Biology Chapter 5 Notes:
DNA, Gene Expression and Biotechnology
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Watson and Crick figured out the exact structure of the double helix deoxyribonucleic acid
(DNA)
DNA is a nucleic acid: consists of individual units called nucleotides; molecule of sugar +
phosphate group (4 oxygen atoms + phosphorus atom) + nitrogen-containing molecule called a
base (adenine, thymine, guanine, cytosine); 1 DNA molecule can have as many 200m base pairs
backbones of DNA: sugar + phosphate sequence
Base pairs: Adenine + Thymine / Cytosine + Guanine
Genes: sections of DNA that contain instructions for making proteins; sequence of bases in a
DNA molecule that carries the information necessary for producing a functional product (usually
a protein or RNA molecules) full set of DNA present is called a genome; DNA exists in
chromosomes; 23 unique pieces of DNA; two copies of each piece for a total of 46
Alleles: alternative versions of a gene that codes for a feature; any feature of that organism is a
trait
Not all DNA contains instructions for making proteins: in humans, genes make up less than 5% of
DNA; non-coding DNA may be referred as "junk DNA"
25% of non-coding DNA are within genes, 75% are between genes; these regions are called
introns
Genotype: carrier for a particular trait; Phenotype: the appearance of the dominating trait
From Gene to Protein: Transcription & Translation
Transcription: a copy of a gene's base sequence is made
1. Recognize and bind: the enzyme RNA polymerase recognizes a promoter site (a part of the DNA
molecule that indicates the start of a gene); RNA polymerase binds to the DNA molecule at the
promoter site and unwinds it just a bit so only one strand of DNA can be read
2. Transcribe: as the DNA strand is being processed by the RNA polymerase, the RNA polymerase
builds a copy (transcript); this copy is the messenger RNA (mRNA); it can move elsewhere in the
cell and its message can be translated into proteins; as the DNA is being replicated, it is being
rewound; mRNA transcript is constructed from 4 different molecules called ribonucleotides;
RNA polymerase transcribes a specific sequence of DNA; mRNA moves throughout the cell to
where then info is needed
3. Terminate: when RNA polymerase meets a sequence of bases on the DNA at the end of the gene
(termination sequence) it stops creating the transcript and detaches from the DNA molecule;
mRNA molecule is released as free-floating, single-strand copy of gene after termination
4. Capping and editing: prokaryotic cells are ready to make protein after mRNA transcript
separates from DNA; eukaryotes need to edit the transcript in several ways; a cap and tail may
be added to protect the mRNA from damage and help the protein-making machinery recognize
the mRNA; introns are snipped out if it is present; after editing, it leaves the nucleus for the
cytoplasm
Translation: the copy of the transcript is used for protein production
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begins when mRNA molecule moves out of the cell's nucleus and into the cytoplasm
requires large numbers of free amino acids floating around; ribosomal subunits (protein
production factories where amino acids are linked together in the proper order to produce the
protein); molecules that can read the mRNA code and transplate it (tRNA)
 Transfer RNA (tRNA): interprets the mRNA code and link specific base sequences on the mRNA
with specific amino acids; a particular amino acid is attached to one side and an attachment site
consisting of 3-base sequence that matches up with a 3-base sequence on the mRNA transcript;
each 3-base sequence in mRNA is called a codon;
1. Recognize and initiate protein building: begins in the cell's cytoplasm when the subunits of a
ribosome essentially a two-peice protein-building factory recognizes and assembles around a
start sequence on the mRNA transcript; start sequence is always AUG; subunits assemble
themselves into a ribosome, one side of a tRNA molecule also recognizes the start sequence on
the mRNA and binds to it; the initiator tRNA has the amino acid methionine; methionine is the
first amino acid in the protein produced (sometimes edited out)
2. Elongate: next codon on the mRNA specify which amino acid carrying tRNA molecule should
bind to the mRNA; ribosomes then facilitate the connection of the second amino acid to the
first; after this, the tRNA molecule floats away and a new tRNA attaches; this process is called
protein synthesis
3. Terminate: eventually the ribosome arrives at the 3-base sequence on the mRNA that signals
the end of translation; the assembly is complete once this happens; the amino acid sequence
folds and bends as it is produced based on the chemical features in the side chain; the original
mRNA strand might be translated a few times or a few hundred times; eventually the mRNA
strand is broken down by enzymes in the cytoplasm
Causes of Mutation
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Mutation: a sequence of bases in an organism's DNA is altered; can lead to changes in the
structure and function of the proteins produced; wide range of effects
Point Mutation: where one nucleotide base pair in the DNA is replaced with another, inserted,
or deleted; insertions and deletions can be more harmful than substitutions because the amino
acid sequence of a protein is determined by reading the codon on an mRNA molecule (if a single
base is added or removed, the 3-base groupings get thrown off and the sequence of amino acids
is stipulated "downstream" from that point will be all wrong)
Chromosomal aberrations: changes to overall organization of the genes on a chromosome;
manipulation of large chunks of data; can involve complete deletion of entire section of DNA,
moving of a gene from one part of a chromosome to elsewhere or duplication of a gene with the
new copy inserted elsewhere on the chromosome or on a different chromosome; can be altered
and affect the expression of the genes around it
1. Spontaneous mutations: arise by accident as long strands of DNA are duplicating themselves at
the rate of more than a thousand bases a minute in humans; most errors are repaired by DNA
repaired enzymes when cells are dividing
2. Radiation-induced mutations: ionizing radiation has enough energy to disrupt atomic structure
