Organelle Structures and Functions

Centrosome

Structure: Microtubule organizing center

Function: Microtubules form spindle fibers and contribute to cell division (mitosis / meiosis)

Chloroplast

Structure: Double membrane structure with internal stacks of membranous discs

Function: Site of photosynthesis – manufactured organic molecules are stored in various plastids

Cytoskeleton

Structure: A filamentous scaffolding within the cytoplasm

Function: Provides internal structure and mediates intracellular transport

Cytosol / Cytoplasm

Structure: Mostly water, but full of enzymes and other molecules

Function: Holds organelles in place and catalyzes reactions (like glycolysis)

Endoplasmic Reticulum (Rough)

Structure: Folded membrane studded with ribosomes

Function: Protein synthesis for export

Endoplasmic Reticulum (Smooth)

Structure: Folded membrane continuous with the nuclear envelope

Function: Production of lipids and metabolism of toxins

Golgi

Structure: An assembly of vesicles and folded membranes located near the cell membrane

Function: Involved in the sorting, storing, modification and export of secretory products

Lysosome

Structure: Membranous sacs filled with hydrolytic enzymes

Function: Breakdown / hydrolysis of macromolecules

Mitochondrion

Structure: Double membrane structure, inner membrane highly folded into internal cristae

Function: Site of aerobic respiration (ATP production)

Nuclear Envelope

Structure: Double membrane that surround the nucleus

Function: Control movement in and out of the nucleus

Nucleoid Region

Structure: Area in prokaryotes where the bacterial DNA is concentrated

Function: Holding place for DNA

Nucleolus

Structure: Dense, darker region in nucleus

Function: Site of ribosome synthesis

Nucleus

Structure: Double membrane structure with pores

Function: Stores genetic material (DNA) as chromatin

Peroxisome

Structure: Membranous sac containing a variety of catabolic enzymes

Function: Catalyses breakdown of toxic substances (e.g. H2O2) and other metabolites

Plasma Membrane (Cell Membrane)

Structure: Phospholipid bilayer embedded with proteins

Function: Semi-permeable and selective barrier surrounding the cell

Ribosome

Structure: Two subunits made of rRNA and protein; larger in eukaryotes (80S) than prokaryotes (70S)

Function: Site of polypeptide synthesis (this process is called translation). In general, cytoplasmic ribosomes synthesize proteins for use within the cell, and bound ribosomes (on the RER) synthesize proteins for secretion (export)

Vacuole

Structure: Fluid-filled internal cavity surrounded by a membrane (tonoplast)

Function: Maintains hydrostatic pressure in plants, animal cells may have small, temporary vacuoles, fungal vacuoles have a variety of functions

Vesicle

Structure: Membranous sac

Function: Moves proteins and other products around the cell

Cell Wall

Structure: External outer covering made of cellulose (plants), peptidoglycan (bacteria), chitin (fungi)

Function: Provides support and mechanical strength; prevents excess water uptake