Cell Structure and Functions:
Cytology, the Science of Cells: Let's begin with cytology, which is the scientific study of cells. It delves into the form, structure, and composition of these tiny units of life.
The Cell: Life's Building Block: A cell is the fundamental structural and functional unit of life. Think of it as the building block of living organisms. In unicellular organisms like amoeba and bacteria, a single cell performs all essential life functions.
Cell Theory Founders: Back in the day, Anton Von Leeuwenhoek was the first to observe and describe live cells under a microscope. Later, Robert Brown discovered something crucial, the nucleus.
Cell Theory, the Bedrock of Biology: In the mid-19th century, Matthias Schleiden and Theodore Schwann put forth the cell theory. It stated that all living organisms are made up of cells and their products. Furthermore, they emphasized that all cells come from pre-existing cells. This theory was later refined by Rudolf Virchow.
Prokaryotic Cells:
The Simple Prokaryotic Life: Prokaryotic cells are less complex. They lack a membrane-bound nucleus and are generally smaller. These cells usually have a single chromosome and lack membrane-bound organelles.
Shapes Galore: Prokaryotic cells can come in various shapes. Some are rod-shaped (bacillus), spherical (coccus), comma-shaped (vibrio), or spiral (spirillum).
The Cell Envelope: In prokaryotes, a chemically complex cell envelope surrounds the cell membrane. This envelope consists of three layers: glycocalyx, cell wall, and cell membrane. The outermost layer, glycocalyx, can be either a loose sheath or a tough capsule.
Plasmid DNA: In some bacteria, there's plasmid DNA that carries special features, like antibiotic resistance.
Bare-Bones Organelles: Unlike eukaryotic cells, prokaryotes lack organelles such as mitochondria and Golgi bodies. Instead, they have mesosomes, a specialized cell membrane.
Ribosomes in Action: Prokaryotes have ribosomes for protein synthesis, but they're slightly different from those in eukaryotic cells. Prokaryotic ribosomes are known as 70S ribosomes.
Reserved Materials: Prokaryotic cells store reserved materials in the cytoplasm as inclusion bodies. These can contain various substances like phosphate or glycogen granules.
Motility and Attachment: Some prokaryotic cells are motile, thanks to flagella. They also have pili and fimbriae for attachment to other cells or surfaces.
Eukaryotic Cells:
Eukaryotic Diversity: Eukaryotic cells are more complex and are found in protists, plants, animals, and fungi.
Nuclear Organization: Eukaryotic cells have a well-organized nucleus with a nuclear membrane. The genetic material is neatly arranged in chromosomes.
Plant and Animal Differences: Plant cells have a few unique features like a cell wall, plastids, and a large central vacuole. Animal cells, on the other hand, have centrioles, which aren't present in plant cells.
Cell Membrane Story: The cell membrane is made up of lipids and proteins. In a landmark model known as the fluid mosaic model, scientists Singer and Nicholson proposed that lipids in the membrane enable proteins to move laterally.
Transport Mechanisms: The cell membrane is essential for transporting molecules. Cells use active and passive transport, with active transport requiring energy and moving against the concentration gradient.
Cell Walls and More: In plants and fungi, you'll find cell walls. Algae have cell walls made of cellulose and minerals, while other plants use cellulose, hemicellulose, pectin, and proteins.
Endomembrane System: Eukaryotic cells have an endomembrane system that includes the endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles. These help with various cellular functions.
Mitochondria, the Powerhouses: Mitochondria are the energy powerhouses in eukaryotic cells, producing ATP through aerobic respiration. They also have their own DNA and ribosomes.
Plastids in Plants: Plants contain plastids with specific roles. Chloroplasts, for instance, have chlorophyll to capture sunlight for photosynthesis. Chromoplasts provide colorful pigments, and leucoplasts store various substances.
Ribosomes in Action: Eukaryotic cells use 80S ribosomes for protein synthesis, which have two subunits.
Centrosomes and Nuclei: Eukaryotic cells have centrosomes, containing centrioles, and a complex nucleus with chromatin that transforms into visible chromosomes during cell division.
Chromosomes Come in Types: Chromosomes can be classified based on the position of the centromere, and some have secondary constrictions, giving rise to small fragments called satellites.
These notes provide you with a conversational overview of cell structure and functions, emphasizing the differences between prokaryotic and eukaryotic cells and the various organelles in eukaryotic cells.
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