Cell Structure
Cell Theory
Structures of Prokaryotic and Eukaryotic Cells
The Cell Theory
First Principle:
All organisms are composed of one or more
cells, and the life processes of metabolism
and heredity occur within these cells
The Cell Theory
Second Principle:
Cells are the smallest living things, the basic
units of organization of all organisms
The Cell Theory
Third Principle:
Cells arise only by division of a previously
existing cell
Nucleoid
Area in prokaryotic cells where DNA
resides; not membrane-bound
Peptidoglycan
Carbohydrate and polypeptide
structure of which most eubacterial
cell walls are composed
Organelle
Any macromolecular structure
specialized for a particular function
Plasma membrane
Phospholipid bilayer embedded with
proteins
Cytoplasm
Semi-fluid matrix which contains all
the sugars, amino acids, and proteins
the cell uses for everyday activities
Cytosol
The part of the cytoplasm containing
organic molecules and ions in
solution
Cytoskeleton
Made of actin filaments, microtubules, and intermediate
filaments that help move materials within cells
Central vacuole
1. Contains channels for water that are used
to help a plant cell maintain osmotic
balance
2. Helps in plant growth by expanding instead
of increasing cytoplasmic volume
Nuclear Envelope (Membrane)
Double membrane structure dotted
with pores; houses deoxyribonucleic
acid in eukaryotes
Nucleus
1. Large structure, usually centrallylocated, often cradled in place by a
network of fine cytoplasmic filaments
2. A repository for genetic information
Nucleolus
Region where rRNA is intensely
synthesized and can be easily seen as
dark-staining regions
Endomembrane system
Allows for compartmentalization
in eukaryotic cells by weaving
through cytoplasm and organelles
Ribosomes
Composed of two rRNA subunits where protein
synthesis occurs
Rough endoplasmic reticulum
Flattened sacs where the surface appears pebbly
due to presence of ribosomes; proteins are
sorted here destined to be exported
Smooth endoplasmic reticulum
1. Tube-like structures involved in the synthesis of a
variety of carbohydrates and lipids;
2. Stores Ca2+, which is used in diverse signaling pathways;
3. Modifies foreign substances to make them less toxic
Golgi apparatus
Flattened stacks of interconnected membranes that
are especially abundant in glandular cells; function
in the collection, packaging, and distribution of
molecules synthesized by other organelles.
Click here for short animation showing rough and smooth ER and Golgi apparatus
(Go to scene 2)
Vesicles
Small sacs that store and transport a
variety of materials
Lysosomes
Contain enzymes used to break
down and recycle molecules
Click here for short video on Lysosomes
Peroxisome
Microbody containing enzymes involved in the
oxidation of fatty acids which also uses catalase to
break down
H2 O 2  H 2 O + O 2
Endosymbiont Theory
Two possible origins of eukaryotic cells:
The engulfing cell (left) is an archaeon
that gave rise to the nuclear genome
and cytoplasmic contents.
The engulfing cell (right) consists of a
nucleus derived from an archaeon in a
bacterial cell. This could only arise by
a fusion event or by engulfment of the
archaeon by the bacterium.
Click here for short video on Endosymbiont Theory
Mitochondria
1.
2.
3.
Contain inner folded membrane (cristae) and outer membrane,
Contain protein-/enzyme-rich matrix involved in oxidative
metabolism,
Contain their own DNA and are believed to have originated from
endosymbiotic prokaryotes capable of carrying out oxidative
metabolism.
Chloroplasts
1.
2.
3.
Contain photosynthetic pigment chlorophyll,
Surrounded by two membranes which have stacked grana lying inside
inner membrane,
Contain their own DNA and are believed to have originated from
endosymbiotic prokaryotes capable of photosynthesizing.
Contractile vacuole
Maintains water balance in protists
EXTRACELLULAR STRUCTURES:
Flagellum (flagella, pl.)
Originate directly from a basal body and are long,
threadlike structures used for locomotion
EXTRACELLULAR STRUCTURES:
Cilia
Short, cellular projections often organized into
rows with 9 + 2 arrangement of microtubules
EXTRACELLULAR STRUCTURES:
Cell Wall
Found in plants, fungi, and some protists (algae)
and are made of cellulose or chitin which protect
and support the cell
Eubacteria Cell
Animal Cell
Plant Cell
Additional Resources
From Khan Academy:
Organelle overview
Nuclei, membranes, ribosomes, eukaryotes and prokaryotes
Endoplasmic reticulum and Golgi bodies
Cell Tutorial, Game, and Quiz
Cells Alive! Eukaryotic Cell Structures and Functions