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Chapter 6 A Tour of The Cell and Chapter 7 Membrane Structure and…
Chapter 6 A Tour of The Cell and Chapter 7 Membrane Structure and Function
Concept 7.2 Membrane structure results in selective permeability
The Permeability of the Lipid Bilayer
Polar Molecules (like glucose and other sugars) pass slowly through a lipid bilayer. Water is the same.
proteins built in the membrane play key roles in regulating transport.
Transport Proteins
span the membrane
channel proteins
function by having a hydrophilic channel that allow certain molecules or ions tunnel through the membrane
Ex: passage of H2O molecules thru the membrane in certain cells is greatly facilitated by channel proteins known as
aquaporins
aquaporin allows entry up to 3 billion h2o molecules/sec, passing thru single channel, which fits 10 at a time.
carrier proteins
hold onto passengers and change shape in a way that shuttles them across membrane
Allows only a certain substance to travel; Ex; "glucose transporter" rejects fructose.
Concept 6.5 Mitochondria and chloroplasts change energy from one form to another
Mitochondria
sites of cellular respiration
metabolic process that uses oxygen to drive the generation of ATP by extracting energy from sugars, fats and other fuels.
Chloroplast
found in plants and algae
site of photosynthesis
Evolutionary Origins of Mitochondria and Chloroplasts
Endosymbiotic Theory
states an early ancestor of eukaryotic cells engulfed an oxygen-using nonphotosynthetic prokaryotic cell
Both have 2 membranes surrounding them
contain ribosomes and circular DNA molecules
both are autonomous organelles that grow and reproduce within the cell
Mitochondria: Chemical Energy Conversion
Two membranes enclosing the mitochondrion is a phospholipid bilayer w/ a collection of embedded proteins
Outer membrane is smooth
inner membrane has foldings called cristae
Divides mitochondrion into two compartments:
1) inter membrane space: region b/w inner and outer membranes
2) mitochondrial matrix: enzymes catalyze some of the steps of cellular respiration; cristae give inner mitochondrial membrane a large surface area
Chloroplasts: Capture of Light Energy
contents are partitioned from cytosol envelope of two membranes separated by a narrow inter membrane space
Thylakoids
are flattened interconnected sacs
Granum
are a stack of thylakoid
Stroma
is fluid outside the thylakoid; contains the chloroplast DNA, ribosomes and enzymes
Membrane of Chloroplast: Three Compartments
1) Intermembrane space, stroma, thylakoid space
enables chloroplasts to convert light energy to chemical energy during photosynthesis
2) Mobile and Pinch in two, reproducing themselves
3) member of specialized plant organelles called plastids
Peroxisomes: Oxidation
Metabolic Compartment bounded by a single membrane
use enzymes that remove hydrogen atoms from substrates and transfer them to oxygen, making
hydrogen peroxide
; hydrogen peroxide is toxic but peroxisome uses an enzyme to convert it to water
use oxygen to break down fatty acids
Glycosomes
found in fat storing tissues of plant seeds
Contains enzymes that convert fatty acids into sugar.
Concept 6.2 Eukaryotic cells have internal membranes that compartmentalize
Comparison
Plasma Membranes
are selective barrier that allows oxygen, nutrients, & wastes to service cells.
Cystosol
: semifluid, jelly-like substance, suspended
Ribosomes
make proteins according to instructions from genes
Chromosomes
carry genes in the form of DNA
Contrast
Eukaryotic
"True Nucleus"
DNA
is inside the Nucleus: Bounded by a double membrane
Cytoplasm
region b/w the nucleus & plasma membrane
Prokaryotic
"Before Nucleus"
DNA
is not membrane-enclosed; called Nucleoid
NO cytoplasm
mycoplasmas
smallest bacteria (b/w (0.1 & 1.0 mcm)
Panoramic View of the Eukaryotic Cell
Figure 6.8
show all organelles within an Animal and Plant cell needed for functions in daily living.
