Molecular Genetics

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Molecular Genetics

• 1. Nucleic Acids
• 2. Deoxyribose Nucleic Acid
• 3. Ribose Nucleic Acid
• 4. Protein Synthesis

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Nuclein

• 1. Meischer, 1869- isolated nuclein from
  leukocyte nuclei
• 2. High concentrations of phosphorus
• 3. First thought to be a protein with phosphorus
  contaminants
• 4. Nuclein later found to be chromosomes
  http//www.fredonia.edu/bio120/
  nucleic.htm

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Nucleic Acids

• 1. Linear polymers of nucleotides, contain plan
  for all cellular activity
• 2. Deoxyribose Nucleic Acid- millions of
  nucleotides, double strand
• 3. Ribose Nucleic Acid- thousands of nucleotides,
  single strand

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Nucleotide

• 1. Three part molecule sugar, phosphate,
  nitrogen base
• 2. Pyrimidines- cytosine, thymine (DNA), uracil
  (RNA)
• 3. Purines- adenine, guanine
• 4. Represented by
• A, T, G, C, U

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Nucleotide Polymerization

• 1. Hydroxyl group of C3 of one nucleotide sugar
  bonds to phosphate of C5 of another nucleotide .
  . .
• 2. Alternating sugar phosphate groups joined by
  phosphodiester bonds

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DNA

• 1. Hereditary portion of chromosomes
• 2. Transmitted
• a. Cell to cell during cell division
• b. Parents to progeny during
• reproduction

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DNA Description

• 1. Polymer of nucleotides
• 2. Nucleotide- Deoxyribose, 5 C sugar PO4 group
  and one of 4 Nitrogen bases
• 3. Purines- Double ring- Adenine or Guanine
• 4. Pyrimidines- Single ring Thymine or Cytosine

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DNA Model
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DNA Structure

• 1. Double helix- twisted ladder, sugar phosphate
  uprights base pair rungs
• 2. Bacterial, viral, mitochondrial- chromosoid,
  DNA is single loop, highly coiled
• 3. Eukaryote- chromosomes, DNA is looped around
  histones

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Histones (CEN, 4-5-04)

• 1. DNA wraps around histones
• 2. Part of packaging of chromosomes
• 3. Histone code- may determine which genes are
  transcribed
• 4. Five main histones in humans

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DNA Base Pairing

• 1. Base pairing crucial in protein synthesis
• 2. Cytosine always pairs with guanine, G-C or C-G
• 3. Adenine always pairs with thymine, A-T or T-A

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DNA Functions

• 1. Stores genetic information
• 2. Controls inheritance
• 3. Determines RNA protein synthesis

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DNA Replication

• 1. DNA makes an exact copy of itself
• 2. When a cell reproduces, each new cell needs a
  copy of the original cells information
• 3. Interphase, S phase
• 4. Process

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Replication Process

• 1. DNA unwinds unzips
• 2. Open strands are templates for new DNA strands
• 3. DNA polymerase assembles DNA nucleotides found
  in nucleus
• 4. DNA polymerase aligns DNA nucleotides with
  complementary nucleotides in unzipped portion of
  original DNA strand

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Replication Process, cont

• 5. Complementary base pairing forms new strands
• 6. Nucleotides link by hydrogen bonding
• 7. Semiconservative- replicated DNA is half old
  half new

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DNA repair enzymes

• 1. Protection and maintenance of the information
  encoded in DNA, fidelity of genetic information
• 2. Minimize the mutagenic consequences oxidative
  damage
• 3. Human DNA Polymerase b- functions by filling
  in gaps in DNA
• 4. Evolution carcinogenesis

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Ribose Nucleic Acid

• 1. Single strand of nucleotides
• 2. Ribose- a 5 C sugar
• 3. Uracil instead of Thymine

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RNA Types

• 1. rRNA- 60 of structure of ribosomes, sites of
  protein synthesis
• 2. mRNA- carries genetic message for protein from
  DNA to ribosome, codon
• 3. tRNA- transfers amino acids to ribosomes,
  anticodon

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RNA Transcription

• 1. RNA genes used to make rRNA tRNA
• 2. DNA protein message is transcribed to mRNA
  prior to protein synthesis
• 3. Interphase, G1 phase
• 4. Why RNA?
• 5. Process

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Transcription Process

• 1. DNA portion unwinds unzips
• 2. Open 5-3 strand is template for mRNA
• 3. RNA polymerase assembles free RNA nucleotides
• 4. RNA polymerase aligns RNA nucleotides with
  complementary DNA nucleotides in the unzipped
  portion of DNA, U with A

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Transcription Process, cont

• 5. Complementary base pairing forms mRNA
• 6. RNA polymerase moves 5-3
• 7. Nucleotides link by hydrogen bonding
• 8. When RNA is completed, it separates from the
  DNA
• 9. Modeling RNA transcription

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Codons

• 1. Groups of three mRNA nucleotides that code for
  a specific amino acid or start or stop of protein
• 2. Total of 64 codons AUG is start codon Met
  UAA, UAG, UGA are stop codons
• 3. mRNA codon complements tRNA anticodon

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Translation

• 1. Translate the genetic code into a protein
• 2. Activation, initiation, elongation, termination

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Activation

• 1. tRNA bonds to specific amino acid
• 2. Bonding of amino acid to tRNA activates its
  anticodon

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Initiation

• 1. Start codon, AUG, of mRNA bonds to small
  subunit of ribosome
• 2. tRNA anticodon with methionine base pairs with
  mRNA start codon
• 3. Large subunit of ribosome joins small subunit
  to initiate protein synthesis

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Elongation

• 1. Complementary tRNA anticodon with its specific
  amino acid attaches to next mRNA codon
• 2. New amino acid peptide bonds to methionine
• 3. tRNA released from methionine
• 4. Process is repeated elongating protein
• 5. Several ribosomes can translate same strand of
  mRNA

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Termination

• 1. Translation continues until stop codon is
  reached
• 2. Protein released from ribosome
• 3. Methionine removed from peptide chain

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Protein Synthesis

• 1. DNA RNA are composed of groups three
  nucleotides called triplets
• 2. Each DNA triplet codes for an amino acid
• 3. Every triplet in mRNA is called a codon and is
  complementary to a DNA triplet

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Protein Synthesis, cont

• 4. Transcription- mRNA picks up the genetic code
  from DNA and goes to the ribosome
• 5. Translation
• a. tRNA brings specific AA from cytoplasm
• b. tRNA anticodon matches up to the codon of
  mRNA
• c. Amino acids form peptide bonds tRNA
  releases its AA

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Editing

• 1. Exons introns
• 2. Alternate gene splicing

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Protein Synthesis, cont
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Central Dogma of Molecular Biology
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