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 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 Ca 2+, 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 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 H 2 O 2  H 2 O + O 2

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 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