ORGANELLES TUTORIAL

Definition of an organelle

A specialized structure within a cell designed to carry out a specific function within the cell.

Cytoplasm

a gel-like substance that fills out the cell between the cell membraneOrganelles are contained within the cytoplasm.

Cytoskeletona scaffolding or skeleton of a sort within the cell that is made of proteins and helps to maintain cell shape and cell motility (that is, independent movement)It allows for cell locomotion, muscle fiber contraction, and the movement of cell organelles

The colored lines represent the fibers of the cytoskeleton

Ciliavery small, hair-like structures attached beneath the cell membrane They move in synchronized patterns that result in rows of cilia beating in coordinated waves of motion

• the wave that is created moves fluids (e.g., mucus) over the surfaces of certain tissues (e.g., the inner linings of respiratory tubes)

This cell’s cilia can be seen around the border of

the cell membrane

Flagella

Similar structure to the cilia but longer, and there is generally only one flagellum in a cell.It moves in a wavelike motion beginning at its base.The only example of a flagellum in humans is the tail of the sperm cell which allows it to swim.

Microvilli

tiny cellular membrane protrusions that increase the cell’s surface areaThey help to perform various functions, e.g.:

• absorption• secretion• movement of white blood cells

Centrioles

• usually found in eukaryotic animal cells• come in pairs and are found near the nucleus when the cell is about to divide

• aid the cell in mitosis and meiosis (i.e., they are necessary for the completion of cell division)

Lysosomes• composed of small membranous sacs• known as “the garbage disposals of the cell”• destroy damaged cell parts• contain powerful enzymes that break down nutrient

molecules and/or foreign substances• example: some white blood cells can absorb bacteria

which is digested by lysosomal enzymes in the cell

Smooth endoplasmic reticulum (SER)• found in both animal and plant cells• composed of tubules and vesicles that form a network of

“branches”• increases surface area of usage/storage of important

enzymes and their products• serves a variety of other functions, including:

• synthesis of lipids and steroids• metabolism of carbohydrates• regulation of calcium concentration• steroid metabolism• attachment of receptors on cell membrane proteins

(See picture on following slide)

Rough endoplasmic reticulum (RER)• covered in protein-producing ribosomes (this causes the

“rough” appearance, giving the RER its name)• Is most important for acting as a “home base” for

ribosomes• as the ribosomes produce an amino chain, the chain is pushed in

to the RER and once complete, sent from the RER to the cell membrane or other part of the cell

• also used for the transport of lipids and small molecules

(See picture on previous slide)

Ribosomes

• composed of complexes of RNAs and ribonucleoproteins• structure is divided into two subunits

• synthesize protein chains in a process known as translation

These “dots” are ribsomes on the rough ER

Mitochondria• provide energy• known as the “power centers” of the cell• structure consists of a smooth outer membrane and an inner

membrane that forms folds called “cristae” which increase the inner membrane’s surface area• on the cristae, sugar is combined with oxygen to create ATP

– the cell’s primary energy source

Golgi apparatus• structure consists of a series of pancake-shaped membranes• gathers simple molecules and combines them to make more

complex molecules which are either stored in vesicles or sent out of the cell

• builds lysosomes (used for digestion in the cell)

Vesicle• a small, membrane-enclosed sac that can store/transport

substances• because of this, vesicles are mainly used for organizing

and transporting substances within the cell • they are also used in:

• metabolism• maintaining the buoyancy of the cell• enzyme storage

Nucleus• composed of a nuclear envelope, a triple cell membrane,

and an outer membrane that encloses the entire organelle• contains most of the cell’s genetic material through

chromatin• the nucleus controls these genes and directs the activities

of the cell

Nucleolus

• composed of proteins and nucleic acids• located inside the nucleus• the organelle where ribosomal RNA is transcribed and assembled