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THE CELLChapter 6
HISTORY OF CYTOLOGY
Initial microscopes Robert Hooke
Origin of term cell Antoni Van Leeuwenhoek
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
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Visible light is refracted (bent) through glass lenses
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
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)
CELLULAR CLASSIFICATION Prokaryotes- before nucleus
NO nucleus (nucleoid region) NO organelles Single, circular DNA Smaller, less complex E.g bacteria, archaea
Eukaryotes- true nucleus 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
PlantAnimal
GENETIC CONTROL OF THE CELL Nucleus is the control center that directs the cell
Enclosed by a double membrane called a nuclear envelope
Nuclear pores allow substances to enter and leave Nuclear lamina protein filaments that maintain shape
Chromosomes are the structures that carry genetic info 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
Free ribosomes formed in cytosol Proteins will remain/function in cytosol
Bound ribosomes are attached to endoplasmic reticulum or nuclear envelope Make proteins that are shipped out of initial cell
Can change building location/type Structurally identical
TRAFFICKING AND METABOLISM
Endomembrane system Multiple responsibilities Related through connections or vesicle transport
Endoplasmic reticulum Separates internal compartment of ER from
cytosol Smooth ER lacks ribosomes
Synthesis lipids and carbs; detoxes alcohol and poisons Detox induces proliferation = increase tolerance to
drugs Rough ER
Site of protein synthesis Secrete proteins in vesicles that bud from membrane Expands itself (makes own phospholipids)
GOLGI APPARATUS
Modifies, stores, and sends products elsewhere Cis = closest to Er
Receive vesicles from ER Trans = opposite side
Ships products in vessels Modified as move between two sides
Manufactures and refines products instages
LYSOSOMES
Made by rough ER and sent to golgi Use hydrolytic enzymes to phagocytize food
or damaged organelles Best in acidic conditions Decreased reaction if they break open
Can lead to cell destruction
Fuse with phagocytotic cells to break down polymers 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 Hydrolysis in plants and
fungi b/c no lysosomes Central vacuole
transports solutes in plant cells; disposes of by-products 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
Innermost layered is folded to form cristae Matrix is enclosed by inner and outer membranes
Chloroplasts Contain chlorophyll or green pigment
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
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
MICROTUBULES
Thickest fibers, made of dimers of tublin
(α- and β) A ring of 9 triplets
comprise a centriole produced in a centrosome Produce spindle fibers
during cell division Provides the mobility of
cilia Beat like an oar
A ring of 9 doubles and 2 singles produce a flagella
MICROFILAMENTS
Solid rods of double twisted actin subunits Sometimes mixed with
myosin Form structural networks Allow dynein, a large
motor protein to ‘walk’ Interactions allow
amoebas to move pseudopodia
INTERMEDIATE FILAMENTS Made of different protein subunits including
keratin Maintain and bear tension Remain after death
E.g keratinized skin
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