Endoplasmic Reticulum | Golgi Complex | Lysosomes | Vacuoles

ENDOMEMBRANE SYSTEM

• It is a grouping of some membrane bound organelles which function in close coordination with each other , i.e. , endoplasmic reticulum , Golgi complex , lysosomes and vacuoles .

Endoplasmic Reticulum ( ER )

• ER was discovered by Porter and Thompson in 1945.
• It is the largest of the internal membranes .

Structure

• ER is an interconnected system of membrane lined channels that run through cytoplasm .
• It is complicated organelle that exists in three forms  cisternae , vesicles and tubules.
• It is of two types smooth endoplasmic reticulum ( SER , without ribosomes ) and rough endoplasmic reticulum ( RER , with ribosomes ) .

Functions

• RER provides surface for protein synthesis .
• The proteins in ER lumen are processed and are packed in membrane bound vesicles for storage .
• SER is involved in the synthesis of lipids and other biosynthetic activities .

Golgi Complex

• At various locations within the endomembrane system , flattened stacks of membranes occur which are often interconnected with one another .
• There are known as Golgi bodies and collectively referred to as the Golgi apparatus .
• The Golgi apparatus was discovered by Camillo Golgi in 1898 and was also named after him .

Structure

• It is a parallel arrangement and interconnected system of a cluster of smooth membranous disc - shaped sacs or cisternae .
• Golgi complex is made up of four parts : cisternae , tubules , vesicles and Golgian vacuoles .
• One face of Golgi apparatus is convex or forming ( cis face ) while other is concave side or maturing face ( trans face ) .

Functions

• Golgi apparatus helps in processing , packaging , transport and release of secretory proteins .
• Glycosylation of proteins and lipids to form glycoproteins and glycolipids .
• They act as primary lysosomes as they store digestive enzymes obtained through ER in the inactive state .
• Transformation and recycling of plasma membrane takes place here .

Lysosomes

• These were first reported by Christian de Duve in 1955 through fractionation technique .
• They are found in all animal cells except RBCs . In plants and fungi , their function is taken over by vacuoles.

Structure

• These are single membrane bound , small vesicular organelles containing hydrolytic enzymes.
• The organelle passes through various stages and shows polymorphism .
• There are four types of lysosomes :
• ( i ) primary lysosome , ( ii ) secondary lysosome , ( iii ) residual bodies and ( iv ) autophagic vacuoles .

Functions

• They help in digestion of food obtained through phagocytosis .
• Harmful and unwanted materials are disposed off by lysosomes . Thus , lysosomes are called disposal bags or units .
• In injured and dead cells , the lysosome membrane ruptures spontaneously releasing the digestive enzymes or acid hydrolases that lyse the weakened cells. Therefore , these are called ' suicide bags ' of the cell.

Vacuoles

• Vacuoles are non - cytoplasmic areas present inside the cytoplasm .

Structure .

• These are surrounded by single membrane called tonoplast .
• These are formed by expansion and pinching off from endoplasmic reticulum .
• They are small in animal cells and large in fungal and plant cells .
• Depending upon the contents and function , these are of four types - sap vacuoles , food vacuoles , contractile vacuoles and air vacuoles .

Functions

• Vacuoles maintain osmotic pressure and turgidity and also help in osmoregulation . They provide buoyancy , mechanical strength and protection .
• In plants, the tonoplast facilitates the transport of a number of ions and other materials against concentration gradient .

======================================================

===== Connecting With Me For More Knowledge Of Biology =====

MANISH MEVADA

M.Sc, M.Phil, B.Ed

GUJARAT BIOLOGY NEET

NEET MATERIAL IN GUJARATI 

KNOWLEDGE ON THE WAY....................