Surface Area V. Volume Ratio
When a cell increases in size, the surface are grows less than its volume.
Area = linear dimension squared, volume = linear dimension cubed
smaller objects have a greater ratio of surface area to volume
Large surface area to accommodate the volume explains microscopic cells & elongated ones like nerves cells
larger organisms contain more cells than small organisms
high ratio of surface area to volume, cells that exchange a lot of material w/ their surroundings (intestinal cells).
microvilli increase surface are w/o an appreciable increase in volume.
Concept 6.3 The eukaryotic cell's genetic instructions are housed in the nucleus and carried out by the ribosomes
The Nucleus: Information Center
Nucleus
contains most of the genes; 5 mcm; directs protein synthesis by synthesizing mRNA according to instructions provided by DNA.
The mRNA is then transported to the cytoplasm via nuclear pores.
ribosomes translate the mRNA's genetic message into the primary structure of a specific polypeptide.
Nuclear Envelope
Encloses Nucleus
separates nucleus contents from the cytoplasm
double membrane
Pore Complex
lines each pore and regulates entry and exit of proteins, RNA and macromolecules
Nuclear Lamina
line the nuclear side
maintains the shape of nucleus by mechanically supporting the nuclear envelope.
works with nuclear matrix to help organize the genetic material to function efficiently.
Nuclear Matrix
framework of protein fibers extending through the nuclear interior
much like intermediate filaments
works with nuclear lamina to help organize genetic mater to function efficiently
Chromosomes
structures that carry genetic information
each carries one long DNA molecule associated w/many proteins
Chromatin
the complex of DNA and proteins making up the chromosomes
Nucleolus
rRNA is synthesized from instructions in the DNA
proteins that are also imported from the cytoplasm are assembled w/ rRNA into large and small subunits of ribosomes.
Ribosomes: Protein Factory
made of rRNA and proteins
cellular components that carry out protein synthesis
bound ribosomes makes proteins destined for insertion into membranes like lysosomes or for export from the cell
ex: cells of the pancreas secrete digestive enzyme; have high proportions of
bound ribosomes
free ribosomes
function in the cytosol; ex: enzymes that catalyze the first step of sugar breakdown
build proteins into two cytoplasmic locales:
free ribosomes
(suspended within cytosol), &
bound ribosomes
(attached to the outside of ER or nuclear envelope).
Concept 6.7 Extracellular components and Connects between cells help coordinate cellular activities
Cell Walls of Plants
Extracellular structure of plant cells
much thicker than the plasma membrane
primary cell wall:
relatively thin and flexible
Middle Lamella
b/w primary cell walls; layer rich in sticky polysaccharides called
pectins
glues adjacent cells together
Secondary Cell Wall
strong durable matrix
wood consists mainly of secondary walls
Extracellular Matrix in Animal Cells
Glycoproteins and Carbohydrate containing molecules secreted by the cells
Most abundant glycoprotein found in the ECM is
collagen
forms strong fibers
accounts for 40% of protein in human body
proteoglycan
has a small core protein w/many carbohydrate chains covalently attached
Fibronectin
:ECM glycoproteins
bind to cell surface receptor proteins called
integrins
that are built into the plasma membrane
transmit signals between the ECM and cytoskeleton
regulates a cell's behavior
Cell Junctions
Plasmodemata in Plant Cells
Channels that connect cells
Water and small solutes pass freely from cell to cell
Macromolecules reach the plasmodesmata by moving along fibers of the cytoskeleton
Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells
Tight Junctions
very tightly pressed against each other
establish a barrier that prevents leakage of extracellular fluid across a layer of epithelial cells
EX: Tight Junctions b/w skin cells make us watertight
Desmosomes (
anchoringjunction
)
function like rivets, fastening cells together into strong sheets
Intermediate filaments made of sturdy keratin proteins anchor desmosome in the cytoplasm
Attach muscle cells to each other in a muscle cell; "muscle tears" involve rupture of desmosomes
Gap Junctions (
communicating junctions
)
provide cytoplasmic channels from one cell to an adjacent cell & make it similar in their function to plasmodesmata in plants
consist of membrane proteins that surround a pore through which ions, sugars amino acids & other small molecules may pass
necessary for communication b/w cell in many types of tissues, such as heart muscle, and in animal embryos
Concept 7.5 Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
Exocytosis
the cell secretes certain molecules by the fusion of vesicles with the plasma membrane.
