Transcript Chapter 6 - juan

A Tour of the Cell
Eukaryotic cells have internal membranes that
compartmentalize their functions
•
Basic features of all cells: plasma membrane, cytosol, chromosomes,
ribosomes
•
Prokaryotic vs Eukaryotic cells
–
–
prokaryotic cells  Bacteria and Archaea
•
No nucleus
•
DNA in an unbound region called the nucleoid
•
No membrane-bound organelles
•
Cytoplasm bound by the plasma membrane
eukaryotic cells  Protists, fungi, animals and plants
•
DNA in a nucleus bounded by nuclear envelope
•
Membrane-bound organelles
•
Cytoplasm in the region between the plasma membrane and
nucleus
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Fig. 6-6
Prokaryotic cell
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 µm
Flagella
Eukaryotic Animal Cell
Fig. 6-9a
ENDOPLASMIC RETICULUM (ER)
Flagellum***
(not in plants)
Rough ER
Nuclear
envelope
Nucleolus
NUCLEUS
Smooth ER
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate
filaments
Microtubules
Ribosomes
Microvilli
Golgi
apparatus
Peroxisome
Mitochondrion
Lysosome***
(not in plants/prokaryotes)
Fig. 6-9b
Eukaryotic Plant Cell
NUCLEUS
Nuclear envelope
Nucleolus
Chromatin
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Ribosomes
Central
vacuole***
Golgi
apparatus
Microfilaments
Intermediate
filaments
Microtubules
CYTO-SKELETON
Mitochondrion
Peroxisome
Plasma
membrane
Chloroplast***
Cell
wall***
Plasmodesmata***
Wall of adjacent cell
***specific to plants
Organelles to know
•
Nucleus – Genetic information
•
Ribosomes – protein factories
•
Endoplasmic Reticulum – protein trafficking and metabolic functions
•
Golgi Apparatus – shipping and receiving center
•
Lysosomes – digestive compartments
•
Vacuoles – maintenance compatments
•
Mitochondria – chemical energy conversion (site of cellular respiration)
•
Chloroplasts – light energy conversion (site of photosynthesis)
•
Peroxisomes - oxidation
•
Cytoskeleton – support, motility and regulation
•
Extracellular Matrix – support, adhesion, movement, regulation
•
Intercellular Junctions – facilitate contact between cells
Nucleus: Information Central
–
nuclear envelope encloses the nucleus, separating it from the
cytoplasm
–
nuclear membrane is a double membrane; each membrane
consists of a lipid bilayer
–
Pores regulate the entry and exit of molecules from the nucleus
–
The shape of the nucleus is maintained by the nuclear lamina,
which is composed of protein
–
In the nucleus, DNA and proteins form genetic material called
chromatin
–
Chromatin condenses to form discrete chromosomes
–
The nucleolus is located within the nucleus and is the site of
ribosomal RNA (rRNA) synthesis
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Fig. 6-10
Nucleus
1 µm
Nucleolus
Chromatin
Nuclear envelope
Nuclear pore
Pore
complex
Surface of
nuclear envelope
Ribosome
1 µm
0.25 µm
Close-up of nuclear
envelope
Pore complexes
Nuclear lamina
Ribosomes: Protein factories
–
particles made of ribosomal RNA and protein
–
Protein synthesis occurs here
• Free ribosomes are localized to the cytosol
• Bound ribosomes are on the ER or the nuclear envelope
Cytosol
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large subunit
Fig. 6-11
Small subunit
Diagram of a ribosome
Endoplasmic Reticulum (ER): Protein Trafficking
–
The ER membrane is attached to the nuclear envelope
–
There are two distinct regions of ER:
• Smooth ER  lacks ribosomes
–
Synthesizes lipids
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Metabolizes carbohydrates
–
Detoxifies poison
–
Stores calcium
• Rough ER with ribosomes
–
Secretes glycoproteins (proteins covalently bonded to
carbohydrates)
–
Distributes transport vesicles, proteins surrounded by
membranes
–
membrane factory for the cell
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Fig. 6-12
Smooth ER
Rough ER
Nuclear
envelope
Ribosomes
Transport vesicle
Rough ER
Smooth ER
Golgi apparatus: Shipping and Receiving Center
–
shipping and receiving center
–
consists of flattened membranous sacs called cisternae
–
Functions:
• Modifies products of the ER
• Manufactures certain macromolecules
• Sorts and packages materials into transport vesicles
Cisternae
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Lysosome: Digestive Compartment
–
a membranous sac of hydrolytic enzymes that can digest macromolecules
–
Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and
nucleic acids
•
After phagocytosis (engulfing of another cell) lysosomes fuse with the
food vacuole and digests the molecules
•
Autophagy uses enzymes to recycle the cell’s own organelles and
macromolecules
(a) Phagocytosis
Lysosome
(b) Autophagy
Digestive
enzymes
Plasma
membrane
Lysosome
Peroxisome
Digestion
