divides by fission (Figure . ). Functions: • Photosynthesis • Light reactions takes place in granum, • Dark reactions take place in stroma, • Chloroplast is involved in photo respiration. .
. Ribosome Ribosomes were first observed by George Palade ( ) as dense particles or granules in the electron microscope. Electron microscopic observation reveals that ribosomes are composed of two rounded sub units, united together to form a complete unit. Mg + is required for structural cohesion of ribosomes.
Biogenesis of ribosome is a de nova formation, auto replication and nucleolar origin. Each ribosome is made up of one small and one large sub-unit Ribosomes are the sites of protein synthesis in the cell. Ribosome is not a membrane bound organelle (Figure . ).
are free in non-protein synthesising cells. In protein synthesising cells they are linked together with the help of Mg + ions. Types of Ribosomes 70S Ribosomes (sub unit 30S and 50S) 80S Ribosomes (sub units 40S and 60S) RNA molecule (i) 16SrRNA in 30S subunit (ii) 23S and 5S in 50S large subunit (Prokaryotic cells of bluegreen algae bacteria, mitochondria and chloroplast of many algae and higher plants) RNA molecule (i) 18SrRNA in 40S small subunit (ii) 28S, .8S and 5S in larger 60S subunit (Eukaryotic cells of plants and animals) . .
Lysosomes (Suicidal Bags of Cell) Lysosomes were discovered by Christian de Duve ( ), these are known as suicidal bags . They are spherical bodies enclosed by a single unit membrane. They are found in eukaryotic cell. Lysosomes are small vacuoles formed when small pieces of golgi body are pinched off from its tubules.
Figure . : Structure of Ribosomes Svedberg unit (s). The size of ribosomes and their subunits are usually given in Svedberg unit (named after Theoder Svedberg, Swedish Chemist Noble Laureate ), a measure of a particle size dependent on the speed with which particle sediment in the ultracentrifuge. Ribosome consists of RNA and protein: RNA % and protein %.
During protein synthesis, many ribosomes are attached to the single mRNA and is called polysomes or polyribosomes