Biology Campbell Chapter 6 Def. And Concepts

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Chapter 6

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A Tour of the Cell

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Overview

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The Fundamental Units of Life

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Concept 6.1

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To study cells, biologists use microscopes and the tools of biochemistry

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Microscope

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Light Microscope (LM)

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An optical instrument with lenses that refract (bend) visible light to magnify images of specimens. Can be used to study living cells.

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Magnification

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The ratio of an object's image size to its real size.

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Resolution

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A measure of the clarity of the image; it is the minimum distance two points can be separated and still be distinguished as two points.

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Contrast

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Accentuates differences in parts of the sample.

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Organelles

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Membrane-enclosed compartments which are simply too small to be resolved by the light microscope.

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Electron Microscope (EM)

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Uses magnets to focus an electron beam on or through a specimen, resulting in resolving power a thousandfold greater than that of a light microscope. Methods used to prepare the specimen kills the cells. Can introduce artifacts, structural features seen in micrographs that do not exist in the living cell. Resolution is inversely related to the wavelength of the radiation a microscope uses for imaging, and electron beams have much shorter wavelengths than visible light.

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Scanning Electron Microscope (SEM)

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Used to study the fine details of cell surfaces. Can see 3-D image of the surface of a specimen.

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Transmission Electron Microscope (TEM)

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Used to study the internal structure of thin sections of cells. Can see cross section of specimen.

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Cytology

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The study of cell structure.

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Biochemistry

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The study of the molecules and chemical processes (metabolism) of cells.

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Cell Fractionation

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Cell Fractionation

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Takes cells apart and separates the major organelles and other subcellular structures from one another.

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Pellet

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A fraction of the cell components that settle to the bottom of a tube after centrifuge. At lower speeds, the pellet consists of larger components, and higher speeds yield a pellet with smaller components.

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Ultracentifuges

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The most powerful machine which spins up to 130,000 revolutions per minute (rpm) and apply forces on particles of more than 1 million times the force of gravity.

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Results of Differential Centrifugation

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At 1,000 g (1,000 times force of gravity), pellet rich in nuclei and cellular debris. At 20,000 g, pellet rich in mitochondia and chloroplasts if cells are from plant. At 80,000 g, pellet rich in "microsomes" (pieces of plasma membranes and cells' internal membranes). At 150,000 g, Pellet rich in ribosomes.

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Concept 6.2

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Eukaryotic cells have internal membranes that compartmentalize their functions

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Comparing Prokaryotic and Eukaryotic Cells

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Plasma Membrane

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The membrane at the boundary of every cell that acts as a selective barrier, regulating the cell's chemical composition.

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Cytosol

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The semifluid, jelly-like substance of the cytoplasm in which organelles and other components are found.

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Chromosomes

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Carry genes in the form of DNA. Found in the nucleus of eukaryotic cells.

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Ribosomes

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Tiny complexes that make proteins according to instruction from the genes.

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Eukaryotic Cell

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Most of the DNA is in a organelle called the nucleus, which is bound by a double membrane. Organisms of the domain Protists, fungi, animals, and plants consist of these.

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Prokaryotic Cell

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The DNA is concentrated in a region that is not membrane-enclosed. Organisms of the domain Bacteria and Archaea consist of these.

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Nucleoid

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A dense region of DNA in a prokaryotic cell.

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Cytoplasm

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The contents of the cell, exclusive of the nucleus and bounded by the plasma membrane.

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Mycoplasma

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Smallest cells of bacteria, which have diameters between 0.1 and 1.0 um. These are perhaps the smallest packages with enough DNA to program metabolism and enough enzymes and other cellular equipment to carry out the activities necessary for a cell to sustain itself and reproduce.

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Surface Area to Volume Ratio of a Cell

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For each square micrometer of membrane, only a limited amount of a particular substance can cross per second. As a cell increases in size, its volume grows proportionately more than its surface area. A smaller object has a greater ratio.

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Microvilli

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The long, thin projections from a cell's surface which increase surface area without an appreciable increase in volume.

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A Panoramic View of the Eukaryotic Cell

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Concept 6.3

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The eukaryotic cell's genetic instructions are housed in the nucleus and carried out by the ribosomes

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The Nucleus: Information Central

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Nucleus

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Contains most of the genes in the eukaryotic cell.

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Nuclear Envelope

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Encloses the nucleus, separating its contents from the cytoplasm. It is a double membrane, the inner and outer membranes are continous.

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Pore Complex

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An intricate protein structure that lines each pore and plays an important role in the cell by regulating the entry and exit of most proteins and RNAs, as well as large complexes of macromolecules.

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Nuclear Lamina

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At the pores, the nuclear side of the envelope is lined by a netlike array of protein filaments that maintains the shape of the nucleus by mechanically supporting the nuclear envelope.

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Nuclear Matrix

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A framework of fibers extending throughout the nuclear interior.

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Chromatin

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The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope.

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Nucleolus

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A specialized structure in the nucleus, consisting of chomatin regions containing ribosomal RNA genes along with ribosomal proteins imported from the cytoplasmic site of rRNA synthesis and ribosomal subunits assembly.

