ch. 6-7
Microscopy
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Light microscope (LM), visible light is passed through the specimen and then through the glass
magnification, resolution, and contrast
magnification is the ratio of the object image size to the real size
resolution, measure of clarity of the image
contrast, the differences in brightness between light and dark areas of an image
staining or labeling cell components so they stand out visually
electron microscope (EM), focuses a beam of electrons through the specimen or onto the surface
scanning electron microscope (SEM), used for detailed study of the topography of a specimen (resulting image is in 3D)
transmission electron microscope (TEM), used for internal structure of the cell (in 2D)
cell fractionation, study of cell structure and function
takes the cells apart and separates major organelles and subcellular structures from one another
using a centrifuge that spins test tubes holding the mixtures of disrupted cells at different speeds
each speed, the force causes the cells components to settle at the bottom of the tube forming a pellet
lower speeds the pellets consists of larger components
higher speeds pellet has smaller components
prokaryotic and eukaryotic
prokaryotic (before nucleus), domain bacteria and archaea
eukaryotic (true nucleus), protists, fungi, animals, and plants
DNA is concentrated in the region that is not membrane enclosed the nucleoid
DNA is in the organelle called the nucleus that is bounded by a double membrane
cytoplasm region between the nucleus and plasma membrane
cytoplasm in this cell suspended in cytosol are a variety of organelles of specialized form and function
doesn't have organelles, the cytoplasm is organized into different regions
plasma membrane
functions as a selective barrier
allows a passage of enough oxygen, nutrients, and waste to service the cell
a limited amount of particular substance can cross per second so the ratio of surface area to volume is critical
a cell increases in size the surface grows proportionally less than its volume
area is proportional to a linear dimension squared, volume is proportional to the linear dimension cubed
so a smaller object has a greater ratio of surface area to volume
has extensive arranged internal membranes dividing the cells compartments the organelles
they provide local environments supporting metabolic functions so incompatible process can occur simultaneously in a single cell
plasma membrane and organelle participate directly in the cells metabolism b/c enzymes are built into the membranes
nucleus houses DNA and ribosomes, that use information from DNA to make proteins
nucleus of eukaryotic cell contains most of the genes, some genes are located in the mitochondria and chloroplasts
nuclear envelope surrounds the nucleus to separate the contents from the cytoplasm
the envelope is a double membrane, it is pierced with pores
they play an important role regulating the entry and exit of proteins and RNA and also macromolecules
the nuclear lamina are protein filaments that maintain the shape of the nucleus that mechanically support the nuclear envelope
within the nucleus the DNA is organized into unites called chromosomes structures that carry genetic info
each chromosome has one long DNA with many proteins, they help coil DNA so that it can fit into the nucleus
complex DNA and proteins making up the chromosome are called chromatin
ribosomes made of ribosomal RNA and protein, they carry out protein synthesis
the lamina and matrix help organize genetic material so it functions properly
there is also a nuclear matrix, protein fibers extending throughout the interior of the nucleus
free ribosomes
bound ribosomes
suspended in the cytosol
attached to the outside of the endoplasmic reticulum or nuclear envelope
free and bound have identical structures and ribosomes can alternate between them
proteins function within the cytosol
make proteins that are inserted into the membrane for packaging within certain organelles such as lysosomes or export from cell
endomembrane system
includes nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles and vacuoles, the plasma membrane
it does protein synthesis, transport of proteins, into membrane and organelles or out of the cell
endoplasmic reticulum, extensive network of membranes that have tubules and sacs cristae
smooth ER, outer membrane lacking ribosomes
rough ER, studded with ribosomes on the outer membrane
metabolic processes of lipids, metabolism of carbohydrates, detoxification of drugs and poisons, storage of calcium ions
enzymes of smooth ER synthesize lipids, oils, and steroids and new membrane phospholipid
other enzymes detoxify drugs and poisons in liver cells
Golgi apparatus, warehouse for receiving, sorting, shipping and manufacturing
products of the ER, proteins are stored and sent to other destinations
it looks like a stack of peta bread
membrane of each cristae in the stack separates the internal space from the cytosol
