A group of ribosomes attached to mRNA is known as :
polysomes
Understanding Ribosomes and mRNA in Protein Synthesis
Protein synthesis is a fundamental process in all living cells. It involves decoding the genetic information carried by messenger RNA (mRNA) to build specific protein molecules. This process takes place on structures called ribosomes.
Ribosomes are complex molecular machines responsible for translation, where the sequence of codons on the mRNA molecule is read, and the corresponding amino acids are assembled into a polypeptide chain. A single mRNA molecule contains the genetic instructions for one or more proteins.
What Happens When Ribosomes Attach to mRNA?
During active protein synthesis, multiple ribosomes can bind to a single mRNA molecule simultaneously. As soon as a ribosome moves far enough along the mRNA sequence, another ribosome can attach to the starting point (usually the initiation codon). This allows for the production of many copies of the same protein from a single mRNA template molecule in a relatively short period.
When a group of ribosomes are attached to a single mRNA molecule, all working together to translate the mRNA into proteins, this structure is called a polysome or polyribosome.
Analyzing the Options
Let's look at the provided options to identify the correct term for a group of ribosomes attached to mRNA:
- polypeptide: A polypeptide is the resulting chain of amino acids that is synthesized during protein synthesis. It is the product formed by the ribosomes translating the mRNA, not the structure of ribosomes attached to mRNA. So, this option is incorrect.
- polysomes: As discussed, a polysome (or polyribosome) is precisely the term used to describe multiple ribosomes attached to a single mRNA molecule. This arrangement increases the efficiency of protein production. This option matches the description.
- polymer: A polymer is a large molecule composed of many repeated subunits (monomers). While proteins and nucleic acids (like mRNA) are polymers, the term "polymer" itself is too general and does not specifically refer to a group of ribosomes on mRNA. So, this option is incorrect.
- monomer: A monomer is a single unit that can join with other monomers to form a polymer. For example, amino acids are monomers of proteins, and nucleotides are monomers of mRNA. This term does not describe a group of ribosomes attached to mRNA. So, this option is incorrect.
Conclusion on Ribosomes Attached to mRNA
Based on the analysis, the term for a group of ribosomes attached to mRNA is polysomes.
| Term | Description | Related to Question? |
|---|---|---|
| Polypeptide | A chain of amino acids (the protein product) | No (product, not the translation machinery arrangement) |
| Polysomes | Multiple ribosomes translating a single mRNA molecule | Yes (direct answer) |
| Polymer | A large molecule made of repeating subunits | No (too general a term) |
| Monomer | A single subunit that forms a polymer | No (not related to the ribosome-mRNA structure) |
Revision Table: Key Concepts in Protein Synthesis
| Component | Function |
|---|---|
| mRNA (messenger RNA) | Carries genetic code from DNA to ribosomes |
| Ribosomes | Site of protein synthesis (translation) |
| tRNA (transfer RNA) | Brings specific amino acids to the ribosome |
| Amino Acids | Building blocks of proteins |
| Polypeptide | Chain of amino acids formed during translation |
| Codon | Three-nucleotide sequence on mRNA specifying an amino acid |
| Anticodon | Three-nucleotide sequence on tRNA complementary to an mRNA codon |
| Polysome/Polyribosome | Multiple ribosomes translating a single mRNA molecule simultaneously |
Additional Information: Significance of Polysomes
The formation of polysomes is crucial for efficient protein synthesis in cells. By allowing multiple ribosomes to translate the same mRNA molecule at the same time, the cell can produce many copies of the required protein rapidly. This is particularly important for proteins that are needed in large quantities.
Polysomes can be found freely in the cytoplasm, synthesizing proteins destined for use within the cytosol, or they can be attached to the endoplasmic reticulum (ER) membrane, synthesizing proteins destined for secretion, insertion into membranes, or delivery to specific organelles like lysosomes.
The number of ribosomes in a polysome can vary depending on the length of the mRNA molecule and the rate of initiation of translation.
Important Questions from Cell Structure
Within the nucleus of eukaryotic cells, which of the following structures contains the tightly coiled genetic material?
Chromosomes are composed of DNA and:
Bacteria have an undefined nuclear region which lacks a nuclear membrane and contains only DNA without proteins. Such a region is called:
Which of the following statements is/are correct?
I. Amoeba ingests its food with the help of pseudopodia.
II. Amoeba constantly changes its shape and position.
Which of the following cell organelles functions both as a passageway for intracellular transport and as a manufacturing surface?
