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Chapter 4

Chapter 4: Nucleic Acids and the Origin of Life.docx

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CAS BI 108
Francis Monette

BI108 Chapter 4 Notes: NucleicAcids and the Origin of Life 4.1—Chemical Structures and Functions of NucleicAcids NucleicAcids: polymers specialized for storage, transmission, and use of genetic information 1. DNA: macromolecule, encodes hereditary info and passes from generation to generation 2. RNA: through RNAintermediates DNAspecifies amino acid sequences of proteins and control expression synthesis of other RNAs Nucleotides are the building blocks of nucleic acids • Nucleic acids (polymers) composed of monomers: nucleotides • Nucleotides: nitrogen-base, pentose sugar, one-to-three phosphate groups • Nucleosides: pentose sugar and nitrogenous base *no phosphate base • Bases of nucleic acids: o Pyrimidine: six-membered single-ring structure o Purine: double-ring structure • DNAsugar: deoxyribose, RNAsugar: ribose • NucleicAcid formation—nucleotides added to chain one at a time, pentose sugar of previous nucleotide undergoes condensation rxn with phosphate of new nucleotide; phosphodiester linkage • Grow in 5’-to-3’direction; phosphate new (5’), pentose sugar (3’) Oligonucleotides: RNA that function as primers to duplicate DNA; RNAthat regulate expression of genes; synthetic DNAfor amplifying/analyzing nucleotides Polynucleotides: nucleic acids (DNA, RNA) Base pairing occurs in both DNAand RNA Four bases in DNA(and complementary base pairing) (A)Adenine — (T) Thymine (C) Cytosine — (G) Guanine **RNA—(U) Uracil instead of (T); (U) — (A) • Base pairs held together by hydrogen bonds; polar C=O and N—H • So many hydrogen bonds in DNA/RNA, they collectively provide great force of attraction—to bind polynucleotide strands RNA • Portions of single strand fold back and pair with each other; complementary hydrogen bonding between ribonucleotides determines 3D shape • Adenine can pair with uracil (RNA) or with thymine (DNA) • Diversity in 3D structure DNA • Hydrogen bonds hold base pairs together; uniform • Polynucleotide strands form ladder—twists into double helix BI108 Chapter 4 Notes: NucleicAcids and the Origin of Life • Sugar-Phosphate groups form sides of the ladder; bases with hydrogen bonds form rungs on inside • Carries genetic info in sequence of base pairs; keep difference among DNAmolecules DNAcarries information and is expressed through RNA DNAtransmits info in two ways: 1. DNAreplication (reproduced exactly); done by polymerization; use existing strand as base-pairing template 2. Gene Expression: (two parts)—DNAcan be copied into RNA(transcription); then, sequence in RNAcan be used to specify a sequence of amino acids in polypeptide chain (translation) df • DNAreplication and transcription depend on base-pairing properties • DNAreplication involves entire DNAmolecule • Genome: complete set of DNAin a living organism • Genes: sequences of DNAthat are transcribed into RNA DNAbase sequence reveals evolutionary relationships • Aseries of DNAmolecules stretches through the lineage of every organism to the beginning of evolutionary time • Closely related species have similar base sequences Nucleotides have other important roles ATP: energy transducer in biochemical rxns GTP: energy source (in protein synthesis); transfer info from environment to cells cAMP: nucleotide w/ additional bond between sugar and phosphate group; transmission of info by nervous system Nucleotides: carriers in synthesis and breakdown of carbo and lipids 4.2—How and Where Did the Small Molecules of Life Originate? All life has come from life that existed before. Spontaneous generation of life from unanimate nature is not/has not happened Experiments disproved the spontaneous generation of life • Redi—flies did not arise from decaying meat • Pastuer shows that microorganisms can arise only from other microorganisms, and that environment without life remains lifeless Life began in water • Ancient Earth probably had a lot of water in its atmosphere, but planet was very hot • As it cooled, it was possible for water to condense on the planets surface BI108 Chapter 4 Notes: NucleicAcids and the Orig
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