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Ribosomes: Protein Factories

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Ribosomes

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Complexes made of ribosomal RNA and protein, are the cellular components that carry out protein synthesis. Cells that have high rates of protein synthesis have particularly large numbers of ribosomes. Also, cells active in protein synthesis prominent nucleoli. Ex. human pancreas cell has a few million

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Free Ribosome

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Is suspended in the cytosol and structurally idential to bound ribosome. Most of the proteins made on free ribosomes function within the cytosol; ex. enzymes that catalyze the first steps of sugar breakdown.

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Concept 6.4

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The endomembrane system regulates protein traffic and performs metabolic functions in the cell

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Bound Ribosome

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Are attached to the outside of the endoplasmic reticulum or nuclear envelope and are structurally identical to free ribosomes. Bound ribosomes generally make packaging within certain organelles such as lysomes, or for export from the cell (secretion).

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Endomembrane System

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Carries out various task in the cell such as synthesis of proteins and their transport into membranes and organelles or out of the cell, metabolism and movement of lipids, and detoxification of poisons. The membranes of this system are related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles.

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Vesicles

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A sac made of membrane in the cytoplasm.

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The Endoplasmic Reticulum: Biosynthetic Factory

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Endoplasmic Reticulum (ER)

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An extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions.

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Smooth ER

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The portion of the endoplasmic reticulum that is free of ribosomes. Functions include the synthesis of lipids, metabolism of carbohydrates, and detoxification of drugs and poisons.

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Rough ER

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The portion of the endoplasmic reticulum studded with ribosomes. Functions include secreting proteins, growing membrane proteins and phospholipids, transfers to other components of the endomembrane system.

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Functions of Smooth ER

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Functions of Rough ER

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Glycoproteins

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Proteins that have carbohydrates covalently bonded to them.

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Transport Vesicles

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Vesicles in transit from one part of the cell to another.

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The Golgi Apparatus: Shipping and Receiving Center

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Golgi Apparatus

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An organelle in eukaryotic cells consisting of stacks of flat membanous sacs. Functions as a center of manufacturing, warehousing, sorting, and shipping products of the endoplasmic reticulum and synthesize some products, notably non-cellulose carbohydrates. It has two polar sides, the cis face is for receiving and the trans face is for shipping.

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Lysosomes: Digestive Compartments

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Lysome

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A membranous sac of hydrolytic enzymes that an animal cell uses to digest macromolecules.

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Phagocytosis

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A type of endocytosis win which large particulate substances are taken up by a cell. It is carried out by some protists and by certain immune cells of animals.

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Autophagy

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A cell's hydolytic enzymes are used to recycle it's own organic material.

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Vacuoles: Diverse Maintenance

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Food Vacuoles

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A membranous sac formed by phagocytosis of microorganisms or particles to be used as food by the cell.

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Contractile Vacuole

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A membranous sac that helps move excess water out of certain fresh-water protists.

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Central Vacuole

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A membranous sac in a mature plant cell with diverse roles in repoduction, growth, and development.

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The Endomembrane System: A Review

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Concept 6.5

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Mitochondria and chloroplasts change energy from one form to another

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Mitochondria

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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. Contain their own ribosomes and DNA.

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Chloroplast

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An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water. Contain their own ribosomes and DNA.

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Peroxisome

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An oxidative organelle that is not part of the endomembrane system. Imports it's proteins primarily from the cytosol. May increase in number by splitting in two when they reach a certain size.

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Mitchondria: Chemical Energy Conversion

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Cristae

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An infolding of the inner membrane of a mitochondion that houses electrons transport chains and molecules of the enzyme catalyzing the synthesis of ATP.

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Mitochondrial Matrix

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The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the citric acid cycle.

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Chloroplasts: Capture of Light Energy

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Plastid

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One of a family of closely related organelles that includes chloroplasts, chromoplasts, and amyloplasts (leucoplasts). Plastids are found in cells of photosynthetic organisms.

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Thylakoid

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A flattened membranous sac inside a chloroplast. Exist in an interconnected system in the chloroplast and contain the molecular "machinery" used to convert light energy to chemical energy.

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Granum

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A stack of membrane-bounded thylakoids in the chloroplast. Grana function in the light reactions of photosynthesis.

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Stroma

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Within the chloroplast, the dense fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water. Contains the chloroplast DNA and ribosomes as well as many enzymes.

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Peroxisomes: Oxidation

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Glyoxysomes

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Specialized peroxisomes found in the fat-storing tissues of plant seeds.

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Concept 6.6

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The cytoskeleton is a network of fibers that organize structures and activities in the cell

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Cytoskeleton

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A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical, transport, and signaling functions.

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Roles of the Cytoskeleton: Support, Motility, and Regulation

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Motor Proteins

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A protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell.

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Components of the Cytoskeleton

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Microtubules

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Microtubule

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Structure: Hollow tubes; wall consists of 13 columns of tubulin molecules
Diameter: 25 nm with 15-nm lumen
Protein Subunits: Tubulin, a dimer consisting of alpha-tubulin and beta-tubulin
Main Functions: Maintenance of cell shape (compression-resisting "girders"), cell motility (as in cilia or flagella), chromosome movement in cell division, and organelle movement.

