Download DNA, RNA, and Protein Synthesis

DNA, RNA, and Protein
Synthesis
Chapter 10
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
• 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)
– Pyrimidine's- (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 models
• Since the sugarphosphate “backbone”
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!)
– The order of the nitrogenous bases on DNA is
called its base sequence
– So if one strand has a base sequence of
TGCC, the other strand will have ACGG.
Let’s Practice
• Write the complimentary strand for…
TGACCGAT
TGGCCAATATA
END DAY 1
DNA Replication
• DNA Replication is the process by which DNA is
copied in a cell before the cell divides.
DNA Replication
• Step 1:
Enzymes called Helicases separate the two strands of
DNA
• Hydrogen bonds are broken
• Replication fork: Y-shaped region formed as bonds are broken
DNA Replication
• Step 2:
Enzymes called DNA polymerases add
nucleotides to the separated strands
• Nucleotides are found floating free in the nucleus
• The addition of new nucleotides occurs in opposite
directions
addition towards
the replication fork
addition away
from the
replication fork
DNA Replication
• In Eukaryotes, several replication forks form and
replication continues until all of the DNA has been
replicated.
– If only 1 was formed it would take too long to replicate DNA (53 days for
humans!!)
• Once replication is complete, 2 DNA molecules
exist.
– Each molecule is made from one old strand and one new
• This is called semi-conservative replication since each new
strand has kept one of the original strands.
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
“proof-reads” the DNA and fixes any errors during
replication
DNA Replication
• If an error does occur, it results in a different
nucleotide sequence in the new DNA strands called
a mutation
– A change in even one nucleotide can be very
harmful to an organism
– Some mutations can affect the growth of cells,
causing growth to accelerate, resulting 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 which is first translated
into amino acids
• DNA codes for all of the body’s proteins (like enzymes)
Protein Synthesis
– Genes are sequences located in 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
Protein Synthesis
However,
• 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
– Responsible for
• chemical reactions
• hereditary characteristics (such as eye color)
– Recall the monomers of proteins are amino
acids
– DNA holds the recipe for the amino acid
sequence of all the proteins we make
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 (U)
instead of thymine (T) used in DNA
• RNA is single stranded, while DNA is
double stranded
• RNA is usually MUCH shorter than DNA
END DAY 2
Protein Synthesis
• There are three major
types of RNA
– Messenger RNA (mRNA)
– carries the genetic
instructions from the DNA
to the ribosomes
Protein Synthesis
– Ribosomal RNA (rRNA) – part of the
structure of ribosome
• Remember ribosomes make proteins
Protein Synthesis
– Transfer RNA
(tRNA)
– transfers the
amino acids to
the ribosomes to
make proteins
Protein Synthesis
Transcription
• The first step in protein
synthesis is transcription:
– RNA polymerase (enzyme)
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
Transcription cont.
• The RNA polymerase adds
complimentary nucleotides
resulting in a straight chain
RNA molecule
– The DNA code
determines what bases
will be added
– 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!!
Transcription cont.
• The copying of DNA
continues until the RNA
polymerase reaches a
termination signal
– That is a specific sequence
of nucleotides that tells the
RNA polymerase to
“STOP” and release the
RNA and DNA
– The RNA is called mRNA,
because it is the
messenger of the “code”
from the DNA to the
ribosomes
END DAY 3
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
• START signal
• Amino Acid
• STOP signal
Translation cont.
• Example, the sequence
AUG codes for the amino
acid Methionine a START
signal (This is the only
start signal)
– ALL mRNA molecules
start with AUG,
otherwise, they would
not have a start region
for protein synthesis
Translation cont.
• 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
Translation cont.
• When the ribosome reads the
start sequence (AUG), a tRNA
molecule comes along with
the anticodon
– The anticodon is the
complementary sequence.
– The complementary bases
bond with each other and
the amino acid methionine
begins the protein synthesis
within the ribosome
– So, tRNA transfers amino
acids to the ribosome
Amino Acids
• Recall there are only 20
amino acids
• Most amino acids have
more than one codon
– Example, Leucine’s
codons are UUA, UUG,
CUU, CUC, CUA, and
CUG
• But each codon codes for
ONLY 1 amino acid
– Example, CUU only
codes for Leucine and
nothing else
Translation cont.
• 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 for that
codon attaches to the
ribosome carrying the
amino acid Valine.
– The amino acid Valine
attaches to the
Methionine from before
(now we have a
dipeptide!)
Translation cont.
• 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 - Overview
• Amino Acids are listed by their CODON!!!
– That would be the 3 nucleotide sequence on the
mRNA
Protein Synthesis - Overview
• Now use the CODON
chart to figure out the
amino acid sequence
Protein Synthesis - Overview
•1 – Methionine
(start)
•2 - Threonine
•3 – Glutamic acid
•4 - Leucine
•5 - Arginine
•6 - Serine
•7 - STOP
Some Great Resources
• http://nobelprize.org/educational_games/me
dicine/dna_double_helix/index.html
– DNA games