Download DNA, RNA, AND PROTEIN SYNTHESIS

DNA, RNA, AND
PROTEIN SYNTHESIS
Chapter 10
IMPORTANCE OF DNA
Why is DNA important?
• DNA contains the instructions for how the
cells of all living things construct proteins,
including enzymes.
• We have discussed how proteins and enzymes
are important to living things.
• Your skin, muscles, and bones are made of proteins.
• Any chemical reaction in your body requires enzymes,
which are proteins.
• DNA in universal
• Me, you, grass, ant, mushroom, pond scum…all based on DNA –
sugar, phosphate, bases…the bases are just in different orders!
Why do we study DNA?
• It is the central importance to all living things on
Earth!
• It is the answer to all those questions we ask…why do I look
like my parents, how do I get sick, will I get cancer, why do I
act the way I do???
• Medical benefits/biotech – cures for diseases,
understanding cancer and birth defects, genetic
testing, production of desired product (i.e. Insulin)
• Better food crops (?) GMO’s are genetically modified
organisms (usually food); taste better, grow larger
• CSI – DNA provides the evidence to prove a criminal’s
involvement in a crime
Genetic Engineering
• As genetics allows us to
turn the tide on human
disease, it's also granting
the power to engineer
desirable traits into
humans. What limits
should we create as this
technology develops?
• Genetics is our next unit…
HISTORY OF DNA
History of DNA
• There were many
experiments conducted
early in the 20th century
that provided evidence to
support that DNA, not
proteins or RNA, is the
genetic material in all
living cells.
• 1928 – Frederick Griffith
• 1944 – Avery, McCarthy,
& MacLeod
• 1950 – Erwin Chargaff
• 1952 – Hershey & Chase
• 1953 – Franklin & Wilkins
– Watson & Crick
History of DNA
• 1950 – Erwin Chargaff
• Proposes two rules regarding composition of DNA:
1. Number of complimentary bases is always equal in DNA
• #Cytosine always equal #Guanine
• #Adenine always equal #Thymine
• In human DNA, bases are always found in the following
percentages: A=30.9% and T=29.4%; G=19.9% and C=19.8%
• This data suggested the base pairing among DNA (although
Chargaff never stated it! He did tell Watson and Crick though!)
2. Composition of DNA varies from one species to another in the
relative amounts of A, G, T, and C bases. This evidence of
molecular diversity, which had been presumed absent from
DNA, made DNA a more credible candidate for the genetic
material than protein.
Chargaff’s Rules
Conclusion
• By 1952, the experiments of Griffith, Avery and his
colleagues, and Hershey and Chase led most
scientists to accept (based on the evidence we’ve
discussed) that DNA was the hereditary material of
living things.
• Chargaff also shed light on the composition of DNA.
• It was yet to be determined…
• The structure of DNA…
• How is replicates…
• How it has the ability to store and transmit information
in a cell…
History of DNA
• 1953 – James Watson, Francis
Crick, Rosalind Franklin, &
Maurice Wilkins
• Franklin & Wilkins discover
DNA is helical by use of X-ray
diffraction
• “Photo 51”
• Watson and Crick obtain the
famous photograph without
permission
• They are able to build a model of
DNA with help of photo and other
information
• They ALL published their findings
in the same issue of Nature.
1962 Nobel Prize winners – Physiology &
Medicine
• Rosalind Franklin died of ovarian cancer in 1958 at
the age of 37.
• Sadly, Nobel Prizes are only awarded to the living.
STRUCTURE OF DNA
DNA:
DEOXYRIBONUCLEIC ACID
Recall
4 classes of
macromolecules
1 class are
Nucleic Acids
Examples are
DNA & RNA
 Monomers are small units that make up larger
units called polymers.
 Nucleic acids are polymers. This means
DNA is a polymer.
 Who can remember what the monomer
of a nucleic acid is?
DNA Structure
• NUCLEOTIDES!
• Nucleotides have 3 parts:
1. Nitrogenous base
(there are 4 kinds)
2. Phosphate Group
3. 5 carbon sugar:
Deoxyribose
DNA Structure
• Nitrogenous bases:
• Contain nitrogen and is
a base
• Purines – double ringed
• Adenine (A)
• Guanine (G)
• Pyrimidines – single
ringed
• Cytosine (C)
• Thymine (T)
Hydrogen Bonding
• A purine (A or G) will easily form a hydrogen bond with a
pyrimidine (T or C). This is because of their structure and
the availability of bonding sites.
• Hydrogen bonds are weak but there are millions and
millions of them in a single molecule of DNA.
phosphate
One strand of
DNA is a long
polymer of
nucleotides.
One strand of
DNA has
many millions
of nucleotides!
nucleotide
deoxyribose
bases
DNA is Double-Stranded
• 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 is a Double Helix
• Double helix means
two sides twisted in a
spiral.
• Backbone –
alternating sugars
and phosphates.
