Unit 8 The Ultimate
Instruction Manual
A LITTLE HISTORY:
In the 1850’s Gregor Mendel experimented with pea plants and
documented many principles of genetics.
In 1869 Johannes Miescher isolated an acid from the nuclei of a cell,
it was DNA.
In 1928 Griffith experimented with pneumonia and mice to discover
that DNA is the substance that causes bacterial transformation.
In 1952 Hershey & Chase confirmed that DNA was the genetic
material by experimenting with radioactive Phosphorus-32 and
Sulfer-35, proving for certain that DNA not proteins transmitted
inherited information.
In 1953 Watson, Crick, Wilkins and Franklin uncovered the chemical
structure of DNA.
http://biology.clc.uc.edu/courses/bio104/dna.htm
LETS REVIEW
We all know that the DNA molecule in humans is about 2 m long. To accommodate
this great size the molecule must be super-coiled, which is a series of 6
successive foldings around histone protein molecules. Each histone protein with
him DNA wrapped around it is considered a nucleosome. Nucleosome’s are tightly
bound together in a larger coil which coils and coils to eventually create a
chromosome.
http://www.cengage.com/biology/book_content/9781111425692_starr_udl13e/ani
mations/PowerPoint_Lectures/chapter8/videos_animations/chromosome_structur
e.html
Chromatin, chromosomes, chromatids.
Chromosome number –
 somatic cells contain diploid chromosome numbers
o diploid cells contain homologous chromosomes.
o Every cell contains one set of sex chromosome, but all the rest are
called autosomes
 Sex sells contain haploid chromosome numbers
Karyotyping is a method in which an individual’s DNA is treated to make the
chromosomes condense, they are stained, put under a microscope, and a
photomicrograph is taken. What can this show???
Overview of Experiments………
Griffith’s Mice and Pneumonia
Avery-MacLeod-McCarty
Hershey-Chase Experiment
Watson, Crick, Wilkins, Franklin
Chargaff
https://www.youtube.com/watch?v=qoERVSWKmGk#!
Nucleotide Structure
Nucleotides are composed of three main components…
1. Nitrogenous Bases (either Adenine, Thymine, Cytosine, or Guanine)
2. Deoxyribose sugar
3. Phosphate group
The Backbone is composed of the Deoxyribose and Phosphate, while the rungs are
composed of the nitrogenous bases.
 Deoxyribose and phosphate have an alternating pattern.
 They are covalently bonded to one another for strength
The Rungs are composed of adenine, thymine, cytosine, and guanine.
 Adenine and guanine are double ringed bases, which are called purines.
 Thymine, cytosine are single ringed bases, which are called Pyrimidines
 adenine and thymine bond together with 2 hydrogen bonds.
 Cytosine and guanine bond together with 3 hydrogen bonds.
 A purine always pairs with a pyrimidines , so that the rungs are of equal
length
OKAY, NOW ON TO SOMETHING NEW!
You will hear the term nucleoside sometimes. In brief it means that it only
contains a sugar and base.
I found this and thought that it was great diagrams so I also brought the
explanations too.
3.3.2 State the names of the four bases in DNA (1).
State means to give a specific name,
value or other brief answer without
explanation or calculation.
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Nucleosides are the combination of sugar
and base only and are not required for the
syllabus. You will however see the terms
used in the literature.
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These are the four bases which are universally found in living things.
In 1950 Edwin Chargaff determined that within an organism there was same approx the same
amount of A as T and the same amount of G=C.
Chargaff surveyed a wide variety of organsims and found in the ratio of A:T, G:C consistently
across the range of his specimens
These ratios became known as Chargaff's ratio's and would later prove to be a significant clue to
the structure of DNA.
NB: As of July 2011 there are now be more than four bases. The new addtions to the list tend to be
modifications of the bases above (e.g. adding methyl groups to cytosine) and are invloved in processes
that modify transription/ translation or silnce genes. The details are not examined on this course.
top
3.3.3 Outline how DNA nucleotides are linked together by covalent bonds into a single strand
(2).
Outline means to give a
brief summary.


DNA is composed
of two
polynucleotides
chains.
Nucleotides are
covalently bonded
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between the phosphate of one nucleotide to the C3 of the second nucleotide.