vesicles in the Golgi apparatus transfer material between parts of the Golgi and other structures
Golgi has two sides, cis and trans face
cis, on the same side located near the ER
trans, on the opposite side gives rise to vesicles that pinch off and travel to other sites
faces act as receiving and shipping department
transport vesicles move material from the ER to the golgi
vesicles bub from the ER adds its membrane & its contents of its lumen to the cis by fusing with the Golgi membrane
Golgi dispatches products by budding vesicles from the trans face,
it sorts the products and targets them for various parts of the cell
lysosomes, is a membranous sac of hydrolytic enzymes
they work best in acidic environments
if a lysosomes breaks open or leaks, the enzymes that were released aren't very active b/c the cytosol in near neutral pH
too much leakage of lysosome destroys a cell by self digestion
lysosomes are like trash cans they dispose what the cell doesn't want or need
lysosomes carry out intracellular digestion
ex: amoebas and unicellular eukaryotes eat by engulfing small organisms or food particles called phagocytosis
lysosomes use hydrolytic enzymes to recycle the cells own organic material called autophagy
vacuoles, derived from the endoplasmic reticulum and Golgi apparatus
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food vacuoles formed by phaocytosis
contractile vacuoles, pump excess water out of the cell, maintaining suitable concentrations of ions and molecules
mature plant cells contain a central vacuole
develops by the coalescene of smaller vacuoles
solution inside this vacuole is called cell sap, is the plants main repository of inorganic ions, includes potassium and chloride
this vacuole plays a role in plant growth of plant cells, enlarging as the vacuole absorbs water
mitochondria, sites for cellular respiration, process that drive ATP
chloroplast, in plants and algae are sites for photosynthesis
found in unicellular eukaryotes
a phospholipid bilayer encloses the mitochondrion
the outer membrane is smooth, the inner membrane is convoluted with infoldings called cristae
inner membrane divides the mitochondrion into two compartments
1) intermembrane space, the narrow region between the inner and outer membrane
2) mitochondrial matrix, enclosed by the inner membrane
it contains different enzymes as well as mitochondrial DNA an ribosomes
enzymes in the matrix catalyze some steps of cellular respiration
other proteins functioning in respiration including the enzyme that make ATP are built into the inner membrane
cristae give the inner mitochondrional membrane large surface area enhancing productivity of cellular respiration
divided from the cytosol by an envelope with two membranes separated by a narrow intermembrane space
inside the chloroplasts are sacs called thylakoids, they a stacked like poker chips and each stack is called a granum
outside of the thylakoids is a fluid called the stroma, containing chloroplasts DNA and ribosomes as well as enzymes
chloroplasts are mobile like mitochondria and other organelles, move around the cell along tracks of the cytoskeleton
cytoskeleton network of fibers extending throughout the cytoplasm
it gives mechanical support and maintains the shape of the cell
three fibers that make up the cytoskeleton
microtubules, hollow rods constructed from a protein called tubulin
each tubulin is a dimer made of two subunits
the consists of two polypeptides, a tubulin and b tubulin
microtubules grow in length by adding tubulin dimers
microtubules shape and support the cell, guiding movement of organelles and separating chromosomes during cell division
in animals microtubules grow out from a centrosome located near the nucleus
the microtubules function as compression resisting girders of the cytoskeleton
with the centrosome are a pair of centrioles composed of nine sets if triplet microtubules arranged in a ring
flagella
are limited to just one or a few per cell and they are longer than cilia
flagellum has a motion like the tail of a fish
cilia act as locomotor appendages
cilium also acts as a signal receiving antenna for the cell
has group of microtubules sheathed in a extension of the plasma membrane, cilia also has this similar structure
nine doublets of microtubules arranged in a ring with two single microtubules in the center this called the 9+2 pattern
this is usually in motile flagella and cilia
nonmotile primary cilia have a 9+0 pattern which lacks a pair of microtubules
they also share common structure such as a basal body which anchors the cilia and flagella in the cell
dynein's are also a common structure which is a motor protein that drives the cilia and flagella to have bending movements
microfilaments thin solid rods, and are also called actin filaments b/c they ae built from actin a globular protein
the filament is twisted in a double chain of actin subunits
their structural role is to bear tension (pulling forces)
