GENETICS HEREDITY and CHROMOSOMES. CHROMOSOMES Contain genetic information for organism Made of DNA.
Molecular Genetics What are chromosomes made of?.
-
date post
21-Dec-2015 -
Category
Documents
-
view
220 -
download
1
Transcript of Molecular Genetics What are chromosomes made of?.
![Page 1: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/1.jpg)
Molecular Genetics
What are chromosomes made of?
![Page 2: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/2.jpg)
I. Introduction
• A. Current definition of a gene• 1. a unit factor controlling the inheritance
of some external trait• 2. a spot on a chromosome which
influences some trait• 3. a poppit bead on a string of poppet
beads in the laboratory• 4. going to flesh out in more detail what a
gene is made of and what it does in our next unit
![Page 3: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/3.jpg)
• B. Two questions are going to be answered in this part of the course
• 1. What is a gene made of?• 2. What do genes do? How do genes
control the activity of a cell?
![Page 4: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/4.jpg)
II. Two traits are necessary to be a good candidate for the stuff genes are made of
• A. a genetic molecule must be able to replicate with very few mistakes
• B. a good genetic candidate must be able to direct the activities of the cell’s cytoplasm from the confines of the nucleus
![Page 5: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/5.jpg)
III. Protein vs. DNA
• A. Basic structure of the two
• 1. protein• 2. DNA• B. Which is likely
candidate?
![Page 6: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/6.jpg)
B. Series of historical experiments that determined the chemical nature of chromosomes
1. Friedrich Miescher (1869)– a. 1869-not too long ago– b. exposed cells to pepsin-a
proteolytic enzyme– c. the proteins in the cell’s
cytoplasm were liquefied but the contents of the nucleus were left relatively intact
– d. it was believed at this time that the genes or controlling factors of inheritance were housed in the cell’s nucleus
![Page 7: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/7.jpg)
2. Feulgen• a. developed a stain specific
for nucleic acids• b. what region of the cell took
up the stain?• c. all the somatic cells of an
individual stained with the same intensity-what does that tell us about developmental processes?
• d. the germ cells of an organism stain with half the intensity as the somatic cells
![Page 8: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/8.jpg)
3. Griffiths Work
a.Work involved two different strains of pneumococcus
b.Smooth-virulent strain
c. Rough-benign strain
![Page 9: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/9.jpg)
d. protocol
![Page 10: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/10.jpg)
e. results
• Dead S bacteria transformed the living R bacteria into a virulent strain
• Later determined that the fraction of the dead S bacteria that was the transforming agent was DNA
![Page 11: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/11.jpg)
4. Herschey and Chase
![Page 12: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/12.jpg)
a. structure of a bacteriophage
![Page 13: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/13.jpg)
b. how do viruses work?
![Page 14: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/14.jpg)
c. phage infection
![Page 15: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/15.jpg)
d. protocol
![Page 16: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/16.jpg)
IV. Molecular Structure of DNA
• A. Monomers of nucleic acids are nucleotides which consist of three basic parts
• 1. pentose sugar• 2. phosphate and nitrogen
base • 3. notice that there are two
classes of nitrogen containing bases
• a. purines• b. pyrimidines
![Page 17: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/17.jpg)
Four examples of DNA nucleotides
![Page 18: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/18.jpg)
B. Polymers
• 1. Polymers of nucleotides are produced by dehydration synthesis of nucleotides in a 5’ to 3’ direction
• 2. this represents a single strand of DNA
• 3. If another nucleotide were to join this existing strand-to where would it attach? Which end?
![Page 19: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/19.jpg)
C. Watson and Crick built their model of DNA on the work of others
Early sixties
Done in England
Physically built model seen to fit data of others
Pieced together information
Which one is which?
![Page 20: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/20.jpg)
1. Chargaff’s rule
• a. a number of species were investigated
• b. the percentage of different bases found in the DNA of each species was investigated
• c. found that the amount of adenine was about the same as the thymine
• d. the amount of guanine was about the same as the amount of cytosine
• e. at the time, did not know what to make of the discovery
• f. Chargaff data • h. analysis
![Page 21: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/21.jpg)
![Page 22: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/22.jpg)
2. Rosalind Franklin and X-ray diffraction study
![Page 23: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/23.jpg)
2. Rosalind Franklin
• a. Watson came across knowledge of the work at a tea party
• b. had not been exposed to the information before
• c. like a light bulb going off in his head• d. recurring periodicities seen• -.34 nm• -3.4 nm• -2.0nm
![Page 24: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/24.jpg)
3. Work of Linus Pauling
• a. worked on helical nature of proteins
• b. saw parallel in nucleic acid structure
• c. denied travel visa to attend a DNA conference that was being held in England
• d. linked to the communist movement in USA because he had opposed nuclear bomb used against Japan
![Page 25: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/25.jpg)
Diary of Pauling
• Diary shows complementary base pairing before proposed by Watson and Crick
![Page 26: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/26.jpg)
I believe that Linus Pauling won the Nobel Peace prize later in life
![Page 27: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/27.jpg)
V. DNA double helix
• A. Complementary base pairing as suggested by work of Chargaff and Franklin
![Page 28: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/28.jpg)
B. Double helix
![Page 29: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/29.jpg)
C. Properties
• 1. antiparallel• 2. complimentary base pairing• 3. periodicities seen• 4. covalent vs. hydrogen bonding
– Importance of accessibility of information– Where is information stored in the molecule
![Page 30: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/30.jpg)
• 5. The information in the DNA molecule is carried in the base pair sequence of the molecule
• 6. Notice also that because of complimentary base pairing, the two sides of the molecule are mirror images of each other
• 7. each strand contains the information needed to produce the second strand
• 8. Watson and Crick proposed an early model of replication in their first paper describing the structure of DNA
![Page 31: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/31.jpg)
VI. Replication• A. Size of the problem• 1. approximately 40,000 human genes in a nucleus• 2. the length of the DNA in one human cell is
approximately 3 meters• 3. (length of 1 bp)(number of bp per cell)(number of cells in the
body) = (0.34 x 10-9 m)(6 x 109)(1013) = 2 x 1013 meters• 4. That is the equivalent distance from the earth to the sun and
back.
