SEMINAR WEEK 4

Question 1

How is glucose transported into the cells?

Answer 1

FACILITATED DIFFUSION:
- extracellular glucose binds to transporter–>alter conformation–>facilitated diffusion
- glu concentration gradient
- Glu transporters 1–>5 (tissue speciifc expression)
- 1=ery (most tissues)
- 4= muscle , adipose

COTRANSPORT- sodium and atp dependent
- happens in spithelial cells of intestine, renal tubules, choroid plexus
- energy requiring: glucose again conc gradient
- NA down electrochemical gradient
- rquires uptake of NA+ the tranportter is a sodium dependnet glucose cotransporter

Question 2

first regulatory enzyme in glycolysis

Answer 2

HEXOKINASE/GLUCOKINASE

• glu phsophorylation–>glu-6-phos

hexokinase:’
- regulatory
- all tissues not liver
- broad specificity-several hexoses
- inhibited by glu-6-p and high ration of atp/adp
- low Km–>lower glu lvl

glucokinase:
- liver and B cells of the pancreas
- not inhibited by glu-6-p

Question 3

second regulatory enzyme in glycolysis:

Answer 3

PHOSPHOFRUCTOKINASE 1

fru-6-p–>fru-1,6-bis-p

• most imp regulatory step
  Regulation
• high atp and citrate->inhibition
• low amp->activation
  regulaiton by fru-2,6-bis-p
• acitvat pfk 1
• inhibit fru-1,6-bisphosphatase (neogenesis)

Question 4

what do we get form the second phase

Answer 4

4, atp, 2 nadh, 2 pyruvates (3C) molecules from one glu (6C)

Question 5

third regulatory enzyme of glycolysis

Answer 5

PYRUVATE KINASE
phosphoenolpyruvtae->pyruvate

feed forwrads, regualtion:
liver–>fru-1,6,bis-P activate PK- (not in muscles)

covalent modification:
- phosphorylation->cAMP dependent protein kinase
high glucagon->high camp–>phosphorylation of PK->inactibe
-dephosphorylation: phosphatase->Pk acitve -insulin

Question 6

Conversion of pyruvate to lactate

Answer 6

• anaerobic glycolysis
• reduction to lacate is major fate for pyruvate in tissues poorly vascularized: lens, cornea, kidney medulla, or in RBC that lacks mitochondria

FORMATION IN muscles
excersizing skeletal muscle, NADH prduction(by glyceraldehyde-3-p DH)–>exceed oxidative capacity of the ETC.–>elevated NADH/NAD+ratio favouring the reduction of pyruvate to lactate.
When intense ecxersice–> lactate accumulates in muscle–>drop in intracellular ph–>cramp. Much if this lactate diffuses into bloodstream and can be used by liver to make glucose

LACTATE CONSUPMTION/UTILIZATION

2. Lac consumption – alternative metabolic substrate for heart
   - LD metabolic function
   liver: a) Lac → Pyr → Glu (gluconeogenesis) (high in low Glu)
   b) Lac → Pyr → Krebs cycle (low)

myocard: Lac → Pyr → Krebs cycle (alternative source of energy)
heart: lactate–>carbondioxide and water via the TCA cycle

-

Question 7

energetic yield of glycolysis: anaerobic

Answer 7

1. Anaerobic glycolysis
   Glu + 2 Pi + 2 ADP → 2 Lac´ + 2 ATP + 2H2O

a) ATP production
- 2 molecules ATP on 1 molecule of Glu
- small energetic yield
- cells and tissues without or very limited amount of MIT → Ery, Leu, kidney medulla

b) NADH production
- no net NADH yield
- 1x NADH + (glyceraldehydedehydrogenase) - production
- 1x NADH – (lactate dehydrogenase) - consumptio

Question 8

energetic yield of glycolysis: aerobic

Answer 8

2. Aerobic glycolysis
   Glu + 2 Pi + 2 NAD+ + 2 ADP → 2 Pyr´ + 2 ATP + 2 NADH + 2 H+ + 2 H2O

• 2 ATP consumption (phosphorylation in the first phase of glycolysis)
• 4 ATP production (2 ATP per one triose)
• net yield = 2 ATP
• 2 x NADH → 2,5 ATP per one NADH
  Comparison of the yield
  from Glu after lactic acid production:
  glycolysis: 2 ATP (substrate level)
  Glu oxidation to CO2 and H2O in aerobic conditions:
  glycolysis + citrate cycle + terminal oxidation: 30- 32 ATP !!!
  Main pathway for energy production- brain, muscle, heart, kidney!!!

Question 9

glycolysis reg

Answer 9

1. short-term (min or hrs)
   - allosteric activation/inhibition
   - phosphorylation/dephosphorylation
2. long-term (hrs – days)
   - hormones (insulin+ , glucagon - )
   - 10 – 20 x increase of the enzymatic activity
3. regulatory enzymes
   a/ hexo/glucokinase
   b/ phosphofructokinase 1
   c/ pyruvate kinase

Question 10

what is lactic acidosis

Answer 10

increase of NADH/NAD+ ratio->inhibition of pyruvate DH

Question 11

where does gluconeogenesis happen

Answer 11

as the brain, erythrocytes, kidney medulla, lens
and cornea of the eye, testes, and exercising skeletal muscle,
require a continuous supply of glucose as a metabolic fuel.

