The Molecular Basis of Inheritance: Chp 16

Question 1

Alfref Hershey and Martha Chase

Answer 1

used a radioactive isotope of phosphorus to tag the DNA in one culture of bacteriophages and radioactive sulfer to tagethe protein in a second culture. their results clearly showed that only the DNA entered bacteria infected by the virus; the radioactive protein never entered the cell. this research convinced scientists that DNA must be the genetic material

Question 2

james watson and francis crick

Answer 2

were the first to solve the puzzle of the structure of DNA. critical to their success was the work of Rosalind franklin and maurice wilkins, both working in the field of xray crystallography

Question 3

xray crystallography

Answer 3

a process used to visualize molecules three-dimensionally. x rays are diffracted as they pass through the molecule, and they bounce back to produce patterns that can be interpreted through mathematical equations

Question 4

DNA structure

Answer 4

a double helix made up of sugar-phosphate components and pairs of nitrogenous bases. the right side (3’ to 5’) chain runs in one direction and the left side (5’ to 3’) chain runs in the opposite direction. this called antiparallel.

Question 5

DNA nitrogenous bases

Answer 5

adenine (A), thymine (T), guanine (G), and cytosine (C)

Question 6

replication

Answer 6

the making of DNA from an existing DNA strand. DNA replication is semiconservative meaning that at the end of replication, each of the daughter molecules has one old strand, derived from the parent strand of DNA, and one strand that is newly synthesized.

Question 7

Six major replication points

Answer 7

1: the replication of DNA begins at sites called for origins of replication
2: initiation proteins bind to the origin of replication and separate the two strands, forming a replication bubble. DNA replication then proceeds in both directions along the DNA strand until the molecules is copied
3: a group of enzymes called DNA polymerases catalyzes the elongation of new DNA at the replication fork
4: DNA polymerase adds to nucleotides to the growing chain one by one, working in a 5’ to 3’ direction, matching adenine with thymine and guanine with cytosine
5: recall that the strands of DNA are antiparallel. this means that DNA replication occurs continuously along the 5’ to 3’ stand, which is called the leading strand. the strand that runs 3’ to 5’ is copied in series of segments and termed the lagging strand.
6: the lagging strand is synthesized in separate pieces called okazaki fragments, which are then sealed together by DNA ligase, forming a continuous DNA strand

Question 8

several factors contributing to the accuracy of DNA replication

Answer 8

• specificity of base pairing
• mismatch repair (which soecial repair enzymes fix incorrectly paired nucleotides)
• nucleotide excision repair (which incorrectly placed nucleotides are excisedor removed by enzymes termed nucleases, and the gap left over is filled in with the correct nucleotides)

Question 9

telomeres

Answer 9

short, repetitive nucleotide sequences that do not contain genes and “cap” the ends to important genes are not removed during replication

Question 10

chromatin

Answer 10

dna and proteins packed together

Question 11

euchromatin

Answer 11

highly extended form of most chromatin during interphase

Question 12

heterochromatin

Answer 12

condensed chromatin EX: barr bodies