Cells
Functions and structure
• Can we see cells?
• How many cells do you have in your
body?
• All living organisms on Earth are divided in
pieces called cells. There are smaller pieces to
cells that include proteins and organelles. There
are also larger pieces called tissues and
systems.
• A cell is a small, membrane enclosed structure
filled with an aqueous solution where organelles
and other subcellular structures are found.
• Cells are small compartments
that hold all of the biological
equipment necessary to keep
an organism alive and
successful on Earth.
Looking at cell functions
• A main purpose of a cell is to organize.
Cells hold a variety of pieces but in the big
picture, a cell's purpose is much more
important than acting as small
organizational pieces, there are several
main functions that the cell has to carry
out: molecule transport, reproduction, and
energy conversion.
Cell types
• Living cells are divided into two types procaryotic and eucaryotic (sometimes
spelled prokaryotic and eukaryotic).
This division is based on internal
complexity.
PROKARYOTES - MISSING A
NUCLEUS
• If you're looking to learn
about
cells
with
a
nucleus, this is the wrong
place. Prokaryotes do not
have
an
organized
nucleus. Their DNA is
kind of floating around
the cell. It's clumped up,
but not inside of a
nucleus.
Most prokaryotes are
bacteria and bacteria
can do amazing things.
Although they are very
simple organisms, they
are found everywhere on the planet. Some
scientists even think that they may be
found on other planets (maybe even Mars).
Some places you can find bacteria every
day are in your intestines, a cup of natural
yogurt, or a bakery. Prokaryotes are the
simplest of simple organisms.
• Prokariotic main characteristics are:
(1) Prokaryotes have no organized nucleus. Like we said,
the DNA is clumped in an area but there is no organized
nucleus with a membrane.
(2) Prokaryotes do not usually have any organelles. They
will probably have ribosomes inside of their cells, but
ribosomes are not technically considered organelles. No
chloroplasts. No mitochondria. No nucleus. Not much at all.
(3) Prokaryotes are very small. Because
they don't have all of the normal cell
machinery, they are limited in size. As
always in biology, there are exceptions,
but generally, prokaryotes are very
small (compared to other cells). Mind you, compared to a
virus they are big, but next to an amoeba, tiny.
Prokaryotic structure
Internal Structure
External Structure
Internal Structure
Bacteria have a very simple internal
structure, and no membrane-bound
organelles.
Back
Nucleoid:
DNA in the bacterial cell is generally
confined to this central region. Though
it isn't bounded by a membrane, it is
visibly distinct (by transmission
microscopy) from the rest of the cell
interior.
Back
Ribosomes:
Ribosomes give the
cytoplasm of bacteria a
granular appearance
in electron micrographs. Though smaller than
the ribosomes in eukaryotic cells, these
inclusions have a similar function in translating
the genetic message in messenger RNA into the
production of peptide sequences (proteins).
Back
Surface Structure
Beginning from the
outermost structure
and moving inward, bacteria have some
or all of the following structures:
Back
Capsule:
This layer of polysaccharide (sometimes
proteins) protects the bacterial cell and
is often associated with pathogenic
bacteria because it serves as a barrier
against phagocytosis by white blood
cells.
Back
• cell wall:
Composed of peptidoglycan
(polysaccharides + protein), the cell wall
maintains the overall shape of a bacterial
cell. The three primary shapes in bacteria
are coccus (spherical), bacillus (rodshaped) and spirillum (spiral).
Mycoplasma are bacteria that
have no cell wall and
therefore have no definite
shape.
Back
• Plasma membrane:
This is a lipid bilayer much like the
cytoplasmic (plasma) membrane of other
cells. There are numerous proteins
moving within or upon this layer that are
primarily responsible for transport of
ions, nutrients and waste across the
membrane.
Back
• Pili:
These hollow, hairlike
structures made of
protein allow bacteria
to attach to other cells. A specialized
pilus, the sex pilus, allows the transfer
of plasmid DNA from one bacterial cell
to another. Pili (sing., pilus) are also
called fimbriae (sing., fimbria).
Back
Flagella:
The purpose of flagella (sing., flagellum)
is motility. Flagella are long appendages
which rotate by means of a "motor"
located just under the cytoplasmic
membrane. Bacteria may have one, a
few, or many flagella in
different positions on
the cell.
Back
QUIZ
• Which of these would not be found in a prokaryotic
cell?
A. ribosomes
B. cell membrane
C. nucleus
D. DNA
• Prokaryotic cells have the following structures:
A. Ribosomes, cell membrane, nucleus, cell
wall
B. Capsule, cell wall, plasma membrane,
nucleoid ,
ribosomes
C. cell wall, plasma membrane, nucleoid,
ribosomes and mitochondria
D. Capsule, cell wall, plasma membrane, nucleus ,
ribosomes
• http://www.cellsalive.com/cells/cell_model.htm
• http://www.biology4kids.com/files/cell2_main.h
tml
• The cell song:
http://www.youtube.com/watch?v=oNZsvG_OD
G4&feature=related
• How the body works (video):
http://www.neok12.com/php/watch.php?v=zX60
6f017b425c70037a435d&t=Cell-Structures
• Cell structure Video:
http://www.mhln.com/ob/assets/00035501/ht
m/00035804/00035804.htm