overview of the cellular basis of life -...
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Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Overview of the Cellular Basis of Life
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Cells and Tissues
Cells:
Carry out all chemical activities needed to
sustain life
Cells are the building blocks of all living
things
Cells vary in length, e.g. 2 micrometers to
over a meter (nerve cells)
Cells vary in function
Tissues
Tissues are groups of cells that are similar in
structure and function
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Anatomy of a Generalized Cell
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Anatomy of the Cell
Cells are not all the same
All cells share general structures
All cells have three main regions
Nucleus
Cytoplasm
Plasma membrane
Figure 3.1a
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The Nucleus
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The Nucleus
Control center of the
cell
Contains genetic
material, DNA,
(genes) for cell
reproduction
Three regions
Nuclear envelope
(membrane)
Chromatin
Nucleolus
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Nuclear envelope (membrane)
Barrier of the nucleus
Consists of a double
membrane
Where membrane fuses,
becomes nuclear pore
Contains nuclear pores that
allow for exchange of material
with the rest of the cell
Relatively large pores
allows substances to pass
freely than elsewhere
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Nucleoli
Nucleus contains
one or more nucleoli
Dark staining,
round bodies
Sites of ribosome
assembly
Ribosomes migrate
into the cytoplasm
through nuclear
pores into the
cytoplasm serve as
sites of protein
synthesis
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Chromatin
When the cell is not
dividing DNA
combined with protein
forms loose, bumpy
threads called
chromatin
Scattered throughout
the nucleus
Condenses to form
chromosomes when
the cell divides
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The Plasma Membrane
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Plasma Membrane (Cell Membrane)
Barrier for cell contents
Plays a dynamic role cellular
activities
Double phospholipid layer
Allows membranes to reseal
quickly
Hydrophilic (water loving) heads
Hydrophobic tails (water hating)
Impermeable to most water
soluble molecules
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Plasma Membrane (Cell Membrane)
Proteins scattered in lipid bilayer
Specialized functions include:
Enzymes
Receptors
Anchoring the cell to fibers
Protein channels
Branching sugars
Glycoproteins
Blood type, receptors, cell-
to-cell interactions
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Plasma Membrane
Figure 3.2
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Specialization of the Plasma Membrane
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Plasma Membrane Specializations
Microvilli
Finger-like projections
that increase surface
area for absorption
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Plasma Membrane Specializations
Membrane junctions (3 types)—
binds cells together
Tight junctions (zipperlike)
Impermeable junction
(e.g. in sm. Intestine
keeps enzymes from
bloodstream)
Desmosomes (buttonlike)
Anchoring junction
Keeps cell from being
pulled apart (e.g. skin
cells)
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Plasma Membrane Specializations
Membrane junctions (3
types)—binds cells together
Continued…
Gap junctions
Allows communication
between cells (e.g.
heart cells)
Neighboring cells
connected by
connexons
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Cytoplasm
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Cytoplasm
Cytoplasm is the material outside the nucleus and inside
the plasma membrane
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Cytoplasm (factory area)
Site of most cellular activities
Contains 3 major elements (seen by electron microscope)
Cytosol
Largely water fluid that suspends organelles
Dissolved nutrients & solutes
Organelles
Metabolic machinery of the cell
“Little organs” that perform functions for the cell
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Cytoplasm (factory area)
Continued…
Inclusions
Chemical substances specific to the cell type
such as stored nutrients e.g. glycogen
granules in the liver
Pigments in skin & hair
Lipid droplets in fat cells
Mucus & other secretory products
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Cytoplasmic Organelles
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Cytoplasmic Organelles
Figure 3.4
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Cytoplasmic Organelles
Mitochondria
Change shape continuously
Consists of a double membrane
Smooth outside, shelflike protrusions called
cristae
Enzymes inside carry out reactions where oxygen is
used to break down food
Most energy lost as heat but some is used to form
ATP molecules (“Powerhouses” of the cell)
Metabolically busy cells have hundreds of
mitochondria (liver and muscle)
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Cytoplasmic Organelles
Ribosomes (tiny, bilobed dark bodies)
Made of protein and ribosomal RNA (rRNA)
Sites of protein synthesis
Found at two locations
Free in the cytoplasm
As part of the rough endoplasmic reticulum
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Endoplasmic reticulum (ER)—fluid filled tubes
Mini-circulatory system for cell
Carries proteins from one to another part of cell
Two types of ER
Rough endoplasmic reticulum
Studded with ribosomes
Synthesizes proteins
E.g. pancreas cells producing digestive
enzymes to be delivered to sm. intestine
See next slide…
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Rough Endoplasmic Reticulum
Figure 3.5
Ribosome
Protein
Protein inside
transport vesicle
Transport
vesicle buds off
mRNA
Rough ER
As the protein is synthesized
on the ribosome, it migrates
into the rough ER cistern.
In the cistern, the protein folds
into its functional shape. Short
sugar chains may be attached
to the protein (forming a
glycoprotein).
The protein is packaged in a
tiny membranous sac called a
transport vesicle.
The transport vesicle buds from
the rough ER and travels to the
Golgi apparatus for further
processing or goes directly to
the plasma membrane where its
contents are secreted.
