DNA Guided Notes – Pre-AP
Early DNA Experiments Section
(1) Frederick Griffith – 1928
Griffith’s experiments showed that hereditary material can __________________________________
_____________________________________.
 In 1928 Griffith was studying a bacterium called Streptococcus pneumoniae. He was trying to
__________________________________________ against a virulent strain of the bacterium.
 _____________ – disease causing
 _____________– a substance that is prepared from killed or weakened microorganisms
& introduced into the body to protect it from future infection by that microorganism.
 S bacteria is ___________________ because it has a ___________________. The capsule
protects it from attacks by the __________________________________. It is able to survive
long enough in the human body to ________________________________________.
 R bacteria is __________________________ because it lacks a___________________. Without
the capsule it is left defenseless against the human immune system. Therefore it is destroyed in
the human body _____________________________________________________.
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Griffith’s experimental procedure
Injected mouse with ________________________________ (w/o capsule).
 DID NOT kill mice
Injected mouse with ________________________________ (w/ capsule).
 Killed mice
Injected mouse with ________________________________.
 DID NOT kill mice
Injected mouse with _____________________________________________________________.
 Killed mice
Griffith’s Conclusion
The R bacteria ___________________________ found in the ________________________ and
became ___________________________________.
The transfer of genetic material from ____________________________________ or from one
organism to another organism is called _____________________________.
We utilize bacteria’s ability to do this in one form of __________________ – the use of biology
for human benefit (we will study this subject in more detail at the end of the unit once you have
gained an understanding of how DNA works)
(2) Chargaff - 1950
• Discovered that ______________________________ and _____________________________
occurred in equal percentages in DNA.
• For Example: If you had ___ Adenine and ____ Cytosine then you would have ____ Thymine and
___ Guanine.
• Led to base pairing discovery (that A pairs with T and that C pairs with G)
• The structure of DNA was not known at this time so he did not realize that A-T / C-G had
complimentary binding
(3) Hershey and Chase – 1952
 In 1952, two researchers, Martha Chase and Alfred Hershey, set out to test whether ________
___________________ was the hereditary material viruses transfer when viruses enter bacteria.
 Used ______________________________ (viruses that infect bacteria)
 Remember “phage” means to eat. The viruses aren’t literally eating the bacteria
(bacteria are much larger than viruses, but they are infecting/destroying them).
 Hershey and Chase’s experimental procedure
 Grew bacteriophage (with ____________________________) in dish of e.coli (sulfur is only
found in __________________)
 Grew bacteriophage (with _____________________________ ) in dish of e.coli (phosphorous is
only found in ____________________)
 They traced the radioactive elements that had entered the e. coli to see which one was injected
into the cell.
 The ___________ of the virus and ____________________ was what was in the e.coli causing it
to _________________________________________________.
Hershey and Chase’s conclusion
 Hershey and Chase confirmed that _________________________________________________
____.
(4) Watson and Crick – 1953
Watson and Crick used the information gathered by others to determine one of the most important
discoveries in human history – ____________________________________.
 Until Hershey and Chase’s experiment, most people believed that ______________________
________________________ (because protein was involved in basically everything to do with
cells and because it was believed DNA’s structure was too simple to encode the secret to life).
 After the Hershey and Chase experiment in 1952 proved DNA was in fact the hereditary
material, the race was on to discover it’s structure to gain a better understanding of it.
 Watson and Crick discovered the shape of DNA (double helix) in 1953 using information gained
from __________________________, mainly ________________________________________.
 Crick actually studied ___________________________ and Watson _____________________
before 1952.
 Watson and Crick went to lectures from other scientists concerning DNA and compiled
information they gained from them.
 Watson _______________________________________________ showing a vague picture
DNA’s shape (you could tell that it was the same thickness all the way through).
 Watson, Crick, and Wilkins received a Nobel prize from it while Franklin (who did most of the
work) died from cancer due to her exposure to X-rays. She did not receive the Nobel prize
because they cannot be given
posthumously (after death).
DNA Structure Section
Nucleic Acids –
Functions: Serve as hereditary information that
passes on information on how to code for
proteins
Two types:
1._________ (deoxyribonucleic acid)
2._________ (ribonucleic acid)
Nucleotides are the ______________ (building
blocks of) _________________ __________.
3 parts of a nucleotide
1.
2.
3.
Draw in generic nucleotide here:
Orientation of a nucleotide
• The sugar in DNA (deoxyribose) has ___ carbons. Those carbons are numbered starting at the
carbon attached to the ________ and going ______________. This is done to tell you the
direction the nucleotide is facing. (Number these on your notes)
Types of bases
• The sugar and phosphate backbone (side) of DNA is the ______________________ living
creatures (plants, animals, bacteria).
