07BIS1012013ReplicLect_7

Denature it should also be noted that because of

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Unformatted text preview: mol. kcal/mol. ­ Watson/Crick base pairing between antiparallel strands of DNA: Watson/Crick base q q ­ (a) reduces rotation around the phosphodiester bond and thus reducing writhing and (a) reduces helix instability (b) protects reactive groups on the bases from chemical modification that could lead (b) protects to mutation. The weak nature of these bonds allows strands of DNA to separate or denature during replication or transcription. denature It should also be noted that because of intramolecular complementarity, single It intramolecular single stranded DNA molecules (and RNA molecules) can form double helices with themselves. The transfer RNA (tRNA) is a good example of this. themselves. *Gibbs energy (Gibbs free energy) is the thermodynamic potential that measures the “useful” or *Gibbs “process-initiating” work obtainable in a closed thermodynamic system. As a process changes states (e.g., from double strand DNA to single strand DNA) Gibbs energy changes from - ∆ G to + ∆ G. (e.g., to BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 21 Intramolecular complementarity Intramolecular Transfer RNA Transfer BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 22 Alternate DNA Forms: January 9, 1981 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 23 Alternate DNA Forms ­ DNA structure can vary in nature. Although the double-stranded B helix is the DNA predominant form, other helical and some completely unexpected forms can be found. be B-DNA A-DNA BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez Z-DNA 24 Alternate DNA Structures: A form DNA ­ ­ ­ ­ The A form helix is not the predominant form of doublepredominant stranded RNA A-form DNA or RNA has 11 A-form bases per turn rather instead of the 10 in B-DNA the A-form DNA is wider and shorter A-form than the B helix, and the distinction between the major and minor grooves is reduced and This helix is favored under This conditions of dehydration conditions A-DNA Minor groove Major groove BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 25 Alternate DNA Structures: Z form DNA ­ ­ ­ ­ ­ The Z helix (so-named because the The helix backbone has a zigzag shape) is a more radical departure from the B helix theme. radical Although double stranded, the Z helix is a left-handed helix and has 12 base pairs per turn instead of the 10 in B-DNA...
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