Download DNA Notes

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* 1866 – Mendel’s Laws of Heredity
* 1869 – Miescher discovers nuclein
* 1928 – Griffith discovers bacterial transformation
* 1944 – Avery et. al. reveals DNA carries genetic information
* 1950 – Chargaff develops base pairing rule
* 1952 – Hershey & Chase confirm Avery’s
* 1952 – Franklin produces images of DNA structure
* 1953 – Watson & Crick confirm and publish the DNA structure
* 1961 – Nierenberg “cracks” the genetic code
* 1984 – Jeffreys develops DNA fingerprinting
* 1990 to 2003 – Human genome project
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* Began studying white blood cells in 1869
* White blood cells are a major component of pus
* Collected pus samples from bandages at a local hospital
* Isolated a substance he called “nuclein” from the nuclei of
the white blood cells
* After chemical analysis, nuclein was later re-named DNA
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* In 1928, discovers bacterial transformation while
studying streptococcus pneumonieae.
* Tried to learn how certain types of bacteria caused
pneumonia
* He isolated two different strains
* S-strain:
* R-strain:
Smooth cells; caused pneumonia
Rough cells; harmless
* His experiments led to the discovery of substance known
as DNA
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* In 1944, repeated Griffith’s experiment with purified
cell extracts
* Discovered that the transforming principle is DNA
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* Discovered that DNA consists of 4 nitrogen bases
(Adenine, Guanine, Cytosine, Thymine)
* Adenine (A) always pairs with Thymine (T)
* Guanine (G) always pairs with Cytosine (C)
* Chargaff’s Rule
* The concentration of Adenine is equal to the
concentration of Thymine
* The concentration of Guanine is equal to the
concentration of Cytosine
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* Performed x-ray diffraction studies to identify
the 3-dimensional structure of DNA
* Discovered that DNA is helical
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* In 1953, described the structure of DNA as a
long double helix with a sugar-phosphate
backbone bonded to nitrogenous bases.
* They were awarded the Nobel Prize in 1962 for
their discovery.
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* Launched in 1990
* Goals:
* Identify all of the estimated 30,000 genes in the human DNA
* Determine the sequence of the 3 billion chemical base pairs
of DNA
* Storage of this information in databases for future analysis
* Address any legal, ethical, or social issues that arise from this
study
* Completed in April, 2003
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● DNA is located in the nucleus, tightly wound to form genes,
which are located on chromosomes
●DNA is described as a double helix (a twisted ladder)
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* DNA is a complex molecule made up of units
called nucleotides
* Nucleotides
* Sugar (deoxyribose)
* Phosphate
* Nitrogen Base (4)
* Adenine
Purines
* Guanine
* Thymine
Pyrimidines
* Cytosine
* DNA bases pair up in a specific way
*A – T
*G - C
* DNA is built like a twisted ladder, called a
double helix
* It is made up of 2 chains of nucleotides joined
together by weak hydrogen bonds
* Human cells contain about 6.6 billion base pairs in
their DNA
* The order of the bases makes up the genetic code
* Differences in the order of the bases is what makes
one species different from another
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*Pass on the genetic code
*Replication
*Codes for protein synthesis
*Making proteins
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* Each strand of the double helix has all the
information needed to make copies or
REPLICATE the DNA
* Sites where separation and replication occur
are called replication forks
* DNA helicase splits the 2 DNA strands at the
hydrogen bonds
* DNA polymerase joins individual nucleotides and
proofreads the base pairings as they form
* DNA ligase seals the two newly formed strands
together
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* DNA unwinds and unzips, the weak hydrogen bonds break
* Bases of the unzipped nucleotides are exposed to free
nucleotides also found in the nucleus
* New nucleotides attach to the exposed nucleotides from
the original parent strand
* DNA polymerase proofreads the newly formed strands
* Results in two new strands that are identical to each other
and to the original parent strand.
