Download 1 A Tour of the Cell

A Tour of the Cell
Chapter 6
• Objectives
• Distinguish between prokaryotic and eukaryotic cells.
• Distinguish between free and bound ribosomes in terms
of location and function.
• List the components of the endomembrane system, and
describe the structure and functions of each component.
• Briefly describe the roles of the mitochondrion,
chloroplast and peroxisome.
• Describe the functions of the cytoskeleton and compare
the structure and functions of microtubules,
microfilaments, and intermediate filaments.
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• Explain how the ultrastructure of cilia and flagella relates
to their functions.
• Describe the basic structure of a plant cell wall.
• Describe the structure and function of the extracellular
matrix in animal cells.
• Describe four different intercellular junctions
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Introduction
• Cell is smallest functional unit of life
– cell theory:
• all organisms composed of cells
• all existing cells arise from pre-existing cells
• Common characteristics of all cells:
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–
–
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cell contents surrounded by plasma membrane
cytoplasm consists of semifluid matrix
organelles are embedded in cytoplasm
contain genes in the form of DNA
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Fundamental Features of Life
• Features of cells are characteristic of life
– cells are highly structured
– cell structure and function are related
– cell membranes separate the cell from the
external environment
– each cell has DNA as the genetic material
– each cell carries out metabolism
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Cell Organization
• Two types of cells-prokaryotic and eukaryotic
• Prokaryotic:
– small
– lacks nucleus
• the DNA is in the nucleoid region
– cytoplasm surrounded by plasma membrane and
outer cell wall
– flagella and pili may be present
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Cell Organization
• Eukaryotic
– Larger than prokaryotic cells
– complex internal structure with membranous and
non-membranous organelles
• membranous: nucleus, endoplasmic reticulum, Golgi
apparatus,mitochondria, lysosomes and peroxisomes
• non-membranous: ribosomes, microtubules, centrioles,
flagella and cytoskeleton
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• The plasma membrane functions as a
selective barrier
– allows sufficient passage of nutrients and waste
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A Panoramic View of the
Eukaryotic Cell
• Eukaryotic cells have extensive and
elaborately arranged internal membranes,
which form organelles
• Plant and animal cells have most of the same
organelles
– animal cells surrounded by plasma membrane
only
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– plant cells surrounded by plasma membrane and
rigid cell wall; also have central vacuole and
chloroplasts
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Eukaryotic Cell Organization
• Eukaryotic organelles form four functional
groups:
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–
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manufacture
breakdown
energy processing
support, movement and communication
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• Manufacturing
–
–
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nucleus
ribosomes
endoplasmic reticulum: rough and smooth
Golgi apparatus
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The Nucleus: Genetic Library of the
Cell
• Nucleus is cell’s genetic control center
– surrounded by double membrane
• contains pores to allow passage of material between
nucleus and cytoplasm
– DNA normally present as strands of chromatin
– During cell division, chromatin coils up to form
chromosomes
– Nucleolus-organelle within nucleus-responsible
for ribosome synthesis
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Ribosomes: Protein Factories in
the Cell
• Ribosomes synthesize proteins
– two populations of ribosomes within cells
• free ribosomes
– suspended in cytosol
• bound ribosomes
– attached to the outside of endoplasmic reticulum or
nuclear membrane
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The Endoplasmic Reticulum:
Biosynthetic Factory
• Endomembrane system
– smooth endoplasmic reticulum synthesizes lipids,
metabolizes carbohydrates, detoxifies drugs and
poisons
• stores Ca2+ in muscle cells
– rough endoplasmic reticulum synthesizes proteins
on attached ribosomes which are distributed by
transport vesicles
• known as secretory proteins
– many modified in rough ER by addition of carbohydrates
• also synthesize membrane proteins and phospholipids
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The Golgi Apparatus: Shipping and
Receiving Center
• Golgi apparatus finishes, sorts and ships cell
products transported in vesicles from ER
– consists of flattened membranous sacs called
cisternae
• Functions of the Golgi apparatus include
– modification of the products of the rough ER
– manufacture of certain macromolecules
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• Breakdown
– lysosomes
– vacuoles
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Lysosomes: Digestive
Compartments
• Lysosomes contain enzymes to digest food
and wastes
– defective lysosomes cause fatal diseases
• Lysosomes carry out intracellular digestion
by
– phagocytosis
– autophagy
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Vacuoles: Diverse Maintenance
Compartments
• Vacuoles function in general cell
maintenance
– a plant or fungal cell may have one or several
vacuoles
– food vacuoles are formed by phagocytosis
– contractile vacuoles pump excess water out of
protist
• Central vacuoles are found in plant cells
– hold reserves of important organic compounds
and water
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The Endomembrane System: A
Review
• The organelles involved in synthesis of
