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NUCLEIC ACIDS

NUCLEIC ACIDS. 0. Nucleic acids are information-rich polymers of nucleotides Nucleic acids such as DNA and RNA Serve as the blueprints for proteins and thus control the life of a cell. H. H. N. N. N. H. OH. N. H. N. O. P. O. CH 2. Nitrogenous base (A). O. O . H. H.

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NUCLEIC ACIDS

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  1. NUCLEIC ACIDS 0 • Nucleic acids are information-rich polymers of nucleotides • Nucleic acids such as DNA and RNA • Serve as the blueprints for proteins and thus control the life of a cell

  2. H H N N N H OH N H N O P O CH2 Nitrogenous base (A) O O H H Phosphate group H H H OH Sugar 0 • The monomers of nucleic acids are nucleotides • Composed of a sugar, phosphate, and nitrogenous base

  3. Nucleotide A T C G T Sugar-phosphate backbone 0 • The sugar and phosphate • Form the backbone for the nucleic acid or polynucleotide

  4. C A T C G C G A T C G A T A T Base pair G C T A A T A T 0 • DNA consists of two polynucleotides • Twisted around each other in a double helix

  5. 0 • RNA, by contrast • Is a single-stranded polynucleotide

  6. 0 • Stretches of a DNA molecule called genes • Program the amino acid sequences of proteins

  7. Sugar-phosphate backbone Phosphate group Nitrogenous base A A Sugar Nitrogenous base(A, G, C, or T) Phosphategroup C C DNA nucleotide O H H3C C C N O C C T CH2 H T O P N O O O– Thymine (T) O C C H H H H G G C C H O Sugar(deoxyribose) T T DNA nucleotide DNA polynucleotide • DNA and RNA are polymers of nucleotides • Made of long chains of nucleotide monomers

  8. H H H H O N N O C H C H H3C C C H N N N C C N C N N C H H C C C C C C C C C C H O H N N N O H N N H N N H H H H H Adenine (A) Guanine (G) Thymine (T) Cytosine (C) Purines Pyrimidines • DNA has four kinds of nitrogenous bases • A, T, C, and G Figure 10.2B

  9. Nitrogenous base (A, G, C, or U) Key Hydrogen atom O Phosphategroup Carbon atom C H Nitrogen atom H N C Oxygen atom O C C Phosphorus atom H O P O CH2 O N Uracil (U) O– O C C H H H H C C OH O Sugar(ribose) • RNA is also a nucleic acid • But has a slightly different sugar • And has U instead of T

  10. 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

  11. Twist • The structure of DNA • Consists of two polynucleotide strands wrapped around each other in a double helix

  12. G C O T A OH P Hydrogen bond –O O A T OH O H2C A T Basepair O CH2 O O C G P O O– –O C G O P O H2C O O C T G A O CH2 C G O O P O O– – O O P O H2C O O G C A T O CH2 O O A T P O – O O– O P A T O O H2C O A T A T CH2 O OH O O– P G C HO O T A Partial chemical structure Ribbon model Computer model • Hydrogen bonds between bases • Hold the strands together • Each base pairs with a complementary partner • A with T, and G with C

  13. T A T T A A T A T A G C G G G C C C G C C C G G G C G C C A A T A T A A T T A T T T A A A T Both parental strands serve as templates Two identical daughtermolecules of DNA Parental moleculeof DNA DNA REPLICATION • DNA replication depends on specific base pairing • DNA replication • Starts with the separation of DNA strands • Then enzymes use each strand as a template • To assemble new nucleotides into complementary strands Nucleotides

  14. G C T A G C G C A T T A C G A T C G G C C G G C C C G G A C A T A T T G A T T G T T A A A A A C T T T A • DNA replication is a complex process • Due in part to the fact that some of the helical DNA molecule must untwist

  15. Parental strand Origin of replication Daughter strand Bubble Two daughter DNA molecules • DNA replication: A closer look • DNA replication • Begins at specific sites on the double helix

  16. 5 end 3 end P HO 5 4 2 3 A T 3 1 1 4 2 5 P P C G P P G C P P A T OH P 3 end 5 end • Each strand of the double helix • Is oriented in the opposite direction

