Download Chapter 6

Chapter 6 - Cells
Overview: The Importance of Cells
• All organisms are made of cells
• The cell is the simplest collection of matter
that can live
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Microscopy
• Scientists use microscopes to visualize cells
too small to see with the naked eye
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• Light microscopes (LMs)
– Pass visible light through a specimen
– Magnify cellular structures with lenses
– Able to view living specimens
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• Electron microscopes (EMs)
– Focus a beam of electrons onto its surface
(SEM) or through a specimen (TEM)
– Can view much smaller cell structures
– Specimen must be dead
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• The scanning electron microscope (SEM)
– Provides for detailed study of the surface of a
specimen
RESULTS
1 µm
Cilia
Figure 6.4 (a)
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• The transmission electron microscope (TEM)
– Provides for detailed study of the internal
ultrastructure of cells
Longitudinal
section of
cilium
Figure 6.4 (b)
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Cross section
of cilium
1 µm
Cell Types
• Two types of cells make up every organism
– Prokaryotic
– Eukaryotic
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Comparing Prokaryotic and Eukaryotic Cells
• All cells have several basic features in common
– They are bounded by a plasma membrane
– They contain a semifluid substance called the
cytosol
– They contain chromosomes
– They all have ribosomes
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Distinguishing Characteristics
• Prokaryotic cells
– Do not contain a nucleus
– Have their DNA located in a region called
the nucleoid
– Small
– Simple
– Old (3.5 Billion years old)
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Pili: attachment structures on
the surface of some prokaryotes
Nucleoid: region where the
cell’s DNA is located (not
enclosed by a membrane)
Ribosomes: organelles that
synthesize proteins
Bacterial
chromosome
Plasma membrane: membrane
enclosing the cytoplasm
Cell wall: rigid structure outside
the plasma membrane
Capsule: jelly-like outer coating
of many prokaryotes
(a) A typical
rod-shaped bacterium
Figure 6.6 A, B
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
0.5 µm
Flagella: locomotion
organelles of
some bacteria
(b) A thin section through the
bacterium Bacillus coagulans
(TEM)
• Eukaryotic cells
– Eukaryotic cells have internal membranes that
compartmentalize their functions
– Contain a true nucleus, bounded by a
membranous nuclear envelope
– Are generally quite a bit bigger than
prokaryotic cells
– Complex
– “Newer” (only 1.5 Billion years old)
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• The plasma membrane
– Functions as a selective barrier
– Allows sufficient passage of nutrients
and waste
Outside of cell
Carbohydrate side chain
Hydrophilic
region
Inside of cell
0.1 µm
Hydrophobic
region
Figure 6.8 A, B
(a) TEM of a plasma
membrane. The
plasma membrane,
here in a red blood
cell, appears as a
pair of dark bands
separated by a
light band.
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
A Panoramic View of the Eukaryotic Cell
• Eukaryotic cells
– Have extensive and elaborately arranged
internal membranes, which form organelles
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• Plant and animal cells
– Have most of the same organelles
– Only Animals have
• Lysosomes, Centrioles, Flagella (in some
plant sperm)
– Only Plants have
• Chloroplasts, Central vacuole, Cell wall,
Plasmodesmata
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• A animal cell
ENDOPLASMIC RETICULUM (ER)
Rough ER
Smooth ER
Nuclear envelope
Nucleolus
NUCLEUS
Chromatin
Flagelium
Plasma membrane
Centrosome
CYTOSKELETON
Microfilaments
Intermediate filaments
Ribosomes
Microtubules
Microvilli
Golgi apparatus
Peroxisome
Figure 6.9
Mitochondrion
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Lysosome
In animal cells but not plant cells:
Lysosomes
Centrioles
Flagella (in some plant sperm)
• A plant cell
Nuclear envelope
Nucleolus
Chromatin
NUCLEUS
Centrosome
Rough
endoplasmic
reticulum Smooth
endoplasmic
reticulum
Ribosomes (small brwon dots)
Central vacuole
Tonoplast
Golgi apparatus
Microfilaments
Intermediate
filaments
CYTOSKELETON
Microtubules
Mitochondrion
Peroxisome
Plasma membrane
Chloroplast
Cell wall
Plasmodesmata
Wall of adjacent cell
Figure 6.9
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
In plant cells but not animal cells:
Chloroplasts
Central vacuole and tonoplast
Cell wall
Plasmodesmata
1) Nucleus and Ribosomes
•The nucleus
– Contains most of the genes in the
eukaryotic cell
– Bound by a nuclear envelope
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• The nuclear envelope
– Encloses the nucleus, separating its contents
from the cytoplasm
Nucleus
1 µm
Nucleolus
Chromatin
Nucleus
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Rough ER
Surface of nuclear
envelope.
