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Cells and Their
Housekeeping
Functions –
Metabolic Process
Shu-Ping Lin, Ph.D.
Institute of Biomedical Engineering
E-mail: [email protected]
Website: http://web.nchu.edu.tw/pweb/users/splin/
Metabolism

Cell metabolism: sum of all chemical reactions in living cell used for
production of useful energy and subsequent synthesis of cell constituents




Intake of food by cells from bloodstream: messenger substances
(hormones) released from endocrine glands into blood stream to affect
metabolism of cells that have receptors for that hormone
Hormone:



Anabolism: cells steadily remodel and replace their structures
Catabolism: structures worn out and no longer needed are broken down into small molecules
and either reused or excreted
Alter permeability of cell membrane to extracellular substances, Ex: glucose
Alter activity of key intracellular enzymes (pacemaker enzymes) controlling major chemical
pathways, Ex: insulin increases glucose uptake by muscle cells and increases storage of
glycogen. Type 1 diabetes (insulin deficiency) – depress glucose uptake and increase glycogen
breakdown, causing abnormally high levels of glucose in blood ↑osmotic pressure Remove
tissue water, cellular dehydration, and electrolyte loss Cells break down structural lipids and
proteins when glucose starves. Protein deficiency and weight loss in type 1 diabetes
Animals in low blood glucose levels Secreting epinephrine (adrenaline) from
adrenal gland and glucagon from pancreas Lead to an increase in conversion
of glycogen to glucose in liver. Opposite directions: glucagon and insulin
establish levels in circulation  Excess nutrients not immediately used are
stored as glycogen (in liver and skeletal muscle; sufficient for a few hours) and
fat reserve-triglyceride (sufficient fat stored for several weeks of starvation)



Generation of Useful Energy from Food
First stage of metabolism: large
molecules split into smaller units in digestive
tract, no useful energy is produced; Ex:
proteins  20 amino acids, carbohydrates
 glucose, fats glycerol and fatty acids
Second stage: occurs in cytoplasm small
organic units convert into simple units, Ex:
sugars, fatty acids, glycerol, and amino
acids are converted into acetyl unit of acetyl
CoA; process does not require oxygen,
yields small amount of ATP
Third stage: useful food energy, citric acid
cycle and oxidative phosphorylation carried
out under aerobic conditions in
mitochondria

Oxygen for contracting muscle cells is insufficient,
pyruvate convert to lactate releasing useful
energy But accumulation of lactate in muscle
tissues is responsible for muscle cramps. Yeast
(anaerobic organisms), pyruvate transform into
ethanol
Oxidation-Reduction Reactions

Oxidation-reduction or redox reaction: food degradation, chemical reactions
in which one or more electrons are transferred from one reactant to
another, each reaction requires an electron donor and an electron acceptor
Oxidation
Give up e- by removing H, loss of electrons
Adds O
Called an electron donor or a reducing agent
(reduces the accepting molecule, makes it more -)
Releases energy - exergonic
Reduction
Gain e-(more -), addition of electrons
Removes O
Called an electron acceptor or oxidizing
agent (oxidizes donor molecule)
Stores energy - endergonic
Oxidation
Xe- + Y  X + YeReduction

Xe- is being oxidized (losing e-), acts as a reducing agent because it reduces Y
Y is being reduced (gaining e-), acts as an oxidizing agent because it oxidizes Xe-
Electron-transfer potential of NADH convert into phosphate-transfer
potential of ATP  NAD+(oxidized form) +RH2 NADH (reduced form) +H++R
Redox potential: Oxidized form X  reduced form X-  G 0'  nFE 0'

Chemical reactions: degradation of food are exergonic redox (△G<0)
NAD+
Oxidized form
NADH Reduced
form
Degradation of Glucose



