The document discusses several topics related to cellular metabolism: 1) Fungi like Aspergillus niger contain enzymes that break down plant cell walls through catabolic reactions. 2) A deficiency in the ALDH2 enzyme can cause negative reactions to alcohol due to its build up into toxic acetaldehyde. 3) Taq DNA polymerase aids in DNA replication by duplicating DNA during the replication process. Its presence can be detected using Western blot analysis.

1. Funga such as Aspergillus niger contains glycoside hydrolases that can
break down plant cell wall.
Inherited deficiency (rs671) in the enzyme aldehyde
dehydrogenase 2 (ALDH2) cause facial flushing,
nausea, and tachycardia, as alcohol is converted to
toxic acetaldehyde, but cannot be further oxidized into
acetic acid.
Taq DNA polymerase (thermostable DNA
polymerase named after the thermophilic
bacterium Thermus aquaticus) with a short
piece of DNA in magenta and green. DNA
polymerase duplicates all DNA of a cell
during replication process.
Presence of protein, such as Taq
DNA polymerase, can be detected
using a methods called Western
Blot, which the protein was
separated by size, then
immunoblotted with an antibody,
here with anti-polA antibody.

2. 3.1 Chemical
reactions in
the cells

3. Objectives
• Anabolism and catabolism are metabolic processes.
• Activation energy is required for chemical reactions.

4. Metabolism 新陈代谢
• Metabolism refers to all the chemical reactions in a cell.
• It includes anabolism 同化作用 and catabolism 异化作用.
• In anabolism/synthetic reaction 合成反应, the cell utilizes simple
molecules to manufacture complex organic molecules.
• Condensation reactions
• Syntheses of protein and glycogen
• In catabolism/breakdown reaction 分解反应, complex organic
compounds are broken up into simple molecules.
• Hydrolysis reactions
• Sugar is broken down into water and carbon dioxide, releasing energy

5. Energy is required for activities

6. Activation energy 激活能
• All chemical reactions between molecules involves both bond
breaking and bond forming.
• Reaction can only occurs when the molecules are in an unstable
transition state.
• To reach this transition state, the reactant molecules must absorb
energy from the surrounding.
• The energy absorb is called the activation energy.
• Extra energy is released when new bonds are formed.
• The product molecules return to a more stable shape with lower
energy then the transition state.
• The more activation energy required, the slower a reaction will occur.

7. Quiz
• We use a match to light a fireplace, but we get much more heat back
from the firewood than the amount put into it by the match. The
energy of the match represents the
A) entropy needed to start the fire.
B) activation energy of a chemical reaction.
C) oxidizing agent that makes the wood burn.
D) free energy of the system.

10. The activation energy is a barrier that
determines the rate of the reaction.
Activation energy

11. Enzyme as catalyst 催化剂 of reactions
• Enzymes lowers the activation energy required by an reaction.
• Enzymes allow reactants to occur more readily and increase the rate
of reactions.

13. Enzyme increases the rate of reaction

14. Quiz
• The graph on the right shows the activation
energy required for a reaction under two
different conditions. Which reaction is
carried out in the presence of a catalyst?
Explain.
A. Reaction B, as the product formed has a
lower energy.
B. Reaction B, as it requires less energy to
begin.
C. Reaction A, as the product formed has a
lower energy.
D. Reaction A, as it requires more energy to
begin.

16. Conclusion
• Metabolism refers to all the chemical reactions in a cell and includes
anabolism and catabolism.
• Reactant molecules absorb energy from the surrounding to reach an
unstable transition state so that reactions may occur.
• The energy absorbed is called the activation energy.
• The more activation energy required for a reaction, the slower the
reaction will occurs.
• Enzyme reduces the activation energy required for the reaction, thus
increase the rate of reaction.