• All living things also have the following 4 bases, but what makes us all different is the order of
these bases.
– Think of it like reading a book. All books use the same 26 letters, but the order of those
letters makes every book say something different.
• DNA nitrogenous bases are
– ________________________
– ________________________
– ________________________
– ________________________
• RNA has A, C, and G as well, but has U (Uracil) instead of T
Classes of bases
There are 2 classes of nitrogenous bases:
1) Pyrimidines = ________________, _______________, and
______________________.
2) Purines = ___________________ and
______________________
Double Helix
Two DNA strands wrap around each other to form a _____________ ____________.
–
The two strands are connected by a _________________ ____________between
___________________________________________________.
–___ pairs with___
–RNA
has U instead of T (so U binds to __ as well)
–___ pairs with ___
RNA is usually a ___________ strand
Direction of polynucleotides in a double helix
• The 2 polynucleotide strands in a double helix run ______________________ to each other.
• This means that they remain parallel, but they run in _________________________________.
• One side is oriented with the nucleotides going from the __________ direction while the other
is oriented with the nucleotides running in the __________ direction.
• This occurs to keep the double helix the same thickness throughout and because of the way
DNA is replicated (we will learn this tomorrow).
Types of bonds in a double helix
1. _____________________ - Polynucleotides (one side of a double helix) are formed from its
monomers bonding together through ____________________. Remember this means to pull
out water to make ________________________. In DNA, these bonds are called ____________
____________. This is because a polynucleotide sequence is never needed to be separated.
– The _________________________ group of one nucleotide bonds to the
________________ of the next.
– The result is a repeating sugar phosphate backbone.
2. ______________________ - As we will learn later, to use DNA you must separate the two
strands; therefore, they are held together by _______________________________.
– Think of the structure like a zipper, the sides are strong but they can be separated easily
Important DNA terms
These terms are often used interchangeably. Make sure you understand the differences between them.
• ______________ – organic compound that serves as the hereditary material for all living things
(the rest of these terms simply refer to different forms / amounts of DNA)
• ______________ – a segment of DNA that codes for 1 polypeptide
• __________________ - DNA in a dividing cell (DNA is wrapped around histone proteins)
• __________________ – DNA in a non-dividing cell (DNA is not wrapped around histone
proteins)
 Genes (enough DNA to code for ___________________________) codes for the sequence in
which the ___________________________ are arranged (primary structure of proteins).
 Genes (DNA) DO NOT code directly.
 Genes use an intermediary (__________).
 This is because the DNA is too important to leave out in the cytoplasm where it can be
damaged (so it remains in the nucleus where it is safe).
 If we were to damage our DNA and could not fix it, then the cell would no longer be able
to function.
 It is okay if we damage RNA because it is just a copy of DNA, and we can make more.
 The DNA is transcribed into RNA, which is then translated into the amino acid sequence.
 Flow of information:
 ___________ ___________  _________________
DNA usage
• DNA is read in groups of _____________________.
– As stated earlier, DNA does not directly code for proteins themselves. DNA uses RNA as
an intermediate.
• DNA is used as a template to make _____________________________________.
– This mRNA (messenger RNA) is read by ribosomes in groups of
_______________________________________________.
– Each codon codes for 1 ____________________________ (remember that amino acids
are the _____________________________________________________).
Amino Acid Structure
Differences in DNA and mRNA
• Both DNA and RNA are nucleic acids; therefore, they have similarities (1. both are made of
nucleotides [sugar, phosphate, and base], 2. both have the same purine bases [adenine and
guanine], both are used in the passage of hereditary information, etc.)
• Even so, there are 3 major differences in DNA and mRNA (there are other types of RNA that will
be discussed later.
DNA
mRNA
Pyrimidine bases
Sugar
Size
DNA replication section – Occurs during S phase of Interphase
Overview – Semiconservative Model
 Copying DNA is based on the strands of DNA being __________________ (Adenine pairs with
__________________ and ________________ pairs with Guanine….or
_______________________________________________________)
 The two strands of the parental DNA separate and both become a ________________________
of ________________________________ strands of free nucleotides.
 Nucleotides line up one a time along the strand to create 2 new complete __________________
____________________ molecules.
 The new DNA molecules is ½ of the original and ½ new so it is considered “semi-conservative”
Note
Humans, with over 6 billion base pairs in 46 diploid chromosomes, require only a few hours to replicate.
Even so, only about 1 DNA nucleotide per several billion is incorrectly paired.
In other words, your body is pretty dang impressive.
Enzymes involved in DNA replication
 Remember that enzymes end in “ase” and the start of the name tells what the enzyme works on.
Notice the name of each of the enzymes tells you what they do.
