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DNA Replication


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DNA Replication

  1. 1. Introduction to DNA & RNA Replication Transcription Translation
  2. 2. Why Did Caesar Die?The Roman emperor Claudius Caesar (10 B.C.– A.D. 54) had an appetite for the delicate taste of mushrooms. Historians believe that Caesar’s wife, Agrippina, wanted to poison him. She mixed into Caesar’s favorite dish of mushrooms a few of the poisonous species Amanita caesarea. These poisonous mushrooms contain a substance that blocks the activity of an enzyme required for the cells to transcribe messenger RNA from DNA.For the first 10 hours after Caesar ate the mushrooms, all seemed well as the mushroom poisons entered the blood stream and were absorbed by the liver and kidneys. About 15 hours after eating the mushrooms, Caesar’s liver cells stopped functioning. Nausea, diarrhea, and delirium affected him as his liver and kidneys could no longer filter and detoxify wastes and other harmful substances from the blood. He died two days later from liver failure.
  3. 3. DNA (Deoxyribonucleic Acid) DNA holds the instructions for all cell functions and all production of proteins Chromosomes are just tightly wound and packaged strands (molecules) of DNA DNA is made up of repeating segments called nucleotides
  4. 4. DNA Nucleotide Nitrogenous bases: Adenine Guanine Thymine Cytosine  Every living thing on earth shares these same 4 nucleotides
  5. 5. Nucleotide Sequence An elk, elm and eel all have the same four nucleotides that make up their DNA Like the letters in their names, the order (or sequence) of their nucleotides determine different traits that result in very different organisms being produced
  6. 6. DNA Base-pairing•DNA is made from 2 rows of side-by-sidenucleotides arranged in a specific order• DNA has specific pairing between the bases:  Guanine must pair with Cytosin  Adenine must pair with Thymine
  7. 7. DNA StructureP G CP T P AP C G P H-bonds P
  8. 8. DNA Double Helix Nitrogenous bases form the “rungs” of the DNA “ladder” 1. Adenine (A) 2. Guanine (G) 3. Thymine (T) 4. Cytosine (C)
  9. 9. DNA Replication In order for cells to reproduce (make more of themselves), DNA must be copied Each of the 46 strands of the original DNA serve as a template for new copies A single strand of human DNA, stretched out, would be about 6 feet long, containing over 80 million base pairs That’s about 46,000 books worth of information in 1 cell! With incredible accuracy, all of a cell’s DNA can be replicated in about one hour
  10. 10. Replication First, DNA strands are unwound and enzymes “unzip” the molecule Next, new nucleotides are added according to base pairing rules This occurs simultaneously at many different places along a single strand of DNA Parental DNA New DNA Templates
  11. 11. DNA Replication Video
  12. 12. REPLICATION: DNA is copied A codon is a 3-nuceotide segment which signals something • Start and stop codons signal where replication can begin and end.
