Cell StructureCell 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 centrally-located, 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

H2O2 H2O + O2

Endosymbiont Theory

Click here for short video on 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.

Mitochondria

1. Contain inner folded membrane (cristae) and outer membrane,2. Contain protein-/enzyme-rich matrix involved in oxidative

metabolism,3. Contain their own DNA and are believed to have originated from

endosymbiotic prokaryotes capable of carrying out oxidative metabolism.

Chloroplasts

1. Contain photosynthetic pigment chlorophyll,2. Surrounded by two membranes which have stacked grana lying inside

inner membrane,3. 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

Nuclei, membranes, ribosomes, eukaryotes and prokaryotes

Endoplasmic reticulum and Golgi bodies

From Khan Academy:

Organelle overview

Cell Tutorial, Game, and Quiz

Cells Alive! Eukaryotic Cell Structures and Functions