  17. DNA polymerase molecule 3 5 Daughter strandsynthesizedcontinuously Parental DNA 5 3 Daughter strandsynthesizedin pieces 3 5 5 3 DNA ligase Overall direction of replication • Using the enzyme DNA polymerase • The cell synthesizes one daughter strand as a continuous piece • The other strand is synthesized as a series of short pieces • Which are then connected by the enzyme DNA ligase

  18. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN • The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits • The information constituting an organism’s genotype • Is carried in its sequence of its DNA bases • A particular gene, a linear sequence of many nucleotides • Specifies a polypeptide

  19. DNA Transcription RNA Translation Protein • The DNA of the gene is transcribed into RNA • Which is translated into the polypeptide

  20. Genetic information written in codons is translated into amino acid sequences • 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

  21. DNA molecule Gene 1 Gene 2 Gene 3 DNA strand A A A C A C G G A A C A Transcription U U U G U G C C U U G U RNA Codon Translation Polypeptide Amino acid

  22. Second base U C A G U UAU UGU UGC UGA Stop UUU UCU Cys Phe Tyr UUC UAC C UCC Ser U UCA UUA UAA Stop A Leu UCG UAG Stop UGG Trp G U CAU CGU CUU CCU His C CAC CGC CUC CCC C Pro Arg Leu CUA CCA CAA CGA A Gln CAG CGG CUG CCG G Third base First base U ACU AUU AAU AGU Ser Asn ACC AGC AUC AAC Ile C A Thr AUA AGA ACA AAA A Lys Arg Met or start ACC AGG AAG AUG G U GUU GAU GGU GCU Asp C GGC GCC GUC GAC Gly Ala G Val GUA GCA GGA GAA A Glu GUG GCG GGG GAG G • The genetic code is the Rosetta stone of life • Nearly all organisms • Use exactly the same genetic code UUG

  23. Strand to be transcribed T A C T T C A A A A T C DNA A T G A A G T T T T A G Transcription G U U U A G A U A A G U RNA Startcondon Stopcondon Translation Met Polypeptide Lys Phe • An exercise in translating the genetic code

  24. RNA nucleotides RNA polymerase A C C A T T A U T C T G U G A C A U C C A C C A G A T T T A G G Direction of transcription Template Strand of DNA Newly made RNA • Transcription produces genetic messages in the form of RNA • A close-up view of transcription

  25. In the nucleus, the DNA helix unzips • And RNA nucleotides line up along one strand of the DNA, following the base pairing rules • As the single-stranded messenger RNA (mRNA) peels away from the gene • The DNA strands rejoin

  26. RNA polymerase DNA of gene Promoter DNA Terminator DNA Area shown In Figure 10.9A Growing RNA Completed RNA RNA polymerase • Transcription of a gene 1 Initiation 2 Elongation 3 Termination

  27. Exon Intron Exon Intron Exon DNA Transcription Addition of cap and tail Cap RNA transcript with cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Cytoplasm • Eukaryotic RNA is processed before leaving the nucleus • Noncoding segments called introns are spliced out • And a cap and a tail are added to the ends

  28. Transfer RNA molecules serve as interpreters during translation • Translation • Takes place in the cytoplasm

  29. 0 Amino acid attachment site Hydrogen bond RNA polynucleotide chain Anticodon • A ribosome attaches to the mRNA • And translates its message into a specific polypeptide aided by transfer RNAs (tRNAs)

  30. Amino acid attachment site Anticodon • Each tRNA molecule • Is a folded molecule bearing a base triplet called an anticodon on one end • A specific amino acid • Is attached to the other end

  31. tRNAmolecules Growingpolypeptide Largesubunit mRNA Small subunit • Ribosomes build polypeptides • A ribosome consists of two subunits • Each made up of proteins and a kind of RNA called ribosomal RNA

  32. The subunits of a ribosome • Hold the tRNA and mRNA close together during translation tRNA-binding sites Largesubunit Next amino acid to be added to polypeptide Growing polypeptide tRNA mRNA-binding site mRNA Smallsubunit Codons

  33. Start of genetic message End • An initiation codon marks the start of an mRNA message

  34. Large ribosomalsubunit Met Met Initiator tRNA P site A site U C U A C A A U G AUG Startcodon Small ribosomalsubunit mRNA 1 2 • mRNA, a specific tRNA, and the ribosome subunits • Assemble during initiation

  35. Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation • Once initiation is complete • Amino acids are added one by one to the first amino acid

