REVISION: TOPICs 2.6 & 2.7 – DNA & RNA STRUCTURE DNA REPLICATION The structure of DNA allows efficient storage of genetic information. IB Biology Miss Werba

NUCLEIC ACIDS Both DNA and RNA are examples of nucleic acids They are polymers of monomers called nucleotides J WERBA – IB BIOLOGY 2

NUCLEIC ACIDS Each nucleotide consists of: a nitrogenous base a pentose sugar a phosphate group (hydrogens have been removed) J WERBA – IB BIOLOGY 3

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 J WERBA – IB BIOLOGY 4

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 J WERBA – IB BIOLOGY 5

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 J WERBA – IB BIOLOGY 6

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) J WERBA – IB BIOLOGY 7

WATSON & CRICK NOS 1.10 – James Watson and Francis Crick used model making to discover the structure of DNA. J WERBA – IB BIOLOGY 8

DNA REPLICATION DNA double helix “unwinds”. Two strands of DNA “unzip”. Free DNA nucleotides pair up with exposed bases. A new complementary strand forms. J WERBA – IB BIOLOGY 9

DNA REPLICATION DNA replication depends on complementary base pairing. Means that the new strand will match one of the parent strands. J WERBA – IB BIOLOGY 10

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 J WERBA – IB BIOLOGY 11

MESELSON & STAHL Their work helped establish semi-conservative replication as the sole theory of DNA replication. J WERBA – IB BIOLOGY 12

MESELSON & STAHL J WERBA – IB BIOLOGY 13

HELICASE Unwinds the double helix and separates the two strands by breaking hydrogen bonds. Requires ATP J WERBA – IB BIOLOGY 14

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 J WERBA – IB BIOLOGY 15

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 J WERBA – IB BIOLOGY 16

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 J WERBA – IB BIOLOGY 17