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DNA Replication &
Protein Synthesis
• The student will investigate and
understand common mechanisms of
inheritance and protein synthesis.
• Key concepts include:
– f) the structure, function, and replication of
nucleic acids (DNA and RNA); and
– g) events involved in the construction of
proteins.
•
•
The student will investigate and
understand common mechanisms of
inheritance and protein synthesis.
Key concepts include:
– h) use, limitations, and misuse of genetic
information; and
– i) exploration of the impact of DNA
technologies.
History
• Before the 1940’s scientists didn’t know
what material caused inheritance.
• They suspected it was either DNA or
proteins.
History
• A series of experiments proved that DNA
was the genetic material responsible for
inheritance.
History
• In 1952, Alfred
Hershey and Martha
Chase did an
experiment using a
virus that infects E.
coli bacteria.
• The experiment
proved that DNA and
not protein is the
factor that influences
inheritance.
History
• Erwin Chargaff
discovered the base
pairing rules and ratios
for different species.
• Adenine pairs with
Thymine
• Cytosine pairs with
Guanine.
History
• Rosalind Franklin & Maurice Wilkins had
taken the 1st pictures of DNA using X-ray
crystallization
This proved that DNA had a helical
shape.
History
• The Nobel Prize in Medicine 1962
Francis Harry Compton Crick
James Dewey Watson
Rosalind Franklin
(Died of cancer 1958)
Maurice Hugh Frederick Wilkins
Watson
Crick
Wilkins has become a
historical footnote and
Watson & Crick are
remembered as the
Fathers of DNA
DNA
Phosphate
Group
O
O=P-O
O
Nitrogenous base
(A, T, G, C)
5
CH2
O
N
C4
Sugar
C1
(deoxyribose)
C3
C2
Nitrogen Bases
• 2 types of Nitrogen Bases
– Purines
PGA
• Double ring
–G & A
– Pyrimidines
• Single ring
–C & U & T
CUT PY
DNA - double helix
5
T
O
A
3
3
P
5
O 5
O
C
G
1
P
3
2
4
4
2
3
P
1
5
O
T
3
P
3
A
O
P
5
O
5
P
DNA
• The genetic code is a
sequence of DNA
nucleotides in the
nucleus of cells.
DNA
• DNA is a doublestranded molecule.
• The strands are
connected by
complementary
nucleotide pairs (A-T &
C-G) like rungs on a
ladder.
• The ladder twists to form
a double helix.
DNA
• During S stage in
interphase, DNA
replicates itself.
• DNA replication is
a semiconservative
process.
DNA
• Semi-conservative
means that you
conserve part of
the original
structure in the
new one.
• You end up with 2
identical strands of
DNA.
DNA
• Gene - a segment of
DNA that codes for a
protein, which in turn
codes for a trait (skin
tone, eye color, etc.)
• A gene is a stretch of
DNA.
DNA
• A mistake in DNA
replication is called a
mutation.
• Many enzymes are
involved in finding and
repairing mistakes.
Mutations
• What causes mutations?
– Can occur spontaneously
– Can be caused by a mutagen
• Mutagen: An agent, such as a chemical,
ultraviolet light, or a radioactive element,
that can induce or increase the frequency
of mutation in an organism.
Mutations
•
Some mutations can:
•
Have little to no effect
•
Be beneficial (produce organisms that are
better suited to their environments)
•
Be deleterious (harmful)
Mutations
• Types of mutations
– Point Mutations or Substitutions: causes
the replacement of a single base
nucleotide with another nucleotide
• Missense- code for a different amino
acid
• Nonsense- code for a stop, which can
shorten the protein
• Silent- code for the same amino acid
(AA)
Mutations
• Example: Sickle Cell Anemia
Mutations
• Types of mutations
– Frame Shift Mutations: the
number of nucleotides
inserted or deleted is not a
multiple of three, so that
every codon beyond the
point of insertion or deletion
is read incorrectly during
translation.
