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DNA

DNA. The Genetic Code…. The genetic code is made up of DNA. It’s functions are to: Instruct in the form a of special code. Pass information from one generation to the next. DNA. Stands for Deoxyribonucleic Acid Say it… “ deoxy ” “ ribo ” “nu-clay- ic ” “acid”.

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DNA

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  1. DNA

  2. The Genetic Code… • The genetic code is made up of DNA. • It’s functions are to: • Instructin the form a of special code. • Pass information from one generation to the next.

  3. DNA • Stands for Deoxyribonucleic Acid • Say it… “deoxy” “ribo” “nu-clay-ic” “acid” • It is located in the nucleus of each cell. • It replicates and divides.

  4. Structure of DNA • DNA is a polymer, which means it is made of monomers. • Called nucleotides

  5. Structure of a nucleotide • Each nucleotide contains: • 5-carbon sugar (Deoxyribose) • Phosphate group • Nitrogenous Base • There are 4 possible Nitrogenous Bases

  6. Back to DNA… • DNA has a double helix structure. • It looks like a twisted ladder. • It is made up of different combinations of the 4 nucleotides. • Sugars and Phosphates make up the sides of the ladder-like structure. • Nitrogenous bases make up the steps of the ladder. • Weak hydrogen bonds (like velcro) hold the nitrogenous bases together from each side.

  7. What does DNA store the information for??? • The information stored in the DNA is used to make proteins. • Why proteins? • Proteins can directly make hair, hormones, and enzymes. • Enzymes are proteins that act as catalysts to facilitate chemical reactions. • Proteins are important molecules of cells and are responsible for cell movement (cilia and flagella).

  8. How was DNA discovered? • There were several discoveries that happened that informed scientists that DNA existed BEFORE they actually discovered the structure. • All discoveries were related and helped scientists come to a full understanding later…

  9. Experiments: Griffith • 1. Frederick Griffith 1928 • Griffith studied 2 types of bacteria • Type “R” Bacteria :harmless to mice • Type “S” Bacteria: gave mice a fatal strain of pnemonia.

  10. Experiments: Griffith

  11. Experiments: Griffith • What happened? • The non-invasive bacteria R was transformed into an invasive/deadly form! • Descendants of the transformed bacteria carried the invasive characteristic!

  12. Experiments: Griffith • Conclusion: • Whatever transformation the bacteria made was heritable and could be passed down to the next generation.

  13. Experiments: Avery • 2. Oswald Avery 1944 • Avery studied Griffith’s work and wanted to know what his “transforming factor” was… • He knew several things: • Chromosomes function in heredity. • Chromosomes are made up of DNA and proteins.

  14. Experiments: Avery • So was this “transforming factor” in Griffith’s experiment DNA or proteins? • Avery treated Griffith’s “heat killed S cells/living R cells” combination with a “protein destroying enzyme” • Result: the new colonies of bacteria still killed the mice. • Avery treated Griffith’s “heat killed S cells/living R cells” combination with a “DNA destroying enzyme” • Result: the new colonies of bacteria did not kill the mice.

  15. Experiments: Avery • What did this mean?? • If the Proteins were destroyed… nothing changed. • If the DNA was deestroyed… the mice were now fine. • Avery concluded that the lethal trait was being held in and passed on through DNA. • Heritable factors were in DNA.

  16. Experiments: Hershey and Chase • 3. Alfred Hershey and Martha Chase 1952 • Hershey and Chase studied viruses.

  17. Experiments: Hershey and Chase • Structure of a virus: • Nucleic Acids (like DNA) wrapped in a protein coat. • Bacteriophage- virus that infects bacteria cells

  18. Experiments: Hershey and Chase • Viruses can only reproduce by infecting a living cell with its genetic material (nucleic acids) and making the cell copy it. • By Hershey and Chase studying virsus, there was a better understanding of how DNA is passed down through generations. • Also, it concluded that viruses are definitely NOT living.

  19. Experiments: Hershey and Chase

  20. The discovery of the DNA structure… • Rosalind Franklin • She x-rayed DNA and saw its double helix

  21. The discovery of the DNA structure… • Erwin Chargaff • Noticed that the number of Adenine bases in a sample of DNA was equal to the number of Thymine bases, but not to the number of Guanine or Cytosine. • Also, the number of Guanine bases was equal to the number of Cytosine, but not to the number of Adenine or Thymine. • He came up with the base-pairing rule.

  22. The discovery of the DNA structure… • James Watson and Francis Crick- 1953

  23. DNA Replication • During DNA Replication, an exact copy of DNA is made. • Replication of DNA occurs during the S Phase of Interphase during the cell cycle. • Each strand of DNA holds specific information to create the other strand in the base-pairing pattern.

  24. DNA Replication • Replication occurs in segments, call replication bubbles. • Each new strand consists of one old strand and one new strand, making it a semi-conservative process.

  25. Enzymes involved in DNA replication • 1. Helicase unzips and untwists the double helix. • 2. DNA Polymerase adds nucleotides to the leading DNA strand in the 5’ to 3’ direction, which is continuous. • 3. Primase adds RNA primer to the lagging DNA strand in the 5’ to 3’ direction, which is discontinuous, making Okazaki fragments. • 4. A different DNA Polymerase comes through and adds nucleotides to the lagging strand fragments. • 5. Ligase binds the Okazaki fragments together.

