Download Ch. 5 Notes Microscopes Revolving Nosepiece or Turret: This is

Ch. 5 Notes
Microscopes
Eyepiece Lens: The eyepiece is the dark
cylinder that one looks through to view the object
under magnification.
Tube: The tube connects the eyepiece to the
objective lenses
Arm: The arm Supports the tube and connects it to
the base portion of the microscope.
Base: The base is the solid bottom of the
microscope which supports the whole microscope.
Illuminator: A steady light source (110 volts)
used in place of a mirror. If your microscope has a
mirror, it is used to reflect light from an external light
source up through the bottom of the stage.
Stage: The flat platform where you place your
slides. Stage clips hold the slides in place. If your
microscope has a mechanical stage, you will be able to
move the slide around by turning two knobs. One
moves it left and right, the other moves it up and down.
Revolving Nosepiece or Turret: This is
the part that holds two or more objective lenses and
can be rotated to easily change power.
Objective Lenses: Usually you will find 3 or 4 objective lenses on a microscope. They almost always consist of 4X,
10X, 40X and 100X powers. When coupled with a 10X (most common) eyepiece lens, we get total magnifications of 40X (4X
times 10X), 100X , 400X and 1000X. To have good resolution at 1000X, you will need a relatively sophisticated microscope with
an Abbe condenser. The shortest lens is the lowest power, the longest one is the lens with the greatest power. Lenses are
color coded and if built to DIN standards are interchangeable between microscopes. The high power objective lenses are
retractable (i.e. 40XR). This means that if they hit a slide, the end of the lens will push in (spring loaded) thereby protecting the
lens and the slide. All quality microscopes have achromatic, parcentered, parfocal lenses.
Rack Stop: This is an adjustment that determines how close the objective lens can get to the slide. It is set at the factory
and keeps students from cranking the high power objective lens down into the slide and breaking things. You would only need to
adjust this if you were using very thin slides and you weren't able to focus on the specimen at high power. (Tip: If you are using
thin slides and can't focus, rather than adjust the rack stop, place a clear glass slide under the original slide to raise it a bit higher)
Condenser Lens: The purpose of the condenser lens is to focus the light onto the specimen. Condenser lenses are
most useful at the highest powers (400X and above). Microscopes with in stage condenser lenses render a sharper image than
those with no lens (at 400X). If your microscope has a maximum power of 400X, you will get the maximum benefit by using a
condenser lenses rated at 0.65 NA or greater. 0.65 NA condenser lenses may be mounted in the stage and work quite well. A
big advantage to a stage mounted lens is that there is one less focusing item to deal with. If you go to 1000X then you should
have a focusable condenser lens with an N.A. of 1.25 or greater. Most 1000X microscopes use 1.25 Abbe condenser lens
systems. The Abbe condenser lens can be moved up and down. It is set very close to the slide at 1000X and moved further
away at the lower powers.
Diaphragm or Iris: Many microscopes have a rotating disk under the stage. This diaphragm has different sized holes
and is used to vary the intensity and size of the cone of light that is projected upward into the slide. There is no set rule
regarding which setting to use for a particular power. Rather, the setting is a function of the transparency of the specimen, the
degree of contrast you desire and the particular objective lens in use.
Cell Structure
Cell: The structural, functional and biological unit of all organisms.
Cell Wall: A membrane of the cell that forms outside cell membrane whose main role is to
give cell protection against mechanical stress. Cell walls are found in cells of plants
bacteria, archaea, fungi, and algae. Animals and most protist do not have cell walls.
Membrane: Something that separates the inside and outside of an object.
Diffusion: When the small objects can pass through a membrane (barrier).
The cell membrane are “semi­permeable”, meaning it regulates the flow of material IN and OUT
of the cell. Only objects that are the correct size can fit through. These molecules can flow IN
and OUT of the cell.
Cells maintain a balance between themselves and the environment. The cells can adjust to
change in the environment, but there is a limit to amount of change they can withstand.
