QOD 1/3/12
• What is the shape of DNA?
DNA, RNA, and Protein
Synthesis
Discovery of DNA
• 1928- Fredrick Griffith
– He found that when harmless
bacteria are mixed with dead
harmful bacteria, the harmless
will absorb the genetic material
of the harmful and become
harmful themselves
– Transfer of genetic material is
called transformation
Discovery of DNA
• 1940s- Avery and colleagues
– Wanted to know what caused
transformation (DNA, RNA, or
protein)
– They separated these
individual parts and tested
them.
– They found DNA was the
cause of transformation
– In other words, they found if
harmless bacteria took in
harmful bacteria’s DNA, the
harmless became harmful.
Discovery of DNA
• 1952- Hershey and Chase
– Wanted to test whether DNA or
protein was the genetic material
that viruses pass on when they
infect an organism.
– They used viruses that infect
bacteria (called bacteriophages)
– They radioactively labeled the
DNA and the protein (this allowed
them to trace the path of each)
– They found DNA was injected into
the bacteria to infect it, not protein.
So DNA was the genetic material
Discovery of DNA
• 1950s- Watson, Crick,
Franklin, and Wilkins
– Franklin and Wilkins
discover DNA is helical
– Watson and Crick build a
model of DNA and
determine it is a double
helix
DNA Structure
•DNA is a double helix
DNA Structure
• It is made of nucleotides
(so nucleotides are the
monomers of DNA!)
– Nucleotides have 3
parts:
1.Nitrogenous base
(there are 4 kinds)
2.Phosphate Group
3.5 carbon sugar
called deoxyribose
phosphate
deoxyribose
bases
nucleotide
DNA Structure
• Nitrogenous bases:
– Contain nitrogen and is
a base
– Purines- (double ringed)
• Adenine (A)
• Guanine (G)
– Pyrimadines- (single
ringed)
• Cytosine (C)
• Thymine (T)
DNA Structure
• DNA is made up of 2
straight chains of
nucleotides
• The bases on each of
those chains are attracted
to each other and form
hydrogen bonds
• The force of thousands or
millions of hydrogen bonds
keeps the two strands of
DNA held tightly together
DNA Structure
• If DNA was a spiral
staircase…
– The alternating sugar
and phosphates would
be the hand rails.
– The bases would be the
steps
– But, they would be
weak steps as they are
only held together by
hydrogen bonds
DNA models
• Since the sugarphosphate “hand rails”
of DNA never change,
we often simplify DNA
into the letters of the
nitrogenous bases.
• For example, this DNA
strand can be simplified
to…
TGAC
ACTG
DNA Structure
• Base pairing rules in DNA:
– Hydrogen bonds form between specific pairs
– Adenine ALWAYS pairs with Thymine
– Cytosine ALWAYS pairs with Guanine
– These pairs (A-T and C-G) are called
complementary base pairs
– Each complimentary pair contains one single
and one double ringed base
DNA Structure
• Because of the base pairing rules, one
strand of DNA is complementary to the
other strand (otherwise they would not
stick together!)
– So if one strand has a base sequence of
TGCC, the other strand will have ACGG.
Let’s Practice
• Right the complimentary DNA strand for…
TGACCGAT
ACTGGCTA
QOD 1/4/12
• Which scientists built the first model of
DNA?
DNA Replication
• DNA Replication is the process by which DNA is
copied in a cell before the cell divides.
DNA Replication
• First, enzymes called
Helicases separate the two
strands of DNA
– Helicases break hydrogen
bonds
DNA Replication
• Next, enzymes called DNA
polymerases add
complimentary nucleotides
to the separated strands of
DNA
– Nucleotides are found
floating freely in the
nucleus
DNA Replication
• When replication is
finished, there are 2 DNA
molecules, each had one
old strand and one new
strand
DNA Replication
• Replication is usually very accurate
– There is only about 1 error for every BILLION
nucleotides added!
– The reason is that DNA Polymerases also
“proofread” the DNA and fix any errors during
replication
DNA Replication
• If an error does occur, it results in a different
nucleotide sequence in the new DNA strands
– This is called a mutation
– A change in even one nucleotide can be very
harmful to an organism (for reasons we will see
later)
– Some mutations can affect the growth of cells,
causing growth to accelerate, this results in
cancer
– Changes can be good- mutations sometimes lead
to adaptations and therefore evolution
Protein Synthesis
• DNA is the “code” for hereditary
characteristics.
• The genetic code is how organisms store
hereditary information and translate it into
proteins
Protein Synthesis
• DNA codes for all of the bodies proteins (like
enzymes)
– Genes are sequences located in the DNA that
code for specific characteristics
– The code (or gene) for the production of the
protein melanin is in your DNA and creates your
hair and skin color
– The code or recipe for all of the enzymes that help
you digest your food is located in your DNA
Protein Synthesis
• The “code” or “recipe” within DNA cannot be
read directly– DNA cannot leave the nucleus and
proteins are made in the cytoplasm of cells
– So the code is transcribed (copied) and
translated (turned into something useful)
by ribonucleic acid (RNA)
Protein Synthesis
• Remember, proteins make us who we are
– They are responsible for chemical reactions
occurring in us (enzymes) and for the
hereditary characteristics that we have (such
as eye color)
– The building blocks (or monomers) of proteins
are amino acids
– DNA holds the recipe for the amino acid
sequence of all the proteins we need to make
Protein
Synthesis
• RNA directs
protein
synthesis, which
is the making of
proteins from
DNA
DNA vs RNA
• Both are made of nucleotides
• Both are involved in protein synthesis
• DNA has the sugar deoxyribose, while
RNA has the sugar ribose
• RNA uses the nitrogenous base uracil
instead of thymine (used in DNA)
• RNA is single stranded, while DNA is
double stranded
• RNA is usually MUCH shorter than DNA
Protein Synthesis
• There are several types of
RNA involved in protein
synthesis
– Messenger RNA (mRNA)
– carries the genetic
instructions from the DNA
to the ribosomes
Protein Synthesis
– Ribosomal RNA (rRNA) – part of the
ribosome
• Remember ribosomes make proteins
Protein Synthesis
– Transfer RNA
(tRNA) –
transfers the
amino acids to
the ribosomes to
make proteins
QOD 1/6/12
• What type of RNA carries the
genetic instructions from the DNA
to the ribosomes?
