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DNA AND THE LANGUAGE OF LIFE

DNA AND THE LANGUAGE OF LIFE. NUCLEIC ACIDS STORE INFORMATION IN THEIR SEQUENCES OF CHEMICAL UNITS. NUCLEIC ACIDS STORE INFORMATION IN THEIR SEQUENCES OF CHEMICAL UNITS. The Building Blocks of DNA Deoxyribonucleic acid (DNA) stores the genetic information of organisms

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DNA AND THE LANGUAGE OF LIFE

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  1. DNA AND THE LANGUAGE OF LIFE NUCLEIC ACIDS STORE INFORMATION IN THEIR SEQUENCES OF CHEMICAL UNITS

  2. NUCLEIC ACIDS STORE INFORMATION IN THEIR SEQUENCES OF CHEMICAL UNITS • The Building Blocks of DNA • Deoxyribonucleic acid (DNA) stores the genetic information of organisms • It is a polymer built from monomers called nucleotides and is a nucleic acid as is ribonucleic acid (RNA). • There are four types of nucleotides, each with three parts. • A ring shaped sugar called deoxyribose • A phosphate group (phosphorus surrounded by

  3. NUCLEOTIDES

  4. NUCLEIC ACIDS STORE INFORMATION IN THEIR SEQUENCES OF CHEMICAL UNITS four oxygen atoms. • A nitrogenous base: single or double ring of carbon and nitrogen atoms with functional groups. • Nitrogenous Bases • The nucleotides differ only in their nitrogenous bases. • Pyramidines: single ring structures or thymine (T) or cytosine (C) • Purines: larger, double ringed of adenine (A) or guanine (G)

  5. NITROGENOUS BASES: PURINES AND PYRAMIDINES

  6. NUCLEIC ACIDS STORE INFORMATION IN THEIR SEQUENCES OF CHEMICAL UNITS • DNA Strands • The nucleotides are connected by covalent bonds that connect the sugar of one nucleotide to the phosphate group of the next. • The repetition of the sugar-phosphate is the sugar-phosphate “backbone.” • In a similar fashion to amino acid monomers combining to form polypeptides, nucleotides of nucleic acid polymers can combine in many different sequences. • The length of a nucleotide chain can vary from a

  7. COVALENT BONDS BETWEEN SUGAR AND PHOSPHATE

  8. NUCLEIC ACIDS STORE INFORMATION IN THEIR SEQUENCES OF CHEMICAL UNITS few hundred to millions, allowing for an unlimited number of sequences. • DNA’s Structure • In the early 1950s, Franklin and Wilkins photographed DNA using a method called x-ray crystallography, which showed the basic shape to be a helix. • The Double Helix • Watson and Crick used wire and tin to model the DNA structure.

  9. FRANKLIN & WILKINS, WATSON & CRICK

  10. NUCLEIC ACIDS STORE INFORMATION IN THEIR SEQUENCES OF CHEMICAL UNITS • They continued their work until Watson saw one of Franklin’s photographs. • The then created a new molecule of two strands of nucleotides wound around each other, called a double helix. • Their model had the sugar-phosphate backbones on the outside of the double helix and the nitrogenous bases on the inside. • They hypothesized that the bonds between the bases were hydrogen bonds. • They had constructed the actual DNA molecule!

  11. NUCLEIC ACIDS STORE INFORMATION IN THEIR SEQUENCES OF CHEMICAL UNITS • Complementary Base Pairs • They discovered that there were specific base pairs between the purines and pyramidines: • purine adenine with pyramidine thymine • Purine guanine with pyramidine cytosine • A is complementary to T and G is complementary to C. • The sequence on one strand can vary but the bases on the second strand are determined by the sequence on the first strand.

  12. COMPLEMENTARY BASE PAIRING

  13. NUCLEIC ACIDS STORE INFORMATION IN THEIR SEQUENCES OF CHEMICAL UNITS • Each base must pair up with its complement. • This was first reported by Watson and Crick in 1953, in the journal Nature. With them subsequently receiving the Nobel prize for their work.