One end can accumulate or release tubulin dimers at a much higher rate than the other.

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Centrosomes and Centrioles

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Centrosome

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Structure present in the cytoplasm of animal cells, important during cell division; functions as a microtubule-organizing center. A centrosome has two centrioles.

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Centrioles

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A structure in the centrosome of an animal cell composed of a cylinder of microtubule triplets arranged in a 9 + 0 pattern. A centrosome has a pair of centrioles.

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Cilia and Flagella

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Flagellum
(plural, Flagella)

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A long cellular appendage specialized for locomotion. Like motile cilia, eukaryotic ones have a core with nine outer doublet microtubules and two inner single microtubules ensheathed in an extension of the plasma membrane. Prokaryotic ones have a different structure.

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Cilium
(plural, Cilia)

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A short cellular appendage containing microtubules. A motile one is specialized for locomotion and is formed from a core of nine outer doublet microtubules and two inner single microtubules (the "9 + 2" arrangement) ensheathed in an extension of the plasma membrane. A primary one is usually nonmotile and plays a sensory and signaling role; it lacks the two inner microtubules (the "9 + 0" arrangement).

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Basal Body

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A eukaryotic cell structure consisting of a 9 + 0 arrangement of microtubule triplets. It may organize the microtubule assembly of a cilium or flagellum and is structurally very similar to a centriole.

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Dynein

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In cilia and flagella, a large contractile protein extending from one microtubule doublet to the adjacent doublet. ATP hydrolysis drives changes in it's shape that lead to bending of cilia and flagella.

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Microfilaments

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Microfilaments

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Structure: Two intertwined strands of actin, each a polymer of actin subunits
Diameter: 7nm
Protein Subunits: Actin
Main Functions: Maintenance of cell shape (tension-bearing elements), Changes in cell shape, Muscle contraction, Cytoplasmic streaming, Cell motility (as in pseudopodia), and Cell division (cleavage furrow formation)

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Actin

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A globular protein that links into chains, two of which twist helically about each other, forming microfliaments in muscle and other kinds of cells.

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Cortex

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(1) The outer region of cytoplasm in a eukaryotic cell, lying just under the plasma membrane, that has a more gel-like consistendy than the inner regions, due to the presence of multiple microfilaments. (2) In plants, ground tissue that is between the vascular tissue

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Myosin

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A type of protein filament that acts as a motor protein with actin filaments to cause cell contraction.

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Pseudopodium
(plural, Pseudopodia)

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A cellular extension of amoeboid cells used in moving and feeding.

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Cytoplasmic Streaming

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A circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of materials within cells.

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Intermediate Filaments

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Intermediate Filaments

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Structure: Fibrous proteins supercoiled into thicker cables
Diameter: 8 -12 nm
Protein Subunits: One of several different proteins of the keratin family, depending on cell type
Main Functions: Maintenance of cell structure (tension-bearing elements), Anchorage of nucleus and certain other organelles, Formation of nuclear lamina

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Concept 6.7

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Extracellular components and connections between cells help coordinate cellular activities

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Cell Walls of Plants

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Cell Wall

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A protective layer external to the plasma membrane in the cells of plants, prokaryotes, fungi, and some protists. Polysaccharides such as cellulose (in plants and some protists), chitin (in fungi), and peptidoglycan (in bacteria) are an important structural component of cell walls.

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Primary Cell Wall

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In plants, a relatively thin and flexible layer first secreted by a young cell.

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Middle Lamella

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In plants, a thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young cells.

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Secondary Cell Wall

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In plants, a strong and durable matrix often deposited in several laminated layers for cell protection and support.

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The Extracellular Matrix (ECM) of Animal Cells

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Extracellular Matrix (ECM)

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The substance in which animal cells are embedded, consisting of protein and polysaccharides synthesized and secreted by cells.

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Collagen

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A glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom.

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Proteoglycan

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A glycoprotein consisting of a small core protein with many carbohydrate chains attached, found in the extracellular matrix of animal cells. A proteoglycan may consist of up to 95% carbohydrate.

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Fibronectin

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A glycoprotein that helps animal cells attach to the extracellular matrix.

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Integrin

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In animal cells, a transmembrane receptor protein that interconnects the extracellular matrix and the cytoskeleton.

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Intercellular Junctions

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Plasmodesmata in Plant Cells

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Plasmodesma
(plural, Plasmodesmata)

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An open channel in the cell wall of a plant through which strands of cytosol connect from an adjacent cell.

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Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells

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Tight Junctions

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A type of intercellular junction in animal cells that prevents the leakage of material between cells.

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Desmosome

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A type of intercellular junction in animal cells that functions as a rivet.

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Gap Junctions

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A type of intercellular junction in animals that allows the passage of materials between cells. They are similar in their function to the plasmodesmata in plants.

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The Cell: A Living Unit Greater Than the Sum of Its Parts

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