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2. Part 2 – Cytoplasm
All cellular material that is located between the plasma membrane and the nucleus
Composed of:
Cytosol: gel-like solution made up of water and soluble molecules such as proteins, salts, sugars, etc.
Inclusions: insoluble molecules; vary with cell type (examples: glycogen granules, pigments, lipid droplets, vacuoles, crystals)
Organelles: metabolic machinery structures of cell; each with specialized function; either membranous or nonmembranous
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3. 3.7 Cytoplasmic Organelles
Membranous
Mitochondria
Endoplasmic reticulum
Golgi apparatus
Peroxisomes
Lysosomes
Nonmembranous
Ribosomes
Cytoskeleton
Centrioles
Membranes allow compartmentalization, which is crucial to cell functioning
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4. Mitochondria
Called the “power plant” of cells because they produce most of cell’s energy molecules (ATP) via aerobic (oxygen-requiring) cellular respiration
Enclosed by double membranes; inner membrane has many folds, called cristae
Cristae are embedded with membrane proteins that play a role in cellular respiration
Mitochondria contain their own DNA, RNA, and ribosomes
Resemble bacteria; capable of same type of cell division bacteria use, called fission
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5. Outer mitochondrial membrane Ribosome Mitochondrial DNA Inner
Figure 3.15 Mitochondrion.
Outer
mitochondrial
membrane
Ribosome
Mitochondrial
DNA
Inner
mitochondrial
membrane
Cristae
Matrix
Enzymes
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6. Endoplasmic Reticulum (ER)
Consists of series of parallel, interconnected cisterns—flattened membranous tubes that enclose fluid-filled interiors
ER is continuous with outer nuclear membrane
Two varieties:
Rough ER
Smooth ER
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7. Figure 3.16 The endoplasmic reticulum.
Nucleus
Smooth ER
Nuclear
envelope
Rough ER
Ribosomes
Diagrammatic view of smooth and
rough ER
Electron micrograph of smooth
and rough ER (25,000)
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8. Figure 3.17 Golgi apparatus.
New vesicles forming
Cis ­­face—­
“receiving” side of
Golgi apparatus
Transport vesicle
from rough ER
Cisterns
New vesicles
forming
Transport
vesicle
from
trans face
Trans face—
“shipping” side of
Golgi apparatus
Secretory vesicle
Newly secreted
proteins
Golgi
apparatus
Transport vesicle at
the trans face
Many vesicles in the process of pinching off
from the Golgi apparatus
Electron micrograph of the Golgi
apparatus (90,000)
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9. Peroxisomes
Membranous sacs containing powerful detoxifying substances that neutralize toxins
Free radicals: toxic, highly reactive molecules that are natural by-products of cellular metabolism; can cause havoc to cell if not detoxified
Two main detoxifiers: oxidase uses oxygen to convert toxins to hydrogen peroxide (H2O2), which is itself toxic; however, peroxisome also contains catalase, which converts H2O2 to harmless water
Peroxisomes also play a role in breakdown and synthesis of fatty acids
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10. Figure 3.19 Electron micrograph of lysosomes (20,000).
Light green areas are
regions where materials
are being digested.
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11. Clinical – Homeostatic Imbalance 3.4
Lysosomal storage diseases result when one or more lysosomal digestive enzymes are mutated and do not function properly
Tay-Sachs disease is a condition in which the patient lacks a lysosomal enzyme needed to break down glycolipids in brain cells
Glycolipids build up as a result of this defect, interfering with nervous system functioning
Seen predominantly in infants of Central European Jewish descent
Causes seizures, mental retardation, blindness, and death before age 5
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12. Cytoskeleton Elaborate network of rods that run throughout cytosol
Hundreds of different kinds of proteins link rods to other cell structures
Also act as cell’s “bones, ligaments, and muscle” by playing a role in movement of cell components
Three types:
Microfilaments
Intermediate filaments
Microtubules
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13. Cytoskeleton (cont.) Microfilaments
Thinnest of all cytoskeletal elements
Semi-flexible strands of protein actin
Each cell has a unique arrangement of strands, although share common terminal web
Dense, cross-linked network of microfilaments attached to cytoplasmic side of plasma membrane
Strengthens cell surface and helps to resist compression
Some are involved in cell motility, changes in cell shape, or endocytosis and exocytosis
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14. Strands made of spherical protein subunits called actin
Figure 3.21a Cytoskeletal elements support the cell and help to generate movement.