Food vacuole
Vesicle
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Mitochondrion
Digestion
Fig. 6-15
Vacuoles: Maintenance Compartment
–
–
–
–
Diverse
Maintenance
Compartments
Central
vacuole
Food
vacuoles are
formed by
phagocytosis
Contractile
vacuoles
pump excess
water out of
cells
Cytosol
Nucleus
Cell wall
Chloroplast
Central
vacuoles (in
many mature
plant cells)
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Education, Inc., publishing as Pearson Benjamin Cummings
hold
organic
Central
vacuole
The Endomembrane System: A Review
• The endomembrane system is a complex and dynamic
player in the cell’s compartmental organization
– Nuclear envelope
– ER
– Golgi apparatus
– Lysosomes
– Vacuoles
– Plasma membrane
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Fig. 6-16-3
Nucleus
Rough ER
Smooth
ER
Transport vessicle
Golgi
Transport vessicle
Lysosome
Plasma
membrane
•Nuclear envelope is connected to rough ER
•Proteins produced by the ER flow in transport vessicles to the Golgi
•Golgi pinches off vessicles that give rise to lysosomes, vessicles and vacuoles
•Lysosomes can fuse with another vessicle for digestion
•Transport vessicle carries proteins to plasma membrane for secretion
•Plasma membrane expands by fusion of vessicles; proteins are secreted from the cell
Mitochondria: Chemical Energy Conversion
–
sites of cellular respiration, a metabolic process that generates ATP
–
Have a double membrane
–
Contain their own DNA
–
Mitochondria are in nearly all eukaryotic cells
–
They have a smooth outer membrane and an inner membrane folded
into cristae
• Cristae present a large surface area for enzymes that
synthesize ATP
–
The inner membrane creates two compartments: intermembrane
space and mitochondrial matrix
• Some metabolic steps of cellular respiration are catalyzed in the
mitochondrial matrix
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Fig. 6-17
Intermembrane space
Outer
membrane
Free ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
0.1 µm
Chloroplasts: Light Energy Conversion
– Capture light energy, are the sites of photosynthesis
– found in plants and algae
– Have a double membrane (similar to mitochondria)
– Contain their own DNA (similar to mitochondria)
– contain chlorophyll and other molecules that function in photosynthesis
– found in leaves and other green organs of plants and in algae
Ribosomes
Stroma
Inner and outer
membranes
Granum
Thylakoid
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1 µm
Peroxisome: Oxidation
– oxidative organelles
– specialized
metabolic
compartments
bounded by a single
membrane
Chloroplast
Peroxisome
Mitochondrion
– produce hydrogen
peroxide and convert
it to water
– Oxygen is used to
break down different
types of molecules
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1 µm
Cytoskeleton: Support, Motility and Regulation
–
a network of fibers extending throughout the cytoplasm
–
organizes the cell’s structures and activities, anchoring many
organelles
–
composed of three types of molecular structures:
• Microtubules are the thickest of the three components
• Microfilaments, also called actin filaments, are the thinnest
components
• Intermediate filaments are fibers with diameters in a middle
range
–
helps to support the cell and maintain its shape
–
interacts with motor proteins to produce motility
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Microtubules
•
•
•
Functions
–
Shaping the cell
–
Guiding movement of organelles
–
Separating chromosomes during cell division
Centrosomes
–
The centrosome is a “microtubule-organizing center”
–
microtubules grow out from a centrosome near the nucleus and
attach to chromosomes during mitosis
Cilia and Flagella
–
Microtubules control the beating of cilia and flagella
–
A core of microtubules sheathed by the plasma membrane
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Microtubules separate chromosomes during mitosis
Centrosome
microtubules
Microtubule
centrosome
Fig. 6-22
Microtubules assist in motility
(a) EX: Motion of flagella in sperm
Fig. 6-23
(b) EX: Motion of cilia in aquatic life
Fig. 6-24
Microtubule structure in cilia
Plasma
membrane
Microtubules
Plasma
membrane
(b) Cross section of
cilium
Basal body
(a) Longitudinal
section of cilium
(c) Cross section of basal body
Microfilaments (Actin Filaments)
•
Microfilaments are solid rods
built as a twisted double chain of
actin subunits
•
The structural role: bear tension
and resist pulling forces within the
cell
•
Cellular function: cellular motility
–
•
Microvillus
Microfilaments
(actin filaments)
Myosin and actin contribute to
this
Examples
–
Muscle contraction
–
Ameoboid movement occurs
through Pseudopodia