Think of a cell like a building. A cell likes a certain temperature ranges. The temperature range
will vary depending on the particular cell type. Cells try to regulate their temperature and may
compensate in order to survive. If a cell becomes too hot or cold, the cell will try to adjust their
temperature to better match that of their environment. There are limits to the overall temperature
swings that they can withstand. If the cell becomes too hot or cold, it will not longer function.
Passive Transport
Diffusion is the movement of any molecules across a membrane and does NOT require energy.
Osmosis is the movement of WATER across a membrane and does NOT require energy.
Molecules are in constant motion. As these molecules continuously move they will move to
areas that are LESS crowded or CONCENTRATED. Molecules will always move from areas of
higher concentration to areas of lower concentration.
Think of being at a sporting event and you are trying to watch the game. There is a large crowd
watching the game at a certain part of the sports stadium. You cannot see what is going on and
you and a few others try to move to a less crowded part of the stadium to see what is going on.
You have moved from a CONCENTRATED part of the stadium to a LESS CONCENTRATED
part of the stadium.
In both Diffusion and Osmosis, molecules will continue to move until they are evenly distributed.
When they are equally distributed they have reached what is known as EQUILIBRIUM, which
means balanced.
The ability of a molecule to pass through a membrane depends on the size of the MOLECULE
and the structure of the MEMBRANE it is trying to pass through. Semi­permeable membranes
REGULATE which molecules enter and exit the cell.
Molecules will move across a cell membrane and try to establish equilibrium. When the
molecules try to do this we call the process DIFFUSION. When water moves across a cell
membrane, we call that process OSMOSIS. Water will enter a cell or leave a cell depending on
the concentration of water inside the cell and in the surrounding environment.
ISOTONIC environments can be best described as when the CONCENTRATION of molecules
is EQUAL inside and outside of the cell. In this case, the same amount of water enters and
leaves the cell.
Now we are going to talk about some other environments. HYPOTONIC environments are best
described as those were the concentration of molecules is LOWER outside the individual cell
than inside the cell. Hypo means “below” or “under”. The opposite of this situation is called a
HYPERTONIC environment. In these situations, the concentration of molecules is HIGHER
outside the cell than inside the cell. Hyper mean “above” or “higher”.
Most DNA molecules are double­stranded helix which are basically two ropes of long
biopolymers. Biopolymers are made up of smaller, simpler units called nucleotides.
Nucleotides are made up of bases (Guanine, Adenine, Thymine, and Cytosine). G, A, T, and C
are the building blocks of DNA. The inside pairing and their nitrogen bases only pair with their
specific mate (A and T & G and C)
DNA Structure
The DNA strand is known as the “backbone”. Nucleotides can be joined together in any order
and any sequence is possible.
DNA replicates, the molecules split into TWO strands. DNA appears to unzip when it splits into
two parts. The inside pairs only match up with a specific nitrogen base. When the strand splits
it serves as a template to make a whole new molecule.
Nucleotide Based
DNA has two strands and is known as a “double helix”. There are the four nucleotide bases.
A=Adenine
G=Guanine
T=Thymine
C=Cytosine
Purines
Pyrimidines
Always Purine and Pyrimidine
Also remember that thymine and cytosine have Y in them like pyrimidine.
You CUT a pie (Pyrimidine) (U is another base we will learn
Chargaff’s Rule
The Austrian chemist Erwin Chargaff discovered that Scientist noticed the number of A’s
equaled the number of T’s and that the number of G’s equaled the number of C’s. The overall
distribution is listed below
A=21%
T=21%
C=28%
G=28%
Replication is very important. Each “daughter” cell needs to have the same amount of DNA.
The HELICASE is the process in which the DNA “unzips”. This is the enzyme which breaks the
strand apart. The DNA POLYMERASE binds, and this forms a “replication fork”. It brings in all
the nucleotide to form a new strand. The End result is that you have two strands of DNA formed.
