DNA, RNA, Amino Acids, Proteins, and Genes! DNA • DNA is a nucleic acid, made of long chains of nucleotides Phosphate group Nitrogenous base Sugar Phosphate group Nitrogenous base (A, G, C, or T) Nucleotide Thymine (T) Sugar (deoxyribose) DNA nucleotide Polynucleotide Sugar-phosphate backbone Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.2A • DNA has four kinds of bases, A, T, C, and G Thymine (T) Cytosine (C) Adenine (A) Guanine (G) Figure 10.2B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • RNA is also a nucleic acid – different sugar – Uracil instead of Thymine – Single strand Nitrogenous base (A, G, C, or U) Phosphate group Uracil (U) Sugar (ribose) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.2C, D DNA is a double-stranded helix • James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin Figure 10.3A, B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Hydrogen bonds between bases hold the strands together: A and T, C and G Hydrogen bond Ribbon model Partial chemical structure Computer model Figure 10.3D Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Untwisting and replication of DNA • each strand is a template for a new strand Figure 10.4B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The information constituting an organism’s genotype is carried in its sequence of bases – The DNA is transcribed into RNA, which is translated into a protein DNA TRANSCRIPTION RNA TRANSLATION Protein Figure 10.6A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA transcripts of DNA Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Translation of nucleic acids into amino acids • The “words” of the DNA “language” are three bases in a row called codons – The codons in a gene specify the amino acid sequence of a protein Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gene 1 Gene 3 DNA molecule Gene 2 DNA strand TRANSCRIPTION RNA Codon TRANSLATION Polypeptide Figure 10.7 Amino acid Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Virtually all organisms share the same genetic code “unity of life” Second Base C U UUU UUC UUA UUG C CUU CUC CUA CUG A AUU AUC ile AUA AUG met (start) ACU ACC ACA ACG G GUU GUC GUA GUG GCU GCC GCA GCG phe leu leu val UCU UCC UCA UCG CCU CCC CCA CCG A ser UAU UAC UAA UAG pro CAU CAC CAA CAG thr AAU AAC AAA AAG ala GAU GAC GAA GAG G tyr stop stop his gln asn lys asp glu UGU UGC UGA UGG CGU CGC CGA CGG AGU AGC AGA AGG GGU GGC GGA GGG cys stop trp arg ser arg gly U C A G U C A G U C A G U C A G Third Base First Base U • An exercise in translating the genetic code Transcribed strand DNA Transcription RNA Start codon Polypeptide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Translation Stop codon Figure 10.8B Transfer RNA molecules serve as interpreters during translation • In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide • The process is aided by transfer RNAs Amino acid attachment site Hydrogen bond RNA polynucleotide chain Anticodon Figure 10.11A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Ribosomes build proteins Next amino acid to be added to polypeptide Growing polypeptide tRNA molecules P site A site Growing polypeptide Large subunit tRNA P A mRNA mRNA binding site Codons mRNA Small subunit Figure 10.12A-C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • mRNA, a specific tRNA, and the ribosome subunits assemble during initiation Large ribosomal subunit Initiator tRNA P site A site Start codon mRNA Small ribosomal subunit 1 Figure 10.13B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 Elongation • The mRNA moves a codon at a time relative to the ribosome – A tRNA pairs with each codon, adding an amino acid to the growing polypeptide – A STOP codon causes the mRNA-ribosome complex to fall apart Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Amino acid Polypeptide A site P site Anticodon mRNA 1 Codon recognition mRNA movement Stop codon New peptide bond 3 Translocation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 Peptide bond formation Figure 10.14 Table 14.2 Types of RNA Type of RNA Functions in Messenger RNA (mRNA) Nucleus, migrates to ribosomes in cytoplasm Transfer RNA (tRNA) Cytoplasm Provides linkage between mRNA and amino acids; transfers amino acids to ribosomes Ribosomal RNA (rRNA) Cytoplasm Structural component of ribosomes Function Carries DNA sequence information to ribosomes Review: The flow of genetic information in the cell is DNARNAprotein • The sequence of codons in DNA spells out the primary structure of a polypeptide – Polypeptides form proteins that cells and organisms use Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mutations can change the meaning of genes • Mutations are changes in the DNA base sequence – caused by errors in DNA replication or by mutagens – change of a single DNA nucleotide causes sickle-cell disease Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Normal hemoglobin DNA mRNA Mutant hemoglobin DNA mRNA Normal hemoglobin Sickle-cell hemoglobin Glu Val Figure 10.16A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Types of mutations NORMAL GENE mRNA Protein Met Lys Phe Gly Ala Lys Phe Ser Ala BASE SUBSTITUTION Met Missing BASE DELETION Met Lys Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Leu Ala His Figure 10.16B •Chromosomal changes can be large or small Deletion Homologous chromosomes Duplication Inversion Reciprocal translocation Nonhomologous chromosomes Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.23A, B • Summary of transcription and translation TRANSCRIPTION DNA mRNA RNA polymerase Stage 1 mRNA is transcribed from a DNA template. Amino acid TRANSLATION Enzyme Stage 2 Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. tRNA Initiator tRNA mRNA Figure 10.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Anticodon Large ribosomal subunit Start Codon Small ribosomal subunit Stage 3 Initiation of polypeptide synthesis The mRNA, the first tRNA, and the ribosomal subunits come together. New peptide bond forming Growing polypeptide Codons Stage 4 Elongation A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. mRNA Polypeptide Stop Codon Figure 10.15 (continued) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Stage 5 Termination The ribosome recognizes a stop codon. The polypeptide is terminated and released.
