[STPM] [BIOLOGY] [NOTES] CHAPTER 1 : BASIC CHEMISTRY OF A CELL (PART 5)
Monday, May 12, 2014 | 8:44 PM | 0 comments
Here is the chapter 1 of the last subtopic(nucleic acids) :)
Nucleic acids
The amino acid sequence of a polypeptide is programmed by a unit of inheritance known as gene.
Genes consists of DNA, a polymer belonging to the class of compounds known as nucleic acids.
Roles of nucleic acids
The two types of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid(RNA), enable living organisms to reproduce their complex components from one generation to the next.
DNA is the genetic material that organisms inherit from their parents. Each chromosome contains a long DNA molecule, usually carrying several hundred or more genes.
RNA is the intermediate between DNA and proteins which involves in the synthesis of proteins from the codes in DNA.
Structure of nucleic acids
Nucleic acids are macromolecules that exist as polymers called polynucleotide.
As indicated by the name, each polynucleotide consists of monomers called nucleotides.
A nucleotide itself composed of three parts: a phosphate group, a nitrogenous base and a five-carbon sugar (pentose).
The portion of this unit without the phosphate group is called a nucleoside.
What difference between RNA and DNA?Let's see the below of the diagram :)
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| DNA RNA |
Ans:The difference between RNA and DNA is the loss of one oxygen atom on the pentose sugar.
There are five types of bases present in the nucleotide
Three are single ringed called the pyrimidine and two are double-ringed called purine.
The nitrogenous bases found in DNA are adenine, guanine, cytosine and thymine.In RNA, the nitrogenous bases are adenine, guanine, cytosine and uracil instead of thymine.
Adenine is always paired with cytosine in DNA and uracil in RNA. On the other hand, cytosine is always paired with guanine in both DNA and RNA.
The phosphate group is derived from the phosphoric acid and it gives the acidic property to nucleic acid.
Deoxyribonucleic acid (DNA)
Each DNA molecule is a double-stranded polynucleotide held antiparallel to eachother by hydrogen bonds between the nitrogenous bases on both strands.
One strand runs from 5’ end to 3’ end direction and the other strand runs from 3’end to 5’ end.
The bonding between one nucleotide and the other in a strand is called the phosphodiester bond.
The backbone of DNA is made up of phosphate groups and pentose sugars.
5’ end and 3’ end mean that the fifth carbon and third carbon of the pentose sugar.
From X-ray diffraction, it is found that the diameter of DNA helix is 2nm. The distance between base pairs is 0.34nm and a complete turn of the DNA consists of 10 base pairs with a distance of 3.4nm.
The number of hydrogen bonds formed between adenine with thymine or uraciland cytosine and guanine are two and three respectively.
Ribonucleic acid (RNA)
RNA molecule is a single strand of polynucleotide chain which is much shorter than DNA.
There are three types of RNA: messenger RNA (mRNA), transfer RNA (tRNA)and ribosomal RNA (rRNA).
Messenger RNA is a linear single strand polynucleotide.
It is found during protein synthesis. It consists of a nucleotide sequence transcribed from triplet codes of the DNA in the nucleues.
Ribosomal RNA is synthesized in nucleolus. It is one of the structural components of ribosome.
Transfer RNA is a folded polynucleotide strand. It helps in the protein synthesis.
By : Gemini
Image from Google
