Nucleic Acids ??

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Nucleic Acids ??

• all living organisms contain nucleic acids
• in form of
• - deoxyribonucleic acid (DNA ??????)
• - ribonucleic acid (RNA ????)
• Some viruses may contain only RNA (e.g. tobacco
  mosaic virus??????)
• while others have DNA (phages???)

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DNA other than eukaryotic chromosomes
mitochondrial DNA, chloroplast DNA, bacterial
plasmid
Mitochondrial DNA ???DNA
???DNA
Plasmid DNA ????DNA
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Nucleotides ???

• the monomeric?? units of nucleic acid

• 2. Each nucleotide consists of 3 components
• a phosphoric acid??
• 5-C sugar ???
• (deoxyribose???? / ribose??)
• A nitrogenous base??

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Nucleotide triphosphate ?????
Nucleotide diphosphate ?????
Nucleotide monophosphate ?????
Nucleoside??
??
??pentose
?? Phosphate (s)
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5-carbon sugar ( pentose ??)
??
????
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2 groups of organic nitrogenous bases????
(i) Purine (s) ?? large molecule with 2
rings?? e.g Adenine ??? (A) ,
Guanine??? (G)
(ii) Pyrimidine (s) ?? smaller molecules
with 1 ring?? e.g Cytosine???(C) ,
Thymine ???? (T, in DNA) or Uracil ???(U, in
RNA)
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in RNA only
in DNA only
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types of nucleotides??????

• Polymer ???
• - polynucleotide ???? / nucleic acids
• Non-polymer ????
• - mononucleotides ????
• - dinucleotides????

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Non-polymeric nucleotides???????

• i. ATP ?????
• (Adenosine triphosphate)
• - a mononucleotide (????)
• ---gt energy rich compound,
• release energy by bond breaking
• ii. NAD ??(?)????????
• (Nicotinamide adenine dinucleotide)
• a dinucleotide (????)
• ---gt cofactor (???) of enzyme
• (e.g. in respiration ????)

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?????????????? Nucleotide monophosphate
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Polymer ( polynucleotide ) ????

• - includes RNA and DNA
• ---gt heredity??
• ---gt protein synthesis
• ?????

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DNA (??????) ???

• DNA??
• ?????(deoxynucleotides) ?? (base)
• ???? (doxyribose) ?? (phosphate)
• ??????
• ???(A)????(G)?
• ????(T)????(C)

Source The University of Arizona
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??????RNA RNA in Eukaryotic cells

• Single stranded molecules ????
• - Nitrogenous base ?? A, U, G, C (no T)
• - Pentose ribose ??

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??????RNA RNA in Eukaryotic cells

• Ribosomal RNA (rRNA, ???????)
• 2. Transfer RNA (tRNA, ??????)
• 3. Messenger RNA (mRNA, ??????)
• 4. Nuclear RNA (nRNA, ??????)

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DNA????????? DNA is a double-stranded
polynucleotide chains coiling round each other to
form a double helix.
??????????????? ??????? A?T C?G
???????????????????
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??
????
C5
C1
C3 to P of other nucleotide
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The two strands of polynucleotide chain in DNA
are Anti-parelle DNA ?????????????????
3 end
C3
5 end
C5
C5
5 end
3 end
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• 1. DNA is heat resistant??????
• 2. DNA content
• haploid cells????? 50 of diploid cells?????
• 3. DNA structure and DNA expression (??) can be
  altered by
• Chemical factors (????) and
• Physical factors (????)
• e.g. colchicine, nitrous acid and physical
  factors (e.g. X-ray, UV light) can alter
  molecular structure of DNA which is the source of
  the mutation.
• 4. All organisms have DNA
• including bacteria ??and virus??

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??????????DNABiochemical investigation and
genetic material DNA
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The researches for genetic material led to DNA.
The process involved different scientific
investigation
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in vitro investigation ?????
???????????????(???????????????????)?????(????????
????????)????????????????,????????????????????????
????????????,????????????,???????????????????,????
??????????????????????????????????????????
(biochemistry) ????????
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F. Miescher

• ????????DNA?????1866-1869??????? F. Miescher
  ????,????????????????????????????,????????????????
  ??,?????????????,
• ??Miescher?????????(nucleic acid)?

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• ???? (1866?)
• ??? (Mendel)?????????????

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• ????????,?????????????????

