Download E. coli - Madeira City Schools

I. DNA is the genetic material
A. Time Line
1. 1866- Mendel's Paper
2. 1875- Mitosis worked out
3. 1890's- Meiosis worked out
4. 1902- Sutton connect chromosomes to Meiosis (pg. 286)
a. Developed the “Chromosome Theory of Inheritance”.
b. Mendelian factors or alleles are located on
chromosomes.
c. Chromosomes segregate and show independent
assortment.
5. 1911- Morgan (pg. 293)
a. discovered sex linked traits
b. There are many genes, but only a few chromosomes.
c. Therefore, each chromosome must carry a number of
genes together as a “package”.
6. 1928, 1944, 1950,1952 follow (see next slides)
B. Experiments show DNA is genetic material not protein
1. Frederick Griffith (1928 British)
a. Studied two strains of Streptococcus
S strain has capsule and caused disease
R strain does not have capsule and is
harmless
b. saw process of transformation =
What substance was
being transformed?
2. Avery, McCarty, Macleod
a. purified various chemicals
from the heat-killed
pathogenic bacteria (DNA,
RNA, and protein).
b. tried to transform live
nonpathogenic bacteria with
each chemical. Only DNA
worked.
a. 1944 announced that the
transforming agent was
DNA
b. received a lot of doubt
3. Alfred Hershey and Martha Chase (1952 American)
a. Studied bacteriophage T2 (virus that attacks bacteria)
b. Knew T2 was made of just DNA and protein
c. Knew T2 could make E. coli produce more T2
d. The experiment: next slide
Bacteria
with
Phages
Picture Proof
4. Erwin Chargaff 1950
a. knew components of DNA, not structure
b. analyzed base components of different organisms
c. amounts of bases vary, but are present in a
characteristic ratio.
Adenines = Thymines
in humans A = 30.9%
T = 29.4%
and
Guanines = Cytosines
G = 19.9%
C = 19.8%
C. Double Helix discovered by James Watson and Francis Crick 1953
1. Built models to conform to X-ray data
2. Knew arrangement of atoms, not 3D structure
3. Others working on this: Linus Pauling (California)
Maurice Wilkins and Rosalind Franklin
(London)
4. Watson saw an X-ray photo of DNA produced by Rosalind
while visiting Kings
a. crystallography was how
photo was created
5. Published paper
April 2, 1953
C. The structure
1. Monomer is a nucleotide
a. phosphate
(source of the acid)
b. sugar (5 carbon)
c. nitrogen base
(purine or pyrimidine)
II. DNA Replication
“ It has not escaped our notice that the specific pairing we have
postulated immediately suggests a possible coupling mechanism for the
genetic material” –Watson and Crick
A. Meselson-Stahl experiment: 1950’s
1. Tested three hypotheses for DNA replication.
What data would look like
with different densities.
RESULTS: semiconservative
B. Origins of Replication =
1. Bacteria
2. Eukaryotes
3. replication proceeds in both
directions forming a bubble
C. Replication Fork =
D. Elongating a new DNA strand
1. Catalyzed by DNA polymerase
2. Nucleotides that serve as the
substrate for DNA polymerase
are actually nucleoside
triphosphates.
a. as monomer joins, they lose
2 phosphates which provides
energy for the reaction.
E. The two DNA strands are antiparallel =
1. DNA polymerase only adds nucleotides to free 3’ end of
a growing DNA strand, never to a 5’ end.
2. Thus a new DNA strand can elongate only in the 5’---> 3’
direction.
3. Leading Strand
a. polymerase is located in replication fork and moves
along template as fork opens.
4. Lagging Strand
a. polymerase works away from replication fork
b. Okazaki Fragments (100-200 bases long)
c. DNA ligase joins the fragments
F. Priming DNA synthesis
1. DNA polymerase can’t add nucleotides unless it is adding to
an already existing chain.
a. Primase =
b. DNA polymerase III makes strand
c. DNA polymerase I later replaces the RNA nucleotides of
primer with DNA
d. For lagging strand, each fragment must be primed, then
primers are converted to DNA before ligase joins fragments.
G. Other proteins assisting replication
1. Helicase =
2. Single-strand binding protein =
3. Topoisomerase =
H. Enzymes Proofread and repair
mistakes
1. Mismatch Repair =
a. A DNA polymerase does this as
soon as nucleotide is added
b. other proteins do this as well
(they continually monitor)
2. Excision Repair =
a. enzyme nuclease cuts segment
of strand containing damage
b. resulting gap is filled (A DNA
polymerase and DNA ligase)
I. Replicating the ends of DNA strand
1. If ends are not replicated, DNA strand gets shorter and shorter
2. Prokaryotes = circular DNA, no problem
3. Eukaryotes = have telomeres at the ends of their DNA
a. do not contain genes
b. consist of multiple repetitions of one short nucleotide sequence
---> in humans, TTAGGG
c. the # of repititions varies between 100 to 1000 or so
d. protects the organism's genes from being eroded through
successive rounds of DNA replication and protects DNA from
unwinding and sticking together.
e. Serve as a “clock” to count how many times DNA has
replicated. Telomeres are involved with the aging process.
f. When the telomeres are too short, the cell dies by apoptosis
Limits how many times a cell line can divide.
4. Telomerase
a. Enzyme that uses RNA to rebuild telomeres
b. Can make cells “immortal”.
c. Found in cancer cells.
d. Found in germ cells.
e. Limited activity in active cells such as skin cells
f. Control of Telomerase may stop cancer, or extend the life
span.
 Helicase unzips/unwinds DNA at origins of replication
 Single strand binding proteins hold strands apart at replication forks
 Primase constructs a primer
 DNA polymerase III makes strand building in the 5’--3’ direction.
 DNA polymerase I replaces the primer
 For lagging strand, DNA ligase joins fragments
 Telomeres are present at the end of the strand so DNA doesn’t shorten
 DNA is proof read for mistakes
Enzyme Summary