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DNA BIOLOGY

DNA BIOLOGY. Double – stranded, twisted ladder Rungs are paired nucleotides Complementary pairing: hydrogen bonds A pairs with T G pairs with C Given any sequence, can write complementary strand. DNA Replication Copy in each cell Doubles before mitosis or meiosis Double helix unzips

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DNA BIOLOGY

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  1. DNA BIOLOGY • Double – stranded, twisted ladder • Rungs are paired nucleotides • Complementary pairing: hydrogen bonds • A pairs with T • G pairs with C • Given any sequence, can write complementary strand

  2. DNA Replication • Copy in each cell • Doubles before mitosis or meiosis • Double helix unzips • New complementary strand for each side  two helices DNA polymerase synthesizes new strands

  3. Transcription: DNA  mRNA • Translation: mRNA  protein • RNA Structure • Ribose instead of deoxyribose • Uracil instead of thymine • Single stranded

  4. TRANSCRIPTION • DNA unwinds – girase enzyme • Complementary mRNA synthesized by RNA polymerase • Specific sequences indicate start and stop points

  5. TRANSLATION • Nucleotide code  amino acids • Codon = triplet of nucleotides (64 different combinations) • Why three? 20 amino acids are possible • Transfer RNA (tRNA) is translator • One end has anticodon(complementary to codon) • Other end has correct amino acid

  6. Ribosomes • Two subunits lock together around mRNA • When “AUG” is found, Met-tRNA binds = initiation • Ribosome moves along mRNA • Amino acids added to chain = elongation • STOP codon ends protein chain = termination

  7. MUTATIONS • Changes in the sequence of DNA • Point mutation: one nucleotide • Some change protein, others don’t (silent) • UCU = serine UCC = serine UGU = cysteine • Addition or deletion of nucleotide = frameshift mutation • Disruptive because all downstream codons changed

  8. RECOMBINANT DNA • Genetic code same in all creatures • Genes can be moved to other creatures • Example: Eukaryotic genes that code for the molecule insulin – moved to bacteria • Cut: restriction enzyme • Paste: DNA ligase • Plasmid: small circular molecule of DNA found in bacteria

  9. Examples of Genetic Engineering • Plant crops: pest resistance, herbiside resistance • Farm animals: disease resistance, growth hormones, increased milk production • Environmental cleanup – bacteria that eat oil • Medicines and vaccines • Cloning from adults – would human clones be the same person?

  10. Forensic DNA Analysis • Polymerase chain reaction (PCR) • cell – free replication of DNA • Crime scene: blood spot, hair, skin cells, etc. • DNA fingerprint • Repeated sequences between genes vary for individuals • Restriction enzymes and electrophoresis

  11. CANCER: Growth of a Malignant Tumor • One cell breaks constraints of cell cycle • Multiplies out of control • Forms a mass of cells = tumor • If confined, benign; if spreading, malignant • At certain size, nutrients do not fuse to center • Tumor can make chemicals that stimulate formation of blood vessels

  12. Blood vessels bring nutrients; cells escape – metastasize. • Spread to lymph nodes, lungs • Death results from cncerous cells replacing normal cells, blocking blood vessels or air passages

  13. Rules that Cancer Cell Break • Divide only when called for • Divide 60 times maximum (telomeres) • Divide only when attached to solid surface • Suicide when DNA is damaged • Proteins (Genes) that Control Cell Division • Stimulators (growth factors) = proto- oncogenes • Inhibitors (p 53) = tumor suppressors • DNA damage to cells can change these genes

  14. Proto-oncogene  oncogene • Example: Growth factor overproduced • Inhibitor genes damaged  loss of tumor suppressor • Several mutations needed to cause cancer • Mutations accumulate throughout life • Genetic inheritance • Viruses • Chemicals that damage DNA or stimulate cell division = carcinogens • Radiation (cosmic rays, UV, radon, medical X-rays)

  15. TREATMENTS • Surgery – can cure if still early in disease, all cells removed • Radiation – can be directed to particular part of body; kills all rapidly dividing cells by DNA damage; side effects – nausea, sterility, hair loss, anemia • Chemotherapy – reaches all parts of the body; side effects similar to radiation • Experimental drugs and gene therapy

  16. PREVENTION • Quit smoking!!! • Less meat, more vegetables • Avoid sun exposure • Detect early: women breast exams, Pap smears; men – prostate checks

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