nucleic acid

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NUCLEIC ACID
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NUCLEIC ACID

• Nucleic acids are biological macromolecules
• They are members of a family of biopolymers
  essential for life, and include DNA and RNA
• nucleic acids function in encoding, transmitting
  and expressing genetic information.
• Nucleic acids were first discovered by Friedrich
  Miescher in 1871.

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Molecular composition

• Each nucleotide consists of three components a
  purine or pyrimidine nucleobase, a pentose sugar,
  and a phosphate group.
• The sugars and phosphates are connected to
  phosphodiester linkages

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DNA RNA
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Pirimidine and Purine bases

• Pyrimidine and Purine are heterocyclic aromatic
  organic compound
• Pirimidine basesCytosin,Urasil and Thymine
• Purine basesAdinine and guanine

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Adininine

• Adenine (a purine derivative) 9H-purin-6-amine
• A chemical component of DNA and RNA.
• The shape of adenine is complementary to either
  thymine in DNA or uracil in RNA.

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Guanine

• Guanine (a purine derivative)
• found in DNA and RNA
• guanine is only paired with cytosine.
• 2-amino-6-hydroxypurine

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Cytosine

• Cytosine found in DNA and RNA
• It is a pyrimidine derivative
• It forms three hydrogen bonds with guanine
• 4-amino-1H-pyrimidine-2-one

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Thymine

• Thymine (pyrimidine nucleobase) found only in DNA
  
• Thymine is also known as
  5-Methylpyrimidine-2,4(1H,3H)-dione
  (5-methyluracil)
• Thymine (T) binds to adinine (A) via two hydrogen
  bonds

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Uracil

• Uracil (pyrimidine derivative) found only in RNA.
  
• uracil (U) binds to adenine (A) via two hydrogen
  bonds.
• 2,4-dihydroxypyrimidine

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Phosphodiester bond

• A phosphodiester bond is a group of strong
  covalent bonds between a phosphate group and two
  5-carbon ring carbohydrates (pentoses) over two
  ester bonds.

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Chargaffs Rules

• Erwin Chargaff (1947) provides more evidence that
  DNA genetic material
• Analysis of base composition of DNA compared
  between different organisms
• Nitrogenous bases
• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)
• Conclusions of Chargaff
• DNA composition is species specific
• The amounts of A,G,C and T are not the same
  between species
• Ratios of nitrogenous bases vary between species

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Deoxyribonucleic acid

• DNA contains the genetic instructions used in the
  development and functioning of all known living
  organisms.
• The main role of DNA molecules is the long-term
  storage of information
• DNA is often compared to a set of blueprints,
  since it contains the instructions needed to
  construct other components of cells, such as
  proteins and RNA molecules.
• The DNA segments that carry this genetic
  information are called genes

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Structure of DNA

• DNA consists of two long polymer of simple units
  called nucleotides, with backbones made of sugars
  and phosphate groups joined by ester bonds.
• These two strands run in opposite directions to
  each other and are therefore anti-parallel.
• Attached to each sugar is one of four types of
  molecules called nucleobases
• It is the sequence of these four nucleobases
  along the backbone that encodes information.

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DNA Double Helix

• The easiest way to visualize DNA is as an
  immensely long rope ladder, twisted into a
  cork-screw shape.
• The sides of the ladder are alternating
  sequences of deoxyribose and phosphate (backbone)
  while the rungs of the ladder (bases) are made in
  two parts with each part firmly attached to the
  side of the ladder.
• Although most DNA exists as open ended double
  helices, some bacterial DNA has been found as a
  cyclic helix.

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Properties

• DNA is a long polymer made from repeating units
  called nucleotides
• DNA of all species comprises two helical chains
  each coiled round the same axis, and each with a
  pitch of 34 Å and a radius of 10 Å
• DNA does not usually exist as a single molecule,
  but instead as a pair of molecules that are held
  tightly together
• The DNA double helix is stabilized primarily by
  two forces hydrogen bonds between nucleotides
  and base-stacking interactions among the aromatic
  nucleobases

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Grooves

• Grooves are spaces between the strands
• These voids are adjacent to the base pairs and
  may provide a binding site
• The major groove, is 22 Å wide and the minor
  groove, is 12 Å wide

Major and minor grooves of DNA
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Alternate DNA structures

• DNA exists in many possible conformations that
  include A-DNA, B-DNA, and Z-DNA forms

  A, B and Z DNA
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Form Direction Bases/360o Turn HelixDiameter
A Right 11.0 23A
B Right 10.0 19A
Z Left 12.0 18A
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DNA replication
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Transcription
Initiation Elongation Termination
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Translation
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RNA
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Ribonucleic acid

• RNA is made up of a long chain of components
  called nucleotides.
• The sequence of nucleotides allows RNA to encode
  genetic information.
• All cellular organisms use messenger RNA (mRNA)
  to carry the genetic information that directs the
  synthesis of proteins.
• In addition, some viruses use RNA instead of DNA
  as their genetic material perhaps a reflection
  of the suggested key role of RNA in the
  evolutionary history of life on Earth.

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Synthesis of RNA

• Synthesis of RNA is usually catalyzed by an
  enzymeRNA polymeraseusing DNA as a template, a
  process known as transcription.
• The DNA double helix is unwound by the helicase
  activity of the enzyme.
• The enzyme then progresses along the template
  strand in the 3 to 5 direction, synthesizing a
  complementary RNA molecule with elongation
  occurring in the 5 to 3 direction.
• The DNA sequence also dictates where termination
  of RNA synthesis will occur

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Types of RNA

• Messenger RNA (mRNA)
• Transfer RNA (tRNA)
• Ribosomal RNA (rRNA)

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mRNA

• Messenger RNA is a molecule of RNA encoding a
  chemical "blueprint" for a protein product.
• mRNA is transcribed from a DNA template, and
  carries coding information to the sites of
  protein synthesis the ribosomes.
• In mRNA as in DNA, genetic information is encoded
  in the sequence of nucleotides arranged into
  codons consisting of three bases each.

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tRNA

• Transfer RNA is an adaptor molecule composed of
  RNA, typically 73 to 93 nucleotides in length,
  that is used in biology to bridge the
  three-letter genetic code in messenger RNA with
  the twenty-letter code of amino acids in
  proteins.
• One end of the tRNA carries the genetic code in a
  three-nucleotide sequence called the anticodon.
  The anticodon forms three base pairs with a codon
  in mRNA during protein biosynthesis.

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rRNA

• Ribosomal ribonucleic acid is the RNA component
  of the ribosome.
• Ribosomal RNA provides a mechanism for decoding
  mRNA into amino acids and interacts with tRNAs
  during translation by providing peptidyl
  transferase activity.

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Mutations
In biology, mutations are changes to the base
pair sequence of genetic material (either DNA or
RNA). Mutations can be caused by copying
errors in the genetic material during cell
division and by exposure to ultraviolet
or ionizing radiation, chemical mutagens, or
viruses, or can occur deliberately under cellular
control during processes such as meiosis or
hypermutation  
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The genetic material (DNA) of a cell can become
damaged or changed. This damage produces
mutations (DNA changes) that affect normal cell
growth and division. When this happens, cells do
not die when they should and new cells form when
the body does not need them. The extra cells may
form a mass of tissue called a tumor.
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Genetic engineering

• Genetic engineering is a scientific development
  that involves the artificial manipulation of an
  organism's genes by using techniques such as
  molecular cloning and transformation in order to
  alter their nature and structure.
• Many of these transformations are achieved by
  manipulation of an organism's DNA, which
  effectively is the code inscribed in every cell
  to determine how it will function.

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K.Shanmugha Rajan