BIOLOGICAL SCIENCE. Lecture Presentation by Cindy S. Malone, PhD, California State University Northridge. FIFTH EDITION Freeman Quillin Allison

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1 BIOLOGICAL SCIENCE FIFTH EDITION Freeman Quillin Allison 4 Lecture Presentation by Cindy S. Malone, PhD, California State University Northridge

2 In this chapter you will learn that Nucleic acids store the information that encodes life by asking What is a nucleic acid? 4.1 comparing/contrasting and by asking DNA structure and function specialized for RNA structure and function Could life have evolved from an RNA? Stability and storage Versatility and catalysis

3 A nucleic acid is a polymer of nucleotide monomers Three components of a nucleotide: 1. A phosphate group 2. A five-carbon sugar 3. A nitrogenous (nitrogen-containing) base The phosphate is bonded to the sugar molecule In turn, the sugar molecule is bonded to the nitrogenous base

4 Ribonucleotides The sugar is ribose Deoxyribonucleotides The sugar is deoxyribose (deoxy means lacking oxygen) These two sugars differ by a single oxygen atom Ribose has an OH group bonded to the 2 carbon Deoxyribose has an H instead at the same location In both of these sugars An OH group is bonded to the 3 carbon

5 There are two groups of nitrogenous bases: 1. Purines Adenine Guanine 2. Pyrimidines Cytosine Uracil Thymine The base uracil (U) is found only in ribonucleotides The base thymine (T) is found only in deoxyribonucleotides

6 Figure 4.1 (a) Nucleotide Phosphate group is bonded to carbon of sugar (c) Nitrogenous bases Nitrogenous base Phosphate group 5-carbon sugar Nitrogenous base is bonded to 1 carbon of sugar Cytosine (C) Uracil (U) in RNA Thymine (T) in DNA Pyrimidines (b) Sugars Purines are larger than pyrimidines Guanine (G) Adenine (A) Ribose in RNA Deoxyribose in DNA Purines

7 The sugar-phosphate backbone of a nucleic acid is directional (has polarity) One end has an unlinked 5 carbon The other end has an unlinked 3 carbon The nucleotide sequence is written in the 5 3 direction Reflects the order that nucleotides are added to a growing molecule The nucleic acid s primary structure is the nucleotide sequence

8 Figure 4.3 The sugar-phosphate backbone of RNA end of nucleic acid and carbons joined by phosphodiester linkage end of nucleic acid: new nucleotides are added to the unlinked hydroxyl

9 James Watson and Francis Crick determined 1. DNA strands run in an antiparallel configuration 2. DNA strands form a double helix The hydrophilic sugar-phosphate backbone faces the exterior Nitrogenous base pairs face the interior

10 3. Purines always pair with pyrimidines Strands form complementary base pairs A-T and G -C A-T have two hydrogen bonds C-G have three hydrogen bonds 4. DNA has two different-sized grooves: The major groove The minor groove

11 Figure 4.6 Sugar-phosphate backbone (a) Only purine-pyrimidine pairs fit inside the double helix. Purine-purine pair NOT ENOUGH SPACE (b) Hydrogen bonds form between G-C pairs and A-T pairs. Guanine Cytosine Antiparallel strands Pyrimidine-pyrimidine pair TOO MUCH SPACE Purine-pyrimidine pair JUST RIGHT Adenine Hydrogen bonds Thymine Space inside sugarphosphate backbones DNA contains thymine, whereas RNA contains uracil

12 DNA s secondary structure consists of Two antiparallel strands twisted into a double helix The molecule is stabilized by Hydrophobic interactions in its interior By hydrogen bonding between The complementary base pairs A-T and G-C

13 Length of one complete turn of helix (10 rungs per turn) 3.4 nm (a) Cartoons of DNA structure (b) Space-filling model of DNA double helix Major groove Minor groove Distance between bases 0.34 nm Base pairing Double helix Width of helix 2.0 nm

14 DNA can store and transmit biological information DNA carries the information required for the organism s growth and reproduction The language of nucleic acids is contained in the sequence of the bases DNA carries the information required for the growth and reproduction of all cells

15 Step 1 Step 3 Heating or enzyme-catalyzed Complementary base reactions pairing allows Cause the double helix to Each strand of a DNA separate double helix to be copied Step 2 exactly Free deoxyribonucleotides form Producing two identical hydrogen bonds with daughter molecules complementary bases on the original strand of DNA Called a template strand Sugar-phosphate groups form phosphodiester linkages to: Create a new strand Called a complementary strand

16 DNA replication requires two steps: 1. Strand separation 1. Separation of the double helix 2. Hydrogen bonding of deoxyribonucleotides with complementary bases 2. Base pairing with template On the original template strand 3. Polymerization Followed by phosphodiester bond formation between the deoxynucleotides to form the complementary strand New Old Old New The original molecule has been copied.

17 RNA (like DNA) has a primary structure consisting of a sugar-phosphate backbone Formed by phosphodiester linkages Extending from that backbone, a sequence of four types of nitrogenous bases The primary structure of RNA differs from DNA 1. RNA contains uracil instead of thymine 2. RNA contains ribose instead of deoxyribose The presence of the OH group on ribose makes RNA Much more reactive Less stable than DNA

18 Figure 4.9 Hairpin Stem Loop Single-stranded region forms a loop Double-stranded region forms a double helix Nitrogenous bases

19 RNA molecules can also have tertiary structure Forms when secondary structures fold into more complex shapes RNA (like DNA) can function as An information-containing molecule Capable of self-replication Structurally/chemically, RNA is intermediate between The complexity of proteins The simplicity of DNA

20 Summary Table 4.1

21 1. Complementary bases pair. 4. Copy serves as new template. Template strand New copy strand 2. Copied strand polymerizes. 5. New copy polymerizes. Copied strand New template strand 3. Copy and template separate. 6. New copy is identical to original template.

22 Figure 4.11 Folding brings widely spaced nucleotides together at the active site of this catalytic RNA

23 The theory of chemical evolution Life began as a naked self-replicator A molecule that existed by itself in solution Without being enclosed in a membrane To make a copy of itself, the first living molecule had to Provide a template that could be copied Catalyze polymerization reactions that would link monomers into a copy of that template RNA is capable of both processes Most origin-of-life researchers propose that the first life-form was made of RNA

24 RNA is not very stable But it might have survived long enough in the prebiotic soup to replicate itself And so it may have been the first life-form RNA replicase is a ribozyme that Can catalyze the addition of ribonucleotides to a complementary RNA strand Can replicate RNA