CELL BIOLOGY (Cell Fundamental Unit of Life)

• All living things are built from cells: small, membrane-enclosed units filled with a concentrated aqueous solution of chemicals
• Cells have the extraordinary ability to create copies of themselves by growing and then dividing in two
• The simplest forms of life are solitary cells, while higher organisms are communities of cells derived by growth and division from a single founder cell
• Every animal or plant is a vast colony of individual cells, each performing a specialized function integrated by intricate systems of cell-to-cell communication
• Cell biology is the study of cells and their structure, function, and behavior, providing answers to questions about life on Earth and ourselves
• Biologists estimate there may be up to 100 million distinct species of living things on the planet
• Cells differ vastly in form and function, with animal cells differing from plant cells
• All present-day cells appear to have evolved from a common ancestor
• Cells vary enormously in appearance and function
• Cells vary in size, shape, and chemical requirements, reflecting differences in cell function
• Cells can be specialized factories for the production of substances or engines that burn fuel to do mechanical work
• Living cells all have a similar basic chemistry
• Cells are composed of the same sorts of molecules and participate in the same types of chemical reactions
• Genetic information in cells is carried in DNA molecules, which are transcribed into RNA and translated into proteins
• Proteins dictate the appearance and behavior of a cell, serving as structural supports, chemical catalysts, and molecular motors
• The self-replication of cells involves duplicating genetic material and other components, then dividing in two to produce daughter cells capable of replication
• The relationship between DNA, RNA, and proteins enables self-replication in living things
• Viruses are not considered living because they parasitize the reproductive machinery of cells they invade to make copies of themselves
• Viruses are chemical zombies: inert and inactive outside their host cells but able to exert control once they gain entry
• Mutations can lead to offspring that are changed for the worse, better, or in a neutral way
• Mutations in DNA can change the genetic plan from the previous generation
• The struggle for survival eliminates the worse changes, favors the better changes, and tolerates the neutral changes
• Genes of the next generation will be the genes of the survivors
• All living cells have apparently evolved from the same ancestral cell
• Evolution is the process by which living species become gradually modified and adapted to their environment
• Life is an autocatalytic process where DNA and RNA provide sequence information to produce proteins and copy themselves
• Proteins provide catalytic activity needed to synthesize DNA, RNA, and themselves
• Differentiated cell types are generated during embryonic development from a single fertilized egg cell
• Cells express different genes to produce some RNAs and proteins depending on their internal state and cues from their surroundings
• Cells have a genome that provides a genetic program instructing them how to behave
• Electron microscopes, invented in the 1930s, use beams of electrons to greatly extend the ability to see the fine details of cells
• Light microscopes were invented in the 17th century, allowing biologists to see the intricate structure of cells
• Cells are formed by the growth and division of existing cells, a principle known as the cell theory
• The theory of evolution explains how random variation and natural selection gave rise to diversity among organisms that share a common ancestry
• Typical animal cells visualized in specific ways have distinct anatomy
• Cells have a sharply defined boundary, indicating the presence of an enclosing membrane called the plasma membrane
• Cells have a large, round structure called the nucleus near the middle
• The cytoplasm fills the cell's interior and is a transparent substance filled with various components
• With a good light microscope, specific components in the cytoplasm can be distinguished and classified
• Structures smaller than about 0.2 μm cannot normally be resolved with light microscopy