Lecture Notes from Dr. Ryan Martinus on the 10/7/13.
What are cells and how do we study them?
Know the defining features of a cell
Know the difference between prokaryotic and eukaryotic cells and
plant and animal cells
Know how we study the structure and function of cells
Organism – organ system – organ – tissue – cellular – chemical/molecular
Biologists classify cells into three domains:
Bacteria (Eubacteria), Archaea (Archaebacteria) and Eucarya (Eucaryotes).
Qs to consider: How did this complexity arise? How did cells evolve?
Prokaryotes = “before” nucleus
Eukaryotes= “true” nucleus
Viruses Prokaryotes Eukaryotes
Size ~50-500nm ~0.3-5um >5um
What are the characteristic features of cells?
Homeostasis (constant internal environment)
Reproduce, grow and develop
Take energy from the environment
Respond to stimuli
Adapt to the environment
What do cells look like?
There is no “typical” cell.
They vary in size and shape.
What features distinguish prokaryotic and eukaryotic cells?
Prokaryotic Cells Eukaryotic Cells
Small cells (<5um) Larger cells (>10um)
Always unicellular Often multicellular
No nucleus or any membrane- Always have nucleus and other
bound organelles membrane-bound organelles Circular DNA without proteins Linear DNA, associated with
Ribosomes are small proteins to form chromatin
No cytoskeleton Ribosomes are large
Motility by rigid rotating Always has a cytoskeleton
flagellum Motility by flexible waving cilia
Cell division by binary fission or flagellae
Asexual reproduction Cell division by mitosis/meiosis
Huge variety of metabolic Reproduction either asexual or
Common metabolic pathways
Q. How do we study cells?
Microscopes provide a window into the world of cells
The first light microscopes were used in the 17 century.
Basic Terminology used in microscopy:
Magnification is the ratio of an objects image to its real size
Resolution is the ability to discriminate two points close together
Best resolution with a light microscope is about 2.0um (small bacterium).
Maximum magnification achievable with a light microscope is about 1,000
times the size of the actual specimen.
Cells can be viewed stained – dyes enhance contrast and preserve cells – or
unstained – light passes directly through specimen and the image has little
The confocal microscope
Confocal microscopy yields more detail especially with thick
While a light microscope can resolve individual cells, it cannot resolve much
of the internal anatomy, especially the organelles.
To resolve smaller structures we use an electron microscope (EM), which
focuses a bean of electrons through the specimen or onto its surface.
The resolution of a modern EM is ~2nm.
Transmission electron microscopy (TEM)
Uses electromagnets to focus electron beam through thin section of the
Image is focused onto a screen Contrast of the image is enhanced by staining sections with heavy
metals (they attach to cellular structures).
These are used to study internal structures of cells
Resolves cellular details as small as 1-2nm
Scanning electron microscopy (SEM)