since they are like us
What mechanisms cause drug resistance?
- intrinsic resistance (absence of target for drug, Mycoplamsa has no cell wall)
- acquired drug resistance (change in bacterial DNA or acquire new DNA
- DNA mediated transformation- acquire DNA from other bacterial cell
- bacteriophage- can introduce DNA
- Conjugation- exchange DNA, uses F pili, plasmid
How can drug resistance be minimized or prevented?
- take full round of antibiotics
- don’t over prescribe
- vaccinations to prevent infection
- prevent transmission (isolate pathogen and break chain of contagion)
What is the therapeutic index?
high therapeutic index means fewer adverse affects
How can you determine alpha, beta, or gamma from hemolysis?
alpha hemolytic = green ring
beta hemolytic = clearing around colonies
gamma hemolytic = no hemolysis
What is the nucleoside for adenine?
adenosine
What is the nucleoside for the base guanine?
guanosine
What is the nucleoside for the base hypoxanthine?
inosine (used as a fuel source)
What is the nucleoside for the base cytosine?
cytidine
What is the nucleoside for the base thymine?
thymidine
What is the nucleoside for the base uracil?
uridine
What is the first committed step in purine synthesis?
transfer of an amine from glutamine by glutamine phosphoribosyl amidotransferase
-creates 5 phosphoribosyl 1-amine
How is PRPP formed?
-enzyme PRPP synthase converts Ribose 5-P from PPP to PRPP
What allosterically inhibits PRPP synthase?
GDP and ADP (purine diphosphonucleosides)
What does Glutamine + PRPP (plus a lot) finally make during purine synthesis?
IMP
What 2 products can come from IMP?
+ glutamine to make GMP
+ aspartate to make AMP
What enzyme converts XMP + Glutamine to GMP plus glutamate?
GMP synthase
What protein redox cofactor takes OH to convert NDP to dNDP?
thioredoxin, 2 sulfurs can be oxidized (bridge) or reduced
Which is the only nucleotide that can be directly phosphorylated to AMP by adenosine kinase?
adenosine
Which enzyme deficiency is associated with Lesch-Nyhan Syndrome?
HGPRT (hypoxanthine- guanine phosphoribosyltransferase)
- X linked disorder
- self injury, elevated uric acid, often die in 30s from renal failure
What does a deficiency in purine nucleoside phosphorylase (PNP) cause?
- can’t convert inosine to hypoxanthine or guanosine to guanine
- low T cells, chronic infections, buildup of insoine is toxic to developing T cells and lymphocytes
What does a deficiency in adenosine deaminase (ADA) cause?
- autosomal recessive SCID (severe combined immunodeficiency)
- accumulation of 2-deoxyadenosine in blood
- low lymphocytes and costochondral junction dysplasia (skeletal abnormalities)
- treatment is bone marrow transplant
What is gout caused by?
hyperuricemia (too much uric acid in blood)
- from purine degradation, xanthine oxidase isn’t working
- salt crystals can form in fingers and toes
What do GMP and AMP degrade to? and by what enzyme?
xanthine
-xanthine oxidase
What enzyme starts path to convert glutamine (as N donor) to UMP in pyrimidine synthesis?
CPS 2 (carbamoyl phosphate 2) in cytoplasm
What are the 2 products of pyrimidine degradation? Are they harmful?
- beta alanine
- beta aminoisobutyrate
- no pathologies from accumulation
What are the main features of cholesterol?
- 4 rings
- fully saturated
- branches
What is the key regulatory enzyme in cholesterol synthesis?
HMG CoA reductase
-HMG-CoA to Mevalonate
What type of drug inhibig HMG CoA reductase?
statins
How many HMG CoA reductase enzymes are there? Where are they found?
- 1 in mitochondria for ketone body synthesis and 1 in cytosol for cholesterol synthesis
What Apo protein do al chylomicrons have?
Apo B-48
What Apo proteins do mature chylomicrons have?
Apo B-48, Apo C-2, Apo E
What are chylomicrons composed of?
mostly TAGs, some proteins, cholesterol, cholesterol esters, and phopholipids
What causes congenital adrenal hyperplasia and what are the symptoms?
- mutation in steroid hormone biosynthesis gene Cyp21
- low aldosterone and cortisol
- high androgen levels
What are xanthomas?
Cholesterol rich tumors on body, from familial hypercholesterolemia/ too much LDL in blood
What is vitamin D important for in body?
Calcium homeostasis
