Molecular Biology of the Gene PART 2 Debbi Ann Morrissette Graduate Student Researcher Laboratory of Molecular Neuropathogenesis University of California, Irvine

PART 1 Structure of DNA Structure of DNA DNA Replication DNA Replication DNA vs. RNA DNA vs. RNA PART 2 Flow of Genetic Info Mutations Cloning Differentiation X Chromosome Inactivation

The 2 Main Functions of DNA Passing genetic information to daughter cells Passing genetic information to daughter cells Through DNA replication Through DNA replication Directing the synthesis of proteins Directing the synthesis of proteins Through transcription of the DNA code and translation of the nucleotide code into an amino acid sequence Through transcription of the DNA code and translation of the nucleotide code into an amino acid sequence

Basic Nucleotide Stucture Sugar Phosphate Nitrogenous Base

H Deoxyribose Sugar Phosphate Nitrogenous Base Sugar Phosphate Nitrogenous Base DNA vs. RNA Deoxyribonucleic AcidRibonucleic Acid Nitrogenous Bases TCAG UCAG OH Uracil Thymine H CH 3 Ribose

Base Pairing DNA:DNA (replication) DNA:DNA (replication) A:T A:T C:G C:G T CG A GC A A T T DNA:RNA (transcription) DNA:RNA (transcription) A:U A:U C:G C:G T:A T:A T A A CC A C T C CA A U T T G G GT T A A C U A C G G T A

From DNA to Proteins DNA RNA Protein Translation Transcription Genotype Phenotype

DNA molecule Gene 1 Gene 2 Gene 3 AAA AA C C GGC C C GG G UUU UU U U AA DNA strand Transcription RNA Translation Polypeptide Amino acid Codon Overview Genotype Phenotype Note: U pairs with A A still pairs with T

The RNA “Players” mRNA = messenger RNA mRNA = messenger RNA “The Mailman” “The Mailman” rRNA = ribosomal RNA rRNA = ribosomal RNA “The Recruiter” “The Recruiter” tRNA = transfer RNA tRNA = transfer RNA “The Translator” “The Translator” G A A UU G UU A G

Transcription Termination RNA reaches the terminator sequence on the DNA strand and releases from the DNA Elongation RNA polymerase moves along the DNA strand adding complementary RNA nucleotides to make the mRNA strand Initiation Initiation RNA polymerase attaches to the promoter sequence on DNA strand RNA polymerase attaches to the promoter sequence on DNA strand RNA polymerase Initiation Promoter DNA Terminator DNA Initiation Elongation Termination Growing RNA Completed RNA RNA polymerase DNA of gene

Elongation –A Closer Look RNA polymerase RNA nucleotides Template strand of DNA Direction of transcription Newly made RNA T A A CC A C T C CA A U T T G G U G T T A A C C U A C G G T A

mRNA Following transcription, the “message” is brought from the nucleus to the cytoplasm. _______________

The RNA “Players” mRNA = messenger RNA mRNA = messenger RNA “The Mailman” “The Mailman” rRNA = ribosomal RNA rRNA = ribosomal RNA “The Recruiter” “The Recruiter” tRNA = transfer RNA tRNA = transfer RNA “The Translator” “The Translator” G A A UU G UU A G

Translation rRNA recruits both mRNA and tRNA rRNA recruits both mRNA and tRNA rRNA G A A UU G UU A G mRNA tRNA Met Small ribosomal subunit C A U A G U Large ribosomal subunit

tRNA tRNA must translate the RNA message carried by mRNA Translation of RNA nucleotides to amino acids tRNA has to be “bilingual” Anticodon Amino acid attachment site

Translation of the Genetic Code 3 nucleotide bases = 1 amino acid 3 nucleotide bases = 1 amino acid Every group of 3 mRNA nucleotides = Codon Every group of 3 mRNA nucleotides = Codon Corresponding triplet of bases on the tRNA = Anticodon Corresponding triplet of bases on the tRNA = Anticodon C C GG G UUU UU U U Amino acid Codon Anticodon Amino acid attachment site

The mRNA to Amino Acid Dictionary AUG =Start AUG =Start UAA and UAG = Stop UAA and UAG = Stop The code is redundant: The code is redundant: Just as “drink” and “beverage” both represent Just as “drink” and “beverage” both represent GCU and GCG both code for alanine GCU and GCG both code for alanine

Translation Overview Intitiation Intitiation Elongation Elongation Termination Termination

Translation Intitiation Intitiation Initiator tRNA binds to START codon Initiator tRNA binds to START codon Met C A U A G U Amino acid tRNA rRNA mRNA Anticodon Codon

Translation Polypeptide mRNA Codons Anticodon Amino acid Condon recognition Peptide bond formation New peptide bond Translocation Stop codon mRNA movement Elongation Elongation Codon recognition Codon recognition Translocation Translocation Peptide bond formation Peptide bond formation rRNA also functions as an enzyme rRNA also functions as an enzyme

Translation Stop codon Growing polypeptide New peptide bond forming mRNA Polypeptide Codons Elongation Termination The ribosome recognizes a stop codon. The poly- peptide is terminated and released. Termination Termination STOP codon on mRNA STOP codon on mRNA Polypeptide (protein) is released Polypeptide (protein) is released

Summary The DNA code that makes up a gene is transcribed into mRNA The DNA code that makes up a gene is transcribed into mRNA rRNA brings mRNA and tRNA together rRNA brings mRNA and tRNA together tRNA translates the code from nucleotides to amino acids tRNA translates the code from nucleotides to amino acids Newly made protein is released Newly made protein is released Genotype Phenotype