nucleic acid Flashcards
what are nuclic acids?
- polymers of nucleotides
- macromolecule
- 2types :
a) deoxyribonuclic acid(DNA)
b) ribonucleic acid(RNA) - nucleotides serves as building blocks for nucleic acid
what is a nucleotide composed of?
a nucleotide is composed of the following :
1)phosphate group: phosphoric acid, phosphate ions
2)five-carbon sugar or pentose sugar(monosaccharide ):
ribose sugar in RNA and deoxyribose sugar in DNA.
3)base
explain base.
it is a heterocyclic nitrogen-containing compound.
- adenine, cytosine, guanine, thymine are the four common bases
- RNA contains adenine, cyanine, guanine and uracil
- purines- double-ring base. eg: adenine and cytosine
- pyrimidines: single-ring base. eg: guanine and thymine.
explain the structure of nucleoside and nucleotide?
nucleoside: sugar molecule combines with base molecule by a glycosidic bond
nucleotide: nucleoside molecule combines with a phosphate group by ester group.
explain the structure of nucleic acid.?
phosphate moiety link 3 carbon of one nucleotide with 5 carbon of succeeding nucleotide, the bond formed between phosphate and hydroxyl group of sugar is an ester bond. as there are one such bond on either side it is called a phosphodiester bond
nucleic acid exhibits a wide variety of secondary structures, one such secondary structure exhibited by the DNA is the Waston crick model
what is DNA?
it is the genetic material and the molecular basis of heredity in all organisms. exception: in tobacco mosaic virus (TMV) RNA is the genetic material.
what does the Waston crick model say?
- DNA exists as a double helix with two unbranched polynucleotide strands, that run opposite to each other (antiparallel)
- each polynucleotide strand consists of nucleotides held together by a phosphodiester bond
- the double strand is coiled upon itself around a common axis with a backbone made up of sugar and phosphate, the bases are perpendicular to the backbone. this called Plectonemic coiling
- two polynucleotide strands are held together by hydrogen bonds between bases of opposite strands
- adenine and thymine form 3 hydrogen bonds
- guanine and cytosine form 5 hydrogen bonds
- one end of the strand is called 5’ where the fifth carbon of the pentose sugar is free and the other end is called 3’, where the third carbon of the pentose sugar is free
- at each base pair there is a turn of 36 degrees, and there are 10 nucleotide strands in a complete turn
- they have complementary base pairing.
- each base pair is 3.4 Armstrong apart and each pitch is 34 Armstrong apart.
- its 20 Armstrong wide
- this type of DNA is called B DNA.
explain complementary base pairing.
- the base pairing is specific
- adenine is always paired with thymine
- guanine is always paired with cytosine
- there for each base pair has a purine and pyrimidine
- the two strands of DNA double helix is complementary (not identical)
explain the chargaff’ rule?
1) the amount of purine and pyrimidine is equal
2) amount of adenine = thymine and guanine = cytosine.
3) ratio of A+T / G+ C is constant for a gives species but can vary from one species to another
4) deoxyribose sugar and phosphate group occur in equal proportions
what is an exception for the chargaff rule?
in reovirus and rice dwarf virus have single-stranded RNA, their purine to pyrimidine ratio is not equal to 1:1 therefore they do no follow the chargaff rule, this is due to signle stranded nature and lack of complimentarity
explain the three types of RNA.
1) messenger RNA (mRNA): carries codons for protein synthesis, they are produced in the nucleus and helps in the transcription process. discovered DNA by Jacob and Monod(1961)
2) transfer RNA(tRNA): it contains anticodons, decodes the information and transfers it to cytoplasm and ribosomes. it helps in the translation process. it is found in the cytoplasm and collects amino acids from the cytoplasm for protein synthesis. the smallest type of RNA and takes up 10 to 15 percentage of cellular RNA content.
3)ribosomal RNA (rRNA): help in the initiation of protein synthesis. they are found in the ribosomes and takes up 80 per cent of the RNA content of the cell, the largest type of RNA.
what are the different forms of right-handed DNA?
1) B type: 10 nucleotides in one turn
2) A type: 11 nucleotides per turn and the base pairs are not perpendicular to the axis, they are slightly tilted.
3) c form: 9 nucleotides in one turn
4) d form: 8 nucleotides in one turn
what is Z-DNA?
DNA with left-handed coil and 12 nucleotides in one turn.
when was DNA first isolated?
DNA was first isolated in 1869, from the nuclei of a WBC, because the material found in the nucleus was acidic called nucleic acid.
