Robert Hooke
first scientist to see cell walls with microscope in 1665
light microscope
visible light is passed through the specimen and then glass lens
lenses refact the light to magnify the image
maximum magnification is ~1000x
maximum resolution is about 0.2 micrometer
electron microscope
developed in the 1950s
focuses beam of electrons through specimen or on its surface
100x better than light microscope
transmission electron microscope (TEM)
aims electron beam through thin section of a specimen
specimen is stained with atoms of a heavy metals
electrons passing through are scattered more in dense areas
scanning electron microscope (SEM)
electron beam scans the surface of the sample
beam excites the electrons on the surface
secondary electrons are detected by a device
cell fractionalization
process of placing broken up cells in centrifuge
largest cell components settle to the bottom
enables researchers to use biochemical tests on specific cell parts and organelles
features common to all cells
plasma membrane: selective barrier
cytosol: semifluid, jellylike substance
chromosomes: carry genes in the form of DNA
ribosomes: tiny complexes that make proteins
eukaryotic cell characteristics
DNA in a nucleus with a double membrane
cytoplasm is the only region between nucleus and membrane
variety of organelles
tend to be larger
prokaryotic cell characteristics
DNA concentrated in nucleoid not bounded by membrane
factors affecting cell size
requirement for cellular metabolism sets lower bound on cell size
ratio of surface area to volume of cell sets upper bound on cell
volume grows proportionally bigger than surface area
composition of membranes
double layer of phospholipids and other lipids
proteins are embedded in lipid bilayer
lipids and proteins are suited to membrane functions
plasma membrane
membrane enclosing the cell
cytoskeleton
reinforces cell’s shape
functions in cell movement
components are made of protein
types are microfilaments, intermediate filaments, microtubules
flagellum
motility structure present in some animal cells
composed of a cluster of microtubules within an extension of the plasma membrane
nuclear envelope
double membrane enclosing the nucleus
each membrane is a lipid bilayer with associated proteins
seperated by a space of 20-40 nm
perforated by pores that are 100 nm in diameter
continuous with the ER
nucleolus
non-membranous structure involved in production of ribosomes
ribosomal RNA (rRNA) is synthesized
proteins from cytoplasm assembed with rRNA into ribosomes
nucleus has one or more nucleoli
chromatin
material consisting of DNA and proteins
appears as diffuse mass
visible in a dividing cell as individual condensed chromosomes
ribosomes
complexes that synthesize proteins
free in cytosol or bound to rough ER or nuclear envelope
bound ribosomes make proteins for:
insertion in membranes
packaging within certain organelles such as lysosomes
export from the cell (secretion)
golgi apparatus
organelle active in synthesis, modification, sorting, and secretion of cell products
consists of flattened membranous sacs called cisternae
golgi stack has distinct structural directionality: cis face receives, trans face ships
manufactures some macromolecules
lysosome
digestive organelle where macromolecules are hydrolyzed
acidic environment that is not ctive in cytosol
only in animal cells
mitochondrion
organelle where cellular respiration occurs and most ATP is generated
peroxisome
organelle with various specialized metabolic functions
produces hydrogen peroxide as a by-product then converts it to water
microvilli
projections that increase the cell’s surface area
centrosome
region where the cell’s microtubules are initiated
contains a pair of centrioles
only in animal cells
endoplasmic reticulum
network of membranous sacs and tubes
active in membrane synthesis and other synthetic and metabolic processes
has rough (ribosome studded) and smooth regions (lacks ribosomes)
centrole vacuole
prominent organelle only in older plant cells
functions include storage, breakdown of waste products, hydrolysis of macromolecules
enlargement of vacuole is a major mechanism of plant growth
only in plant cells
chloroplast
photosynthetic organelle
converts energy of sunlight to chemical energy stored in sugar molecules
only in plant cells
plasmodesmata
channels through cell walls that connect the cytoplasms of adjacent cells
only in plant cells
cell wall
outer layer that maintains cell’s shape and protects the cell from mechanical damage
made of cellulose, other polysaccharides, and protein
