Table 3.2: Some Eukaryotic OrganellesOrganelle Function
Ribosomes Involved in making proteins
Golgi apparatus Packagesproteinsandsomepolysaccharides
Mitochondria Makes ATP
Smooth ER Makes lipids
Chloroplast Makes sugar (photosynthesis)
Lysosomes Digests macromoleculesThe Nucleus and Chromosomes
The nucleus, which is found exclusively in eukaryotic cells, is a membrane-enclosed structure
that contains most of the genetic material of the cell (Figure3.10). Like a library, it holds
vitalinformation, mainlydetailedinstructionsforbuildingproteins. Thenuclear envelope,
a double membrane that surrounds the nucleus, controls which molecules go in and out of
the nucleus.
Inside the nucleus are the chromosomes, the DNA all wrapped in special proteins. The
geneticinformationonthechromosomesisstoredmadeitavailabletothecellwhennecessary
and also duplicated when it is time to pass the genetic information on when a cell divides.
All the cells of a species carry the same number of chromosomes. For example, human cells
each have 23 pairs of chromosomes. Each chromosome in turn carries hundreds or thousands
of genes that encode proteins that help determine traits as varied as tooth shape, hair color,
or kidney function.
The Cell Factory
Just as a factory is made up of many people, machines, and specific areas, each part of the
whole playing a different role, a cell is also made up of different parts, each with a special
role. For example, the nucleus of a cell is like a safe containing the factory’s trade secrets,
including how to build thousands of proteins, how much of each one to make, and when. The
mitochondriaare powerhouses that generate the ATP needed to power chemical reactions.
Plant cells have special organelles calledchloroplaststhat capture energy from the sun
and store it in the chemical bonds of sugar molecules - in the process called photosynthesis
(Figure3.11). (The cells of animals and fungi do not photosynthesize and do not have
chloroplasts.)
Thevacuolesare storage centers, and thelysosomesare the recycling trucks that carry
waste away from the factory. Inside lysosomes are enzymes that break down old molecules
into parts that can be recycled into new ones. Eukaryotic cells also contain and internal
skeleton called thecytoskeleton. Like our bony skeleton, a cell’s cytoskeleton gives the cell