Glucose metabolism:
C6H12O6 + 6O2  6CO2 + 6H2O + energy
Blocks indicate 4 separate pathways in cellular energy
process, each pathway is composed of multiple
consecutive reactions catalyzed by enzyme. 
Anaerobic Respiration
Glycolysis in cytoplasm, others in mitochondria (called (Respiration without O2)
cellular respiration)
Glycolysis: consists of 10 reactions to convert glucose
into 2 molecules of 3-carbon compounds (i.e. pyruvic
acid and pyruvate)




First 5 reactions consume energy: 2 ATP molecules are
used to phosphorylate and activate glucose to 3-carbon
sugar phosphate
Aerobic Respiration
nd
2 set of reactions: hydrogen atoms are removed (Respiration using O2)
(oxidation) by NAD+ forming NADH (reduction):
2NAD+ + 4H (oxidation)  2 NADH (that’s a total of 4 e) -- Four ATP were produced from energy released by
substrate-level phosphorylation
Exergonic process with ∆G = -140kcal/mol
Glycolytic pathway do not involve oxygen
Glucose+ 2Pi+ 2ADP+ 2NAD+  2 pyruvate+ 2ATP+ 2NADH+ 2H++ 2H2O

Glycolysis is highly regulated.
blood to meet the need for ATP.
Cells acquire enough glucose from
Vesicular Transport mechanism



The transport mechanism which
proteins use to progress
through the Golgi apparatus
Cisternal maturation model:
the cisternae of the Golgi
apparatus move by being built
at the cis face and destroyed at
the trans face.
Vesicular transport model:
Vesicular transport views the
Golgi as a very stable organelle,
divided into compartments in
the cis to trans direction.
Vesicular Transport
Type
Description
Exocytotic
vesicles
Example
Vesicle contains proteins destined for extracellular release.
After packaging the vesicles bud off and immediately move
(continuous) towards the plasma membrane, where they fuse and
release the contents into the extracellular space in a
process known as constitutive secretion.
Antibody
release by
activated
plasma B
cells
Secretory
vesicles
Vesicle contains proteins destined for extracellular release.
After packaging the vesicles bud off and are stored in the
cell until a signal is given for their release. When the
appropriate signal is received they move towards the
membrane and fuse to release their contents. This process
is known as regulated secretion.
Neurotrans
mitter
release
from
neurons
Lysosomal
vesicles
Vesicle contains proteins destined for the lysosome, an
organelle of degradation containing many acid hydrolases,
or to lysosome-like storage organelles. These proteins
include both digestive enzymes and membrane proteins.
The vesicle first fuses with the late endosome, and the
contents are then transferred to the lysosome via unknown
mechanisms
Digestive
proteases
destined for
the
lysosome
(regulated)
Metabolic Process and
Mitochondria
Degradation of Glucose



Glucose metabolism:
C6H12O6 + 6O2  6CO2 + 6H2O + energy
Blocks indicate 4 separate pathways in cellular energy
process, each pathway is composed of multiple
consecutive reactions catalyzed by enzyme. 
Anaerobic Respiration
Glycolysis in cytoplasm, others in mitochondria (called (Respiration without O2)
cellular respiration)
Glycolysis: consists of 10 reactions to convert glucose
into 2 molecules of 3-carbon compounds (i.e. pyruvic
acid and pyruvate)




First 5 reactions consume energy: 2 ATP molecules are
used to phosphorylate and activate glucose to 3-carbon
sugar phosphate
2nd set of reactions: hydrogen atoms are removed
(oxidation) by NAD+ forming NADH (reduction):
2NAD+ + 4H+ (oxidation)  2 NADH + 2H+ (that’s a
total of 4 e-) -- Four ATP were produced from energy
released by substrate-level phosphorylation
Exergonic process with ∆G = -140kcal/mol
Aerobic Respiration
(Respiration using O2)
Glycolytic pathway do not involve oxygen
Glucose+ 2Pi+ 2ADP+ 2NAD+  2 pyruvate+ 2ATP+ 2NADH+ 2H++ 2H2O