  14. REVIEW • What are the three parts of a nucleotide? Which parts make up the backbone of a DNA strand? • List the two base pairs found in DNA. • If six bases on one strand of a DNA double helix are AGTCGG, what are the six bases on the complementary section of the other strand of DNA.

  15. DNA REPLICATION IS THE MOLECULAR MECHANISM OF INHERITANCE • The Template Mechanism • Dividing cells receive a complete set of genetic instructions in each new cell. • One generation passes genetic instructions to the next generation. • Before DNA was discovered as the genetic material, it was proposed that gene-copying was based on the template mechanism.

  16. DNA REPLICATION IS THE MOLECULAR MECHANISM OF INHERITANCE • Like reproducing pictures from negatives, the negative of DNA is used to make more DNA. • Applying the complementary base rule allows you to pair the specific base with its complement: A to T, C to G. • Using enzymes, the double helix separates with each “negative” producing a new complementary strand. • Enzymes link the nucleotides together to form

  17. DNA REPLICATION

  18. DNA REPLICATION IS THE MOLECULAR MECHANISM OF INHERITANCE two new DNA strands, called daughter strands. • This process of copying the DNA molecule is called DNA replication. • Replication of the Double Helix • There are more than one dozen enzymes involved in DNA replication. • DNA polymerases also act to make the covalent bonds between the nucleotides of the new strand.

  19. DNA REPLICATION IS THE MOLECULAR MECHANISM OF INHERITANCE • The replication begins at specific sites called origins of replication and the copying proceeds outward in both directions, creating replication bubbles. • Eukaryotic DNA molecules has many origins where replication starts at the same time. • Eventually all the bubbles merge, yielding two double stranded DNA molecules, each with one original strand and one new strand.

  20. REPLICATION OF THE DOUBLE HELIX

  21. DNA REPLICATION

  22. REPLICATION BUBBLE

  23. DNA REPLICATION IS THE MOLECULAR MECHANISM OF INHERITANCE • DNA replication occurs before cells divide, ensuring that all the cells contain the same genetic information. • The same mechanism produces DNA copies that subsequent generations inherit from their parents during reproduction.

  24. REVIEW • Describe how DNA replicates by using a template. • List the steps involved in DNA replication. • Under what circumstances is DNA replicated.

  25. A GENE PROVIDES THE INFORMATION FOR MAKING A SPECIFIC PROTEIN • One Gene, One Polypeptide • The genotype of an organisms is it’s genetic makeup, or the sequence of nucleotide bases in its DNA. • The phenotype, or the organism’s specific traits, is found in proteins and their wide variety of functions. • Beadle and Tatum, in the 1940s found the relationship between genes and proteins

  26. A GENE PROVIDES THE INFORMATION FOR MAKING A SPECIFIC PROTEIN working with the orange bread mold Neurospora crassa. • They found that mutant strains of the mold could not grow on the usual medium and they lacked a single enzyme to produce the mold. • They attributed this to a single gene; hence, the one gene, one enzyme hypothesis. • This hypothesis states that the function of an individual gene is to dictate the production of a specific enzyme.

  27. ORANGE BREAD MOLD

  28. A GENE PROVIDES THE INFORMATION FOR MAKING A SPECIFIC PROTEIN • Since that time, it has been learned that genes dictate the production of a single polypeptide that make up part of an enzyme or another protein, now changing the one gene, one enzyme to one gene, one polypeptide. • Information Flow: DNA to RNA to Protein • RNA is the messenger between DNA and proteins.

  29. RIBONUCLEIC ACID (RNA)

  30. A GENE PROVIDES THE INFORMATION FOR MAKING A SPECIFIC PROTEIN • Ribonucleic acid (RNA) has a ribose as the sugar instead of a deoxyribose, only one strand instead of two, and uracil instead of thymine. • Several types of RNA molecules play a part in the intermediate steps from gene to protein. • As you already know, the language of genes is written as a sequence of bases along the length of a DNA chain.

