Nucleic Acids CHEM 2221 PDF

# Nucleic Acids ## CHEM 2221 ## Nucleic acids store, transmit, and help express hereditary information - The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene. - Genes are made of DNA, a nucleic acid made of monomers called nucleotides. ## The roles of nuc...

# Nucleic Acids ## CHEM 2221 ## Nucleic acids store, transmit, and help express hereditary information - The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene. - Genes are made of DNA, a nucleic acid made of monomers called nucleotides. ## The roles of nucleic acids - There are two types of nucleic acids: - Deoxyribonucleic acid (DNA) - Ribonucleic acid (RNA) - DNA provides directions for its own replication. - DNA directs synthesis messenger RNA (mRNA) and, through mRNA controls protein synthesis. - Protein synthesis occurs on ribosomes. ## Figure 5.25-1 The figure shows a cell. The nucleus is a darker colored circle, while the cytoplasm is a lighter colored circle. The nucleus contains DNA, from which an mRNA molecule is being transcribed. The arrow indicates movement of mRNA from the nucleus to the cytoplasm. ## Figure 5.25-2 The figure shows a cell progressing in protein synthesis. mRNA leaves the nucleus, but this time the arrow indicates movement toward the cytoplasm. ## Figure 5.25-3 The figure shows a cell at a more advanced point in protein synthesis. The mRNA has moved to the cytoplasm, and a ribosome is shown attaching to the mRNA molecule. The mRNA molecule indicates the correct amino acid sequence for the polypeptide chain. ## The components of nucleic acids - Nucleic acids are polymers called polynucleotides. - Each polynucleotide is made of monomers called nucleotides. - Each nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups. - The portion of a nucleotide without the phosphate group is called a nucleoside. ## Figure 5.26ab The figure is a drawing of a polynucleotide chain. The chain is made up of sugar and phosphate groups. The phosphate groups are connected to the sugars, forming a backbone. Each sugar is linked to a nitrogenous base. - (a) Polynucleotide or nucleic acid - (b) Nucleotide ## Figure 5.26c - Nitrogenous bases - Pyrimidines: cytosine, thymine, and uracil. Have a single six-membered ring. - Cytosine (C) - structural formula - Thymine (T, in DNA) - structural formula - Uracil (U, in RNA) - structural formula - Purines: adenine and guanine. Have a six-membered ring fused to a five-membered ring. - Adenine (A) - structural formula - Guanine (G) - structural formula - Sugars - Deoxyribose (in DNA) - structural formula - Ribose (in RNA) - structural formula ## Figure 5.26c - Nucleoside = nitrogenous base + sugar - There are two families of nitrogenous bases: - Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring. - Purines (adenine and guanine) have a six-membered ring fused to a five-membered ring. - In DNA, the sugar is deoxyribose; in RNA, the sugar is ribose. - Nucleotide = nucleoside + phosphate group ## Nucleotide polymers - Nucleotide monomers are linked together to build a polynucleotide. - Adjacent nucleotides are joined by covalent bonds that form between the -OH group on the 3' carbon of one nucleotide and the phosphate on the 5' carbon on the next. - These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages. - The sequence of bases along a DNA or mRNA polymer is unique for each gene. ## The structures of DNA and RNA molecules - RNA molecules usually exist as single polypeptide chains. - DNA molecules have two polypeptides spiraling around an imaginary axis, forming a double helix. - In the DNA double helix, the two backbones run in opposite 5'->3' directions from each other, an arrangement referred to as antiparallel. - One DNA molecule includes many genes. ## DNA and proteins as tape measures of evolution - The linear sequences of nucleotides in DNA molecules are passed from parents to offspring. - Two closely related species are more similar in DNA than are more distantly related species. - Molecular biology can be used to evaluate evolutionary kinship.