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Cytology
The Study of Cells
Relative sizes
Cell Theory
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Basic unit of life
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Everything that organisms do is to keep the cells alive
All living things are made of cells
Cells come from other cells
Smallest unit capable of life
Life?
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Organization
Metabolism – use energy
Homeostasis – maintain conditions
Growth/development
Responsiveness
Reproduction – sexual and asexual
Adaptation – change as environment changes
How Cells Are Studied
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Microscope: # 1 tool
 1665 Robert Hooke; “Cells”
Two types of microscopes:
 Light: 1500x; light passes through lens
 Electron Microscope: electrons instead of light
waves; electromagnets aim electron beam
How Cells Are Studied
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3 types of electron microscopes:
 Transmission Electron
Microscope; TEM; electrons
pass through subject, 100,000x
 Scanning Electron
Microscope; SEM; electrons
bounce off a thin gold plate
on the surface of the object;
60,000x; 3d
 Scanning-tunneling STM;
1,000,000 x
How Cells Are Studied
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Cell Fractionation:
Disrupt cell; centrifuge
organelles to the bottom
 ‘Pellet’
Separate and isolate pellets
Study function independently
Size of Cells
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Limited by surface area/volume
ratio
-Volume increases 8 x faster than
S.A.
- Problems with diffusion
Limited by the amount of DNA
 DNA must be able to keep up with demands of the
cytosol
2 Types of Cells
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Prokaryote
Bacteria
No nucleus (nucleoid)
 No nuclear membrane
No internal membranes
No membrane-bound
organelles
 Ribosomes
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Eukaryote
Animal, plants, fungi,
protists
Nucleus (DNA)
 Nuclear membrane
Internal membranes
Membrane-bound
organelles
Nucleus
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Nucleus: 2 parts:
 DNA – most of the cell’s
genes
 Nuclear DNA
 Mitochondria and
chloroplasts
 Nuclear envelope:
 Phospholipid bilayer
 Pores
Nucleus
DNA:
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Chromatin = DNA
wrapped around protein
(histone)
 Chromosomes = coiled,
condensed chromatin
 Genes = sections of DNA
that code for proteins
Nucleus
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Nucleolus: large, obvious
structure in non-dividing cells
Ribosomes in production
Ribosomes
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Protein synthesis
No membrane
(prokaryotes)
Prokaryotes have slightly different
ribosome molecular structure
(tetracycline, streptomycin)
Free ribosomes - float in cytosol;
 Proteins within the cell; muscle
Bound ribosomes (ER)
 Proteins for secretion; pancreas, liver, etc
Endomembrane System
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System of folded internal membrane
Endoplasmic reticulum
Vesicles
Golgi
Lysosomes
Vacuoles
Endoplasmic Reticulum (ER)
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Folded membrane
Network of tubules and
sacs (cisternae)
Continuous with outer
nuclear membrane
Endoplasmic Reticulum
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2 types: Smooth and Rough
Smooth - Makes lipids, steroids, phospholipids
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Adrenal glands; gonads, skin oil glands
Detoxifies poisons/drugs
Endomembrane
System
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Rough ER: make proteins
Endomembrane System
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Vesicles = membrane sacs that are pinched off
portions of ER membranes moving from one
membrane to another
Secretory vesicles –
pancreas, salivary
glands
Golgi
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Stacked, flattened discs; sacs (cisternae)
Stores, modifies and routes products
from ER
Modifies proteins from
ER
Sorts products for
secretion
Endomembrane System
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Lysosomes = digestive enzymes
Tay-Sachs – build up of lipids
 Arthritis – release of hydrolytic enzymes
 Recycle - worn out organelles
 Remodeling - metamorphosis
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Endomembrane System
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Vacuoles: membrane-bound sac
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3 types and functions:
 Food vacuole: phagocytosis; intracellular
digestion
 Water vacuoles – store water
 Contractile vacuole – excrete
water
Central Vacuole
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Large vacuole found in plant cells
Storage - minerals, water (turgor
pressure), poisons
Helps provide shape,
support in plant cells
Endo membrane System
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ER
Vesicles
Golgi
Lysosomes
Vacuoles
Mitochondria
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Aerobic respiration
Found in nearly all eukaryotic cells;
plants
Number depends upon metabolic activity and
cell type; muscle, nerve, sperm
DNA – self-replicate
Matrix
Inner membrane; Cristae
Intermembrane space
Plastids
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Plastids: plant cells
Chromoplast: store pigments; chromo = ‘color’;
flowers
Chloroplast
 Thylakoid
 Thylakoid space
 Grana
 Stroma
Peroxisomes
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Organelle with enzymes
Detoxification:
 Alcohol (liver cells)
 Hydrogen peroxide – waste product of cell
metabolism
Cytoskeleton
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Network of protein fibers within cytosol
Function:
 Framework
 Support
 Movement
Cytoskeleton
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3 parts:
Microtubules
Microfilaments
Intermediate filaments
Microtubules
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Straight, hollow fibers
Maintain structure, support
Movement of organelles within the cell
Spindle; move chromosomes during mitosis
 Taxol, colchicine
 Poisons that interfere with microtubule
formation - mitosis
 Taxol – cancer treatment
Microtubules
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Cilia; short, hairlike, oarlike movement
Flagella: long; few or one; undulate
Microfilament
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Actin filaments
Smallest of cytoskeleton structure
Muscle contraction
(along with myosin)
Elongation of pseudopodia in
amoeba, macrophages
Cleavage furrows during mitosis
Pseudopodia
Intermediate Fibers
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Between microtubules and
microfilaments in size
Framework for cytoskeleton
NOT disassembled, reassembled
frequently
ALS – degeneration of intermediate
filaments
Plant Cell Surface
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Plant cells: cell walls composed of cellulose
within a matrix of polysaccharides and protein
 Fungi – chitin
 Bacteria - peptidoglycans
Cell Surface: Plants
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Plasmodesmata = linking channels between
two plant cells
Cell-to-cell communication; one solid organism
Intercellular Junctions
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Joints between cells (tissue formation)
Plants - Plasmodesmata
Animals –
 Tight junctions
 Desmosomes
 Gap junctions
Animal Cell Surface
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Glycocalyx – sticky
oligosaccharides
‘Glues’ cells together, stick to
lipids, proteins of adjacent cells
 Strength, identification with
other cells
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Animal Cell Junctions
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Tight junctions = cells closely ‘knit’ together;
block intercellular junctions; prevents
intercellular fluid loss (brain block, tubular
leakage)
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Epithelial tissues
Cells are ‘fused’ together
Animal Cell Junctions
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Desmosomes - intercellular junctions that
anchor one cell to the adjacent cell
Also called anchoring junctions
Strengthen linkages between cells –
skin cells
Animal Cell Junctions
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Gap junctions = channels between cells
 Allows substances to pass through, especially
in tissues that need to communicate rapidly
 Heart muscle cells, liver, stem cells