Key concepts (intro to module) Flashcards
what is the structure of B-form DNA?
a double helix consisting of two polynucleotide chains that are antiparallel.
how do the bases of DNA pair?
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.
what is the diameter of the double helix?
20 Å
what is the distance of a complete turn of the double helix? How many base pairs per turn?
a complete turn every 34 Å, with 10 base pairs per turn (about 10.4 base pairs per turn in solution).
what does a nucleotide consist of?
of a purine or pyrimidine base linked to the 1′ carbon of a pentose sugar.
what is the difference between DNA and RNA?
The difference between DNA and RNA is in the group at the 2′ position of the sugar. DNA has a deoxyribose sugar (2′–H); RNA has a ribose sugar (2′–OH).
how are successive (deoxy)ribose residues of a polynucleotide chain joined?
by a phosphate group between the 3′ carbon of one sugar and the 5′ carbon of the next sugar.
what do the 2 ends of a chain have free?
One end of the chain (conventionally written on the left) has a free 5′ end and the other end of the chain has a free 3′ end.
how many bases are there in DNA? what are they?
4 bases:
- adenine
- guanine
- cytosome
- thymine
which base is different in RNA than DNA?
RNA has uracil instead of thymine.
what are nucleotides?
Nucleotides are small molecules composed of an aromatic group known as a base (also called a nucleobase), a sugar, and one or more phosphate groups
what does the one gene–one enzyme hypothesis summarizes the basis of modern genetics?
that a typical gene is a stretch of DNA encoding one or more isoforms of a single polypeptide chain.
how is genetic code read?
read in triplet nucleotides called codons.
how are the triplets read?
The triplets are nonoverlapping and are read from a fixed starting point.
what causes a shift in the triplets? what are these mutations called?
- Mutations that insert or delete individual bases cause a shift in the triplet sets after the site of mutation
- these are frameshift mutations.
is RNA a simply structured molecule?
NO!
- RNA is a versatile cellular molecule with the ability to adopt a number of complex structural conformations.
- Although RNA is often thought of as a single-stranded molecule it is actually highly structured.
