Download Early Discoveries related to DNA…con`t

Molecular Biology of the Gene
Spring 2013 - Althoff Reference: Mader & Windelspecht Ch. 12)
• Genetic Material
• Structure of DNA
• Replication of DNA
• Function of Genes
Lec
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What does DNA do?
 Is ___________, therefore accounting
for species
___________ so every cell gets a copy
during cell division
 Stores information needed to ________
the cell
__________ mutations, thus accounting
for evolution of new species
Early Discoveries related to DNA…
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•
•
1869- JOHANN MIESCHER: discovered nuclei
from pus cells contained the chemical nuclein…a
chemical rich in phosphorus but no sulfur (thus
distinguishing it from a protein)
Subsequent work by other chemists said “nuclein”
contain acidic substances called nucleic acid
This was followed by fleshing out that there are 2
types of nucleic acids:
DNA - deoxyribonucleic acid
RNA - ribonucleic acid
Early Discoveries related to DNA…con’t
• Early 1900s, it was determined that nucleic
acids consisted of only _______________
__________________: molecules
composed of
______________________
______________________
______________________
1
2
3
Early Discoveries related to DNA…con’t
• This “limited” base set (only 4 nucleotides)
•
•
lead to a conclusion that the nucleotides
could _____ be responsible for the genetic
material.
They thought it was the ___________
component because they had identified 20
amino acids…thus, allowing for seemingly
more variability.
This view was held until the late ______.
Early Discoveries related to DNA…con’t
•
In _____, bacteriologist ___________________
while working on a vaccine against Streptococcus
pneumoniae determined the “_______________”
______________ where heat inactivated S strain
bacteria converted the R strain to the virulent S
strain. It wasn't until several years later that
Griffith's "transforming principle" was identified as
______.
•
Lead researchers to look closer at the _________
nature of genetic material
Griffith’s Transformation Experiment - A
Bacteria encapsulated
S strain was virulent
(“smooth looking”)
Injected live S strain has
capsule and caused
mice to die
Griffith’s Transformation Experiment - B
Non-encapsulated
R strain was not virulent
(“rough looking”)
Injected live R strain has
no capsule and
mice did NOT die
Griffith’s Transformation Experiment - C
Heated encapsulated
S strain to kill it
Injected heat-killed
S strain
into mice…they did
NOT die
Griffith’s Transformation Experiment - D
Injected heat-killed S strain
plus live R strain caused
mice to die.
Live S strain is
withdrawn from
dead mice
Conclusion: “some” substance necessary to the synthesis
of a capsule, and therefore, virulent, must have been passed
from the dead S strain bacteria to the living R strain
transforming the R strain. (rough  smooth colonies)
Early Discoveries related to DNA…con’t
• In _____, OSWALD AVERY, COLIN MACLEOD,
1)
2)
3)
4)
and MACLYN MCCARTY published paper
demonstrating that DNA was the ____________
substance. The evidence:
DNA from S strain causes R strain bacteria to be
transformed
Enzymes that degrade proteins cannot prevent
transformation
Enzymatic digestion of the transforming
substance with DNase does prevent
transformation
Molecular weight of the transforming substance
is so great that it must contain about _______
nucleotides!
Early Discoveries related to DNA…con’t
•
•
•
•
In ______, ALFRED HERSHEY and MARTHA
CHASE conducted experiments with
bacteriophages to finally confirm that the
“transforming” substance was _____ and not
_________
______________ = viruses that infect bacteria
Experimental procedure determined that the
DNA of the virus entered the host (bacteria), not
the protein.
The bacteria then contained all the genetic
information needed to produce new viruses
What are genes made of ?
DNA
Protein coat - Capsid
E. coli
Virus has 2 parts: Capsid (a protein) and DNA (nucleic acid).
Hershey and Chase determined DNA part was what the virus
was injecting into the bacteria allowing it to take control…
because the _____ rules!!!
DNA – contains 4 different
types of nucleotides
• A _________
• G _________
DNA “minute”
NITROGEN-CONTAINING BASES
DOUBLE
RINGS
A
• C _________
• T _________
PURINES
G
SINGLE
RINGS
C
T
PYRIMIDINES
U
Erwin ________ and the ______
• Austrian _________
DNA – contains 4 different
types of nucleotides
DNA “minute”
• A Adenine
• T Thymine
Amounts of these always
_______ in a cell. In humans cell,
31% Adenine & 31% Thymine
• C Cytosine
• G Guanine
Amounts of these always
________ in a cell. In humans cell,
19% Cytosine & 19% Guanine
Chargaff’s Rules:
1) _______________________________________________
2) _______________________________________________
A = Adenine
T =Thymine
C = Cytosine
G = Guanine
___________________ Model
• Published in _______
• Complimentary pairing results in rungs,
always A + T and G +C
• “_________________”
a) base pairs can be in any order
b) in any order accounts for genetic
variability between species
c) provides a “copying” mechanism
for genetic material
Hydrogen bonds
Always will be
these base pairings.
