Lessons 9, 10, and 11 - glycolysis and gluconeogenesis

Question 1

describe stage 1 of glycolysis

Answer 1

stage 1 is the trapping and preparation phase. no ATP is generated. it begins with conversion of glucose into fructose 1,6 - biphosphate

Question 2

what is the strategy of the initial steps of glycolysis

Answer 2

to trap the glucose in the cell and form a compound that can be readily cleaved into phosphorylated three-carbon units.

Question 3

when is stage 1 completed

Answer 3

with the cleavage of fructose 1,6-biphosphate

Question 4

what is a reversible reaction

Answer 4

in a reversible reaction all reagents and products are always the same

Question 5

what is an irreversible reaction

Answer 5

some (but not all) of the products may still be converted into reagents through an alternative path

Question 6

what are committed steps

Answer 6

they’re irreversible reactions in which none of the products may be converted to reagents

Question 7

what is the importance of metabolically irreversible reactions

Answer 7

these reactions are always points of regulation in all metabolic pathways. since they are irreversible, blocking or activating them only affects a pathway in one direction, leaving the opposing pathway unaffected

Question 8

what does glycolysis do

Answer 8

it converts 1 glucose into 2 pyruvate molecules. pyruvate can be further metabolized to: lactate or ethanol (anaerobic) or acetyl CoA (aerobic). acetyl CoA is further oxidized to CO2 and H2O via the citric acid cycle

Question 9

what is the net reaction of glycolysis

Answer 9

2 ATP are produced and 2 NAD+ are reduced to NADH

Question 10

what doe hexokinase do in glycolysis

Answer 10

it phosphorylates glucose to make glucose 6-phosphate

Question 11

what does phosphoglucose isomerase do in glycolysis

Answer 11

isomerizes glucose 6-phosphate into fructose 6-phosphate

Question 12

what does phosphofructokinase do in glycolysis

Answer 12

phosphorylates fructose 6-phosphate to form fructose 1,6-biphosphate

Question 13

what does aldolase do

Answer 13

transforms fructose 1,6 biphosphate into glyceraldehyde 3-phosphate.

Question 14

what does triose phosphate isomerase do

Answer 14

isomerizes between dihydroxyacetone phosphate and glyceraldehyde 3-phosphate as dihydroxyacetone phosphate isn’t on the main glycolysis pathway

Question 15

what does glyceraldehyde 3-phosphate dehydrogenase do

Answer 15

converts glyceraldehye 3-phosphate into 1,3 biphosphoglycerate while reducing NAD+ to NADH

Question 16

what does phosphoglycerate kinase do

Answer 16

converts 1,3 -biphosphoglycerate into 3-phosphoglycerate and creates 1 ATP

Question 17

what does phosphoglycerate mutase do

Answer 17

converts 3-phosphoglycerate into 2-phosphoglycerate

Question 18

what does enolase do

Answer 18

converts 2-phosphoglycerate into phosphoenolpyruvate and discards an H2O

Question 19

what does pyruvate kinase do

Answer 19

converts phosphoenolpyruvate into pyruvate and creates 1 ATP

Question 20

what happens when pyruvate is metabolized into lactate

Answer 20

NADH is oxidized to NAD+

Question 21

what happens when pyruvate is metabolized to acetyl CoA

Answer 21

CO2 is created and Acetyl CoA goes onto further oxidation

Question 22

what happens when pyruvate is metabolized to acetalaldehyde

Answer 22

CO2 is produced and the NADH is oxidized to NAD+ to form ethanol

Question 23

what does pyruvate decarboxylase do

Answer 23

converts pyruvate to acetaldehyde (producing CO2)

Question 24

what does alcohol dehydrogenase do

Answer 24

converts acetalaldehyde to ethanol (oxidizing NADH)

Question 25

what does lactate dehydrogenase do

Answer 25

converts pyruvate to lactate (oxidizing NADH)

Question 26

in anaerobic metabolism where is the NADH obtained to keep on converting pyruvate into lactate