• Bases down the
middle held together
by hydrogen bonds
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
Base Pairing Rules
Adenine
ALWAYS pairs with
Thymine
Cytosine
ALWAYS pairs with
Guanine
• Each pair contains one
single and one double
ringed base
• They “compliment” each
other
Complimentary Base
Pairing
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
ACTGGCTA
TGGCCAATATA
ACCGGTTATAT
DNA REPLICATION
DNA Replication
• DNA Replication is the process by which DNA is copied
during interphase of mitosis before the cell divides.
DNA Replication
• First, enzymes called
Helicases separate (or “unzip”)
the two strands of DNA
• Helicases break hydrogen
bonds
• The Y-shaped region formed
as bonds are broken is called
the replication fork
DNA Replication
• Next, enzymes called DNA
polymerases add
complimentary nucleotides to
the separated strands of DNA
• Nucleotides are found floating
freely in the nucleus
• The addition of new
nucleotides occurs in opposite
directions on each strand (one
toward the replication fork and
one away from it)
DNA Replication
• In Eukaryotes, several replication
forks form on the DNA and the
process 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!)
• When replication is finished, there are
2 DNA molecules, each has one old
strand and one new strand
• This is called semi-conservative
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 COULD 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
create new variations that may be
advantageous and lead to evolution.
UNDERSTANDING THE
GENETIC CODE
PROTEIN SYNTHESIS
Protein Synthesis
• DNA is the “code” for hereditary characteristics.
• The genetic code is how organisms store
hereditary information and translate it into amino
acids.
Protein Synthesis
• DNA codes for all of the bodies proteins
• Genes are sequences located in the DNA that code for
specific characteristics.
• For example, 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.
The Human Genome
• A genome is the complete genetic
content of an organism.
• HGP was an international research project with the
goal of determining the sequence of our base pairs in
DNA
• Started in October 1990 and completed in June
2000!
• Biologists have deciphered 3.2 billion base pairs in
the 23 human chromosomes
• These sequences code for about 22,000 genes
• We are still researching which sequences code
for which genes.
Protein Synthesis
• The “code” or “recipe” within DNA cannot
be read directly…
• DNA cannot leave the nucleus and
proteins are made by ribosomes 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 cell structures,
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
RNA & Protein
Synthesis
• RNA stands for:
Ribonucleic acid
• RNA directs protein
synthesis, which is
the making of
proteins from DNA
Comparing DNA & RNA
• Both are made of
nucleotides
• Both are needed for
protein synthesis
Comparing DNA vs RNA
DNA
RNA
• Double-stranded
• Single-stranded
• Sugar: Deoxyribose
• Sugar: Ribose
• Bases: A, T, C, G
• Bases: A, U, C, G
• Thymine
• URACIL replaces
Thymine
• Much shorter than
DNA
TYPES OF RNA
There are 3 types of RNA involved in protein
synthesis…
Messenger RNA
• Abbreviated: mRNA
• Carries the genetic
instructions from the
DNA to the ribosomes
Ribosomal RNA
• Abbreviated: rRNA
• Part of the ribosome
• Remember ribosomes make proteins
Transfer RNA
• Abbreviated:
tRNA
• Transfers the
amino acids to the
ribosomes to
make proteins
January 8, 2013
Core Objective
• How are DNA and
RNA different?
• Agenda: Notes, RNA
coloring
• Homework: RG,
Prelab
Catalyst
PROTEIN SYNTHESIS
If the instructions for making proteins are
housed in the nucleus in DNA, then there must
be a way for the instructions to get to the
ribosomes where proteins are made…
PROTEIN SYNTHESIS:
TRANSCRIPTION
Step 1: Transcription (to re-write)
DNA is too large to go from the nucleus to the
cytoplasm, so only pieces of DNA are copied into
RNA. This RNA then travels from the nucleus to
the cytoplasm.
Transcription
• Step 1:
• 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
• DNA begins to uncoil
Transcription
• Step 2:
• The RNA polymerase adds
complimentary nucleotides
resulting in a straight chain
RNA molecule
• The DNA code determines
what bases will be added
•A → U T → A G ↔ C
• For example:
ATCCGTT
• RNA: UAGGCAA
• *Remember, RNA does
not have thymine, it has
Uracil!!
• DNA:
Transcription
• Step 3:
• Copying of DNA continues
until the RNA polymerase
reaches a termination
signal
• 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
ribosome
Transcription - Overview
RNA polymerase –
starts unwinding the
DNA when it attached to
the “promoter” (specific
nucleotide sequence)
2. RNA polymerase –
adds RNA nucleotides
3. RNA polymerase –
stops when “termination
signal” (specific
nucleotide sequence) is
reached.
1.
Last slide – not in note outline
Before going on… let’s review
• Transcribe this DNA strand into mRNA:
ATTGGCTGCTTAGC
UAACCGACGAAUCG
PROTEIN SYNTHESIS:
TRANSLATION
Step 2: Translation (to make useful)
The RNA is then made into something useful, like
assembling amino acids into proteins in the
ribosome.
Translation
• Once the newly made mRNA
leaves the nucleus it attaches
to a ribosome at the promoter
region.
