22'1 Components of Nucleic Acids

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Chapter 22 Nucleic Acids and Protein Synthesis

• 22.1 Components of Nucleic Acids
• 22.2 Nucleosides and Nucleotides
• 22.3 Primary Structure of Nucleic Acids
• 22.4 DNA Double Helix A Secondary
• Structure
• 22.5 DNA Replication

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Nucleic Acids

• Nucleic acids are
• Molecules that store information for cellular
  growth and reproduction.
• Deoxyribonucleic acid (DNA) and ribonucleic acid
  (RNA).
• Large molecules consisting of long chains of
  monomers called nucleotides.

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Nitrogen Bases

• The nitrogen bases in nucleic acids consist of
  the
• Pyrimidines C, T, and U
• And purines A and G.

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Pentose Sugars

• The pentose (five-carbon) sugar
• In RNA is ribose.
• In DNA is deoxyribose.
• Has carbon atoms numbered with primes to
  distinguish them from the nitrogen bases.

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Nucleosides

• A nucleoside
• Has a nitrogen base linked by a glycosidic bond
  to C1 of a ribose or deoxyribose.
• Is named by changing the the nitrogen base ending
  to -osine for purines and idine for pyrimidines

HO
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Nucleotides

• A nucleotide
• Is a nucleoside that forms a phosphate ester with
  the C5 OH group of ribose or deoxyribose.
• Is named using the name of the nucleoside
  followed
• by 5-monophosphate.

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Names of Nucleosides and Nucleotides

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Nucleosides and Nucleotides with Purines

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Nucleosides and Nucleotides with Pyrimidines
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AMP, ADP, and ATP

• Adding phosphate groups to AMP forms the
  diphosphate ADP and the triphosphate ATP.

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Primary Structure of Nucleic Acids

• In the primary structure of nucleic acids
• Nucleotides are joined by phosphodiester bonds.
• The 3-OH group of the sugar in one nucleotide
  forms an ester bond to the phosphate group on the
  5-carbon of the sugar of the next nucleotide.

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Primary Structure of Nucleic Acids

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Structure of Nucleic Acids

• A nucleic acid polymer
• Has a free 5-phosphate group at one end and a
  free 3-OH group at the other end.
• Is read from the free 5-end using the letters of
  the bases.
• This example reads
• 5ACGT3.

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Example of RNA

• In RNA, A, C, G, and U are linked by 3-5 ester
  bonds between ribose and phosphate.

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Example of DNA

• In DNA, A, C, G, and T are linked by 3-5 ester
  bonds between deoxyribose and phosphate.

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DNA Double Helix

• In DNA
• There are two strands of nucleotides that wind
  together in a double helix.
• Two hydrogen bonds form between the complementary
  base pairs A-T.
• Three hydrogen bonds form between the
  complementary base pairs G-C.

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DNA Double Helix Structure
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DNA Replication

• DNA replication involves
• Unwinding the DNA
• Pairing the bases in each strand with new bases
  to form new complementary strands.
• Producing two new DNA strands that exactly
  duplicate the original DNA.

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Hydrolysis Energy

• Energy from the hydrolysis of each nucleoside
  triphosphate adding to the complementary strand
  is used to form the phosphodiester bond.

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Direction of Replication

• During replication, helicase unwinds the parent
  DNA at several sections.
• At each open DNA section called a replication
  fork, DNA polymerase catalyzes the formation of
• 5-3ester bonds of the leading strand.
• The lagging strand, which grows in the 3-5
  direction, is synthesized in short sections
  called Okazaki fragments.
• The Okazaki fragments are joined by DNA ligase to
  give a single 3-5 DNA strand.

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Direction of Replication