Download Big DNA Unit PPT - Madison County Schools

Griffith’s experiments showed that
hereditary material can pass from one
bacterial cell to another.

In 1928 Griffith was studying a bacterium
called Streptococcus pneumoniae. He was trying
to develop a vaccine against a virulent strain of
the bacterium.

Virulent – disease causing

Vaccine – 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 virulent because it has a capsule.
The capsule protects it from attacks by the
human immune system. It is able to survive
long enough in the human body to replicate
and cause disease.
R bacteria is NOT virulent because it lacks a
capsule. Without the capsule it is left
defenseless against the human immune system.
Therefore it is destroyed in the human body
before it is able to cause disease.

Injected mouse with live R bacteria (w/o
capsule).


Injected mouse with live S bacteria (w/
capsule).


Killed mice
Injected mouse with heat killed S bacteria.


DID NOT kill mice
DID NOT kill mice
Injected mouse with heat killed S bacteria
mixed with live R bacteria.

Killed mice



The R bacteria took up the DNA found in the heat
killed S bacteria and became virulent.
The transfer of genetic material from one cell to
another cell or from one organism to another organism
is called transformation.
We use bacteria’s ability to do this in one form of
BIOTECHNOLOGY – 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)

Spider goat video
•
•
•
Discovered that Adenine / Thymine and Cytosine / Guanine occurred in
equal percentages in DNA.
For Example: If you had 22 Adenine and 5 Cytosine then you would have
22 Thymine and 5 Guanine.
Led to base pairing discovery (that A pairs with T and 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

In 1952, two researchers, Martha Chase and
Alfred Hershey, tested whether DNA or
protein was the hereditary material viruses
transfer when viruses enter bacteria.

Used bacteriophages (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).




Grew bacteriophage (with radioactive sulfur) in
dish of e.coli (sulfur is only found in proteins)
Grew bacteriophage (with radioactive
phosphorous) in dish of e.coli (phosphorous is only
found in DNA)
They traced the radioactive elements that had
entered the e.coli to see which one was injected
into the cell.
The DNA of the virus and not the proteins was
what was in the e.coli causing it to produce more
viral DNA.
Hershey and Chase confirmed that
DNA, and not protein, is the hereditary
material.
Watson and Crick used the information
gathered by others to determine one of
the most important discoveries in
human history – the Double Helix.



Until Hershey and Chase’s experiment, most
people believed that protein was the hereditary
material (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 other scientists, mainly Wilkins /
Franklin.




Crick actually studied mostly proteins and Watson
studied neither before 1952.
Watson and Crick went to lectures from other scientists
concerning DNA and compiled information they
gained from them.
Watson “borrowed” X-rays done by Wilkins / Franklin
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).

Two types:
DNA
(deoxyribonucleic acid)

RNA
(ribonucleic acid)

Nitrogenous
base
(adenine)
Phosphate
group
Sugar
The sugar is either:
1. deoxyribose (DNA)
2. ribose (RNA)

The sugar in DNA (deoxyribose) has 5 carbons.
Those carbons are numbered starting at the carbon
attached to the base and going clockwise. This is
done to tell you the direction the nucleotide is
facing. (Number these on your notes)
5’
carbon
4’
carbon
3’
carbon
2’
carbon
1’
carbon


The sugar and phosphate backbone (side) of
DNA is the same for ALL 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.


DNA nitrogenous bases are





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.
adenine (A)
thymine (T)
cytosine (C)
guanine (G)
RNA has A, C, and G as well, but has U
(Uracil) instead of T

Two DNA strands (polynucleotides) wrap
around each other to form a double helix
–
–
The two strands are connected by a
hydrogen bond between complementary
base pairs.
A pairs with T
– RNA has U instead of T (so U binds to A as well)
–

C pairs with G
RNA is usually a single strand




The 2 polynucleotide strands in a double helix run
anti-parallel to each other.
This means that they remain parallel, but they run
in opposite directions.
One side is oriented with the nucleotides going
from the 5’ to 3’ direction while the other is
oriented with the nucleotides running in the 3’ to
5’ 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).
1.
Covalent Bonds - Polynucleotides (one side of a double helix) are
formed from its monomers bonding together through dehydration
synthesis. Remember this means to pull out water to make strong
covalent bonds. In DNA, these bonds are called phosphodiester
bonds. This is because a polynucleotide sequence is never needed to
be separated.


