Download Introduction to the Cell

Introduction to the Cell
Both living and nonliving things are made of atoms that
make up molecules. The organization of these molecules
into cells is one feature that separates living from nonliving.
A cell is the smallest unit of matter that can carry on the
processes of life.
Discovery of the cell
• Robert Hooke was credited with
coining the term “cell” after viewing
cork cells under an early microscope
(1665)
• The first person to observe LIVING
cells was Dutch microscope maker
Leeuwenhoek. (1673).
Another 150 years pass…and scientists
start making sense of their findings.
• The Cell Theory
1. All living things are composed of one or more
cells.
2. Cells are the basic units of structure and function
in an organism.
3. Cells only come from the reproduction of existing
cells.
Cell Diversity
• Not all cells are alike, even cells within the
same organism show tremendous diversity.
• They are specialized for their specific function.
For example, a nerve cell and a muscle cell are
going to look and act very differently.
Size
• Cells can range from 2 m ( taller than you!) to only 2
micrometers (2µm = .000002m).
• The average plant and animal cells are only 50 μm
(.002 inches).
• Most cells are only visible with a microscope.
• Cell size is limited by the surface area to volume
ratio. This is important because the materials a cell
needs enter through it’s surface.
Shape
• Just like they come in a variety or size, they
also come in a variety of shapes.
• The shapes tend to be well suited for their
function.
Ex: skin cells are flat, nerve cells branch out,
and white blood cells can change shape to fit
through small openings.
Types of Cells
• 1. Prokaryotic – “before nuclei”
• 2. Eukaryotic – “true cells”
Characteristics of all cells
• Have DNA
• Have a cell membrane—separates what is
inside the cell from what is outside the cell—
also controls what goes into and out of the
cell
• Have cytoplasm—jelly-like substance that
occupies most of the cell interior
• Most cells have ribosomes—small structures
on which proteins are made
Prokaryotes
• Single celled organisms with no nucleus or
other organelles
• Simplest living organisms
• Some varieties can live in extreme conditions
(high heat, ice, no oxygen, high salt, high
pressure)
• Some are heterotrophs (must eat to live)
• Some are autotrophs (can make their own
food from sunlight or chemicals)
• Include things like bacteria
• Have cytoplasm with no internal
compartments
• DNA is a single circular strand not enclosed in
a nucleus
• Have a cell wall to give it shape
• Many have flagella—thread-like structures
that allows the cell to move in its environment
Eukaryotes
• Have a nucleus with a nuclear membrane that
holds the cell’s DNA
• Plant cells have a cell wall—animal cells do
not
• Have organelles—structures which are
specialized for different functions
• May have cilia—short hair like projections
from the cell surface that can move the cell
through it’s environment or substances past
the cell surface
• Cytoskeleton—a framework of protein fibers
that gives the cell structure and shape
Viruses
•
•
•
•
Have RNA or DNA
No cell membrane or organelles
Have a capsid—protein coat
Are not considered living because they are not
cells
• Cannot reproduce without a host cell