Chapter 24 Nucleotides, Nucleic Acids, and Heredity Nucleotides, Nucleic Acids, and Heredity

The Molecules of Heredity Each cell has thousands of different proteins. How do cells know which proteins to synthesize out of s possible amino acid sequences? From the end of the 19th century, biologists suspected that the transmission of hereditary information took place chromosomes in the nucleus, more specifically in structures called chromosomes. genesThe hereditary information was thought to reside in genes within the chromosomes. histonesnucleic acidsChemical analysis of nuclei showed chromosomes are made up largely of proteins called histones and nucleic acids.

The Molecules of Heredity deoxyribonucleic acids (DNA)By the 1940s, it became clear that deoxyribonucleic acids (DNA) carry the hereditary information. Other work in the 1940s demonstrated that each gene controls the manufacture of one protein. Thus the expression of a gene in terms of an enzyme protein led to the study of protein synthesis and its control. protein work

Structure of DNA and RNA ( based on Nucleic Acids ) Two Kinds in cells: ribonucleic acids (RNA) deoxyribonucleic acids (DNA) RNA & DNA: polymers built from monomers (nucleotides) A nucleotide is composed of: 1. a base, 2. a monosaccharide, 3. a phosphate, (e.g. AMP)

1. Purine/Pyrimidine Bases Base Pairing: DNA: A-T;C-G RNA: A-U;C-G note:

Nucleosides (base and sugar) compound that consists of D-ribose or 2-deoxy-D-ribose bonded to a purine or pyrimidine base by a  -N-glycosidic bond.

Nucleotides a nucleoside w/ molecule of phosphoric acid esterified with an -OH of the monosaccharide, most commonly either the 3’ or the 5’-OH. ATP- a nucleotide

In Summary Nucleoside = Base + Sugar Nucleotide = Base + Sugar + Phosphoric acid Nucleic acid = chain of nucleotides

Structure of DNA and RNA - bases arranged in various patterns (like A.A.s for Proteins) GENE  ((protein)) sequence is read from the 5’ end to the 3’ end start finish Primary Structure

DNA - 2° Structure the ordered arrangement of nucleic acid strands. the double helix model of DNA 2° structure was proposed by James Watson and Francis Crick in Double helix: Double helix: 2° structure of DNA in which two polynucleotide strands are coiled around each other in a screw-like fashion. Using Chargaff rules: (A-T; C-G) -X-ray (Franklin, Wilkins) (R. Franklin, ) Watson, Crick and Wilkins (Nobel Prize 1962)

The DNA Double Helix -Polynucleotide chains run anti-parallel -Bases (hydrophobic) avoid water & stabilize d. helix w/ H-bonds (below)

Base Pairing

Higher Structure of DNA histones.DNA is coiled around proteins called histones. Histones are rich in the basic amino acids Lys and Arg, whose side chains have a positive charge. The negatively-charged DNA molecules and positively- charged histones attract each other and form units called nucleosomes. Nucleosome:Nucleosome: a core of eight histone molecules around which the DNA helix is wrapped. _+__+_

Chromosomes chromatin. Nucleosomes are further condensed into chromatin. chromosomes. Chromatin fibers are organized into loops, and the loops into the bands that provide the superstructure of chromosomes.