a transport vesicle that has budded from the GA moves along microtubules of the cytoskeleton to the plasma membrane.
vesicle and plasma membrane come into contact, rearrange the lipid molecules of the two bilayers to fuse both membranes; contents are spilled out of the cell.
Many secretory cells use exocytosis to export products.
Ex: cells in the pancreas that make insulin secrete it into extracellular fluid by exocytosis
Endocytosis
the cells take in molecules & particulate matter by forming new vesicles from the plasma membrane.
small area of plasma membrane sinks inward to form a pocket
As pocket, deepens, it pinches in, forming a new vesicle containing material that had been outside the cell
in hypercholesterolemia (high level of cholesterol in the blood), LDLs cannot enter cells bc the LDL receptor proteins are defective.
Pinocytosis
: a cell continually "gulps" droplets of extracellular fluid into tiny vesicles, formed by inholdings of the plasma membrane
Phagocytosis:
a cell engulfs a particle by extending pseudopodia around it & packaging it within a membranous sac called a food vacuole.
Receptor-Mediated Endocytosis:
specialized type of pinocytosis that enables the cell to acquire bulk quantities of specific substances, even though those substances may not be very concentrated in the extracellular fluid.
Concept 7.4 Active transport uses energy to move solutes against their gradients
The Need for Energy in Active Transport
the cell must expend energy to pump a solute across a membrane against its gradient
Active Transport
: transport proteins move solutes against their conct. gradients are all carrier proteins.
Enables a cell to maintain internal concentrations of small solutes that differ from concentration in its environment.
Sodium-Potassium Pump
exchanges Na+ and K+ across the plasma membrane of animal cells.
How Ion Pump Maintain Membrane Potential
The cytoplasmic side of the membrane is negative in charge relative to the extracellular bc of an unequal distribution of anions & cations on the two sides.
Membrane Potential
: voltage across a membrane, ranges from -50 to -200 mV; source that affects the traffic of all charged substances across the membrane.
the membrane potential favors the passive transport of cations into the cell & anions out of the cell.
Electrochemical Gradient
Chemical Force: ion's concentration gradient
Electrical Force: the effect of the membrane potential on the ion's movement.
An ion diffuses not simply down its concentration gradient but, down its electro chemical gradient; EX: Na+ inside a resting nerve cell is much lower than outside it.
Electrogenic Pump
: transport protein that generates voltage across a membrane
Proton Pump
: main electrogenic pump of plants, fungi, and bacteria which actively transport protons (H+) out of the cell; transfers positive charge from cytoplasm to extracellular solution
Cotransport: Coupled Transport by a Membrane Protein
In a mechanism called
cotransport
, a transport protein can couple the "downhill" diffusion of the solute to the "uphill" transport of a second substance against its own conct. gradient.
Ex: a plant cell uses the gradient of H+ generated by its ATP-powered proton pumps to drive the active transport of amino acids, and several other nutrients into the cell.
The H+ uses the transport protein as an avenue to diffuse down its own electrochemical gradient, which is maintained by the proton pump.