Microfilaments
Strands made of spherical
protein subunits called actin
Actin subunit
7 nm
Microfilaments form the blue
batlike network in this photo.
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15. Cytoskeleton (cont.) Intermediate filaments
Size is in between microfilaments and microtubules
Tough, insoluble, ropelike protein fibers
Composed of tetramer (4) fibrils twisted together, resulting in one strong fiber
Help cell resist pulling forces
Filaments attach to desmosome plaques and act as internal guy-wires
Some have special names
Called neurofilaments in nerve cells and keratin filaments in epithelial cells
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16. Intermediate filaments
Figure 3.21b Cytoskeletal elements support the cell and help to generate movement.
Intermediate filaments
Tough, insoluble protein fibers
constructed like woven ropes
composed of tetramer (4) fibrils
Tetramer subunits
10 nm
Intermediate filaments form the
lavender network surrounding the
pink nucleus in this photo.
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17. Cytoskeleton (cont.) Microtubules
Largest of cytoskeletal elements; consist of hollow tubes composed of protein subunits called tubulins, which are constantly being assembled and disassembled
Most radiate from centrosome area of cell
Determine overall shape of cell and distribution of organelles
Many organelles are tethered to microtubules to keep organelles in place
Many substances are moved throughout cell by motor proteins, which use microtubules as tracks
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18. Hollow tubes of spherical protein subunits called tubulin
Figure 3.21c Cytoskeletal elements support the cell and help to generate movement.
Microtubules
Hollow tubes of spherical
protein subunits called tubulin
Tubulin subunits
25 nm
Microtubules appear as gold
networks surrounding the cells’
pink nuclei in this photo.
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19. Cytoskeleton (cont.)
Motor proteins: complexes that function in motility
Can help in movement of organelles and other substances around cell
Use microtubules as tracks to move their cargo on
Powered by ATP
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20. Centrosome and Centrioles
Centrosome, which is located near the nucleus, means “cell center”
It is a microtubule organizing center, consisting of a granular matrix and centrioles—a pair of barrel-shaped microtubular organelles that lie at right angles to each other
Newly assembled microtubules radiate from centrosome to rest of cell
Some microtubules aid in cell division, and some form cytoskeletal track system
Centrioles form the basis of cilia and flagella
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21. Centrosome matrix Centrioles Microtubules Figure 3.22a Centrioles.
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22. 3.8 Cellular Extensions
Certain cells have structures extending from the cell surface:
Cilia and flagella aid in the movement of the cell or of materials across the surface of the cell
Microvilli are fingerlike projections that extend from the surface of the cell to increase surface area
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23. Cilia and Flagella
Cilia are whiplike, motile extensions on surfaces of certain cells (such as respiratory cells)
Thousands of cilia work together in sweeping motion to move substances (example: mucus) across cell surfaces in one direction
Flagella are longer extensions that propel the whole cell (example: tail of sperm)
Both structures are made up of microtubules synthesized by centrioles that are called basal bodies because they form the base of each cilium and flagellum
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24. Figure 3.23 Structure of a cilium.
Outer microtubules
doublet
Dynein
arms
The doublets also
have attached
motor proteins,
the dynein arms.
Central
microtubule
Cross-linking
protein between
outer doublets
The “9 + 2”
pattern:
microtubule
doublets encircle
two central
microtubules.
Microtubules are
held together by
cross-linking
proteins and
radial spokes.
