The Molecular Basis of Inheritance - DNA Flashcards
1860’s scientist
Mendel-Particulate Inheritance. Worked with pea plants
1900 event
Mendel rediscovered. “nuclein”-stuff in the nucleus. Later named DNA
1928 scientist
Fred Griffith. Transforming principle. Streptococcus pneumonia added to mice. Smooth and rough. Smooth killed, and had a slime layer/capsule. Rough could kill if mixed with dead smooth.
1944 scientists
Avery, McCleod, and McCarty. DNA is genetic material for Bacteria. Added live Rough with smooth heat killed and either lipids, proteins, DNA or CHO’s (sugars). Only DNA had a dead mouse.
1952 scientists
Hershey & Martha Chase. DNA is genetic material for viruses. Experimented with Escherichia coli virus. Put isotope phosphorus in DNA and isotope sulfur in protein, and only isotope phosphorus was found in the bacteria. Waring blender experiment. Used S35 and P32.
1953 scientists
Watson & Crick. Double helix structure of DNA. Chargaff - ratios of the four nitrogenous bases Adenine equal to Thymine, Guanine equal to Cytosine, “Chargaff’s Rules.” Stole stuff from Wilkins and ROSALIND Franklin. X-ray crystallography. Diameter of DNA - constant. (1962 - Watson, Crick & Wilkins - Nobel piece prize (Rosalind Franklin died)).
1958 scientists
Meselson and Stahl. Method of DNA replication, Semi-conservative. Other possible methods were conservative and Dispersive.
Used N15(heavier) and N14(lighter) to distinguish DNA
DNA Model
G & C (3 H-bonds) and A & T (2 H-bonds). Sides/backbone: Sugar with 3’ end, phosphate @ 5’ end. ANTIPARALLEL (arms). If you know the % of any single nucleotide in dsDNA, can calculate all of the others.
Chargaff’s Law
Figured out that no matter which species the DNA was isolated from, [A]=[T] and [C]=[G].
Number of Nucleotides needed
8 (d)ATP, (d)GTP, (d)TTP, (d)CTP. d = deoxy.
Origin of Replication or Origin
Location of DNA spread. Bacteria/proks have one origin, eukaryotes have multiple origin.
Robert’s rules of polymerase
-Read template from 3’ - 5’, MEANING
–Make new strand from 5’ - 3’
-Internal mechanism to check for mistakes
–Proofread by removing bad nucleotides using 3’ - 5’ exonuclease activity
Topoisomerase
An enzyme that helps relieve the strain by breaking swiveling, and rejoining DNA strands. Remove twists at the other end of helicase.
Helicase
Denatures/separates DNA strands, unravels twists, breaks H-bonds. Requires ATP energy.
Enzymes that untwist the double helix at the replication forks, separating the 2 parental strands and making them available as template strands.
Primase
Enzyme that synthesizes primer. Starts a complementary RNA chain with a single RNA nucleotide and adds RNA nucleotides one at a time, using the parental DNA strand as a template.
Primer
The RNA chain that is synthesized by the enzyme primase.
DNA polymerases
Enzymes that catalyze the synthesis of new DNA by adding nucleotides to the 3’ end of a preexisting chain. Main ones are DNA pol III and DNA pol I, but there are at least 11 different DNA polymerases discovered so far.
Catalyzes the addition of each monomer to the growing end of a DNA strand by a condensation reaction in which 2 phosphate groups are lost.
DNA Polymerase III
DNA Pol III. Adds a DNA nucleotide to the RNA primer and then continues adding DNA nucleotides, which are complementary to the parental DNA template strand.
DNA polymerase I
Replaces the RNA with DNA, adding nucleotides to the 3’ end of fragment 1 (and, later, of fragment 2).
Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides added to 3’ end of adjacent fragments.
ATP v. dATP
The only difference between the ATP of energy metabolism and dATP, the adenine nucleotide used to make DNA, is the sugar component, which is deoxyribose in the building block of DNA but ribose in ATP.
ssDNA binding protein
Single-strand. Bind to unpaired DNA strands to keep them from re-pairing.
Replication bubble
Shape made by DNA strand separating.
Replication forks
A Y-shaped region where the parental strands of DNA are being unwound. Helicase is here.
Direction of new strand
DNA polymerases can only add nucleotides to the free 3’ end of a primer (due to their structure), never to the 5’ end. Thus, a new DNA strand can only elongate in the 5’ - 3’ direction.
Okazaki Fragments
Fragments of the lagging strand. Discovered by Reiji Okazaki. Fragments are about 100 - 200 nucleotides long in eukaryotes, and about 1,000 - 2,000 nucleotides long in E. coli.
Leading strand v. Lagging strand
-Leading strand: Made from only one primer, one long continuous strand.
-Lagging strand: synthesized discontinuously, as a series of segments called Okazaki fragments.
DNA Ligase
an enzyme that joins the sugar-phosphate backbones of all the Okazaki fragments into a continuous DNA strand.
Telomeres
Special nucleotide sequence. Eukaryotic chromosomal DNA (proks have round DNA). Do not contain genes; instead, the DNA typically consists of multiple repititions of one short nucleotide sequence. i.e. humans sequence is TTAGGG, repeated between 100 and 1,000 times.
Shortens every round of replication, thus, telomeric DNA tends to be shorter in dividing somatic cells of older individuals and in cultured cells that have divided many times.
Regenerate with Telomerase
Germ cells, whose genome must persist virtually unchanged, have an enzyme called telomerase. Catalyzes the lengthening of telomeres in eukaryotic germ cells.
Active in single-celled eukaryotes, embryonic development, in some cancers!!
Nucleotide Excision Repair
DNA repair mechanism that eliminates various structurally unrelated DNA lesions by a multiwise ‘cut and patch’-type reaction. Imagine pac-man.
Exonuclease vs Endonuclease
Exonuclease = pac-man, go back over DNA, rip it out and repair it. DNA and RNA repair system.
Endonuclease = Scissors, cut the phosphodiester bonds between nucleotides, think topoisomerase.