primary cell wall and secondary cell wall
only in plant cells
nucleus
contains most of the genes in the eukaryotic cell
most conspicuous cell; averages 5 µm in diameter
includes nuclear envelope, pore complex, nuclear lamina, chromosomes, chromatin, nucleolus
pore complex
protein structure that lines each pore
regulates entry and exit of proteins and RNAs
nuclear lamina
lines nuclear side of nuclear envelope
netlike array of protein filaments that maintain shape of nucleus
chromosomes
discrete unit of DNA in the nucleus
carry genetic information
each contains one long DNA molecule associated with proteins
messenger RNA (mRNA)
sythesized by the nucleus
transported to cytoplasm
translated by ribosomes into specific polypeptides
functions of smooth ER
synthesis of lipids including oils, phospholipids, steroids
detoxify drugs and poisons especially in liver cells
detoxification involves adding hydroxyl groups to drugs
stores calcium ions
functions of rough ER
secretes proteins (glycoproteins) produced by ribosomes attached to rough ER
polypeptide chain grows from a bound ribosome
chain is threaded into the ER lumen through a pore
polypeptide folds into its functional share
phagocytosis
process of surrounding smaller organism
autophagy
recycle cell’s own organic mateiral
contractile vacuole
pump excess water out of the cell
maintain suitable conditions for ions and molecules
common in freshwater protists
endosymbiont theory
early ancestor of eukaryotic cells
engulfed energy using non-photocynthetic prokaryotic cell
eventually becomingendosymbiont (cell within another cell)
consistent with characteristics: two membrans, contain ribosomes and DNA
mitrochondrial matrix
enclosed by inner membrane of mitochondria
contains many different enzymes and mitochondrial DNA
catalyze some of the steps of cellular respiration
large surface area of inner membrane increases productivity
thylakoids
membrane system inside the chloroplast
flattened, interconnected sacs
granum: stacks of thylakoids
stroma: fluid outside the thylakoid containing chloroplast DNA
types of plastids
chloroplast
amyloplast: colorless organelle that stores starch
chromoplast: pigments in fruits and flowers
peroxisomes
specialized metabolic compartment bounded by a single membrane
microtubules
hollow rods constructed from globular portein called tubulin
tubulin protein is a dimer – molecule made of two subunits
serves as track for organelles with motor proteins
grow out from centrosomes and centrioles
cilia and flagella
microtubule-containing extensions of some cells
flagella drive the cell through liquid
cilia can drive the cell or move objects along surface of cell
9+2 pattern
nine doublets of microtubules are arranged in a ring
two single microtubules in the center
9+0 pattern
nine doublets of microtubules are arranged in ring
no microtubules in center
non-motile primary cilia
basal body
anchors the cilium or flagellum in the cell
dyneins
large motor proteins that cause bending
two feet walk along the microtubule
one foot maintains contact while the other moves
microfilaments
thin solid rods built from actin moelcules, granular protein
bear tension and support muscle contraction
intermediate filaments
larger than microfilaments, smaller than microtubules
maintain cell shape
anchor nucleus and othe organelles
formation of nuclear lamina
extracellular matrix (ECM)
made of glycoproteins and other carbohydrate containing molecules
collegen is one of most abundant glycogens
forms strong fibers outside the cell
integrins
membrane proteins with two subunits
bind to the ECM on one side and to associated proteins attached to microfilaments
fibronectin
attaches the ECM to integrins embedded in the plasma membrane
collagen
fibers are embedded in a web of proteoglycan complexes
plasmodesmata
type of cell junction in plant cells
perforates cell walls
membrane lined channel filled with cytosol
joins adjacent cells and unifies plant into single organism
water and small solutes can pass freely
tight junction
plasma membrane of neighboring cells are very tightly pressed together
bound together by specific proteins and forming a continuous seal
desmosomes
funtion like rivets to fasten cells together in strong sheets
intermediate filaments made of strudy keratin proteins anchor desmosomes
attach muscle cells to each other muscle
gap junction
provide cytoplasmic channels from one cell to an adjacent cell
consist of membrane proteins that surround a pore
ions, sugars, amino acids and other small molecules can pass