Glycolysis is highly regulated.
blood to meet the need for ATP.
Cells acquire enough glucose from
Mitochondria



Mitochondrion (singular): organelles that release
energy ATP by burned (oxidized) food molecules –
aerobic respiration
Have their own DNA and synthesize some of their
own proteins, its ribosomes similar in composition to
prokaryotic ribosomes, change shape easily and
move efficiently to provide ATP to sites of high ATP
consumption, roughly of the size of a bacterial
(0.5~10 μm in diameter), divide asexually, live and
maintain by nucleus and cytoplasm  Highly
metabolic cells such as liver cells contain up to 2,000
mitochondria
2 membranes:



Smooth outer membrane (Transport protein porin allow
small proteins and molecules to enter intermembrane space)
Inner membrane (impermeable to ions, innermembrane proteins selectively transport molecules into
matrix) with many folds separating into 2 compartments –
internal matrix space and narrower intermembrane space.
Less lipid and much more protein than cell membrane
(membrane-bound proteins= enzymes). Membrane-bound
proteins produce ATP and facilitate the entry of pyruvate
and fatty acids into matrix.
Pyruvate Oxidzation




Enzymes on inner mitochondrial membrane oxidized pyruvate (CH3COCO2)
to acetate (CH3COO-) and yield free energy and CO2
Part energy from oxidization is saved by the reduction of NAD+ to NADH+
H+, some is stored by linking acetate to an enzyme – coenzyme A (CoA)
to produce energy-rich compound acetyl CoA (C23H38N7O17P3S)
Coenzyme A (CoA) also plays a central role in metabolism.
Terminal sulfhydryl group in CoA is reactive site. Acetyl CoA donate
acetate to acceptors, much as ATP can donate phosphate to various
acceptors.
Hydrolysis of Acetyl CoA





ΔG0’ for the hydrolysis of acetyl CoA has a large value
comparable to that of ATP.
Carriers such as ATP, NAD and CoA mediate the interchange
of activated groups in many biochemical reactions.
Conversion of pyruvate to acetyl CoA are catalyzed by a
complex of enzymes consisting of 72 subunits and 24
different proteins.
Enzyme complex cooperates with coenzymes, such as thiamin
 Higher animals lost capacity to synthesize vitamins,
organic molecules, and obtain them in their diet.
Most water-soluble vitamins are components of coenzymes
such as CoA.
Degradation of Glucose



Glucose metabolism:
C6H12O6 + 6O2  6CO2 + 6H2O + energy
Blocks indicate 4 separate pathways in cellular energy
process, each pathway is composed of multiple
consecutive reactions catalyzed by enzyme. 
Anaerobic Respiration
Glycolysis in cytoplasm, others in mitochondria (called (Respiration without O2)
cellular respiration)
Glycolysis: consists of 10 reactions to convert glucose
into 2 molecules of 3-carbon compounds (i.e. pyruvic
acid and pyruvate)




First 5 reactions consume energy: 2 ATP molecules are
used to phosphorylate and activate glucose to 3-carbon
sugar phosphate
Aerobic Respiration
nd
2 set of reactions: hydrogen atoms are removed (Respiration using O2)
(oxidation) by NAD+ forming NADH (reduction):
2NAD+2 + 4H (oxidation)  2 NADH (that’s a total of 4
e-) -- Four ATP were produced from energy released by
substrate-level phosphorylation
Exergonic process with ∆G = -140kcal/mol
Glycolytic pathway do not involve oxygen
Glucose+ 2Pi+ 2ADP+ 2NAD+  2 pyruvate+ 2ATP+ 2NADH+ 2H++ 2H2O

Glycolysis is highly regulated.
blood to meet the need for ATP.
Cells acquire enough glucose from
Citric-Acid Cycle (Aka Krebs Cycle)