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• ??,?????????????????????????,????????????????,????
  ???,???????????????

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• ????????????????,?????????

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• ?????????????????????????????????,???????

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• ???????????????????????????????????????????????

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• ????,?????????????????????????????????????????????
  ???

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• ?????????????????,?????????????????????????
  (organic molecules)???
• ?????? (proteins)?
• ?? (carbohydrates)?
• ?? (lipids)?
• ?? (nucleic acids)

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• ???????????
• ???? (genetic information) ????
• ----- ??? (chromosomes) ??
• - ??? (proteins) ?
• - ?? (nucleic acids)
• ???????

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?????????????????????
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1928?Frederick Griffith????

• ????????? ????? (Streptococcus pneumoniae)

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• ???????
• S strain????????
• R strain??????
• ??????????????????,
• ?R strain ??????

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Griffith (1944) Experiment with Pneumococcus
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1944?O.Avery,C.M.MacLeod?M.McCarty

• ????????
• ???(S)??????????????(??????????RNA?????DNA)??????
  ????????

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?????????????DNA????????
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• ???DNA????????

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• ???????????????????????????????????,??????????????
  ????(A?T?C?G)?????????????????????????????

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• 1952? Alfred Hershey (??)?Martha
  Chase(??)????????? (Transduction experiment)

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????????????T2 (bacteriophage T2)
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Hershey-Chase T2?????(Transduction experiment
?????? )
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• ?????????DNA???????????????????????????,??????????
  ??(DNA of the bacteriophage alone is enough to
  control the reproduction process of virus in the
  bacterial host. )

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• DNA??????????????? (it was proved that DNA,
  instead of proteins, was the hereditary material)
  
• ??????,??DNA????????????,?????RNA????????????????
  ??????

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• 1950???????E. Chargaff(???)??????DNA?????????(pape
  r chromatography)

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• ??adenine?????thymine????,???,guanine?cytosine????
  ??,??Chargaffs rule?

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Chargaffs ruleA T 11 C G 11
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30??X?????????????
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1953?Watson(??)?Crick(???)???DNA????????????
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?????????

• ?????????????????????????

The two polynucleotide chains are not identical
but are complementary, one chain is the reverse
of the other and runs in opposite direction (it
is called antiparallel) and are twisted to form a
double helix (right handed direction twisting)
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• ????????????
• ?? ??????

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• ?????????,???????,?A?T?C?G,?????
• The two chains are held together by
  complementary pairs of bases (AT, C?G) bounded
  by loose H-bonds

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• ?????????????????????????

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• ???????????3.4nm,????????10???
• 10 pairs of nucleotides are present in a full
  turn of the DNA helix (i.e. 3.4 nm for the
  secondary repeat distance)

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• ??????2.0nm
• ??????????????,??????0.34nm
• (The distance between two bases along the
  backbone 0.34 nm)

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• ??????????????,?????????A?T??,C?G??
• ? ??Chargaffs rule?
• ???????

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All researches on genetic material give the
evidences to show the role of DNA ---

• DNA is the genetic material.

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?????????DNA???????

• ?????????????????
• ????DNA?????A?T??C?G?????,
• ??????DNA??????DNA???????????

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DNA replication
I

• Different hypotheses

II
III

• Study the work of Meselson and Stahl E.coli
  grew in 15N medium
• http//vector.cshl.org/dnaftb/20/concept/index.htm
  l
• Refer to Chapter 6

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????
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Evidence in the work of Meselson and Stahl

• http//vector.cshl.org/dnaftb/20/concept/index.htm
  l

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Mechanism of DNA replication

• Before replication of DNA takes place, the
  following conditions must be available
• (1) free nucleotides, A, T, C, G, are present
• (2) The enzymes required for DNA replication are
  present (e.g. DNA polymerase)

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http//www.ncc.gmu.edu/dna/repanim.htm
http//biotech-adventure.okstate.edu/low/basics/dn
a_replication/replication2/animation/
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Mechanism of DNA replication

• During DNA replication, base pairing enables
  existing DNA strands to serve as templates for
  new complementary strand.
• 2. Two polynucleotide chains unwind and separate
  by breaking the hydrogen bonds just before
  mitosis or meiosis (S-phase of cell cycle)

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• the bases of each chain then pair with the bases
  of the free nucleotides in a complementary
  pattern
• (AT, C?G)
• 4. the newly lined up nucleotides are joined
  together by sugar-phosphate bonds forming two new
  DNA chains identical to the parent one

It is the mechanism of semi-conservative
replication.
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5
3
3
5
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• N.B. Replication of DNA takes place during
  interphase, shortly before mitosis / meiosis.
• Therefore when the chromatids appear during
  prophase, each has a double helix of DNA.

