[Unit 1.5] Nucleic acids Flashcards
Biological Molecules
what does a nucleotide look like
deoxyribose pentagon with a nitrogenous base rectangle on the right and a phosphate circle on the left
describe the structure of DNA
polymer of nucleotides
formed from deoxyribose, phosphate and nitrogenous base
joined by phosphodiester bonds
coiled in a double helix held by hydrogen bonds
between adenine thymine cytosine guanine
why are phosphodiester bonds strong, what benefit does it have
protects against mutations
what bond forms between nucleotides
phosphodiester
what are the four bases in DNA
adenine, thymine, cytosine, guanine
what is Chargaff’s rule
adenine pairs with thymine
cytosine pairs with guanine
what and which bases are purines
double ringed structure:
adenine and guanine
what and which bases are pyrimidines
single ringed structure:
thymine and cytosine and uracil
what bond forms between nitrogenous bases
hydrogen bonds. (2 between adenine and thymine) (3 between cytosine and guanine)
why is DNA a good molecule for carrying genetic code
-very stable so persistent mutations are rare
-2 strands joined by H bonds so can separate during replication and protein synthesis
-very large molecule so carries lots of genetic information
-sugar-phosphate backbone on outside to protect genetic information from corruption from outside chemical and physical forces
-4 bases can be arranged into thousands of combinations
how does DNA replication work
helicase unzips double helix
free nucleotides are activated by ATP
they are attracted to the exposed nucleotides
DNA polymerase binds adjacent nucleotides through condensation
DNA molecule consists of one original and one new strand
how does DNA polymerase move
from 5’ - 3’ end
what does the Meselson & Stahl experiment prove
semi conservative replication
how did Meselson & Stahl conduct their experiment
- grow ecoli in 14N for control
- grow ecoli in 15N for 14 generations
- transfer 15N ecoli into 14N culture
- grow for 4 generations (20 mins each) taking samples at each new generation
what was the percentages of light, intermediate and heavy nitrogen in the DNA for generations: 0, 1, 2, 3. (Meselson & Stahl experiment)
0 - 100% heavy
1 - 100% intermediate
2 - 50 % light, 50% intermediate
3 - 75% light 25% intermediate
What are the differences between RNA and DNA
DNA:
-double stranded
-double helix
-deoxyribose sugar
-H bonds between bases
-T pairs with A
RNA:
-single stranded (usually)
-not a helix
-ribose sugar
-no H bonds between bases
-U pairs with A
what are all the base pairings in RNA
A-U
T-A
C-G
G-C
what are the three types of RNA
ribosomal RNA
transfer RNA
messenger RNA
