Cells require constant energy to maintain their internal organization and carry out metabolic reactions. This energy is primarily derived from food and is transformed and stored in ATP molecules, which act as the "energy currency" of cells. Enzymes catalyze metabolic reactions and help minimize energy loss. The chloroplasts and mitochondria work together to transfer energy from sunlight through photosynthesis into cellular respiration to power the energy needs of organisms.

1. Unit 5 – Metabolism: Energy
and Enzymes

2. ENERGY
Energy – The ability to do work.
Living organisms need to acquire energy for
survival
Cells require energy to:
Maintain organization
Carry out reactions
Develop, Grow and Reproduce

3. Forms of Energy
Kinetic Energy – energy of motion
Potential Energy – stored energy
Source of Potential Energy
FOOD – called Chemical Energy
Organisms convert chemical energy into a form
of kinetic energy called Mechanical Energy.

4. Energy Flow
Is unidirectional in ecosystems (no cycling)
Law of thermodynamics explains this:
1st Law: Energy cannot be created or destroyed, but
can be transformed.
2nd Law: Energy transformation results in a loss of
usable energy.
Loss of usable energy is typically in the form of heat.

5. Flow of energy

6. Cells and Entropy
The term entropy is used to indicate the relative state of
disorganization.
Cells need a constant supply of energy to maintain their
internal organization.
Complex molecules tend to break apart into their
building blocks.
Ex: Glucose —> Carbon Dioxide + Water
Greater Organization = less stable
The result is a loss of potential energy and an increase in entropy.

7. Cells and Entropy
Increased Entropy = Dispersion of Energy
Ex: Glucose —> Carbon Dioxide + Water
Decreased Entropy = Organization
Requires Energy to maintain organization.

8. Cells and entropy

9. Metabolic Reactions and Energy
Transformations
Metabolism is the sum of all the chemical reactions that
occur in a cell.
Reactants are substances that participate in a reaction;
products are substances that form as a result of a reaction.
A reaction will occur spontaneously if it increases entropy.
Biologists use the term “free energy” instead of entropy
for cells.
Free energy, ∆G, is the amount of energy to do work after
a reaction has occurred.

11. ATP: Energy for Cells
ATP (adenosine triphosphate) is the energy currency of cells.
ATP is constantly regenerated from ADP (adenosine
diphosphate) after energy is expended by the cell.
Use of ATP by the cell has advantages:
It can be used in many types of reactions.
When ATP --> ADP + P, energy released is sufficient for
cellular needs and little energy is wasted.
ATP is coupled to endergonic reactions in such a way that it
minimizes energy loss.

12. The ATP cycle

13. Coupled Reactions
In coupled reactions, energy released by an
exergonic reaction drives an endergonic
reaction.

14. Coupled reactions

15. Function of ATP
Cells make use of ATP for:
1. Chemical work – ATP supplies energy to
synthesize macromolecules, and therefore the
organism
2. Transport work – ATP supplies energy needed to
pump substances across the plasma membrane
3. Mechanical work – ATP supplies energy for
cellular movements

16. Metabolic Pathways and Enzymes
Cellular reactions are usually part of a metabolic
pathway, a series of linked reactions, illustrated as
follows:
E1 E2 E3 E4 E5 E6
A —> B —> C —> D —> E —> F —> G
A-F are reactants or substrates
B-G are the products in the various reactions
E1-E6 are enzymes.

17. Energy of Activation
The energy that must be added to cause
molecules to react with one another is called
the energy of activation (Eact).
The addition of an enzyme does not change
the free energy of the reaction, rather an
enzyme lowers the energy of activation.

18. Energy of activation (Ea)

19. Enzyme-Substrate Complexes
Every reaction in a cell requires a specific enzyme.
Enzymes are named for their substrates:
SUBSTRATE ENZYME
Lipid Lipase
Urea Urease
Maltose Maltase
Ribonucleic acid Ribonuclease

20. Enzymatic reaction

22. Induced fit model

23. Factors Affecting Enzymatic Speed
Enzymatic reactions proceed with great
speed provided there is enough substrate to
fill active sites most of the time.
Enzyme activity increases as substrate
concentration increases because there are
more collisions between substrate molecules
and the enzyme.

24. Temperature and pH
As the temperature rises, enzyme activity increases
because more collisions occur between enzyme and
substrate.
If the temperature is too high, enzyme
activity levels out and then declines rapidly
because the enzyme is denatured.
Each enzyme has an optimal pH at which the
rate of reaction is highest.

25. Rate of an enzymatic reaction as a
function of temperature and pH
DRAW RELATIONSHIP ON BOARD

26. Enzyme Inhibition
Enzyme inhibition occurs when an active enzyme
is prevented from combining with its substrate.
When the product of a metabolic pathway is in
abundance, it binds competitively with the
enzyme’s active site, a simple form of feedback
inhibition.
Other metabolic pathways are regulated by the
end product binding to an allosteric site on the
enzyme.

27. Feedback inhibition

30. Enzyme Cofactors
Presence of enzyme cofactors may be necessary
for some enzymes to carry out their functions.
Inorganic metal ions, such as copper, zinc, or
iron function as cofactors for certain enzymes.
Organic molecules, termed coenzymes, must be
present for other enzymes to function.
Some coenzymes are vitamins.

31. Oxidation-Reduction and the Flow of
Energy
Oxidation is the loss of electrons and
reduction is the gain of electrons.
Because oxidation and reduction occur
simultaneously in a reaction, such a reaction
is called a redox reaction.
Oxidation also refers to the loss of hydrogen
atoms, and reduction refers to the gain of
hydrogen atoms in covalent reactions in cells.

33. Photosynthesis
The overall reaction for photosynthesis can be written:
6CO2 + 6H2O + energy ---> C6H12O6 + 6O2
During photosynthesis, hydrogen atoms are transferred
from water to carbon dioxide, and glucose is formed.
Water has been oxidized; carbon dioxide has been
reduced.
Energy to form glucose comes from the sun.

40. Cellular Respiration
The overall equation for cellular respiration is opposite
that of photosynthesis:
C6H12O6 + 6O2 --> 6CO2 + 6H2O + Energy
In this reaction, glucose is oxidized and oxygen is reduced
to become water.
The complete oxidation of a mol of glucose
releases 686 kcal of energy that is used to
synthesize ATP.

41. Glycolysis Citric Acid Cycle

42. Electron Transport Chain

44. Organelles and the Flow of Energy
During photosynthesis, chloroplasts capture solar
energy and use it to convert water and carbon
dioxide into carbohydrates that provide food for
other living things.
Cellular respiration, the breakdown of glucose into
carbon dioxide and water, occurs in mitochondria.
It is the cycling of molecules between chloroplasts
and mitochondria that allows a flow of energy
from the sun through all living things.

45. Relationship of chloroplasts to
mitochondria

46. Chapter Summary
Two laws of thermodynamics state that
energy cannot be created or destroyed, and
energy transformations result in a loss of
energy, usually as heat.
As a result of these laws, we know the
entropy of the universe is ever increasing,
and that it takes energy to maintain the
organization of living things.