Introduction to Cells
Why does this cell look like a fried
egg?
• Cells vary greatly in their size and shape.
• A cell’s shape reflects its function.
• Cells can be branched, flat, round, or
rectangular.
– The Cell theory has three principles.
• All organisms are made of cells.
• All living cells are produced by other living cells.
• The cell is the most basic unit of life.
– All cells share certain characteristics.
• All cells are enclosed
by a membrane.
• All cells are filled with
cytoplasm.
• All cells have DNA.
• All cells have ribosomes.
cell membrane
cytoplasm
Bacterium
(colored SEM; magnification 8800x)
• There are two cell types: eukaryotic cells
and prokaryotic cells.
– Eukaryotic cells have a
nucleus.
nucleus
– Eukaryotic cells
have membranebound organelles.
organelles
cell membrane
– Prokaryotic
cells do not
have a nucleus.
– Prokaryotic
cells do not
have
membranebound
organelles.
nucleus
organelles
cell membrane
cytoplasm
Prokaryotic and Eukaryotic cells
Cytoskeleton
•The cytoskeleton helps the cell move, keep
its shape, and organize its parts.
Click to animate the image.
A
B
C
D
• Several organelles are involved in making
and processing proteins.
– The nucleus stores genetic information.
The Nucleus
B
C
D
A
The nucleolus is a structure within the nucleus where
ribosomes are made.
– Many processes occur in the endoplasmic
reticulum.
There are two types of
endoplasmic reticulum
• rough endoplasmic
reticulum
• smooth endoplasmic
reticulum
• Rough ER has ribosomes and takes part
in the production of protein
• Smooth ER lacks ribosomes. Smooth ER
makes lipids and breaks down drugs and
alcohol.
– Ribosomes link amino acids to form proteins.
– Ribosomes link amino acids to form proteins.
– Vesicles are membrane-bound sacs that hold
materials.
– Vesicles help maintain homeostasis by storing
and releasing a variety of substances as the
cell needs them.
Golgi apparatus
Protein Processing
Making and Exporting Proteins
• The ribosomes located on the rough ER make
proteins which then cross into the membranes of
the ER. The ER membrane then pinches off and
forms a vesicle around the proteins.
• Vesicles transport the proteins from the rough
ER to the Golgi apparatus, where they are
modified by enzymes and repackaged in new
vesicles.
• These new vesicles transport the modified
proteins to the cell membrane to be released
outside the cell.
Lysosomes
• A lysosome is a vesicle
produced by the Golgi
apparatus that contains
enzymes that break down
large molecules.
• Lysosomes recycle old or
damaged organelles and
digest food particles to
provide nutrients for the
cell.
Mitochondrion
• Mitochondria supply energy
to the cell.
• Mitochondria use energy from organic
compounds to make ATP.
• Vacuoles are fluid-filled sacs that hold
materials.
Centrioles are tubes found in the
centrosomes.
• Centrioles help divide
DNA.
• Centrioles form cilia and
flagella.
• Plant cells have cell walls and
chloroplasts.
– A cell wall provides rigid support.
– Chloroplasts convert solar energy to chemical
energy.