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Cells and Membrane Structure and Function (Membrane Structure and Function…
Cells and Membrane Structure and Function
Cells
Microscopes and biochemistry are used to study cells
light microscope: visible light is passed through specimen and then through glass lenses
the lenses refract the light in such a way that the image of the specimen is magnified as it is projected into the eye
binocular compound light microscope: more than 1 lens; 2D; the microscope commonly used in laboratories
equivalent to transmission electron microscope
dissecting light microscope: stereomicroscope; 3D
equivalent to scanning electron microscope
electron microscope: focuses beam of electrons through specimen or onto its surface; use electromagnets as lenses to bend paths of the electrons instead of glass lenses
resolution is inversely related to the wavelength of the light a microscope uses for imaging; electron beams have much shorter wavelengths than visible light (up to 0.002 nm resolution)
scanning electron microscope: the electron beam scans the surface of the sample, usually coated with a thin film of gold
the beam excites electrons on the surface, and these secondary electrons are detected by a device that translates the pattern of electrons into an electronic signal sent to a video screen
the microscope shows an image of the specimen's surface that appears 3D; detailed study of the topography of a specimen
transmission electron microscope: aims electron beam through avery thin section of the specimen, like a light microscope aims light through a sample on a slide
specimen is stained with atoms of heavy metals, enhancing the electron density of some parts of the cell more than others to emphasize certain cellular structures
the electrons passing through the specimen are scattered more int eh denser regions, so fewer are transmitted; the image displays the pattern of transmitted electrons; 2D
cell fractionation: useful technique for studyingn cell structure and functions, which takes cells apart and separates major organelles from one another
the centrifuge is the equipment that is used to fractionate cells into their component parts
cell fractionation enable scientists to determine the functions of organelles
example: on one cell fraction, biochemical test sowed the presence of enzymes involved in cellular respiration
biochemistry and cytology help correlate cell function with structure
spins test tubes holding mixtures of disrupted cells at a series of increasing speeds
the resulting force causes a subset of cell compunds to settle to the bottom of the tube, forming a pellet
All cells contain plasma membrane, cytosol, chromosomes, and ribosomes
eukaryotic cell: has nucleus, membrane-bound organelles, cytoplasms between plasma membrane and nucleus
nucleus: where most DNA is; bounded by double membrane
nuclear envelope: encloses the nucleus, separating it from the cytoplasm; double layer, each consisting of a lipid bilayer
endomembrane system: regulates protein traffic and performs metabolic functions in the cell
endoplasmic reticulum: accounts for more than half of the total membrane in many eukaryotic cells
smoooth ER: lack ribosomes; synthesizes lipids, metaolizes carbohydrates, tores calium ions
rough ER: surface is studded with ribosomes; ribosomes secrete glycoprotein, distributes transport vesicles, membrane factory
golgi apparatus: consists of flattened membranous sacs called cisternae
modifies products of the ER, manufactures certain macromolecules, sorts and packages materials into transport vesicles
lysosomes; a mebranous sac of hydrolytic enzymes that can digest macromolecules
phagocytosis forms a food vacuole which lysomes fuse with and digest the molecules
vacuoles: large vesicles derived from the ER and golgi apparatus
food vacuoles form in phagocytosis
contractile vacuoles: pump excess water out of cells
central vacuoles: hold organic compounds and water
mitochondria: site of cellular respiration(oxygen to ATP)
chloroplasts: site of photosynthesis
peroxisomes: specialized metaboloc compartments bounded by single membrane; oxidative organlles
produce hydrogen peroxide and convert it to water; erform rections with many different functions
thylakoids: membranous sacs stacked to from a granum; stroma: internal fluid; plastids are groups of chloroplasts
;smooth outer membrane and inner membrane folded into cristae; inner membrane creates towo compartment: intermembrne space and mitochondrial matrix
cristae present a large surface area ofr enzymes to synthesize ATP, compared to the volume ratio, it provides more space for enzymes ot do their job
cytoskelton: network of fibers xtending throughout cytopplasm
organizes cell's structures and activities
microtubules: maintain cell shape, chromosome movement in cell division, organelle movements
centriole is groups of mictrotubules constructed of dimers of tubulin
control flagella and cilia ( made up of microtubules)
microfilaments: maintian cell shape, muscle contraction, cytoplasmic streaming in plant cells, cell motility, division of animals cells
from a cortex outside of plasma membrane to support cell's shape
intermediate filaments: maintain cell shape, anchorage of nucleus and other organlles, formatin of nuclear lamina
fix organelles in place
cell wall: extraellular structure that distinguishes plat cells form animal cells; protects plant cell, maintains shpae, and prevents excessive uptake of water
made up cellulose fibers embedded in other polysaccharides and protein
primary cell wall: relatively thin and flexible
middle lamella: tthinlayer between primary walls of adjacent cells
secondary cell wall: added between plasma membrne and primary cell wall
prokaryotic cell: no nucleus, has nuceloid, no membrne-bound organelles, cytoplasm bound by the plasma membrane
nucleoid: region thta is not membrane-enclosed where DNA is concentrated
some have cell wall
plamsa membrane: selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell
ribosomes: made of ribosomal RNA and protein; carry out protein syntheis in cytosol and outside of endoplasmic reticulum
Membrane Structure and Function
membrane protein functions
peripheral proteins: bound to the surface of the membrane
integral proteins: penetrate the hydrophobic core
transmembrane proteins: integral proteins that span the membrane
cell-surface embranes can carry out several functions: transport, enzymatic activty, signal transduction, cell-cell recognition, intercellulr joining, attachment to cytoskeleton and extracellular matrix
membrane is a collage of different proteins, often clustered in groups, embedded in the fluid matrix of the lipid bilayer
membrane structure
plasma membrane: selective permeability, regulate cell's moleculr traffic
lipid bilayer: hydrophilic molecules don't cross thorugh membrane easily
transport proteins: allow pasage of hydrophilic substances cross the membrane;
channel proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel
carrier proteins: bind to molecules and change shape to shuttle them across the membrane
diffusion: the tendency for molecules to spread out evenly into available space; passive transport; any molecuke; go through air, water, membrane; equilibrium alog a concentration gradient
osmosis: diffusion of water across a semi-permeable membrane
has to go through membrane
hypertonic: higher percentage of solute
hypotonic: higher percentage of solvent
isotonic: equal amount of solvent and solute
facilitated diffusion: protein transport
channel
carrier
tonicity: he ability of surrounding solution to cause a cell to gain or lose water
depends on its concentration of solutes that cannot cross the membrane relative to that inside the cell
isotonic solution: solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
hypertonic solution: solute concentration is greater than that inside the cell; cell loses water
hypotonic solution: solute concentration is less than that inside the cell; cell gains water
active transport: requires energy, usually in the form of ATP hydrolysis to move substances against their concentration gradients
electrogenic pump: a transport protein that generates voltage across a membrane
sodium- potassium pump: forces sodium out, pushes potassium in;
a transport protein that i energized by transfer of a phospphate group form the hydrolysis of ATP
proton pump: actively transports hydrogen ions out of the cell
main pump of plants, fungi, and bacteria
cotransport:
symport: molecules move in same direction
antiport: molecules move in different directions