Concept 7.1 Cellular membranes are fluid mosaics of lipids and proteins
The Fluidity of Membranes
membranes are held together by hydrophobic reactions
sideways movement of phospholipids within the membrane is rapid
adjacent phospholipids switch 10^7 times per second
membrane proteins draft also
Membrane remains fluid as temperature decreases
Phospholipids settle closely together into packed arrangement to resolidify the membrane
temperature at which the membrane solidifies depends on the types of lipids it is made of
Cholesterol has different effects on membrane fluidity at different temperatures
at 37 degrees C, cholesterol makes the membrane less fluid by retraining phospholipid movement
lowers the temp required for the membrane to solidify;
may be known as a fluidity buffer
Must be fluid like to work properly
Affect permeability and ability of membrane proteins tumor to where their function is needed
membrane that are too fluid can't support protein function
Evolution of Differences in Membrane Lipid Composition
Variations in cell membrane lipid compositions of many species appear to be evolutionary adaptations that maintain membrane fluidity under specific environment conditions.
the ability to change the lipid composition of cell membranes in response to changing temperatures has evolved in organisms where temps vary.
Natural Selection favors organisms who mix of membrane lipids ensures an appropriate level of membrane fluidity for their environment.
Membrane Proteins and Their Functions
Phospholipids form the main fabric of a membrane but proteins determine membrane's function.
Peripheral proteins
are not embedded in the lipid bilayer; loosely bound to the surface of the membrane; exposed to parts of integral
Integral Proteins
penetrate the hydrophobic interior of the lipid bilayer.
hydrophobic regions - consist of one or more stretches of non polar amino acids
Majority of
transmembrane proteins
, span the membrane; or integral proteins extend into the hydrophobic interior.
20-30 amino acids; coiled in alpha helices
Proteins on a cell's surface are important in the medical field.
CD4 on the surface of immune cells helps HIV infect these cells, leading to AIDS.
HIV must also bind to CCR5 as a "co-receptor" to infect most cells
Absence of CCR% on the cells of resistant individuals, due to gene alteration, prevents the virus from entering the cell
CCR5 co-receptor is safer target for the development of drugs that mask this protein and block HIV entry.
Figure 7.7 Some functions of membrane proteins
Transport
: a protein that spans the membrane may provide hydrophilic channel across the membrane that is selective for a solute; other shuttle a substance from one side to the other by changing shape; hydrolyze ATP as an energy source to actively pump substances across a membrane
Enzymatic Activity
: protein built into membrane is an enzyme w/its active site exposed to substances in the adjacent solution.
Attachment to the cytoskeleton & ECM
: microfilaments or other elements by cytoskeleton noncovalently bond to membrane proteins, helps maintain cell shape & stabilize location of certain membrane proteins. Proteins coordinate w/ extracellular & intracellular changes.
Signal Transduction
: may have a binding site w/ a specific shape that fits the shape of a chemical messenger, like a hormone.
Cell-cell recognition
: some glycoproteins serve as identification tags that are specifically recognized by membrane proteins of other cells.
Intercellular joining
: membrane proteins may hook together in various kinds of junctions like gap or tight junctions. longer lasting
The Role of Membrane Carbohydrates in Cell-Cell Recognition
cells recognize other cells by binding to molecules w/carbs on the extracellular surface of a membrane
Glycolipids
: cells covalently bond to
Glycoproteins
: most cells covalently bonded to
Ex; A, B, AB, O reflect variation in the carb part of glycoproteins on the surface of RBCs.
Synthesis and Sidedness of Membranes
Figure 7.9 Synthesis of membrane components & their orientation in the membrane
1)Membrane Protein and lipids synthesized in association w/ the ER. In the ER, carbs are added to the transmembrane proteins making them glycoproteins.
2) Inside the GA, glycoproteins undergo further carb modification, & lipids acquire carbs, becoming glycoproteins.
3) Glycoproteins, Glycolipids, & secretory proteins are transported in vesicles to plasma membrane.
4) outside face continuous with inside face of plasma membrane, this release secretory proteins from cell, process called exocytosis. and positions the proteins on the outside face of plasma membrane.
Selective Permeability
allows some substances to cross it more easily than others
A phospholipid is an
amphipathic
molecule meaning it has both hydrophilic and hydrophobic region.
A PB can exist as a stable boundary b/w two aqueous compartments b/c the molecular arrangement shelters the hydrophobic tails, and exposing hydrophilic heads to water
Fluid Mosaic Model
- the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids.
