Rheumatic Heart Disease: Genes, Inflammation and - OMICS Group
Rapid Pace of Disease Gene Discovery Susceptibility genes Total disease genes identified- 1,112 (as...
-
Upload
joel-parks -
Category
Documents
-
view
218 -
download
0
Transcript of Rapid Pace of Disease Gene Discovery Susceptibility genes Total disease genes identified- 1,112 (as...
Rapid Pace of Disease Gene Discovery
Susceptibility genesTotal disease genes identified- 1,112 (as of yr 2000)
• 1940’s- T.H. Morgan’s group showed that genes are located on chromosomes
• But…. Are _________ or DNA the genetic material??
• Most believed it to be protein
• However, this was not consistent with experiments with microorganisms, like bacteria and viruses.
1. The search for genetic material lead to DNA
History
DNA Structure and Function Chapter 10
• 1928- Frederick _______ - He studied Streptococcus pneumoniae, a bacterium that causes pneumonia in mammals.
• One strain, the R strain, was harmless.
• The other strain, the S strain, was ___________.
• Experiment- Griffith mixed _____________ S strain with live R strain bacteria and injected this into a mouse.
• Result- Mouse died, but the S strain was recovered from the mouse’s blood. S R Killed S R + Killed S
LivesDies Lives Dies
Injection
• Griffith called this phenomenon, ______________-a change in genotype and phenotype due to the assimilation of a foreign substance (now known to be DNA) by a cell.
Live S found
Fig. 16.1
• What was the transforming substance in Grifith’s experiments??
• Finally in 1944, Oswald_______, Maclyn McCarty and Colin MacLeod announced that the transforming substance was _____ .
• Still, many biologists were skeptical.
• In part, this reflected a belief that the genes of bacteria could not be similar in composition and function to those of more complex organisms.
• In 1952, Alfred Hershey and Martha Chase showed that DNA was the genetic material of the phage T2
• Phage T2 is a ______ that infects bacteria
• Viruses consist of a DNA (sometimes ____ ) enclosed by a protective coat of protein.• To replicate, a virus infects a host cell and takes over the cell’s metabolic _________________ .
What is a virus??
• The T2 phage, consisting almost entirely of DNA and protein, attacks Escherichia coli (E. coli), a common _______________ bacteria of mammals.
• This phage can quickly turn an E. coli cell into a ___________ factory that releases phages when the cell ruptures.
Fig. 16.2a
• The Hershey and Chase Experiment-Designed to determine the source of genetic material in the phage
• Procedure: Two parallel experiments#1Grow T2 phage in the presence of _____________sulfur,
marking the ___________ but not DNA
#2 Grow T2 phage in the presence of _____________ phosphorus , marking the _______ but not proteins
•Allow each batch to infect separate E. coli cultures.
•Shortly after infection, use blender to “shake loose” any remaining phage components
•Recall that sulfur is a component of some_____________.
•Recall that __________is a component of DNA
Fig. 5.29
ATP
• Now centrifuge – bacteria pellet and phage do not.
• Tested the pellet and ____________ of the separate experiments for the presence of radioactivity.
Hershey-Chase experiment (cont.)virus particle labeled with 35S
virus particle labeled with 32P
bacterial cell (cutaway view)
label outside cell
label inside cell
• Results of Hershey-Chase experiment-
• If used radioactive sulfur (proteins labeled)- most of the radioactivity was in the______________, not in the pellet.
• If used radioactive phosphorous(DNA labeled)- most of the ______________ was in the pellet with the bacteria.
•Conclusion- injected _______ of the phage provides the _________ information for new viruses.
Hershey-Chase experiment (cont.)
• Circumstantial evidence that DNA is the genetic material in eukaryotes
1. Cells double the amount of DNA in a cell prior to ________________ and then distribute the DNA equally to each daughter
2. Diploid sets of chromosomes have twice as much DNA as the __________ sets in gametes of the same organism.
• 1947- Erwin Chargaff had developed a series of rules based on a survey of DNA composition in organisms.
• Known that DNA was a polymer of nucleotides consisting of a nitrogenous base, deoxyribose, and a phosphate group.
• Known that there were four bases -adenine (A), thymine (T), guanine (G), or cytosine (C).
• Chargaff noted that the four bases are found in characteristic, but not necessarily equal, ratios
• He also found a peculiar regularity in the ratios of nucleotide bases which are known as Chargaff’s rules.