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Why is DNA so stable ?

• (1) The two strands are held tightly by a large
  number of H-bond between the base pairs.
• (2) the base pairings are highly specific. This
  maximizes the number of effective hydrogen bonds
  formed.

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The importance of stability in DNA

• 1. The stable complementary nature of two strands
  of DNA makes it suitable for storing genetic
  information and transmitting the information from
  one generation to another.
• 2. The hydrogen bonds between the base pairs tend
  to drive the double helix to reform spontaneously
  after uncoiling in replication and transcription.

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????? Gene Expression

• ???DNA??????,Watson???????????
• ???????DNA?RNA?????,?????
• DNA?RNA?protein?
• ???????????,?????????????????????

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• DNA?????????? (genetic code transcription)?mRNA
• ??? (ribosomes) ??mRNA????? ?????(????
  translation)

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???? (genetic codes)

• ???????,??????? (genetic codes) ?????????????
  (triplet codon ?????)
• ????????????

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?? (gene)

• ??? (gene) ????????????????
• ????????????????,???????????????????????

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What is a gene ?

• The genetic information of the gene is
  represented by the sequence of bases along the
  nucleotide chains
• A gene is represented by a certain length of
  consecutive nucleotide units on the DNA molecule
• All genes have similar chemical nature, but they
  all have different kinds, numbers, and sequences
  of the nitrogenous bases on the nucleotide
  chains.

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The structure of DNA related to its roles as
genetic material

1. The configuration of the DNA molecule is highly
   stable, allowing it to act as a template for the
   replication of new DNA molecules, and for
   transcription to form the mRNA molecule.
2. A sequence of nitrogenous bases along the
   nucleotide of DNA represents the genetic
   information. This is called a gene and codes for
   the cell's synthesis of a specific protein.
3. During DNA replication, base pairing enables
   existing DNA strands to serve as templates for
   new complementary strand. The new strands are
   copied by the same principle of hydrogen-bond
   pairing between bases that exists in the double
   helix. Two new double-stranded molecules of DNA
   are produced, each containing one of the original
   strands and one new strand. This
   "semiconservative" replication is the key to the
   stable inheritance of genetic traits.

http//www.uwinnipeg.ca/simmons/DNA/sld010.htm
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Experiment DNA extraction

• ?????????
• 60?????
• ???
• ??
• ??
• ????
• ??????
• ???DNA ????????
• ??
• ??? ?????
• ?????? (??)

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Some probelems encoutered 1. I'm pretty sure
I'm not seeing DNA. What did I do wrong?

• First, check one more time for DNA. Look very
  closely at the alcohol layer for tiny bubbles.
  Often, clumps of DNA are loosely attached to the
  bubbles.
• If you are sure you don't see DNA, then the next
  step is to make sure that you started with enough
  DNA in the first place. Many food sources of DNA,
  such as grapes, also contain a lot of water. If
  the blended cell soup is too watery, there won't
  be enough DNA to see. To fix this, go back to the
  first step and add less water. The cell soup
  should be opaque, meaning that you can't see
  through it.
• Another possible reason for not seeing any DNA is
  not allowing enough time for each step to
  complete. Make sure to stir in the detergent for
  at least five minutes. If the cell and nuclear
  membranes are still intact, the DNA will be stuck
  in the bottom layer. Often, if you let the test
  tube of pea mixture and alcohol sit for 30-60
  minutes, DNA will precipitate into the alcohol
  layer.

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2. Why does the DNA clump together?

• Single molecules of DNA are long and stringy.
  Each cell of your body contains six feet of DNA,
  but it's only one-millionth of an inch wide. To
  fit all of this DNA into your cells, it needs to
  be packed efficiently. To solve this problem, DNA
  twists tightly and clumps together inside cells.
  Even when you extract DNA from cells, it still
  clumps together, though not as much as it would
  inside the cell.
• Imagine this the human body contains about 100
  trillion cells, each of which contains six feet
  of DNA. If you do the math, you'll find that our
  bodies contain more than a billion miles of DNA!

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