a network formed by microfilaments inside the plasma membrane (cortical microfilaments) help support cell structure
the network also gives the outer cytoplasmic layer of the cells the cortex the consistency of a gel
in some animal cells such as nutrient absorbing intestinal cells, bundles of microfilaments make up the core of microvilli that increase the cells surface area
motility is another role that microfilaments are known for
actin filaments & thicker filaments made of protein called myosin interact to cause contraction of muscle cells
the unicellular eukaryote amoeba, their crawling movement are contraction brought by actin and myosin
the cell crawls along a surface by extending cellular extensions called pseudopodia (false feet)
in plants cells actin and myosin interactions contributes to cytoplasmic streaming a circular flow of cytoplasm within cells
this movement speeds up distribution of materials within the cell
intermediate filaments
they are larger than the diameter of microfilaments but smaller than that of microtubules
they are specialized for bearing tension
these filaments are more permanent and persistent
they are sturdy and play an important role in reinforcing the shape of the cell and fixing position of certain organelles
cell wall extracellular structure of plant cells
it protects the plant cell and maintains it shape, and prevents excessive uptake of water
young plant cells secretes a thin and flexible wall called primary cell wall
between primary walls of adjacent cell is the middle lamella a thin layer rich in sticky polysaccharides called pectin
secondary cell wall between the plasma membrane and the primary cell wall
secondary wall has a strong durable matrix that affords cell protection and support
extracellular matrix
most abundant glycoprotein in animals cells is collagen that forms strong fibers outside the cell
collagen fibers are embedded in a network woven out of proteoglycans secreted by cells
some cells are attached to the ECM glycoproteins such as fibronectin
fibronectin and other ECM proteins bind to cell surface receptor proteins called integrins
cell junction
cell walls are perforated with plasmodesmata
tight junction, plasma membrane of neighboring cell are tightly pressed against each other bound to specific proteins
forms seals around the cell, the junctions establish a barrier that prevents leakage
desmosomes, fastens cell together into strong sheets, they also attach muscle cells to each other in a muscle
gap junction, they are the communicating junction
phospholipid is amphipathic thus it has a hydrophilic head and hydrophobic tails
the fluid mosaic model, the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids
groups of proteins are associated in specialized patches, carrying out common function
the fluidity of membranes
membrane is held together by hydrophobic interactions
it remains fluid as temp decreases until phospholipids settle in closely packed arrangement and the membrane solidifies
it remains fluid at a lower temp if it is rich in phospholipids with unsaturated hydrocarbon tails
b/c unsaturated hydrocarbons cannot pack together closely which makes the membrane more fluid
membrane
when it solidifies it permeability changes and the enzymatic proteins in the membrane become inactive
it also cant be to fluid b/c it cannot support protein function
phospholipid are the main fabric of the membrane, but proteins determine most of membranes function
must be fluid to work properly it affects the permeability
and the ability of membrane proteins to move where function is needed
two membrane proteins
integral proteins, penetrate hydrophobic interior of the lipid bilayer
peripheral proteins, are not embedded into the lipid bilayer at all, they are appendages loosely bound to the surface of the membrane
have a majority that are transmembrane proteins, other integral proteins extend only partway in to hydrophobic interior
role of membrane carbohydrates
cell-cell recognition, the cell distinguishes one type of neighboring cell from another
it is also basis for the rejection of foreign cells by the immune system
cell recognize each other binding to molecules usually carbohydrates on the extracellular surface of the plasma membrane
membrane structure
small molecules and ions move across the plasma membrane in both directions
sugars, amino acids, and other nutrients enter the cell and metabolic waste leaves
cell takes in O2 for cellular respiration and expels CO2
permeability of the lipid bilayer
nonpolar molecules, hydrocarbons, CO2 and O2 are hydrophobic. so they dissolve in the lipid bilayer w/ out help of membrane proteins
polar molecules, glucose and other sugars pass only slowly through a lipid bilayer and even water a small molecule does not cross rapidly
lipid bilayer responsible for a cell permeability
proteins built into the membrane play key roles in regulating transport
hydrophilic substances can avoid contact w/ the lipid bilayer by passing through transport proteins that span the membrane
