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Biochem > Lect 3- TCA To Glycoproteins > Flashcards

Lect 3- TCA To Glycoproteins Flashcards

1
Q

What happens to pyruvate before the TCA cycle can begin?

A 
Pyruvate is converted to acetyl CoA by
Pyruvate dehydrogenase (PDH) complex
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2
Q

What are the three enzymes that make up the pyruvate dehydrogenase (PDH) complex?

A 
Pyruvate dehydrogenase (E1)
Dihydrolipoyl transacetylase (E2)
Dihydrolipoyl dehydrogenase (E3)
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3
Q

List the 5 coenzymes utilized in PDH complex and which enzyme they assist with

A

E1- thiamine pyrophosphate (TPP)
E2- lipoic acid and CoA
E3- FAD and NAD+

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4
Q

Specifically how arsenic poisoning works

A

Due to inhibition of enzymes that require lipoic acid as a coenzyme
Ex: PDH

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5
Q

What causes congenital lactic acidosis?

A

A deficiency in the E1 component

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6
Q

What is the first step of the TCA cycle and the enzyme used?

A

Condensation of oxaloacetate and acetyl CoA by
Citrate synthase to form
Citrate

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7
Q

What happens to citrate in TCA?

A

Isomerized to isocitrate by

Aconitase

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8
Q

Step 3 of TCA, what happens to isocitrate? Why is this step important?

A

Isocitrate is oxidized and decarboxylated via isocitrate dehydrogenase with NAD+ to form
a-ketoglutarate

  • NADH and CO2 produced
  • *rate limiting step (regulators)
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9
Q

What happens to a-ketoglutarate in TCA?

A

Converted to succinyl CoA via
a-ketoglutarate dehydrogenase complex

*CO2 and NADH produced

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10
Q

What inhibits and activates a-ketoglutarate dehydrogenase complex?

A

Inhibitors; NADH, succinyl CoA

Activator; Ca2+

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11
Q

What happens to succinyl CoA in TCA?

A

Succinyl CoA is cleaved by
Succinyl CoA synthetase (succinate thiokinase)
To form
Succinate
*rxn is coupled to phosphorylation of GDP to GTP

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12
Q

What happens to succinate in TCA cycle?

A

Succinate is oxidized to fumarate by
Succinate dehydrogenase

*FAD is reduced to FADH2

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13
Q

What cycles/places is succinate dehydrogenase found?

A

The TCA cycle and in complex II of the ETC

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14
Q

What is the only enzyme of the TCA cycle embedded into the membrane?

A

Succinate dehydrogenase

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15
Q

What happens to fumarate in TCA?

A

Fumarate is hydrated to Malate by

Fumarase

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16
Q

What happens to malate in the TCA?

A

Malate is oxidized to oxaloacetate by
Malate dehydrogenase

*NADH is produced

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17
Q

What are the three most highly regulatory enzymes in TCA?

A

Citrate synthase
Isocitrate dehydrogenase
a-ketoglutarate dehydrogenase complex

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18
Q

In a human, how much ATP is produced from 1 molecule of glucose?

A

31 ATP

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19
Q

Where does gluconeogenesis primarily occur during an OVERNIGHT fast?

A

90% in the liver

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20
Q

Where does gluconeogenesis primarily increase during PROLONGED fasting?

A

Kidneys

40% of total glucose production

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21
Q

What are the three substrates for gluconeogenesis?

A

Glycerol
Lactate
Amino acids

22
Q

Where is glycerol released and where does it then go?

A

Released in adipose tissue and then enters the bloodstream and travels to the liver

23
Q

Explain the Cori cycle

A

Lactate is released into the blood by exercising skeletal muscle and RBCs, then taken up by the liver. Lactate dehydrogenase converts it to pyruvate, then converted to G6P, then to glucose and sent back to skeletal muscle

24
Q

Where do the amino acids that provide the major source of glucose during a fast come from?

