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Gene Cloning and DNA Analysis: An Introduction, Sixth Edition ...

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134<br />

Figure 8.7<br />

One possible scheme for c<strong>DNA</strong> cloning. Poly(A) =<br />

polyadenosine, oligo(dT) = oligodeoxythymidine.<br />

Part I The Basic Principles of <strong>Gene</strong> <strong>Cloning</strong> <strong>and</strong> <strong>DNA</strong> <strong><strong>An</strong>alysis</strong><br />

(a) First str<strong>and</strong> synthesis<br />

5’ 3’<br />

AAAAA<br />

mRNA Poly(A)<br />

tail<br />

(b) RNA degradation<br />

(c) Second str<strong>and</strong> synthesis<br />

RNA fragments<br />

act as primers <strong>DNA</strong><br />

(d) Ligation into a vector<br />

(e) Transform<br />

<strong>An</strong>neal an<br />

oligo(dT) primer<br />

Reverse transcriptase<br />

<strong>DNA</strong> pol I<br />

AAAAA<br />

TTTTT<br />

TTTTT<br />

TTTTT<br />

AAAAA<br />

TTTTT<br />

AAAAA<br />

TTTTT<br />

Primer<br />

transferred to a nitrocellulose or nylon membrane (Figure 8.9a) <strong>and</strong> then treated to<br />

remove all contaminating material, leaving just <strong>DNA</strong> (Figure 8.9b). Usually this treatment<br />

also results in denaturation of the <strong>DNA</strong> molecules, so that the hydrogen bonds between<br />

individual str<strong>and</strong>s in the double helix are broken. These single-str<strong>and</strong>ed molecules can<br />

then be bound tightly to the membrane by a short period at 80°C if a nitrocellulose<br />

membrane is being used, or with a nylon membrane by ultraviolet irradiation. The<br />

molecules become attached to the membrane through their sugar–phosphate backbones,<br />

so the bases are free to pair with complementary nucleic acid molecules.<br />

RNA<br />

<strong>DNA</strong><br />

RNase HI<br />

RNA fragments<br />

Double-str<strong>and</strong>ed <strong>DNA</strong><br />

Attach sticky<br />

ends, ligate<br />

c<strong>DNA</strong><br />

c<strong>DNA</strong> clones<br />

Gliadin clone

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