unit 5

replication fork

A Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are growing.

Virus

consist of little more than DNA or some RNA contained a protein coat. They reproduce by infecting a cell and commandeering that cell's metabolic machinery.

topoisomerase

helps relieve the strain from the twisting of DNA strands in from of helices.

semiconservative replication

method of DNA replication in which parental strands separate, act as templates, and produce molecules of DNA with one parental DNA strand and one new DNA strand. Watson and Cricks model.

telomere

multiple repetitions of a short nucleotide sequence at the ends of chromosomes, called ___________, protect an organism's genes from being shortened during successive DNa replication. they don't contain genes. in human this sequence is TTAGGG, repeated between 100 to 1000 times.

Griffith

1928, discovered the genetic role of DNA, studied Streptococcus pneeumoniae bacterium. one strain was harmless the other one was pathogenic. he mixed heat killed one with the live one and injected into a mouse and mouse died. he recovered the pathogenic strain from the mouses blood. and he called this phenomenon transformation.

Chargaff

1950. noted that the ratio of nitrogenous bases in the DNA from various organisms was species specific. Also determined that the number of adenines and thymine was approximately equal. and the number of guanines and cytosines was also equal.

Hersey and Chase

1952, showed that DNA was the genetic material of a phage known as T2 that infects the bacterium E.coli. they used radioactive isotopes.

Chargaff's Rule

A=T, G=C properties of DNA

why continuous synthesis of both DNA strands is not possible

Because synthesis *must* go from the 5' end to the 3' end of the DNA strand. DNA is set up such that the 5' end is opposite the 3' end. DNa polymerase can dd nucleotides only to the free 3' end of a growing DNA strand.

why base pairing rule is significant

It explains Chargaff's rules. Since A must pair with T, their amounts in a given DNA molecule will be about the same. Similarly, the amount of G equals the amount of C. It suggests the general mechanisms for DNA replication. If bases form specific pairs, the information on one strand complements that along the other. It dictates the combination of complementary base pairs, but places no restriction on the linear sequence of nucleotides along the length of a DNA strand. The sequence of bases can be highly variable which makes it suitable for coding genetic information.

dispersive model

all four strands of the two DNA molecules are a mixture of parental and new DNA

Primase

an enzyme called _____ can start an RNA chain from scratch. it joins RNA nucleotides together one at a time, making a primer complementary to the template strand at the location where initiation of the new DNA strand will occur

why researchers originally thought protein was the genetic material?

by the 1940s scientists knew that chromosomes carried hereditary material and consisted of DNA and protein. Most researchers thought protein was the genetic material because; proteins were macromolecules with great heterogeneity and functional specificity. Little was known about nucleic acids. The physical and chemical properties of DNA seemed too uniform to account for the multitude of inherited traits.

transformation

change in genotype and phenotype sue to the assimilation of external DNA by a cell.

Watson Crick model of DNa structure

discovered the double helix by building models to conform to X-ray data. Watson learned from Wilkins and Franklins research that DNA is helical and deduced the width of the helix and the spacing of nitrogenous bases. they worked on a model of DNA with two strands the double helix. from Franklin's work they knew sugar=phosphate backbone were on the outside of the double helix.in their model the two sug-phos backbones are antiparallel with subunits running in opposite directions. they determined that chemical side groups of the nitrogenous bases form hydrogen bonds, connecting the two strands. adenine with two Hbonds, G with C 3Hbonds

DNA polymerase

enzyme that controls each newly added nucleotide against its template and remove incorrect nucleotides.

helicase

enzyme unwinds te helix and separates the parent strands at replication forks

mismatch repair

enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors

DNA polymerases

enzymes that catalyze DNA synthesis by adding new nucleotides, remove RNA primer and replaces it with DNA nucleotides. DNA pol III sits in the replication fork on that template strand and continuously adds nucleotides to the new complementary strand as the fork progresses.

why DNA molecules are antiparallel

in order to match the charges and for better conformational configuration.sugar-phosphate backbones run in opposite directions. each DNA strand has a 3' end with a free hydroxyl group attached to the deoxyribose, and a 5' end with a free phosphate group attached to deoxyribose.

Xeroderma pigmentosum

inherited disorder, hypersensitivity to the sun light. mutations in the skin cells are left uncorrected and cause skin cancer.

proofreading and repairing DNA

initial repairing errors in nucleotide placement may occur as often as 1 per 100,000 base pairs.

single strand biding proteins

keep the separated strands apart

leading strand

new continuous strand being formed along one template strand by DNA polymerase III and requires single primer

nuclease

nucleotide excision repair is a repair system that removes (by DNA-cutting enzyme - _____) and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide

lagging strand

series of short segments copied away from the fork. each fragment requires a primer.a continuos strand of DNa is produced after the DNA polI replaces the RNA primer with DNA nucleotides and an enzyme called DNA ligase joins the sugar-phosphate backbones of the fragments. it looped back through the complex. this looping enables more okazaki fragments to be synthesized in less time.

okazaki fragments

short segments formed in the 5' to 3' direction away from the replication fork.

conservative model

the parent double helix re-forms and the duplicated molecule is totally new,

gene expression

the process by which DNA directs protein synthesis, includes two stages called transcription and translation

telomerase

the shortening of telomeres may limit cell division. In eukaryotic germ cells, however, the enzyme ______________ lengthens.

describe the Watson and Crick model of DNA structure and explain the significance of Rosalind Franklin;s work to their model

they worked on a model of DNA with two strands, the double helix. Franklin and Wilkins used x-ray crystallography to study the structure of DNA. Watson learned from this research that DNA is helical, and he deduced the width of the helix and the spacing of nitrogenous bases.

Avery, McCarty and MacLeo

they worked to identify the transforming agent by testing the DNA RNA and proteins from heat killed pathogenic cells. and in 1944 announced that DNA was the molecule that transformed bacteria.

base pairing rule of DNA

this rule sets up a mechanism for its replication. each side of the double helix is an exact complement to the other when the two sides of DNA molecule separate each strand seres as a template for rebuilding a double stranded molecule.

thymine dimer

ultraviolet light can produce ________ between adjacent thymines and this buckles DNA double helix and interferes with replication

Wilkins and Franklin

used X-ray crystallography to study the structure of DNA. X-rays are diffracted as they pass through aligned fibers of purified DNA, the diffraction pattern can be used to deduce the three-dimensional shape of molecules.

bacteriphage/phage

viruses that infect bacteria

origins of replication

where proteins that initiate replication bind to specific sequence of nucleotides and separate the two strands to form a replication bubble.