CELLS

Structure

Cell Membrane Surrounds the cell to separate it from its external

environment Composed of a phospholipid bilayer that has proteins

embedded in it Cholesterol is also an important component of cell

membranes since it keeps the membrane intact yet fluid The membrane acts as a selective barrier by controlling

what substances enter and leave the cell

Membrane Structures Microvilli (microvillus):

extensions of the cell membrane used to increase the surface area of the cell

Cilia (cillium): short, hair-like extensions on the cell membrane used for movement

Flagella (Flagellum): long, whip-like structures used for movement

Cell Interior

Cytoplasm: A semi-fluid substance in which all of

the cell’s organelles are suspended Located between the nucleus and the

cell membrane Contains the cytoskeleton

Cytoskeleton: a network of microtubules that support the cell and give it shape

Nucleus Nucleus: the control center of the cell

and where the cell’s DNA is located Nuclear Membrane:

Separates the nucleus from the cytoplasm Contains pores so that substances may enter

or leave the nucleus Nucleolus: structure within the nucleus

that is responsible for making rRNA Nucleoplasm: similar to the cytoplasm, it

is a semifluid substance in which the DNA and nucleolus are suspended

Organelles Endoplasmic reticulum (ER):

Extensive network of membranes There are 2 types:

Rough ER: contains ribosomes that make proteins destined to leave the cell

Smooth ER: makes lipids, steroids, and is involved in detoxification; important in cells that are responsible for ridding the body of toxic substances (i.e. liver)

Organelles (cont.) Ribosomes:

Structures involved in protein synthesis

Found attached to the RER or suspended in the cytoplasm

Mitochondria: structures used to make ATP (energy compound)

Golgi complex (apparatus): Series of flat membrane-bound sacs Packages proteins made from the

RER and sends them in membrane-bound vesicles to their destination

Organelles (cont.)

Vacuole: Membrane-bound compartment that

serves many functions (i.e. absorbs water, stores proteins, stores wastes, etc.)

Plant cells have one large central vacuole whereas animal cells contain several small vacuoles

Organelles (cont.) Lysosome:

Membrane-bound organelles filled with hydrolytic enzymes

These enzymes are used to break down substances (i.e. carbohydrates, proteins, lipids, old organelles, etc.)