Question 12

gluconeogenic precursors

Answer 12

Precursors
1. Lactate (anaerobic glycolysis, RBC, muscle):

2. aminoacids (muscle proteins,
   or glutamin): hydrolysis by tissue protein, major source of glucose during fast. metabolism generate a-keto acids like pyruvate thats converted to glucose, or a-ketoglutarate that enter TCA and forom oxoloacetat for PEP
3. glycerol (adipose): form hydrolysis of TAG and delivered by blood to liver.

Question 13

first regulatory enzyme of gluconeogenesis

Answer 13

PYRUVATE KINASE: PEP->PYR

Question 14

second regulatory enzyem in glyconeogenesis

Answer 14

dephos of fru-1,6 bis-p

• regulatory step:
  a) cell energetic status ↓ AMP+; ↑ATP+
  ↑ AMP

b) regulation by Fru-2,6-bisphosphate
- allosteric inhibition of fructose 1,6-bisphosphatase

Question 15

3rd regulatory enzyme in glconeogenesis

Answer 15

dephos of glu-6-p

All enzymes are exclusively localized:
Liver (90%), kidney medulla (10%)
Intestinal mucosa (10% !!!

Question 16

substrates for gluconeogenesis

Answer 16

Substrates for gluconeogenesis:
1. lactate- immediate substrate
Cori cycle – Glu (liver) → blood → exercising muscle, RBC → lactate
(blood) → liver (gluconeogenesis)

2. Amino acids and α-ketoacids from muscle proteins send as ALANINE
   - Glu-Ala cycle:- starvation- glucagon
   i)Glucogenic AA – Ala, Ser, Gly, Cys, Thr (pyruvate);
   Asp (oxalacetate); Glu (alfa-ketoglutarate)
   ii) pyruvate, oxalacetate, alfa-ketoglutarate
3. glycerol- prolonged starvation – degradation of adipose in conn. tiss.
   - product of lipolysis (TAG) in the adipose tissue by Hormone sens. lipase
   - transport into the liver- cortisol
   - phosphorylation → glycerol-P (oxidation) → dihydroxyacetone-P

Question 17

regulation of gluconeogenesis

Answer 17

Regulation of gluconeogenesis:
➢ simultaneous inhibition of enzymes of
glycolysis and activation of gluconeogenesis!
1. Pyruvate → PEP
Fosfoenolpyruvatecarboxykinase
- Induction (glukagon, adrenalin, cortisol)
- inhibition (insulin)
2. Fructose-1,6-P → Fructose-6-P
Fructose-1,6-bisphosphatase – inhibition
(fructose-2,6-P)
3. Glucose-6-P → Glucose
Glucose -6-phosfatase – induction by fastin

Question 18

cori cycle

Answer 18

The Cori cycle, also known as the lactic acid cycle, is a metabolic pathway that describes the interconversion of glucose and lactate between tissues, particularly between muscle and liver. It plays a crucial role in maintaining blood glucose levels and recycling lactate produced by muscles during anaerobic glycolysis.

The Cori cycle allows for the conversion of lactate produced in muscles under conditions of high energy demand or oxygen shortage (anaerobic conditions) back into glucose in the liver. This glucose can then be released into the bloodstream to supply energy to other tissues, including muscles, where it can be utilized during subsequent physical activity. The cycle helps in the maintenance of blood glucose levels and contributes to the efficient utilization of lactate as an energy source, preventing the buildup of excess lactate in the body.

Question 19

glucose-alanine cycle

Answer 19

Glucose – alanine cycle
- anaerobic glycolysis → lactate and alanine, later muscle proteolysis (cortisol)
- blood: alanine is transfered to the liver
- liver: a/ ammonia is released → converted to urea- excretion via kidneys
b/ pyruvate → gluconeogenesis → glucose
- less productive process than the Cori cycle
- Side product - urea
- removal of the urea is energy-dependent → total ATP production is lower!!

Question 20

regulation of gluconeogenesis

Answer 20

Regulation of gluconeogenesis
* Glucagon – stimulation of gluconeogenesis
a) decreases level of Fru-1,6-bisphosphate which leads to
→ activation of fructose 1,6-bisphosphatase (gluconeogenesis)
→ inhibition of phosphofructokinase 1 (glycolysis)
b) covalent modification of the enzymatic activity
- ↑ cAMP → active protein kinase A → inactive pyruvate kinase (P)
=> phosphoenolpyruvate accumulation
* Cortisol-stimulation of muscle proteolysis- sarcopenia
+cachexia
* Cortisol stimulated of adipose TAG hydrolysis- cachexia
* Substrate availability
↓ insulin → mobilization of proteins → glucogenic AA
* Allosteric activation by acetyl-CoA
↑ acetyl-CoA → stimulation of pyruvate carboxylase during prolonged
starvation (liver