Course review
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Learning objective
• DNA is the genetic material of all living organisms • DNA occurs in chromosomes and also in mitochondria and chloroplasts • Some viruses use RNA, but viruses are not considered living organisms
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Learning objective
• A nucleotide contains a phosphate group, pentose sugar, and nitrogenous base • DNA nucleotides use deoxyribose; RNA nucleotides use ribose • Bases include purines A/G and pyrimidines C/T/U
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Learning objective
• Condensation reactions link nucleotides by sugar-phosphate bonds • The sugar-phosphate backbone is a continuous covalent chain • Bases project from the backbone and carry sequence information
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Learning objective
• Genetic information lies in the order of nitrogenous bases • DNA uses A, T, G, C; RNA uses A, U, G, C • Triplet codons specify amino acids in protein synthesis
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Learning objective
• RNA is a single-stranded polynucleotide formed by condensation • RNA contains ribose and the bases A, U, G, and C • mRNA, tRNA, and rRNA have different roles in protein synthesis
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Learning objective
• DNA has two antiparallel polynucleotide strands in a double helix • Complementary bases pair by hydrogen bonding: A-T and G-C • Draw bases attached to sugars, not phosphates
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Learning objective
• DNA is usually double-stranded; RNA is usually single-stranded • DNA uses deoxyribose and thymine; RNA uses ribose and uracil • RNA molecules are usually much shorter than DNA molecules
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Learning objective
• A pairs with T in DNA and U in RNA; C pairs with G • Complementary base pairing enables accurate DNA replication • It also enables transcription and translation in gene expression
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Learning objective
• DNA can vary in length and in base sequence • Genome size and gene number vary widely between organisms • Base-sequence diversity gives DNA enormous information-storage capacity
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Learning objective
• The 64 codons have nearly the same meanings across life • Conserved genes for transcription, translation, and ribosomes support common ancestry • Synonymous mutations can preserve amino acid sequences
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Learning objective
• 3'-5' phosphodiester bonds create 5' and 3' strand ends • DNA strands are antiparallel: one 5' to 3', the other 3' to 5' • RNA is synthesized and translated in the 5' to 3' direction
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Learning objective
• Purine-pyrimidine pairing keeps DNA helix width constant • A-T and C-G pairs have equal length and fit the model • Hydrogen bonding between complementary bases stabilizes DNA
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Learning objective
• DNA wraps nearly twice around an octamer of histone proteins • H1 histone binds linker DNA to the histone core • Nucleosomes package DNA and allow regulated access to genes
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Learning objective
• Hershey-Chase used bacteriophages labelled with ³²P in DNA or ³⁵S in protein • ³²P-labelled DNA entered E. coli and appeared in new viruses • Results showed DNA, not protein, carries genetic information
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Learning objective
• Chargaff found purines equal pyrimidines across DNA samples • A = T and G = C supported complementary base pairing • These data falsified the tetranucleotide hypothesis
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