![Page 32: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/32.jpg)
B. Semi-conservative model as proposed
![Page 33: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/33.jpg)
C. There were three possible modes of replication
1. conservative mode-the parent molecule would remain intact while the newly synthesized molecule is totally brand new
2. semi-conservative model-each new molecule of DNA is half new and the other half comes as a template from the parent
3. dispersive model-the two strands of the old molecule would break up and be scattered in the composition of the two new molecules
![Page 34: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/34.jpg)
D. Work of Meselsohn and Stahl
1. Verified the semiconservative nature of DNA replication
2. Used heavy nitrogen technology introduced by Kornberg along with in vitro DNA replication
![Page 35: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/35.jpg)
3. Protocol
![Page 36: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/36.jpg)
E. Replication-the real story
• 1. Mentioned above the sheer size of the DNA molecules in the nucleus
• a. the amount of information held in the nucleus is enough to fill 600 volumes of 500 pages each
• b. the enzymes copying DNA add 100 nucleotides together per second in mammals
• c. 1000 nucleotides together per second in bacterial cells
• d. huge amount of information to be processed
![Page 37: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/37.jpg)
2. Very accurate process-not a duplication event
• a. one in every billion base pairs there is a mistake
• b. in the typing of the 600 volumes above, that would translate to about 4 mistakes
![Page 38: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/38.jpg)
3. Replication origins
• replilcation can start at the beginning of the molecule as well as internally at special recognition sites
![Page 39: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/39.jpg)
4. Helicases unwind double helix
• a. double helix must be unwound in order for the templates to be accessed by free nucleotides
• b. single stranded binding proteins also keep the separated strands separated
![Page 40: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/40.jpg)
5. DNA polynucleotide strands cannot start from nothing
• a. the first nucleotide must connect to something else
• b. RNA primer piece must be laid down firstc. notice that with many replication forks, this piece of primer must be laid down every time a new section of DNA is manu.
![Page 41: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/41.jpg)
6. Nucleotides add to a growing chain in the 5’ to 3’ direction
a. new bases cannot add onto the 5’ end of the polynucleotide chain
b. DNA is an antiparallel molecule
c. at the replication fork this causes confusion
d. DNA polymerase can only operate in one direction
![Page 42: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/42.jpg)
6. cont.
e. terms to know: leading strand, lagging strand, Okazaki fragments, ligase
f. the Okazaki fragments are 1000-2000 fragments long in bacteria
g. the Okazaki fragments are 100-300 fragments long in mammals
h. the Okazaki fragments are joined by an enzyme called ligase
![Page 43: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/43.jpg)
![Page 44: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/44.jpg)
7. Summary Slide
![Page 45: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/45.jpg)
8. The final problem
• a. Chromosomes shorten with repeated divisions
• b. The position where the primer RNA was found on the leading strand leaves a gap at the end with each replication
• c. The daughter molecules get shorter and shorter
• d. Important information can be eroded
![Page 46: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/46.jpg)
• e. telomeres are basically like buffers• f. able to be eroded away without getting into the coding sequence
of the chromosomes• g. repeating nucleotide base sequence TTAGGG• h. there may be over 100 to 1000 of these repeats
![Page 47: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/47.jpg)
8. The final problem cont.
• i. telomerase not present in all cells
• j. lack of enzyme and shortening of chromosomes may be a built in clock for life of cell
• k. telomerase is present in germ lines
• l. also present in tumors which exhibit uncontrolled mitotic divisions
![Page 48: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/48.jpg)
VII.
VII. What is a chromosome anyways?
2
• A. Recall that each nucleus possesses about 3 meters of DNA
• B. It appears as chromatin in a nondividing cell
• C. In a mitotic cell the chromatin must be organized to accomplish an efficient division process
![Page 49: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/49.jpg)
D. Terms to remember
• 1. Histone proteins• 2. Nucleosomes• 3. Scaffolding proteins
![Page 50: Molecular Genetics What are chromosomes made of?.](https://reader030.fdocuments.us/reader030/viewer/2022032704/56649d585503460f94a379e7/html5/thumbnails/50.jpg)