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DNA - PowerPoint PPT Presentation

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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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the genetic code
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.
  • 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.
structure of dna
Structure of DNA
  • DNA is a polymer, which means it is made of monomers.
    • Called nucleotides
structure of a nucleotide
Structure of a nucleotide
  • Each nucleotide contains:
    • 5-carbon sugar (Deoxyribose)
    • Phosphate group
    • Nitrogenous Base
  • There are 4 possible Nitrogenous Bases
back to dna
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.
what does dna store the information for
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).
how was dna discovered
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…
experiments griffith
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.
experiments griffith2
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!
experiments griffith3
Experiments: Griffith
  • Conclusion:
    • Whatever transformation the bacteria made was heritable and could be passed down to the next generation.
experiments avery
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.
experiments avery1
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.
experiments avery2
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.
experiments hershey and chase
Experiments: Hershey and Chase
  • 3. Alfred Hershey and Martha Chase 1952
    • Hershey and Chase studied viruses.
experiments hershey and chase1
Experiments: Hershey and Chase
  • Structure of a virus:
    • Nucleic Acids (like DNA) wrapped in a protein coat.
    • Bacteriophage- virus that infects bacteria cells
experiments hershey and chase2
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.
the discovery of the dna structure
The discovery of the DNA structure…
  • Rosalind Franklin
    • She x-rayed DNA and saw its double helix
the discovery of the dna structure1
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.
the discovery of the dna structure2
The discovery of the DNA structure…
  • James Watson and Francis Crick- 1953
dna replication
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.
dna replication1
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.
enzymes involved in dna replication
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.
  • 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.
  • 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!)
  • 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.
protein synthesis
Protein Synthesis
  • The whole point of all of this is to make proteins.
  • DNA RNA amino acid sequence Protein

***Why are proteins so important?***

protein synthesis1
Protein Synthesis
  • Protein synthesis happens in the ribosomes (located in the cytoplasm OR on the rough ER)
proteins synthesis transcription
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.
proteins synthesis transcription1
Proteins Synthesis: Transcription
  • Nucleotides are arranged into triplets called codons.
    • Example: AAC CG T TAC


    • 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.
proteins synthesis transcription2
Proteins Synthesis: Transcription
  • What kind of RNA is DNA transcribed into?
    • mRNA
  • Why?
    • Because mRNA can leave the nucleus.
protein synthesis transcription
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.
protein synthesis transcription2
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?



protein synthesis transcription3
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!
protein synthesis translation
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?
protein synthesis translation1
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!
  • Mutation: any change in the nucleotide sequence of a DNA strand.
  • 2 types:
    • Point mutations
    • Frame-shift Mutations
point mutations
Point Mutations
  • Base-substitution
    • 1 base (nucleotide) is substituted with another.
point mutations1
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!
frame shift mutations
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.
frame shift mutations1
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.
what causes mutations
What causes mutations?
  • Mutagen: any physical or chemical agent that causes a mutation
  • Most mutations are harmful…
    • Sickle Cell Anemia
      • Caused by 1 base substitution on a gene with 438 bases!
    • Tay Sachs Disease
      • Caused by several frame shift mutations
  • Some mutations are actually beneficial…
    • There is a mutation that occurs in monarch butterflies that changes a protein that determines color.
    • This results in the butterfly being bright orange instead of dull orange or dull brown.
    • Why might this be beneficial?