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⇒ Why Endoplasmic Reticulum which help in protein synthesis are rough not smooth ?
⇒ Name an eukaryotic cell in which endoplasmic reticulum absent.
Answers
Answer of first question -
First of all we have to understand that which cell organelle helps Endoplasmic reticulum to synthesise Protein and the answer is Ribosome. Ribosomes are the structure found in cell matrix which helps in synthesis of Protein. In Endoplasmic Reticulum only Rough Endoplasmic Reticulum contains ribosomes, Smooth Endoplasmic Reticulum doesn't contains any ribosome that's why only Rough Endoplasmic Reticulum helps in Protein synthesis.
Answer of second question -
Well it's true that almost all eukaryotic cells have Endoplasmic Reticulum but there are few eukaryotic cells which lacks Endoplasmic Reticulum.
Examples are :
1. Spermatozoa (sperm)
2. Red Blood Cells (RBCs)
Answer :
1) Rough endoplasmic reticulum (RER) with ribosomes attached on its surface for synthesizing of protein. Because, Ribosomes are dense, spherical and grannular particles which occur freely in the matrix or remain attached to the endoplasmic reticulum (RER). Chemically, the major constituents of ribosomes are the ribonucleic acid (RNA) and proteins. Ribosomes are not bounded by a membrane. They are present in both prokaryotic and eukaryotic cells (except mammalian RBC). Therefore, Rough ER is concerned with the transport of protein which are synthesize by ribosome on their surface.
2) Red Blood cells which is also known as Erythrocytes and Spermatozoa which is also known as Sperm are an eukaryotic cell in which endoplasmic reticulum is absent.