2012-11-26 1&2: Intro to Carbs; Glycolysis in RBCs

Question 1

What f(x)s do carbs serve?

Answer 1

1) metab fuel, 2) protein components, 3) RNA/DNA components, 4) structure in plants, 4)

Question 2

Which form of glucose is transported in the blood?

Answer 2

99% is cyclized; alpha-D-glucose is major (2/3) form

Question 3

Is it glucose and oxidizing or reducing sugar? When is this important? What would the metab product be useful for?

Answer 3

it is a reducing sugar (i.e. it reduces other things will becoming OXIDATED itself); makes glucuronic acid which detoxifies things like heme by conjugating them

Question 4

How does hyperglycemia cause neuro- and retin-opathy?

Answer 4

1. Glucose—aldose reductase—>sorbitol
2. lens, retina, kidney and nerve cells lack sorbitol DH
3. sorbitol builds up—>cataracts, periph neurop, retinop, nephrop

Question 5

Which of the following is NOT true regarding glucose?

a. It spontaneously forms a cyclic, hemiacetal in solution.
b. It is a diastereoisomer of ribulose.
c. It is the form in which carbohydrate is transported from the liver to skeletal muscle.
d. It reacts chemically to form a covalent bond! with hemoglogin.

Answer 5

B

Question 6

What can glucose be metabolized to in humans?

Answer 6

lactate, CO2, pentoses or glycogen

Question 7

What does the heart do with lactate?

Answer 7

sends it thru CAC to make ATP

Question 8

What does liver do with lactate?

Answer 8

converts it to glucose via gluconeogenesis

Question 9

What is made with the pentose phosphate pathway?

Answer 9

pentoses, NADPH, and ATP

Question 10

Where does pentose phosphate pathway occur?

Answer 10

in RBCs

Question 11

Which pathway(s) of glucose metab is(are) anaerobic?

Answer 11

glycolysis and pentose phosphate pathway

Question 12

How can RBCs use glucose

Answer 12

glycolysis and pentose phosphate pathway ONLY

Question 13

How and where do we make fructose?

Answer 13

glucose—reduced to alcohol—>sorbitol—oxidized—>fructose; occurs in seminal vesicles and liver

Question 14

How is HbA1c formed?

Answer 14

glucose slowly reacts with NH2 groups on Hb

Question 15

GAGs vs. proteoglycans

Answer 15

GAGs = glycosaminoglycans = polysaccs w/ carboxy, amino and sulfate groups (e.g. chondroitin, heparin, hyaluronic acid, keratan sulfate)

proteoglycans are proteins with GAGs added onto them; form joint lubes and c.t.

Question 16

Which glycosidic linkages can humans digest? Not?

Answer 16

We can: α-1,4 glycosidic bond

We can’t digest: ß-1,4, glycosidic bonds (e.g. cellulose)

Question 17

What is the first step glucose undergoes upon entering the cell?

Answer 17

glucose—>G6P

Question 18

What is the next step for G6P headed to glycolysis?

Answer 18

G6P—>F6P

Question 19

What is the next step for G6P headed to glycogen synthesis?

Answer 19

G6P—>G1P

Question 20

What is the next step for G6P headed to pentose phosphate pathway?

Answer 20

6-phosphogluconate

Question 21

Why phosphorylate glucose?

Answer 21

Phosphorylation of glucose lowers its intracellular concentration and promotes glucose influx.

Question 22

Why do RBCs need ATP?

Answer 22

to maintain membrane potential w/ Na/K ATPase

Question 23

How many ATP/glucose in glycolysis?

Answer 23

2

Question 24

Which enzymes regulate glycolysis?

Answer 24

hexokinase, phosphofructokinase-1 and pyruvate kinase

Question 25

What is the overall formula for anaerobic glycolysis in an RBC?

Answer 25

glucose + 2 ADP + 2Pi —> 2 lactate + 2 ATP

Question 26

Where is glucokinase present?

Answer 26

liver and pancreas

Question 27

Which has a higher Km, glucokinase or hexokinase? What does that mean?

Answer 27

Glucose kinase's Km (10mM) is 100X higher than hexokinase; allows pancreatic ß cells to sense glucose amt AND high vMax allows it to allow liver to take up high amts of blood glucose

Question 28

What inhibits hexokinase?

Answer 28

G6P

Question 29

Draw glycolysis with important enzymes!

Answer 29

1. glucose—gluco-/hexo-kinase—>G6P 2. G-6-P—>F-6-P 3. F-6-P—PFK-1—>F-1,6-BP 4. F-1,6-BP—>G3P (and DHAP) 5. G3P—>1,3-BPG 6. 1,3,-BPG—>2-PG 7. 2-PG—>3-PG 8. 3-PG—>PEP 9. PEP—>pyruvate kinase—>pyruvate 10. pyruvate—LHD—>lactate

Question 30

What regulates PFK-1?

Answer 30

stimulated by: AMP, ADP, and F-2,6-BP | inhibited by: ATP, citrate

Question 31

What regulates pyruvate kinase?

Answer 31

inhibited by: glucagon, ATP

Question 32

How is glucokinase regulated?

Answer 32

It's not? at least it's not inhibited by G6P like hexokinase is

Question 33

What are the steps involved in insulin secretion?

Answer 33

1. Glucose enters pancreatic ß cell via GLUT-2 2. gluc—glucokinase—>G6P 3. resultant higher ATP closes ATP-sensitive K+ channel 4. K+ can no longer leak out, and the resulting depolarization opens Ca2+ channel 5. incr intracell Ca causes exocytosis of insulin granules

Question 34

Which steps of glycolysis are NOT reversible?

Answer 34

1. glucose—gluco- or hexo-kinase—>G6P 2. F6P—PFK-1—>F1,6BP 3. PEP—pyruvate kinase—>pyruvate (i. e. the steps w/ the important enzymes)

Question 35

What is the deal w/ PFK-2?

Answer 35

PFK-2 is bifunctional with kinase and phosphatase sides kinase side does: F6P—>F-2,6-BP F-2,6-P activates PFK-1 inhibited by glucagon (via cAMP via PKA)

Question 36

How does arsenic poisoning inhibit glycolysis?

Answer 36

arsenate subs for phosphate in G3P—>1,3-BPG

Question 37

Where/how much ATP is req'd in glyoclysis?

Answer 37

Two total: - 1 by the hexokinase rxn - 1 by F-6-P—>F-1,6-P

Question 38

What is 2,3-BPG?

Answer 38

made from 1,3-BPG decr o2 affinity of hemoglobin

Question 39

What are the isozymes of LDH?

Answer 39

- LDH is tetramer - h4 in heart: lactate—>pyruvate - m4 in SKM & liver: pyruvate—>lactate

Question 40

High plasma [H4-LDH] is indicative of what pathology?

Answer 40

acute M.I. (recall that H4 is heart-specific isozyme)

Question 41

In the conversion of glucose to lactate by glycolysis, how many of the enzymes involved exist as different “isozymes” in different tissues? 1, 2, 3 or 4?

Answer 41

3—pyruvate kinase, LDH and hexo-/gluco-kinase

Question 42

Why bother making lactate?

Answer 42

need to oxidize NADH—> to NAD+