Introduction to cell biology week 1
Chapter 1
All living organisms are constructed from one or more cells: small,
membrane-enclosed units filled with a concentrated aqueous
solution of chemicals and endowed with the extraordinary ability to
create copies of themselves by growing and then dividing in two
Cells arise from pre-existing cells by growth and division. They do
not arise spontaneously
Cells vary enormously, but all have a similar basic chemistry:
o Genetic information is carried in DNA molecules..
o .. and written in the same genetic code
The central dogma
Genetic information is carried in DANN molecules
Information in DNA is transcribed into RNA
mRNA molecules are translated into proteins
cells under the microscope
resolution (= resolving power): least distance at which
two points can be distinguished as individual points
the resolution (d) can be determined as follows
λ = wavelength oft he light used
N.A. = numerical aperture (written on the lens)
A smaller d means a better resolution (so you see more details)
When light with a shorter wavelength is used, for instance UV-light,
the value of ‘d’ becomes lower corresponding to an improved
resolving power
Improving contrast
Limited absorption and light scattering by cells yields low image
contrast (exceptions: chloroplast and dense objects like cell wall).
Histological stains improve contrast but are often incompatible with
live cells
Light microscope (LM)
Absorption and scattering of photons (light)
Glass lenses
Cells in liquid (live cell imaging)
Dynamic processes can be visualized
Moderate magnification (103 x)
Smallest distance resolvable is 200 nm (human eye is 200 µm)
The diaphragm is varies to obtain the best contrast
microtome
Fluorescence microscopy
, Select fluorophores (dyes) bind to specific cellular structures (e.g.
DAPI – DNA; DIOC6 – lipid membranes)
A fluorescent molecule (fluorophore) absorbs photons of a specific
colour (excitation) and produces photons with a longer
wavelength/less energy (emission) a insertion of a colour filter
makes it possible to only display the emitted light in the final image
Better contrast
When multipule fluorophores become too close, they will not be
visible as individual items because of the limits in resotion
Electron microscopy (EM) (T = transmission) (S = scanning)
No light but an electron beam
Average wavelength electron beam: 0,004 nm
Resolution around 0,1 nm (1x10-10 m)
Absorption and scattering of electrons
Magnetic lenses
Cells in vacuum (fixed tussue)
Heavy metals for contrast (e.g. OsO4)
High magnification (106 x)
Ultra-microtome
SEM = shows surface structeres scans the surface of the sample
using a focussed electron beam. A detector detects secondary
electrons that are generated at the surface. (frozen and/or
dehydrated)
Prokaryotes
Prokaryotes (bacteria and archeae) have limited internal
organization
Unicellular organisms, divided into two domains: bacteria and
archaea
The cell wall found in prokaryotes are differend from the ones
found in eukaryotes
Circular DNA strand is concentrated in the nucleoid, which
lacks a nuclear membrane
Protein synthesis by ribosomes in the cytosol
Some bacteria are photosynthetic
o Cyanobacteria are an phylum of bacteria that obtain
energy through photosynthesis
o Cyanobacteria are the precursors of chloroplast in plants
important for live on earth
Eukaryotes
Plants, animals, fungi
Have membrane-enclosed organelles
Internal membranes create distinct environments that enable
different chemical processes
Chapter 1
All living organisms are constructed from one or more cells: small,
membrane-enclosed units filled with a concentrated aqueous
solution of chemicals and endowed with the extraordinary ability to
create copies of themselves by growing and then dividing in two
Cells arise from pre-existing cells by growth and division. They do
not arise spontaneously
Cells vary enormously, but all have a similar basic chemistry:
o Genetic information is carried in DNA molecules..
o .. and written in the same genetic code
The central dogma
Genetic information is carried in DANN molecules
Information in DNA is transcribed into RNA
mRNA molecules are translated into proteins
cells under the microscope
resolution (= resolving power): least distance at which
two points can be distinguished as individual points
the resolution (d) can be determined as follows
λ = wavelength oft he light used
N.A. = numerical aperture (written on the lens)
A smaller d means a better resolution (so you see more details)
When light with a shorter wavelength is used, for instance UV-light,
the value of ‘d’ becomes lower corresponding to an improved
resolving power
Improving contrast
Limited absorption and light scattering by cells yields low image
contrast (exceptions: chloroplast and dense objects like cell wall).
Histological stains improve contrast but are often incompatible with
live cells
Light microscope (LM)
Absorption and scattering of photons (light)
Glass lenses
Cells in liquid (live cell imaging)
Dynamic processes can be visualized
Moderate magnification (103 x)
Smallest distance resolvable is 200 nm (human eye is 200 µm)
The diaphragm is varies to obtain the best contrast
microtome
Fluorescence microscopy
, Select fluorophores (dyes) bind to specific cellular structures (e.g.
DAPI – DNA; DIOC6 – lipid membranes)
A fluorescent molecule (fluorophore) absorbs photons of a specific
colour (excitation) and produces photons with a longer
wavelength/less energy (emission) a insertion of a colour filter
makes it possible to only display the emitted light in the final image
Better contrast
When multipule fluorophores become too close, they will not be
visible as individual items because of the limits in resotion
Electron microscopy (EM) (T = transmission) (S = scanning)
No light but an electron beam
Average wavelength electron beam: 0,004 nm
Resolution around 0,1 nm (1x10-10 m)
Absorption and scattering of electrons
Magnetic lenses
Cells in vacuum (fixed tussue)
Heavy metals for contrast (e.g. OsO4)
High magnification (106 x)
Ultra-microtome
SEM = shows surface structeres scans the surface of the sample
using a focussed electron beam. A detector detects secondary
electrons that are generated at the surface. (frozen and/or
dehydrated)
Prokaryotes
Prokaryotes (bacteria and archeae) have limited internal
organization
Unicellular organisms, divided into two domains: bacteria and
archaea
The cell wall found in prokaryotes are differend from the ones
found in eukaryotes
Circular DNA strand is concentrated in the nucleoid, which
lacks a nuclear membrane
Protein synthesis by ribosomes in the cytosol
Some bacteria are photosynthetic
o Cyanobacteria are an phylum of bacteria that obtain
energy through photosynthesis
o Cyanobacteria are the precursors of chloroplast in plants
important for live on earth
Eukaryotes
Plants, animals, fungi
Have membrane-enclosed organelles
Internal membranes create distinct environments that enable
different chemical processes
