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