–
Cytoplasmic streaming
Intermediate
filaments
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Intermediate Filaments
•
They support cell shape and fix organelles in place
•
more permanent cytoskeleton fixtures than the other two classes
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Cell Walls of Plants
• Prokaryotes, fungi, and some protists also have cell walls
• Functions: protects the plant cell, maintains its shape, prevents
excessive uptake of water
• made of cellulose fibers
• Plant cell walls may have multiple layers:
– Primary cell wall: relatively thin and flexible
– Middle lamella: thin layer between primary walls of
adjacent cells
– Secondary cell wall (in some cells): added between the
plasma membrane and the primary cell wall
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Fig. 6-28
Secondary
cell wall
Primary
cell wall
Middle
lamella
1 µm
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
Plasmodesmata
The Extracellular Matrix (ECM) of Animal Cells
•
Functions
–
–
–
–
•
•
Support
Adhesion
Movement
Regulation
made up of
glycoproteins
(collagen,
proteoglycans, and
fibronectin)
Collagen
EXTRACELLULAR MATRIX
Proteoglycan
complex
Fibronectin
ECM proteins bind
to receptor proteins
in the plasma
membrane called
integrins
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Integrins
Microfilaments
CYTOPLASM
Intercellular Junctions
•
Neighboring cells in tissues, organs, or organ systems often adhere,
interact, and communicate through direct physical contact
•
Intercellular junctions facilitate this contact
•
There are several types of intercellular junctions
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Plasmodesmata – channels that perforate cell walls
–
Tight junctions - membranes of neighboring cells are pressed
together, preventing leakage of extracellular fluid
–
Desmosomes (anchoring junctions) fasten cells together into
strong sheets
–
Gap junctions (communicating junctions) provide cytoplasmic
channels between adjacent cells
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Fig. 6-32
Tight
junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
Desmosomes fasten
cells together in sheets
Tight junction
Intermediate
filaments
Desmosome
Desmosome
Gap
junctions
Space
between
cells
Plasma membranes
of adjacent cells
Extracellular
matrix
Gap junctions all cells to
communicate with one
another via cytoplasmic
channels
Gap
junction
0.1 µm
Fig. 6-UN1
Cell Component
Concept 6.3
The eukaryotic cell’s genetic
instructions are housed in
the nucleus and carried out
by the ribosomes
Structure
Surrounded by nuclear
envelope (double membrane)
perforated by nuclear pores.
The nuclear envelope is
continuous with the
endoplasmic reticulum (ER).
Nucleus
Function
Houses chromosomes, made of
chromatin (DNA, the genetic
material, and proteins); contains
nucleoli, where ribosomal
subunits are made. Pores
regulate entry and exit of
materials.
(ER)
Two subunits made of riboProtein synthesis
somal RNA and proteins; can be
free in cytosol or bound to ER
Ribosome
Concept 6.4
The endomembrane system
regulates protein traffic and
performs metabolic functions
in the cell
Concept 6.5
Mitochondria and chloroplasts change energy from
one form to another
Extensive network of
membrane-bound tubules and
sacs; membrane separates
lumen from cytosol;
continuous with
the nuclear envelope.
Smooth ER: synthesis of
lipids, metabolism of carbohydrates, Ca2+ storage, detoxification of drugs and poisons
Golgi apparatus
Stacks of flattened
membranous
sacs; has polarity
(cis and trans
faces)
Modification of proteins, carbohydrates on proteins, and phospholipids; synthesis of many
polysaccharides; sorting of Golgi
products, which are then
released in vesicles.
Lysosome
Membranous sac of hydrolytic
enzymes (in animal cells)
Vacuole
Large membrane-bounded
vesicle in plants
Digestion, storage, waste
disposal, water balance, cell
growth, and protection
Mitochondrion
Bounded by double
membrane;
inner membrane has
infoldings (cristae)
Cellular respiration
Endoplasmic reticulum
(Nuclear
envelope)
Chloroplast
Peroxisome
Rough ER: Aids in synthesis of
secretory and other proteins from
bound ribosomes; adds
carbohydrates to glycoproteins;
produces new membrane
Breakdown of ingested substances,
cell macromolecules, and damaged
organelles for recycling
Typically two membranes
Photosynthesis
around fluid stroma, which
contains membranous thylakoids
stacked into grana (in plants)
Specialized metabolic
compartment bounded by a
single membrane
Contains enzymes that transfer
hydrogen to water, producing
hydrogen peroxide (H2O2) as a
by-product, which is converted
to water by other enzymes
in the peroxisome