Download A Tour of the Cell

THE CELL
Chapter 6
HISTORY OF CYTOLOGY
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Initial microscopes
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Robert Hooke
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Antoni Van Leeuwenhoek
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Origin of term cell
First to visualize living cells
Cell Theory developed by Schleiden, Schwann,
and Virchow
Every organism is composed of 1+ cells
 A cell is the simplest unit to demonstrate the
properties of life
 Cells arise only from previously existing cells

Visible light is
refracted (bent)
through glass
lenses
LIGHT MICROSCOPY
Magnification
is ratio of image
size to real size
Resolution is
minimum
distance 2
points can be
separate and
still
distinguishable
ELECTRON MICROSCOPE (EM)
Scanning (SEM)
Transmission (TEM)
Details of cell surfaces, 3D image Details of internal cell structures
•Uses a beam of electrons = higher resolution
•Can’t use on living cells
SIMILARITIES IN ALL LIVING CELLS

Plasma membrane: allows selective passage of
molecules
Double layer of phospholipids
 Variety of proteins spread throughout
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Varies with cell location and function
Cytosol or cytoplasm: semisolid substance
enclosed by the plasma membrane
 Chromosome(s): carry genes as DNA
 Ribosomes: tiny complexes that make proteins
(genes direct)
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CELLULAR CLASSIFICATION

Prokaryotes- before nucleus
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NO nucleus (nucleoid region)
NO organelles
Single, circular DNA
Smaller, less complex
E.g bacteria, archaea
Eukaryotes- true nucleus
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Nucleus
Membrane bound organelles
DNA arranged on multiple
chromosomes
Larger
E.g protists, fungi, plants,
animals
THE SIMPLICITY OF CELLS

Many small cells
advantaged over few
large cells
As cells grow, volume
increases faster than
surface area
 Ratio constrains size
b/c limits amount of
nutrients in and
wastes out


Effects shapes and body
plans too
EUKARYOTIC CELL TYPES
Plant
Animal
GENETIC CONTROL OF THE CELL

Nucleus is the control center that directs the cell
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Chromosomes are the structures that carry
genetic info
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Enclosed by a double membrane called a nuclear
envelope
Nuclear pores allow substances to enter and leave
Nuclear lamina protein filaments that maintain
shape
Consists of chromatin, a protein and DNA structure
that coils before cell division
Nucleolus is where rRNA is synthesized from
DNA instructions

Form small and large subunits that exit the nuclear
pores to form ribosomes in the cyoplasm
RIBOSOMES
Use DNA to make proteins
 Made of rRNA and protein complexes
 Build proteins in 2 locations

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Free ribosomes formed in cytosol
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Bound ribosomes are attached to endoplasmic
reticulum or nuclear envelope
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Proteins will remain/function in cytosol
Make proteins that are shipped out of initial cell
Can change building location/type

Structurally identical
TRAFFICKING AND METABOLISM
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Endomembrane system
Multiple responsibilities
 Related through connections or vesicle transport
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Endoplasmic reticulum
Separates internal compartment of ER from cytosol
 Smooth ER lacks ribosomes
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Synthesis lipids and carbs; detoxes alcohol and poisons
 Detox induces proliferation = increase tolerance to drugs
Rough ER
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Site of protein synthesis
 Secrete proteins in vesicles that bud from membrane
 Expands itself (makes own phospholipids)
GOLGI APPARATUS
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Modifies, stores, and sends products elsewhere
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Cis = closest to Er
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Trans = opposite side
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Receive vesicles from ER
Ships products in vessels
Modified as move between two sides
Manufactures and
refines products in
stages
LYSOSOMES
Made by rough ER and sent to golgi
 Use hydrolytic enzymes to phagocytize food or
damaged organelles
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Best in acidic conditions
 Decreased reaction if they break open
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Fuse with phagocytotic cells to break down
polymers
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Can lead to cell destruction
E.g WBC’s attack and destroy bacteria
Autophagy recycles cell’s own materials

Continuous renewal of cell
VACUOLES
Used for storage or
transport of substances
made by the ER
 Contractile vacuoles
remove excess water from
cell
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Hydrolysis in plants and
fungi b/c no lysosomes
Central vacuole
transports solutes in plant
cells; disposes of byproducts
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Pigmented to attract
pollinators and signal
poisonous
EXCHANGING ENERGY

Mitochondria
Convert E to usable forms
 Site of cellular respiration = synthesis of ATP
 Number in a cell is related to membrane activity
 2 membranous layers
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Innermost layered is folded to form cristae
 Matrix is enclosed by inner and outer membranes
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Chloroplasts
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Contain chlorophyll or green pigment
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Found in leaves and green plants
2 membrane layers
Innermost is a group of interconnected sacs called thylakoids
 Stacks are grana
 Fluid outside thylakoids is the stroma
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PEROXISOMES
Transfer H to O2 = H2O2 (hydrogen peroxide)
 Break down fatty acids
 Detoxify alcohol in liver
 Don’t bud from ER, grow by incorporating
proteins from cytosol and lipids
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MICROTUBULES
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Thickest fibers, made of
dimers of tublin
(α- and β)
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A ring of 9 triplets comprise
a centriole produced in a
centrosome
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Provides the mobility of
cilia
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Produce spindle fibers
during cell division
Beat like an oar
A ring of 9 doubles and 2
singles produce a flagella
MICROFILAMENTS
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Solid rods of double twisted
actin subunits
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Sometimes mixed with
myosin
Form structural networks
 Allow dynein, a large motor
protein to ‘walk’
 Interactions allow amoebas
to move pseudopodia
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INTERMEDIATE FILAMENTS
Made of different protein subunits including keratin
 Maintain and bear tension
 Remain after death
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E.g keratinized skin