Radial spoke
A cross section through the
cilium shows the “9 + 2”
arrangement of microtubules.
Cross-linking
proteins between
outer doublets
Radial spoke
Plasma
membrane
Cilium
Triplet
A cross section through the
basal body. The nine outer
doublets of a cilium extend
into a basal body where each
doublet joins another
microtubule to form a ring
of nine triplets.
Basal body
(centriole)
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25. Figure 3.24 Ciliary function.
Power, or
propulsive, stroke
Recovery stroke, when
cilium is returning to its
initial position 1 2 3 4 5 6 7
Phases of ciliary motion.
Layer of mucus
Cell surface
Traveling wave created by the activity of
many cilia acting together propels mucus
across cell surfaces.
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26. Animation: Cilia and Flagella
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27. Microvilli
Minute, fingerlike extensions of plasma membrane that project from surface of select cells (example: intestinal and kidney tubule cells)
Used to increase surface area for absorption
Have a core of actin microfilaments that is used for stiffening of projections
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28. Microvillus Actin filaments Terminal web Figure 3.25 Microvilli.
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29. Part 3 – Nucleus
Largest organelle; contains the genetic library of blueprints for synthesis of nearly all cellular proteins
Responds to signals that dictate the kinds and amounts of proteins that need to be synthesized
Most cells are uninucleate (one nucleus), but skeletal muscle, certain bone cells, and some liver cells are multinucleate (many nuclei)
Red blood cells are anucleate (no nucleus)
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30. 3.9 Structure of the Nucleus
The nucleus has three main structures:
Nuclear envelope
Nucleoli
Chromatin
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31. Chromatin (condensed)
Figure 3.26a The nucleus.
Nuclear
pores
Nuclear envelope
Nucleus
Chromatin (condensed)
Nucleolus
Cisterns of rough ER
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32. The Nuclear Envelope
Double-membrane barrier that encloses the jelly-like fluid, the nucleoplasm
Outer layer is continuous with rough ER and, like the rough ER, is studded with ribosomes
Inner layer, called nuclear lamina, is a network mesh of proteins that maintains nuclear shape and acts as scaffolding for DNA
Nuclear pores allow substances to pass into and out of nucleus; they are guarded by the nuclear pore complex, which regulates transport of specific large molecules
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33. Surface of nuclear envelope.
Figure 3.26b The nucleus.
Surface of nuclear envelope.
Fracture
line of outer
membrane
Nuclear
pores
Nucleus
Nuclear pore complexes. Each pore
Is ringed by protein particles.
Nuclear lamina. The netlike lamina composed
of intermediate filaments formed by lamins lines
the inner surface of the nuclear envelope.
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34. Nucleoli
Dark-staining spherical bodies within nucleus that are involved in ribosomal RNA (rRNA) synthesis and ribosome subunit assembly
Associated with nucleolar organizer regions that contain the DNA that codes for rRNA
Usually one or two per cell
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35. Chromatin
Consists of 30% threadlike strands of DNA, 60% histone proteins, and 10% RNA
Arranged in fundamental units called nucleosomes, which consist of DNA wrapped around histones
Chemical alterations of histones have an effect on DNA and therefore can help regulate gene expression
Chromosomes are condensed chromatin
Condensed state helps protect fragile chromatin threads during cell division
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36. Figure 3.27b Chromatin and chromosome structure.
Tight helical fiber
(30-nm diameter) 3
Chromatid
(700-nm diameter) 4
Metaphase
chromosome
(at midpoint
of cell division)
consists of two
sister chromatids 5
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37. Figure 3.26 The nucleus.
Surface of nuclear envelope.
Fracture
line of outer
membrane
Nuclear
pores
Nuclear envelope
Nucleus
Chromatin (condensed)
Nucleolus
Nuclear pore complexes. Each pore is
ringed by protein particles.
Cisterns of rough ER
Nuclear lamina. The netlike lamina composed
of intermediate filaments formed by lamins lines
the inner surface of the nuclear envelope.
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