3_CHO_Metabolism.pdf for a nursing student

Biochemistry and nutrition nursing lecture

1. Field of Nursing
Nursing Program
Lecture : CHO metabolism
Date :23/2/2025Dr : HidiAzmy El Tahawy

2. Introduction to Metabolism
Carbohydrates Metabolism

3. Objectives:
By the end of this lecture, the student will be able to:
1.Overview the different concepts of metabolism.
2.Recognize the metabolic pathways of glucose formation and
degradation.
3.Identify the process of glycogen synthesis and breakdown
4.Define gluconeogenesis and recognize its importance.

4. General Concepts of Metabolism
•All the chemical reactions that take place
inside of a cell are collectively called the
cell’s metabolism.
•Metabolic pathways can be divided into two
categories based on their effects:
1.Pathways in which a macromolecule is
formed from smaller molecules " Anabolic”
pathway.
2.Pathways in which macromolecules are
broken into smaller molecules “Catabolic”
pathway.

5. General Concepts of metabolism
Fuel Metabolism.
Source of fuel: carbohydrates, fats, and proteins in
diet.
Foodstuffs are digested and absorbed. The products
of digestion (glucose, Fatty acids, amino acids) are
taken up by the cells to produce energy .
The three stages of the conversion of food into cellular
energy in the form of ATP:
1) hydrolysis of macromolecules, 2) conversion to
acetyl CoA (CH3CO~SCOA), 3) oxidation of acetyl CoA
in citric acid cycle and ATP generation in the electron
transport chain (in mitochondria).

6. 1. General Concepts of metabolism
Oxidative Phosphorylation:
The electrons carried by NADH+H
+ can be used to
produce 2.5 ATP molecules, and those carried by
FADH2 can be used to produce 1.5 ATP molecules in
a series of reactions called oxidative
phosphorylation.

7. Carbohydrate metabolism
Digestion of Carbohydrates:
•In the mouth
Starch Dextrin + Maltose
Digestion of Carbohydrates:
•In the small intestines
maltose + isomaltose
2 glucose
glucose + galactose
glucose + fructose
Starch
Maltose
Lactose
Sucrose
•End Products:
➢glucose, galactose & fructose

8. Carbohydrate metabolism
Fate of absorbed glucose:
1.Uptake and oxidation in tissues mainly by glycolysis and krebs cycle
(or Citric acid cycle) to CO2 and H2O with the release of energy
which is stored as ATP.
2.Excess glucose is converted and stored as glycogen by glycogenesis
3.Excess glucose is stored as fat.
•When the liver and muscle glycogen stores are full, any extra
glucose is converted into fat.
4.Synthesis of non-essential amino acids.

9. Carbohydrate metabolism
Products: 2 pyruvate, 4 ATP + 2 NADH + H
+
(each NADH+H
+= 2.5 ATP)
NET ATP gained: 9 gain - 2 lost (in the first 2 steps) = 7 ATP
Glycolysis:
Site : cytosol of all cells
"glycolysis" means breakdown of glucose
➢It is major pathway that oxidizes the six-
carbon atoms of glucose into
i)3 carbon atoms pyruvate under aerobic conditions
OR
ii)3 carbon atoms lactate under anaerobic conditions.

10. Carbohydrate metabolism
Glycolysis (Net gain of ATP):
1.Under aerobic conditions:
Glucose + 2 ATP+ 2 NAD
+ + 4 ADP + 2 Pi →
2 Pyruvate + 2 ADP + 2 NADH + 2 H
+ + 4 ATP + 2 H2O
NET ATP gained: 9 gain - 2 lost= 7 ATP
2. Under anaerobic conditions, NADH + H
+ are re-used to ti
produce lactate.
NET ATP gained: 2 ATP
-O
2 +O
2

11. Carbohydrate metabolism
Importance of Glycolysis:
1)Energy production:
a)under aerobic condition it gives 7 ATP.
b)under anaerobic condition it gives only 2 ATP.
2)It is the only source of energy to RBCs which lack mitochondria.
3)It gives dihydroxy acetone phosphate DHAP which is important for
lipogenesis.
Regulation of Glycolysis :
1)Insulin stimulate glycolysis.
2)Anti insulin (glucagon and adrenaline) & high level of ATP inhibit glycolysis.

12. Carbohydrate metabolism
Hexose Monophosphate Pathway (HMP shunt)
Definition:
➢ It is minor pathway that converts glucose to ribose-5-phosphate with production
of NADPH.
Site:
➢ Cytosol of the liver, adipose tissue, ovaries, testis & RBCs.
Importance:
1)It provides the body with ribose-5-phosphate essential for biosynthesis of
nucleotides and nucleic acids.
2)It is the major source of NADPH required for the reactions of reductases and
hydroxylases as:
a)Glutathione reductase which is important for removal of H
2O
2 that causes damage to cells.
b)Reductases of fatty acid synthesis.
Favism: impaired HMP in the RBCs (--- NADPH) make RBCs liable for lysis under certain
conditions.

13. Carbohydrate metabolism
Glycogen synthesis and breakdown:
Glycogen is the main storage form of carbohydrates
➢if blood sugar rises after a meal, insulin is released from the pancreas which
converts the glucose into glycogen (glycogenesis) in the liver and muscles
➢Glycogenesis is the synthesis of glycogen from glucose.
➢site of glycogenesis in Cytosol of liver and muscles.
Regulation of glycogenesis: Insulin activates glycogenesis in both liver and muscles.
epinephrine decreases the rate of glycogenesis in both liver and muscles.
➢If blood sugar falls during fasting, liver glycogen is converted into glucose which
enters the blood (glycogenolysis).

14. Carbohydrate metabolism
➢Glycogenolysis is the breakdown of glycogen to form glucose
➢site of glycogenolysis in Cytosol of liver and muscles.
The liver glycogen helps keep blood-sugar levels in the normal range.
**Muscle glycogen is only used by the muscle.
Regulation of glycogenolysis: Insulin decreases glycogenolysis in both
liver and muscles. epinephrine activates the rate of glycogenolysis in
both liver and muscles.

15. Carbohydrate metabolism
Gluconeogenesis
Definition:
➢ It is the synthesis of glucose from non-
carbohydrate sources.
Site:
➢ Cytosol of liver and kidney cells.
Gluconeogenic substrates:
➢ They include lactate, glucogenic amino acids
and glycerol
Regulation:
1)Insulin inhibits gluconeogenesis.
2)Anti insulin hormones stimulate
gluconeogenesis

16. Carbohydrate metabolism
Importance of gluconeogenesis:
•Gluconeogenesis maintains blood glucose especially in starvation
(mainly for tissues that depends on glucose as a source of
energy: the brain, RBCs.
•re-synthesis of glucose from lactate is a major route for lactate
disposal
•It removes glycerol produced by lipolysis in adipose tissues.

17. Reference:
– Lippincott's Illustrated Reviews: Biochemistry, 5th Edition. Chapter 6, 8, 9,
10& 11.