1. REVISION: TOPICs 2.6 & 2.7 – DNA & RNA STRUCTURE DNA REPLICATION
The structure of DNA allows efficient storage of genetic information.
IB Biology
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2. NUCLEIC ACIDS Both DNA and RNA are examples of nucleic acids
They are polymers of monomers called nucleotides
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3. NUCLEIC ACIDS Each nucleotide consists of: a nitrogenous base
a pentose sugar
a phosphate group
(hydrogens have been removed)
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4. NUCLEOTIDE STRUCTURE D R DNA: RNA: Phosphate group Deoxyribose sugar
One of four nitrogen bases:
A = Adenine
T = Thymine
U = Uracil
G = Guanine
C = Cytosine D R
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5. NUCLEIC ACID STRUCTURE
DNA:
RNA:
double stranded
single stranded
deoxyribose sugar
ribose sugar
Bases used are A, T, C & G
Bases used are A, U, C & G C G A T
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6. DRAW STRUCTURE OF DNA Draw 2 strands Draw strands anti-parallel:
use the 5’ and 3’ direction markers
face the pentose sugars in the opposite ways
Show complementary base pairs:
A bonded to T
C bonded to G
Label the phosphate, deoxyribose sugar and nitrogen bases
Label the covalent and hydrogen bonds
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7. DRAW STRUCTURE OF RNA Draw 1 strand
Label phosphate, ribose sugar and nitrogen bases
Label the covalent bonds
Identify the nitrogen bases present (including Uracil)
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8. WATSON & CRICK
NOS 1.10 – James Watson and Francis Crick used model making to discover the structure of DNA.
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9. DNA REPLICATION DNA double helix “unwinds”.
Two strands of DNA “unzip”.
Free DNA nucleotides pair up with exposed bases.
A new complementary strand forms.
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10. DNA REPLICATION DNA replication depends on complementary base pairing.
Means that the new strand will match one of the parent strands.
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11. DNA REPLICATION DNA replication is semi- conservative.
Means that the new molecules have half of the old molecule joined to a new strand ie. the parent molecule has been partially conserved
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12. MESELSON & STAHL
Their work helped establish semi-conservative replication as the sole theory of DNA replication.
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13. MESELSON & STAHL
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14. HELICASE
Unwinds the double helix and separates the two strands by breaking hydrogen bonds.
Requires ATP
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15. DNA POLYMERASE
Links free-floating nucleotides together to form a new strand, using the pre-existing strand as a template.
The nucleotides align opposite their complementary base partner
Forms covalent bonds between the nucleotides
Works in a 5’ 3’ direction
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16. Taq DNA POLYMERASE
Taq DNA polymerase is a thermostable DNA ploymerase (ie. stable at high temps)
Used in polymerase chain reaction (PCR).
Used to rapidly produce multiple copies of a specific DNA target sequence.
PCR is useful when only a small sample is available – eg. crime scene samples
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17. POLYMERASE CHAIN REACTION (PCR)
Process:
Denaturation: Heat DNA to separate the strands
Annealing: DNA primers attach to the 2 ends of the target sequence
Elongation: heat-tolerant Taq DNA polymerase copies the strands
One cycle yields two identical copies
Standard PCR includes 30 cycles, yielding over a billion copies of the DNA sample
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