Concept 6.4 The endomembrane system regulates protein traffic and performs metabolic functions
The Endoplasmic Reticulum: Biosynthetic Factory
Functions of the Smooth ER
Enzymes of the smooth ER: synthesis of lipids; including oils, steroids, and new membrane phospholipids
The cells that synthesize & secrete hormones - ex: in the testes and ovaries are rich in smooth ER, a structural feature that fits the function of these cells.
Detoxification usually involves adding hydroxyl groups to drug molecules making them more soluble & easier ti flush from the body.
other enzymes of smooth ER help detoxify drugs & poison, especially in liver cells.
stores calcium ions; for example, In muscle cells, the smooth ER membrane pumps Ca+ ions from the cytosol into the ER lumen.
when stimulated by a nerve impulse, the muscle cell Ca+ rush back across the ER membrane into the cytosol & trigger contraction of the muscle cell ; can trigger other responses such as secretion of vesicles w/newly synthesized proteins.
Functions of Rough ER
Most secretory proteins are glycoproteins (proteins w/ carbohydrates covalently bonded to them).
The carbohydrates are attached to the proteins in the ER lumen by enzymes built into the ER membrane.
Secretory proteins depart from the ER wrapped in the membranes of vesicles that bud like bubbles from transitional ER region.
Transport vesicles
are vesicles in transit from one part of the cell to another.
Membrane Factory: grows in place by adding membrane proteins & phospholipids to its own membrane.
Golgi Apparatus: Shipping and Receiving Center
Transport vesicles
transit from one part of the cell to another
transport vesicles
travel to the Golgi
GA is the warehouse for receiving sorting, shipping and manufacturing.
products from the ER are modified, stored, then sent to other locations
Specialized for Secretion
Consists of flattened sacs,
cisternae
; membrane of cisternae in a stack separates its internal from cytosol.
Two Sides of Golgi stack:
cis
face and
trans
face
Act as the receiving & shipping departments
Cis
Face located near ER
vesicle that buds from the ER can add its membrane & other contents of its lumen to the cis face by fusing w/ a Golgi membrane on that side.
Trans
Face "opposite" gives the rise to vesicles that pinch off and other sites.
Golgi Manufactures Molecules
polysaccharides secreted by cells are Golgi products
nonprotein Golgi products depart from the
trans
face of the Golgi inside transport vesicles
Cisternal Maturation Model
Cisternae of the Golgi process forward from the cis to the trans face
Golgi will sort products & targets them for various parts of the cell.
Molecular ID tags, phosphate groups added to the Golgi aid in sorting (like zip codes)
Transport vesicles have external molecules on their membranes that recognize "docking sites" on specific organelles or the plasma membrane
Figure 6.12 The Golgi Apparatus
3) Cisternal Maturation: Golgi cisternae move a cis-to-trans direction
4) Vesicles form & leave Golgi, carrying specific products to other locations to the plasma membrane for secretion
2) Vesicles coalesce to form new cis Golgi cisternae
5) Vesicles transport some proteins backward to less mature Golgi cisternae, where they function.
1) Vesicles move from ER to Golgi
6) Vesicles also transport certain proteins back to ER, their site of function.
Lysosomes: Digestive Compartment
membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest ( hydrolyze)macromolecules
lysosomal enzymes work better in the acidic environment found in lysosomes
some lysosomes arise by budding from the trans face of the Golgi
3-D shapes of lysosomes proteins protect vulnerable bond from enzymatic attack
carry out intracellular digestion
Phagocytosis
how unicellular eukaryotes eat (Amoebas)
food vacuole forms in this way then fuses w/ lysosomes
Enzymes digest the food
Humans carry out phagocytosis (WBCs) - use hydrolytic enzymes to recycle the cell's organic material, process known as
autophagy
damaged organelle or small amount of cytosol is surrounded by a double membrane
lysosome fuses w/ outer membrane of this vesicle
cell continues renew itself w/help from lysomes
EX: human liver cell recycles half of its macromolecules each week
In Tay-Sachs disease, for example, a lipid-digesting enzyme is missing or inactive, and the brain becomes impaired by an accumulation of lipids in the cells.