The phosphate group creates a bridge connecting C5 on one pentose with the C3 on the next
pentose.
The bond is a phosphodiester bond which indicates that there are two covalent bonds formed
between the -OH and the acidic phosphate group.
top
Polynucleotide
The image is of one polynucleotide chain.
Note:
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The sugar phosphate backbone which provides the
stable backbone of one of the helices.
Covalent bonds that link the nucleotides along the
backbone of the molecule.
The bases projecting into the centre.
At one end there is pentose with 5' (said "five prime"
) carbon which is free from bonding.
At the other end there is a 3' carbon free from
bonding to other nucleotides.
Additional nucleotides are joined to the 3' end of the
existing polynucleotide chain.
This is where it is from.
http://click4biology.info/c4b/3/chem3.3.htm
DNA replication (the S-phase) –
As you will remember, a cell spends most of his life in interphase, where it will go
through the G1 phase, the S phase, and the G2 phase. Then it will prepare for cell
division.
DNA replication requires a lot of energy, and several enzymes to occur.
In eukaryotes, DNA polymerase will assemble a new set of nucleotides to each
template strand of DNA as a separates. Inhibitor proteins bind to a certain
sequence of nucleotides, and enzyme called topoisomerase untwist the double
helix. To pop open the strand we need an enzyme called helicase.
Helicase unzips the molecule breaking the hydrogen bonds.
RNA primers that base pair with the open areas of DNA act as attachment points
for DNA polymerase.
DNA polymerase moves down the strand of DNA using the sequence of bases as a
template to assemble a new strand of DNA from free nucleotides.
DNA polymerase always works from the 5’ to 3’ direction.
Only one strand can be synthesized continuously the other strand is made up of
small segments called Okazaki fragments.
The enzyme DNA ligase seals any gaps so DNA strands are continuous.
Since the template strand is from the original cell. This is referred to as
semiconservative replication.
http://www.hhmi.org/biointeractive/dna-replication-advanced-detail
MUTATIONS
DNA is always replicated perfectly, bassist get lost, extra ones are added, or the
wrong base is put in place.
Replication errors are inevitable of DNA catalyzes about 50 nucleotides per
second in eukaryotes, and 1000 bases per second in bacteria.
DNA polymerase proofread their own work, also a set of enzymes and other
proteins function to prepare DNA by splicing out and replacing damaged or
mismatched bases before replication occurs.
Environmental causes –
electromagnetic energy in the form of wavelengths shorter than 320 nm can
knock electrons out of atoms, breaking chromosomes into pieces that get lost
during replication.
This energy also leaves behind free radicals which are destructive and wake
bonds.
UV light in the range of 322 400 nm has enough energy to open the double bonds
in the high remedy basis (T, C)
the now open ring can form a covalent bond with the ring of and adjacent
pyrimidine.
The resulting pyrimidine dimer makes 18 into DNA strand, or causing DNA
polymerase to make a replication.
This often causes skin cancer.
Natural or synthetic chemicals can also cause mutations. 55& have been found in
tobacco alone.
Cloning- creating an exact genetic duplicate of an organism.
 Everyday clones are made usually through asexual reproduction.
 Another natural cloning process is embryo splitting resulting identical twins.
 Artificial embryo splitting is done in research and animal husbandry.
o Artificial twinning and any other technique that yields genetically
identical individuals is called reproductive cloning.
 Somatic cell nuclear transfer (SCNT)-involves cloning an adult organism.
o 1st, you must transform a mature somatic cell into and on
differentiated cell
o next, researchers remove the nucleus from it unfertilized egg.
o They insert into the egg a nucleus from an adult animal cell.
o If all goes well, the egg cytoplasm reprograms the transplanted DNA
to direct the development of an embryo, which is then transplanted
into a surrogate mother.
o The animal or is genetically identical with the donor of the nucleus.
o This is now a common practice among people who breed prized
livestock.
o In this way offspring can be produced from animals which are
castrated or even dead.
 SCNT with human cells is called therapeutic cloning, producing embryos that
are used for steps cell research
 Do you see any possible benefits of cloning?
 Is there anything ethically wrong with cloning?
 Is this cheating?