1. Introduction to Metabolism

2. Objectives Understand the concept of metabolic pathway
Identify types & characters of metabolic pathways- anabolic and catabolic
Identify ATP as the energy currency of cells
Understand the transport of major metabolic fuel- Glucose

3. Metabolism
All the chemical reactions taking place inside a cell are collectively known as METABOLISM

4. Metabolism
Metabolic Pathways are chemical reactions organized in multisteps sequences where:
The product of one reaction of the pathway serves as substrate of the subsequent reaction
Most pathways can be classified as anabolic (synthetic) or catabolic (degenerative)
Integrated pathways= Metabolism

5. Glycolysis, an example of a metabolic pathway

6. Basic functions of metabolism
To obtain energy from fuel molecules
To convert nutrients into precursors of cellular components.
3. To assemble precursors utilizing energy into cellular components.

7. ANABOLIC CATABOLIC Biosynthetic Degradative Reductive Oxidative
large complex organic molecules are constructed from small molecules
Decomposition of large complex molecules into small molecules
Biosynthetic
Degradative
Reductive
Oxidative
Energy Required
Energy Liberated
Diverging
Converging

8. Catabolism
Anabolism
(diverging)
(converging)
Few
Many
Many
Few

9. Catabolic Pathway

10. Anabolic Pathway Combine small moles as a.a. to form complex as ptn
It is a divergent process w needs ATP (endergonic) & reducing power (mostly NADPH)

11. Catabolism(oxidative, exergonic) Anabolism (reductive, endergonic)
Macromolecules
Proteins
Polysaccharides
Lipids
Nucleic acids
Nutrients
Carbohydrates
Fats
Proteins
GTP
ATP
NADPH
Catabolism(oxidative, exergonic)
Anabolism (reductive, endergonic)
NADPH
Chemical energy
NADPH
NADH
ATP
ATP
Precursor Molecules
Amino acids
Sugars
Fatty acids
Nitrogenous bases
End products
H2O, CO2, NH3
Catabolism and anabolism are always related.

12. Amphibolic Pathway For example,
Amphi = Dual, amphibolic: dual pathway
For example,
Krebs cycle is mainly a catabolic cycle, but with some anabolic features,
e.g., part of Krebs cycle is used for the synthesis of glucose from amino acids
Therefore, Krebs cycle is amphibolic 12

13. Metabolic Map
Different pathways can intersect, forming an integrated and purposeful network of chemical reactions “The Metabolic Map”

15. Chemical energy
ATP - energy currency. It serves as the driving force for nearly all biochemical processes
NADH,NADPH - reducing power.
NADH for oxidation and energy yielding.
NADPH for biosynthetic processes

16. ATP is the energy currency of the cell
ATP + H2O ADP +Pi
The free energy liberated in the hydrolysis of ATP is used to drive the endergonic reactions
ATP is formed from ADP and Pi when fuel molecules are oxidized
This ATP-ADP cycle is the fundamental mode of energy exchange in biological systems

17. Adenosine Triphosphate (ATP)
Δ Gº -7.3 kcal/mol/bond

18. Oxidation-Reduction in Metabolism
E-rich compounds e.g.,
E-rich
reduced coenzymes
Oxidation
ETC 18

19. Oxidation/Reduction Oxidation: Loss of hydrogen Loss of electrons
Gain of hydrogen
Gain of electrons

20. NAD/NADH

21. Metabolism Regulation

22. Intracellular Regulation
Imp. for moment-to-moment regulation of metabolism which elicit rapid responses by:
availability of substrate
product inhibition or
alteration in the levels of allosteric activators or inhibitors

23. Intercellular Regulation
Provides long-range integration of metabolism
Usually is slower than intracellular signals, it is done by : surface to surface
the most important is
chemical signaling by hormones or neurotransmitters
This results in the production of second messengers

24. Metabolic Fuel
Carbohydrates & lipids (mainly) and proteins (little extent) are used for energy production
These are- glucose, fatty acids and amino acids
Glucose is the major metabolic fuel of most tissues

25. Glucose Transport Na+-Monosaccharide Cotransporter:
Against concentration gradient
Energy dependent
Carrier-mediated
Coupled to Na+ transport
Small intestine, renal tubules & choroid plexus
Na+-Independent Facilitated Diffusion:
With concentration gradient
Energy Independent
Glucose Transporters (GLUT 1-14)

26. Glucose Transport: Facilitated Diffusion

27. Glucose Transporters Tissue-specific expression pattern
GLUT-1 RBCs and brain
GLUT-2 Liver, kidney & pancreas
GLUT-3 Neurons
GLUT-4 Adipose tissue & skeletal muscle
GLUT-5 Small intestine & testes
GLUT-7 Liver (ER-membrane)
Functions:
GLUT-1, 3 & 4 Glucose uptake from blood
GLUT-2 Blood & cells (either direction)
GLUT-5 Fructose transport

28. Take Home Message
Metabolism is the sum of all biochemical pathways that occur inside the cells.
A metabolic pathway is a multistep sequences of enzyme-catalyzed reactions.

29. Catabolism is a convergent process that provides energy to cells in the form of ATP.
Anabolism is a divergent process that consumes energy for the synthesis of complex molecules.
Metabolic pathways are tightly regulated and highly integrated.

30. ATP is the energy currency of the cells
Glucose is transported in/out of the cells by:
Energy-dependent active transport
Energy-independent facilitated transport