Vacuoles: Diverse Maintenance Compartments
large vesicles derived by ER and Golgi
Membrane selective in transporting solutes
The solution inside differs in composition from the cytosol
Food Vacuoles: Formed by phagocytosis
Contractile Vacuoles: pump excess water out of the cell, maintaining a suitable concentration of ions & molecules
unicellular eukaryotes have contractile eukaryotes
plants and fungi: certain vacuoles carry out enzymatic hydrolysis
small vacuoles in plants hold reserves of important organic compounds
help protect plants against herbivores by storing poisons.
Central Vacuole: develops by the coalesce of smaller vacuoles
mature plant cells
Cell Sap
plant cell's main repository
plays role in growth of plant cells
Concept 7.3 Passive transport is diffusion of a substance across a membrane with no energy investment
Molecules have thermal energy due to their constant motion.
Diffusion: movement of particles at any substance so that they spread out into available space
substance will diffuse from where it is more concentrated where it's less concentrated.
spontaneous process
dynamic equilibrium will be reached
Concentration Gradient
: region along which the density of a chemical substance increases or decreases; reps potential energy & drives diffusion.
Passive Transport
: diffusion of a substance across a biological membrane; cells do not have to expend energy
Effects of Osmosis on Water Balance
osmosis
: diffusion of free water across a selectively permeable membrane, whether artificial or cellular; refers to water only.
hypertonic
hypotonic
volume will increase on hypertonic side
Water Balance of Cells without Cell Walls
Tonicity: ability of a surrounding solution to cause a cell to gain or lose water
Higher concentration of nonpenetrating solutes in the surrounding solution = water to leave the cell and vice versa.
*Isotonic
"same"*: no net movement of h2o
volume of an animal cell is stable
Hypertonic
"more"
cell will lose water,
shrivel
, & die
Ex: increase in salinity of a lake
Hypotonic
"less"
water will enter the cell faster than it leaves
cell will lyse "
burst
"
Seawater is isotonic to marine invertebrates
Osmoregulation
: control of solute concentrations & water balance
Paramecium that live in pond water use their contractile vacuole
Bacteria & Archaea: living in hyper saline environments balance internal and external solute conct. to ensure no water leaves.
Water Balance of Cells with Cell Walls
Plants, prokaryotes, fungi and some unicellular eukaryotes
hypotonic solution like rainwater, cell will maintain its h2o balance
turgid: very firm, healthy state for plant cells
flaccid: limp; if plant cell is under isotonic solution
plasmolysis: plant in a hypertonic solution; shrivels & will lead to death.
Facilitated Diffusion: Passive Transport Aided by Proteins
passage of molecules or ions down they electrochemical gradient across a biological membrane
aquaporins facilitate massive levels of diffusion of water (osmosis) that occur in plants cells and red blood cells.
kidney cells have high number of aquaporins
ion channels: channel proteins that transport ions
function as gated channels, which open or close in response to a stimulus
stimulus may be electrical
Ex: nerve cell response to electrical stimulus;
Carrier proteins involved in facilitated diffusion result in the net mvmt of a substance down its concentration gradient
Concept 6.1 Biologists use microscopes and biochemistry to study cells
Cell Fractionation
Takes cells apart and separates major organelles & other sub cellular structures from one another.
a centrifuge spins the test tubes holding mixtures of disrupted cells at a series of increasing speeds.
higher speeds = smaller components
lower speeds = larger components
Ex: Biochemical tests showed the presence of enzymes involved in cell respiration, while microscopy discovered organelles like mitochondria.
Microscopy
invented 1590, refined in 1600s; cell walls first seen by Robert Hooke in 1665 as he determined dead cells from the bark of an oak tree.
Light Microscope (LM)
(0.2mcm)
visible light passed through the specimen then through glass lenses.
