1. DNA, RNA structure 2. DNA replication 3. Transcription, translation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA is a nucleic acid, made of long chains of nucleotides DNA and RNA are polymers of nucleotides Nucleotide Phosphate group Nitrogenous base Sugar PolynucleotideSugar-phosphate backbone DNA nucleotide Phosphate group Nitrogenous base (A, G, C, or T) Thymine (T) Sugar (deoxyribose)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA has four kinds of bases, A, T, C, and G Pyrimidines Thymine (T)Cytosine (C) Purines Adenine (A)Guanine (G)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA is also a nucleic acid –different sugar –U instead of T –Single strand, usually Phosphate group Nitrogenous base (A, G, C, or U) Uracil (U) Sugar (ribose)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hydrogen bonds between bases hold the strands together: A and T, C and G Ribbon modelPartial chemical structureComputer model Hydrogen bond
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Untwisting and replication of DNA each strand is a template for a new strand helicase DNA polymerase
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Each strand of the double helix is oriented in the opposite direction 5 end3 end 5 end P P P P P P P P
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DNA polymerase works in only one direction 5 end P P Parental DNA DNA polymerase molecule Daughter strand synthesized continuously Daughter strand synthesized in pieces DNA ligase Overall direction of replication 5 3 Telomere sequences are lost with each replication. Cancer, aging telomeres
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –The DNA is transcribed into RNA, which is translated into the polypeptide DNA RNA Protein TRANSCRIPTION TRANSLATION The information constituting an organism’s genotype is carried in its sequence of bases
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Transcription produces genetic messages in the form of mRNA RNA polymerase RNA nucleotide Direction of transcription Newly made RNA Template strand of DNA
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In transcription, DNA helix unzips –RNA nucleotides line up along one strand of DNA, following the base-pairing rules –single-stranded messenger RNA peels away and DNA strands rejoin –occurs in nucleus RNA polymerase DNA of gene Promoter DNA Terminator DNA Initiation Elongation Termination Growing RNA RNA polymerase Completed RNA
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The “words” of the DNA “language” are triplets of bases called codons –The codons in a gene specify the amino acid sequence of a polypeptide Translation of nucleic acids into amino acids
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An exercise in translating the genetic code Start codon RNA Transcribed strand Stop codon Translation Transcription DNA Polypeptide
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide The process is aided by transfer RNAs Transfer RNA molecules serve as interpreters during translation Hydrogen bond Amino acid attachment site RNA polynucleotide chain Anticodon
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other Anticodon Amino acid attachment site
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The sequence of codons in DNA spells out the primary structure of a polypeptide –Polypeptides form proteins that cells and organisms use Review: The flow of genetic information in the cell is DNA RNA protein
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mutations are changes in the DNA base sequence –caused by errors in DNA replication or by mutagens Mutations can change the meaning of genes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Types of mutations mRNA NORMAL GENE BASE SUBSTITUTION BASE DELETION ProteinMetLysPheGlyAla MetLysPheSerAla MetLysLeuAlaHis Missing