A

AAs derived from the hydrolysis of tissue proteins

25
Q

Describe the glucose-alanine cycle

A

Muscle broken down to AAs, to glutamate reacts with pyruvate with alanine transaminase to yield alanine. Travels through bloodstream, reacts with alanine transaminase to yield pyruvate. Gluconeogenesis to produce glucose. Sent back to muscle

26
Q

What 5 AAs can be used to yield pyruvate in gluconeogenesis?

A 
Alanine
Serine
Glycine
Cysteine
Threonine
27
Q

What two AAs can yield oxaloacetate?

A

Aspartate

Asparagine

28
Q

What 3 steps must be circumvented when generating glucose from lactate or pyruvate (in glycolytic cycle)?

A
  1. Synthesis of PEP from pyruvate
  2. Synthesis of F6P from F1,6BP
  3. Synthesis of glucose from G6P
29
Q

What two main hormones stimulate and inhibit gluconeogenesis?

A

Glucagon from a-cells of pancreatic islets stimulate

Insulin inhibits

30
Q

Where does the TCA cycle take place?

A

Mitochondria

31
Q

Where are the main stores of glycogen in the body?

A

Liver

Skeletal muscle

32
Q

How does the function of glycogen in the liver and skeletal muscle differ?

A

In the liver, to produce glucose for the entire body

In muscle, to produce glucose for the muscle

33
Q

Describe the structure of glycogen

A 
A branched chain polysaccharide made from a-D-glucose. 
Primarily a(1->4) linkages
Branch with a(1->6) linkage every 8-10 glucosyl residues
34
Q

Difference between amylose and amylopectin?

A

Amylose is a straight chain

Amylopectin is branched

35
Q

When does glycogen synthesis occur?

A

After a meal, when blood glucose levels are high

36
Q

First step of glycogenesis?

A

Glucose-6-phosphate catalyzed by
Phosphoglucomutase to make
Glucose-1-phosphate (G1P)

37
Q

What is the next main step in glycogenesis one G1P is formed?

A

Synthesis of UDP-glucose via

UDP-glucose pyrophosphorylase

38
Q

Glycogenesis:

What happens after UDP-glucose is formed?

A

Glycogenin acts as a primer for
glycogen synthase to make
Glycogen

39
Q

How are branches formed in glycogenesis?

A

Amylo-a(1,4)->a(1,6)-transglucosidase removes a chain of 6-8 residues from nonreducing end: a(1,4)->a(1,6) bond

40
Q

What is glycogenolysis?

A

Degradation of glycogen

41
Q

How are chains shortened during glycogenolysis?

A

Glycogen phosphorylase cleaves the a(1,4) bonds by phosphorolysis (producing glucose-1-phosphate)

42
Q

What enzyme removes the outer 3 of 4 glucosyl residues attached at a branch during glucogenolysis?

A

Oligo-a(1->4)->a(1,4)-glucan transferase

43
Q

What enzyme releases a single glucose residue of branch in glucogenolysis?

A

Amylo-a(1->6)-glucosidase

*releasing free glucose

44
Q

A deficiency is glucose-6-phosphate causes…

A

Glycogen storage disease Type1a (Von Gierke disease)

45
Q

What are the three main hormones involved in glycogen synthesis and degradation, and how do they regulate?

A

Glucagon- stimulates glycogenolysis, inhibits glycogenesis
Epinephrine- stimulates glycogenolysis, inhibits glycogenesis
Insulin- stimulates glycogenesis, inhibits glycogenolysis

46
Q

What is the other name for the pentose phosphate pathway?

A

Hexose monophosphate shunt

47
Q

What are the 4 main functions of NADPH in the pentose phosphate pathway?

A
  1. Used in reductive biosynthesis
  2. Reduction of H2O2
  3. Produce reducing equivalents required by the cytochrome P450 monooxygenase (adds an O) system
  4. Maintain hemoglobin in its reduced form and protects against hemolysis
48
Q

What is a glycosaminoglycan composed of?

A

Repeating disaccharide unit containing amino sugars and acidic sugars

49
Q

What is a proteoglycan?

A

Constructed of protein and glycosaminoglycans

50
Q

What are glycoproteins composed of?

A

Proteins to which oligosaccharides are covalently attached

Relatively short

Biochem (8 decks)

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