Magnification
Resolution
Contrast
Scanning Electron Microscope (SEM)
useful for detailed study oft the topography of a specimen
the electron beam scans the surface of the sample, usually coated w/ thin film of gold.
The beam excites electrons on the surface, then translates the pattern into an electronic signal sent to a video screen.
Appears 3D
Electron Microscope (EM)
(0.002nm)
organelles
are membrane enclosed structures within eukaryotic cells.
focuses a beam of electrons through the specimen or onto its surface.
resolution - inversely related to the wavelength of the light a microscope uses
Electron beams - wavelengths than visible light
Transmission Electron Microscope (TEM)
used to study the internal structure of cells
aims electron beam through a very thin section of the specimen
SEM & TEM contain electromagnets to bend paths of the electrons
Concept 6.6 The cytoskeleton is a network of fibers that organizes structures and activities in the cell
Cytoskeleton
: network of fibers extending through the cytoplasm
Roles of the Cytoskeleton: Support and Motility
Stabilized b/w opposing forces exerted by its elements
provides anchorage for many organelles and even cytosolic enzyme molecules
more dynamic than animal skeleton
Quickly dismantled and reassembled in a new location
Motility includes changes in cell location and movements of cell parts
Requires interaction of cytoskeleton w/motor proteins
vesicles and other organelles use motor protein "feet" to "walk" to their destinations
Neurotransmitter molecules migrate to the tips of atoms
Manipulates plasma membrane
Components of the Cytoskeleton
Microtubules
hollow rods constructed from globular proteins called tubules
tubulin dimer
consist of an Alpha tubulin and Beta tubulin
one end can accumulate or release tubulin dimers at a much higher rate than the other
shape and support the cell
guide vesicles from the ER to Golgi, from the Golgi to the plasma membrane
Involved in separation of chromosomes
Cilia & Flagella
unicellular eukaryotes are propelled through water by cilia and flagella
locomotor appendages
ciliated lining of the trachea sweeps mucus w/debris of our lungs
helps move egg towards a woman's uterus
Flagella are limited to one or a few cells ; longer than cilia; share a common structure
9+2 pattern: 9 doublets of microtubules arranged in a ring w/ two single microtubules in the center
Basal Body
anchors the microtubule assembly of a cilium or flagellum
Dyeins
are the motor proteins
has two "feet" that "walk" along the microtubule of the adjacent doublet using ATP
Centrosomes and Centrioles
Centrosome: located near the nucleus
Microtubules grow from the centrosomes
act as compression-resisting girders
Centrioles are inside the centrosome
composed of 9 sets of triplet microtubules in a ring
Microfilaments
Thin Solid Rods
Actin Filaments (protein)
twisted double chain of actin subunits
structural is to bear tension
supports the cells shape (cortical microfilaments)
cortex
is the outer region of cytoplasm, lying under plasma membrane
Well known for motility
Actin and Thicker filaments make a protein known as
myosin
interact to contract muscles
pseudopodia
are cellular extensions that crawl
cytoplasmic streaming
in plant cells , a circular flow of cytoplasm within cells; speeds the movement of organelles, especially in large cells
Intermediate Filaments
named for their diameter
only found in the cells of some animals
bear tension
after cells die, intermediate filaments network persist
outer layer of our skin consists of dead skin cells called keratin filaments
reinforce shape of the cell
make up nuclear lamina
Concept 6.8 A Cell is greater than the sum of its parts
Figure 6.31
The large cell is a macrophage; helps defend the mammalian body against infections by ingesting bacteria into phagocytic vesicles
The macrophage crawls along a surface and reaches the bacteria with thin pseudopodia
Actin Filaments interact w/other elements of the cytoskeleton in these mvmts.
After macrophage engulfs the bacteria, they are destroyed by lysosomes
The digestive enzymes of the lysosomes and cytoskeleton are made of ribosomes.
The synthesis of these proteins is programmed by genetic messages dispatched from the DNA in the nucleus
All of which require energy, located in mitochondria in form of ATP.