DNA Biology - De Anza College

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Dec 14, 2012 (4 years and 11 months ago)

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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


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