A&P Cell Structures and Organelles

Mitochondria

Structure: Rodlike, double-membrane structures; inner membrane folded into cristae

Function: Site of ATP Synthesis; powerhouse of the cell

Plasma Membrane

Structure: Made of phospholipid bilayer within which proteins and cholesterol are embedded. Sugars can be found attached to most external facing proteins and some lipids.

Function: Control what comes in and out of cell; maintains cell’s boundaries

Ribosomes

Structure: Consists of 2 subunits (large and small), each composed of rRNA and protein; can be free-floating or found attached to Rough ER

Function: Sites of protein synthesis

Rough Endoplasmic Reticulum (RER)

Structure: Membranous system enclosing a cavity (called cistern) and coiling through cytoplasm; externally studded with ribosomes

Function: Binds proteins synthesized by ribosomes within vesicles for transport to Golgi; synthesizes lipids on external face; manufactures integral proteins and phospholipids; attaches sugars to external facing membrane proteins within cistern

Smooth Endoplasmic Reticulum (SER)

Structure: Membranous system of sacs and tubules; free of ribosomes

Function: Site of lipid and steroid synthesis, lipid metabolism, drug detoxification, andCa^{2+} storage

Golgi Apparatus

Structure: A stack of flattened membranes and associated vesicles close to the nucleus

Function: Packages, modifies, and segregates proteins for secretion from the cell, inclusion in lysosomes, and incorporation into the plasma membrane; modifies carbohydrates on proteins

Peroxisomes

Structure: Membranous sacs containing catalase and oxidase enzymes

Functions: Its enzymes detoxify toxic substances; catalase breaks down hydrogen peroxide

Lysosome

Structure: Membranous sacs containing acid hydrolases

Function: Site of intracellular digestion

Nucleus

Structure: Largest cytoplasmic organelle at 5\mu m in diameter, and is most often found in spherical or oval shape (but can change to conform to cell’s shape); surrounded by nuclear envelope and contains fluid nucleoplasm, nucleoli, and chromatin

Function: Control center of the cell; responsible for transmitting genetic information and providing the instructions for protein synthesis (houses DNA)

Nuclear Envelope

Structure: Double membrane barrier separated by fluid-filled space; outer membrane continuous with Rough ER and is also externally studded with ribosomes and punctured with nuclear pores

Function: Maintain shape of nucleus; separates nucleoplasm from cytoplasm; regulates passage of substances to and from the nuclei

Nucleolus

Structure: Dark-staining spherical bodies found within nucleus, but is not bounded to membrane

Function: Site of rRNA synthesis and ribosomal subunit assembly

Centrioles

Structure: Paired cylindrical bodies, each composed of 9 triplets of microtubules

Function: Organize the microtubule network as part of centrosome; forms spindle and asters during mitosis; forms basis of cilia and flagella as basal bodies

Cytoskeleton

Structure: Elaborate network of rods (microfilaments, intermediate filaments, and microtubules) running through cytosol and hundreds of accessory proteins that link these rods to other cell structures

Function: Acts as cell’s “bones,” “muscles,” and “ligaments” by supporting cell structure and providing machinery to generate various cell movements.

Cytoplasm

Structure: Cellular material between plasma membrane and nucleus containing cytosol, inclusions, and organelles

Function: Site of most cellular activities

DNA

Structure: Double-helix strand made up of sugar-phosphate backbone and nucleotide base pairs, which connect the helix via hydrogen bonds to its complementary base pair

Function: Contains the instructions for protein synthesis; contains cell’s genetic information