2.
The phosphate group of one nucleotide bonds to the sugar of the next.
The result is a repeating sugar phosphate backbone.
Hydrogen bonds - As we will learn later, to use DNA you must
separate the two strands; therefore, they are held together by weak,
hydrogen bonds.

Think of the structure like a zipper, the sides are strong but they can be
separated easily
These terms are often used interchangeably. Make sure
you understand the differences between them.




DNA – 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)
Genes – a segment of DNA that codes for 1
polypeptide
Chromosomes - DNA in a dividing cell (DNA is
wrapped around histone proteins)
Chromatin – DNA in a non-dividing cell (DNA is
not wrapped around histone proteins)



Genes (enough DNA to code for one protein) codes
for the sequence in which the amino acids are
arranged (primary structure of proteins).
Genes (DNA) DO NOT code directly.
Genes use an intermediary (RNA).
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  RNA  Proteins


DNA is read in groups of 3 bases.
 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 messenger RNA
 This mRNA (messenger RNA) is read by ribosomes
in groups of 3 bases called codons.
 Each codon codes for 1 amino acid (remember that
amino acids are the monomers for proteins).


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], 3. 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
C, T
C, U
Sugar
Deoxyribose
Ribose
Size
Double
stranded
Single strand




Copying DNA is based on the strands of DNA being
complementary (Adenine pairs with Thymine and Cytosine pairs
with Guanine….or Purines pair with Pyrimidines)
The two strands of the parental DNA separate and both become a
template for the assembly of complementary strands of free
nucleotides.
Nucleotides line up one a time along the strand to create 2 new
complete daughter DNA molecules.
The new DNA molecules is ½ of the original and ½ new so it is
considered “semi-conservative”



Humans, with over 6 billion base pairs in 46
diploid chromosomes, require only a few hours
to replicate.
Even so, only about 1 DNA nucelotide per
several billion is incorrectly paired.
In other words, your body is pretty dang
impressive.

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.
Helicase – breaks hydrogen bond between DNA strands
to “unzip” the double helix
2.
Primase – Adds an RNA “primer” that Polymerase can
bind to so it can begin making a new strand of DNA
3.
DNA Polymerase – Adds nucleotides to the 3’ end of a
nucleotide build a new DNA strand. It builds a “DNA
polymer”
4.
DNA Ligase – Adds a few nucleotides to close the gap
between Okazaki fragments on the lagging strand. It
“links” DNA.
Helicases
Helicases are enzymes responsible for the unwinding
of the DNA molecule. They unwind the DNA in both
directions
37


Begins at several sites along the DNA called
origins of replication
Replication then proceeds in both directions
creating replication bubbles

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.
5’
carbon
4’
carbon
3’
carbon
2’
carbon
1’
carbon



DNA’s strands are
antiparallel – they run in
opposite directions. (One
strand runs from 5’ to 3’ and
the other runs from 3’ to 5’).
VERY IMPORTANT in
replication because DNA
polymerases only add to the
3’ end, never to the 5’ end.
In other words, daughter
strands only grow 5’ to 3’.
DNA always grows from 5’ to 3’ on the daughter template because
DNA polymerase can only add nucleotides to the 3’ end because there
is a phosphate attached to the 5’ carbon. (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).
 Leading Strand - Because DNA polymerases can only add
nucleotides to the 3’ end, only one daughter DNA can be
constructed continuously toward the replication fork. Remember
that DNA strands run anti-parallel.
 Lagging Strand – The other daughter DNA must be constructed in
segments as DNA polymerase adds nucleotides away from the
replication fork to the 3’ end.




This strand has to be constructed AWAY from the fork.
Therefore, as the fork opens up, DNA polymerase will
create a short DNA segment that will build toward the part
of the daughter strand that has already been constructed.
These segments are called Okazaki segments and are
attached to the rest of the DNA strand by an enzyme called
DNA ligase.
Then, as the fork continues to open up, another segment will
be added in the same manner.
The Lagging Strand and Ligase
This animation, shows the leading strand being
synthesized followed by the lagging strand. The
enzyme named ligase ties them together.
43


DNA replication ensures that every somatic
cell in a multicellular organism has the same
genetic information (done during Interphase
before Mitosis).
DNA ligase and DNA polymerase also serve a
role as proof readers to quickly remove
incorrectly paired base-pairs.