  13. 13. Think of it this way… Replication • Making exact copies • DNA  DNA • Like a copy machine
  14. 14. DNA Replication Quiz1. Why is replication necessary? So both new cells will have the correct DNA2. When does replication occur? During Interphase (S phase). A---? T3. Describe how replication works. G---? C Enzymes unzip DNA and complementary C---? G nucleotides join each original strand. T---? A4. What happens to the original DNA? A---? T It serves as a template and half is incorporated G---? C into each of the two new strands. A---? T5. Use the base pairing rule to T---? A create the complementary strand:
  15. 15. Transcription - portable copies During Interphase G1 or G0 (normal cell function), DNA supplies the “codes” for proteins to be built DNA first must be transcribed into smaller mRNA segments, serving as portable copies Why? • Smaller segments are easier to move around • Sending strands 80 million nucleotides long would be inefficient (might be too long to find the “start”) • It’s safer to send a copy than the original
  16. 16. RNA vs. DNA Ribose instead of deoxyribose Uracil instead of Thymine Shorter strands Single-stranded
  17. 17. TRANSCRIPTION: DNA to mRNA mRNA = “messenger” RNA DNA partially “unzips” mRNA nucleotides line up on one side to form a matching mRNA strand RNA retains DNA sequences • Uracil replaces Thymine when matching with Adenine mRNA takes the code to ribosomes in the cytoplasm
  18. 18. Think of it this way… Transcription • Same information, portable packaging • DNA  RNA • Like Bible-time scribes
  19. 19. Transcription Quiz1. Why is transcription necessary? Shorter mRNA strands are copied from DNA to carry codes to ribosomes outside the nucleus. A-- U2. Describe transcription. C-- G DNA strands separate, then one side is used as a template to assemble mRNA nucleotides. C-- G3. What are the main differences between G-- C DNA and RNA. T-- A RNA has ribose instead of deoxyribose; DNA has C-- G 2 strands while RNA has one; RNA has uracil instead of thymine and RNA has shorter strands. A-- U4. Use base pairing rules to create an C-- G mRNA strand from this DNA template: G-- C
  20. 20. TRANSLATION: mRNA to Protein Messenger RNA carries the pieces of copied genetic code out of the nucleus to a ribosome mRNA is “fed” into the ribosome Ribosome helps tRNA "read” the code and assemble a protein
  21. 21. Transfer RNA - tRNA tRNA = “transfer” RNA One tRNA molecule is composed of ~ 80 nucleotides, three exposed nitrogen bases (the anticodon) and one amino acid tRNA anticodons match up with tRNA mRNA codons inside a ribosome molecule As each tRNA molecule binds to an mRNA codon, its amino acid is Amino dropped off and linked together acids These assembled amino acid chains (polypeptides) fold into specific shapes to become new proteins anticodon The order of amino acids determines what kind of protein is made codon mRNA
  22. 22. mRNA Amino Acid “codes” U C A G UUU Phenylalanine UCU UAU Tyrosine UGU Cysteine U UUC (Phe) UCC UAC (Tyr) UGC (Cys) C SerineU UUA UCA (Ser) UAA Stop UGA Stop A UUG UCG UAG Stop UGG Tryptophan (Trp) G CUU Leucine CCU CAU Histidine CGU U CUC (Leu) CCC CAC (His) CGC C Proline ArginineC CUA CCA (Pro) CAA CGA (Arg) A Glutamine CUG CCG CAG (Gln) CGG G AUU ACU AAU Asparagine AGU Serine U Isoleucine (Asn) (Ser) AUC ACC Threonine AAC AGC CA (Ile) AUA ACA (Thr) AAA AGA A Lysine Arginine AUG Methionine (Met) ACG AAG (Lys) AGG (Arg) G GUU GCU GAU Aspartic Acid GGU U GUC GCC GAC (Asp) GGC C Valine Alanine GlycineG GUA (Val) GCA (Ala) GAA GGA (Gly) A Glutamic Acid GUG GCG GAG (Glu) GGG G
  23. 23. How Cells make Proteins mRNA copies small segments of DNA and carries the code out of the nucleus to the ribosomes  mRNA is fed through ribosomes in cytoplasm  tRNA match up with mRNA codons (inside ribosomes) and drop off amino acids  Ribosomes bond amino acids together to form proteins
  24. 24. Translation Quiz1. Why is translation necessary? It makes sure the right amino acids are joined together to form the correct protein.2. Describe translation. Information from mRNA is used to produce proteins during normal cell functions.3. What are codons? mRNA segments containing 3 nucleotides that code for a specific amino acid.4. Using a chart, identify the amino acids coded for by this mRNA strand: UGG - tryptophan CAG - glutamine UGGCAGUGC UGC - cysteine
  25. 25. Think of it this way… Translation • Information changes forms • RNA  Protein • Like translating English to French or translating blueprints into a building
  26. 26. A helpful way to remember… Replication • Making exact copies • DNA  DNA • Like a copy machine Transcription • Same information, new packaging • DNA  RNA • Like sticky notes Translation • Genetic info interpreted • RNA  Protein • Like translating English to French or translating blueprints into a building