Unit 5: DNA and DNA Replication Flashcards
Describe
Genome
All of the genes in a cell (or organism)
Multicelled organisms’ cells each contain all genes for the organism
Describe
Chromosomes
A molecule of DNA and all associated proteins; often used to refer specifically to its most coiled/ condensed state
Compare and contrast
Prokaryotic and eukaryotic chromosomes
Prokaryotes: Single, small, circular chromosome
Eukaryote: Multiple, larger, linear chromosomes
Define
Chromatin
All of the chromosomes (in their relaxed state) found in the nucleus; DNA and proteins
How is eukaryotic DNA coiled?
- DNA is coiled around histone proteins to make nucleosomes
- Nucleosomes interact to make a 30 nm fiber
- 30 nm fiber loops and condenses further
Types of chromatin
Euchromatin and heterochromatin
Define
Euchromatin
“True chromatin”
Loosest form of DNA
Accessible to enzymes for replication or gene expression
Define
Heterochromatin
More condensed chromatin; genes not being expressed often take this form
Thomas Hunt Morgan
Hint: The fruitfly guy
Showed that genes exist as part of chromosomes; helped disprove the blending theory of inheritance
Blending Theory of Inheritance
Explanation of how traits are inherited; states that parental traits blend together in offspring
Disproven; replaced with the Chromosomal Theory of Inheritance
Chromosomal Theory of Inheritance
Explanation of how traits are inherited; states that traits/genes are found on chromosomes, which are passed from parents to offspring
See Thomas Hunt Morgan
Outline Griffith’s experiment and its importance
Hint: Pathogenic and nonpathogenic mice
Injected mice with bacteria
Live pathogenic strain -> killed mice
Live non-pathogenic strain -> did not kill mice
Killed pathogenic strain -> did not kill mice
Killed pathogenic strain with live non-pathogenic strain -> killed mice
What did Griffith conclude after his experiment with pathogenic and non-pathogenic strains of bacteria with mice?
Some physical aspect of the pathogenic strain had transformed the nonpathogenic bacteria into the pathogenic form -> Transforming principle!
Define
Transformation
A change in genes or physical traits of an organism, due to its cells taking up external DNA
Outline Hershey & Chase’s experiment and its importance.
Hint: Radioactive isotopes with bacteriaphages and E. coli
- Bacteriophages grown with radioactive phosphorus incorporated P into their DNA; Bacteria infected with these phages had radioactive phosphorus in them
- Bacteriophages grown with radioactive sulfur incorporated S into their proteins; Bacteria infected with these phages did not have radioactive sulfur in them
- Conclusion: Phages inject DNA (but not protein) into host cells — DNA is genetic material?
How was Chargaff relevant in the understanding the structure of DNA?
Found that the amount of G and C in DNA was always equal; T and A was always equal
His work was used by Watson and Crick to understand how nitrogenous bases paired
Chargaff’s Rule
Amount of A = Amount of T
Amount of C = Amount of G
Complementary base pairing rule
A binds to T
C binds to G
What two factors cause DNA to have complementary base pairing?
- Purines must bind with pyrimidines to maintain the width of the helix
- The number of hydrogen bonds between pairs
Identify the two purines in DNA
Guanine
Adenine
Identify the two pyrimidines in DNA
Cytosine
Thymine
Number of hydrogen bonds between nitrogenous bases
C and G: 3
A and T: 2
What binds to 1’ carbon in deoxyribose?
Nitrogenous base
What binds to 2’ carbon in deoxyribose?
Hydrogen
(Hydroxyl in ribose, hence “de-“oxy)
What binds to 3’ carbon in deoxyribose
Hydroxyl group
Used in dehydration reaction between nucleotides
Phosphodiester bond
Covalent bond between 5’ phosphate of one nucleotide and 3’ hydroxyl of another nucleotide
What makes up the “backbone” of DNA?
Sugar and phosphates
What makes up the “rungs” of a DNA “ladder”
Nitrogenous base pairs
How was Franklin relevant in the understanding the structure of DNA
She produced an image using X ray crystallography that suggested the shape (helical) and size of DNA
Watson and Crick
Discovered structure of DNA
Outline Meselson & Stahl’s experiment and its significance
Hint: 14-N and 15-N for making DNA
Showed that DNA replicated via semi-conservative mechanism; each strand of DNA remained intact and served as a template for synthesis of new strand
Compare and contrast DNA replication (overall) in proks v. euks
Proks: one origin of replication
Euks: Multiple origins of replication, which each make replication bubbles that eventually fuse together
Helicase
Enzyme in DNA replication that breaks hydrogen bonds between nitrogenous bases
Topoisomerase
Enzyme in DNA replication that relieves tension from the unwinding of the double helix
Primase
Enzyme in DNA replication that adds RNA primer to uncoiled, single-stranded segments of DNA
Single-stranded binding proteins
Bind to single stranded segment of DNA near replication fork so that DNA strands do not rejoin
Direction of DNA polymerase
Builds new strand in 5’ -> 3’ direction
(Moves along existing strand in 3’ -> 5’ direction)
DNA Ligase
Enzyme in DNA replication that joins Okazaki fragments
Telomere
Regions at the end of chromosome which act as “extra” DNA that can be lost when DNA replication occurs (prevents the important DNA from being lost)
Leading strand
In DNA replication, this is the strand on which DNA polymerase is able to work continuously
Lagging strand
In DNA replication, this is the strand on which DNA polymerases move away from the replication fork, creating short segments of DNA discontinuously
Okasaki fragment
A short segment of DNA that is made on the lagging strand during DNA replication
