Here is an in depth explanation of Cell and Subcellular Organelles.
Cells are the basic unit of life, and they are found in all living organisms, from simple single-celled organisms to complex multicellular organisms like humans. A cell can be defined as a microscopic, self-contained unit of living matter that can perform all the necessary functions of life, including metabolism, growth, and reproduction.
The structure of a typical animal cell can be divided into several main parts. These include the cell membrane, cytoplasm, nucleus, and various organelles. The cell membrane is a thin, flexible barrier that surrounds the cell, and it controls the movement of substances into and out of the cell. The cytoplasm is the gel-like substance that fills the cell, and it contains many of the cell’s organelles. The nucleus is a large organelle that contains the cell’s genetic material, including the DNA. The organelles in the cell include structures like the mitochondria, which produce energy, and the endoplasmic reticulum and Golgi apparatus, which are involved in protein synthesis and transport.
Cells are categorized into two main categories: prokaryotic and eukaryotic. Prokaryotic cells are found in simple organisms like bacteria, and they do not have a nucleus or other membrane-bound organelles. Eukaryotic cells, on the other hand, are found in more complex organisms like animals and plants, and they have a distinct nucleus and other membrane-bound organelles.
Cells carry out many important functions in the body, including producing energy, repairing and maintaining tissues, and fighting off infections. They do this through a wide variety of cellular processes, including cellular respiration, photosynthesis, and protein synthesis. In addition, cells are capable of responding to changes in their environment, and they can communicate with other cells through chemical signals.
- Most prominent organelle in the cell.
- Present in all cells except mature RBCs in circulation.
- Nucleus occupies most of the available space in some cells, such as small lymphocytes and spermatozoa.
- Surrounded by two membranes: the inner perinuclear membrane with numerous pores, and the outer membrane continuous with the membrane of endoplasmic reticulum.
- Contains DNA, the chemical basis of genes that governs all the functions of the cell.
- DNA molecules are complexed with proteins to form chromosomes.
- DNA replication and RNA synthesis (transcription) occur inside the nucleus.
- Nucleolus is a lighter shaded area of the nucleus and is the area for RNA processing and ribosome synthesis.
- Nucleolus is very prominent in cells actively synthesizing proteins.
- Overall, cells are the building blocks of life, and they play a vital role in the functioning of all living organisms. Understanding the structure and function of cells is essential for understanding the basic biology of life.
Endoplasmic Reticulum (ER)
- Network of inter connected membranes enclosing channels or cisternae.
- From perinuclear envelope to outer plasma membrane.
- Gives a railway track appearance under the electron microscope.
- Very prominent in cells actively synthesizing proteins, such as immunoglobulin-secreting plasma cells.
- Proteins, lipoproteins and glycoproteins are synthesized in the ER.
- The enzyme cytochrome P-450, present in the ER, detoxifies various drugs.
- The Golgi Apparatus is where the glycoproteins from the ER are further processed before secretion.
- Carbohydrate groups are added to proteins successively while they move through the ER.
- Glycoproteins then reach the Golgi apparatus where further carbohydrate chains are added before secretion.
- The Golgi apparatus functions in protein sorting, packaging and secretion.
- Lysosomes are bags of enzymes inside the cell that decompose waste materials
- They contain enzymes that break down polysaccharides, lipids, proteins, and nucleic acids
- Endocytic vesicles and phagosomes are fused with lysosomes to form secondary lysosomes or digestive vacuoles
- Foreign particles are progressively digested inside these vacuoles.
- Mitochondria are spherical, oval or rod-like bodies, about 0.5–1 micrometers in diameter and up to 7 micrometers in length.
- Erythrocytes do not contain mitochondria, while the tail of spermatozoa is packed with mitochondria.
- Mitochondria are the powerhouse of the cell, where energy from food oxidation is trapped as ATP.
- Mitochondria have two membranes, the inner membrane convolutes into folds or cristae, and contains enzymes of electron transport chain. The fluid matrix contains enzymes of citric acid cycle.
- Mitochondria contain specific DNA which encodes information for the synthesis of certain mitochondrial proteins.
- The division of mitochondria is controlled by mitochondrial DNA.
- Antibiotics that inhibit bacterial protein synthesis do not affect cellular processes but can inhibit mitochondrial protein biosynthesis.
- The plasma membrane separates the cell from the external environment and compartmentalizes cellular activities.
- The membrane has highly selective permeability properties.
- The plasma membrane is composed mainly of lipids, proteins, and small amounts of carbohydrates. The carbohydrate is present as glycoproteins and glycolipids.
- Phospholipids are the most common lipids present in membranes, and they are amphipathic in nature. Cholesterol is also present.
- The fluid mosaic model states that membranes are made up of a lipid bilayer, with the polar head groups oriented towards the extracellular side and the cytoplasmic side forming a hydrophobic core.
- Membrane proteins can be peripheral or integral. Integral membrane proteins are deeply embedded in the bilayer and can serve as receptors, tissue-specific antigens, ion channels, membrane-based enzymes, etc.