1 µm
Ribosome
0.25 µm
Close-up of
nuclear
envelope
Figure 6.10
Pore complexes (TEM).
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Nuclear lamina (TEM).
Ribosomes: Protein Factories in the Cell
• Ribosomes
– Are particles made of ribosomal RNA
and protein
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
– Carry out protein synthesis
Ribosomes
ER
Cytosol
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large
subunit
0.5 µm
TEM showing ER and ribosomes
Figure 6.11
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Small
subunit
Diagram of a ribosome
2) Endomembrane System
The endomembrane system
– Includes many different structures
• Nuclear envelope
• Endoplasmic reticulum (ER)
• Golgi apparatus
• Lysosomes
• Vacuoles
• Plasma membrane
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
The Endoplasmic Reticulum: Biosynthetic Factory
• The endoplasmic reticulum (ER)
– Accounts for more than half the total
membrane in many eukaryotic cells
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• The ER membrane
– Is continuous with the nuclear envelope
Smooth ER
Rough ER
Nuclear
envelope
ER lumen
Cisternae
Ribosomes
Transitional ER
Transport vesicle
Smooth ER
Rough ER 200 µm
Figure 6.12
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• There are two distinct regions of ER
– Smooth ER, which lacks ribosomes
– Rough ER, which contains ribosomes
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Functions of Smooth ER
• The smooth ER
– Synthesizes lipids
– Metabolizes carbohydrates
– Stores calcium
– Detoxifies poison
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Functions of Rough ER
• The rough ER
– Has bound ribosomes
– Produces proteins and membranes, which are
distributed by transport vesicles
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
The Golgi Apparatus: Shipping and
Receiving Center
• The Golgi apparatus
– Receives many of the transport vesicles
produced in the rough ER
– Consists of flattened membranous sacs called
cisternae
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
•Functions of the Golgi
apparatus include
– Modification of the
products of the rough
ER
– Manufacture of certain
macromolecules
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
3) Lysosomes: Digestive Compartments
• A lysosome
– Is a membranous sac of hydrolytic enzymes
– Can digest all kinds of macromolecules
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• Lysosomes carry out intracellular digestion by
a) Phagocytosis – eating by engulfing
Nucleus
1 µm
Lysosome
Lysosome contains
active hydrolytic
enzymes
Food vacuole
fuses with
lysosome
Hydrolytic
enzymes digest
food particles
Digestive
enzymes
Lysosome
Plasma membrane
Digestion
Food vacuole
Figure 6.14 A
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
(a) Phagocytosis: lysosome digesting food
b) Autophagy
• Recycling cell’s own organic
material
Figure 6.14 B
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
4) Vacuoles: Diverse Maintenance Compartments
• A plant or fungal cell
– May have one or several vacuoles
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• Central vacuoles
– Are found in plant cells
– Hold reserves of important organic
compounds and water
Central vacuole
Cytosol
Tonoplast
Nucleus
Central
vacuole
Cell wall
Chloroplast
Figure 6.15
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
5 µm
5) Mitochondria and Chloroplasts
• Mitochondria
– Are the sites of cellular respiration
• Chloroplasts
– Found only in plants, are the sites of
photosynthesis
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Mitochondria: Chemical Energy Conversion
• Mitochondria
– Are found in nearly all eukaryotic cells
– Cells may have a few or 1000’s
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• Mitochondria are enclosed by two membranes
– A smooth outer membrane
– An inner membrane folded into cristae
Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
Figure 6.17
Mitochondrial
DNA
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
100 µm
Chloroplasts: Capture of Light Energy
• The chloroplast
– Contains chlorophyll