Enzymes involved in replicated (listed in the order they are used)
1. __________________ – breaks hydrogen bond between DNA strands to “unzip” the double helix
2. ____________________ – Adds an RNA “primer” that Polymerase can bind to so it can begin
making a new strand of DNA
3. _______________________________ – Adds nucleotides to the 3’ end of a nucleotide build a
new DNA strand. It builds a “DNA polymer”
4. _______________________ – Adds a few nucleotides to close the gap between Okazaki
fragments on the lagging strand. It “links” DNA.
DNA Replication – Specifics
 Begins at several sites along the DNA called _______________________________________
 Replication then proceeds in ____________________________ creating ___________________
________________________
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Note that there is a Phosphate attached to the 5’ carbon. There is an –OH attached to the 3’
carbon that will be removed during dehydration to combine with hydrogen to make water.
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DNA’s strands are _________________ (they run in opposite directions). (One strand runs from
_____________ and the other runs from 3’ to 5’)
VERY IMPORTANT in replication because _____________________________________________
_____________________________________
In other words, daughter strands only _________________________________________
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Leading vs. Lagging strands during replication
DNA always grows from 5’ to 3’ on the daughter template because DNA polymerase can only add
nucleotides to the 3’ end. (This means that the parent template will be read in the 3’ to 5’ direction.
Remember that the new template being built will be antiparallel to the parent template).
 ___________________________- Because DNA polymerases can only add nucleotides to the
___ end, only one daughter DNA can be constructed ____________________ toward the
______________________. Remember that DNA strands run anti-parallel.
 ____________ __________– The other daughter DNA must be constructed in segments as DNA
polymerase adds nucleotides ________ from the __________________________ to the ___end.
Lagging Strand – A closer look
 This strand has to be constructed ____________________ from the fork.
 Therefore, as the fork opens up, __________________________ will create a ______________
________________ that will build toward the part of the daughter strand that has __________
______________________
 These segments are called ________________________ and are attached to the rest of the DNA
strand by an enzyme called _____________________.
 Then, as the fork continues to open up, another segment will be added in the same manner.
DNA replication summary
 DNA replication ensures that every ___________________ in a _________________________
has the same __________________________________ (done during Interphase before Mitosis).
 ______________________________________________ also serve a role as ________________
to quickly remove _________________________________________.
Mutations
 Any change in ______________________ is considered a mutation because changing DNA
sequence will change amino acid sequence/protein (and thus the physical appearance of the
organism)
 A _____________________________ during replication results in a daughter cell that is
different than its parent cell. The protein produced by the mutated gene will be different than
the original, thus the trait caused will be different as well.
 Somatic cell mutations affect the individual but not their offspring.
 Gamete cell mutations do not affect the individual but do affect the offspring.
 Mutagenesis – production of mutations
 Mutagen – chemical or physical agent causing mutation
2 major kinds:
1. ______________________________ – Sub 1 nucleotide for another
 Not as bad because only 1 codon is changed (which may mean 1 amino acid change or
possibly no amino acid change at all)
 We will study how amino acids are coded for later
2. ________________________________ – insert or delete a base
 Alters the entire reading frame (triplet grouping)
 This type of mutation is very bad because it changes the entire DNA sequence and thus
the entire polypeptide that is being coded for
** Note: Although mutations are almost always harmful, they are also very important. This is because
mutations can on rare occasions be beneficial. Mutations provide the diversity of life that evolution can
then act upon.
Protein synthesis section (Transcription and Translation)
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•
•
DNA is the genetic code for all life. Even so, DNA does not directly “do” anything.
Therefore, the processes of 1) _________________________________________ and
2) ____________________allow a cell to carry out the process of taking the code of __________
to ___________________ and eventually from ____________________ to _________________.
In other words, the flow of information in a cell goes from:
DNA
mRNA
Protein
Transcription – DNA is “transcribed” into mRNA
• What? _________________________________________
• Where? _______________________________
• Why? DNA is _____________________________________ to get out of the nucleus through the
nuclear pores. (mRNA is __________________________________ and can escape the nucleus).
Also, DNA is too important to the cell to risk allowing it to be unprotected in the cytoplasm.
Methylation
 DNA Methylation permanently “_____________” DNA so it cannot be transcribed.
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DNA that is not methylated will be transcribed, but DNA that is methylated will not.
This is how all of your cells can have the same DNA but look/behave differently. The DNA that is
not needed for that cell is methylated and thus turned off.