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Cell Diversity
Figure 3.8f
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Endoplasmic reticulum (ER)—fluid filled tubes
Smooth endoplasmic reticulum
Functions in lipid metabolism
(cholesterol & fat synthesis &
breakdown) and detoxification of
drugs and pesticides
E.g. liver cells and testes that
manufacture testosterone
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Cell Diversity
Figure 3.8d
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Golgi apparatus—Traffic Director
Stack of flattened membranous sacs
Modifies and packages proteins sent by the rough ER
via transport vesicles
As the sac swells with proteins it pinches off to form
Secretory vesicles—3 pathways:
Vesicles fuse with plasma membrane, it ruptures,
& contents ejected to outside of cell, e.g. mucus &
digestive enzymes
Vesicles destined to form plasma membrane
Vesicles form Lysosomes that contain digestive
enzymes to rid cell of worn-out structures or
foreign substances
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Figure 3.6
Extracellular fluid
Plasma membrane
Golgi vesicle containingmembrane componentsfuses with the plasmamembrane
Golgi vesicle containingdigestive enzymesbecomes a lysosome
Proteins in cisterna
Lysosome fuses withingested substances
Membrane
Transportvesicle
Pathway 3
Pathway 2
Secretory vesiclesPathway 1
Golgiapparatus
Golgi vesicle containingproteins to be secretedbecomes a secretoryvesicle
Cisterna
Rough ER
Proteins
Secretion by
exocytosis
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Cell Diversity
Figure 3.8e
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Peroxisomes
Membranous sacs of oxidase enzymes
Converts free radicals to H2O2 then catalase
converts to H2O & O2
Oxidase enzymes contain O2 to detoxify
harmful substances such as alcohol and
formaldehyde
Replicate by pinching in half, as do
mitochondria (NOT formed by Golgi
apparatus)
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Cytoskeleton—cell’s bones & muscles
Network of protein structures that extend
throughout the cytoplasm
Provides the cell with an internal framework
Figure 3.7a
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Figure 3.7b–d
Cytoplasmic Organelles
Cytoskeleton
Three different types of
elements
Microfilaments—cell
motility/change shape, e.g.
muscle cells
Intermediate filaments—
resist pulling forces,
e.g.from desmosomes
Microtubules—determine
overall shape of cell
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Cell Diversity
Figure 3.8c
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Cell Diversity
Figure 3.8b
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Centrioles
Rod-shaped bodies made of microtubules lie at right
angles to each other
Generate microtubules & mitotic spindle during cell
division
Centrioles make cilia (hair-like projections) & flagella
(tail-like projections)
Cilia move materials across the cell surface
Located in the respiratory system to move mucus
Flagella propel the cell
The only flagellated cell in the human body is
sperm
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Cell Diversity
Figure 3.8g
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Cell Diversity
Figure 3.8a
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Video: A Tour of the Cell
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Cell Physiology—Cell Division
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Events of Cell Division
The cell life cycle is the series of
changes a cell goes through from the
time it is formed until it divides. The
cycle has two major periods:
Interphase: the cell grows & carries
its usual metabolic activities, longer
phase of cycle (metabolic phase)
Cell division:
the reproduction of itself
Function is to produce more
cells for growth and repair
processes
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DNA Replication
Function of cell division to produce more cells for
growth & repair processes
All body cells have the same genetic material
DNA molecules duplicate exactly before cell division
Genetic material is duplicated and readies a cell for
division into two cells
Occurs toward the end of interphase
DNA uncoils and each side serves as a template
Two DNA molecules are formed that are identical to
the original: one old one & one newly assembled
strand
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DNA Replication
Figure 3.14
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Events Of Cell Division
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Cell Division: Consists of 2 events:
Mitosis—division of the nucleus
Results in the formation of two daughter nuclei
Cytokinesis—division of the cytoplasm
Begins when mitosis is near completion
Results in the formation of two daughter cells with
the same genetic information
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Prophase
(Remember, due to DNA
replication, for a short time the
nucleus contains a double dose of
genes)
First part of cell division
Centrioles migrate to the poles to
direct assembly of mitotic spindle
fibers
DNA appears as double-stranded
chromosomes
Nuclear envelope breaks down
and disappears
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Metaphase
Chromosomes are aligned in the center of the cell on
the metaphase plate
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Anaphase
Chromosomes are pulled apart and toward the opposite
ends of the cell
Cell begins to elongate
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Telophase
Chromosomes uncoil to become
chromatin
Nuclear envelope reforms around
chromatin
Spindles break down and disappear
Cytokinesis
Begins during late anaphase and
completes during telophase
A cleavage furrow forms to pinch
the cells into two parts
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Stages of Mitosis
Cell division takes between 5 minutes-2 hours
Two daughter cells exist
Each is smaller with less cytoplasm than mother
cell, but genetically identical
The daughter cells grow & carry out normal cell
activities unit it is their turn to divide for body
growth in youth & repair body tissue
Mitosis gone wild is the basis for tumors &
cancers
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Video: How To Stain Cheek Cells
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Stained Cheek Cells