  31. TRANSCRIPTION

  32. TRANSCRIPTION

  33. TRANSCRIPTION AND TRANSLATION

  34. A GENE PROVIDES THE INFORMATION FOR MAKING A SPECIFIC PROTEIN • The RNA is the messenger from the DNA to the ribosome for the construction of the polypeptide chain. • DNA’s nucleotide sequence in converted to the single strand RNA molecule by transcription. • RNA is a different form of the DNA message. • In the next step, translation takes place, converting nucleic acid language to amino acid language.

  35. TRANSLATION

  36. TRANSLATION

  37. A GENE PROVIDES THE INFORMATION FOR MAKING A SPECIFIC PROTEIN • This is done based on codons for the flow of information from gene to protein. • The codon is a three base word that codes for a specific amino acid. • Each codon brings forth an amino acid that translates into a polypeptide. • The Triplet Code • Nirenburg, an American biochemist, began cracking the codes in the early 1960s.

  38. A GENE PROVIDES THE INFORMATION FOR MAKING A SPECIFIC PROTEIN • He found that by putting just UUU on an RNA molecule and putting this in a test tube containing all 20 of the amino acids, a polypeptide containing only phenylalanine (Phe) was made. • He and other scientists, using this method, concluded the other amino acids represented by each codon. • There are 64 sequences (4³) with start and stop codes.

  39. CODON CODES

  40. CODON WHEEL

  41. A GENE PROVIDES THE INFORMATION FOR MAKING A SPECIFIC PROTEIN • Almost all organisms share the same coding system. • In experiments, genes can be transcribed and translated after being transferred from one species to another.

  42. REVIEW • How did Beadle and Tatum’s research in the “one gene-one polypeptide” hypothesis? • Which molecule completes the flow of information from DNA to protein? • Which amino acid is coded for by the RNA sequence CUA? • List two ways RNA is different from DNA.

  43. THERE ARE TWO MAIN STEPS FROM GENE TO PROTEIN • Transcription: DNA to RNA • There are three types of RNA involved in making proteins from the instructions carried in genes. • Messenger RNA (mRNA) is transcribed from the DNA template. • This resembles replication but only one strand is produced from the template. • The two DNA strands separate at the place where transcription will start and then the RNA bases pair with complementary DNA bases.

  44. TRANSCRIPTION

  45. THERE ARE TWO MAIN STEPS FROM GENE TO PROTEIN • The only difference between this and DNA replication is that the base pairing is different-uracil instead of thymine pairs with adenine. • RNA polymerase, a transcription enzyme, links the RNA nucleotides together telling the polymerase where to begin and end the transcribing process. • Editing the RNA Message • In prokaryotes only, the mRNA transcribed from a gene directly serves as the messenger molecule that is translated into a protein.

  46. EDITING THE RNA TRANSCRIPT

  47. EDITING THE RNA TRANSCRIPT

  48. THERE ARE TWO MAIN STEPS FROM GENE TO PROTEIN • In eukaryotes, the RNA transcribed is modified or processed before it leaves the nucleus as mRNA to be translated. • Certain regions on the RNA are noncoding regions called introns. • Exons are the coding regions of the RNA transcript (those parts of the gene that remain in the mRNA) and are, therefore, translated, or ‘expressed.”

  49. THERE ARE TWO MAIN STEPS FROM GENE TO PROTEIN • Introns are removed and exons spliced together before the RNA leaves the nucleus, a process called RNA splicing. • Translation: RNA to Protein • Translating the nucleic acid language to protein language requires enzymes, ATP, ribosomes, and transfer RNA (tRNA).

  50. THERE ARE TWO MAIN STEPS FROM GENE TO PROTEIN • The Players • An interpreter is needed to translate the message from mRNA to the polypeptide chain, that interpreter being tRNA. • Transfer RNA (tRNA) translates the three letter codons of mRNA to the amino acids that make up proteins. • This process involves: • the tRNA becoming bound to the appropriate amino • recognizing of the appropriate codon in the mRNA • A different version of tRNA molecule per codon

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