Chapter 16: The Molecular Basis of Inheritance

Question 1

Double Helix Model

Answer 1

James Watson and Francis Crick developed this model for DNA (blueprint)

Question 2

DNA Replication

Answer 2

• Process by which a DNA molecule is copies

- Also called DNA synthesis

Question 3

Transformation

Answer 3

Change in genotype and phenotype due to the assimilation of external DNA by a cell

Question 4

Virus

Answer 4

• Infectious particle incapable of replicating outside of a cell
• Consists of an RNA or DNA genome surrounded by a protein coat (capsid)
• Some have a membranous envelope

Question 5

Double Helix

Answer 5

Form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape

Question 6

Anitparallel

Answer 6

Referring to the arrangement of the sugar-phosphate backbones in a a DNA double helix (they run in opposite 5’ -> 3’ directions)

Question 7

Origin of Replication

Answer 7

Site where the replication of a DNA molecule begins consisting of a specific sequence of nucleotides

Question 8

Replication Fork

Answer 8

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

Question 9

Single-Strand Binding Protein

Answer 9

Protein that binds to the unpaired DNA strands during DNA replication, stabilizing them and holding them apart while they serve as templates for the synthesis of complementary strands of DNA

Question 10

Topoisomerase

Answer 10

• Protein that breaks, swivels, and rejoins DNA strands

- During DNA replication it helps to relieve strain in the double helix ahead of the replication fork

Question 11

Primase Primer

Answer 11

Short stretch of DNA synthesized by primase

Question 12

DNA Polymerase

Answer 12

Enzyme that catalyzes the elongation of new DNA at a replication fork by the addition of nucleotides to the 3’ end of an existing chain

Question 13

Leading Strand

Answer 13

-New complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5’ to 3’ direction

Question 14

Lagging Strand

Answer 14

Discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5’ to 3’ direction away from the replication fork

Question 15

Okazaki Fragment

Answer 15

• Short segment of DNA synthesized away from the replication fork on a template strand during DNA replication
• Many of these segments are joined together to make up the lagging strand of newly synthesized DNA

Question 16

DNA Ligase

Answer 16

• Linking enzyme essential for DNA replication

- Catalyzes the covalent bonding of the 3’ end of a new DNA fragment to the 5’ end of a growing chain

Question 17

Mismatch Repair

Answer 17

Cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides

Question 18

Nuclease

Answer 18

Enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides

Question 19

Nucleotide Excision Repair

Answer 19

Repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide

Question 20

Erwin Chargaff

Answer 20

• 1950
• Analyzed base composition of DNA in different species
• Observed that # of adenines = to # of thymines and # of guanines = # of cytosines
• Conclusion:
  - Base composition of DNA varies between species
  - In each species, % of A & T is = and % of G & C is =

Question 21

Alfred Hershey and Martha Chase

Answer 21

• 1952
• Used lytic phage & wanted to identify the substance the phage injects into bacterial cells
• Labeled phosphorus isotope (for DNA) and sulfur isotope (for proteins)
• Conclusion:
  - Viruses inject DNA, not protein, into bacteria

Question 22

Maurice Wilkins and Rosalind Franklin

Answer 22

• 1953
• Rosalind: Used x-ray diffraction to analyze DNA
• Maurice: studied the fractions of DNA fibers
• Conclusion:
  - Showed helical structure of DNA
  - Prepared a more oriental DNA fiber

Question 23

James Watson and Francis Crick

Answer 23

• 1953
• Developed a detailed molecular model of DNA
  - Included phosphodiester backbone & specific base-pairs
• Each DNA molecule consists of 2 chains of nucleotides (double helix)
• Conclusion:
  - Introduced double helix, refined into an accurate representation of DNA molecularly

Question 24

Frederick Griffith

Answer 24

• 1928
• Infected mice with 2 forms of bacteria : S= virulent & R= nonvirulent
• Mice infected with the S form died of pneumonia: polysaccharide coat is needed from virulence
• Conclusion:
  - Virulence is transferred from one cell to another
  - Bacterial Transformation: genetic material can be transferred between cells

Question 25

Meselson and Stahl

Answer 25

• 1958
• 3 models for DNA replication
• Studied how DNA is replicated through bacteria using nitrogen isotopes
• Supported & rejected 3 predicted DNA models
  1) Conservative: rejected - density in bonds
  2) Semiconservative: accepted - first round of replication had similar densities; second round had different densities
  3) Dispersive: rejected - after each replication, the model had = densities