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