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FOM > Week3biochem > Flashcards

Week3biochem Flashcards

1
Q

vitamin precursor of active cofactors (i carbon transfer units)

A

folate

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2
Q

where do we get folate from in our diet?

A

green leafy veggies, liver, legumes, yeast & fortified flour

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3
Q

what part of the folate molecule is digested in the gut

A

glutamate tail–digested down to monoglutamate

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4
Q

WHat happens to folate in the intestinal epithelial cells?

A

folate is reduced to N5-methyl THF

**becomes major form in the blood

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5
Q

What happens to folate in the liver

A

poly-glutamated in the liver

**resets/starts pathway?

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6
Q

spina bifida

A
  • neural tube defects associated with folate deficiency before & during pregnancy
  • *affected w/ SB cant make DNA
  • **megaloblastic anemia: big RBCs but few
  • ***DNA synthesis/division is delayed but cytoplasmic contents can still be made =BIG
  • **found in bone marrow most often, blood occasional
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7
Q

Hereditary folate malabsorption

A

inherited mutation in proton coupled folate transporter (PCFT: gene SCL46A1
**causes functional folate deficiency despite adequate folate in the diet

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8
Q

causes of folate deficiency

A
  • malabsorption

* not enough in diet

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9
Q

What is the importance of dihydrofolate reductase (DHFR)

A
  • enzyme that reduces folate –>dihydrofolate (FH2) –>tetrahydrofolate (FH4)
  • *For metabolism of dietary folate & recycling oxidized folate to FH4
  • **DHFR is a drug target: cancer, athritis, anitbacterial, & antimalarial
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10
Q

What are the important Nitrogens in the tetrahydrofolate (THF or FH4)

A

N-5 & N-10

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11
Q

ketogenic amino acids

A

AA can be degraded into Acetyl CoA and/or acetoacetate

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12
Q

FH4 + formate gives us what product?

A

N10-formyl FH4

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13
Q

N10-formyl FH4 can then make what compounds?

A

n10-formyl FH4 5,10methenyl THF 5,10methylene THF –> 5methyl THF —->methyl cobalmin

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14
Q

Which step in the reduction of N10 formyl THF is not reversible? importance?

A

5,10 methylene THF –> 5 methyl THF is not reversible!

**called “methyl trap”

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15
Q

THF + histidine –>?

A

FIGLU: 5-formimino THF

**can be made into 5,10 Methenyl THF

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16
Q

When would you get a build up of FIGLU?

A

B12 deficiency

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17
Q

which AA is the most important contributor to the 1-C pool?

A

serine!!

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18
Q

THF + serine—> ?

A

5, 10 methylene THF

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19
Q

contributors to the 1 C pool?

A

serine, glycine, choline, histidine, & formate

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20
Q

Products of 1 carbon donations?

A

thymidine neucleotide, purine bases, methionine & s-adenosyl methinonine

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21
Q

Important things about making thymidine nucleotide

A
  • uses enzyme thymidylate synthase (TS)
  • dUMP–>dTMP
  • reduces methylene C to CH3 in process
  • leaves cofactor in oxidized FH2 form to be reduced and accept 1 C grp from
  • makes nucleotide for DNA
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22
Q

what should a lady planning to b pregnant start taking? why?

A
  • should take 400 ug/day of folate 1 month prior and up until 3 months after becoming pregnant
  • prevents spina bifida
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23
Q

Why does inhibitting DHFR or thymidylate synthase work as cancer drug/

A
  • cancer cells divide rapidly & use lots of deoxynucleotides
  • inhibition of these 2 enzymes prevents cell from getting nucleotides for DNA synthesis–>can’t grow or divide
  • *harsh side effects because inhibits healthy cells as well as cancerous ones
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24
Q

2 main cancer drugs

A

5-FU : 5- flourouracil

methotrexate

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25
Q

SAM: s-adenosyl methionine

A

provides methyl grps for biosynthetic reactions & can regenerate homocysteine

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26
Q

methyl trap hypothesis:

A
  • N5methyl FH4 can only donate its 1 C to cobalamin –> methylcobalamin
  • Methylcobalamin only donates methyl to homocysteine –> methionine
  • *If B12 is missing, leaves folate trapped in N5methyl THF form & cant participate in other C transfers
  • Sx’s look like folate deficiency but are B12 deficiciency
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27
Q

Why does inhibitting DHFR or thymidylate synthase work as cancer drug/

A
  • cancer cells divide rapidly & use lots of deoxynucleotides
  • inhibition of these 2 enzymes prevents cell from getting nucleotides for DNA synthesis–>can’t grow or divide
  • *harsh side effects because inhibits healthy cells as well as cancerous ones
28
Q

