Fundamental Concepts of Cell Biology

Fundamental Concepts of Cell Biology

• Cells are the basic units of life, exhibiting a wide range of shapes and sizes.
• Cells are enclosed by a plasma membrane, a selectively permeable barrier that controls the movement of substances into and out of the cell.
• Cells contain various organelles that perform specific functions, like the nucleus, mitochondria, and ribosomes. Different cell types have different sets of organelles based on their specialized roles.
• Genetic material (DNA) within the nucleus directs the cell’s activities and dictates protein synthesis.
• The cytoplasm, the region outside the nucleus, houses various cellular structures and processes.
• Cells exhibit a continuous dynamic activity encompassing metabolic reactions, movement of molecules and the cell itself, and cell division.

Cell Membrane Structure and Function

• The cell membrane is a phospholipid bilayer, which is a double layer of phospholipid molecules.
• Embedded within the phospholipid bilayer are proteins, which act as transporters, receptors, and enzymes.
• Cholesterol molecules are also present in the membrane to maintain fluidity and stability at varying temperatures.
• The membrane is selectively permeable, meaning it regulates the movement of substances in and out of the cell.
• Transport across the membrane occurs through passive transport (diffusion and osmosis) or active transport.
• Diffusion is the movement of molecules from a high concentration to a low concentration.
• Osmosis is the movement of water across a semipermeable membrane from a high water concentration to a low water concentration.
• Active transport requires energy to move molecules against their concentration gradient.
• Membrane proteins facilitate both passive and active transport.

Cellular Organelles

• Nucleus: Contains the cell’s genetic material (DNA) organized into chromosomes. Controls cellular activities through gene expression.
• Mitochondria: Known as the powerhouse of the cell, they generate ATP (adenosine triphosphate) – the cell’s primary energy currency – through cellular respiration.
• Endoplasmic Reticulum (ER): A network of membranes involved in protein synthesis and lipid metabolism. Rough ER has ribosomes attached for protein synthesis, smooth ER lacks ribosomes and is involved in lipid synthesis.
• Golgi apparatus: Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.
• Ribosomes: Sites of protein synthesis. They can be free in the cytoplasm or bound to the rough ER.
• Lysosomes: Contain enzymes that break down waste materials and cellular debris.
• Vacuoles: Storage sacs for water, nutrients, or waste products. Particularly prominent in plant cells.
• Cytoskeleton: A network of protein fibers that provides structural support, facilitates cell movement, and allows for intracellular transport.
• Peroxisomes: Contain enzymes that carry out specific metabolic reactions, such as breaking down fatty acids.

Cell Division

• Cell division is essential for growth, repair, and reproduction in organisms.
• Mitosis is the process of nuclear division that results in two identical daughter cells, crucial for growth and repair.
• Meiosis is the process of nuclear division that results in four genetically different daughter cells, essential for sexual reproduction.

Types of Cells

• Prokaryotic cells lack a nucleus and membrane-bound organelles, whereas eukaryotic cells possess a nucleus and various membrane-bound organelles.
• Prokaryotes include bacteria and archaea.
• Eukaryotes include plant, animal, fungi, and protist cells, characterized by more complex structures and functions.
• Plant cells have unique features including cell walls and chloroplasts for photosynthesis.
• Animals cells vary in shape and function, possessing specialized structures for respective roles.

Basic Cellular Processes

• Cellular respiration converts food molecules into a usable energy form (ATP).
• Photosynthesis converts light energy into chemical energy (sugars) in plants and some other organisms.
• Protein synthesis involves the production of proteins using genetic information from DNA.
• Intracellular transport involves the movement of molecules and organelles within the cell.
• Metabolism encompasses all chemical reactions occurring within a cell, involving breaking down molecules (catabolism) and building up molecules (anabolism).