Download DNA structure

Announcements
Properties of DNA molecules
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Polymers
Consist of four types of subunit
Usually consist of a pair of strands
Sequence provides nearly infinite
variation
• Have direction (polarity)
• SOD research
positions
available this
spring.
• make sure your
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indicated on
homework.
DNA molecules are polymers with 4 types of subunit
DNA molecules consist of a pair of strands
Phosphate linked to 5’
carbon of deoxyribose
Next nucleotide linked to 3’
carbon of deoxyribose
What makes a nucleotide?
Parts of DNA nucleotide
• Nucleotides consist of 3 components
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– phosphate
– sugar
– nitrogeneous base
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Phosphate Deoxyribose
Nitrogeneous base
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DNA molecules are polymers with 4 types of subunit
Nucleotide polymers
• Bond between phosphate at 5’ end of
one nucleotide
• and hydroxyl group at 3' carbon of
adjacent molecule.
• Bonding at different ends of the
molecule confers its polarity.
Phosphate linked to 5’
carbon of deoxyribose
Next nucleotide linked to 3’
carbon of deoxyribose
Unnumbered Figure (page 292) Purine and pyridimine
Base pairing in DNA
• One purine and one pyrimidine
– 2 purines would be too big
– 2 pyrimidines too small
• Hydrogen bonds between nucleotides on each
strand
– 2 hydrogen bonds between adenine and thymine
– 3 hydrogen bonds between cytosine and guanine
Figure 16.6 Base pairing in DNA
Watson and Crick model for
DNA structure
• 2 helices coiled around one another
• Sugar-phosphate backgrounds opposite
each other on outside
• Bases on inside
• Helices only fit together if they run in
opposite directions.
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Figure 16.7 DNA molecules have polarity
Figure 16.7 Nearly infinite possibilities for sequence variation
RNA has OH on 2’ carbon
RNA: the other nucleic acid
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Also a polymer of nucleic acids
Consists of four types of subunits
Molecules have direction (polarity)
Used to produce proteins from genes
What types of bases are found in
DNA and RNA?
• Purines (found in RNA & DNA)
– Adenine
– Guanine
RNA is
single
stranded
• Pyrimidines
– Cytosine
– Thymine (found only in DNA)
– Uracil (found only in RNA)
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Figure 17.14 The structure of transfer RNA (tRNA)
RNA: the other nucleic acid
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Also a polymer of nucleic acids
Consists of four types of subunits
Molecules have direction (polarity)
Used to produce proteins from genes
Figure 17.13 A summary of transcription and translation in a eukaryotic cell
DNA structure suggests a
mechanism for its replication
• The ‘semiconservative’ model for DNA
replication was verified after Watson
and Crick
• Each DNA strand serves as a template
for production of a new daughter strand
Figure 16.10 Three alternative models of DNA replication
Chemical reaction for DNA
synthesis
• {(dNMP)n} + dNTP --> {(dNMP)n+1} + PP (fig 16.13)
• DNA chain acts as a primer: existing chain to which
new nucleotides can be added
• Synthesis goes in the 5' to 3' direction
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Figure 16.13 Incorporation of a nucleotide into a DNA strand
Chemicals needed for DNA
synthesis
• Subunits: deoxyribose nucleotide triphosphates
(dNTPs)
– dATP
– dGTP
– dTTP
– dCTP
• Existing DNA or RNA fragment (primer)
• Enzymes to catalyze DNA synthesis
The structure and hydrolysis of ATP
Source of energy for DNA
replication
• dNTP molecules have energy rich
chemical bonds
• Energy is released when those
bonds are broken to attach new
monomers to the existing chain.
What do enzymes do?
• They are catalysts- make chemical
reactions occur more rapidly
• They are not ‘used’ up- can be reused
to catalyze more chemical reactions
• Names determined by function, e.g.
DNA polymerase helps to make DNA
What are enzymes?
• Polymers of amino acids- proteins
• Amino acids held together in a
polypeptide chain
• Amino acid composition of a protein is
determined by sequence of DNA in
genes
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