(even breaking apart chromosomes); X rays, UV rays, nuclear power plants
3. Chemical-induced mutations: many chemicals such as those found in cigarette smoke and
exhaust from internal combustion engines can react with the atoms in DNA molecules
Faulty Genes
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faulty genes can code for faulty enzymes and lead to sickness
Alcohol responses arise from this difference; can come down to a difference in a single base pair
in their DNA; cannot completely break down alcohol because of a defective gene that can not
synthesis aldehyde dehydrogenase enzyme
A mutated gene codes for a non-functioning protein; commonly an enzyme
The non-functioning enzyme can't catalyze the reaction as it normally would, bringing the
reaction to a halt
The molecule with which the enzyme would have reacted accumulates, just as half-made
products would pile up on a blocked assembly line
The accumulating chemical causes sickness and/or death
Biotechnology
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Genetic engineering: manipulation of organisms' genetic material by adding, deleting, or
transplanting genes from one organism to another
 Biotech: producing medicines to treat diseases, cure diseases, prevent diseases
1. Chop up the DNA from donor organism that exhibits the trait of interest; use of restriction
enzymes target a particular base-pair sequence on either side of the gene; restriction enzymes
bind to their target base-pair sequence and cut the strand of DNA; gene of interest is separated
from the donor's DNA
2. Amplify the small amount of DNA into more useful quantities; use polymerase chain reaction
(PCR) which allows a tiny piece of DNA to be duplicated repeatedly; DNA is heated which
separates the double-stranded DNA into separate, single strands; DNA is cooled and an enzyme
called DNA polymerase and a large number of free nucleotides are added to the DNA mixture;
DNA polymerase uses one of the two strands of DNA as a template to build a complementary
strand; process is repeated until there are billions of identical copies of the target sequence; can
also be done to amplify a DNA fragment with a specific sequence
3. Inserting foreign DNA into the target organism: transgenic organisms are created; researchers
have to physically deliver the DNA of interest into the recipient; often accomplished by using
plasmids (circular pieces of DNA that can be incorporated into a bacterium's genome); genes
might sometimes be incorporated into viruses which can be then used to infect organisms and
thus transfer the genes of interest to those species
4. Growing bacterial colonies that carry the DNA of interest: every time the bacterium divides, it
creates a clone; production of genetically identical cells, organisms or DNA molecules; a large
amount of DNA may be chopped up with restriction enzymes; all different bacterial cells
containing all of different fragments of the original DNA are called a clone library or gene library
5. Identifying bacterial colonies that have received the gene of interest: the gene library would be
in no particular order; hybridization uses a DNA probe that contains a small part of the
sequence of the gene of interest and has had some of its nucleotides modified that they carry
radioactive elements; bacteria are washed with a chemical that separates the DNA strands; the
radioactive probe is then washed over the single-stranded DNA; the complementary sequence is
then binded to the probe and will glow with radioactivity
Treatment Using Biotechnology
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Recombinant DNA technology: combination of DNA from two or more sources into a product;
Swanson, Boyer and Cohen used it for providing a source of insulin 1982
Human Growth Hormone: until 1994, HGH needed to be produced by extracting cadaver's
pituitary gland; now can use a similar bacteria technique as insulin
Gene therapy has had limited success: hard to get specific cells where it is needed; hard getting
the working gene into enough cells and at the right rate to ahve a physiological effect; problems
with the transfer of organisms getting into unintended cells
it is possible to test the baby to see if there will be a genetic disease; prenatal genetic screening
use some fetal cells or from umbilical cord
Biotechnology and Food
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beta-carotene found in rice plants inserted into rice for more vitamin A efficient rice
can be more ecofriendly and efficient through biotechnology; 45% of corn grown in U.S. is
genetically modified, 76% of cotton, 85% of soybeans
Insect resistance, herbicide resistance, faster growth
Has unanticipated consequences; organisms that we want to kill may become invincible (weedresistant canola plants spread to farms grew out of control); organisms that we don't want to kill
may be killed inadvertently (destruction of milkweed has affected monarch butterflies);
genetically modified crops are not tested or regulated adequately (results are still yet to be
known); eating G.M. foods is dangerous (hidden allergies to random foods); Loss of genetic
diversity among crop plants; hidden costs may reduce financial advantages (some of the seeds
to not grow again in the following year)
DNA as an Individual Identifier
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99.9% of the human DNA sequences are the same
Variable Number of Tandem Repeats (VNTRs): regions that vary; VNTR 1 might have a short
sequence of 15 to 100 bases that repeats over and over again; 14 repeats in one chromosome
while 3 repeats in the other chromosome (14/3); VNTR 2 might have 7/34; DNA fingerprinting
can be built by sampling 10 different VNTR regions
Projects
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human genome project: to decode 3 billion base pairs in humans and to identify all the genes
present in it; only 20,000 to 25,000 genes
building earth's family tree (phylogenetic trees): a way to group organisms
Dolly: isolate an egg cell from one sheep and a mammary cell from another while removing the
nucleus from the egg cell; fuse mammary cell including its nucleus with egg cell; initiate cell
division; grow embryo culture; place in surrogate mother sheep; surrogate mother gives birth to
cloned sheep from original egg cell