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Difference between 70s and 80s ribosomes is basically of the sedimentation rate and of the fact that 70s ribosomes are found in prokaryotes and 80s ribosomes are found in eukaryotes. The 70s ribosomes are lighter and smaller in size than 80s ribosomes. The 70s ribosomes are freely present in the cytoplasm whereas the 80s ribosomes are present associated with different cell organelles.
Key Terms: cell structure, prokaryotes, eukaryotes, ribosomes, difference between 70s and 80s ribosomes
Cell and cell structure
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Cell is the basic structure of a living being for both plants and animals. The plant cells have a cell wall outside the cell membrane whereas the animal cell lacks a cell wall. In eukaryotic cells, a number of membranes bound organelles are present which serve a lot of different functions. These are, nucleus, Golgi apparatus, ribosomes, mitochondria, endoplasmic reticulum (ER) etc.
Also Read: Cell: Definition, Structure and Function.
What are Prokaryotes and Eukaryotes?
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The cells that have a membrane bound nucleus are known as eukaryotes. They also have a number of organelles present in the cytoplasm that are also membrane bound. They include plants and animal cells and also different protists and fungi. There is a difference between animal and plant cells. The plant cells have a cell wall, plastids and large central vacuole which are absent in animal cells.
Whereas the prokaryotes have a non-membrane bound nucleus, thus a not so well-defined nucleus. Also, organelles are absent except ribosomes. They include bacteria, mycoplasma, blue-green algae etc.
Also Read: Prokaryotic and Eukaryotic Cells- Characteristics and Structure Biology
What are ribosomes?
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Ribosomes are the organelles which are non-membrane bound, and are found in both the eukaryotic and prokaryotic cells. Their main function is to synthesize proteins, which are important for the structural growth of the organism. Ribosomes are present in two subunits, one smaller and other larger.
Ribosomes are found in the cell, present in the cytoplasm in prokaryotes and associated with other organelles like ER, mitochondria and chloroplasts (in plants). Ribosomes are composed of RNA and protein. If ribosomes are present on ER, they are known as rough endoplasmic reticulum.
Also Read: Endoplasmic Reticulum- Structure, Types, Functions Biology
Plant cell: showing rough endoplasmic reticulum
Prokaryotic ribosome (70s type)
The ribosomes which are present in prokaryotic cells are known as prokaryotic ribosomes. It is made up of two subunits i.e., 30s and 50s which make 70s prokaryotic ribosomes, where s signifies Swedberg’s sedimentation rate. They are present along with the plasma membrane. They are small, around 15-20 nm in size.
Ribosomes are the site of protein synthesis. They work by attaching a large number of ribosomes together on mRNA known as polysomes. They then translate mRNA into protein.
Eukaryotic ribosome (80s type)
The ribosomes found in eukaryotic cells are of the 80s types, which have two subunits of 40s and 60s. The Swedberg's sedimentation rate defines the measure of density and size of the subunits. The ribosomes are membrane less and are present along with the organelles and also along with the plasma membrane.
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Difference between 70s and 80s ribosomes
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The table below enlists the key differences between 70s and 80s Ribosomes:
| 70s | 80s | |
|---|---|---|
| Occurrence | Present in the cytoplasm and along with plasma membrane | Present along with plasma membrane and also with cell organelles like ER, mitochondria, chloroplasts (in plants) |
| Type | Prokaryotic ribosome | Eukaryotic ribosome |
| Weight | Lighter | Heavier |
| Size | Smaller | Larger |
| Weight | 2-3 million Dalton | 4-4.5 million Dalton |
| Subunits | Small- 30s Larger- 50s | Small- 40s Larger- 60s |
| Sedimentation coefficient* | 70 | 80 |
| RNA to protein ratio | 2:1 | 1:1 |
| Synthesis in: | Synthesis in prokaryotic cytoplasm | Synthesis in eukaryotic nucleolus |
| Antibiotic effect: | Inhibit protein synthesis | No effect on protein synthesis |
Also Read: Nucleolus
Things to remember
- Ribosomes are responsible for the synthesis of protein in the cell, protein in turn is important for all the important structural synthesis of the organism.
- The prokaryotes as well as eukaryotes have ribosomes i.e.- 70s and 80s respectively.
- Ribosomes are non-membranous structures, found in cytoplasm in prokaryotes and along with organelles in eukaryotes.
- The 70s types are smaller in size and lighter in weight than the 80s type.
- The 70s types have subunits as 30s and 50s.
- The 80s types have a subunit as 40s and 60s.
- S stands for svedberg unit, which defines the sedimentation coefficient of the ribosome.
Sample Questions
Ques 1: What is the Swedberg coefficient? (1 mark)
Ans The Swedberg coefficient defines the sedimentation coefficient of the ribosomal subunit. It is the measure of density and size of the subunits.
Ques 2: What are ribosomes composed of? (1 mark)
Ans The ribosome is composed of subunits which are further made up of RNA and protein. The RNA to protein ratio is more in the 70s types of ribosomes which is 2:1.
Ques 3: Define a eukaryotic cell with example. (1 mark)
Ans Eukaryotic cells are the cells having a well-defined nucleus and confined genetic material. Also, there are a number of membranes bound cell organelles. Some examples of eukaryotic cells are cells of plants and animals.
Ques 4 Mention the subunits of prokaryotic and eukaryotic ribosomes. (2 marks)
Ans For prokaryotes, the subunits are 30s and 50s.
For eukaryotes, the subunits are 40s and 60s.
Ques 5: Briefly mention the functions of ribosomes. (2 marks)
Ans. The ribosomes have following functions:
- They are responsible for protein synthesis.
- Many mRNAs cluster together and form polysomes which in turn translate mRNA into protein.
- They accumulate amino acids together to form protein within the cell.
Ques 6: Why do prokaryotic cells have unconfined genetic material? (1 mark)
Ans The prokaryotic cells do not have a well-defined nuclear membrane, thus a not so defined genetic material.
Ques 7: What are the characteristics of prokaryotic cells? (3 marks)
Ans. The prokaryotic cells have following characteristics:
- The nucleus is without any membrane.
- Membrane bound organelles are absent.
- Ribosomes are of the 70s types.
- Nucleolus is not found in these cells.
- E.g.- amoeba, blue-green algae, bacteria
Ques 8: How are prokaryotic ribosomes different from eukaryotic ribosomes? (3 marks)
Ans The prokaryotic ribosome differs from eukaryotic ribosomes in the following ways:
- The prokaryotic ribosome is 70s type and eukaryotic ribosome is 80s type.
- The 70s types are smaller in size and lighter in weight, whereas the 80s type is bigger in size and heavier in weight.
- The 70s types have more RNA content as compared to the 80s types.
- There is no effect of antibiotics on the 80s types whereas in 70s type, protein synthesis stops.
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