dna: deoxyribonucleic acid biology. structure of dna dna nucleotide has 3 parts: sugar molecule...
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DNA:Deoxyribonucleic
Acid
Biology
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Structure of DNAStructure of DNA
• DNA nucleotide has 3 parts:• Sugar molecule
• Deoxyribose
• Phosphate group• Nitrogen-
containing base
• DNA nucleotide has 3 parts:• Sugar molecule
• Deoxyribose
• Phosphate group• Nitrogen-
containing base
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Nitrogen-containing basesNitrogen-containing bases
• Adenine = A• Guanine = G• Cytosine = C• Thymine = T
• Adenine = A• Guanine = G• Cytosine = C• Thymine = T
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Nucleotide StructureNucleotide Structure
• Purines• Bases that
have two rings of carbon and nitrogen atoms
• Adenine and guanine
• Purines• Bases that
have two rings of carbon and nitrogen atoms
• Adenine and guanine
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Nucleotide StructureNucleotide Structure
• Pyrimidines• Bases that
have only one ring of carbon and nitrogen atoms
• Cytosine and thymine
• Pyrimidines• Bases that
have only one ring of carbon and nitrogen atoms
• Cytosine and thymine
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The Origin of the Double Helix
The Origin of the Double Helix
• Rosalind Franklin• X-ray photographs
of DNA crystals • Research partner
Maurice Wilkins
• Rosalind Franklin• X-ray photographs
of DNA crystals • Research partner
Maurice Wilkins
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The Origin of the Double Helix
The Origin of the Double Helix
• Watson & Crick• Used
Franklin’s stolen research and photographs to determine the structure of DNA
• 1953
• Watson & Crick• Used
Franklin’s stolen research and photographs to determine the structure of DNA
• 1953
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The Double HelixThe Double Helix
• DNA is composed of two nucleotide chains that wrap around each other to form a double spiral, like a spiral staircase• Double helix
• DNA is composed of two nucleotide chains that wrap around each other to form a double spiral, like a spiral staircase• Double helix
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The Double HelixThe Double Helix
• The “backbone” of the double helix• Alternating sugar
and phosphate molecules
• Nitrogen-containing bases attach to the sugar molecules in the “backbone” and occupy the space in the center
• The “backbone” of the double helix• Alternating sugar
and phosphate molecules
• Nitrogen-containing bases attach to the sugar molecules in the “backbone” and occupy the space in the center
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Complementary Base Pairing
Complementary Base Pairing
• DNA nucleotides pair in specific combinations• Base-pairing rules
• Cytosine & Guanine
• C - G
• Adenine & Thymine
• A - T
• DNA nucleotides pair in specific combinations• Base-pairing rules
• Cytosine & Guanine
• C - G
• Adenine & Thymine
• A - T
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Complementary Base Pairing
Complementary Base Pairing
• The complementary base pairs are a combination• Purine with a
pyrimidine• Two rings paired
with a single ring
• The complementary base pairs are a combination• Purine with a
pyrimidine• Two rings paired
with a single ring
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Complementary Base Pairing
Complementary Base Pairing
• Base pairs are connected to one another by hydrogen bonds
• Base pairs are connected to one another by hydrogen bonds
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Replication of DNAReplication of DNA
• Replication• The process of
copying DNA in the cell
• Replication• The process of
copying DNA in the cell
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Replication of DNA-Step 1Replication of DNA-Step 1
• The separation of the two nucleotide strands
• The point at which the two chains separate• Replication
fork
• The separation of the two nucleotide strands
• The point at which the two chains separate• Replication
fork
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Replication of DNA-Step 1Replication of DNA-Step 1• The
nucleotide chains are separated by enzymes • Helicases
• Run down the strand and break the bonds holding the complemen-tary bases together
• The nucleotide chains are separated by enzymes • Helicases
• Run down the strand and break the bonds holding the complemen-tary bases together
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Replication of DNA-Step 2Replication of DNA-Step 2
• DNA polymerase binds to the separated chains of DNA• Runs along
the separated strands
• DNA polymerase binds to the separated chains of DNA• Runs along
the separated strands
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Replication of DNA-Step 2Replication of DNA-Step 2
• New chains of DNA are assembled using nucleotides in the surrounding medium that are complementary to the existing DNA chains
• New chains of DNA are assembled using nucleotides in the surrounding medium that are complementary to the existing DNA chains
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Replication of DNA-Step 3Replication of DNA-Step 3
• Once the DNA is copied the cell is ready to undergo cell division
• Once the DNA is copied the cell is ready to undergo cell division
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Accuracy and RepairAccuracy and Repair• Replication is
very accurate• One error in
every 10,000 pairs of nucleotides
• Mutations do occur• A mistake that
results in a change in the nucleotide sequence
• Replication is very accurate
• One error in every 10,000 pairs of nucleotides
• Mutations do occur• A mistake that
results in a change in the nucleotide sequence
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Accuracy and RepairAccuracy and Repair• The number of
errors and mutations are reduced by proofreading enzymes• They detect errors
and replace the wrong nucleotide with the correct nucleotide
• Doesn’t always work• Skin cancer
• The number of errors and mutations are reduced by proofreading enzymes• They detect errors
and replace the wrong nucleotide with the correct nucleotide
• Doesn’t always work• Skin cancer