Begins when acetyl CoA combines with oxaloacetate (a 4-C molecule) to
produce citric acid and releases Coenzyme A
Each turn of the citric acid cycle consumes one acetyl CoA molecule
(originally a pyruvate, since glycolysis produces 2 pyruvates, 1 glucose
molecule produces 2 turns of the citric acid cycle )
One turn of the Krebs cycle oxidizes the remaining citric acid, or citrate,
producing 1 ATP, 3 NADH, 1 FADH2, and the byproduct 2 CO2 which is
exhaled
Glucose Metabolism

The citric-acid cycle of glucose produces: 4 CO2, 2 ATP,
6 NADH, 2H+, and 2 FADH2
Glucose+ 2Pi+ 2ADP+ 2NAD+  2 pyruvate+ 2ATP+ 2NADH+ 2H++ 2H2O
2X
2X
2X

Respiratory Chain

FADH2 & NADH are energy carriers and
used to produce ATP. Couple
oxidization of NADH or FADH2 to produce
ATP
1
NADH  H   O2  NAD   H 2O
2
Intermembrane space
G  52.4
Matrix
ADP  Pi  nH P  ATP  nH N
kcal
mol
Oxidization of NADH by oxygen is
exergonic. (Hydrolysis of ATP=-12kcal/mol)

Occur on inner membrane of
mitochondria (capable of rapid electronexchange, i.e. oxidation & reduction) and
involve sequential transfer of electrons
through membrane-associated molecules
http://www.life.illinois.edu/crofts/bioph354/lect10.html
Electron-transport system (ETS): high energy electron-carrying enzyme
deliver electrons to more electronegative enzyme  Each successive carrier is
more electronegative than the last so electrons are pulled downhill  One
carrier reduces another, energy released is used to pump hydrogen ions
across the membrane into the intermembrane space  Remaining energy is
used to reduce the next carrier

ElectonsETSSynthesize ATP




Proton (H+) accumulate in the intermembrane space  Cause
concentration gradient and charge gradient across membrane
Concentration gradient forces protons to pass channel protein ATP
synthase  Relaxation of the proton flux couples formation of ATP.
Free-energy change (△G) in transporting uncharged molecule from
concentration 1 to 2 is: (R:gas constant=1.987 cal/mol, T:absolute
temperature in Kelvin= 273.15 °+ ℃)
G  RT ln( C 2 )
C1
Membrane electric potential and ion concentration gradient provide
driving force for moving ions (charged particles) across membrane. 
△G of transporting ion might be large enough to drive other processes.
(Z:electrical charge of transported species, △V:potential in volts(V) across
membrane 12, F:Faraday constant=23.062 kcal/Vmol )
G  RT ln( C 2 )  ZFV
C1


ATP Synthase
ATP synthase catalyzes the formation of
ATP Proton-conducting unit F0 spans the
lipid bilayer. ATP synthesizing unit F1 faces
matrix. Hydrogen flow form intermembrane
space to matrix through F0. 3 catalytical β
subunits of F1 are structurally identical but in
different configurations at any particular point



Catalytic site in open (O) form
(configuration): little affinity for substrates
Loose (L) form: bind to either ATP or
ADP+Pi loosely and is catalytically inactive
Tight (T) form: bind to either ATP or
ADP+Pi tightly and is active
Energy input from proton flux
converts T site to O site O site to
L site L site to T site: New L site
binds new ADP and phosphate
and begins a new reaction sequence
Proton flux: not needed in ATP from
ADP+Pi, but can release tightly
bound ATP and cycle continues
△G<0 in intermembrane space 
Flow protons through ATPase and
ADP+Pi bind to ATPase  Enzyme
catalyzes formation of ATP  ATP
detaches from ATP synthase when
proton flux
http://www.sigmaaldrich.com/life-science/metabolomics/learning-center/metabolic-pathways/atp-synthase.html
http://www.sigmaaldrich.com/sigma-aldrich/areas-of-interest/life-science/metabolomics/learning-center/metabolic-pathways/atp-synthase/atp-animation.html
Summary of Glycolysis
and Cellular Respiration
Respiratory
Chain:
Anaerobic Respiration
(Respiration without O2)
4ATP+10NADH
+ 2FADH2=
(4+ 3X10+ 2X2)
= 38 ATP
Total Yields
Aerobic Respiration
(Respiration using O2)


