-Hydrases add water to a molecule without splitting it, as do hydrolase.
-In general, enzymes regulate cell functions by regulating metallic pathways.
-Each reaction of a metabolic pathway requires one or more types of enzymes to
-Once inside, they fuse with the membranous walls of lysosomes.
-Enzymes from the lysosomes then digest the particles into their component
-Pinocytosis is a similar process in which fluid and the substances dissolved in its
Cells in Solutions
-Cells placed in solutions that are hypertonic to intracellular fluid always shrivel.
-If cells shrivel too much, they may become permanently damaged, or even die.
0Large amounts of solutes cannot be introduced into the body without
-Other cells use active transport pumps for similar purposes, that is to create a
concentration gradient of a particular solute.
-One type of active transport pump, the sodium potassium pump, operates in the
plasma membrane of all human cel
Active and Passive Transport
-As in channel-mediated and simple diffusion, carrier-mediated diffusion also
transports substances down a concentration gradient.
-Diffusion of any type is a passive process.
-The energy for transport through a membrane does
-A concentration gradient is simply a measureable difference in concentration
from one area to another.
-Because molecules spread from the area of high concentration to the area of
low concentration, they spread down the concentrat
-Simple diffusion through a phospholipid bilayer
-Some small, uncharged molecules can easily pass through the phospholipid
membrane, but water and urea rarely get through the membrane.
-Larger uncharged molecules and ions may not pass through th
-Their molecules contain a nonprotein part called a cofactor.
-Organic ions or vitamins may make up part of a cofactor.
-A very important structural attribute of enzymes is the active site.
-It is the portion of the enzyme molecule that chemically
Organelles and the Cytoplasm
-The cell is the basic functional unit of the body, so it is no wonder that a good
understanding of human physiology begins with an overview of cell function.
-If a cell is to survive, it must be able to move substances to pla
-Electrical changes, others by light, and still others by mechanical or chemical
stimuli trigger some gated channels.
-Open-gated channels may under a certain conditions become inactive, stopping
the flow of molecules and becoming insens
Endocytosis and Exocytosis
-Other active types of transport include endocytosis, exocytosis, and related
vesicle-mediated processes within cells.
-Efforts of the cytoskeleton pull or push large volumes of material into or out of
cells and organelles by wr