Cell organelle Ribosomes and peroxisome

Ribosomes 

RIBOSOMES

Ribosomes are small globular organelles of 250 A diameter. In 1953, Robinson and Brown made the first report of ribosomes in bean roots. In 1956 Palade identified ribosomes from Amphibian oocytes and discovered the presence of RNA in ribosomes. Chloroplasts' mitochondria and nuclei also possess ribosomes. Ribosomes or ribonucleoprotein particles are situated either on the wall of the endoplasmic reticulum or are present in the cytoplasm independently.

Structure of ribosomes

Understanding Cell Organelles: Ribosomes and Peroxisomes

Cells are the fundamental units of life, and within them exists a complex network of structures known as organelles. Each organelle performs a specific function necessary for the cell’s survival and efficiency. Among these, ribosomes and peroxisomes play crucial but very different roles. This article explores their structure, function, and importance in cellular activity.

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Ribosomes: The Protein Factories of the Cell

Ribosomes are small, dense structures found in all living cells. They are primarily responsible for protein synthesis, making them essential for growth, repair, and overall cell function.

Structure

Ribosomes are composed of ribosomal RNA (rRNA) and proteins. They consist of two subunits:

• A large subunit

• A small subunit

These subunits come together during protein synthesis. Ribosomes can be found either:

• Floating freely in the cytoplasm, or

• Attached to the rough endoplasmic reticulum (RER)

Function

The main role of ribosomes is to translate genetic information from messenger RNA (mRNA) into proteins. This process involves:

1. Reading the sequence of the mRNA

2. Linking amino acids together in the correct order

3. Forming a polypeptide chain that folds into a functional protein

Proteins produced by ribosomes are used for:

• Enzymatic reactions

• Structural components

• Cell signaling

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Peroxisomes: The Detoxifiers of the Cell

Peroxisomes are membrane-bound organelles that play a key role in metabolic processes, especially those involving detoxification.

Structure

Peroxisomes are small, spherical structures enclosed by a single membrane. Inside, they contain enzymes that facilitate chemical reactions, particularly oxidation.

Function

Peroxisomes are involved in several important processes:

• Detoxification: They break down harmful substances, including alcohol and toxins.

• Fat metabolism: They help in the breakdown of fatty acids through oxidation.

• Hydrogen peroxide regulation: Peroxisomes produce hydrogen peroxide (H₂O₂) as a byproduct of metabolism and also contain enzymes like catalase to convert it into water and oxygen, preventing cellular damage.

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Key Differences Between Ribosomes and Peroxisomes

Feature	Ribosomes	Peroxisomes
Structure	Non-membrane-bound	Membrane-bound
Main Function	Protein synthesis	Detoxification and metabolism
Composition	rRNA and proteins	Enzymes and oxidative molecules
Location	Cytoplasm or rough ER	Cytoplasm

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Conclusion

Ribosomes and peroxisomes illustrate how specialized cell organelles work together to maintain life. While ribosomes focus on building proteins essential for cellular function, peroxisomes protect the cell by breaking down harmful substances and managing metabolic processes. Understanding these organelles helps us appreciate the intricate and highly organized nature of living cells.

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By studying these microscopic structures, scientists continue to uncover the mechanisms that sustain life, offering insights into health, disease, and biotechnology.

It is estimated that mammalian cells contain 10 million ribosomes per cell and in E.coli 10,000 to 20,000 per set. Ribosomes are many in actively metabolizing cells. They have 2 subunits and 2 types.

a) The ribosomes of the 1970s: They are smaller and have a sedimentation coefficient of 70s.

These ribosomes are present in Bacteria, Mitochondria, and Chloroplasts.

b) 80s Ribosomes: are larger in size with a sedimentation coefficient of 80s ribosomes are found in cells of higher plants & animals.

each of these consists of two subunits. one larger & other smaller subunit. 70s one is coupled with a 50s subunit and a 30s subunit. 80s subunit is coupled with 60s & 40s

S= Sved berg units (sedimentation coefficient)

70s

50s

40s

80s

60s

40s

Types of ribosomes

However, certain exceptional ribosomes are seen in mammalian mitochondria, consisting of 35s and 25s subunits. Yeast possesses 73s ribosomes and fungi pos- ses 77s ribosomes in their mitochondria.

