Depending on how active it is, a cell
may have anywhere from 100 to thousands of mitochon-
; singular is
these small, kidney bean-shaped organelles consists of a
smooth outer membrane and an inner folded membrane
(Figure 3.9). Each fold in the inner membrane is called
a mitochondrial crista (KRIS-ta; plural is
fluid compartment inside the in-
ner membrane is called the mi-
tochondrial matrix. The inner
is studded with nu-
merous enzymes that participate
in a process called oxidative phos-
phorylation. (You will learn more
in Chapter 14.)
Although their primary function is to make ATP, mito-
chondria also participate in the regulation of intracellular
ionized calcium. They contain their own DNA and ribosomes,
both of which make them capable of reproducing themselves
and making new proteins, but the main source of the cell’s
DNA is contained within its largest organelle, the nucleus.
process by which the
movement of electrons
through the inner
membrane of the mito-
chondria is coupled in
The Nucleus Controls
the Cell's Activities
The largest organelle in the cell is the nucleus (Figure
3.10). The nucleus is usually round or oval shaped. Most
cells have only one, but some cells, such as skeletal muscle
Each mitochondrion is composed of a smooth outer membrane
and a folded inner membrane, which contain numerous enzymes
that are involved in making ATP.
Mitochondria • Figure 3.9
Outer mitochondrial membrane
Inner mitochondrial membrane
Function of the Mitochondrion
Generates ATP through reactions
of aerobic cellular respiration.
The nucleus • Figure 3.10
The nucleus consists of three parts: the nuclear envelope, the nucleolus, and the
chromatin. The nuclear envelope is studded with nuclear pores that control the flow of
material into and out of the nucleus. The nucleolus makes ribosomes, and the chromatin
is the cell's genetic material.
Details of the nucleus
Details of the nuclear envelope
Functions of the Nucleus
1. Controls cellular structure.
2. Directs cellular activities.
3. Produces ribosomes in nucleoli.
56 CHAPTER 3
Cells and Tissues