The A-T (T-A) or
G-C (C-G) pairing
DNA and the next cell
• During the ________(remember lab?), DNA
is copied during INTERPHASE—this is
known as _____________________--the
process of copying the DNA molecule
• Old DNA strands (parent cell’s DNA
molecule) serve as template for new DNA
• One strand ends up in the parent cell, with
a new matching strand…and one strand
ends up in the daughter cell with a new
matching strand.
DNA Replication -3 steps
 ______________—the double helix structure is
unwound AND unzipped, forming 2 strands
___________________________ —new
complementary nucelotides , always present in
the nucleus, are “positioned” correctly to match
the “old” strand present
 ______________ —the “old” and “new”
complementary nucelotides join to form new
strands. Thus, each daughter DNA molecule
contains an “old” strand on one side and a “new”
strand on the other
DNA Replication…some extra points
• Step 
•
carried out by an enzyme
complex known as _________________
THE DAUGHTER DNA DOUBLE HELIX
HAS THE SAME _________________
__________ AS THE PARENT DNA
DOUBLE HELIX HAD ORIGINALLY.
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3
The Function of Genes
• Early 1900s, _____________________
suggested relationship between inheritance and
metabolic diseases.
• Garrod among first to hypothesize a link
between ________ and _________
• In _______, George Beadle and Edward Tatum
worked with red bread mold fungus (Neurospora
crassa): work lead them to conclude that each
gene specifies the synthesis of one enzyme.
That is known as the…
_________________________ hypothesis.
E1
E2
E3
E4
E5
E6
A  B  C  D  E  F  G
Genes _________ a Polypeptide
• One-gene-on-one enzyme hypothesis
suggested that genetic mutation causes a
change in structure of a protein
• In 1940s, LINUS PAULING and HARVEY
ITANO studied the hemoglobin molecule in red
blood cells to determine if there was a structural
difference in normal vs. diseased RBCs.
VERNON INGRAM did more follow-up work
• They determined that a gene is a segment of
DNA that _____________________________
_________ in a polypeptide of a protein.
Refinement of a hypothesis….
one-gene-one enzyme hypothesis
from Beadle & Tatum’s work
________________________ hypothesis
from Pauling, Itano, Ingram’s research
From DNA to RNA to Protein
• Geneticists have confirmed many times over that
proteins are the link between genotype and
phenotype
• A gene is a segment of DNA that specifies the
______________________ of a protein
• Among all living things, from _____________ to
_____________________…from ___________
________________ …the same basic
processes of specifying polypeptides and
expressing genes are found.
• The gene doesn’t directly control protein
synthesis. Instead, it passes on the genetic
information onto _____ molecules, which are
more directly involved in protein synthesis.
RNA Structure and Function
• Consist of __________ containing the sugar
ribose
• Is ____________________
• A Adenine
• U Uracil
• C Cytosine
• G Guanine
RNA: Major Function
• RNA is a “helper” to DNA
• RNA “executes”
____________________
according to the genetic
information (“____________”) that DNA
provides
RNA: 3 Types
 ______________________ (mRNA)
is produced in the nucleus during transcription,
goes from DNA to ribosomes in the cytoplasm
 _____________________ (tRNA) is produced
in the nucleus, and “transfers” amino acids to the
ribosomes, resulting in a protein
 _____________________ (in eukaryotic cells)
produced in the nucleolus portion of the nucleus,
joins with proteins made in the cytoplasm to form
subunits of ribosomes—one large and one
small, where they join with other subunits in the
cytoplasm where protein synthesis takes place
RNA: Additional points
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•
•
Only a portion of the DNA is “dupped” to
produce the single RNA strand.
The DNA  RNA strand process is known as
____________________.
•
The RNA  product (i.e, protein synthesis) is
known as ___________________.
•
This RNA strand contains the ‘details’ for
whatever is suppose to be done—exactly!!!!
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Messenger RNA codons
Each amino acid has a
GENETIC CODE. There are
20 amino acids.
Each “code word” for amino
acid is comprised of 3 bases…
These are known as CODONS
This code is apparently
UNIVERSAL to all living things
…with few exceptions.
Example of value…transfer
genes from one organism to
another. This is how some
commercial and medicinal
products can be produced.
Example: insulin
3 different
proteins being
made At same time
RIBOSOMES
Summary of Gene Expression in
Eukaryotes
 DNA serves as template
mRNA is processed
 mRNA moves into
NUCLEUS
NUCLEUS
cytoplasm, becomes
CYTOPLASM
associated with a ribosomes
tRNA with “help” carry amino
CYTOPLASM
acids to mRNA
Summary of Gene Expression in
Eukaryotes…continued
Anticondon-condon
complementary base pairing
on ribosome
 Polypeptide synthesis, 1 amino
acid at a time, takes place
 Ribosome can attach to Rough
ER
 At termination, the ribosome
detaches from ER, ribosomal
subunits and mRNA disassociate
CYTOPLASM
CYTOPLASM
ROUGH ER
CYTOPLASM
Transcription
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Translation
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See Mader p232, Fig. 12.19