The Molecular Basis of Inheritance - DNA

Question 1

1860’s scientist

Answer 1

Mendel-Particulate Inheritance. Worked with pea plants

Question 2

1900 event

Answer 2

Mendel rediscovered. “nuclein”-stuff in the nucleus. Later named DNA

Question 3

1928 scientist

Answer 3

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.

Question 4

1944 scientists

Answer 4

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.

Question 5

1952 scientists

Answer 5

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.

Question 6

1953 scientists

Answer 6

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)).

Question 7

1958 scientists

Answer 7

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

Question 8

DNA Model

Answer 8

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.

Question 9

Chargaff’s Law

Answer 9

Figured out that no matter which species the DNA was isolated from, [A]=[T] and [C]=[G].

Question 10

Number of Nucleotides needed

Answer 10

8 (d)ATP, (d)GTP, (d)TTP, (d)CTP. d = deoxy.

Question 11

Origin of Replication or Origin

Answer 11

Location of DNA spread. Bacteria/proks have one origin, eukaryotes have multiple origin.

Question 12

Robert’s rules of polymerase

Answer 12

-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

Question 13

Topoisomerase

Answer 13

An enzyme that helps relieve the strain by breaking swiveling, and rejoining DNA strands. Remove twists at the other end of helicase.

Question 14

Helicase

Answer 14

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.

Question 15

Primase

Answer 15

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.

Question 16

Primer

Answer 16

The RNA chain that is synthesized by the enzyme primase.

Question 17

DNA polymerases

Answer 17

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.

Question 18

DNA Polymerase III

Answer 18

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.

Question 19

DNA polymerase I

Answer 19

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.

Question 20

ATP v. dATP

Answer 20

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.

Question 21

ssDNA binding protein

Answer 21

Single-strand. Bind to unpaired DNA strands to keep them from re-pairing.

Question 22

Replication bubble

Answer 22

Shape made by DNA strand separating.

Question 23

Replication forks

Answer 23

A Y-shaped region where the parental strands of DNA are being unwound. Helicase is here.

Question 24

Direction of new strand

Answer 24

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.

Question 25

Okazaki Fragments

Answer 25

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.

Question 26

Leading strand v. Lagging strand

Answer 26

-Leading strand: Made from only one primer, one long continuous strand.

-Lagging strand: synthesized discontinuously, as a series of segments called Okazaki fragments.

Question 27

DNA Ligase

Answer 27

an enzyme that joins the sugar-phosphate backbones of all the Okazaki fragments into a continuous DNA strand.

Question 28

Telomeres

Answer 28

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.

Question 29

Regenerate with Telomerase

Answer 29

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!!

Question 30

Nucleotide Excision Repair

Answer 30

DNA repair mechanism that eliminates various structurally unrelated DNA lesions by a multiwise ‘cut and patch’-type reaction. Imagine pac-man.

Question 31

Exonuclease vs Endonuclease

Answer 31

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.