  26. RNA • RNA= Ribonucleic Acid • RNA is a nucleic acid, like DNA, but has different features that make it important. • Functions of RNA: • Acts as a messenger between NDA (which is stuck in the nucleus) and ribosomes (which are in the cytoplasm). • Why does the information from DNA need to get to the ribosome? • To make proteins! • Therefore, RNA helps carry out protein synthesis.

  27. RNA • Structure of RNA • The structure of RNA is very similar to DNA except… • RNA is single stranded • RNA is composed of Nucleotides that have a Ribose sugar instead of Deoxyribose (still has a phosphate group and a base.) • The bases are Adenine, Cytosine, Guanine, and Uracil (there is no Thymine!)

  28. RNA • 3 types of RNA: • mRNA: messenger RNA • Carries the code from the nucleus to the ribosome. • tRNA: transfer RNA • Recognizes codons on mRNA and brings specific amino acids to the ribosome. • rRNA: ribosomal RNA • Found in the ribosome • Interacts with mRNA and tRNA to ensure proteins are made correctly.

  29. Protein Synthesis • The whole point of all of this is to make proteins. • DNA RNA amino acid sequence Protein ***Why are proteins so important?***

  30. Protein Synthesis • Protein synthesis happens in the ribosomes (located in the cytoplasm OR on the rough ER)

  31. Proteins Synthesis: Transcription • DNA is trapped in the nucleus. The cell does not want the DNA to leave the nucleus because then it will not be protected. • Proteins are made in the ribosome. Somehow, the code from the DNA needs to get to the ribosomes so that the correct proteins are made.

  32. Proteins Synthesis: Transcription • Nucleotides are arranged into triplets called codons. • Example: AAC CG T TAC T TG GCA ATG • Each codon specifies (codes for) a particular amino acid. • The sequence of the codons in the DNA will be transferred to the RNA, which will then determine the sequence of amino acids.

  33. Proteins Synthesis: Transcription • What kind of RNA is DNA transcribed into? • mRNA • Why? • Because mRNA can leave the nucleus.

  34. Protein Synthesis: Transcription • Steps for Transcription: • 1. A portion of the DNAuntwists and unzips (Helicase) • 2. RNA Polymerase adds the RNA nucleotides with the corresponding base sequence of the transcribing strand. • 3. Elongationoccurs. Regions with introns and exons signal start and stop areas. • 4. The mRNA moves away from the DNA molecules and goes into the cytoplasm. • 5. The DNA zips back up and twists into its normal double helix.

  35. Protein Synthesis: Transcription

  36. Protein Synthesis: Transcription • When RNA is being synthesized by enzymes, they pair the bases just like they would during DNA replication. • There is one BIG difference, though. • RNA does not have the base Thymine. • Instead, if the enzymes come across an Adenine base, they pair it with Uracil. • Can you transcribe the following DNA strand? DNA: ATC GGA TAC GGG CCA mRNA:

  37. Protein Synthesis: Transcription • But let’s remember the goal here… Proteins! Proteins! Proteins! • Now that we have our mRNA with the DNA code, the mRNA can leave the nucleus and head to the ribosome!

  38. Protein synthesis: Translation • During translation, the codons are translated into an amino acid sequence. • tRNA is structured to carry specific amino acids to the ribosome. • mRNA has the code for tRNA. • tRNA has 3 exposed bases called the anticodon. • What does this remind you of? • Codon • What was a codon? • 3 nucleotides • What do you think the anticodon does?

  39. Protein synthesis: Translation • Steps to translation: • 1. the ribosome attaches to the mRNA strand. • 2. the tRNA (carrying an amino acid) with the matching anticodon pairs with the mRNA strand. • 3. The ribosome moves down the strand and complimentary tRNAs line up the amino acids in the order specified by the bases. • 4. The amino acids are then bonded together by a peptide bond forming a polypeptide. • 5. The polypeptide is then folded in a specific way according to the amino acids and their structures- forming a function PROTEIN!

  40. Protein synthesis: Translation

  41. Mutations • Mutation: any change in the nucleotide sequence of a DNA strand. • 2 types: • Point mutations • Frame-shift Mutations

  42. Point Mutations • Base-substitution • 1 base (nucleotide) is substituted with another.

  43. Point Mutations • A base substitution can be a silent mutation, meaning that it does not cause any change in the amino acid sequence. • How is this possible? • Because more than 1 codon can code for the same amino acid. Remember, there are 64 possible codons, and only 20 amino acids. • Example: GAA and GAG both code for Glucine!

  44. Frame shift Mutations • Insertion • An extra nucleotide is added. • This alters the rest of the sequence because each codon downstream is changed. • This usually results a non-functional protein.

  45. Frame shift Mutations • Deletion • A nucleotide is removed. • This also alters the rest of the sequence because each codon downstream is changed. • This usually results a non-functioning protein.

  46. What causes mutations? • Mutagen: any physical or chemical agent that causes a mutation

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