Protein Synthesis
- Transcription
• The first step in protein
synthesis is transcription:
– An Enzyme called RNA
polymerase binds to a
genes promoter region
• A promoter is just a
specific nucleotide
sequence where the
RNA polymerase can
attach
– The RNA attaches to the
RNA polymerase and the
DNA begins to uncoil
Protein Synthesis Transcription
• The RNA polymerase adds
complimentary nucleotides
resulting in a straight chain
RNA molecule
– The DNA code
determines what bases
will be added (A with U,
T with A, and G with C)
– For example if the DNA
code for a gene is
ATCCGTT, then the
RNA will be UAGGCAA
– Remember, RNA does
not have thymine, it has
Uracil!!
Protein Synthesis Transcription
• The copying of DNA
continues until the RNA
polymerase reaches a STOP
signal
– That is a specific sequence
of nucleotides that tells the
RNA polymerase to
“STOP” and release the
RNA and DNA
– The RNA is mRNA,
because it is the
messenger of the “code”
from the DNA to the
ribosomes
Let’s Practice
• What is the mRNA strand for the following
DNA sequences??
– DNA - ATCGGT
– mRNA - UAGCCA
Let’s Practice
• What is the DNA sequence that the
following mRNA strands came from??
– mRNA - GUCAUG
– DNA - CAGTAC
Protein Synthesis -
Translation
• Once the newly made RNA
leaves the nucleus it
attaches to a ribosome at
the promoter region.
• Ribosomes will “read” 3
nucleotides in the RNA
code at a time
– These 3 nucleotides are
called codons.
– Each Codon codes for
an amino acid, a START
signal, or a STOP signal
Protein Synthesis -
Translation
• For example, the
sequence AUG codes for
the amino acid Methionine
and means START
(it
is the only one that means
start)
– ALL mRNA molecules
start with AUG,
otherwise, they would
have a start region for
protein synthesis
Protein Synthesis -
Translation
• So, in translation, the
RNA is translated into
amino acids, which are
put together to form
proteins (or polypeptides)
• The translation occurs
with the help of tRNA,
which carries the amino
acids
Protein Synthesis -
Translation
• When the ribosome reads the
start sequence (AUG), a tRNA
molecule comes along with
the anticodon
– The anticodon is the
complementary sequence,
which would be UAC.
– The complementary bases
bond with each other and
the amino acid methionine
begins the protein synthesis
within the ribosome
– tRNA transfers amino
acids to the ribosome
Protein Synthesis -
Translation
• There are only 20 amino
acids
• Most amino acids have
more than on codon
– For example, Leucine’s
codons are UUA, UUG,
CUU, CUC, CUA, and
CUG
• But each codon codes for
ONLY 1 amino acid
– For example, CUU only
codes for Leucine and
nothing else
Protein Synthesis -
Translation
• After the start sequence,
the ribosome moves to the
next codon.
– Let’s say the next codon
is GUC
– Now a tRNA that has
the anticodon CAG
would attach to the
ribosome and it would
carry the amino acid
Valine.
– The amino acid Valine
would attach to the
Methionine from before
(now we have a
dipeptide!)
Protein Synthesis -
Translation
• This process continues
and the polypeptide
grows until the STOP
codon is reached
– UAA, UAG, and UGA
are the only stop
codons
– The protein, ribosome
and all RNA is
released to perform
other needed
functions
Protein Synthesis - Summary
• Let’s learn how to BREAK THE CODE!!
Protein Synthesis - Summary
•This is an mRNA strandfigure out what the DNA code
was that it came from:
Protein Synthesis - Summary
•1 - TAC
•2 - TGC
•3 - CTC
•4 - GAA
•5 - GCC
•6 - TCG
•7 - ATC
Protein Synthesis - Summary
•Now figure out the anticodons
(which will be found on the
tRNA)
Protein Synthesis - Summary
•1 - UAC
•2 - UGC
•3 - CUC
•4 - GAA
•5 - GCC
•6 - UCG
•7 - AUC
Protein Synthesis - Summary
• Now use the CODON
chart to figure out the
amino acid sequence
Protein Synthesis - Summary
•1 – Methionine (start)
•2 - Threonine
•3 – Glutamic Acid
•4 - Leucine
•5 - Arginine
•6 - Serine
•7 - STOP
QOD 1/11/12
• What is the amino acid for AUG?
Genetic Mutations
•
Can effect reproductive and body cells.
–
–
Reproductive cells: Offspring may have genetic
disease.
Body cells: Can cause cancer or may have no effect.
•
Can change the entire structure of a protein,
and effect the shape of the protein.
•
MYTH: All mutations are bad.
Point mutations
Occurs when a single base
changes. Types:
– Silent mutation- no
amino acid change
– Missense- changes
amino acid that is coded.
– Nonsense- changes
sequence to a stop
codon.
Frameshift mutations
• Frameshift is a shift in
the reading frame of
DNA sequence
• changes everything
“downstream” (after)
• Types:
– Insertions- adding
base(s)
– Deletions- losing
base(s)