Carbohydrates

Question 1

What is the net yield of glycolysis from 1 glucose?

Answer 1

2 pyruvates + 2 ATP + 2 NADH + 2H+

Question 2

What are the 3 fates of pyruvate?

Answer 2

1. Anaerobic (lactic acid fermentation) uses 1 NADH
2. Aerobic oxidation needs NADH, so we gain one
3. Anaerobic (alcoholic fermentation) uses 1 NADH because we don’t need it for the krebs cycle/oxidative phosphorylation

Question 3

Explain the lactic acid fermentation reaction.

Answer 3

Pyruvate is turned into lactate using the enzyme lactate dehydrogenase and NADH.

Question 4

What does the pyruvate dehydrogenase complex do?

Answer 4

Uses pyruvate to gain acetyl coA + NADH + CO2

Question 5

What are the 2 enzymes yeast use to give us alcohol from …?

Answer 5

1. Pyruvate decarboxylase, giving us CO2 and acetaldehyde

2. Alcohol dehydrogenase, using NADH and giving us ethanol

Question 6

What is the anaerobic glycolysis reaction?

Answer 6

Glucose + 2 ADP + 2Pi –> 2 lactate + 2 ATP + 2H2O

Question 7

What is the first enzyme in glycolysis, and what regulates it?

Answer 7

1. Hexokinase is for extrahepatic cells, and glucokinase is for liver cells.
2. Insulin (+ activates)
3. Glucose 6-P (- inhibits)

Question 8

What is the difference between PFK-1 and PFK-2?

Answer 8

Phosphofructokinases work on fructose 6-P.
PFK-1 results in Fructose 1,6-BP

PFK-2 results in F-2,6-BP

Question 9

What is the rate limiting step in glycolysis?

Answer 9

PFK-1

from F 6-P to F 1,6-P

Question 10

What regulates the rate limiting step in glycolysis?

Answer 10

ATP, citrate and H+ inhibits it.

F 2,6-P, AMP and ADP activate it.

Question 11

Write the last chemical reaction in glycolysis.

Answer 11

Phosphoenolpyruvate -PK-> pyruvate

PK = pyruvate kinase

Question 12

What regulates Pyruvate Kinase?

Answer 12

ATP, acetyl coA and alanine inhibit PK.

Insulin, AMP, F-1,6-P activate it.

Question 13

Which reactions in glycolysis are irreversible using the same enzymes?

Answer 13

1. hexokinase/glucokinase
2. PFK
3. PK (which is why we gain fat, as acetyl coA is eventually converted into fatty acids and choelsterols)

Question 14

What enzymes use the same coenzymes as pyruvate dehydrogenase complex (oxidative decarboxylation)?

Answer 14

1. alpha-ketoglutarate complex

2. Branched-chain alpha-keto acid dehydrogenase complex

Question 15

What are the coenzymes the pyruvate dehydrogenase complex uses?

Answer 15

thiamine pyrophosphate (TPP) from thiamine (B1)

FAD from riboflavin (B2)

NAD+ from niacin (B3)

lipoic acid

coenzyme A

Question 16

Which enzymes have TPP as a coenzyme?

Answer 16

pyruvate dehydrogenase complex

transketolase

2-hydroxyphytanoyl-coA lyase

Question 17

PDHc or pyruvate dehydrogenase complex is acitvated by … and deactivated by …

Answer 17

PDHc or pyruvate dehydrogenase complex is acitvated by PDH phosphatase and deactivated by PDH kinase.

active form is dephosphorylated

Question 18

Which enzymes in the Krebs cycle contribute to NADH or FADH2 production?

Answer 18

OxCxI K SxS FxM F
between I K: isocitrate dehydrogenase
between K S: 
alpha-ketoglutarate dehydrogenase c.
between S F: succinate dehydrogenase makes FADH2
between M O: malate dehydrogenase

Question 19

Succinyl-coA synthase

Answer 19

succinyl-coA + GDP +H2O –> succinate + GTP + HS-CoA

Question 20

What is the net output of krebs cycle?

Answer 20

With 1 pyruvate, we gain

1 GTP
2 CO2
1 FADH2
3 NADH + H+

Question 21

What can citrate be turned into?

Answer 21

OAA

Acetyl coA

Question 22

succinyl coA can be used to

Answer 22

synthesize heme and hemoglobin

Question 23

Explain NADH in the electron transport chain

Answer 23

NADH electron moves from
I -> III -> IV
gets us 3 H+ in the intermembrane space, 3 ATP

Question 24

Explain FADH2 path in electron transport chain

Answer 24

II -> III -> IV
gets us 2 H+ (complex II doesn’t move H+ into the intermembrane space)
2 ATP

Question 25

What is the net ATP yield from substrate level phosphorylation from 1 glucose?

Answer 25

2 ATP from glycolysis

2 ATP from the Krebs cycle

Question 26

What is the difference between the malate-aspartate shuttle and the glycerol-3-phosphate shuttle?

Answer 26

The malate-aspartate shuttle gives us NADH. its intermediate is OAA.

the glycerol-3-P shuttle gives us FADH2. It has no intermediates, shuttles between Glycerol-6-P and DHAP

Question 27

What is the different reactions in gluconeogenesis versus glycolysis?

Answer 27

1. in gluconeogenesis, pyruvate carboxylase is used (1 ATP required) to turn pyruvate into OAA, before going back to PEP using PEP carboxykinase (1 GTP required).
2. FBP –> F6P using FBP phosphatase (no ATP required)
3. G6P –> glucose using glucose-6-phosphatase (no ATP required)

Question 28

Where does biotin fit in this?

Answer 28

biotin helps pyruvate carboxylase transform pyruvate into OAA

Question 29

What CAN’T be used for gluconeogenesis?

Answer 29

acetyl coA

the muscles don’t have glucose-6-phosphatase

Question 30

Which step does glucagon, epinephrine and cortisol stimulate in glycolysis?

Answer 30

OAA –> PEP (using PEP carboxykinase)

Question 31

What is the Cori cycle?

Answer 31

1. The muscles undergo anaerobic glycolysis
2. Lactate is moved to the liver
3. The liver converts lactate back to glucose using 4 ATP + 2 GTP.

This entire process has a net yield of 0 NADH, - 2 ATP, and -2 GTP.

Question 32

How long do we subsist on extragenous glucose?

Answer 32

4 hours

Question 33

How long can we fast before using up our glycogen stores?

Answer 33

2 days

Question 34

When does gluconeogenesis start?

Answer 34

gluconeogenesis happens whenever the liver detects that blood glucose is low. 4 hours after a meal.

Question 35

Other than the liver, which organ can contribute to gluconeogenesis?

Answer 35

the kidneys