1. Chapter 4-
Physiology of Cells

2. Passive Transport Processes
Diffusion: the tendency of small particles to spread
out evenly within any given space. Particles move
from an area of high concentration to low
concentration.
• Down the
concentration
gradient

3. Passive Transport Processes
Dialysis: is a form of diffusion in which the
selectively permeable nature of the
membrane causes separation of smaller
solute particles from larger solute particles.

4. Passive Transport Processes
Osmosis: the diffusion of water through a
selectively permeable membrane.

5. Passive Transport Processes
Facilitated Diffusion: diffusion of particles through
a membrane by means of carrier molecules.

6. Passive Transport Processes
Filtration: involves the passing of water and
permeable solutes through a membrane by the
force of hydrostatic pressure.
• Hydrostatic pressure is the force, or weight, of
a fluid pushing against a surface.
• Filtration is driven by a hydrostatic pressure
gradient.
• Example: Movement of water and small
solutes from the capillaries to the interstitial
spaces.

7. Active Transport Processes
Active Transport: refers to a carrier
mediated process in which cellular energy is
used to move molecules “uphill” through a
cell membrane.
• “Uphill” refers to going from a low
concentration to a high concentration. Or
against the concentration gradient.
• Examples: Calcium pumps, Sodium Potassium
pumps.

8. Active Transport Processes
Endocytosis: the plasma membrane
traps some extracellular material and
brings it into the cell.
•There are two forms of endocytosis:
• Phagocytosis: condition of cell eating
• Pinocytosis: condition of cell drinking

9. Active Transport Processes

10. Active Transport Processes
Exocytosis: the process in which large molecules
notably proteins, can leave the cell even though
they are too large to move out through the plasma
membrane.

11. Enzymes
Enzymes: are functional proteins that act as
chemical catalysts that allow metabolic
reactions to occur.
• Structural attribute that is important is the
active site. This is the portion of the enzyme
that chemically “fits” the substrate molecule.
• The action of an enzyme can be described as a
lock and key function.

12. Classification of Naming
Enzymes
Classified according to the kind of
chemical reactions catalyzed.
•Redox enzymes: oxidase,
hydrogenases, dehydrogenases.
•Hydrolyzing enzymes: Digestive
enzymes such as lipase, sucrase,
maltase.

13. Classification of Naming
Enzymes
•Phosphorylating enzymes: add or
remove phosphate groups.
•Carboxylases or Decarboxylases:
add or remove carbon dioxide
•Mutases or Isomerases: rearrange
atoms within a molecule.
•Hydrases: add water to a molecule.

14. General Functions of
Enzymes
• Enzymes regulate cell functions by
regulating metabolic pathways.
• Most enzymes are specific in their actions.
• Allosteric effector: an agent that changes the
shape of a molecule.
• End product inhibition: a chemical product at
the end of a metabolic pathway binds to an
allosteric site and thus inhibits synthesis of
more product.

15. General Functions of
Enzymes
• Most enzymes catalyze a chemical reaction in
both directions.
• Enzymes are continually destroyed and
therefore have to be continually synthesized.
• Many are synthesized as inactive proenzymes.
• Proenzymes are converted or activated by
Kinases.