Download DNA, RNA and Protein Synthesis

DNA, RNA and Protein
Synthesis
Bell work
1. Which number is the Nucleus?
2. Which number are the ribosomes?
3. The endoplasmic reticulum?
4. What is the function of each?
5. Where is the DNA located?
1. 9
2. 4
3. 5/10
4. Nucleus stores DNA “brain” of the cell
Ribosomes aid in making proteins
ER aids in making proteins
5. In the nucleus
Discovery of DNA
Objectives
1. Describe the methods and
experiments that were used by
scientists in their search for the
hereditary molecule.
2. How did scientific experiments lead
the conclusion that DNA and NOT
protein is the hereditary molecule.
Griffith’s Experiments
• Griffith was studying the bacteria that
caused pneumonia to find out how it
made people sick.
– He was also trying to come up with a
vaccine against the VIRULENT strain of the
bacteria.
– S type bacteria are protected from our
bodies’ immune system by a sugar that
surrounds them
– R Type are not
Griffith Explained
• First he did what we call a control for his
experiment – he injected one group of
mice with one type of bacteria and
another group with the other to see
what would happen.
– The group injected with the R type lived. 
– The group injected with the S type died. 
Griffith Continued
• Next he killed the S type bacteria by
heating it up to 60 degrees centigrade
– This is hot enough to change the shape of
proteins but not hot enough to do the
same to DNA!
• When the shape of the protein is changed it
will not function the same way!!!
• After he killed the S type bacteria he
injected it into a third group of mice
– They lived 
Griffith Continued
• Finally in a fourth test he mix the heat
killed (h-k) S type and the normal R
type and injected the mixture in to a
fourth group of mice.
– They died. 
Griffith Conclusion
• Griffith figured that when he killed the S type
whatever causes characteristics to be
passed from parent to offspring was still alive
and got into the R type bacteria
• Because this was not parent to offspring delivery
of this information we call it TRANSFORMATION
– Latin: trans – to cross; forma – a form; Transforma – to
change form
• The hereditary molecule was now outside the h-k
S type bacteria and made its way into the R type
bacteria which allowed the R type to transform
into the S type bacteria!
Griffith’s Experiment
Avery’s Experiments
• 1940’s America
– Wanted to find out if it was DNA, RNA or protein
that caused Griffith’s transformation
– Used three different enzymes to destroy these
molecules in three different batches of h-k S type
bacteria
• Group 1: H-k S type w/ Protease (destroys protein)
• Group 2: H-k S type w/ RNase (destroys RNA)
• Group 3: H-k S type w/ DNase (destroys DNA)
– Then mixed the heat killed S types with the normal
R type and injected three different groups of mice
• Group 1 and 2 died  Group 3 lived 
Avery’s Conclusion
• The groups with the destroyed protein
and RNA were still able to pass on
hereditary information that caused the
mice to die
• The group with the destroyed DNA did
not kill the mice
• So it MUST be the DNA that is the
hereditary molecule.
Hershey-Chase Experiment
• 1952 America
– Martha Chase and Alfred Hershey wanted
to confirm that DNA was the hereditary
molecule
• Used bacteria and bacteriophages (phages)
• Group 1: radioactive phosphorus used to identify
DNA injected into phages
• Group 2: radioactive sulfur used to identify
protein injected into phages
• Each group was allowed to infect a group of
bacteria
Hershey-Chase Conclusion
• When the bacteria was examined
after the infection, it was found that
ALL of the viral DNA and only a little
protein made it into the bacteria
QUIZ
1. Griffith’s experiment with pneumonia
bacteria in mice showed that harmless
bacteria could turn virulent when mixed
with h-k bacteria that cause disease.
True or False?
2. Avery’s experiments clearly
demonstrated that the genetic material
is composed of DNA. True or False?
3. The experiments of Hershey and Chase
cast doubt on whether DNA was the
hereditary material. True or False?
They confirmed that DNA was hereditary material in viruses
DNA STRUCTURE
Objectives
1. Describe the discovery of DNA’s
double helix structure.
2. Describe the structure of DNA and
nucleotides.
3. Explain base pairing.
DNA Double Helix
• By the 1950’s it was accepted that
DNA was the hereditary molecule but
we still didn’t know what it looked like
or how it worked
DNA Double Helix
• 1953 American James Watson and
Englishman Francis Crick complete their
work on the structure of DNA
– For years they came close but couldn’t quite
get the right structure without convincing
Maurice Wilkins to steal Rosalind Franklin’s X-rays
to give to them.
– They concluded that the structure was a double
helix which also help explained how the
molecule could replicate itself.
– In 1962 Watson, Crick and Wilkins won the Nobel
Prize in Physiology or Medicine.
DNA Nucleotides
• DNA is made of repeating sub units
called NUCLEOTIDES.
