Term
| Who created the double-helical model |
|
Definition
| James Watson and Grancis Crik in April 1953 |
|
|
Term
| T.H. Morgan's groups showed that genes are located on chromosomes and so what the the canidiates for the genetic material? |
|
Definition
|
|
Term
| Frederick Griffith in 1928 |
|
Definition
| Discovery of the genetic role of DNA research began with Griffith. He studied Streptococcus pneumoniae, a bacterium that causes pnemonia in mammals. One strain, teh S strain, was apthogenic,; other strain, was harmless. In an experiment Griffith mixed heat-killed S strain with live R strain bacteria and injected this into a mouse. The mouse died and he recovered the pathogenic strain from the mouse's blood |
|
|
Term
|
Definition
| Griffith experiment where a change in genotype and phenotype due to the assimilation of a foreign substance by a cell |
|
|
Term
| 1944 Oswald Avery, Maclyn McCarty, and Colin MacLeod |
|
Definition
| Announced that the transforming substance was DNA. Still many biologist were skeptical. In part, this reflected a belief that the genes of bacteria could not be similar in composition and cunction to those of more complex organisms. |
|
|
Term
| Bacteriphages or just phages |
|
Definition
| further evidence that DNA was teh genetic material was derived from studies that tracked the infection of bacteria by viruses. Viruses that specifically attack bacteria. Viruses consist of a DNA enclosed by a protective coat of protein. Th replicated, a virus infects a host cell and takes over the cell's metabolic machinery. |
|
|
Term
| 1952 Alfred Hershey and Matha Chase |
|
Definition
| Showed that DNA was the genetic material of the phage T2. the T2 phage, consisting almost entierly of DNA and protein, attacks ERscherichia coli )E coli), a common interstinal bacteria of mammals. This phage can quckly turn an E. coli cell into a T2-producing factory that releases phages when the cell ruptures. |
|
|
Term
|
Definition
| Developed a series of rules based on a survey of DNA composition in organizmz. He already knew that DNA was a polymer of nucleotides consisting of anitrogenous base, deoxyribose, and a phosphate group. The bases could be Adenine, thymin, guanin, or gytosin. Chargaff noted that the DNA composition varies from species to species. In any one species, the 4 bases r 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. The number of adenines was approximately equal to the number of thymines (%T=%A)the # of guanines was aprroximately equal to the # of cytosines (%G=%C). human DNA is 30.9% adenine, 29.4% thymine, 19.9% guanine, and 19.8% cytosine. |
|
|
Term
|
Definition
the phosphate group of one nucleotide is attached to the sugar of the next nucleotide in line. The result is a "backbone" of alternating phosphates and sugars, from which the bases project
|
|
|
Term
| Maurice Wilkins and Rosalind Franklin |
|
Definition
| Used x-ray crystallography to study the structure of DNA. in this technique, x-rays r diffracted as they passed through aligned fibers of purified DNA. the diffraction pattern can be used to deduce the 3D shape of molecules |
|
|
Term
| Wilkins and Franklin x-ray allowed James Watson to discover what? |
|
Definition
| learned from their research that DNA was helical in shape and he deduced the width of the heli and the spacing of bases. Watson and his colleague Francis Crick began to work on a model of DNA with 2 strands, the double helix. Using molecular models made of wire, they first tried to place the sugar-phosphate chains on the inside. however, this did not fit the x-ray measurements and other information on the chemstry of DNA |
|
|
Term
| The breakthrough of Watson |
|
Definition
| pu the sugar-phosphate chian on the otside of the nitrogen bases on the inside of the double helix. The sugar-phosphate chains of each strand are like the side ropes of a rope ladder. Pairs of nitrogen bases, one from each strand, from rungs. The ladder forms a twist every ten bases. |
|
|
Term
| How are the nitrogenouse bases paired? |
|
Definition
Adenine with Thymine
Guanine with Cytosine |
|
|
Term
| What connects the two strands? |
|
Definition
|
|
Term
| based on details of their structure |
|
Definition
| Adenine would form 2 hydrogen bonds only with thymine and guanine would form 3 hydrogen bonds only with cytosine. This finding explained Chargaff's rules. |
|
|
Term
| During DNA replication, base pairing enables existing DNA strands |
|
Definition
To serve as templates for the assembly of new complimentary strands |
|
|
Term
When a cell copies a DNA molecule, each strand serves as a template for |
|
Definition
Ordering nucleotides into a new complimentary strand
*one at a time, nucleotides line up along the template strand according to the base-pairing rules
*The nucleotides are linked to form new strands |
|
|
Term
Semiconservative mode of replication |
|
Definition
Watson and Crick’s model that predicts that when a double helix replicates each of the daughter molecules will have one old strand and one newly made strand |
|
|
Term
A Large Team of Enzymes and other proteins carries out DNA replication
|
|
Definition
*A human cell can copy its 6 billion base pairs and divide into daughter cells in only a few hours
*This process is remarkably accurate, with only one error per billion nucleotides.
*More than a dozen enzymes and other proteins participate in DNA replication |
|
|
Term
|
Definition
The replication of a DNA molecule begins at special sites
*in bacteria, this is a single specific sequence of nucleotides that is recognized by the replication enzymes |
|
|
Term
|
Definition
At the origin sites, the DNA strands separate forming a replication “bubble” with replication forks at each end
The replication bubbles elongate as the DNA is replicated in both directions and eventually fuse |
|
|
Term
|
Definition
| Catalyzed the elongation of a new DNA at a replication fork |
|
|
Term
| The rate of elongation is about… |
|
Definition
• 500 nucleotides per second in bacteria and 50 per second in human cells. The raw nucleotides are nucleoside triphosphates.
