Transcript Ch 4 Powerpoint notes

4
A Tour of
the Cell
Overview: The Fundamental Units of Life
• All organisms are made of cells
• The cell is the simplest collection of matter
that can be alive
• All cells are related by their descent from
earlier cells
• Though cells can differ substantially from one
another, they share common features
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Figure 4.1
Concept 4.1: Biologists use microscopes and the tools of
biochemistry to study cells
• Most cells are between 1 and 100 m in
diameter, too small to be seen by the unaided eye
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Microscopy
• Scientists use microscopes to visualize cells too
small to see with the naked eye
• In a light microscope (LM), visible light is passed
through a specimen and then through glass lenses
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• Three important parameters of microscopy
– Magnification
– Resolution
– Contrast
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10 m
0.1 m
Human height
Length of some
nerve and
muscle cells
Chicken egg
1 cm
100 m
10 m
1 m
100 nm
10 nm
1 nm
0.1 nm
Frog egg
Human egg
Most plant and
animal cells
Nucleus
Most bacteria
Mitochondrion
EM
1 mm
LM
1m
Unaided eye
Figure 4.2
Smallest bacteria
Viruses
Ribosomes
Proteins
Lipids
Small molecules
Atoms
Superresolution
microscopy
Figure 4.2b
100 m
100 nm
10 nm
1 nm
EM
1 m
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
Proteins
Lipids
Small molecules
0.1 nm
LM
10 m
Most plant and
animal cells
Atoms
Superresolution
microscopy
• LMs can magnify effectively to about 1,000 times
the size of the actual specimen
• Various techniques enhance contrast and enable
cell components to be stained or labeled
• Most subcellular structures, including organelles
(membrane-enclosed compartments), are too
small to be resolved by light microscopy
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• Two basic types of electron microscopes (EMs) are
used to study subcellular structures
• Scanning electron microscopes (SEMs) focus a
beam of electrons onto the surface of a specimen,
providing images that look three-dimensional
• Transmission electron microscopes (TEMs) focus a
beam of electrons through a specimen
• TEM is used mainly to study the internal structure
of cells
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Figure 4.3a
50 m
Light Microscopy (LM)
Brightfield
(unstained specimen)
Brightfield
(stained specimen)
Phase-contrast
Differential-interference
contrast (Nomarski)
Figure 4.3b
10 m
50 m
Light Microscopy (LM)
Fluorescence
Confocal
Figure 4.3c
Electron Microscopy (EM)
Longitudinal section Cross section
of cilium
of cilium
Cilia
Scanning electron
microscopy (SEM)
2 m
Transmission electron
microscopy (TEM)
Cell Fractionation
• Cell fractionation breaks up cells and separates
the components, using centrifugation
• Cell components separate based on their
relative size
• Cell fractionation enables scientists to determine
the functions of organelles
• Biochemistry and cytology help correlate cell
function with structure
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Concept 4.2: Eukaryotic cells have internal
membranes that compartmentalize their functions
• The basic structural and functional unit of every
organism is one of two types of cells: prokaryotic
or eukaryotic
• Organisms of the domains Bacteria and Archaea
consist of prokaryotic cells
• Protists, fungi, animals, and plants all consist of
eukaryotic cells
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Comparing Prokaryotic and Eukaryotic Cells
• Basic features of all cells
– Plasma membrane
– Semifluid substance called cytosol
– Chromosomes (carry genes)
– Ribosomes (make proteins)
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• Prokaryotic cells are characterized by having
– No nucleus
– DNA in an unbound region called the nucleoid
– No membrane-bound organelles
– Cytoplasm bound by the plasma membrane
• Typically much smaller than eukaryotic cells
(1-5um)
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Figure 4.4
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
(a) A typical rod-shaped
bacterium
Cell wall
Capsule
Flagella
0.5 m
(b) A thin section through
the bacterium Bacillus
coagulans (TEM)
• Eukaryotic cells are characterized by having
– DNA in a nucleus that is bounded by a membranous
nuclear envelope
– Membrane-bound organelles
– Cytoplasm in the region between the plasma
membrane and nucleus
• Eukaryotic cells are generally much larger than
prokaryotic cells (10-100um)
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• The plasma membrane is a selective barrier that
allows sufficient passage of oxygen, nutrients,
and waste to service the volume of every cell
• The general structure of a biological membrane
is a double layer of phospholipids
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Figure 4.5
Outside of cell
Inside
of cell
0.1 m
(a) TEM of a plasma
membrane
Carbohydrate side chains
Hydrophilic
region
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
Figure 4.5a
(a) TEM of a plasma
membrane
Outside of cell
Inside
of cell
0.1 m
• Metabolic requirements set upper limits on the
size of cells
• The ratio of surface area to volume of a cell is
critical
• As the surface area increases by a factor of n2, the
volume increases by a factor of n3
• Small cells have a greater surface area relative
to volume
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Figure 4.6
Surface area increases while
total volume remains constant
5
1
1
Total surface area
[sum of the surface areas
(height  width) of all box
sides  number of boxes]
6
150
750
Total volume
[height  width  length
 number of boxes]
1
125
125
6
1.2
6
Surface-to-volume
ratio
[surface area  volume]
A Panoramic View of the Eukaryotic Cell
• A eukaryotic cell has internal membranes
that divide the cell into compartments—
organelles
• The plasma membrane and organelle
membranes participate directly in the cell’s
metabolism
Animation: Tour of an Animal Cell
Animation: Tour of a Plant Cell
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Figure 4.7a
ENDOPLASMIC RETICULUM (ER)
Flagellum
Smooth ER
Rough ER
Nuclear
envelope
Nucleolus
NUCLEUS
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate
filaments
Ribosomes
Microtubules
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome
Figure 4.7b
Nuclear envelope
Nucleolus
Chromatin
Rough endoplasmic
reticulum
Smooth endoplasmic
reticulum
NUCLEUS
Ribosomes
Central vacuole
Golgi
apparatus
Microfilaments
CYTOIntermediate
SKELETON
filaments
Microtubules
Mitochondrion
Peroxisome
Plasma membrane
Cell wall
Wall of adjacent cell
Chloroplast
Plasmodesmata