Subunits of ribosomes are associated with each other and only during protein synthesis. Mg2+ concentration of 0.001m in the cytoplasm is favorable for subunit association.

Figure showing Mg++ concentration dependent as-association of ribosomes or subunits.

Functions of ribosomes

(A) Ribosomes are involved in protein synthesis. the specific function being codon and anticodon recognition between t-RNA and m-RNA. This is brought about by r- RNA. TRNA also participates in protein synthesis due to its base-pairing quality.

(B) To form the polypeptide chain, peptide bond formation is held between the amino acids.

(C) Translocation is performed with the help of protein factors or the  certain enzymes viz.,

(i) Initiation factor.

(ii) Elongation factors

(iii) Release factors.

PEROXISOMES 

Protozoans, cells of fungi, plants, liver, and kidney of vertebrates possess certain mem- brane-bound spherical bodies of 0.2 to 1.5 µm diameter in close association with the endoplasmic reticulum, mitochondria, or chloroplast. They are called microbodies or peroxisomes.

Peroxisomes are tiny, membrane-enclosed organelles that house enzymes responsible for various metabolic reactions, including several aspects of energy metabolism. Though peroxisomes are morphologically similar to lysosomes they are assembled like mitochondria and Chloroplasts.

Proteins are synthesized on free ribosomes and then brought into peroxisomes as fully-formed polypeptide chains. Despite lacking their own genomes, peroxisomes share similarities with mitochondria and chloroplasts as they undergo replication.

Structure of peroxisome

Peroxisomes occur in many animal cells and in a wide range of plants. That occurs in all photosynthetic plants, brown algae, fungi, and protozoans.

Peroxisomes in which the glyoxylate cycle occurs are often called Glyoxysomes. They can be found in yeasts, Neurospora, oil-rich seeds, and other similar organisms.

Functions of peroxisomes:

Peroxisomes contain at least 50 enzymes involved in biochemical pathways in different types of cells.

(1) Peroxixomes are originally defined as organelles that carry out oxidation reactions leading to the production of hydrogen peroxide.

(2) As H2O2 is harmful to the cell they also contain catalase and enzymes which decompose hydrogen peroxide either by converting it to water or by using it to oxidize another organic compound.

(3) They are thus involved in the oxidation of a variety of compounds, viz., uric acids, amino acids, and fatty acids.

(4) Oxidation of fatty acids is of great importance, as it provides a major source of metabolic energy. 

(5) In animal cells, fatty acids are oxidized only in Peroxisome.

(6)Peroxisomes are also involved in lipid biosynthesis In animal cells Cholesterol and dolichol are synthesized in peroxisomes.

(7) Peroxisomes play a role in the liver by participating in the synthesis of bile acids, which are produced from cholesterol.

(8) Peroxisomes contain enzymes required for the synthesis of plasmalogens, a family of phospholipids. Plasmalogens are important tissue components in the heart and brain.

(9)Peroxisomes serve a dual and crucial function in plant cells. Firstly, in seeds, they are responsible for converting stored fatty acids into carbohydrates, which supply energy and essential materials for the growth of the germinating plant. This conversion process takes place through a series of reactions known as the glyoxylate cycle. As a result of their involvement in this cycle, peroxisomes are sometimes referred to as Glyoxysomes.

(10) In leaves they are involved in photorespiration which serves to metabolize a side product formed during photosynthesis. During photosynthesis, Co2 is converted into carbohydrates by the Calvin cycle. Through successive steps, Glycine is transported to mitochondria. where it is converted to serine. Serine is sent back to the peroxisome, where it is converted to glycerate which again enters the Calvin cycle in the chloroplast. Thus it helps in utilizing most of the carbon in the glycolate.

Cell organelles Golgi body and nucleus - Click here

Cell organelles Chloroplast and mitochondria - Click here