Transcript Cells are Either Prokaryotic or Eukaryotic

BIOLOGY
A GUIDE TO THE NATURAL WORLD
FOURTH EDITION
DAVID KROGH
Life’s Home:
The Cell
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4.1 Cells are the Fundamental Units of Life
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Cells are the Fundamental Units of Life
• With the possible exception of viruses, every
form of life on Earth either is a cell or
is composed of cells.
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Cells are the Fundamental Units of Life
• Cells come into existence only through the
activity of other cells.
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4.2 All Cells are Either Prokaryotic or
Eukaryotic
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All Cells are Either Prokaryotic or
Eukaryotic
• All cells can be classified as prokaryotic or
eukaryotic.
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All Cells are Either Prokaryotic or
Eukaryotic
• Prokaryotic cells either are bacteria or another
single-celled life-form called archaea.
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All Cells are Either Prokaryotic or
Eukaryotic
• Setting bacteria and archaea aside, all other
cells are eukaryotic.
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All Cells are Either Prokaryotic or
Eukaryotic
• Eukaryotic cells have most of their DNA
contained in a membrane-lined compartment,
called the cell nucleus, whereas prokaryotic
cells do not have a nucleus.
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All Cells are Either Prokaryotic or
Eukaryotic
• Eukaryotic cells tend to be much larger than
prokaryotic cells. They have more of the
specialized internal structures called organelles
than do prokaryotic cells.
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All Cells are Either Prokaryotic or
Eukaryotic
• Many eukaryotes are multicelled organisms,
whereas all prokaryotes are single-celled.
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All Cells are Either Prokaryotic or
Eukaryotic
Prokaryotic cells
Eukaryotic cells
DNA
in “nucleoid” region
within membrane-bound
nucleus
much smaller
much larger
always single-celled
often multicellular
only one type of organelle
many types of organelles
Size
Organization
Organelles
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Figure 4.2
4.3 The Eukaryotic Cell
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The Eukaryotic Cell
• There are five principal components to the
eukaryotic cell: the nucleus, other organelles,
the cytosol, the cytoskeleton, and the plasma
membrane.
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The Eukaryotic Cell
• Organelles are “tiny organs” within the cell that
carry out specialized functions, such as energy
transfer and materials recycling.
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The Eukaryotic Cell
nuclear pores
DNA
nucleus
nuclear envelope
nucleolus
smooth endoplasmic
reticulum
free ribosomes
cytosol
cytoskeleton
lysosomes
rough
endoplasmic
reticulum
Golgi complex
plasma membrane
transport vesicle
mitochondria
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Figure 4.4
The Eukaryotic Cell
• The cytosol is the jelly-like fluid outside the
nucleus in which these organelles are
immersed.
• The cytosol should not be confused with the
cytoplasm, which is the region of the cell inside
the plasma membrane but outside the nucleus.
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The Eukaryotic Cell
• The cytoskeleton is a network of protein
filaments.
• It functions in cell structure, cell movement,
and the transport of materials within the cell.
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The Eukaryotic Cell
• The plasma membrane is the outer lining of the
cell.
• A membrane can be defined as the flexible,
chemically active outer lining of a cell or of its
compartments.
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The Eukaryotic Cell
Components of eukaryotic cells
nucleus
other organelles
cytosol
cytoskeleton
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plasma membrane
Figure 4.3
4.4 A Tour of the Animal Cell: Along the
Protein Production Path
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Tour of the Animal Cell: Along the
Protein Production Path
• Information for the construction of proteins is
contained in the DNA located in the cell
nucleus.
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The Protein Production Path
• This information is copied onto a length of
messenger RNA (mRNA) that departs the cell
nucleus through its nuclear pores and goes to
the sites of protein synthesis, structures called
ribosomes, which lie in the cytoplasm.
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The Protein Production Path
• Many ribosomes that receive mRNA chains
process only a short stretch of them before
migrating to, and then embedding in, one of a
series of sacs in a membrane network called the
rough endoplasmic reticulum (RER).
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The Protein Production Path
• The polypeptide chains produced by the
ribosomal “reading” of the mRNA sequences
are dropped from ribosomes into the internal
spaces of the RER.
• There, the polypeptide chains fold up, thus
becoming proteins, and undergo editing.
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Tour of an Animal Cell
Suggested Media Enhancement:
Tour of an Animal Cell
To access this animation go to folder C_Animations_and_Video_Files
and open the BioFlix folder.
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The Protein Production Path
• Some ribosomes are not embedded in the RER
but instead remain free-standing in the cytosol.
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The Protein Production Path
• Materials move from one structure to another in
the cell via the endomembrane system.
• Here a piece of membrane, with proteins or
other materials inside, can bud off from one
organelle, move through the cell, and then fuse
with another membrane-lined structure.
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The Protein Production Path
• Membrane-lined structures that carry cellular
materials are called transport vesicles.
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The Protein Production Path
• Once protein processing is finished in the rough
ER, proteins undergoing processing move, via
transport vesicles, to the Golgi complex.
• They are processed further and marked for
shipment to appropriate cellular locations.
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The Golgi Complex
Golgi complex
1. Transport vesicle from
RER fuses with Golgi
2. Protein undergoes
more processing
in Golgi
cisternae
cisternal
space
vesicle
Side chains are edited
(sugars may be
trimmed, phosphate
groups added).
to cytosol
3. Proteins are
sorted and
shipped…
for export
out of cell
to plasma
membrane
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Figure 4.8
4.5 Outside the Protein Production Path:
Other Cell Structures
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Outside the Protein Production Path:
Other Cell Structures
• The smooth endoplasmic reticulum is a network
of membranes that functions to synthesize
lipids and to detoxify potentially harmful
substances.
