dna biology
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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