• Ribosomes will “read” 3
nucleotides in the mRNA code
at a time
• These 3 nucleotides are
called codons (or triplets)
• Each codon codes for either
an amino acid, a START
signal, or a STOP signal
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 not
have a start region for
protein synthesis
Translation
• So, in translation, the
mRNA 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
• 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
Translation
• There are only 20 amino
acids
• Most amino acids have
more than one 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
mRNA Codon Chart
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!)
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 - Overview
• Amino Acids are listed by their CODON!!!
• That would be the 3 nucleotide sequence on the mRNA
Protein Synthesis - Overview
•This is an mRNA
strand
•Figure out what the
DNA code was that
it came from
Protein Synthesis - Overview
A→T
U→A
C↔G
mRNA Strand:
AUG/ACG/GAG/CUU/CGG/AGC/UAG
DNA Strand:
TAC/TGC/CTC/GAA/GCC/TCG/ATC
Protein Synthesis - Overview
•Now figure out the anticodons
(which will be found on the
tRNA)
Protein Synthesis - Overview
A→U
U→A
C↔G
mRNA Strand:
AUG/ACG/GAG/CUU/CGG/AGC/UAG
tRNA Strand:
UAC/UGC/CUC/GAA/GCC/UCG/AUC
Protein Synthesis - Overview
•1 - UAC
•2 - UGC
•3 - CUC
•4 - GAA
•5 - GCC
•6 - UCG
•7 - AUC
Protein Synthesis - Overview
• Now use the CODON chart
to figure out the amino acid
sequence
• Remember to use the
codons from the mRNA to
determine amino acid
sequence.
Protein Synthesis - Overview
•1 – Methionine
(start)
•2 - Threonine
•3 – Glutamic Acid
•4 - Leucine
•5 - Arginine
•6 - Serine
•7 - STOP
Let’s Break the Genetic Code
1. Start with DNA:
TA C TA G C TAA C C
2. Write the complimentary strand for mRNA
AUGAUCGAUUGG
3. Identify the codons on the mRNA
AUG-AUC-GAU-UGG
4. Identify the anticodons on the tRNA
UAC-UAG-CUA-ACC
5. Identify the amino acid sequence from the mRNA
Met - Iso - Asp - stop
January 9, 2013
Core Objective
• How are DNA and
RNA different?
• Agenda: Notes, RNA
coloring
• Homework: RG,
Prelab
Catalyst
MUTATIONS
Genetic Mutations
• Any change in the DNA sequence is called
a mutation.
• Mutations can effect body cells
• Example = CANCER
• Mutations can effect reproductive cells
• These are called germline mutations and can
be passed from parent to child.
• If a child inherits a germline mutation from
their parents, every cell in their body will have
this error in their DNA.
• Germline mutations are what cause diseases
to run in families
Not All Mutations are BAD!
• Some mutations result in characteristics
that give the organism a greater chance of
survival.
• Example: Sickle cell anemia (deflated look of red
blood cells) is caused by a mutation, however it is
beneficial to people in Africa who often contract
malaria – the parasite can no longer attach to
their red blood cells, therefore they aren't affected
Genetic Mutations
• Types of DNA Mutations:
• Point
• Frameshift
• Inversion
Point Mutation
• A change in a single base pair in DNA
• Silent Mutation – changes a base pair, but no
change to amino acid sequence
• Example: CUU ( Leucine ) to CUC ( Leucine )
• Missense Mutation – changes a base pair,
therefore changing amino acids
• Example: AGU (Serine) to AGA (Arginine)
• Nonsense Mutation – changes a sequence to a
stop codon.
• Example: AGA (Arginine) to UGA (Stop)
Frameshift Mutation
• A single base pair in DNA is
deleted or added.
• Every codon after the deleted
or added base would be
different.
• This type of mutation can
make the DNA meaningless
and often results in a
shortened protein.
Inversion
• In an inversion mutation, an entire section of DNA
is reversed.
• A small inversion may involve only a few bases
within a gene, while longer inversions involve
large regions of a chromosome containing
several genes.
Examples
• Example:
• THE DOG BIT THE CAT.
• THE DOB ITT HEC AT.
• THE DOG BIT THE CAT.
• THE DOG BIT THE CAR.
• Frameshift
• Point
• The fat cat ate the wee rat.
• The fat tar eew eht eta tac.
• Inversion
Causes of Mutations
• Spontaneous:
• Mistake in base pairing during DNA replication
• Mutagen – agent that causes DNA change
• High energy radiation
• X rays
• Chemicals
• Dioxins, asbestos, benzene, cyanide, formaldehyde
• High temperatures
THE END
Some Great Resources
• DNA Replication animations:
• http://207.207.4.198/pub/flash/24/menu.swf
• http://www.ncc.gmu.edu/dna/repanim.htm
• Protein Synthesis animations:
• http://www.lewport.wnyric.org/JWANAMAKER/animations/Prot
ein%20Synthesis%20-%20long.html
• http://www.wisconline.com/objects/index_tj.asp?objID=AP1302
Some Great Resources
• http://nobelprize.org/educational_games/medicine/dna
_double_helix/index.html
• DNA games