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Lysosomes and Cellular Recycling
• Lysosomes are organelles that break down
worn-out cellular structures or foreign materials
that come into the cell.
• Once this digestion is completed, the lysosomes
return the molecular components of these
materials to the cytoplasm for further use.
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Lysosomes and Cellular Recycling
lysosome
worn-out
organelle
digestive
enzymes
1. Lysosome fuses
with worn-out
organelle.
2. Organelle
broken down.
5. Usable molecules
recycled to make
new organelles.
3. Small molecules
returned to cytosol.
4. Waste molecules
expelled from cell.
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Figure 4.9
Mitochondria and Energy
• Mitochondria are organelles that function to
extract energy from food and to transform this
energy into a chemical form the cell can use,
the molecule ATP.
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Mitochondria and Energy
Mitochondrion
food
oxygen
outer
membrane
inner
membrane
water
carbon dioxide
ATP
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Figure 4.10
4.6 The Cytoskeleton: Internal Scaffolding
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The Cytoskeleton: Internal Scaffolding
• Cells have within them a web of protein
strands, called a cytoskeleton.
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The Cytoskeleton: Internal Scaffolding
• The cytoskeleton provides the cell with
structure, facilitates the movement of materials
inside the cell, and facilitates cell movement.
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The Cytoskeleton: Internal Scaffolding
• There are three principal types of cytoskeleton
elements.
• Ordered by size, going from smallest to largest
in diameter, they are microfilaments,
intermediate filaments, and microtubules.
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Microfilaments
(a) Microfilaments
7 nm
(b) Intermediate filaments
10 nm
Main function: changes
in cell shape
(c) Microtubules
25 nm
Main function:
maintenance of cell shape
Main functions: maintenance
of cell shape, movement of
organelles, cell mobility
(cilia and flagella)
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Figure 4.11
Microfilaments
• Microfilaments are made of the protein actin.
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Microfilaments
• They help the cell move and capture prey by
forming rapidly in the direction of movement
and decomposing rapidly at their other end.
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Microfilaments
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Figure 4.12
Intermediate Filaments
• Intermediate filaments provide support and
structure to the cell.
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Microtubules
• Microtubules play a structural role in cells and
facilitate the movement of materials inside the
cell by serving as transport “rails.”
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Microtubules
• Cilia and flagella are extensions of cells
composed of microtubules.
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Cilia
• Cilia extend from cells in great numbers,
serving to move the cell or to move material
around the cell.
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Flagella
• By contrast, one—or at most a few—flagella
extend from cells that have them.
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Flagella
• The function of flagella is cell movement.
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Functions of Microtubules
(a) Transport monorails
transport
vesicle
motor proteins
microtubule
(b) Cilia
(c) Flagellum
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Figure 4.13
4.7 The Plant Cell
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Tour of a Plant Cell
Suggested Media Enhancement:
Tour of a Plant Cell
To access this animation go to folder C_Animations_and_Video_Files
and open the BioFlix folder.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
The Plant Cell
• Plant cells have most of the structures found in
animal cells— ribosomes, a cell nucleus, a
rough ER, and so forth—although plant cells do
not have the lysosomes found in animal cells.
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The Plant Cell
• Plant cells have three structures not found in
animal cells:
– a cell wall
– a large central vacuole
– the organelles called chloroplasts
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The Plant Cell
Plant cells have a cell
wall, chloroplasts, and a
central vacuole, while
animal cells do not.
cytoskeleton
cell wall
nuclear envelope
nuclear pores
nucleus
DNA
nucleolus
rough endoplasmic
reticulum
smooth endoplasmic
reticulum
free ribosomes
chloroplast
Golgi complex
central
vacuole
cytosol
plasma
membrane
mitochondrion
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Figure 4.16
The Central Vacuole
• The central vacuole stores nutrients and
degrades waste products.
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The Cell Wall
• The cell wall gives the plant structural strength
and helps regulate the intake and retention of
water.
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Chloroplasts
• Chloroplasts are the sites of photosynthesis.
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Chloroplasts
water
carbon dioxide
minerals
outer membrane
inner membrane
sugar (food)
oxygen
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Figure 4.18
The Structure of Cells
PLAY
Animation 4.1: The Structure of Cells
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4.8 Cell-to-Cell Communication
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Cell-to-Cell Communication
• Cells are able to communicate with each other
through special structures.
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Communication Among Plant Cells
• Plant cells have channels, called
plasmodesmata, that are always open and
hence have the effect of making the cytoplasm
of one plant cell continuous with that of
another.
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Communication Among Animal Cells
• Adjacent animal cells have channels, called gap
junctions, that are composed of protein
assemblages that open only as necessary.
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Communication Among Animal Cells
• These gap junctions allow the movement of
small molecules and electrical signals between
cells.
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Cell Communication
Plant tissues
plasma
membrane
cell walls
cytoplasm
plasmodesmata
Animal tissues
gap junction
plasma
membranes
cytoplasm
(a) Plasmodesmata
In plants, a series of tiny pores
between plant cells, the
plasmodesmata, allow for the
movement of materials among cells.
Thanks to the plasmodesmata
channels, the cytoplasm of one cell
is continuous with the cytoplasm of
the next; the plant as a whole can
be thought of as having a single
complement of continuous
cytoplasm.
(b) Gap junctions
In animals, protein assemblies
come into alignment with one
another, forming communication
channels between cells. A cluster
of many such assemblies—perhaps
several hundred—is called a
gap junction.
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Figure 4.19
Structures in Plant and Animal Cells
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Table 4.1