Any change in DNA sequence is considered a mutation
because changing DNA sequence will change amino acid
sequence/protein (and thus the physical appearance of the
organism)
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.
Mutagenesis – production of mutations
 Mutagen – chemical or physical agent causing mutation
2 major kinds:
1.
Base substitution – 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.
Insertion or deletion – 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.
We will discuss mutations more when we
discuss exactly how DNA codes for proteins.



DNA is the genetic code for all life. Even so,
DNA does not directly “do” anything.
Therefore, the processes of 1) transcription and
2) translation allow a cell to carry out the
process of taking the code of DNA to mRNA
and eventually from mRNA to protein.
In other words, the flow of information in a cell
goes from:
DNA
mRNA
Protein



What? DNA coding mRNA(messenger RNA)
Where? Nucleus
Why? DNA is double stranded and too large to get
out of the nucleus through the nuclear pores.
(mRNA is single stranded and can escape the
nucleus).
Also, DNA is too
important to the cell
to risk allowing it
to be unprotected
in the cytoplasm.



DNA Methylation permanently “turns off” DNA so it
cannot be transcribed.
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.
1.
2.
mRNA(messenger RNA)- takes DNA message to
ribosomes
Promoter sequence – a nucleotide sequence on DNA
that signals for transcription to begin at this area
1.
3.
4.
5.
This is the site for RNA Polymerase binding and determines
which of the two strands of DNA is to be transcribed
Terminator sequence – sequence of DNA that signals
the end of transcription and the end of the gene
Template strand – strand of DNA used to construct
mRNA
Noncoding/Nontemplate strand- strand of DNA not
used to make mRNA
6. Helicase – transcription enzyme that breaks the Hydrogen
bonds between DNA bases so that transcription can begin
7. RNA Polymerase – transcription enzyme that adds RNA
nucleotides to the DNA template by helping to form
Hydrogen bonds between the bases of DNA and mRNA


1) Initiation – RNA polymerase binds to promoter
DNA on the coding strand after Helicase has
separated the strands
2) RNA elongation – RNA polymerase “slides”
down DNA coding strand creating mRNA as it
goes by 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) Termination - RNA polymerase reaches
terminator DNA and the polymerase detaches
from the RNA and the gene (section of DNA that
has just be transcribed)
Changes
1) G-Cap and Poly-A tail – 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)
RNA Splicing



DNA sequences that code for polypeptides are not continuous
Intron – internal noncoding regions
Exon – 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

tRNA (transfer RNA) – transfers amino acids
from cytoplasm to ribosomes




Has a site on top for amino acid attachment
The bottom of the tRNA is known as an anticodon
Acts as the “interpreter” when translating “nucleic
acid language” to protein “language”
rRNA (ribosomal RNA) – a type of RNA that,
along with proteins, make up the 2 subunits of
ribosomes



What? mRNA is read by
ribosomes (made of rRNA
and proteins) and proteins
are built from these
instructions
Where? Ribosomes in the
cytoplasm
Why? To create proteins to
carry out basically every
function in the body



Codon – mRNA is read by the ribosome in groups of 3
bases. Each codon (3 mRNA bases) codes for 1 amino
acid
Amino acid – monomer (building block) of protein
Anticodon – 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
Ribosome – Reads mRNA codons and sends out signal
to tRNA to bring in appropriate amino acid (by
matching codon of mRNA to anticodon of tRNA)
tRNA – type of RNA that transfers amino acids from
cytoplasm to ribosomes

1) Initiation – 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) Elongation – Amino acids are added one by one to
first amino acid. Occurs in 3 step process.
Codon recognition – Anticodon of incoming tRNA molecule,
carrying its amino acid, pairs with mRNA codon in A site
 Peptide bond formation - Polypeptide separates from tRNA in
P site and attaches by a peptide bond to amino acid carried by
tRNA in A site
 Translocation - 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) Termination – Elongation continues until a
stop codon reaches the A site

Ribosome then breaks apart and finished
polypeptide is released from tRNA where it was
growing



mRNA(messenger RNA)- takes DNA message
to ribosomes where it is gives the code for
constructing proteins to rRNA
rRNA (ribosomal RNA) – rRNA and proteins
combine to make ribosomes. Ribosomes
construct proteins.
tRNA (transfer RNA) – transfers amino acids to
ribosomes so protein can be built