Chargaff’s rules-
• 1. The number of adenines was approximately equal to the number of thymines (%T = %A).
• 2. The number of guanines was approximately equal to the number of cytosines (%G = %C).
• Human DNA is 30.9% adenine, 29.4% thymine, 19.9% guanine and 19.8% cytosine.
Nucleotide Bases
phosphate group
deoxyribose
ADENINE (A)
THYMINE (T)
CYTOSINE (C)
GUANINE (G)
• By the beginnings of the 1950’s, the race was on to move from the structure of a single DNA strand to the three-dimensional structure of DNA.
• Among the scientists working on the problem were Linus ______, in California, and Maurice Wilkins and Rosalind ________, in London.
Watson and Crick discovered the double helix by building models to conform to X-ray data
Fig. 16.3
• The ________group of one nucleotide is attached to the
_____ of the next nucleotide
in line.
• The result is a “__________ ” of alternating phosphates and sugars, from which the bases project.
The basic structure of DNA was known by 1952
Bases
T
A
C
G
Fig. 16.5
The _______________ chains of each strand are like the side ropes of a rope ladder.
The double helix- a _________ homology
The ladder forms a twist every ____ bases
Pairs of nitrogen bases, one from each strand, form rungs.
• In addition, Watson and Crick determined that chemical side groups off the nitrogen bases would form hydrogen bonds, connecting the two strands.
• Adenine could form two ________ bonds only with thymine
• Guanine could form ______hydrogen bonds only with cytosine.
• This finding _________Chargaff’s rules.
Fig. 16.6
• The linear sequence of the four bases can be varied in countless ways.
• Each gene has a unique order of nitrogen bases.
• In April 1953, Watson and Crick published a succinct, one-page paper in Nature reporting their double helix model of DNA.
The Nobel Prize in Chemistry was awarded in later years
• In a second paper, Watson and Crick published their _____________for how DNA replicates.
Base pairing is at the heart of DNA replication
Base pairing enables existing DNA strands to serve as templates for new complimentary strands
Fig. 16.7
Double-stranded
DNA
1.Separate strands
2.Add complementary bases
3.Connect bases
When a cell copies a DNA molecule, each strand serves as a _________
for ordering nucleotides into a new ________________ strand.
DNA Replication
newnew old old
• Each parent strand
remains ________
• Every DNA
molecule is half
“____” and half
“_____”
• Bacterium E. coli (5 million base pairs- )- _______________
• Human cells- (6 billion base pairs)- ___________
DNA replication requires a large number of enzymes and other proteins
A. DNA replication is fast and efficient
Time to copy the entire genome and divide into daughter cells:
• Less than one error per __________nucleotides.
Accuracy
• More than a dozen enzymes and other proteins required
Machinery
B. Where does replication start? –
Bacteria- one site in DNA recognized by specific proteins
Answer- The ______________________
• Eukaryotes- ______________ of origin sites per chromosome. • At each origin site, the DNA strands separate forming a
replication “______ ” with ______________ at each end.
• The replication bubbles _______ as the DNA is replicated and eventually ______ .
Fig. 16.10
Origin of replication (cont.) 15.3
15.215.1
14
13.3
13.11211
11.111.2
12
13.113.213.3
14
15
21
2223.1
23.3
31.131.231.3
3233.133.334
35.1
• DNA polymerases add the ____________ (nitrogen base, deoxyribose, and a triphosphate tail).
• Rate of elongation
• ____nucleotides/second in bacteria
• ___per second in human cells. The raw nucleotides are nucleoside triphosphates.
Fig. 16.11
Two phosphates are removed upon addition of nucleotide
One
phosphate connects
nucleotides
Fig. 16.16
• At the replication fork
• the leading stand is copied ______________ from a single primer
• the lagging strand is copied in ____________ using many primers.
Summary of DNA replication
• Nucleotide pairing errors occur at a rate of one error per __________ base pairs.
• Yet the final error rate is only one per billion nucleotides.
Enzymes proofread DNA during its replication and repair damage in existing DNA
a. ______________ proofreads each new nucleotide against the template nucleotide as soon as it is added. If incorrect, it corrects it.
How do we account for this discrepency??
Answer- ______________
b. Each cell continually monitors and repairs its genetic material, with over ______ repair enzymes identified in humans.