channel proteins, function by having a hydrophilic channel that certain molecules or atomic ions use as a tunnel through membrane
carrier proteins hold onto their passengers and changes shape in a way lets them move across the membrane
channel proteins called aquaporins facilitate the passage of water molecules
diffusion, molecules to spread out evenly into the available space
dynamic equilibrium, molecules crossing the membrane each second in direction as the other
rules of diffusion, a substance will diffuse from where it is more concentrated to less concentrated
substance will diffuse down its concentration gradient which the density of a chemical substances increases or decreases
diffusion requires no energy, it is a spontaneous process
passive transport does not have to expand energy for it to happen
in osmosis the diffusion of water across a selectively permeable membrane
water balance of cells without cell wall
tonicity, the ability of a cell to gain or lose water
animals cell doesn't have a cell wall, when immersed in a isotonic environment it remains stable
b/c there will no net movement of water across the membrane
hypertonic (more), the cell will lose water, shrivel, and probably die
hypotonic (less), water will enter the cell faster than it leaves and the cell will swell and lyse (burst)
osmoregulation, the control of solute concentrations and water balance
water balance of cells with cell walls
plants, prokaryotes, fungi and protists
plants cell in a hypotonic solution, the cell wall helps maintain the cells water balance, the cell becomes turgid
plants cell in isotonic, no net tendency for water to enter and the cell becomes flaccid
plant cells in hypertonic, lose water to its surrounding and shrivel
as the plant shrivels its plasma membrane pulls away from the cell wall at multiple places called plasmolysis
plasmolysis causes the plant to wilt and can lead to cell death
active transport, against it concentration gradient , requires work the cell must expand energy
facilitated diffusion,transport protein speeds the passive movement of molecules across the plasma membrane
channel proteins that transport ions are ion channels
ion channels function as gated channels, which open and close in response to stimulus
carrier proteins change in shape that somehow translocates the solute binding site across the membrane
carrier involved in facilitated diffusion result in net movement of a substance down their concentration gradient
it enables a cell to maintain internal concentration that differ from concentration it is environments
plasma membrane maintain steep gradients by pumping Na+ out of the cell and K- into the cell
ATP supplies the energy for active transport
ATP can power this transport is by transferring the terminal phosphate groups directly to the transport protein
this induces proteins to change its shape in a manner that translocate a solute bound tot he protein across the membrane
the sodium potassium pump, exchanges Na+ and K+ across the plasms membrane
how ion pumps maintain membrane potential
membrane potential voltage across the membrane
voltage is created by differences in the distribution of positive and negative ions across a membrane
the cytoplasmic side of membrane is negative in charge relative to the extracellular side
two combined forces called electrochemical gradient drive the diffusion of ion across a membrane
chemical force, ions concertation gradient
electrical forces, effect on the membrane potential on the ions movement
electrogenic pump, a transport proteins that generates voltage across a membrane
main electrogenic pump of plants, fungi, and bacteria is a proton pump, which actively transports proteins (hydrogen ions H+) out of the cell
the pumping of OH+ transfers positive charge from the cytoplasm to the extracellular solution
by generating voltage across membranes, electrogenic pumps help store energy that can tapped for cellular work
cotransport
occurs when active transport of a solute indirectly drives transport of other substances
exocytosis, the cell secretes certain molecules by the fusion of vesicles with the plasma membranes
transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cell
secretory cells use exocytosis to export products
endocytosis, cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane
it is the reversal of exocytosis involving proteins
three types of endocytosis
phagocytosis (cellular eating)
pinocytosis (cellular drinking)
receptor-mediated endocytosis
a cell engulfs a particle by extending pseudopodia
the vacuoles fuses with a lysosomes to digest the particle
a cell continually gulps droplets of extracellular fluid into tiny vesicles, formed by infoldings of the plasma membrane
binding of specific solutes to receptors triggers vesicle formation
receptor proteins, receptor and other molecules from the extracellular fluid are transported in the vesicles
emptied the receptors are recycled to the plasma membrane
a prominent structure within the nondividing nucleus is the nucleolus