  36. 1 Codon recognition 2 Peptide bondformation Translocation 3 • Each addition of an amino acid • Occurs in a three-step elongation process Aminoacid Polypeptide P site A site Anticodon mRNA Codons mRNAmovement Stopcodon New Peptidebond

  37. The mRNA moves a codon at a time • And a tRNA with a complementary anticodon pairs with each codon, adding its amino acid to the peptide chain

  38. Elongation continues • Until a stop codon reaches the ribosome’s A site, terminating translation

  39. Review: The flow of genetic information in the cell is DNARNAprotein • The sequence of codons in DNA, via the sequence of codons • Spells out the primary structure of a polypeptide

  40. 1     mRNA is transcribed from a DNA template. 2      Each amino acidattaches to its propertRNA with the help of aspecific enzyme and ATP. 3       Initiation ofpolypeptide synthesis The mRNA, the first tRNA, and the ribosomal subunits come together. 4 Elongation A succession of tRNAsadd their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. 5 Termination The ribosome recognizes a stop codon. The poly-peptide is terminated and released. • Summary of transcription and translation DNA Transcription mRNA RNApolymerase Amino acid Translation Enzyme ATP tRNA Anticodon Largeribosomal subunit InitiatortRNA Start Codon Smallribosomal subunit mRNA New peptidebond forming Growingpolypeptide Codons mRNA Polypeptide Stop codon

  41. Normal hemoglobin DNA Mutant hemoglobin DNA C A T T T C mRNA mRNA G A A G U A Normal hemoglobin Sickle-cell hemoglobin Glu Val • Mutations can change the meaning of genes • Mutations are changes in the DNA base sequence • Caused by errors in DNA replication or recombination, or by mutagens

  42. Normal gene U G C U U C A G A A U G A G G mRNA Met Lys Gly Protein Phe Ala Base substitution A A G A U G C A U G A G U U C Lys Met Phe Ser Ala Missing U Base deletion G G C G A C A U A U G A G U U Lys Ala His Met Leu • Substituting, inserting, or deleting nucleotides alters a gene • With varying effects on the organism

  43. Nucleus fromdonor cell Donorcell Clone of donor is born (reproductive cloning) Implant blastocyst insurrogate mother Grow in culture to produce an early embryo (blastocyst) Add somatic cell from adult donor Remove nucleusfrom egg cell Remove embryonic stemcells from blastocyst andgrow in culture Induce stem cells toform specialized cells(therapeutic cloning) ANIMAL CLONING 0 • Nuclear transplantation can be used to clone animals

  44. CONNECTION 0 • Reproductive cloning has valuable applications, but human reproductive cloning raises ethical issues • Reproductive cloning of nonhuman mammals • Is useful in research, agriculture, and medicine

  45. 0 • Critics point out that there are many obstacles • Both practical and ethical, to human cloning

  46. Blood cells Adult stemcells in bone marrow Nerve cells Culturedembryonicstem cells Heart muscle cells Different cultureconditions Different types ofdifferentiated cells CONNECTION 0 • Therapeutic cloning can produce stem cells with great medical potential • Like embryonic stem cells, adult stem cells • Can perpetuate themselves in culture and give rise to differentiated cells

  47. 0 • Unlike embryonic stem cells • Adult stem cells normally give rise to only a limited range of cell types

  48. BACTERIAL PLASMIDS AND GENE CLONING 0 • Plasmids are used to customize bacteria: An overview • Gene cloning is one application of DNA technology • Methods for studying and manipulating genetic material

  49. Plasmid isolated 1 DNA isolated 2 Gene inserted into plasmid 3 Plasmid put into bacterial cell 4 Cell multiplies with gene of interest 5 0 • Researchers can insert desired genes into plasmids, creating recombinant DNA • And insert those plasmids into bacteria Bacterium Cell containing gene of interest Plasmid Bacterial chromosome Recombinant DNA (plasmid) DNA Gene of interest Recombinant bacterium Copies of gene Copies of protein Clone of cells Gene for pest resistance inserted into plants Protein used tomake snow format highertemperature Gene used to alter bacteria for cleaning up toxic waste Protein used to dissolve bloodclots in heart attack therapy

  50. 0 • If the recombinant bacteria multiply into a clone • The foreign genes are also copied

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