Chapter 4 Life process in a cell

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Chapter 4 Life process in a cell a. Enzymes
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What is metabolism?

• All the chemical reactions that take place within
  an organism.
• Including cell respiration, photosynthesis, cell
  division, etc.
• Catabolism (????) vs. Anabolism (????)

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Enzymes

• Enzymes are proteins
• Used as biological catalysts (???)
• To increase the rate of chemical reactions

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Factor 1 Temperature

• Temperature has two effects on enzymes

The rate increases under the area in blue
because the kinetic energy of enzymes and
substrates increase so the rate of collision
increases
The temperature at which the rate is highest is
called the optimum temperature
The rate decreases under the area in pink
because the heat energy breaks the bonds within
the enzyme, changes its shape so the rate
decreases
A
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Factor 2 pH

• Similar to temperature, each enzyme has its own
  optimum pH

Different enzymes may have different optimum pH
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Factor 3 Substrate Concentration
If more enzymes are added
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Factor 4 Enzyme Concentration
If more substrates are added
To Diffusion
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Chapter 4 Life process in a cell b. Transport
across membrane
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Diffusion

• Movement of molecules
• from a region of higher concentration
• to a region of lower concentration

• without the need of extra energy supply
• down a concentration gradient
• until it is evenly distributed

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Osmosis

• Diffusion of water molecules
• across a selectively permeable membranee.g.,
  cell membrane
• without the need of extra energy supply

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Active transport

• Movement of molecules
• against concentration gradient
• with the supply of external energy
• e.g., absorption of glucose in ileum

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Water potential, ?

• Describe the tendency of water molecules to
  diffuse from one place to another.
• ? of pure water is 0
• addition of solutes lower the water potential
  (i.e., lt0)
• Water molecules move from a region of higher
  water potential to a region of lower water
  potential.

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The end of Chapter 4

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