Fundamentals of Anatomy and Physiology

46

Human

chromosomes

Supercoil

within

chromosome

Chromatin

Coiling

within

supercoil

(^)
®^
Lear ni ng^
Chromatin fiber
Cen gage^
©^
Figure 3- 7 Some different levels of
chromosomal organization.
RNA, and proteins. A cell may have more than one nucle-
olus. This structure is the site of ribosomal synthesis. It is
involved in protein synthesis because it makes the ribo-
somes and ribosomes are the sites of protein synthesis.
The Mitochondria
A mitochondrion (singular) or mitochondria (my-toh-
KON-dree-ah) (plural) are small oblong-shaped struc-tures
composed of two membranes (Figure 3-8). The outer
membrane gives a mitochondrion its capsule shape; the
inner membrane folds on itself to provide a surface on
which the energy-releasing chemical reac-tions of the cell
occur. When viewed under a light com-pound microscope,
mitochondria appear only as small, dark granules in the
cytoplasm. It is the electron micro-scope that has revealed
to us the true nature of the mi-tochondria. The folds of the
inner membrane are called cristae (KRIS-tee). It is on the
cristae that cellular respi-ration occurs, where food
(chemical energy) is converted into another usable form of
chemical energy, ATP. For this reason, the mitochondria
are known as the power-houses of the cell.
Chapter 3
Outer Outer membrane (^)
compartment Inner membrane (^)
Crista Matrix (^)
(^) ®
Learning
Cengage ©
Figure 3- 8 The membrane structure of a
typical mitochondrion.
In its most simple expression, cellular respiration can
be stated as follows:
Food (like glucose) 1 oxygen S^ energy 1 waste.^
C 6 H 12 O 6 1 6O 2 S ATP 1 6CO 2 1 6H 2 O.
This chemical reaction is discussed in greater detail in
Chapter 4.
Most of the energy-producing reactions, which -occur
in the mitochondria, take place on the surface of the cristae.
Cells with high-energy requirements (like muscle cells)
will have mitochondria with many folds or cristae. Cells
with low-energy requirements, like the -lining of the cheek
(epithelial cells), will have mitochon-dria with fewer folds
or cristae. All cells will have ap-proximately the same
number of mitochondria. They are inherited from the
mother via the egg cell. Mitochondria also contain
mitochondrial DNA.
Lysosomes
Lysosomes (LIGH-so-sohmz) are small bodies in the
cytoplasm that contain powerful digestive enzymes to
enhance the breakdown of cellular components (see Figure
3 - 1). The structure and size of lysosomes vary but they are
generally spherical. They have three general functions:

1. They act in conjunction with stored food vacuoles.
   When a cell needs more energy, a lysosome will fuse
   with a stored food vacuole to break down the stored
   food into a more usable form that can go to a mito-
   chondrion to be converted into ATP. For example,
   starch, a complex carbohydrate, will be broken down
   into simple sugars, protein into amino acids, and fats
   into fatty acids and glycerol.^


2. Lysosomes also act in the maintenance and repair of
   cellular components. If a section of ER needs to be
   rebuilt, the lysosome will break down the