Acellular Bodies, Viruses, and Cellular Organelles
Acellular Bodies and Viruses
Acellular bodies are not living organisms.
Viruses
-Virus: Small molecules of DNA or RNA covered by a protein capsule (capsid). This capsule, composed of capsomeres, may have a neck, an outer shell, and various structures. Viruses are responsible for numerous parasitic infections and diseases. They are very small and can only live within other cells, using the host cell’s organelles to multiply.
Viral Life Cycle
Cycle of a virus:
- Attachment: The virus binds to the surface of the cell.
- Penetration: The virus’s DNA enters the cell.
- Replication: The viral DNA replicates inside the cell.
- Assembly: Viral components assemble into mature viruses.
- Release: The viruses exit the cell to infect others.
Lysogenic Cycle
Lysogenic life cycle:
- Attachment: The virus attaches to the cell surface.
- Penetration: Viral DNA enters the cell.
- Integration: Viral DNA integrates into the host cell’s DNA.
- Replication: The integrated prophage replicates with the cell’s DNA. The virus remains dormant, passing from generation to generation.
Certain substances or stimuli can trigger the virus to become active.
Cellular Organelles (Prokaryotic Cell)
Cell Membrane
-Cell plasma membrane: A membrane surrounding the cell, composed of lipids and proteins. It is flexible and waterproof, preserving the cell’s internal substances. It also contains proteins that selectively allow substances to pass through.
Cell Wall
-Cell wall: Characteristic of plant cells, made of cellulose, providing protection and rigidity.
Golgi Apparatus
-Golgi apparatus: A series of flattened, interconnected sacs. They grow as the cell grows.
They are involved in the storage and disposal of waste, and produce vacuoles and lysosomes containing digestive enzymes.
Lysosomes and Peroxisomes
-Lysosomes and peroxisomes: Spherical membrane-bound organelles containing enzymes, acting as the cell’s digestive system.
Endoplasmic Reticulum
-Endoplasmic reticulum: A network of sacs, larger and more developed than the Golgi apparatus. They may or may not have ribosomes. There are two types:
- Rough ER: Contains ribosomes.
- Smooth ER: Lacks ribosomes.
They produce and store proteins and other substances.
Ribosomes
-Ribosomes: Organelles composed of two subunits of RNA and proteins, involved in protein synthesis. They are found in mitochondria and chloroplasts.
Cell Nucleus
-Cell nucleus: Contains chromatin (DNA) and the nucleolus. DNA controls protein synthesis and cell division. The nucleolus is involved in ribosome production.
Chromosomes
-Chromosomes: Visible only when the cell is dividing.
Mitochondria
-Mitochondria: Double-membrane organelles. The outer membrane provides shape and filtering, while the inner membrane forms cristae. The interior contains a matrix. The inner membrane cristae are the power plants of the cell, responsible for cellular respiration.
Chloroplasts
-Chloroplasts: Found only in plant cells. They have two membranes, similar to mitochondria. The inner membrane forms thylakoids, which are stacked into grana. The interior contains a liquid called stroma and also has DNA. Chloroplasts contain chlorophyll and perform photosynthesis, producing glucose, which mitochondria then use for energy.
Cytoskeleton
-Cytoskeleton: A network of protein filaments and tubes that provide flexibility and structure to the cell, and are involved in cell movement.
Centrosome
-Centrosome or Diplosoma: Found only in animal cells, composed of nine triplets of protein fibers. They are involved in cell division and chromosome distribution.