Chapter 16: The Molecular Basis of Inheritance Flashcards
Double Helix Model
James Watson and Francis Crick developed this model for DNA (blueprint)
DNA Replication
- Process by which a DNA molecule is copies
- Also called DNA synthesis
Transformation
Change in genotype and phenotype due to the assimilation of external DNA by a cell
Virus
- 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
Double Helix
Form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape
Anitparallel
Referring to the arrangement of the sugar-phosphate backbones in a a DNA double helix (they run in opposite 5’ -> 3’ directions)
Origin of Replication
Site where the replication of a DNA molecule begins consisting of a specific sequence of nucleotides
Replication Fork
Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are being synthesized
Single-Strand Binding Protein
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
Topoisomerase
- 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
Primase Primer
Short stretch of DNA synthesized by primase
DNA Polymerase
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
Leading Strand
-New complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5’ to 3’ direction
Lagging Strand
Discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5’ to 3’ direction away from the replication fork
Okazaki Fragment
- 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
DNA Ligase
- 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
Mismatch Repair
Cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides
Nuclease
Enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides
Nucleotide Excision Repair
Repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide
Erwin Chargaff
- 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 =
Alfred Hershey and Martha Chase
- 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
Maurice Wilkins and Rosalind Franklin
- 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
James Watson and Francis Crick
- 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
Frederick Griffith
- 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
Meselson and Stahl
- 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
