A1.2 Nucleic Acid Flashcards
Nucleic Acids
Nucleic acids are composed of monomers called nucleotides, which join to form polynucleotide chains
Each nucleotide consists of 3 components – a pentose sugar, a phosphate group and a nitrogenous base
The type of sugar and composition of bases differs between DNA and RNA.
DNA vs RNA
DNA (deoxyribonucleic acid) is a more stable double stranded form that stores the genetic blueprint for cells
RNA (ribonucleic acid) is a more versatile single stranded form that transfers the genetic information for decoding
RNA base composition
adenine
thymine
guanine
uracil
DNA base composition
adenine
thymine
guanine
cytosine
DNA structure
Made up of monomers called _nucleotides
There are _hydrogen bonds_between the _complementary base pairs
2 hydrogen bonds between Adenine (A) and Thymine (T)
3 hydrogen bonds between Guanine (G) and Cytosine (C)
The two strands are arranged in _anti-parallel
Winded into a double helix structure
There is 3’ - 5’ linkage between the nucleotide of the same strand, known as phosphodiester bonds
The end with phosphate group attached to the C5 of the deoxyribose is known as the 5’ end_. And the ends with phosphate group that attached to the C3 of the deoxyribose is known as the 3’ end.
purine and pyrimidine
hydrogen bond_between purine_ and pyrimidine
Purine is a nucleotide with a two-ring nitrogenous base. (One 5 ring and one 6ring) For DNA, it’s Adenine and Guanine.
Pyrimidine is a nucleotide with a one-ring nitrogenous base. For DNA, it’s cytosine and _thymine
Only purine will pair with pyrimidine, this is described as complementary base pairing
Genetic Code
codes for specific amino acid sequence
triplet codon
3 bases codes for one specific amino acid without overlapping
Degenerative
20 amino acids existed in nature
(4 bases and 3 bases are being read one at a time, 43 = 64 combination)
universal
Coding system is common in most organism
Chromosome
DNA associate with histone proteins
DNA molecules wrapped around a core of eight histone proteins_held together by an additional histone protein attached to linker DNA
describe how DNA associate with histone proteins
eight histones make up the nucleosome core
DNA wraps twice around the eight histones of the nucleosome core
linker DNA extending from the previous nucleosome
linker DNA going to the next chromosome
histone maintaining the shape of the nucleosome
Hershey-Chase Experiment
Aim : to find out whether DNA or protein was the genetic material of the cell
procedure of Hershey-Chase Experiment
1) Viruses (T2 bacteriophage) were grown in an isotopic medium:
Viruses grown in radioactive sulfur (35S) had radiolabeled _proteins
Viruses grown in radioactive phosphorus (32P) had radiolabeled DNA
2) Viruses were then allowed to _infect a bacterium (E. coli)
3) Then the virus and bacteria were separated via centrifugation
4) The larger bacteria formed a solid pellet_ while the smaller viruses remained in the __supernatant_
results of Hershey-Chase Experiment
The radioactivity appears to be in the bacterial pellet when infected by the 32P-viruses
But the radio activity appears to be in the supernatant when infected by the 35S - viruses
This demonstrated that DNA was the genetic material as DNA was transferred to the bacteria