DNA Packaging and Organization Flashcards
What are the purines?
Adenine and Guanine
What are the pyrimidines?
Cytosine, thymine, uracil
What is the difference between DNA and RNA?
RNA has an extra hydroxyl group on the 2’ carbon
How many hydrogen bonds do guanine and cytosine form?
3
How many hydrogen bonds do thymine and adenine form?
2
What is the most common form of DNA?
B-form
10.5 base pairs per turn of helix, 34A per turn, right handed helix
What are the other forms of DNA?
A-DNA: tighter version. 11 BP per turn, 23A
Z-DNA: looser version. 12 BP per turn. 38A
What are the different types of RNA?
mRNA: messenger RNA transcribed from DNA
hnRNA: precursor of mRNA
tRNA: physical link between mRNA and amino acids they code during translation in ribosomes
rRNA: ribosomal RNA - makes up 50% of ribosomal weight ensures translation is successful
siRNA: small interfering
miRNA: microRNA
^ both inhibit expression of certain genes by interfering with the corresponding mRNA
Chromosomes
what DNA is organized into
eukaryotes have linear chromosomes
humans have 22 distinct and one set of sex –> 22 pairs autosomes, plus two X or one X, one Y for the sex chromosomes
Base pairs
we have approx 3 bill. base pairs
diploid cells will have approx 6 bill
stretched out, we would have about 2 meters of DNA b/c each base pair is about 3.4 A
Histones
proteins that DNA winds around
have various sub proteins - H1, H2A, H2B, H3, H4
core is the dimer of H2A and H2B plus tetramer of H3 and H4.
H1 is the linking unit
Nucleosomes
DNA-histone complexes
approx 200 base pairs each
look like beads on a string with the DNA wrapped around each histone
Chromatin
structures formed by many nucleosomes
Euchromatin
the loose configuration of Chromatin - exists in this form mainly through interphase when DNA is being replicated
Heterochromatin
the tight configuration - visible during cell division
