Chapter 4- Physiology of Cells

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

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.

Passive Transport Processes

Osmosis: the diffusion of water through a selectively permeable membrane.

Passive Transport Processes

Facilitated Diffusion: diffusion of particles through a membrane by means of carrier molecules.

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.

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.

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

Active Transport Processes

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.

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.

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.

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.

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.

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.