Answer 26

from the conversion of glyceraldehyde phosphate into 1,3 biphosphoglycerate

Question 27

describe fructose being converted into the usable glyceraldehyde 3-phosphate

Answer 27

fructokinase turns fructose into fructose 1-phosphate, then fructose 1-phosphate aldolase converts it into glyceraldehyde + dihydroxyacetone phosphate. the glyceraldehyde is turned into glyceraldehyde 3-phosphate by triose kinase

Question 28

what does galactokinase do

Answer 28

converts galactose into galactose 1-phosphate

Question 29

describe process of going from galactose 1-phosphate to glucose 1-phosphate

Answer 29

galactose 1-phosphate uridyl transferase adds a uridine group to it, this allows glucose 1-phosphate to be formed. the leftover UDP-galactose is catalyzed by UDP-galactose 4-epimerase to create a UDP-glucose which is what originally provided the uridine group to galactose 1-phosphate

Question 30

what does lactase do

Answer 30

splits lactose into galactose and glucose

Question 31

what does aldose reductase do

Answer 31

converts galactose to galacitol by oxidizing NADPH to NADP+

Question 32

how does PFK regulate glycolysis

Answer 32

at rest there are high levels of ATP. ATP inhibits phosphofructokinase and pyruvate kinase, while glucose 6-phosphate inhibits hexokinase. glucose 6-phosphate is then converted into glycogen. during exercise the decrease in ATP/AMP ratio resulting from muscle contractions activates PFK and hence glycolysis.

Question 33

how is PFK-1 in liver additionally regulated

Answer 33

fructose 2,6 BP produced by PFK-2 activates PFK, once PFK is activated glycolysis is stimulated and more ATP is produced (and less fructose 6-phosphate)

Question 34

describe glucokinase vs. hexokinase

Answer 34

Km for glucose in glucokinase = 10mM. Km for glucose in hexokinase = 10mM physiological [glucose] = 5mM

Question 35

describe control of catalytic activity of pyruvate kinase

Answer 35

pyruvate kinase is regulated by allosteric effectors and covalent modification. fructose 1,6 bp allosterically stimulates the enzyme, while ATP and alanine (in liver) are allosteric inhibitors. Glucagon, secreted inresponse to low blood glucose, promotes phosphorylation and inhibition of the enzyme. when blood-glucose levels are adequate, the enzyme is dephosphorylated and activated

Question 36

describe gluconeogenesis

Answer 36

happens mostly in liver and also in kidney. the substrates are glycerol, pyruvate, lactate and amino acids. it happens in prolonged fasting and starvation. stimulated by PKA (epinephrine/glucagon) and glucocorticoids

Question 37

what does pyruvate carboxylase do

Answer 37

converts pyruvate into oxaloacetate (using 1 ATP) during gluconeogenesis

Question 38

what does phosphoenolpyruvate carboxykinase do

Answer 38

converts oxaloacetate into phosphenolpyruvate (using 1 GTP)

Question 39

where are the enzymes for gluconeogeneis found

Answer 39

all are found in the cytoplasm except for pyruvate carboxylase (in the mitochondria) and glucose 6-phosphatase (membrane bound in the endoplasmic reticulum)

Question 40

where does glycerol enter gluconeogenesis

Answer 40

it becomes dihidroxyacetone phosphate

Question 41

where do lactate and amino acids enter gluconeogenesis

Answer 41

lactate and some amino acids enter by becoming pyruvate while some other amino acids enter by becoming oxaloacetate

Question 42

what does fructose 1,6 biphosphatase do

Answer 42

converts fructose 1,6 bp into fructose 6-phosphate

Question 43

what does glucose 6-phosphatase do

Answer 43

converts glucose 6-phosphate into glucose

Question 44

what stimulates and what inhibits PFK

Answer 44

fructose 2,6 bp and AMP stimulate while ATP, Citrate, and H+ inhibit

Question 45

what stimulates and inhibits pyruvate kinase

Answer 45

fructose 1,6 bp stimulates while ATP and alanine inhibit

Question 46

what stimulates and inhibits fructose 1,6 biphosphatase

Answer 46

citrate stimulates while AMP and fructose 2,6 bp inhibit

Question 47

what stimulates and inhibits pyruvate carboxylase

Answer 47

acetyl CoA stimulates while ADP inhibits.

Question 48

what inhibits phosphoenolpyruvate carboxykinase

Answer 48

ADP inhibits it