The Central Dogma of Molecular Biology DNA ? RNA ? Proteins

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The Central Dogma of Molecular Biology DNA ?
RNA ? Proteins

• Biology II
• D. Mitchell

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The Central Dogma of Molecular Biology
Reverse Transcription
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DNA

• DNA-Deoxyribonucleic Acid
• The discovery of DNAs structure clarified how
  DNA could serve as the genetic material.

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Contributions of Scientists

• Hershey and Chase
• Confirmed that DNA carries the genetic
  information
• Erwin Chargaff
• The same four bases found in the DNA of all
  organisms
• the amount of adenine the amount of thymine
  the amount of guanine the amount of cytosine.

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• Wilkins and Franklin
• Developed X-ray diffraction photographs of DNA
• X-rays revealed that DNA resembled a tightly
  coiled helix composed of two or three chains of
  nucleotides.

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• Watson Crick
• Used the information from Chargaff, Franklin,
  and Wilkins
• Built a model of DNA with the configuration of a
  double helix, a spiral staircase of strands of
  nucleotides twisted around a central axis.

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Structure of DNA

• Is a molecule that is a double helix -two strands
  twisted around each other.
• Each strand is composed of nucleotides.
• Nucleotides are made of three parts a phosphate
  group, a sugar, and a nitrogen base.
• five-carbon sugar deoxyribose
• nitrogen bases adenine, thymine, guanine, and
  cytosine

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Connecting the DNA molecule

• Rails of the DNA ladder are alternating sugar
  phosphates
• Rungs are composed of pairs of bases
• Strands of nucleotides are held together by
  hydrogen bonds between bases.

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Base Pairing Rules

• Rule a purine on one strand of DNA always pairs
  with a pyrimidine on the opposite strand.
• Adenine and Guanine are purines.
• Thymine and Cytosine are pyrimidines.
• Adenine always pairs with Thymine
• Guanine always pairs with Cytosine

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• Purines are 2 ringed Adenine or Guanine

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• Pyrimidines are 1 ringed Thymine or Cytosine

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• The strictness of the base pairing results in two
  complementary strands.
• The sequence of bases on one strand determines
  the sequence of bases on the other strand.
• Example TCGAACT
• AGCTTGA

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DNA Complementary Strand Practice
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Replication of DNA

• Replication - the making of an exact copy of the
  DNA molecule
• Replication occurs whenever a cell divides
• The copy must be 100 accurate (errors death
  possibly)

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Stages in replication (basic)

• DNA molecule is split in two at the end by the
  work of the enzyme DNA polymerase.
• DNA unzips slightly
• New nucleotides attach to the free ends
• Process continues until completed

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Results of Replication

• results in two (2) double strands of DNA
• each strand is 50 new and 50 old DNA

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Replication Practice
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RNARibonucleic Acid
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RNA

• Function protein synthesis
• Location found in ribosomes and the nucleolus
• Structure Single helix composed of nucleotides
• Nitrogenous Bases Adenine, Uracil, Guanine, and
  Cytosine
• 5-Carbon Sugar Ribose

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Three types of RNA

• rRNA ribosomal RNA - carries protein building
  instructions. Goes from the DNA in the nucleus to
  the ribosome
• mRNA messenger RNA - is the message from DNA
  for the construction of the new protein molecule
• tRNA transfer RNA - delivers amino acids to the
  ribosomes. Has an anticodon specific to the amino
  acid.

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DNA?RNA?Protein

• DNA is TRANSCRIBED to messenger RNA (mRNA)
• mRNA carries the message to transfer RNA (tRNA)
• tRNA is TRANSLATED to an amino acid chain, which
  makes up proteins

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Transcription

• The copying of one side of the DNA molecule that
  results in a single strand of RNA
• During transcription, a DNA strand provides a
  template for the synthesis of a complementary RNA
  strand.
• Transcription of a gene produces a messenger RNA
  (mRNA) molecule.
• mRNA carries the message from the nucleus to the
  ribosomes

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Transcription Practice
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Translation

• The reading of the RNA code to make proteins or
  polypeptides. (protein synthesis)
• The nucleotide sequence of mRNA determines the
  amino acid sequence that codes for a SPECIFIC
  protein.
• Translation occurs at ribosomes.

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mRNA Codon Charts
mRNA codon Charts are used for translation.
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• The genetic code consists of 64 triplets or
  codons of nucleotides.
• groups of three bases on a mRNA strand
• With three exceptions, each codon encodes for one
  of the 20 amino acids used in protein synthesis.

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Processes In Eukaryotes And Prokaryotes

• The basic mechanics of transcription and
  translation are SIMILAR.
• Because bacteria lack nuclei, transcription and
  translation are coupled.
• In a eukaryotic cell, almost all transcription
  occurs in the nucleus and translation occurs
  mainly at ribosomes in the cytoplasm.