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light microscope (LM)

an optical instrument with lenses that refract (bend) visible light to magnify images of specimens

3 important parameters in microscopy

Magnification is the ratio of an object's image size to its real size. Resolution is a measure of the clarity of the image. Contrast accentuates differences in parts of the sample.

organelles

the membrane-enclosed structures within eukaryotic cells

electron microscope (EM)

a microscope that uses magnets to focus an electron beam on or through a specimen, resulting in a practical resolution of a hundredfold greater than that of a light microscope using standard techniques.

scanning electron microscope (SEM)

used to study the fine details of cell surfaces

transmission electron microscope (TEM)

used to study the internal structure of thin sections of cells

cytology

the study of cell structure

biochemistry

the study of the chemical processes (metabolism) of cells

cell fractionation

the disruption of a cell and separation of its parts by centrifugation at successively higher speeds

cytosol

the semifluid portion of the cytoplasm

eukaryotic cell

A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles. Examples of organisms with these cells are protists, plants, fungi, and animals.

prokaryotic cell

A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea.

nucleoid

a non-membrane-bounded region in a prokaryotic cell where the DNA is concentrated

cytoplasm

the contents of the cell bounded by the plasma membrane; in eukaryotes, the portion exclusive of the nucleus

plasma membrane

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

nucleus

(1) an atom's central core, containing protons and neutrons (2) the organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made up of chromatin (3) a cluster of neurons

nuclear envelope

in a eukaryotic cell, the double membrane that surrounds the nucleus, perforated with pores that regulate traffic with the cytoplasm; the outer membrane is continuous with the endoplasmic reticulum

nuclear lamina

a netlike array of protein filaments that lines the inner surface of the nuclear envelope and helps maintain the shape of the nucleus

nucleolus

a specialized structure in the nucleus, consisting of chromosomal regions containing ribosomal RNA genes along with ribosomal proteins imported from the cytoplasm; site of rRNA synthesis and ribosomal subunit assembly

ribosome

a complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. in eukaryotic cells, each subunit is assembled in the nucleolus

chromosome

a cellular structure carrying genetic material, found in the nucleus of eukaryotic cells. Each chromosome consists of one very long DNA molecule and associated proteins. (A bacterial chromosome usually consists of a single circular DNA molecule and associated proteins. It is found in the nucleoid region, which is not membrane bounded.)

chromatin

the complex of DNA and proteins that makes up eukaryotic chromosomes. when the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope

endomembrane system

the collection of membranes inside and surrounding a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles; includes the plasma membrane, the nuclear envelope, the smooth and rough endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, and vacuoles

endoplasmic reticulum (ER)

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

smooth ER

that portion of the endoplasmic reticulum that is free of ribosomes

rough ER

that portion of the endoplasmic reticulum with ribosomes attached

glycoprotein

a protein with one or more covalently attached carbohydrates

transport vesicle

a small membranous sac in a eukaryotic cell's cytoplasm carrying molecules produced by the cell

Golgi apparatus

an organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum and synthesize some products, notably noncellulose carbohydrates

lysosome

a membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of animal cells and some protists

phagocytosis

a type of endocytosis in which large particulate substances or small organisms are taken up by a cell; it is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells)

vacuole

a membrane-bounded vesicle whose specialized function varies in different kinds of cells

food vacuole

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

contractile vacuoles

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

central vacuole

in a mature plant cell, a large membranous sac with diverse roles in growth, storage, and sequestration of toxic substances

mitochondrion

an organelle in eukaryotic cells that serves as the site of cellular respiration; uses oxygen to break down organic molecules and synthesize ATP

chloroplast

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

endosymbiont theory

the theory that mitochondria and plastids, including chloroplasts, originated as prokaryotic cells engulfed by an ancestral eukaryotic cell. The engulfed cell and its host cell then evolved into a single organism

crista

an infolding of the inner membrane of a mitochondrion. The inner membrane houses electron transport chains and molecules of the enzyme catalyzing the synthesis of ATP (ATP synthase)

mitochondrial matrix

the compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the citric acid cycle, as well as ribosomes and DNA

thylakoid

a flattened, membranous sac inside a chloroplast. Thylakoids often exist in stacks called grana that are interconnected; their membranes contain molecular "machinery" used to convert light energy to chemical energy

granum

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

stroma

the dense fluid within the chloroplast surrounding the thylakoid membrane and containing ribosomes and DNA; involved in the synthesis of organic molecules from carbon dioxide and water

plastid

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

peroxisome

an organelle containing enzymes that transfer hydrogen from various substrates to oxygen (O2), producing and then degrading hydrogen per oxide (H2O2); glycoxysomes are specialized peroxisomes

cytoskeleton

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

motor protein

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

microtubule

a hollow rod composed of tubulin proteins that make up part of the cytoskeleton in all eukaryotic cells and is found in cilia and flagella

centrosome

a structure present in the cytoplasm of animal cells that functions as a microtubule-organizing center and is important during cell division. A centrosome has two centrioles

centriole

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

flagellum

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

cilium

a short appendage containing microtubules in eukaryotic cells. a motile cilium is specialized for locomotion or moving fluid past the cell; it is formed from a core of nine outer doublet micro tubules and two inner single microtubules (9+2) ensheathed in an extension of the plasma membrane. a primary cilium is usually nonmotile and plays a sensory and signaling role; it lacks the two inner microtubules (9+0)

basal body

a eukaryotic cell organelle consisting of a 9 + 0 arrangement of microtubule triplets; may organize the microtubule assembly of a cilium or flagellum; structurally similar to a centriole

dynein

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

microfilaments

a cable composed of actin proteins in the cytoplasm of almost every eukaryotic cell, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction; also known as an actin filament

actin

a globular protein that links into chains, two of which twist helically about each other, forming microfilaments (actin filaments) in muscle and other kinds of cells

cortex

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

myosin

a type of motor protein that associates into filaments that interact with actin filaments to cause cell contraction

pseudopodium

a cellular extension of amoeboid cells used in moving and feeding

cytoplasmic streaming

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

intermediate filament

a component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments

cell wall

a protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists. polysaccharides such as cellulose (in plants and some protists), chitin (in fungi), and peptidoglycan (in bacteria) are important structural components of cell walls

primary cell wall

in plants, a relatively thin and flexible layer that surrounds the plasma membrane of a young cell

middle lamella

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

secondary cell wall

in plant cells, a strong and durable matrix that is often deposited in several laminated layers around the plasma membrane and provides protection and support

extra cellular matrix (ECM)

surrounds many animal cells. It consists of glycoproteins, polysaccharides, and proteoglycans synthesized and secreted by the cells

collagen

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

proteoglycan

a large molecule 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

fibronectin

an extracellular glycoprotein secreted by animal cells that helps them attach to the extracellular matrix

integrin

in animal cells, a transmembrane receptor protein with two subunits that interconnects the extracellular matrix and the cytoskeleton

plasmodesma

an open channel through the cell wall that connects the cytoplasm of adjacent plants, allowing water, small solutes, and some larger molecules to pass between the cells

tight junction

a type of intercellular junction between animal cells that prevents the leakage of material through the space between cells

desmosome

a type of intercellular junction in animal cells that functions as a rivet, fastening cells together

gap junction

a type of intercellular junction in animal cells, consisting of proteins surrounding a pore that allows the passage of materials between cells

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