macromolecules form the endomembrane
system
– primarily responsible for protein synthesis
• lipids synthesized to form transport vesicles which fuse
with other membrane-bound organelles
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• Energy Processing
– mitochondria
– chloroplasts
– peroxisomes
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The Evolutionary Origins of
Mitochondria and Chloroplasts
• Mitochondria and chloroplasts have
similarities with bacteria
– Enveloped by a double membrane
– Contain free ribosomes and circular DNA
molecules
– Grow and reproduce somewhat
independently in cells
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• The Endosymbiont theory
– An early ancestor of eukaryotic cells
engulfed a nonphotosynthetic prokaryotic
cell, which formed an endosymbiont
relationship with its host
– The host cell and endosymbiont merged into
a single organism, a eukaryotic cell with a
mitochondrion
– At least one of these cells may have taken
up a photosynthetic prokaryote, becoming
the ancestor of cells that contain
chloroplasts
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Mitochondria: Chemical Energy
Conversion
• Mitochondria:
– found in all eukaryotic cells, except anaerobic
protozoans
– surrounded by double membrane
• a smooth outer membrane
• an inner membrane folded into cristae
– site of cellular respiration
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Chloroplasts: Capture of Light
Energy
• Chloroplasts are specialized members of a
family of closely related plant organelles
called plastids
– contain chlorophyll
– found in plants and algae
– site of photosynthesis
• convert solar energy to chemical energy
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• Surrounded by double membrane
• Separate inner membrane system divided
into two parts
– thylakoids, membranous sacs
– stroma, the internal fluid
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Peroxisomes: Oxidation
• Peroxisomes are involved in the breakdown
of fatty acids and amino acids
– Detoxify blood toxins in liver and kidney
• Examples – alcohol, peroxide
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• Support, Movement, and Communication
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–
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cytoskeleton
centrioles and centrosomes
cilia and flagella
intracellular connections
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Roles of the Cytoskeleton: Support,
Motility, and Regulation
• Internal cell skeleton-cytoskeleton
– composed of 3D meshwork of proteins extending
through the cytoplasm
– gives mechanical support to the cell
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Components of the Cytoskeleton
• There are three components of the
cytoskeleton
– rods of globular proteins-microfilaments
– ropelike strands of fibrous proteins-intermediate
filaments
– hollow tubes of globular proteins-microtubules
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Microtubules
• Microtubules provide anchors for organelles,
act as conveyor belts and form cilia and
flagella
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Centrosomes and Centrioles
• The centrosome is considered to be a
“microtubule-organizing center”
– In animals contains a pair of centrioles
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Cilia and Flagella
• Cilia and flagella
– function to move whole cell
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• Cilia and flagella share a common
ultrastructure
– structure consists of 9 microtubule doublets
arranged around central pair (9+2)
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• Movement of cilia and flagella occurs when
arms consisting of the protein dynein move
the microtubule doublets past each other
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Microfilaments (Actin Filaments)
• Microfilaments are built from molecules of the
protein actin
– microfilaments cause contraction of muscle cells
– they also function in amoeboid movement,
cytoplasmic streaming and support for cellular
projections
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Intermediate Filaments
• Intermediate filaments
– support cell shape
– fix organelles in place
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Eukaryotic Cell Surface
Organization
• Extracellular components and connections
between cells help coordinate cellular
activities
• Cell surfaces protect, support and join cells
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Cell Walls of Plants
• In plants, neighboring cells joined to form
interconnected and coordinated group
– cell walls are multi-layered
• composed of mixtures of polysaccharides and proteins
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The Extracellular Matrix (ECM) of
Animal Cells
• In multi-cellular animals cells are often
surrounded by sticky mixture of
polysaccharides and proteins-no support
• Functions of the ECM include
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support
adhesion
movement
regulation
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Intercellular Junctions
• Several type of junctions between cells
– In plants, plasmodesmata are channels through
cell walls connecting cytoplasm of adjacent cells
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• In animal cells, there are three types of
cellular connections
– tight junctions-leak proof
– anchoring junctions-join cells and allow passage
of materials in spaces between cells or anchor to
extracellular matrix
– communicating junctions-provide channels
between cells
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The Cell: A Living Unit Greater
Than the Sum of Its Parts
• Cells rely on the integration of structures and
organelles in order to function
– For example, a macrophage’s ability to destroy
bacteria involves the whole cell, coordinating
components such as the cytoskeleton,
lysosomes, and plasma membrane
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