dna biology double – stranded, twisted ladder rungs are paired nucleotides complementary pairing:...
TRANSCRIPT
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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
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• 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
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• Transcription: DNA mRNA
• Translation: mRNA protein
• RNA Structure – Ribose instead of deoxyribose– Uracil instead of thymine– Single stranded
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TRANSCRIPTION
• DNA unwinds – girase enzyme
• Complementary mRNA synthesized by RNA polymerase
• Specific sequences indicate start and stop points
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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
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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
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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
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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
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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?
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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
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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
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• 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
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• 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
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– 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)
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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
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PREVENTION
• Quit smoking!!!
• Less meat, more vegetables
• Avoid sun exposure
• Detect early: women breast exams, Pap smears; men – prostate checks