Mitochondria are highly efficiently as energyprocessing plants.
Glucose 2 pyruvates + 2 ATP (in cytoplasm)
Pyruvates imported into mitochondrion and
oxidized by O2 to produce 30 ATP (3ATPX10=30;
since NADH 3ATP molecules, FADH2
2ATP molecules)


Photosynthesis
Photosynthesis: anabolic reaction, convert light energy to
chemical energy of organic compounds – raw materials: water,
carbon dioxide (CO2, inorganic) and energy (sunlight)

Products: glucose (energy rich carbon compounds) and
oxygen (side product)
http://en.wikipedia.org/wiki/Photosynthesis
6CO2 + 12H2 O + energy  C6H12O6 + 6H2 O + 6O2

H2O: used as reactant and released as a product
2 pathways: driven by light energy in 1st pathway;
entrapment of energy received from photons into ATP
molecules in subsequent pathway  Light: radiant
energy (packets of photons)


E=h c/ λ (E:energy, c:3x1010cm/s, h:Planck’s constant
1.584x10-34cal s)
λ:400~700nm; violet (high “E”), blue, green, yellow,
orange, red
Energy of molecule absorbing photon rises from ground
state to excited state and drives electrons to away from
nucleus Loosely held electron then get transferred to
other molecules in subsequent reactions, resulting in
the production of ATP from ADP Common to the
degradation of glucose
http://www.overidon.com/wpcontent/uploads/2010/06/wavelength-light1.jpg
Common Themes in Metabolic Pathways

Central themes of metabolism:
1)
2)
3)
4)

ATP is the universal currency of energy. Hydrolysis of ATP increase equilibrium ratio
of products to reactants in energy-requiring reaction by a factor of about 108.
ATP is generated by the oxidation of fuel molecules such as glucose. Chemical
energy in carbon bonds using electron carriers to create proton gradient across inner
membrane of mitochondria to synthesize ATP.
Metabolic pathways generate ATP and transfer high-potential electrons to
electron carriers such as NADH also provide building blocks for macromolecules.
Biosynthetic and degradative pathways are almost always separate and utilize
different enzymes. Biosynthetic pathway is made exergonic by hydrolysis of ATP.
Recurring motifs in these reactions
1)
2)
3)
Flow of molecules down metabolic pathway is determined by amounts and
activities of certain enzymes. First irreversible reaction in metabolic pathway is
committed step Enzymes catalyzing committed steps are typically regulated by the end
product.
Regulatory enzymes in metabolic pathway are controlled by
phosphorylation. Proteosomes control protein concentration by degradation.
Metabolic pathways involve compartmentalization of chemical reactions.
Whether they are in cytoplasm or in mitochondria, compartmentalization is a useful
tool in separating degradative pathways from biosynthetic pathways.
Molecular Motors &
Membrane Potential


Molecular
Motors
ATP hydrolysis drive many metabolic or anabolic reactions that require
energy, such as ATP hydrolysis to mechanical work Motor protein: an
enzyme and use the resulting energy to drive a chemical or mechanical
change Mechanical energy (form of kinetic energy of motion or elastic
energy stored in the system) – energy-transformation mechanism:
protein motors become strained during transitions, free energy is partly
stored as internal elastic energy and released for driving force for forward or
upward movement.
Motor proteins: convert chemical energy into mechanical energy by
ATPase: ATP ADP; use chemical energy in ATP, a fuel to cause
movement, to cause positional change relative to substrate or
track Myosin and kinesin: have similar structure


