Cell Organelles
Section 3.3
The Nucleus
 The nucleus is an internal compartment that
houses the cell’s DNA. Most functions of a
eukaryotic cell are controlled by the cell’s
nucleus.
 The nucleus is surrounded by a double
membrane called the nuclear envelope
 Scattered over the surface of the nuclear
envelope are many small channels called
nuclear pores
The Nucleus, continued


Ribosomal proteins and RNA are
made in the nucleus
Ribosomes are partially assembled in a
region of the nucleus called the
nucleolus
Ribosomes and the
Endoplasmic Reticulum
Ribosomes are the cellular structures
on which proteins are made.
The Endoplasmic Reticulum or ER is
an extensive system of internal
membranes that move proteins and
other substances through the cell.
Ribosomes and the Endoplasmic
Reticulum, continued
 The part of the ER with attached ribosomes
is called the rough ER
 The rough ER helps transport proteins that
are made by the attached ribosomes
 New proteins enter the ER
 The portion of the ER that contains the
completed protein pinches off to form a
vesicle
 A vesicle is a small, membrane-bound sac
that transports substances in cells
Ribosomes and the Endoplasmic
Reticulum, continued
Packaging and Distribution of Proteins


Vesicles that contain newly made proteins
move through the cytoplasm from the ER to
an organelle called the Golgi apparatus
The Golgi apparatus is a set of flattened,
membrane-bound sacs that serve as the
packaging and distribution center of the cell
Ribosomes and the Endoplasmic
Reticulum, continued
Mitochondria
Mitochondria are organelles that
harvest energy from organic
compounds to make ATP
ATP is the main energy currency of
cells. Most ATP is made inside the
mitochondria
Mitochondria, continued
 Mitochondria have two membranes. The outer
membrane is smooth. The inner membrane is greatly
folded, and has a large surface area.
 Mitochondria have their own DNA. Mitochondria
reproduce independently of the cell. Mitochondrial
DNA is similar to the DNA of prokaryotic cells.
 Mitochondria are thought to be descendents of
primitive prokaryotes.
Summary of Organelles