Modern

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• Modern
• Molecular Genetics

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• By the early 1920s, scientists knew that
  chromosomes were made up of two substances, DNA
  and protein.

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• In recent years, biochemists have found that the
  DNA of chromosomes is the genetic material that
  is passed form generation to generation. (It is
  known as the molecule of life.
• To demonstrate that DNA was the substance that
  determined which traits were inherited, many
  experiments (including the British researcher
  Frederick Griffth) were performed

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Frederick Griffith

• In 1928, Griffith found that a substance from
  dead pneumonia bacteria was transformed into
  pneumonia causing ones.
• He called the substance a transforming factor.
• It was later proven that DNA was the transforming
  factor.
• The transmission of genetic material from the
  pneumonia-causing bacteria into the harmless
  pneumonia bacteria changed it into
  pneumonia-causing bacteria.

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(I) DNA Structure

• A very large molecule consisting of thousands of
  smaller, repeating units known as nucleotides.
• DNA is found within the nucleus of the cell.

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(A) DNA Nucleotide

• A DNA nucleotide is composed of three parts
• 1. A phosphate group
• 2. A deoxyribose (5-carbon sugar)
  molecule
• 3. A nitrogenous base of either adenine,
  thymine, guanine, or cytosine

http//bioweb.wku.edu/courses/BIOL115/Wyatt/Bioche
m/Protein/chime_script1.htm
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(B) Watson-Crick Model

• In 1935 James Watson and Francis Crick developed
  a model of the DNA molecule.
• In this model, the DNA molecule consists of two
  complimentary chains of nucleotides in a ladder
  type organization.
• The four nitrogenous bases of the DNA molecule
  bond together in only one way
• adenine (A) with thymine (T)
• cytosine (C) with guanine (G)

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James Watson (L) and Francis Crick (R), and the
model they built of the structure of DNA
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Double-helix Structure of DNA

• Each step of the ladder consists of nitrogenous
  bases bonded together by weak hydrogen bonds.
• The two chains of the DNA molecule are twisted to
  form a spiral, or double-helix.

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(II) DNA Replication

1. DNA, unlike any other chemical compound, can make
   exact copies of itself by a process known as
   replication.
2. In replication, the double-stranded DNA helix
   unwinds the two strands then separate, or unzip,
   by the breaking of the hydrogen bonds between
   pairs of bases.
3. Free nucleotides in the nucleus then bond to the
   complimentary bases of the DNA strands.

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Replication produces two identical DNA molecules
that are exact copies of the original molecule.
DNA Replication Animation
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Genes and Proteins

• Every cell can be thought as a chemical factory.
• Genes, which instruct cells to make enzymes, are
  therefore really packages of information that
  tell a cell how to make proteins (long chain of
  amino acids).
• Genes are specific sections of DNA molecules that
  are made up of linear sequences of nucleotides.

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(III) RNA (Ribonucleic acid)

• RNA is a nucleic acid, like DNA, composed of
  nucleotide building blocks.
• There are three major differences between the
  structure of DNA and RNA
• 1. In RNA, ribose is substituted for
  deoxyribose.
• 2. uracil (U) is substituted for thymine (T)
• 3. RNA consists of only a single strand of
  nucleotides.

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Genetic Code

• A genetic code contains the information for the
  sequence of amino acids in a particular protein.
• This code is present in mRNA molecules and is
  three bases long. This is known as a codon.
• Ex UAG - is a codon

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Genetic Codes
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DNA Sequencing
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From DNA to RNA

• DNA is copied into RNA by a process called
  transcription.
• Transcription is similar to DNA replication
• 1. The DNA double-helix opens up.
• 2. Special enzymes begin to match up RNA
  nucleotides with the correct nucleotides in DNA.
• 3. A messenger RNA or mRNA molecule is built.

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Messenger RNA (mRNA)

1. When portions of DNA molecules unwind and
   separate, RNA nucleotides pair with complimentary
   bases on the DNA strand. This forms a mRNA that
   is complimentary to the DNA strand.
2. The sequence of nucleotides in the mRNA contain
   the genetic code.
3. The genetic code for each amino acid is a
   sequence of three nucleotides forming a codon.

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mRNA

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tRNA

• Known as transfer RNA
• Contains a triplet of nucleotides called the
  anticodon.
• At the other end of the molecule, the amino acid
  is attached.

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• The anticodon of tRNA matches the codon of the
  mRNA.

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(IV) Translation

1. Also referred to as Protein Synthesis.
2. In the cytoplasm, the mRNA becomes associated
   with a ribosome.
3. Amino acids in the cytoplasm are picked-up by
   molecules of transfer RNA (tRNA).
4. Each codon on the mRNA bonds with a corresponding
   anticodon on a tRNA, which carries a specific
   amino acid.
5. These amino acids are joined together by peptide
   bonds.
6. The resulting chain of amino acids is a
   polypeptide.

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Protein Synthesis Animation
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V. Gene Expression and Cell Differentiation

• The human body is made up of many different types
  of cells.
• All of these cells have the same DNA in them, so
  why are they so different from each other?
• The answer is that only certain genes are used in
  certain cells. The use of the information from a
  gene is called gene expression (which genes are
  turned on).
• Creating the special types of cells through
  controlled gene expression is called cell
  differentiation.

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Without cell differentiation, our bodies would be
made up of only one type of cell.
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VI Genetic Engineering

• Genetic Engineering- is a new technology that
  humans use to alter the genetic instructions in
  organisms.
• a) Biotechnology- The application of
  technology to biological science.
• ex removal of dinosaur DNA from a mosquitos
  last meal.
• b) Selective Breeding- A process that
  produces domestic animals and new varieties of
  plants with traits that are particularly
  desirable.

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DNA Technology

• Makes it possible to put new genes into
  organisms.
• 1. Human genes can be inserted into bacteria.
• 2. These altered bacteria become factories
  that produce human protein.
• ex Gene Splicing
• Recombinant DNA

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Plasmids

• Are small DNA fragments, are known from almost
  all bacterial cells.
• Plasmids carry between 2 and 30 genes. Some seem
  to have the ability to move in and out of the
  bacterial chromosome

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Gene Splicing

• Allows a scientist to make cuts of DNA from 2
  complimentary different organisms, perhaps a frog
  cell and a bacterium.
• Pieces of DNA from one organism can now be glued,
  or spliced, into the DNA of another organism.

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Recombinant DNA

• Allows scientists to insert the insulin gene into
  bacterial plasmids.
• The bacteria that contain this gene produce
  insulin, which is used by people with diabetes.

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Cloning

• Is a technique that accomplishes the same end
  result as asexual reproduction.
• It is a way of making identical genetic copies.
• Cloning is done by inserting a nucleus from a
  parent organisms cell (one that has a complete
  set of genetic information from that individual)
  into an egg cell from which the nucleus has been
  removed. The result is an egg that now contains
  not 50, but 100 of the genetic information from
  a single parent.
• If this new egg cell with all of its genes can be
  made to develop normally, the resulting offspring
  is a clone of the individual that donated the
  original cell (In mammals, the egg would be
  implanted and develop inside the body of the
  female).

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In Vitro Fertilization

• IVF (illustrated in the diagram at right) is
  often used when a woman's fallopian tubes are
  blocked. First, medication is given to stimulate
  the ovaries to produce multiple eggs. Once
  mature, the eggs are suctioned from the ovaries
  (1) and placed in a laboratory culture dish with
  the man's sperm for fertilization (2). The dish
  is then placed in an incubator (3). About two
  days later, three to five embryos are transferred
  to the woman's uterus (4). If the woman does not
  become pregnant, she may try again in the next
  cycle.