Friday 3 May 2013

Molecular biology: definition
Molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic 
material.


This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell, including the interactions between DNA, RNA and protein biosynthesis as well as learning how these interactions are regulated.
Much of the work in molecular biology is quantitative, and recently much work has been done at the interface of molecular biology and computer science in bioinformatics and computational biology.
Since the late 1950s and early 1960s, molecular biologists have learned to characterize, isolate, and manipulate the molecular components of cells and organisms includes DNA, the repository of genetic information; RNA, a close relative of DNA; and proteins, the major structural and enzymatic type of molecule in cells.

components involved in molecular biology are


  •  DNA
  •  RNA
  •  PROTEIN
Gene : Unit of heredity

The DNA segments that carries genetic information are called genes.
It is normally a stretch of DNA that codes for a type of protein or for an RNA chain that has a function in the organism.
Genes hold the information to build and maintain an organism's cells and pass genetic traits to offspring. 


Deoxyribonucleic acid (DNA)


DNA is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses.
DNA is a set of blueprints needed to construct other components of cells, such as proteins and RNA molecules. 
Two long strands makes the shape of a double helix.
Two strands run in opposite directions to each other and are therefore anti-parallel.
Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of base, sugars and phosphate groups.
   The DNA chain is 22 to 26 Ångströms wide (2.2 to 2.6 nanometres), and one nucleotide unit is 3.3 Å (0.33 nm) long.
Phosphate+ sugar + Base  = nucleotide
Bases 
Types:- adenine and guanine (fused five- and six-membered heterocyclic compounds) – Purines
cytosine & thymine (six-membered rings)-Pyrimidines.
A fifth pyrimidine base, called uracil (U), usually takes the place of thymine in RNA and differs from thymine by lacking a methyl group on its ring.
PAIRING :     A =T    and   A=U
                          G≡CTypes:- adenine and guanine (fused five- and six-membered heterocyclic compounds) – Purines
cytosine & thymine (six-membered rings)-Pyrimidines.
A fifth pyrimidine base, called uracil (U), usually takes the place of thymine in RNA and differs from thymine by lacking a methyl group on its ring.
PAIRING :     A =T    and   A=U
                          G≡C
The DNA double helix is stabilized by hydrogen bonds between the bases attached to the two strands.
One major difference between DNA and RNA is the sugar, with the 2-deoxyribose in DNA being replaced by the alternative pentose sugar ribose in RNA. 
Double-stranded RNA
Double-stranded RNA (dsRNA) is RNA with two complementary strands, similar to the DNA found in all cells.
dsRNA forms the genetic material of some viruses (double-stranded RNA viruses).

Types of RNA
Type
Abbr
Function
Distribution
Messenger RNA
mRNA
Codes for protein
All organisms
Ribosomal RNA
rRNA
Translation
All organisms
Transfer RNA
tRNA
Translation
All organisms
 in post-transcriptional modification
Small nuclear RNA
snRNA
Splicing and other functions
Eukaryotes and archaea
Y RNA
RNA processing, DNA replication
Animals
Telomerase RNA
Telomere synthesis
Most eukaryotes



Regulatory RNAs
Antisense RNA
aRNA
Transcriptional attenuation / mRNA degradation / mRNA stabilisation / Translation block
All organisms




Basic differences between eukaryotes and prokaryotes



Attribute
Eukaryotes
Prokaryotes
Organisms
Plants, animals and fungi
 bacteria and cyanobacteria
Cell wall
No (animals); Yes (plants)
yes
Chromosome segregation
Mitotic spindle
Cell membrane
meiosis
+
_
Ribosome size
80 s
70 s
Cell organelle
Nuclear membrane
+
Absent
Endoplasmic reticulum
+
-
Golgi apparatus
+
-
Mitochondria
+
-
Chloroplast
+