Eukaryotic Cell Structures
7-2
In some respects, the eukaryotic cell
is like a factory
It contains several tiny specialized
structures called organelles
Biologists divide the cell into 2 parts:
the cytoplasm and the nucleus
The cytoplasm is the portion of the cell
outside the nucleus
It contains the organelles and is where
some cellular processes take place
Nucleus
Contains nearly all of the cell’s DNA and
instructions for making proteins & other
molecules
It is surrounded by a nuclear envelope,
which is made up of 2 membranes
Contains 1000’s of tiny pores which allow
material (RNA & proteins) to move into and out
of nucleus
Nucleus contains chromatin, which is
DNA bound to proteins
Condenses to form chromosomes during
cell division
May also contain a nucleolus, which is
where ribosomes are made
Ribosomes
Site where proteins are assembled
Composed of RNA & proteins
Found in the cytoplasm or on other
organelles
Produce proteins based on coded
instructions from the nucleus
Endoplasmic Reticulum (ER)
It is an internal membrane system
that synthesizes and exports
materials
Site where lipid components of the
cell membrane are assembled
Exports proteins and other material
for the cell
There are 2 types of ER: smooth and
rough
Rough ER is involved in protein synthesis
Contains ribosomes on its surface
Proteins leave ribosomes and enter ER
to be modified
Smooth ER lacks ribosomes
Contains enzymes the synthesize lipid
membranes & detoxify drugs
Large amounts are found in liver
Golgi Apparatus
Named after Italian scientist Camillo
Golgi
Accepts proteins modified in the
rough ER
Function is to modify, sort, and
package proteins & other materials
from the ER
Lysosomes
Small organelles filled with enzymes
that act like “clean-up crew” in the cell
Functions to digest, or breakdown
lipids, carbohydrates, and proteins
into small molecules
Breaks down old & worn out
organelles
Vacuoles
Saclike structure that stores cellular
materials like water, salts, proteins
and carbs
Plants contain a large vacuole filled
with water, which enables plants to
support the weight of flowers and
leaves
Single-celled organisms contain a
contractile vacuole,
Used to pump out excess water from cell
Helps to maintain homeostasis
Mitochondria & Chloroplasts
Mitochondria are found in plant & animal
cells
Functions as the cell’s “powerhouse” by
converting energy stored in glucose to the
cellular energy ATP
Composed of 2 membranes: inner & outer
The inner membrane is folded to increase
surface area
Chloroplasts are found in plant cells
and in a few other organisms
Contains chlorophyll, which is used to
capture the energy during
photosynthesis
Also composed of 2 membranes
Organelle DNA
Chloroplasts and mitochondria
contain their own DNA
Biologist Lynn Margulis believes they
are descendents from prokaryotic
cells
Developed from symbiotic relationships
Cytoskeleton
Functions as support structure for cell
Consists of a network of protein
filaments that help the cell maintain its
shape
Two types of protein filaments:
microfilaments and microtubules
Microfilaments are made of actin and
their assembly and disassembly
allow cytoplasmic movement
Microtubules are hollow structures
made of tubulin
They are important in cell reproduction
because they form the mitotic spindle
which separates chromosomes
They are also responsible for the
formation of cilia and flagella, which
allow some cells to move
Centrioles are also made of tubulin
and help to organize cell division