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 helicesDNA 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