1B: structure of DNA and genomes Flashcards
what 3 components does DNA consist of?
equal parts:
1) pentose sugar
2) nitrogenous base
3) phosphate
what are the two pentose sugars?
ribose (in RNA)
deoxyribose (in DNA)
what is the general structure of pentose sugars? how do the two pentose sugars differ?
general: ring of 4 carbon atoms and 1 oxygen. one carbon atom branch on C4’ (beside the oxygen).
ribose: an OH and H bound to C2’
deoxyribose: 2 H bound to C2’
what are the 5 nitrogenous bases?
adenine, guanine, cytosine, thymine, uracil
which nitrogenous bases are purines?
adenine and guanine
which nitrogenous bases are pyrimidines?
cytosine, thymine, and uracil
what is the structural difference between purines and pyrimidines? where do pentose sugars connect to them?
purine: double ring, sugar binds to N9
pyrimidine: single ring, sugar binds to N1
what is the difference between adenine and guanine?
adenine: has NH2 group
guanine: has O where adenine has NH2 and NH2 group
what is the difference between cytosine, thymine, uracil
cytosine: has a NH2 group
thymine: has a H3C group
uracil: no additional groups
what is a nucleoside?
a pentose sugar bonded to a nitrogenous base
which carbon on pentose connects to the base?
C1’
what is a nucleotide?
a nucleoside plus triphosphate
what are phosphodiester bonds?
the covalent bonds between nucleotide monomers (the DNA/pentose-phosphate backbone). the C5’ of one sugar connects to an O of the phosphate, and another O of the phosphate connects to C3’ of another sugar
what are the two ends of a DNA strand?
5’ end: one w/ phosphate group bound to C5’ of a pentose sugar
3’ end: one w/ an OH group bound to the C3’ of a pentose sugar
what is the overall charge of DNA? what contributes to this?
overall negative–phosphate groups contribute to this
what did Erwin Chargaff discover about DNA’s structure?
Chargaff's Rule: %A = %T; %C = %G additionally: ➞%purines = %pyrimidines ➞C + G ≠ A + T ➞A C G and T are not present in equal amounts
what could we tell from Rosalind Franklin’s x-ray diffraction studies of DNA?
➞DNA molecules are cylindrical with a ~2 nm diameter
➞0.34 nm periodicity suggests bases are stacked like pennies
➞x-shape pattern indicates helical structure.
what 4 things did Watson and Crick discover about the structure of DNA?
➞two strands of the phosphate-pentose backbone spiral as a double helix about a common axis
➞the two strands are antiparallel (one strand is in the 5’-3’ direction, other is in 3’-5’)
➞a purine on one strand is always base-paired with a pyrimidine
➞the backbone/exterior is hydrophilic, the bases/interior are hydrophobic
what keeps the two strands of DNA together?
hydrogen bonding between base pairs
what is nucleic acid hybridization?
annealing of single strands of DNA or RNA by forming H bonds. the two strands must be complementary in sequence.
where are DNA-RNA hybrids found?
DNA replication, transcription, and reproduction of some RNA viruses.
what is semiconservative replication?
replication where the double helix of the new DNA contains one strand of the original/parent DNA and one new daughter strand.
what structure is DNA stored in in organisms?
in chromosomes
what is chromatin?
given region of DNA with its associated proteins on a chromosome
