DNA
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Transcript of DNA
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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.
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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.
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STRUCTURE OF DNA
• DNA is a polymer, which means it is made of monomers.
• Called nucleotides
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STRUCTURE OF A NUCLEOTIDE
• Each nucleotide contains:• 5-carbon sugar (Deoxyribose)• Phosphate group• Nitrogenous Base
• There are 4 possible Nitrogenous Bases
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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.
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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).
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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…
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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.
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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!
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EXPERIMENTS: GRIFFITH
• Conclusion:
• Whatever transformation the bacteria made was heritable and could be passed down to the next generation.
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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.
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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.
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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.
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EXPERIMENTS: HERSHEY AND CHASE
• 3. Alfred Hershey and Martha Chase 1952
• Hershey and Chase studied viruses.
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EXPERIMENTS: HERSHEY AND CHASE
• Structure of a virus:
• Nucleic Acids (like DNA) wrapped in a protein coat.
• Bacteriophage- virus that infects bacteria cells
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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.
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THE DISCOVERY OF THE DNA STRUCTURE…
• Rosalind Franklin• She x-rayed DNA and saw its double helix
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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.
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THE DISCOVERY OF THE DNA STRUCTURE…
• James Watson and Francis Crick- 1953
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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.
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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.
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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.
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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.
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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!)
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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.
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PROTEIN SYNTHESIS
• The whole point of all of this is to make proteins.
• DNA RNA amino acid sequence Protein
***Why are proteins so important?***
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PROTEIN SYNTHESIS
• Protein synthesis happens in the ribosomes (located in the cytoplasm OR on the rough ER)
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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.
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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.
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PROTEINS SYNTHESIS: TRANSCRIPTION
• mRNA
• Why?• Because mRNA
can leave the nucleus.
• What kind of RNA is DNA transcribed into?
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PROTEIN SYNTHESIS: TRANSCRIPTION• Steps for Transcription:• 1. A portion of the DNA untwists and unzips (Helicase)
• 2. RNA Polymerase adds the RNA nucleotides with the corresponding base sequence of the transcribing strand.
• 3. Elongation occurs. 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.
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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 CCAmRNA:
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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!
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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?
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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!
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MUTATIONS
• Mutation: any change in the nucleotide sequence of a DNA strand.
• 2 types:• Point mutations• Frame-shift Mutations
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POINT MUTATIONS• Base-substitution • 1 base (nucleotide) is substituted with another.
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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!
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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.
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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.
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WHAT CAUSES MUTATIONS?
• Mutagen: any physical or chemical agent that causes a mutation
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MUTATIONS
• 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
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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?