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Cell StructureCell TheoryStructures of Prokaryotic and Eukaryotic Cells

The Cell TheoryFirst Principle:All organisms are composed of one or more cells, and the life processes of metabolism and heredity occur within these cells

The Cell TheorySecond Principle:Cells are the smallest living things, the basic units of organization of all organisms

The Cell TheoryThird Principle:Cells arise only by division of a previously existing cell

NucleoidArea in prokaryotic cells where DNA resides; not membrane-bound

PeptidoglycanCarbohydrate and polypeptide structure of which most eubacterial cell walls are composed

OrganelleAny macromolecular structure specialized for a particular function

Plasma membranePhospholipid bilayer embedded with proteins

CytoplasmSemi-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

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Central vacuoleContains channels for water that are used to help a plant cell maintain osmotic balance 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

NucleusLarge structure, usually centrally-located, often cradled in place by a network of fine cytoplasmic filaments2. A repository for genetic information

NucleolusRegion where rRNA is intensely synthesized and can be easily seen as dark-staining regions

Endomembrane systemAllows for compartmentalization in eukaryotic cells by weaving through cytoplasm and organelles

Ribosomes Composed of two rRNA subunits where protein synthesis occurs

Rough endoplasmic reticulumFlattened sacs where the surface appears pebbly due to presence of ribosomes; proteins are sorted here destined to be exported

Smooth endoplasmic reticulumTube-like structures involved in the synthesis of a variety of carbohydrates and lipids;Stores Ca2+, which is used in diverse signaling pathways;Modifies foreign substances to make them less toxic

Golgi apparatusFlattened 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 downH2O2 H2O + O2

Endosymbiont TheoryClick 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 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 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 vacuoleMaintains 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:CiliaShort, cellular projections often organized into rows with 9 + 2 arrangement of microtubules

EXTRACELLULAR STRUCTURES:Cell WallFound 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 ResourcesNuclei, membranes, ribosomes, eukaryotes and prokaryotes

Endoplasmic reticulum and Golgi bodiesFrom Khan Academy:Organelle overviewCell Tutorial, Game, and QuizCells Alive! Eukaryotic Cell Structures and Functions