Understanding DNA

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Ch 12 DNA and RNA
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What is DNA?

• DNA (deoxyribonucleic acid)- a nucleic acid which
  stores genetic traits in the proteins it codes
  for.
• All living things contain DNA.
• DNA is a nucleic acid.
• Nucleic acids are made of nucleotide subunits
  hooked together.

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Nucleotides

• Nucleotides- subunits of DNA made of
• 1. Phosphate (PO4)
• 2. Sugar (deoxyribose).
• 3. Nitrogen base.

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Nitrogen Bases

• Four different nitrogen bases makes four
  different nucleotides
• Guanine
• Cytosine
• Adenine
• Thymine
• These four nucleotides make up the DNA of almost
  every single living thing.

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Nucleotides
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Chargaffs Rule

• He measured amounts of each base in various
  organisms and found
• of adenine (A) thymine (T)
• of cytosine (C) guanine (G)
• Chargaffs rule told us that A bonds to T and C
  bonds to G
• If 20 of strand is A, what T? C?

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Structure of DNA

• Discovered by Watson and Crick
• Double helix- 2 spiral strands of nucleotides
  bonded together

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Structure of DNA

• Siderail backbone is the sugar and phosphates of
  nucleotides
• Rungs are the nitrogen bases of nucleotides
• A----T
• C----G
• Hydrogen bonds between bases hold two strands
  together

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What is DNA Replication?

• Replicate make exact copies.
• DNA replication- copying of DNA so that a cell
  made divide
• All DNA must be replicated before a cell can
  divide. Why?

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Enzymes and Replication

• Helicase- enzyme that unwinds DNA
• DNA polymerase-enzyme that moves along each
  strand and brings in bases for new strand copy

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DNA Replication

• Can be a mistake in replication
• Mutations-change in DNA
• Mutagens- substances that cause mutations
• X-rays
• Toxins
• Drugs
• UV light, etc.

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Mutations

• 3 types of mutations that can occur during DNA
  replication
• Insertions -extra nucleotides
• Deletions missing nucleotides
• Substitutions placement of wrong nucleotides
• Can be helpful or harmful
• mutations.

Insertion
Deletion
Substitution
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Most Destructive Mutation?

• The bases, A, C, G, and T can be equated to
  letters of a DNA sentence
• THE DOG WAS HOT IN THE SUN
• Substitution
• THE DOG WAS NOT IN THE SUN
• Insertion?
• THE DOG NWA SHO TIN THE SUN
• Deletion?
• THE DOG ASH OTI NTH ESU N
• Why should I care?

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How Much DNA Is In OUR Cells?

• Chromosome-strands of DNA coiled tightly
• Human cell has 46 (23 pairs)
• 23 from Mom
• 23 from Dad
• Other organisms
• have different
• numbers of
• chromosomes

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2 Types of Cells

• Somatic cells all body cells except sex cells
• Diploid?chromosomes are in pairs
• 4623 pairs for humans
• 1 set (23) from mom, 1 set (23) from dad
• Gametes - sex cells
• Egg sperm
• Haploid ?no pairs (only 23 single chromosomes)

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Human Chromosomes

• If all body cells contain the same of
  chromosomes, why are all cells so different?
• Different cells make different proteins due to
  different active segments of DNA.
• Heart cells make proteins needed for the heart to
  work properly
• Brain cells make proteins needed for the brain to
  work properly

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What is the Purpose of DNA?

• DNA stores the genetic information that codes for
  proteins.
• ALL CELL FACTORIES MAKE PROTEINS!

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What is the Purpose of DNA?

• Gene- a segment of DNA that codes for a protein.
• DNA has 1000s of genes to make many different
  types of proteins.
• Why are proteins important?
• Protein - polymer of amino acids
• aaaaaaaaaaaaaaaa protein

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What is the Purpose of DNA?
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RNA (Ribonucleic acid)
_____DNA____ vs._____RNA___

• Stores the genetic code in the nucleus
• Double stranded
• Sugar of DNA nucleotides deoxyribose
• A, C, G, T
• DNA is DNA
• Found in nucleus only

Transmits the genetic code to the rest of the
cell Single stranded Sugar of RNA nucleotides is
ribose A, C, G, U (uracil) NO T! Different
forms mRNA, rRNA, tRNA Found all over cell
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DNA vs. RNA
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Part 1of Protein Synthesis Transcription

• Transcription- copying of DNA to mRNA that occurs
  in the nucleus.
• DNA complementary to mRNA
• ATA-CGG-AAT (DNA)
• transcription in nucleus
• UAU-GCC-UUA (RNA)

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Transcription
cytoplasm
Translation
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Part 2 of Protein Synthesis Translation

• Translation- converting mRNA to protein which
  occurs at ribosomes in the cytoplasm
• mRNA codons
• translation by ribosomes
• a.a.---a.a---a.a (protein)

cytoplasm
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Part 2 of Protein Synthesis Translation

• Codon-three bases of mRNA that code for an amino
  acid
• UAU-GCC-UUA (3 mRNA codons)
• translation by ribosomes
• a.a.---a.a---a.a. (protein)
• mRNA needs the help of tRNA to bring in the amino
  acids to be hooked together

cytoplasm
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Whole Process

• ATA-CGG-AAT (DNA)
• transcription in nucleus
• UAU-GCC-UUA (3 mRNA codons)
• translation in cytoplasm at
  ribosomes
• a.a.-a.a-a.a. (protein)
• How do we know what amino acid results?
• The Codon Wheel!!!

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Part 1 Transcription
cytoplasm
Part 2 Translation
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The Codon WheelHow do we use the wheel? There
are 2 clues.
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The Codon Wheel
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Whole Process

• DNA ATA-CGG-AAT
• transcription in nucleus
• mRNA UAU-GCC-UUA(3 codons)
• translation in cytoplasm
• protein a.a.-a.a-a.a.
• tyrosine-alanine-leucine
• Protein Synthesis Animation!
• How do we know what amino acid results?
• The Codon Wheel!!!

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Amino Acids

• Where do our cells get these amino acids to build
  the proteins?
• From FOOD!
• We eat proteins, then these proteins are broken
  down (metabolized) into amino acids in our
  stomach.
• We reuse these amino acids to build other
  proteins.