Skip to main content

Ribosomes

Ribosomes
Introduction
These are tiny granular structures present in cytoplasm.
Discovery
Palade (1955) was the person, who first time discovered and studied them.
Production
New ribosomes are assembledin the nucleolus of the nucleus from where they are transported to the cytoplasm via the pores in the nuclear membrane.
Chemical Composition
Ribosomes are composed of almost an equal amount of:
  • RNA
  • Proteins
Due to presence of RNA and proteins, these are also called as ribonucleoprotein particles.
Existence
Ribosomes exist in two forms:
  • Freely dispersed in cytoplasm
  • Attached with the endoplasmic reticulum as tiny granules.
Structure
Each eukaryotic ribosome consist of two sub units:
  • Larger subunits sediment at 60S
  • Smaller subunits sediment at 40S
Two subunits on attachment, with each other form 80Sparticles (S = Svedberg unit which specifies sedimentation rate). This attachment is controlled by Mg2+ ions.
When many ribosomes get attached to the same stretch of mRNA they form a structure called ‘Polysome’.
Function
Ribosomes are involved in the synthesis of proteins.

Comments

Post a Comment

Popular posts from this blog

Deoxyribonucleic acid (DNA)

Deoxyribonucleic acid (DNA) DNA is heredity material. It controls the properties and potential activities of a cell. Location in cell DNA occurs in chromosomes, in the nuclei of the cells and in much lesser amounts in mitochondria and chloroplast. Chemical composition of DNA DNA is made of four kinds of  nucleotides; d-adenosine monophosphate (d-AMP) d-guanosine monophosphate (d-GMP) d-cytidine monophosphate (d-CMP) d-thymidine monophosphate (d-TMP) These nucleotides are united with one another through phosphodiester linkages in a specific sequence to form long chains. Two nucleotides join to form  dinucleotide  e.g nicotinamide adenine dinucleotide  (NAD) which is important coenzyme in several oxidation-reduction reactions in the cell. Three nucleotides join to form  trinucleotide . Ratio of Bases in DNA In 1951,  Erwin Chargaff  provided data about the ratios of different bases present in DNA. This data suggested that ade...
Post a Comment
Read more

Mr chips important short questions.

Chapter#1 Question # 1:How does a person spend his time in old age after retirement? Answer : After retirement when a person becomes old, he has nothing to do. His time seems to pass like lazy cattle moving across a landscape(valley). Question # 2:Why did Chips keep on adjusting his timetable according to the school bells even after the retirement? Answer : After spending more than forty three(43) years at Brookfield, it was not possible for Chips to break his ties with school. He began to live across the road and Mrs. Wickets. That's why it was possible for Chips to keep on adjusting his timetable according to the school bells. Question # 3:How did Chips voice sound in old age? Answer : Although Chips had become old yet he did not loose the zeal and zeast for the life. So his voice remained resonant and lively even in his old age. Question # 4:What did Chips do before going to the bed? Answer : Chips was spending a pleasant and placid time at Mrs. Wickets after his retirem...
Post a Comment
Read more

Comparing MOLE OR AVOGADRO'S NUMBER

MOLE  The relative atomic mass of an element, the relative molecular mass of a molecule, the relative formula mass of an ionic substance or ionic mass of ionic specie when expressed in grams is called gram mole or simply mole. One mole of a substance is the amount in grams which contains 6.02×10 23  particles of that substance. It is denoted by “n”. It is abbreviated as “mol”. It is the  basic SI unit of measuring the quantity of substance. Example: (i)  Element                                Na       =          23g      = 1mole (ii) Molecular compound        H 2 O     =          18g      = 1mole (iii) Ionic compound         ...
Post a Comment
Read more