Ribosomes

 TOPIC # 5         RIBOSOMES

RIBOSOME

INTRODUCTION

                          It is a type of tiny organelle present in cell .

Discovered:

              It was first discovered and studied by Palade in 1955.

SIZE:

      Its size is about 20 nanometer.

LOCATION:

                  In eukaryotic cell ribosome is located on Rough endoplasmic reticulum and freely dispersed in cytoplasm while in prokaryotic cell there is no ER so it is found freely dispersed in cytoplasm and rarely attached to cell membrane.

MCQ POINT

It is non membranic structure.

it is the engine of cell.

it consist of 25% of dry weight of cell.

it form protein with the help of rRNA and mRNA.33

COMPOSITION:

                           Eukaryotic ribosomes are almost composed of equal amount of RNA (ribosomal) and protein having ratio of 1:1. but according to some books prokaryotic ribosome is different but according to recent research both are almost same.

Ribosome is also called as ribonucleoproteins.

SYNTHESIS OF RIBOSOMES

       It is synthesized in Nucleolus ( non membranic Darkly stained present in nucleus more in number appear during interphase phase and dissapears during Cell division).

SEDIMENTATION

          Due to small size the ribosome is last organelle sedimented during centrifugation and requires a force of 100,000 times gravity force for 1-2 hours.

Sedimentation has revealed two types of ribosomes

1-80s

       it is present in Eukaryotic cell it have one smaller unit 40s and one larger unit 60s which make 100s but due to overlapping it becomes 80s .

S is the svedberg unit used in ultracentrifugatoion.

2-70s

         It si present in prokaryotic cell but also present in Eukaryotic cell because chloroplast and mitochondria contain 70s ribosome.It smaller unit is 30s while larger unit is 50s which make 80s but due to overlapping it becomes 70s.

MCQ POINT

                  The larger and smaller unit attached with the help pg magnesium divalent ions.

POLYSOMES

            The group of Ribosomes attached to mRNA are called polysomes. 

FUNCTION OF RIBOSOME

1-The important function of synthesis of Protein.

2-Free ribosome in eukaryotic cell form heamoglobin globular protein present in RBCS.

3-Many enzymes also formed by ribosomes because all enzymes are proteins.

IMPORTANT MCQS IN THIS TOPIC

1-The size of ribosome:

Answer: 20nm

2-The eukaryotic cell contain which type of ribosome:

 Answer: 80s and 70s(mitochondria and chloroplast)

3-The prokaryotic cell contain which type of ribosome:

Answer: 70S

4-Free ribosome in eukaryotic cell form:

Answer: HEAMOGLOBIN

5-The ribosome is the _ of cell:

Answer: ENGINE

6-The ribosome have _ membranes:

Answer: Non MEMBRAINIC

7-The ribsome synthesized in :

Answer: NUCLEOLUS OF NUCLEUS

8-The ratio of protein and RNA in Ribosome:

Answer: 1:1

9-The smaller and larger unit of ribosome is attached by:

Answer:  Mg divalent ion

10-The ribosome is also called as:

Answer: RIBINUCLEOPROTEIN

11-They are _ in number in cell:

Answer: ENORMOUS

12-During sedimentation it requires _ times of gravity force:

Answer: 100,000

13- The dissociation of two units of ribosomes depend upon:

Answer : Mg ion and ATP

14-It is prominent organelle in which cell:

Answer: PROKARYOTIC CELL

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