2 main cancer drugs

A

5-FU : 5- flourouracil

methotrexate

29
Q

SAM: s-adenosyl methionine

A

provides methyl grps for biosynthetic reactions & can regenerate homocysteine

30
Q

methyl trap hypothesis:

A
  • N5methyl FH4 can only donate its 1 C to cobalamin –> methylcobalamin
  • Methylcobalamin only donates methyl to homocysteine –> methionine
  • *If B12 is missing, leaves folate trapped in N5methyl THF form & cant participate in other C transfers
  • Sx’s look like folate deficiency but are B12 deficiciency
31
Q

Cobalamin Rxn 2

A

homocysteine –> methionine

  • methyl cobalamin consumed in rxn, but regenerated by methyl from N5methyl THF
  • uses methionine synthase
32
Q

pernicious anemia

A

megaloblastic anemia plus neuropathy

**neurological symtpoms!!

33
Q

movement of dietary b12

A
  • 1st binds to R-binder protein in stomach
  • R-binders digested, b12 binds to intrinsic factor protein
  • complex is taken up by intestinal epi cells & transported into the blood w/ transcobalamin II
  • most is stored in liver w/ cubillin
34
Q

Cabalamin reaction 1

A

methylmalonyl CoA –> Succinyl COA–> TCA

  • use B12 adenosyl cobalamin to methyl transfer (not swap)
  • *adenosyl cobalamin not consumed in rxn
  • use enzyme methylmalonyl CoA mutase
35
Q

Cobalamin Rxn 2

A

homocysteine –> methionine

  • methyl cobalamin consumed in rxn, but regenerated by methyl from N5methyl THF
  • uses methionine synthase
36
Q

hyperhomocysteinemia

A
  • increase in homocysteine caused by:
    1) mutation in methionine synthase
    2) B12 deficiency
    3) B6 deficiency
  • associated with cardiovascular & neuro problems
37
Q

what are glycogens main 2 functions?

A

1) intracellular glucose buffers

2) in hepatocytes, glycogen is the source of glucose for transport out into other cells

38
Q

What are the most important cell types glycogen serves and why?

A
  • skeletal & cardiac muscle: serves as a buffer for glucose 6-p for use in cell
  • liver: serves as glucose buffer for blood
39
Q

what are the 2 most common symptom presentations of glycogen metabolism deficiencies?

A
  • fasting hypoglycemia

* muscle pain during exercise

40
Q

describe the structure of glucose

A

6 carbons with a hexagon ring of 5 carbons and an O

  • side with O in ring is the reducing/1 end
  • side with 2 OH is the non-reducing/4 end
41
Q

@ types of C-C bonds in glycogen, what are they?

A

1: 4 forms linear chains
1: 6 make branch points

42
Q

What is the purpose of forming UDP glucose before making glycogen?

A

1) UDP glucose serves as a handle to carry the glucose to elongating glycogen chain
2) the UDP bond to glucose holds energy to allow the addition of glucose to glycogen chains

43
Q

what is the head protein that is necessary for glycogen synthesis?

A

glycogenin

44
Q

What enzyme is used to link glucoses into glycogen chain & in what direction does this occur?

A

Glycogen synthase links glucose using 1:4 bond sites in the direction of the 4 carbon
(away from glycogenin which links at 1/reducing end of glucose)

45
Q

When can branching occur & what enzyme performs this?

A
  • occurs glycogen chain has reached 11 units long
  • 4:6 transferase transfers a glucose chain from the end of linear chain (4 end) and makes a 1:6 bond to part of the linear chain closer to glycogenin than cleavage site
46
Q

What is the purpose of branching and creating a “protein puffball”?

A
  • increases solubility (many exposed OH groups)

* can have many enzymes (100s) working on degradation or synthesis at 1 time [depending on the body’s needs]

47
Q

Steps in glycogenolysis (degradation)

A

1) glycogen phosphorylase cleaves units of glucose from glycogen chains & adds Pi to make glucose-1-phosphate (works until 4 units away from branch pt)
2) 4:4 transferase cleaves a 1,4 bond off branched chain & transfers 3 glucose units to end of another chain w/ 1:4 linkage
3) a-1,6 glucosidase activity hydrolyzes the remaining glucose’s 1:6 bond to release single glucose
4) glycogen phosphorylase continues degrading chain until reaches another branch or the core

47
Q

Steps in glycogenolysis (degradation)

A

1) glycogen phosphorylase cleaves units of glucose from glycogen chains & adds Pi to make glucose-1-phosphate (works until 4 units away from branch pt)
2) 4:4 transferase cleaves a 1,4 bond off branched chain & transfers 3 glucose units to end of another chain w/ 1:4 linkage
3) a-1,6 glucosidase activity hydrolyzes the remaining glucose’s 1:6 bond to release single glucose
4) glycogen phosphorylase continues degrading chain until reaches another branch or the core

