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 –New complementary strand for each side  two helices DNA polymerase synthesizes new strands

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

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

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

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

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

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

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?

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

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

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

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

–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)

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

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