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Flashcards in Introduction to Molecular Genetics Deck (14)
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Which of the bases are purines?

Adenine and Guanine


What is the difference between purine and pyrimidine?

The purines, adenine and thymine, are smaller two-ringed bases, while the pyrimidines, cytosine and uracil, are larger and have a single ring


Which of the bases are pyrimidines?

Thymine and Cytosine


Is uracil a pyrimidine of purine?

pyrimidine derivative


What does a nucleoside consist of?

a purine or pyrimidine base linked to the 1′ carbon of a pentose sugar


Difference between DNA and RNA?

in the group at the 2′ position of the sugar. DNA has a deoxyribose sugar (2′–H); RNA has a ribose sugar (2′–OH).


What does a nucleotide consist of?

nucleoside linked to a phosphate group on either the 5′ or 3′ carbon of the (deoxy)ribose.


How do the (deoxy)ribose nucleotides link?

phosphate group between the 3′ carbon of one sugar and the 5′ carbon of the next sugar.

phosphodiester bond


Which end of the chain has the free 5' end?

conventionally written on the left
other end is the 3' end


What is the structure of DNA?

B-form of DNA is a double helix consisting of two polynucleotide chains that are antiparallel.

The nitrogenous bases of each chain are flat purine or pyrimidine rings that face inward and pair with one another by hydrogen bonding to form only A-T or G-C pairs.

The diameter of the double helix is 20 Å, and there is a complete turn every 34 Å, with 10 base pairs per turn (about 10.4 base pairs per turn in solution).

The double helix has a major (wide) groove and a minor (narrow) groove.


What is the one-gene one enzyme hypothesis?

that a typical gene is a stretch of DNA encoding one or more isoforms of a single polypeptide chain.


What is an issue with the one-gene one enzyme hopthesis

Some genes do not encode polypeptides, but encode structural or regulatory RNAs. Many mutations in coding sequences damage gene function and are recessive to the wild-type allele.


What is a codon?

triplet nucleotides that the genetic code is read in
triplets are nonoverlapping and are read from a fixed starting point.


What is a frameshift mutation?

Mutations that insert or delete individual bases cause a shift in the triplet sets after the site of mutation