Unit 5: DNA and DNA Replication Flashcards by Andrea Unger

Describe

Genome

All of the genes in a cell (or organism)

Multicelled organisms’ cells each contain all genes for the organism

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Describe

Chromosomes

A molecule of DNA and all associated proteins; often used to refer specifically to its most coiled/ condensed state

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Compare and contrast

Prokaryotic and eukaryotic chromosomes

Prokaryotes: Single, small, circular chromosome
Eukaryote: Multiple, larger, linear chromosomes

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Define

Chromatin

All of the chromosomes (in their relaxed state) found in the nucleus; DNA and proteins

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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

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Types of chromatin

Euchromatin and heterochromatin

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Define

Euchromatin

“True chromatin”
Loosest form of DNA
Accessible to enzymes for replication or gene expression

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Define

Heterochromatin

More condensed chromatin; genes not being expressed often take this form

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Thomas Hunt Morgan

Hint: The fruitfly guy

Showed that genes exist as part of chromosomes; helped disprove the blending theory of inheritance

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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

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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

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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

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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!

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Define

Transformation

A change in genes or physical traits of an organism, due to its cells taking up external DNA

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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?

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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

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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