Myosin: cause movement in relation to actin-rich thin filaments
Kinesin: cause movement along microtubules
Myosin
Kinesin
Myosin Motors & Actins


Myosin: molecular motor of muscle; together with actin and regulatory
proteins for muscle contraction, cell motility, and extension of cell
projections; myosin molecules in muscle cells aggregate and their tails
form thick filaments
Actin: most abundant in cell(10% of cell content); highly conserved
ancient protein of eukaryotes; actin from different species polymerizes
readily to form thin filaments; asymmetrical arrangement in
microfilament: the end to which actin monomers added differs from the
others(directional +  - end); actin decorated with head region of myosin, all
heads in the same direction and give decorated filament flight of an arrow

Myosin and actin have contractile roles in all eukaryotic cells; nonmuscle
cells contain 10- to 100-fold less myosin than actin; motor domains of
“unconventional” myosin hydrolyze ATP, and have variations in tail can
interact with different proteins: actin-based vesicular transport and hearing
http://www.sigmaaldrich.com/life-science/metabolomics/enzymeexplorer/learning-center/structural-proteins/myosin.html

Skeletal
Muscle
Structure
Myosin II: building block of thick filaments, made of 6
polypeptide chains: 2 identical heavy chains (230 kDa each), 4
light chains (20 kDa each); 2 oval-shaped heads of about 60 nm
and a long tail of about 130 nm




Tails: bind together and form backbone of thick filaments
Heads: contain binding sites for actin and ATP (hydrolysis products: ADP and Pi)
α-helical neck region between head and tail: regulate activity of head region
Thick filaments: 16 nm in diameter and 1.5 um long; myosin heads
(cross-bridges) protrude from filament at intervals of 14.3 nm
along filament axis
Regulates activity
of head region
Myosin Filament (Thick Filament)






LMM: myosin molecule embedded in body of thick filaments of muscle fibers
HMM: portion of myosin protruded from body of thick filament
Mechanism of force generation and movement in cells: heads protrude and
interact with active sites on thin actin filaments pulling them against external
load thereby causing muscle contraction
Sarcomere: repeating contraction unit in muscle cells, composed of thick myosin
and thin actin filaments arranged in parallel
Central region of thick filament (H band) spans 150 nm and is devoid of
projecting crossbridges
Myosin heads on each side of bare zone point toward center of thick filament
(thick filament is inherently bipolar)
Sarcomere
150 nm
1.5 um
Actin Filaments (Thin Filament)





Major component is actin, which has high affinity for myosin.
1/3 of mass of thin filaments is tropomyosin and troponin complex.
Each thick filament is surrounded by 6 thin filaments that overlap thick
filament.
Relaxed muscle (low Ca2+): tropomyosin prevents actin from
interacting with myosin heads
Signal for muscle contraction from nervous input through neuromuscular
junctions Results in release of intracellular Ca2+ from specialized ER found
in muscle cells Myosins bind to actin filament Muscle contracts
(myosin heads pull thin filaments toward the center of sarcomeres, resulting
in shortening of muscle)
Sarcomere
http://www.sigmaaldrich.com/life-science/metabolomics/enzymeexplorer/learning-center/structural-proteins/myosin.html
Work Stroke of a Crossbridge



Muscle shortening during contraction: relative movement of actin
filaments with respect to myosin filaments
Relative movement: reversible interaction of myosin heads protruding
from thick filaments with actin binding sites on thin filament
Myosin head has strongest affinity to ATP than actin:



(a), (b), and (c): indicate myosin interacts with actin and produces force and
movement, called attached states
(e) and (d): myosin is free of actin, called detachment
Chains of circles: ATP and ADP; smaller circles: phosphate groups



ATP hydrolysis occurs while
myosin head is free of actin
Change in configuration of
myosin head Allow to
interact with actin
Hydrolysis product Pi Strongly
attached state in which myosin
head pulls thin filament toward
center of sarcomere
Detachment of ADP Binding of
ATP to same site and subsequent
detachment of myosin from actin
and continuation of cycle
Myosin Kinetics Using In-Vitro
Motility Systems



