Glycolysis, Glycogen, Gluconeogenesis, & Pentose Phosphate Pathway

Question 1

Which low-affinity transporter is located in hepatocytes & pancreatic cells ?

Answer 1

GLUT 2 (captures excess glucose primarily for storage)

Question 2

Which glucose transporter is located in adipose tissue & muscle, & responds to the glucose conc. in peripheral blood 🩸 ?

Answer 2

GLUT 4

Question 3

Where does glycolysis take place & what does it convert glucose in to ?

Answer 3

Takes place in the cytoplasm & converts glucose into 2 pyruvate molecules

Question 4

What are the function. of kinases ?

Answer 4

To attach phosphate group from ATP to their substrates

Question 5

How do hexokinase & glucokinase differ ?

Answer 5

H is widely distributed in tissues & is inhibited by G6P, while G is only found in liver cells & pancreatic beta islet cells (also induced by insulin)

Question 6

What is the rate-limiting enzyme & main control point in glycolysis ?

Answer 6

PFK 1 (phosphofructokinase-1)

• Inhibited by ATP & citrate; activated by AMP
• Facilitates rxn of F6P phosphorylated to F1,6BP

Question 7

What are functions of PFK-2 (phosphofructokinase-2) & how do they impact PFK-1?

Answer 7

• Stimulated by insulin
• Facilitate rxn of F6P to F2,6BP which will then activate PFK-1
• Inhibited by glucagon

Question 8

Which enzyme catalyzes the oxidation & addition of an inorganic phosphate to glyceraldehyde 3-phosphate to produce 1,3 bisphosphoglycerate ?

Answer 8

Glyceraldehyde 3-Phosphate Dehydrogenase

-Also results in the reduction of NAD+ to NADH

Question 9

Which enzyme catalyzes the transfer of phosphate from 13BPG to ADP, forming ATP & 3PG ?

Answer 9

3-phosphoglycerate kinase

-A type of substrate level phosphorylation: where ADP IS directly phosphorylated ATP using a high energy intermediate

Question 10

The last enzyme in aerobic glycolysis that catalyzes a substrate-level phosphorylation of ADP via phosphoenolpyruvate substrate is known as ?

Answer 10

Pyruvate kinase

-Activated by F1,6BP (feed-forward activation)

Question 11

What is the key fermentation enzyme in mammalian cells & what is its function?

Answer 11

Lactate dehydrogenase

-Oxidizes NADH to NAD+

Question 12

Dihydroxyacetone phosphate (DHAP) is formed from F1,6BP & can be isomerized to G3P. Where is it used & what is its function ?

Answer 12

Used in hepatic & adipose tissue for triacylglycerol synthesis

Question 13

What are 1,3-bisphosphoglycerate & phosphoenolpyruvate used for ?

Answer 13

Generate ATP by substrate-level phosphorylation (only ATP gained in anaerobic respiration)

Question 14

What enzymes make certain steps of glycolysis irreversible ?

Answer 14

Hexokinase & glucokinase
PFK-1
Pyruvate kinase

Question 15

What do RBCs have that produces 2,3BPG from 1,3BPG in glycolysis ?

Answer 15

Bisphosphoglycerate mutase

Question 16

The rxn of galactose into galactose-1-phosphate, and galactose-1-phosphate into G1P is catalyzed by which enzymes?

Answer 16

Galactokinase & Galactose-1-phosphate uridyltransferase (respectively)

Question 17

What is pyruvate converted into for entry into the citric acid cycle when ATP is needed or for fatty acid synthesis ?

Answer 17

Acetyl coA

*Carried out by pyruvate dehydrogenase complex & is irreversibile

Question 18

Glycogen synthesis & degradation occur primarily in liver & skeletal muscle, but is stored where ?

Answer 18

Cytoplasm (as granules)

Question 19

What is the difference between stored liver glycogen & skeletal muscle glycogen ?

Answer 19

LG is used to maintain blood glucose levels, while SG is used to as an energy reserve for the muscles during exercise

Question 20

What is the rate-limiting enzyme of glycogen synthesis ?

Answer 20

Glycogen synthase

• Stimulated by G6P & insulin
• Inhibited by epinephrine & glucagon

Question 21

What are the functions of a branching enzyme ?

Answer 21

1. To hydrolyze a-1,4 bonds to release oligoglucose (few glucose molecules bonded together)
   2, Forms a-1,6 bond to create branch

Question 22

What enzyme breaks a-1,4 glycosidic bonds & releases G1P from the periphery of the granule ?

Answer 22

Glycogen phosphorylase

*cannot break a-1,6 bonds

Question 23

Slightly different versions of the same protein is known as ?

Answer 23

Isoforms

Question 24

How are the essential gluconeogenic intermediates converted into glycolytic enzymes ?

Answer 24

Lactate—>pyruvate: lactate dehydrogenase
Alanine—->pyruvate: alanine aminotransferase
Glycerol3P—->DHAP: G3P dehydrogenase

Question 25

Which mitochondrial enzyme is activated by acetyl CoA ?

Answer 25

Pyruvate carboxylase

*pyruvate will be shunted through PC to generate more glucose

Question 26

Phosphoenolpyruvate carboxykinase (induced by cortisol & glucagon) works w/ pyruvate carboxylase to do what ?

Answer 26

Convert pyruvate back into phosphoenolpyruvate (PEP)

Question 27

What is the rate limiting enzyme of gluconeogenesis ?

Answer 27

F1,6BP

*Reverses action of PFK-1

Question 28

Where does the pentose phosphate pathway (hexose monophosphate shunt) occur, & what are its 2 main functions ?

Answer 28

• Occurs in cytoplasm

- Produces NADPH & serves as a source of ribose-5-phosphate for nucleotide synthesis

Question 29

The 2st pathway pf PPP that produces NADPH utilizes which rate limiting enzyme ?

Answer 29

G6P dehydrogenase

Question 30

What is the difference between NAD+ & NADPH ?

Answer 30

NAD+ is an e- acceptor that serves as an oxidizing agent that is reduced to NADH which is used in the electron transport chain to generate ATP
NADPH is an e- donor that serves as an reducing agent that is oxidized to NADP+

Question 31

Why do the cells require NADPH?

Answer 31

• Biosynthesis (fatty acids & cholesterol)
• Maintenance of reduced glutathione to protect against reactive O2 species
• Contributing to bactericidal activity

Question 32

Which reducing agent aids in reversing radical formation of O2 before damage is done to the cell ?

Answer 32

Glutathione