• Each has a nitrogen base, deoxribose, and a triphosphate tail. |
|
|
Term
| As each nucleotide is added… |
|
Definition
| The last two phosphate groups are hydrolyzed to form pyrophosphate |
|
|
Term
| DNA polymerases can only add nucleotides to the… |
|
Definition
Free 3’ end of a growing DNA strand.
A new DNA strand can only elongate in the 5’-3’ direction |
|
|
Term
|
Definition
| At the replication fork, one parental strand (3’-> 5’ into the fork), the leading strand, can be used by polymerases as a template for a continuous complimentary strand |
|
|
Term
|
Definition
| The other parental strand (5’->3’ into the fork) is copied away from the fork in short segments (OKAZAKI FRAGMENTS) |
|
|
Term
|
Definition
| Okazaki fragments, each about 100-200 nucleotides, are joined by DNA ligase to form the sugar-phosphate backbone of a single DNA strand |
|
|
Term
DNA polymerases cannot initiate synthesis of a polynucleotide because… |
|
Definition
| They can only add nucleotides to the end of an existing chain that is based-pairing with the template strand |
|
|
Term
|
Definition
1) To start a new chain requires a primer, a short segment of RNA.
The primer is about 10 nucleotides long in eukaryotes
2) Primase, an RNA polymerase, links ribonubleotides that are complementary to the DNA template into the primer
RNA polymerases can start an RNA chain from a single template strand |
|
|
Term
| After formation of the primer… |
|
Definition
DNA polymerases can add deoxyribonucleotides to the 3’ end of the ribonucleotide chain
Another DNA polymerase later replaces the primer ribonucleotides with deocyribonucleotides complimentary to the template |
|
|
Term
The leading strand requires…
The lagging strand requires… |
|
Definition
The formation of only a single primer as the replication fork continues to separate
Formation of a new primer as the replication fork progresses
After the primer is formed, the DNA polymerases can add new nucleotides away from the fork until it runs into the previous Okazaki fragment |
|
|
Term
The primers are converted to… |
|
Definition
| DNA before DNA ligase joins the fragments together |
|
|
Term
|
Definition
| Untwists and separates the template DNA strands at the replication fork |
|
|
Term
Single-strand binding proteins |
|
Definition
| Keep the unpaired template strands apart during replication |
|
|
Term
| Mistakes during the initial pairing of template nucleotides and complementary nucleotides occur at a rate of… |
|
Definition
One error per 100,000 base pairs
If there is an incorrect pairing, the enzyme removes the wrong nucleotide and then resumes synthesis |
|
|
Term
The final error rate is only… |
|
Definition
| One per billion nucleotides |
|
|
Term
Mismatch repair or excision repair |
|
Definition
Special enzymes fix incorrectly paired nucleotides.
A hereditary defect in one of these enzymes is associated with a form of colon cancer |
|
|
Term
Nucleotide excision repair |
|
Definition
A nuclease cuts out a segment of a damaged strand.
The gap is filled in by DNA polymerase and ligase |
|
|
Term
The importance of proper function of repair enzymes is clear from the inherited disorder |
|
Definition
|
|
Term
Limitations in the DNA polymerase |
|
Definition
Created problems for the linear DNA of eukaryotic chromosomes
The usual replication machinery provides no way to complete the 5’ ends of daughter DNA strands
Repeated rounds of replication produce shorter and shorter DNA molecules |
|
|
Term
|
Definition
The ends of eukaryotic chromosomal DNA molecules, the telomeres, have special nucleotide sequences.
In human telomeres, this sequence is typically TTAGGG, repeated between 100 and 1,000 times
Telomeres protect genes from being eroded through multiple rounds of DNA replication |
|
|
Term
|
Definition
Uses a short molecule of RNA as a template to extend the 3’ end of the telomere
There is now room for primase and DNA polymerase to extend the 5’ end
It does not repair the 3’ –end “overhang,” but it does lengthen the telomere
Telomerase is present in germ-line cells, ensuring that zygotes have long telomeres. |
|
|
Term
|
Definition
| Unwinds parental double helix at replication forks |
|
|
Term
Single-strand binding protein |
|
Definition
| Binds to and stabilize single-stranded DNA until it can be used as a template |
|
|
Term
|
Definition
| Corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands |
|
|
Term
|
Definition
Synthesizes a single RNA primer at the 5’ end of the leading strand
Synthesizes an RNA primer at the 5’ end of each Okazaki fragment |
|
|
Term
1) DNA pol III
2) DNA pol I
3) DNA LIgase |
|
Definition
1) Continuously synthesizes the leading strand, adding on to the primer. Elongates each Okazaki fragment, adding on the its primer.
2) Removes primer from the 5’ end of leading strand and replaces it with DNA, adding on to the adjacent 3’ end. Removes the primer from the 5’ end of each fragment and replaces it with DNA, adding on to the 3’ end of the adjacent fragment
3) Joins the 3’ end of the DNA that replaces the primer to the rest of the leading strand. Joins the Okazaki fragments. |
|
|
