Ch. 16: Molecular Basis of Inheritance

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DNA (sometimes RNA) enclosed by a protective coat


Viruses that infect bacteria.



Hershey-Chase Experiment

Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. Agitate in a blender to separate phages outside the bacteria from the cells and their contents. Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. Measure the radioactivity in the pellet and the liquid.

Chargaff's rules

# of A=T and # of G=C


This is a polymer of nucleotides.


This has a nitrogenous base, deoxyribose, and a phosphate group.


The family of nitrogenous bases that have a single ring.


The family of nitrogenous bases that have two organic rings.

Conservative model

The parental double helix reamins intact and an all-new copy is made.

Semiconservative model

The two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand.

Dispersive model

Each strand of both daughter molecules contains a mix of old and newly synthesized parts.

Meselson-Stahl experiment

Tested the three models ofDNA replication by this: bacteria cutured in medium containing 15N and then is transferred to medium containing 14N. The different isotope of nitrogen was distinguishable so after DNA samples were centrifuged, one could tell which model was correct.

Origins of replication

Special sites where the replications of a DNA molecule begins

Replication Fork

This is a Y-shaped region where the new strands of DNA are elongating.

DNA polymerases

These are enzymes that catalyze the elongation of new DNA at a replication fork.

3' end

This is where a hydroxyl group is attaced to the 3' carbon of the terminal deoxyribose.

5' end

This is where the sugar-phosphate backbone terminates with the phosphate group attached to the 5' carbon of the last nucleotide.

where DNA polymerases add nucleotides

DNA polymerases add nucleotides only to the free 3' end of a growing DNA strand.

Which direction do DNA strands elongate

5' -> 3'

leading strand

This strand is made first and is made completely at one time.

Lagging strand

This strand is made starting from the direction away from the replication fork. This is synthesized in a series of short segments.

Okazaki fragments

These are the series of segments first synthesized in the lagging strand.

DNA ligase

This ligates (joins) the sugar-phosphate backbones of the Okazaki fragments to create a single DNA strand.


This is the start of a new chain and is a short stretch of RNA.


This is an enzyme that joins RNA nucleotides to make the primer. This can start an RNA chain from scratch.



single-strand binding protein







This is a change in genotype and phenotype due to the assimilation of external DNA by a cell.

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