DNA structure and function

Major points Genetic information flows from DNA to RNA to protein (“central dogma”) DNA is a double helix of two complementary antiparallel strands Specific pairing occurs between bases of nucleic acid (DNA and RNA) strands

Reading (3) Chapter 5, pp. 76-79 Chapter 16, pp. 278-283

DNA structure and function I. Nucleic acid function 1.Overview (replication, transcription, translation) 2. Genetic information flow (DNA -> RNA -> protein) 3. Definition of gene II. Nucleic acid structure

Nucleic acid function overview DNA Replication Transcription RNA Catalysis Translation Protein

Nucleic acid function DNA stores hereditary information (genes) RNA transmits hereditary information

DNA function (genes) DNA is a polymer that stores and carries genetic information Information is stored as the sequence of monomer subunits (nucleotides)

Definition of gene Genes are the units of heredity Genes direct RNA and protein syntheses (“Central dogma”) “One gene encodes one protein” (with exceptions)

DNA-> RNA-> protein Is this cell eukaryotic or prokaryotic?

“Central dogma” RNA can be reverse transcribed to DNA DNA catalyzed by protein RNA RNA has catalytic activity Protein Transcription RNA synthesis using DNA template Translation Protein synthesis using RNA template

“One gene-one protein” Genes are the units of heredity Each gene encodes one protein However there are exceptions: -multisubunit proteins -alternative RNA splicing or protein processing -regulatory DNA and catalytic RNA

DNA structure and function I. Nucleic acid function II. Nucleic acid structure 1. Nucleotides 2. Double helix 3. Complementary base-pairing 4. Supercoiling

Watson & Crick DNA Double helix

DNA structure Polymer of nucleotide subunits A, T, G, C Base-pairing (complementary) A=T and CG Double helix (Watson & Crick) antiparallel right-handed

Nucleotides Monomeric subunits of nucleic acids Composed of: Phosphate group Five-carbon sugar: ribose (RNA) or deoxyribose (DNA) Nitrogenous base

Nucleotide structure

Double helix Two polynucleotide strands Antiparallel (sugars: 5´ to 3´ and 3´ to 5´) Right-handed (B-form) Held together by: Pairing between bases (H-bonds) Stacking interactions

Double helix structure

Complementary base-pairing A binds T (or U) T (or U) binds A G binds C C binds G Which is stronger?

Levels of DNA structure Primary structure: sequence of nucleotides Secondary structure: path of strands double helix Tertiary structure: path helix takes in space supercoiling

Telephone cord relaxed supercoiled

DNA topoisomerases Enzymes that alter DNA topology DNA gyrase is the only topoisomerase that introduces negative supercoiling

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