1. SoS, Dept. of Biology, Lautoka Campus
BIO508 Cell Biology
Slide Design: Copyright © McGraw-Hill Global Education Holdings, LLC.
Lecturer: Dr.Ramesh Subramani
Topic 5: Metabolism

2. The Energy of Life
The living cell is a miniature chemical factory where thousands of reactions occur.
The cell extracts energy and applies energy to perform work.
Some organisms even convert energy to light, as in bioluminescence.

3. Metabolism
An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics.
Metabolism is the totality of an organism’s chemical reactions.
Metabolism is an emergent property of life that arises from interactions between molecules within the cell.
A metabolic pathway begins with a specific molecule and ends with a product
Each step is catalyzed by a specific enzyme
Enzyme 1
Enzyme 2
Enzyme 3 A B C D
Reaction 1
Reaction 2
Reaction 3
Starting molecule
Product

4. Metabolic Pathways
A sequence of chemical reactions, where the product of one reaction serves as a substrate for the next, is called a metabolic pathway or biochemical pathway.
Most metabolic pathways take place in specific regions of the cell.
Two types of metabolic pathway occur in a cell, Catabolic pathway and Anabolic pathway.

5. Metabolic Pathways
Catabolic pathways release energy by breaking down complex molecules into simpler compounds
Cellular respiration, the breakdown of glucose in the presence of oxygen, is an example of a pathway of catabolism
Anabolic pathways consume energy to build complex molecules from simpler ones
The synthesis of protein from amino acids is an example of anabolism
Bioenergetics is the study of how organisms manage their energy resources

6. Energy Energy is the capacity to cause change.
Energy exists in various forms, some of which can perform work.
Kinetic energy is energy associated with motion.
Heat (thermal energy) is kinetic energy associated with random movement of atoms or molecules.
Potential energy is energy that matter possesses because of its location or structure.
Chemical energy is potential energy available for release in a chemical reaction.
Energy can be converted from one form to another.

7. Transformations between potential
A diver has more potential energy on the platform than in the water.
Diving converts potential energy to kinetic energy.
Transformations between potential
and kinetic energy
Climbing up converts the kinetic energy of muscle movement to potential energy.
A diver has less potential energy in the water than on the platform.

8. The Laws of Energy Transformation
Thermodynamics is the study of energy transformations
A closed system, such as that approximated by liquid in a thermos, is isolated from its surroundings
In an open system, energy and matter can be transferred between the system and its surroundings
Organisms are open systems

9. The First Law of Thermodynamics
According to the first law of thermodynamics
Energy cannot be created or destroyed
Energy can be transferred and transformed

10. The Second Law of Thermodynamics
During every energy transfer or transformation, some energy is unusable, and is often lost as heat
According to the second law of thermodynamics
Every energy transfer or transformation increases the entropy (disorder) of the universe

11. Biological Order and Disorder
Cells create ordered structures from less ordered materials
Organisms also replace ordered forms of matter and energy with less ordered forms
The evolution of more complex organisms does not violate the second law of thermodynamics
Entropy (disorder) may decrease in an organism, but the universe’s total entropy increases.

12. Biological Order and Disorder
Living systems
Increase the entropy of the universe
Use energy to maintain order
A living system’s free energy is energy that can do work under cellular conditions
Organisms live at the expense of free energy
50µm

13. Free Energy
Free energy is the portion of a system’s energy that is able to perform work when temperature and pressure is uniform throughout the system, as in a living cell.
Free energy also refers to the amount of energy actually available to break and subsequently form other chemical bonds.
Gibbs’ free energy (G) – in a cell, the amount of energy contained in a molecule’s chemical bonds (T&P constant).
Change in free energy - ΔG
Endergonic - any reaction that requires an input of energy
Exergonic - any reaction that releases free energy

14. Exergonic reaction: energy released
Exergonic reactions
Reactants have more free energy than the products.
Involve a net release of energy and/or an increase in entropy.
Occur spontaneously (without a net input of energy).
Reactants
Products
Energy
Progress of the reaction
Amount of
energy
released (∆G <0)
Free energy
Exergonic reaction: energy released