• Each NUCLEOTIDE has three parts
– Deoxyribose (five carbon sugar; yellow part
of our model)
– Phosphate group (white part of our model)
• Phosphorus and oxygen covalently bonded
together
– Nitrogenous base (blue, orange, red and
green parts of our model)
• Made of nitrogen and carbon atoms
DNA: How it’s held together
• Deoxyribose and phosphate alternate
on the sides
– These are held together by a covalent
bond
• The Nitrogenous bases (bases) face
the center and join the two strands in
the middle
– They are held together by hydrogen
bonds
Nitrogenous Bases
• Four different kinds
– Adenine (A)
– Thymine (T)
– Guanine (G)
– Cytosine (C)
• If they have a double ring they are
PURINES (A and G)
• If they have a single ring they are
PYRIMIDINES (T and C)
Complementary Bases
• 1949 American Erwin Chargaff
– Observed that in a many different
organisms the amount of Adenine
matched the amount of Thymine and that
the amount of Cytosine matched the
amount of Guanine
• This gave us the BASE-PAIRING RULES and
helped us even more understand what DNA
looked like.
• One complementary base pair contains one
purine and one pyrimidine (A-T, G-C)
• If one strand of DNA is GATTACA then the other
is CTAATGT
Complementary Bases
• Bases are held together by hydrogen
bonds which are not very strong this
allows for the DNA to split and one side
of the DNA to act as a template for
creating a new complementary
strand.
DNA Models
• We have many different ways to
model the structure of DNA
– One you have been staring at during this
entire power point!
– Another you made and is hanging from
the ceiling!
– A third is just using the letters of the base
pairs: ATTCTC
TAAGAG
Quiz
1. What does the abbreviation DNA
stand for?
2. Distinguish between purines and
pyrimidines.
3. What was the significance of Franklin
and Wilkins’s X-ray diffraction
photographs regarding DNA
structure?
Answers
1. DNA = deoxyribonucleic acid
2. Purines are nitrogenous bases made of
two rings of carbon and nitrogen atoms;
Pyrimidines are nitrogenous bases made
of a single ring of carbon and nitrogen
atoms.
3. Their photographs suggested that the
DNA molecule resembled a tightly
coiled helix and was composed of two
or three chains of nucleotides.
DNA Replication
Objectives:
1. Describe the steps in DNA replication
2. Describe the differences between
prokaryotic and eukaryotic DNA
replication
3. Explain the accuracy of replication
and how errors are corrected.
4. Relate mistakes in DNA replication to
cancer
How DNA Replication Occurs
Before we get started you need to know
this: anything that ends in –ase is an
enzyme, used to either break
something apart or put something
together
1. HELICASE brakes the hydrogen bonds
holding the base pairs together
creating a “Y” shape to the DNA, this
is called a REPLICATION FORK
How DNA Replication Occurs
2. DNA polymerases add complementary
nucleotides to each of the original
strands
3. The DNA polymerases release from the
DNA and two new and identical strands
of DNA are left ready for cell division
• In each new double helix there is one
original strand and one new one – SEMICONSERVATIVE REPLICATION
Action at the Replication Fork
• Replication happens in opposite
directions for each strand
– One side of the DNA will be copied and
follow the direction of the replication fork
– The other strand will be pieced together
and seemed by an enzyme called DNA
ligase
Prokaryotic vs Eukaryotic
Replication
• Recall the shape of prokaryotic DNA
and that of eukaryotic DNA
• In prokaryotes there are ONLY TWO
replication forks and they move in
opposite directions until they meet
Prokaryotic vs Eukaryotic
Replication
• In eukaryotes DNA polymerase adds
new nucleotides at 50/second
– if there were only two spots where
nucleotides were being added it would
take 53 days for our DNA to copy!!!
– Replication begins at thousands of
locations on a eukaryotic DNA molecule
DNA Errors in Replication
• Errors occur once for every BILLION
paired nucleotides!
– This is AMAZINGLY ACCURATE!!!
• DNA polymerase not only adds
nucleotides to the growing strand it
ALSO proofreads for errors!
• When an error does happen we call
this a MUTATION
– This has potential to change or harm the
cell’s function
DNA Errors in Replication
• Some errors do not get fixed some can
be caused by UV light or chemicals
• Some mutations can lead to cancer
DNA Replication and Cancer
• If DNA is not replicated correctly a number
of things can happen
1. Nothing at all
2. A mutation that allows the organism to survive
and reproduce better
•
This mutation will usually become more common in
a population
3. The mutation could be harmful
•
One type of harmful mutation is cancer. If the
genes for controlling replication are changed a
cell could begin to reproduce uncontrollably,
creating a tumor
Quiz
1. How is the exact replication of DNA
ensured?
By complementary base pairing and
“proofreading” by DNA polymerase
2. What are replication forks?
Areas of DNA where the double helix
separates prior to replication
Assignment
• Illustrate DNA replication in six steps
– You must label each drawing
• Step one – strand of DNA before replication
• Step two – helicase attaches and unwinds DNA
(show replication fork!)
• Step three – polymerase attaches
• Step four – polymerase adds nucleotides (don’t
forget one strand get added normally and the other
gets added backwards.
• Step five – show ligase mending backwards added
strand
• Step six – show semi-conservative replication of
strands
Protein Synthesis
Objectives:
1. Describe how DNA contains the instructions
for the building of proteins
2. Describe the function and three forms of
RNA
3. Describe how proteins are transcribed
4. Describe the role of each form of RNA in
the steps of translation
5. Describe the importance of studying the
genetic code