DNA, RNA, Amino Acids, Proteins, and Genes!

Sugar-phosphate backbone DNA DNA is a nucleic acid, made of long chains of nucleotides Phosphate group Nitrogenous base Nitrogenous base (A, G, C, or T) Sugar Phosphate group Nucleotide Thymine (T) Sugar (deoxyribose) DNA nucleotide Polynucleotide Sugar-phosphate backbone 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

Nitrogenous base (A, G, C, or U) 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) 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

Partial chemical structure 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

each strand is a template for a new strand Untwisting and replication of DNA each strand is a template for a new strand Figure 10.4B

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

RNA transcripts of DNA

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

Gene 1 Gene 3 Gene 2 Codon Amino acid DNA molecule Gene 2 DNA strand TRANSCRIPTION RNA Codon TRANSLATION Polypeptide Amino acid Figure 10.7

Virtually all organisms share the same genetic code “unity of life” Second Base U C A G UUU UCU UAU UGU U phe tyr cys UUC UCC UAC UGC C U ser UUA UCA UAA stop UGA stop A leu UUG UCG UAG stop UGG trp G CUU CCU CAU CGU U his CUC CCC CAC CGC C C leu pro arg CUA CCA CAA CGA A gln CUG CCG CAG CGG G First Base Third Base AUU ACU AAU AGU U asn ser AUC ile ACC AAC AGC C A thr AUA ACA AAA AGA A lys arg Figure: 14-07 Title: The genetic code dictionary. Caption: If we know what a given mRNA codon is, how can we find out what amino acid it codes for? This dictionary of the genetic code offers a way. In Figure 14.5, you saw that the codon CGU coded for the amino acid arginine (arg). Looking that up here, C is the first base (go to the C row along the “first base” line), G is the second base (go to the G column under the “second base” line) and U is the third (go to the codon parallel with the U in the “third base” line). AUG met (start) ACG AAG AGG G GUU GCU GAU GGU U asp GUC GCC GAC GGC C G val ala gly GUA GCA GAA GGA A glu GUG GCG GAG GGG G

An exercise in translating the genetic code Transcribed strand DNA Transcription RNA Start codon Stop codon Translation Polypeptide 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

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

mRNA, a specific tRNA, and the ribosome subunits assemble during initiation Large ribosomal subunit Initiator tRNA P site A site Start codon Small ribosomal subunit mRNA 1 2 Figure 10.13B

The mRNA moves a codon at a time relative to the ribosome 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

Amino acid Polypeptide A site P site Anticodon mRNA 1 Codon recognition mRNA movement Stop codon New peptide bond 2 Peptide bond formation 3 Translocation Figure 10.14

Table 14.2 Types of RNA Type of RNA Functions in Function Messenger RNA (mRNA) Nucleus, migrates to ribosomes in cytoplasm Carries DNA sequence information to ribosomes Transfer RNA (tRNA) Cytoplasm Provides linkage between mRNA and amino acids; transfers amino acids to ribosomes Figure: Table 14.2 Title: Types of RNA. Caption: Ribosomal RNA (rRNA) Cytoplasm Structural component of ribosomes

Review: The flow of genetic information in the cell is DNARNAprotein The sequence of codons in DNA spells out the primary structure of a polypeptide Polypeptides form proteins that cells and organisms use

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

Sickle-cell hemoglobin Normal hemoglobin DNA Mutant hemoglobin DNA mRNA mRNA Normal hemoglobin Sickle-cell hemoglobin Glu Val Figure 10.16A

Types of mutations NORMAL GENE mRNA Protein Met Lys Phe Gly Ala BASE SUBSTITUTION Met Lys Phe Ser Ala BASE DELETION Missing Met Lys Leu Ala His Figure 10.16B

Chromosomal changes can be large or small Deletion Homologous chromosomes Duplication Inversion Reciprocal translocation Nonhomologous chromosomes Figure 8.23A, B

Summary of transcription and translation DNA Stage mRNA is transcribed from a DNA template. 1 mRNA RNA polymerase Amino acid TRANSLATION Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 2 Enzyme tRNA Initiator tRNA Anticodon Stage Initiation of polypeptide synthesis 3 Large ribosomal subunit The mRNA, the first tRNA, and the ribosomal subunits come together. Start Codon Small ribosomal subunit mRNA Figure 10.15

New peptide bond forming Growing polypeptide Stage Elongation 4 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. Codons mRNA Polypeptide Stage Termination 5 The ribosome recognizes a stop codon. The poly-peptide is terminated and released. Stop Codon Figure 10.15 (continued)