15. Endergonic reaction: energy required
Endergonic Reactions
Reactants have less free energy than the products.
Involve a net input of energy and/or a decrease in entropy.
Do not occur spontaneously.
Energy
Products
Amount of
energy
released (∆G>0)
Reactants
Progress of the reaction
Free energy
Endergonic reaction: energy required

16. Endergonic Exergonic Product Energy supplied Energy must be supplied.
Reactant
Reactant
Energy is
released.
Energy released
Product
Endergonic
Exergonic
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17. Equilibrium and Metabolism
Reactions in a closed system eventually reach equilibrium and can then do no work
Cells are not in equilibrium; they are open systems experiencing a constant flow of materials
A catabolic pathway in a cell releases free energy in a series of reactions
Closed and open hydroelectric systems can serve as analogies

18. Equilibrium and Metabolism
Reactions in a closed system eventually reach equilibrium.
A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium.
∆G < 0
∆G = 0

19. Equilibrium and Metabolism
Cells in our body experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium.
An open hydroelectric system. Flowing water
keeps driving the generator because intake and outflow of water keep the system from reaching equilibrium.
∆G < 0

20. An Analogy For Cellular Respiration – Glucose Catabolism
A multistep open hydroelectric system. Cellular respiration is analogous to this system: Glucose is broken down in a series of exergonic reactions that power the work of the cell. The product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium.
∆G < 0

21. Energy Coupling
Living organisms have the ability to couple exergonic and endergonic reactions:
Energy released by exergonic reactions is captured and used to make ATP from ADP and Pi.
ATP can be broken back down to ADP and Pi, releasing energy to power the cell’s endergonic reactions.

22. The Structure of ATP
ATP (adenosine triphosphate) is the cell’s energy shuttle.
ATP is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups. O
CH2 H OH N C HC
NH2
Adenine
Ribose
Phosphate groups - CH

23. Hydrolysis of ATP
The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis.
Energy is released from ATP when the terminal phosphate bond is broken.
This release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves.

24. Hydrolysis of ATP
Energy is released from ATP when the terminal phosphate bond is broken. P
Adenosine triphosphate (ATP)
H2O +
Energy
Inorganic phosphate
Adenosine diphosphate (ADP)
P i

25. ATP Powers Cellular Work
A cell does three main kinds of work
Mechanical
Transport
Chemical
Energy coupling is a key feature in the way cells manage their energy resources to do this work.
ATP powers cellular work by coupling exergonic reactions to endergonic reactions.

26. Energy Coupling - ATP / ADP Cycle
Releasing the third phosphate from ATP to make ADP generates energy (exergonic):
Linking the phosphates together requires energy - so making ATP from ADP and a third phosphate requires energy (endergonic),
Catabolic pathways drive the regeneration of ATP from ADP and phosphate
ATP synthesis from
ADP + P i requires energy
ATP
ADP + P i
Energy for cellular work
(endergonic, energy-
consuming processes)
Energy from catabolism
(exergonic, energy yielding
processes)
ATP hydrolysis to
ADP + P i yields energy

27. How ATP Performs Work
ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant.
The recipient molecule is now phosphorylated.
The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP.

28. How ATP Performs Work
ATP drives endergonic reactions by phosphorylation, transferring a phosphate to other molecules - hydrolysis of ATP.
(c) Chemical work: ATP phosphorylates key reactants P
Membrane
protein
Motor protein
P i
Protein moved
(a) Mechanical work: ATP phosphorylates motor proteins
ATP
(b) Transport work: ATP phosphorylates transport proteins
Solute
transported
Glu
NH3
NH2 +
Reactants: Glutamic acid
and ammonia
Product (glutamine)
made
ADP

29. How ATP drives chemical work: Energy coupling using ATP hydrolysis

30. Acknowledgements… Any Questions??
The teaching material used in this lecture is taken from: JB Reece, LA Urry, ML Cain, SA Wasserman, PV Minorsky and RB Jackson Campbell Biology (9th Edition), Publisher Pearson is gratefully acknowledged.
Some information presented in this power point lecture presentation is collected from various sources including Google, Wikipedia, research articles and some book chapters from various biology books. Material and figures used in this presentation are gratefully acknowledged. This material is collected and presented only for teaching purpose.
Any Questions??
Dr.Ramesh Subramani, Assistant Professor in Biology