Lect 3- TCA To Glycoproteins

Question 1

What happens to pyruvate before the TCA cycle can begin?

Answer 1

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

Question 2

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

Answer 2

Pyruvate dehydrogenase (E1)
Dihydrolipoyl transacetylase (E2)
Dihydrolipoyl dehydrogenase (E3)

Question 3

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

Answer 3

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

Question 4

Specifically how arsenic poisoning works

Answer 4

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

Question 5

What causes congenital lactic acidosis?

Answer 5

A deficiency in the E1 component

Question 6

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

Answer 6

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

Question 7

What happens to citrate in TCA?

Answer 7

Isomerized to isocitrate by

Aconitase

Question 8

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

Answer 8

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

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

Question 9

What happens to a-ketoglutarate in TCA?

Answer 9

Converted to succinyl CoA via
a-ketoglutarate dehydrogenase complex

*CO2 and NADH produced

Question 10

What inhibits and activates a-ketoglutarate dehydrogenase complex?

Answer 10

Inhibitors; NADH, succinyl CoA

Activator; Ca2+

Question 11

What happens to succinyl CoA in TCA?

Answer 11

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

Question 12

What happens to succinate in TCA cycle?

Answer 12

Succinate is oxidized to fumarate by
Succinate dehydrogenase

*FAD is reduced to FADH2

Question 13

What cycles/places is succinate dehydrogenase found?

Answer 13

The TCA cycle and in complex II of the ETC

Question 14

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

Answer 14

Succinate dehydrogenase

Question 15

What happens to fumarate in TCA?

Answer 15

Fumarate is hydrated to Malate by

Fumarase

Question 16

What happens to malate in the TCA?

Answer 16

Malate is oxidized to oxaloacetate by
Malate dehydrogenase

*NADH is produced

Question 17

What are the three most highly regulatory enzymes in TCA?

Answer 17

Citrate synthase
Isocitrate dehydrogenase
a-ketoglutarate dehydrogenase complex

Question 18

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

Answer 18

31 ATP

Question 19

Where does gluconeogenesis primarily occur during an OVERNIGHT fast?

Answer 19

90% in the liver

Question 20

Where does gluconeogenesis primarily increase during PROLONGED fasting?

Answer 20

Kidneys

40% of total glucose production

Question 21

What are the three substrates for gluconeogenesis?

Answer 21

Glycerol
Lactate
Amino acids

Question 22

Where is glycerol released and where does it then go?

Answer 22

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

Question 23

Explain the Cori cycle

Answer 23

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

Question 24

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

Answer 24

AAs derived from the hydrolysis of tissue proteins

Question 25

Describe the glucose-alanine cycle

Answer 25

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

Question 26

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

Answer 26

``` Alanine Serine Glycine Cysteine Threonine ```

Question 27

What two AAs can yield oxaloacetate?

Answer 27

Aspartate | Asparagine

Question 28

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

Answer 28

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

Question 29

What two main hormones stimulate and inhibit gluconeogenesis?

Answer 29

Glucagon from a-cells of pancreatic islets stimulate Insulin inhibits

Question 30

Where does the TCA cycle take place?

Answer 30

Mitochondria

Question 31

Where are the main stores of glycogen in the body?

Answer 31

Liver | Skeletal muscle

Question 32

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

Answer 32

In the liver, to produce glucose for the entire body | In muscle, to produce glucose for the muscle

Question 33

Describe the structure of glycogen

Answer 33

``` 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 ```

Question 34

Difference between amylose and amylopectin?

Answer 34

Amylose is a straight chain | Amylopectin is branched

Question 35

When does glycogen synthesis occur?

Answer 35

After a meal, when blood glucose levels are high

Question 36

First step of glycogenesis?

Answer 36

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

Question 37

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

Answer 37

Synthesis of UDP-glucose via | UDP-glucose pyrophosphorylase

Question 38

Glycogenesis: | What happens after UDP-glucose is formed?

Answer 38

Glycogenin acts as a primer for glycogen synthase to make Glycogen

Question 39

How are branches formed in glycogenesis?

Answer 39

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

Question 40

What is glycogenolysis?

Answer 40

Degradation of glycogen

Question 41

How are chains shortened during glycogenolysis?

Answer 41

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

Question 42

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

Answer 42

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

Question 43

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

Answer 43

Amylo-a(1->6)-glucosidase *releasing free glucose

Question 44

A deficiency is glucose-6-phosphate causes...

Answer 44

Glycogen storage disease Type1a (Von Gierke disease)

Question 45

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

Answer 45

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

Question 46

What is the other name for the pentose phosphate pathway?

Answer 46

Hexose monophosphate shunt

Question 47

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

Answer 47

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

Question 48

What is a glycosaminoglycan composed of?

Answer 48

Repeating disaccharide unit containing amino sugars and acidic sugars

Question 49

What is a proteoglycan?

Answer 49

Constructed of protein and glycosaminoglycans

Question 50

What are glycoproteins composed of?

Answer 50

Proteins to which oligosaccharides are covalently attached | Relatively short