A Tour of the Cell - Summary Biology

A Tour of the Cell 6.1 “To study cells, biologists use microscopes and the tools of biochemistry” Microscopy  In light microscopes (LM) visible light is passed through the specimen and then through glass lenses. Then lenses refract the light in such a way that the image is magnified  Magnification is the ratio of an object’s image size to its real size. Resolution is a measure of the clarity of the image  Most organelles are too small to be seen by the LM  Electron microscope focuses a beam of electrons through the specimen or onto its surface. It can achieve a resolution of 0.002. Biologists use the term ultrastructure to refer to a cell’s anatomy as revealed by an EM  There are two types of EMs: scanning electron microscope (SEM) and transmission electron microscope (TEM) Isolating Organelles by Cell Fractionation  The goal of cell fractionation is to take cells apart and separate the major organelles from one another. The instrument used is the centrifuge. Ultracentrifuges are the most powerful, spinning as fast as 130,000 revolutions per minute (RPM) 6.2 “Eukaryotic cells have internal membranes that compartmentalize their functions”  Organelles are found in cytosol  The entire region between the nucleus and plasma membrane is called the cytoplasm  The plasma membrane functions as a selective barrier that allows sufficient passage of oxygen, nutrients, and wastes to service the entire volume of the cell 6.3 “The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes” The Nucleus: Genetic Library of the Cell  The nucleus contains most of the genes in the eukaryotic cell. The nuclear envelope encloses the nucleus, separating its contents from the cytoplasm  The nuclear side of the envelope is lined by the nuclear lamina, except at the pores  DNA is organized into discrete units called chromosomes, structures that carry the genetic information within the nucleus  Each chromosome is made up of a material called chromatin, a complex of proteins and DNA  A prominent structure within the nondividing nucleus is the nucleolus Ribosomes: Protein Factories in the Cell  Ribosomes are particles made of ribosome RNA and protein. They are the organelles that carry out protein synthesis 6.4 “The endomembrane system regulates protein traffic and performs metabolic functions in the cell”  Endomembrane system carries out a variety of tasks in the cell  The membranes of this system are related through physical continuity or by the transfer of membrane segments as tiny vesicles  The system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, various kinds of vacuoles, and plasma membrane The Endoplasmic Reticulum: Biosynthetic Factory  The ER consists of a network of membranous tubules and sacs called cisternae  There are two types of ER: smooth ER and rough ER The Golgi Apparatus: Shipping and Receiving Center  In the GA, products of ER are modified and stored and then sent to other destinations Lysosomes  A lysosome is a membranous sac of hydrolytic enzymes that an animal cell uses to digest all kinds of macromolecules  Phagocytosis is a process by which protists ear by engulfing smaller organisms or other food particles Vacuoles: Diverse Maintenance Compartments  Food vacuoles are formed by phagocytosis. Contractile vacuoles pump excess water out of the cell.  Mature plant cells contain a large central vacuole enclosed by a membrane called the tonoplast 6.5 “Mitochondria and chloroplasts change energy from one form to another”  Mitochondria are the sites of cellular respiration, the metabolic process that generates ATP by extracting energy from sugars, fats, and other fuels with the help of oxygen  Chloroplasts are the sites of photosynthesis 6.6 “The cytoskeleton is a network of fibers that organizes structures and activities in the cell”  The cytoskeleton is a network of fibers extending through out the cytoplasm  The roles of the cytoskeleton is support, motility, and regulation  The three fibers that makeup cytoskeleton are microtubules (thickest), microfilaments (AKA actin filaments) are the thinnest, and intermediate filaments are fibers with diameters in the middle range 6.7 “Extracellular components and connections between cells help coordinate cellular activities” Cell Walls of Plants  The cell wall is an extracellular structure of plants cells that distinguishes them form animal cells. It protects the cell, maintains its shape, and prevents excessive uptake of water The Extracellular Matrix (ECM) of Animal Cells  The main ingredients of the ECM are glycoproteins secrete by the cells. The most abundant glycoprotein is the collagen Intercellular Junctions  Plants cell walls are perforated with channels called plasmodesmata