Where is DNA found?
DNA is found in the nucleus. The nucleus acts as the “control center” for the cell. It is packed
very tightly in the chromosomes in all Eukaryotes.
Although DNA is similar, it is not identical. Even if we were 99.99% identical, that still leaves
60,000% differences. DNA fingerprinting uses those differences. It uses those differences to
identify key parts that are different known as “markers”.
DNA Damage, and almost ALL mutations are bad. When DNA replication makes mistakes we
have concerns. Environmental factors can make these concerns even worse.
DNA & RNA
DNA & RNA
● Long chain of nucleotides
● 5­Carbon Sugars
● Phosphate group
● Nitrogen base
● Nucleic acid
RNA: Only
●
●
●
●
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Ribonucleic acid
RNA sugar is ribose
Single­stranded
Thymine replace with URACIL
Swith the “T” for a “U”
(Think “GAUUACA” instead of “GATTACA”)
RNA is a disposable copy of DNA. RNA copes one part of a DNA sequence into many, many
copies of RNA. There are three types of RNA
● Messenger (mRNA)
● Ribosomal (rRNA)
● Transfer (tRNA)
mRNA
mRNA carries copies of genes and acts as a “messenger” RNA copies a gene. When mRNA
called “codons” for each amino acid protein made by the genes.
rRNA
Proteins are assembled (put together) on the ribosomes. Ribosomes are made up of part
protein and part RNA. The mRNA threads through the ribosomes. The rRNA is the major
material within the ribosome, with about 60% of the rRNA and 40% protein by weight.
tRNA
Transfer RNA molecules are very short RNA’s that have a distinctive cloverleaf pattern. They
are located in the cytoplasm and carry each amino acid to the ribosome, where the mRNA
awaits.
Transcription
Transcription is the process by which genes are copied from a DNA template that is stored in
the nucleus and then transmitted to the ribosome by the mRNA in order to synthesized (made).
Translation
Translation if the process of which proteins are synthesized by ribosomes, from a copy (mRNA)
of the DNA template (computer file) that is stored in the nucleus.
RNA Editing
The RNA molecules might need some editing before the final draft is completed.
●
Introns are removed. Think “Intruder”, acts almost like a janitor, it cleans up the waste
and stuff that is not needed and rids the strand of these parts.
Introns are found in multicellular eukaryote animals such as humans. Introns are not always
found in unicellular eukaryotes. An example might include yeast and become less
commonplace in bacteria.
●
Exons stay. Think “excellent” These are the parts that actually code for the proteins.
RNA Letters and Words
The “letters” of mRNA are A, U, C, and G. A “word” of mRNA is called a “Codon”. A Codon is
a combination of three letters which go onto form proteins.
Transcription
Translation
Everything in your body is a protein or made up of proteins. Examples include blood vessels,
finger nails, and hair. These proteins are made of up different sequences of amino acids. The
genetic code is made up of an alphabet. A, C, U, and G. There are 20 letters in a protein’s
polypeptide “alphabet” (The language of amino acids).
Transcription
mRNA Editing
Get rid of Introns
Keep Exons
mRNA exits the nucleus
A >>> U
Make mRNA from DNA
Codon >>>> 3 Letters
Nucleotide
Enzyme: RNA Polymerase
Translation
Share
Start & Stop
Codon
Cytoplasm
mRNA
tRNA
Ribosomp
Amino Acids make Proteins
Anti­Codon
1. Initiation
2. Elongation
3. Growth
Videos of DNA, Transcription, and Translation
Translation: http://www.youtube.com/watch?v=5bLEDd-PSTQ
RNA editing: http://www.youtube.com/watch?v=3ad0Ij3-XJU
Transcription http://www.youtube.com/watch?v=ztPkv7wc3yU
The entire process: http://www.youtube.com/watch?v=41_Ne5mS2ls