Transcript Cell Structure & Function

Cell Structure
& Function
http://koning.ecsu.ctstateu.edu/cell/cell.html
Why Study Cell Biology?
The key to every
biological problem
must finally be sought
in the cell, for every
living organism is, or
at some time has
been, a cell. E.B.
Wilson, 1925
Definition of Cell
A cell is the smallest unit that is
capable of performing life
functions.
Amoeba Proteus
Plant Stem
Bacteria
Red Blood Cell
Nerve Cell
Cells are Us
Cells are Us
Cilia on a protozoan
Sperm meets egg
Cells are Us
A person contains about 100 trillion
cells. That’s 100,000,000,000,000 or
1 x 1014 cells.
There are about 200 different cell
types in mammals (one of us).
Cells are tiny, measuring on average
about 0.002 cm (20 um) across.
That’s about 1250 cells, “shoulderto-shoulder” per inch.
Red and
white blood
cells above
vesselforming
cells.
nerve cell
The Cell Theory
The cell theory (proposed independently in 1838
and 1839) is a cornerstone of biology.
All organisms are composed of one or more cells.
Schleiden
Cells are the smallest living things.
Cells arise only by division of previously existing cells.
All organisms living today are descendents of an
ancestral cell.
Schwann
A Sense of Scale and Abundance – Bacteria on the Head of a Pin
Microscopes
• Anton Von Leuwenhoek invented the first
microscope in 1674 (capable of 200X
magnification)
Light microscopes can resolve structures that are
200nm apart.
Electron microscopes can resolve structures that
are 0.2nm apart.
Why Are Cells So Small?
• However, as cell volume increases the
surface area of the cell does not expand
as quickly.
– If the cell’s volume gets too large it cannot
transport enough wastes out or nutrients in.
• Thus, surface area limits cell
volume/size.
Why Are Cells So Small?
• Strategies for increasing surface
area, so cell can be larger:
– “Frilly” edged…….
– Long and narrow…..
• Round cells will always be small.
Why Are Cells So Small?
• Cells need sufficient surface area to
allow adequate transport of nutrients in
and wastes out.
• As cell volume increases, so does the
need for the transporting of nutrients
and wastes.
Cell Structure
• All Cells have:
– an outermost plasma membrane
– genetic material in the form of
DNA
– cytoplasm with ribosomes
Two Fundamentally Different Types of Cells
A prokaryotic cell
A eukaryotic cell
Prokaryotic Cells
Prokaryotic cells lack a membrane-bound
nucleus.
-genetic material is present in the
nucleoid
Two types of prokaryotes:
-archaea
-bacteria
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Prokaryotic Cell Structure
• Structures
– Plasma membrane
– Cell wall
– Cytoplasm with ribosomes
– Nucleoid
– Capsule*
– Flagella* and pili*
*present in some, but not all prokaryotic cells
Prokaryotic Cells
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Prokaryotic Cells
Prokaryotic cell walls
-protect the cell and maintain cell shape
Bacterial cell walls
-may be composed of peptidoglycan
-may be Gram positive or Gram negative
Archaean cell walls lack peptidoglycan.
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Prokaryotic Cells
Flagella
-present in some prokaryotic cells
-used for locomotion
-rotary motion propels the cell
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Prokaryotic Cells
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Prokaryotic Cell
TEM Prokaryotic Cell
3 Shapes of Prokaryotic Cells
Shapes of Bacteria
Streptococcus pyogenes
aka Necrotizing Fasciitis
“flesh eating bacteria”
Streptococcus pyogenes is one of
the most frequent pathogens of
humans. It is estimated that between
5-15% of normal individuals harbor
the bacterium, usually in the
respiratory tract, without signs of
disease.
Staphylococcus aureus
Staphylococcus aureus
•forms a fairly large yellow colony on rich medium; S.
epidermidis has a relatively small white colony.
•Staphylococci are facultative anaerobes that grow by
aerobic respiration or by fermentation that yields principally
lactic acid.
•S. aureus can grow at a temperature range of 15 to 45
degrees and at NaCl concentrations as high as 15 percent.
•Nearly all strains of S. aureus produce the enzyme
coagulase: nearly all strains of S. epidermidis lack this
enzyme.
•S. aureus should always be considered a potential
pathogen; most strains of S. epidermidis are nonpathogenic
and may even play a protective role in humans as normal
Lactobacillus
acidophilus
Lactic Acid Bacteria (LAB) are Gram-positive, nonsporeforming cocci, coccobacilli or rods with a DNA
base composition of less than 53mol% G+C. They
generally are non respiratory and lack catalase. They
ferment glucose primarily to lactic acid, or to lactic
acid, CO2 and ethanol. All LAB grow anaerobically, but
unlike most anaerobes, they grow in the presence of
O2 as "aerotolerant anaerobes". Although they lack
catalase, they possess superoxide dismutase and
have alternative means to detoxify peroxide radicals,
generally through peroxidase enzymes.
Eukaryotic Cells
• Structures in all eukaryotic cells
– Nucleus
– Ribosomes
– Endomembrane System
• Endoplasmic reticulum – smooth and rough
• Golgi apparatus
• Vesicles
– Mitochondria
– Cytoskeleton
NUCLEUS
CYTOSKELETON
RIBOSOMES
ROUGH ER
MITOCHONDRION
CYTOPLASM
SMOOTH ER
CENTRIOLES
GOLGI BODY
PLASMA
MEMBRANE
LYSOSOME
VESICLE
Fig. 4-15b, p.59
Us vs. Them Eukaryotes and
Prokaryotes