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* DNA holds the code for the making of proteins
* The monomers of proteins are amino acids
*Amino Acids
* There are 20 known amino acids
* 3 consecutive DNA bases act as the code for 1 amino acid
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this is known as a codon
* There are 64 possible codons
* Since there are only 20 amino acids, some amino acids are
represented by more than one codon
* Universal Code – a codon representing an amino acid in one
organism represents the same amino acid in another
organism
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*Protein synthesis occurs in the ribosomes.
Since the DNA code is locked up in the
nucleus, how does the code get to the
ribosome?
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* RNA is composed of nucleotides like DNA
* There are several differences between DNA and RNA
DNA
RNA
Sugar
Deoxyribose
Ribose
A pairs with
T (thymine)
U (uracil)
Appearance
Double stranded
Single stranded
Location
Nucleus
Nucleus,
Cytoplasm,
Ribosomes
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* DNA unzips and unwinds
* TRANSCRIPTION (takes place in the nucleus)
* The DNA code is transcribed to the RNA message
* RNA nucleotides called messenger RNA (mRNA) match up with the
exposed DNA nucleotides
* mRNA breaks away from the DNA in order to move through the
cytoplasm to the ribosomes
* TRANSLATION (takes place in the ribosomes)
* The RNA code is translated to correctly join amino acids
* RNA nucleotides called transfer RNA (tRNA) are bonded to amino acids
* tRNA located in the ribosomes brings amino acids to the mRNA
* Amino acids bond to each other to form protiens
*Codon = 3 base sequence of mRNA
*Anticodon = 3 base sequence of tRNA that
carry an amino acid
DNA
A
G
C
T
T
A
T
C
C
mRNA
(codon)
tRNA
(anticodon)
Amino
Acid
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* A mutation is a change in the DNA sequence
* An organism’s DNA affects how it looks, how it behaves, and
its physiology. Therefore, mutations serve as a source of
genetic variation
* Mutations are an essential mechanism of evolution; without
mutations, evolution cannot occur
* Mutations can affect organisms in three ways
* Beneficial: create traits to allow an organism to adapt/survive
* Detrimental: cause no functionality, disease or death
* Neutral: cause no harm and no benefit (most common)
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* Point Mutations
* Mutations that occur at a specific base pair in the
genome
* An exchange of one base for another
* Chromosomal Mutations
* One DNA fragment is moved from one site on the
genome to another
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* Substitution
* Silent/neutral mutation
* A new codon codes for the same or a similar amino acid as the
original; the protein remains unchanged
* Missense
mutation
* A new codon codes for a different amino acid; the protein is
slightly altered
* Nonsense mutation
* The new codon is a stop codon, creating a non-functional protein
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* Insertion/Deletion
* Insertion = adding in a base into the sequence
* Deletion = removing a base from the sequence
* A frameshift mutation
* A change in the reading frame of the mRNA
* Many amino acids may be changed
* Drastically alters the protein, unless a whole codon
is inserted/deleted
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* Causes of chromosomal mutations
* Spontaneous mutations
* Result from errors occurring during DNA replication that are not
corrected by DNA polymerase
* Caused by errors made during crossing over
* Induced mutations
* Caused by a mutagen (external factors that cause mutations)
* Radiation, Chemicals, Infectious agents (viruses)
* Physical mutagen – physically damage DNA strands
* Chemical mutagen – alter the molecular structure of DNA without
physically altering it
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* Translocation
* A fragment of one chromosome switches places with a
fragment of another chromosome
* Usually occurs between two non-homologous chromosomes
* Results in…
* The inactivation of genes
* The creation of a protein with a completely altered function
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* Inversion
* A section of a chromosome has reversed its orientation
* Results in…
* Inactivation or disruption of genes
* The gene may come under alternate control
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* Duplication
* A portion of a chromosome is replicated, resulting in multiple
copies of that region
* Results in…
* Disruption of genes
* May have no affect at all