48
Q

mutations in muscle glycogen phosphorylase causes:

A 
GSD V (McArdles disease)
*presents with exercise intolerance
48
Q

mutations in muscle glycogen phosphorylase causes:

A 
GSD V (McArdles disease)
*presents with exercise intolerance
49
Q

mutations in liver glycogen phosphorylase cause:

A 
GSD VI (Hers disease)
*presents w/ fasting hypoglycemia
49
Q

mutations in liver glycogen phosphorylase cause:

A 
GSD VI (Hers disease)
*presents w/ fasting hypoglycemia
50
Q

deficiency in a-1,6 glucosidase causes:

A

GSD III
*biggest concern with the=is deficiency is that glycogen gets too big & bursts the cell (since glycogen can only b built)

54
Q

deficiency in a-1,6 glucosidase causes:

A

GSD III
*biggest concern with the=is deficiency is that glycogen gets too big & bursts the cell (since glycogen can only b built)

55
Q

2 forms of glycogen phosphorylase & how to read their activity on a lineweaver-burke plot

A

a & b glycogen phosphorylase

*a is higher activity because lower line on this plot= bigger vmax & lower Km

56
Q

how is glycogen metabolism controlled?

A

by phosphorylation of glycogen phosphorylase & glycogen synthase

  • fed= phosphorylase is inactive, gly. synthase is active, both unphosphorylated
  • fasted= phosphorylase active, gly. synthase inactove, both phosphorylated
57
Q

fasted state glycogen metabolism regulation in hepatocytes

A

epinephrine & glucagon cause cascade & turn off glycogen synthase, but turn on glycogen phosphorylase kinase–> glycogen phosphorylase–>glycogenolysis –>glucose
*glycogen0genesis is inhibitted

58
Q

fed state glycogen metabolism regulation in hepatocytes

A

insulin turns on phosphatase cascade–>protein phosphorylase 1 is on & gly. symthase kinase 3 is off

  • glycogen synthase is active & promotes glycogenogenesis
  • gly. phosphorylase is inactive, inhibtting glycogenolysis
59
Q

name the enzyme glucose 6-phosphorylase’s importance during regulation of glycogen metabolism

A

critical for maintaining the buffer, by breaking down glucose-6-p in the liver into blood glucose (g6p cant cross membranes)

60
Q

fasted state glycogen metabolism regulation in skeletal muscle

A 
B epinephrine (no glucagon receptor) causes cascade to cAMP-->PKA which makes gly. synth inactive & gly. phosphorylase kinase active (latter ends up signaling for glucose production)
*protein phosphatase 1 is inactive while gly. synth kinase 3 is active
61
Q

fed state glycogen metabolism regulation in skeletal muscle

A

insulin signals –> IRS1–>PI3K–>PDK–>PKB–> protein phosphatase 1 active & gly synth kinase3 inactive

  • glycogen synthase is active (glycogenogenesis)
  • gpk & gp are inactive so no genolysis
62
Q

GSD 0

A
  • glycogen synthase deficiency
  • rare, autosomal recesssive
  • norm glucose tolerance
  • exercise intolerance
  • cardiac & muscle hypertrophy
  • may b cause of SIDS
63
Q

GSD 1

A

aka von Giercke disease
*deficit in g6-phosphatase
*fasting hypoglycemia, lactic acidosis, hepatomegaly (gly accumulation)
*hyperuricemia & hyperlipidemia
*liver issue; not going to have exercise Sx’s
Tx: avoid fasts & eat uncooked corn starch

64
Q

GSD III

A

aka Cori disease
*deficit in 1,6-glucosidase activity of debranching enzyme
*fasting hypoglycemia, ketoacidosis, hyperlipidemia, hepatomagaly w/ hi AST/ALT
Tx: frequent hi carb meals

65
Q

Difference between GSD IIIa & GSD IIIb?

A

GSD IIIa: affects liver & muscle

GSD IIIb: affects only the liver & because of this is more preferable

66
Q

GSD IV

A
  • inability to make branches
  • deficit of branching enzyme 4,6-transferase
  • SX: FTT, hepatomegaly, liver failure, FATAL
67
Q

GSD V

A

aka McArdle disease

  • deficit in muscle glycogen phosphorylase
  • late childhood onset of exercise intolerance, myoglobinuria after exercise
  • increased creatine kinase, hi creatine kinase & ammonia after exercise
  • Tx: avoid exercise, try to build tolerance

FOM (6 decks)

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