01/28/2025 DNA RNA and Intro to Bacterial chromosomes Flashcards
(37 cards)
what did rosalin franklin contribute to DNA
she used x-ray diffraction to discover:
- the helical formation of DNA
- the helix was made of more than one strand
- 10 base pairs per complete turn
what does 5’ to 3’ refer to for DNA
it refers to its directionality in terms of the positions of the phosphate sugar, we always add to the 3’ end of the pentose sugar through a phosphodiester bond and link it to a 5’ carbon on the next nucleotide
how did erwin chargaffs experiment contribute to the discovery of DNA
finding a pattern of how the base pairs matched up
% of A= % of T and % of C=% of G
purine is always matched with
a pryimidine
why are purines and pyrimidines matched
to keep a constant diameter in the helix
the number of purines must always equal
must always equal the number of pyrimidines
if you know that a single stranded RNA has 20% uracil, do you know the ratios of the other three bases
no
why can you not predict the composition of a single stranded molecule, like RNA with Chargaff’s rule
Chargaff’s rule only works with double-stranded molecules. The only reason we know the ratios of A, T, G or C is because if we have one, there has to be another to counter balance it
if it is a single-stranded molecule, you could have any number of Cs without it meaning anything about the number of Gs because they do not need to complement each other in a double strand
what helped wattson and crick figure out the structure of DNA
the hydrogen bonding of A to T was structurally similar to that of G to C
what does complimentarity mean
it means there is hydrogen bonding with a double-stranded feature, the nucleotides at each position will be complementary to the anti-parallel strand
how many base pairs per twist?
10
which direction does the B stranded DNA go
it is right handed
what features stabilize DNA
hydrogen bonding between complementary pairs
base stacking
which is stronger? an AT rich region or G-C rich region
GC rich regions because they have three hydrogen bonds
what are the differences in hydrogen bonding between AT and GC, why is it significant
AT has only two hydrogen bonds while GC has three.
why are inactive regions of a genome GC rich
GC is harder to break apart than AT since it has three hydrogen bonds
why is the origin of replication AT rich
AT has two hydrogen bonds so it is easier to pry apart
why is it important that DNA base pairs are flat and planar
it allows stabilization in van der waals interactions and the molecules are hydrophobic so they want to be shielded internally
what is the major and minor part of the DNA? why is this significant
the major groove is more open and can be accessed more easily by DNA
proteins can bind within the groove and interact with a particular sequence
what is a recognition sequence
a recognition sequence is where proteins interact with a specific sequence of bases in a particular way
what is the predominant form of DNA in cells
B DNA
what is A DNA
it is a right handed turn, it does not occur naturally in nature and has 11 bp per turn
what is Z DNA
it is a left handed region of DNA
it is naturally found in nature in certain segments
12 base pairs per turn
tilted bases relative to axis
what is the role of Z DNA
it is recognized by cellular proteins, plays a role in transcription and chromosome structure since it is rich in GC sequences and may be transcriptionally inactive
it can also alter chromosome structure