– Are found in leaves and other green organs of
plants and in algae
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Cytoskeleton
The cytoskeleton is a network of fibers that
organizes structures and activities in the cell
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• The cytoskeleton
– Is a network of fibers extending throughout the
cytoplasm
Microtubule
Figure 6.20
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
0.25 µm
Microfilaments
Roles of the Cytoskeleton: Support, Motility, and Regulation
• The cytoskeleton
– Gives mechanical support to the cell
– Is involved in cell motility, which utilizes motor
proteins
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
•There are three main types of fibers that
make up the cytoskeleton
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Microtubules
• Microtubules
– Hollow rods
– Shape the cell
– Guide movement of organelles
– Help separate the chromosome copies in
dividing cells
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Examples: Centrosomes and Centrioles
•The centrosome
– Is considered to be a “microtubuleorganizing center”
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Examples: Cilia and Flagella
• Cilia and flagella
– Contain specialized arrangements of
microtubules
– Are locomotor appendages of some cells
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Microfilaments (Actin Filaments)
• Microfilaments
– Solid rods
– Bear tension
– Help muscle cells contract
– Form cleavage furrow (when cell divides)
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Intermediate Filaments
• Intermediate filaments
– Support cell shape
– Fix organelles in place
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Extracellular
Extracellular components and connections
between cells help coordinate cellular activities
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
The Extracellular Matrix (ECM) of Animal Cells
• Animal cells
– Lack cell walls
– Are covered by an elaborate matrix, the ECM
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• The ECM
– Is made up of glycoproteins and other
macromolecules
EXTRACELLULAR FLUID
Collagen
A proteoglycan
complex
Polysaccharide
molecule
Carbohydrates
Core
protein
Fibronectin
Plasma
membrane
Integrin
Integrins
Microfilaments
Figure 6.29
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
CYTOPLASM
Proteoglycan
molecule
• Functions of the ECM include
– Support
– Adhesion
– Movement
– Regulation
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
Intercellular Junctions – Animal Cells
• In animals, there are three types of intercellular
junctions
– Tight junctions – prevent leakage of EC fluid
– Desmosomes – fasten cells together
– Gap junctions – provide cytoplasmic channels
from one cell to another
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
• Types of intercellular junctions in animals
TIGHT JUNCTIONS
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
At tight junctions, the membranes of
neighboring cells are very tightly pressed
against each other, bound together by
specific proteins (purple). Forming continuous seals around the cells, tight junctions
prevent leakage of extracellular fluid across
A layer of epithelial cells.
DESMOSOMES
Desmosomes (also called anchoring
junctions) function like rivets, fastening cells
Together into strong sheets. Intermediate
Filaments made of sturdy keratin proteins
Anchor desmosomes in the cytoplasm.
Tight junctions
Intermediate
filaments
Desmosome
Gap
junctions
Space
between Plasma membranes
cells
of adjacent cells
1 µm
Extracellular
matrix
Gap junction
Figure 6.31
Copyright © 2006 Cynthia Garrard publishing under Canyon Design
0.1 µm
GAP JUNCTIONS
Gap junctions (also called communicating
junctions) provide cytoplasmic channels from
one cell to an adjacent cell. Gap junctions
consist of special membrane proteins that
surround a pore through which ions, sugars,
amino acids, and other small molecules may
pass. Gap junctions are necessary for communication between cells in many types of tissues,
including heart muscle and animal embryos.