• Ex.: Crohn’s disease
Insertion
Deletion
Mutations
• Types of mutations
– Chromosomal Inversions: an entire section of
DNA is reversed.
– Ex.: hemophilia,
a bleeding disorder
DNA Repair
• A complex system of
enzymes, active in the G2
stage of interphase,
serves as a back up to
repair damaged DNA
before it is dispersed into
new cells during mitosis.
RNA
Phosphate
Group
O
O=P-O
O
Nitrogenous base
(A, U , G, C )
5
CH2
O
N
Sugar
(ribose)
C4
C3
C1
C2
RNA
• Function: obtain
information from
DNA & synthesizes
proteins
3 differences from DNA
1. Single strand
instead of double
strand
2. Ribose instead of
deoxyribose
3. Uracil instead of
thymine
3 types of RNA
1. Messenger RNA (mRNA)copies information from DNA
for protein synthesis
Codon- 3 base pairs that
code for a single amino
acid.
codon
3 types of RNA
2. Transfer RNA (tRNA)collects amino acids for
protein synthesis
Anticodon-a sequence
of 3 bases that are
complementary base
pairs to a codon in the
mRNA
3 types of RNA
3. Ribosomal RNA (rRNA)combines with proteins to form
ribosomes
Amino Acids
• Amino acids- the
building blocks of
protein
• At least one kind of tRNA
is present for each of the
20 amino acids used in
protein synthesis.
Transcription - mRNA is made from DNA
& goes to the ribosome
Translation - Proteins are made from the
message on the mRNA
Transcription
• In order for cells to make
proteins, the DNA code
must be transcribed
(copied) to mRNA.
• The mRNA carries the
code from the nucleus to
the ribosomes.
Translation
• At the ribosome,
amino acids (AA)
are linked together
to form specific
proteins.
• The amino acid
sequence is
directed by the
mRNA molecule.
Amino acids
ribosome
Make A Protein
• DNA sequence
ATG AAA AAC AAG GTA TAG
• mRNA sequence
UAC UUU UUG UUC CAU AUC
Make mRNA
• mRNA sequence
UAC UUU UUG UUC CAU AUC
• tRNA sequence
AUG AAA AAC AAG GUA UAG
Make mRNA
• tRNA sequence
AUG AAA AAC AAG GUA UAG
• Amino Acid sequence
met lys asn
lys
val stop
Human Genome Project
•
The Human Genome Project is a
collaborative effort of scientists around the
world to map the entire gene sequence of
organisms.
•
This information will be useful in detection,
prevention, and treatment of many genetic
diseases.
DNA Technologies
• DNA technologies
allow scientists to
identify, study, and
modify genes.
• Forensic identification
is an example of the
application of DNA
technology.
Gene Therapy
• Gene therapy is a technique for correcting
defective genes responsible for disease
development.
• Possible cures for:
– diabetes
– cardiovascular disease
– cystic fibrosis
– Alzheimer's
– Parkinson’s
– and many other diseases is possible.
Genetic Engineering
•
•
The human manipulation of the genetic
material of a cell.
Recombinant DNA- Genetically
engineered DNA prepared by splicing
genes from one species into the cells of
a different species. Such DNA becomes
part of the host's genetic makeup and is
replicated.
Genetic Engineering
•
Genetic engineering techniques are used in
a variety of industries, in agriculture, in
basic research, and in medicine.
This genetically
engineered cow
resists infections of
the udders and can
help to increase dairy
production.
Genetic Engineering
•
There is great potential for the development
of useful products through genetic
engineering
•
EX., human growth hormone, insulin, and pestand disease-resistant fruits and vegetables
Seedless
watermelons are
genetically
engineered
Genetic Engineering
•
We can now grow new body parts and soon
donating blood will be a thing of the past,
but will we go too far?
Photo of a mouse
growing a "human ear"