Page 22 - 84 human physiolofy part-1

Chapter 2

• Mitochondria

Mitochondria are the
organelles that function as the cell
"powerhouse", generating ATP,
the universal form of energy used
by all cells. It converts food
nutrients such as glucose, to a fuel
(ATP) that the cells of the body
can use. Mitochondria are tiny
saclike structures found near the
nucleus. Little shelves called
cristae are formed from folds in
the inner membrane. Cells that
are metabolically active such as
muscle, liver and kidney cells
have high energy requirements
and therefore have more
mitochondria.
A cutaway view inside a mitochondria. (GFDL - pschemp)
Mitochondria are unique in that they have their own mitochondrial DNA (separate from the DNA
that is in the nucleus). It is believed that eukaryotes evolved from one cell living inside another cell,
and mitochondria share many traits with free-living bacteria (similar chromosome, similar ribosomes,
etc).

• Endoplasmic Reticulum

Endoplasmic means "within the plasm" and reticulum means "network".

A complex three dimensional internal membrane system of flattened sheets, sacs and tubes, that
play an important role in making proteins and shuttling cellular products; also involved in metabolisms
of fats, and the production of various materials. In cross-section, they appear as a series of maze-like
channels, often closely associated with the nucleus. When ribosomes are present, the rough ER attaches
polysaccharide groups to the polypeptides as they are assembled by the ribosomes. Smooth ER, without
ribosomes, is responsible for various activities, including the synthesis of lipids and hormones,
especially in cells that produce these substances for export from the cell.

Rough endoplasmic reticulum has characteristic bumpy appearance due to the multitude of
ribosomes coating it. It is the site where proteins not destined for the cytoplasm are synthesized.

Smooth endoplasmic reticulum provides a variety of functions, including lipid synthesis and
degradation, and calcium ion storage. In liver cells, the smooth ER is involved in the breakdown of
toxins, drugs, and toxic byproducts from cellular reactions.

• Golgi Apparatus

"Packages" cellular products in sacs called vesicles so that the products can cross the cell

22 | Human Physiology