lecture 1 Flashcards
Scientific method
- observation
2.formulate a testable hypothesis
3.design a controlled experiment - collect data
5.interpret results
6.accept or reject the hypothesis
between 1-2 and 5-6 is consult prior knowledge
3-4 may have to go back and redesign experiment
the cell theory
-all organisms consist of one or more cells
-the cell is the basic unit of structure for all organisms
-all cells arise only from preexisting cells
(ominis cellula e cellula-1855 Rudolf Virchow)
deci (d)
10-1
centi (c)
10-2
milli (m)
10-3
micro (um)
10-6
nano (n)
10-9
what organisms can be seen with the electron microscope?
atoms
small molecules
dna, proteins, lipids
ribosomes
viruses
mitochondrion
most bacteria
nucleus
what organisms can be seen with the light microscope?
mitochondrion
most bacteria
nucleus
light microscope
an instrument that uses light magnifying lenses and an eyepiece to examine objects too small to be seen by the naked eye
-allows identifying membrane-bounded structures (nuclei, mitochondria, chloroplasts
limitation of light microscopy
- only dark objects can be seen well (dense)- difficult to see living internal structure
2.resolution is about 0.2 micron (λ/2 is where λ is the light wavelength)-shorter wavelength hsve better resolutiom - out of focus light reduces clarity
resolution in microscopy
the shortest distance between two points on a specimen that can be still be distinguished by the observer or camera system as separate entities.
-if the limit of resolution is 400nm, objects must be at least 400nm apart to be recognized as separate entities
-the smaller the l.o.r, the greater the resolving power(the ability to see fine details
brightfield microscopy
-unstained: passes light directly through the specimen, unless cell is naturally pigmented or artificially stained, image has little contrast
-stained: staining w various dyes enhances contrast, but most staining procedures requires that cells be fixed (preserved)
phase contrast
+make it possible to see living cells clearly
enhances contrast in unstained cells by amplifying variations in refractive index within specimen (playing w properties of light)
*useful for examining living unpigmented cells
differential interference contrast
+make it possible to see living cells clearly
uses optical modifications to exaggerate differences in refractive index (played w properties of light)
Fluorescence
_shows the locations of specific molecules
_absorb uv (energy is higher, short wavelength) & emit visible light( energy is lower, long wavelength)
_often tag molecules of interest with fluorescent dye/ antibodies
*positively charged dye will bind to negatively charged cell
confocal
USES LASER and special optics to focus illuminating beam on a single plane within the specimen
-only the specific region is imaged (above/ below the region will appear black)
electron microscope: when, where, who
-1913
-germany
-by max knoll & ernst ruska
what is an electron microscope?
_uses a beam of electrons that is deflected & focused by an electromagnetic field
_allows small organelles to be seen (ribosomes, cell membranes, microtubules, microfilaments
_allow macromolecules to be seen (DNA & proteins)
-resolution: 0.2-0.5 nm (1000x more than a light microscope)
-treat w heavy metals
-can only see thru dead cells
two designs of electron microscope
- transmission electron microscope (TEM)
- scanning electron microscope (SEM)
transmission em
forms an image from electrons that are transmitted thru the specimen
scanning em
scans SURFACE of the specimen(heavy metals binds to the surface)
-resolution is limited by the width of the beam
where did the 3 types of cells evolve from
ancestral cells
3 types of cells
- bacteria (prokaryotes)
- archaea (prokaryotes): “extremophiles”-live in extreme climates and conditions
- eukarya
what do bacteria have
contain mostly DNA
no membrane organelles
no nuclear envelope
organelles of plant cells
-shape: fixed (rectangular)
-rarely have cilia, flagella
- chloroplasts & plastids
-cell wall
-one large vacuole
-centrioles (only in lower plants)
organelles of animal cells
shape: round/irregular (can change)
-cilia and flagella
-lysosomes (digestive enzymes)
-few small vacuoles
centrioles ( microtubules that organizes the miotic spindle)