Myosin-coated beads move unidirectionally on oriented actin
cables in the presence of ATP, having the same sense of
direction
Beads coated with skeletal muscle myosin move with speed of
5 um/s and is estimated that 25 myosin molecules on each
bead are sufficient to actuate motion
Actin filaments can move on glass decorated with myosin in the
presence of ATP.
 Forces generated by a single
motor: myosin head can generate 5
pN and myosin molecule can
catalyze hydrolysis about 20 ATP
molecules per second during muscle
contraction
Kinesin Motors



Kinesin: motor protein that powers transport of intracellular
organelles along microtubules (100 eukaryotic motor proteins
interacting with microtubules), facilitate chromosome movement
during cell division
Motile organelles such as mitochondria and vesicles use
kinesins to propel them along microtubules.
Consist of 2 heavy (globular) and 2 light chains, resulting in 400 kDa:




2 globular regions contain ATPase active site and microtubule-binding
site: ATPase activity strongly promoted by microtubules Presence of
microtubules, kinesin hydrolyze up to 100 ATP per second
Globular tail domain: contain binding site for cargo (organelle,
chromosome, etc.)
Various kinesin genes all contain microtubule-binding sites and
have ATPase activity, but differ in their cargo-binding sites
Direct movement toward “+” end of microtubules, but some are
minus-end-directed motors
http://www.imb-jena.de/~kboehm/Kinesin.html
Kinesin Cycle



Their associated cargo move along microtubules for several micrometers =
Kinesin-induced microtubules motion Organelle uses kinesin for
transport can fall off microtubule and reattach if confronted with obstacle
(same microtubule can simultaneously support “+” and “-” end-directed
motion; kinesin-dependent vesicle transport from “-” to “+”)
Kinesin motion is reminiscent of human walking: both heads translocate
in turn by 16-nm steps, each translocation moves center of mass 8 nm
forward; during the translocation motion of one head, the other remains
bound to microtubules
Glass coated with kinesin support gliding of individual microtubules in-vitro:
kinesin binds to cargo-binding region (tubulin) immobilized to slide and
microtubule moves 1 um/s, maximum force produced by kinesin ~5 pN
http://homepage.ntlworld.com/malcolmbowden/kinesin.htm
Dynein


Another family of microtubule-based motor protein
http://people.virginia.edu/~rjl6n/dynein.htm
2 identical heavy chains of about 530 kDa each (dark blue): contain 4 ATPbinding sites, movement along microtubules and microtubule binding site;
2X 74 kDa intermediate chains (magenta and yellow); 4X 53-59 kDa
intermediate chains (green)


74 kDa intermediate chains are thought to bind the dynein to its cargo, cargo is
membrane-bounded vesicle in neuron, golgi vesicle, kinetochore or mitotic spindle astral
microtubule – force to move cargo along microtubule toward its minus end
Ciliary dynein: power flagella motion in some motile single-cell eukaryotes
and is responsible for beating cilia in some tissues of multicellular organisms

Cilia on surface of cells in oviduct are used to move egg, cilia in cells of
respiratory system are used to move mucus.
http://bernstein.harvard.edu/research/motor_protein.htm
http://people.virginia.edu/~rjl6n/dynein.htm
Muscle
Contraction

http://www.maprepaphysique.fr/dossiers/physiologie/l
a-contraction-musculaire.htm
http://en.wikipedia.org/wiki/File:Sarcomere.svg
Signal for muscle
contraction from
nervous input through
neuromuscular
junctions Results in
release of intracellular
Ca2+ from specialized
ER found in muscle
cells Myosins bind
to actin filament
Muscle contracts
(myosin heads pull thin
filaments toward the
center of sarcomeres,
resulting in
shortening of
muscle)