Transcription: Key Terms
1. _______________________________________- takes DNA message to ribosomes
2. _________________________________________ – a nucleotide sequence on DNA that signals
for transcription to begin at this area
• This is the site for RNA Polymerase binding and determines which of the two strands of
DNA is to be transcribed
3. ______________________________________ – sequence of DNA that signals the end of
transcription and the end of the gene
4. ____________________________________ – strand of DNA used to construct mRNA
5. ___________________________________________- strand of DNA not used to make mRNA
6. ______________________________________– transcription enzyme that breaks the Hydrogen
bonds between DNA bases so that transcription can begin
7. _________________________________________________ – transcription enzyme that adds
RNA nucleotides to the DNA template by helping to form Hydrogen bonds between the bases of
DNA and mRNA
Steps of transcription
1) _____________________________________ – RNA polymerase binds to promoter DNA on the
coding strand after Helicase has separated the strands
2) _____________________________________________ – RNA polymerase “slides” down DNA coding
strand creating mRNA as it goes adding RNA nucleotides by correct base pairing rules (A to U and C to G)
• As RNA synthesis continues, the RNA strand peels away from its DNA template and the
two DNA strands come back together
3) __________________________________________ - RNA polymerase reaches terminator DNA and
the polymerase detaches from the RNA and the gene (section of DNA that has just been transcribed)
mRNA processing - mRNA is changed before it leaves the nucleus
Changes
1) ____________________________________________ – A single Guanine base is added to one
end of the mRNA and long tail of 50 to 250 Adenine nucleotides to the other end
• These help to export mRNA from nucleus, protect mRNA, and help ribosome bind to
mRNA
• Neither of these are translated into the protein
2) ____________________________________________
• DNA sequences that code for polypeptides are not continuous
• ___________________________________ – internal noncoding regions
• ___________________________________ – coding regions of DNA that are the parts of
a gene that are to be expressed as amino acids
• Introns are “cut” out of the mRNA and the exons are “pasted” together
Other types of RNA are also produced by transcription
• _____________________________________ – transfers amino acids from cytoplasm to
ribosomes
• Has a site on top for ____________________________________ attachment
• The bottom of the tRNA is known as an ______________________________
• Acts as the “interpreter” when translating “nucleic acid language” to protein “language”
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________________________________________________ – a type of RNA that, along with
proteins, make up the 2 subunits of ribosomes
Translation – mRNA is “translated” into proteins
• What? mRNA is read by _______________________________________________________ and
_________________________ are built from these instructions
• Where? ______________________________ in the ____________________________________
• Why? To create proteins to carry out basically every function in the body
Translation: Key terms
• ________________________________________ – mRNA is read by the ribosome in groups of 3
bases. Each codon (3 mRNA bases) codes for 1 amino acid
• ________________________________________ – monomer (building block) of protein
• _________________________________________________– 3 bases on the bottom of tRNA
that are complementary (opposite) to the codons on mRNA.
• Anticodons on the bottom of tRNA ensure that each codon codes for only 1 amino acid
•
__________________________________– Reads mRNA codons and sends out signal to tRNA to
bring in appropriate amino acid (by matching codon of mRNA to anticodon of tRNA)
•
_______ – type of RNA that transfers amino acids from cytoplasm to ribosomes
Steps of Translation:
• 1) _____________________________ – binding of mRNA to ribosome
• mRNA binds to small ribosomal subunit
• tRNA then binds to the start codon (which is AUG) to bring in first amino acid – MET
• Large ribosomal subunit binds to the small one, creating a functional ribosome
• Ribosome now has 2 binding sites
• P site = holds tRNA with growing polypeptide
• A site = vacant site where next amino-acid bearing tRNA will bind
•
2) ____________________________________ – Amino acids are added one by one to first
amino acid. Occurs in 3 step process.
• ____________________________________ – Anticodon of incoming tRNA molecule,
carrying its ____________________________, pairs with
_____________________________________ in “A” site
•
•
•
____________________________________________________ - Polypeptide separates
from tRNA in P site and attaches by a ________________________________ to amino
acid carried by tRNA in A site
_____________________________________ - P site tRNA now leaves the ribosome,
and ribosome translocates (moves) the tRNA in the A site, with its attached polypeptide,
to the P site. The codon and anticodon remain bonded so tRNA and mRNA move as a
unit. This opens the A site for the next amino acid to be brought in by a tRNA
3) _________________________________________ – Elongation continues until a
___________________________________________________ reaches the “A” site
•
Ribosome then breaks apart and finished polypeptide is released from tRNA where it
was growing
Summary of types of RNA involved in protein synthesis
 _____________________________________- takes DNA message to ribosomes where it is gives
the code for constructing proteins to rRNA
 _____________________________________ – rRNA and proteins combine to make ribosomes.
Ribosomes construct proteins.
 _____________________________________ – transfers amino acids to ribosomes so protein
can be built
Mutations
 A change in DNA during replication results in a daughter cell that is different than its parent cell.
The protein produced by the mutated gene will be different than the original, thus the trait
caused will be different as well.
 Somatic cell mutations affect the individual but not their offspring.
 Gamete cell mutations do not affect the individual but do affect the offspring.