{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lecture 6 - 4.2 DNA Structure and Function U s i n g m o d...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
4.2 DNA Structure and Function • Using models ( Figure 4.8 ), Watson and Crick concluded that two antiparallel DNA strands form a double helix with the hydrophilic sugar-phosphate backbone facing the exterior and purine-pyrimidine pairs of nitrogenous bases on the interior, packed closely together. • The two DNA strands form complementary base pairs A-T and G-C through hydrogen bonding ( Figure 4.9 ). The G-C pair has three hydrogen bonds, whereas the weaker A-T pair has only two. • The double-helix structure explains Franklin and Wilkins’ molecular measurements ( Figure 4.11 ) and Chargaff’s rules that the number of purines equals the number of pyrimidines and that T=A and G=C.
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
DNA Is an Information- Containing Molecule The nitrogenous base sequence of DNA stores information required for all living cells, and complementary base pairing provides a simple mechanism for DNA replication, since each strand can serve as a template for formation of a new complementary strand ( Figure 4.12 ). Is DNA a Catalytic Molecule? • DNA’s stability makes it a reliable store for genetic information; it is less reactive than RNA but more resistant to degradation. Stable molecules such as DNA make poor catalysts. • Because DNA does not appear to be able to catalyze any chemical reaction, biologists think that the first life-form was made of RNA, not DNA. 4.3 RNA Structure and Function • The primary structure of RNA is similar to that of DNA, with two differences: (1) RNA contains uracil instead of thymine, and (2) RNA contains ribose instead of deoxyribose. The presence of the –OH group on ribose makes RNA much more reactive and less stable than DNA. • RNA’s secondary structure, like DNA’s, results from complementary A-U and G-C base pairing. • The bases of RNA typically form hydrogen bonds with complementary bases on the same strand. The RNA strand folds over, forming a hairpin structure where the bases on one side of the fold align with an antiparallel RNA segment on the other side of the fold ( Figure 4.13 ).
Image of page 2
• Sometimes hairpins and other RNA secondary structures have additional folds or are attached to other RNA strands, giving some RNA molecules
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern