DNA & Protein Synthesis
Honors Biology
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.
Frederick Griffith
• Injected mice with different types
of pneumonia bacteria
• Results showed some type of
factor was transferred from killed
cells to live cells
• Griffith called this transformation
Oswald Avery
• Repeated Griffith’s idea to find
how transformation happens
• Result _ DNA was the factor
responsible for transformation
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 Replication
Step 1: Helicase unzips a molecule of DNA
@ the hydrogen bonds between base
pairs (breaking the H bonds).
Step 2: DNA polymerase joins individual
nucleotides to produce a DNA molecule
which is a polymer and it also “proofreads”
each new DNA strand
Step 3: Ligase links the two sections
together.
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.
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.
Transcription
• RNA polymerase binds to DNA (only to
promoters- sections that indicate it to bind
on DNA molecule) & separates the DNA
strands.
• Uses 1 strand as a template from which
nucleotides are assembled into a strand of
RNA.
• Signals (like promoters) tell it to stop
when RNA is complete.
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
Translation
• Begins when mRNA molecule in
cytoplasm attaches to ribosome.
• It begins at AUG (the start codon) which
always binds methionine (amino acid).
• The tRNA contains the anticodon whose
bases are complementary to a codon on
the mRNA strand.
• Then another tRNA comes into ribosome
and binds the next codon to anticodon.
Translation
• The ribosome will then bind the two amino
acids together, using peptide bonds, and
breaks the bond between methionine and
its tRNA.
• The tRNA floats away from the ribosome
allowing ribosome to bind another tRNA.
• The ribosome will move along mRNA
binding new tRNA molecules and amino
acids.
Translation
• Process continues until ribosome reaches
one of the three stop codons:
– UAA
– UAG
– UGA
Then it releases the formed polypeptide and the
mRNA molecule, completing translation.
Make A Protein
• DNA sequence
ATG TAC AAC AAG GTA ATT
• mRNA sequence
UAC AUG UUG UUC CAU UAA
Make mRNA
• mRNA sequence
UAC AUG UUG UUC CAU UAA
• tRNA sequence
AUG UAC AAC AAG GUA AUU
Make mRNA
• tRNA sequence
AUG UAC AAC AAG GUA AUU
• mRNA sequence
UAC AUG UUG UUC CAU UAA
• Amino Acid sequence
met lys asp
lys
val stop
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 : involves changes in
one or a few nucleotides that occur at a
single point in the DNA sequence.
• Substitutions- one base changed to
another
• Insertions- one base is inserted in the
DNA sequence
• Deletions- one base is removed from
the DNA sequence
Mutations
• Example: Sickle Cell Anemia
Sickle Cell Mutation
• Mutation in the haemoglobin gene
– Oxygen carrying protein found on red blood
cells.
Life expectancy is 50- 60 years
old!
Mutations
• Types of mutations
– Frame Shift Mutations:
changes the “reading
frame” of the genetic
message, so that every
codon beyond the point of
insertion or deletion is read
incorrectly during
translation.
• Ex.: Crohn’s disease
Crohn’s Disease
• Bacterial products activate inflammation in
digestive system causing
– Diarrhea
– Constipation
– Cramps
• Mutation in a gene that produces
kininogen protein.
• Mutation on Chromosome 16 too!
Insertion
Deletion
Huntington’s disease
• A progressive brain disorder that
causes uncontrolled
movements, emotional
problems, and loss of thinking
ability.
• Mutations in HTT gene causes
disease.
• HTT-produces huntingtin
protein.
– CAG trinucleotide repeat
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.
Mutations
• Many (most) are neutral and have little or
no effect.
• Polyploidy- a complete set of
chromosomes fails to separate during
meiosis, can produce gametes with:
– 3N (Triploid)
– 4N (Tetraploid)
Ex. Polyploid plants are larger and stronger
than diplid plants.
Gene Regulation
• Only a fraction of the genes in a cell are
expressed at a given time.
• Expressed gene- a gene that is
transcribed into RNA.
How does cell decided which will be
“expressed” and which will be “silent”?
Gene Regulation
• Certain DNA sequences serve as
promoters for DNA-binding proteins to
attach and they help to regulate gene
expression.
• There are “regulatory sites” next to the
promoter in which the action of these
proteins determines whether a gene is
turned on or turned off.
Gene Regulation
• Most Eukaryotic genes are controlled
individually and have regulatory
sequences
• Why is Gene Regulation Important?
Gene Regulation
• Regulation of gene expression is important
in shaping the way a complex organism
develops.
• Differentiation- cells don’t just grow and
divide during embryonic development they
become specialized in structure and
function.
Gene Regulation
• Hox genes- a series of genes that control
the differentiation of cells and tissues in
the embryo.
– A mutation in one of these “master control
genes” can completely change the organs
that develop in specific parts of the body.
– Ex. Fruit fly mutation can replace fly’s
antennae with legs growing on its head!
Human Genome Project
•
The Human Genome Project is a
collaborative effort of scientists around the
world to map the entire gene sequence of
humans.
•
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"