Waging War on Modern Chronic Diseases Primary Prevention Through Exercise Biology
Study Exercise Biology 17 - 20
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Transcript of Study Exercise Biology 17 - 20
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1. Describe the organization of the membranes of a chloroplast.How does this organization differ from that of mitochondria
CHLOROPHYLL
greenpigment found in the chloroplasts of plants, algae, and cyanobacteria
is an extremely important biomolecule, critical inphotosynthesis,which allows plants to
absorb energyfrom light
absorbs light most strongly in the blue portion of the electromagnetic spectrum, followed
by the red portion. However, it is a poor absorber of green and near-green portions of the
spectrum, hence the green color of chlorophyll-containing tissues in plants.
broken down into three major compartments
o stromathe fluid space inside of the chloroplast where chloroplast DN,
en!ymes, and free ribosomes are found
o "hylakoid
flat disks that function in light absorbtion and photosynthesis.
arranged in stacks called granum #plural$ grana%, are connected by
lamella, and have an interior space known as the lumen
o
inner and outer membranes.SIMILARII!S "IH MIOCHO#$RIA
re ovoid or elliptical in shape
re surrounded by an outer membrane and an inner membrane.
o &n the mitochondrion, the term crist%eis applied to the folds of the inner
membrane.
'
https://www.boundless.com/biology/definition/pigment/https://www.boundless.com/biology/definition/photosynthesis/https://www.boundless.com/biology/definition/energy/https://www.boundless.com/biology/definition/pigment/https://www.boundless.com/biology/definition/photosynthesis/https://www.boundless.com/biology/definition/energy/ -
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Have membranes surrounded by fluid.
o &n the mitochondrion, the fluid &%trixis inside the inner mitochondrial
membrane, and fluid in the i'ter&e&(r%'e s)%ceis between the inner and outer
mitochondrial membranes.
o &n the chloroplast, the stro&%surrounding the grana is a fluid, and fluid also
occupies the lu&e'of each thylakoid.
both contain an a(ueous matrix containing en!ymes and coen!ymes, concerned with
dehydrogenations, electron transport and ") exchange, but these en!ymes and
coen!ymes are used in different ways in chloroplasts and mitochondria.
both contain DN and *N, which are involved with the synthesis of the membrane and
en!yme proteins, when the organelles replicate during cell division.
both contain + type ribosomes #*N% which may be free in the matrix or attached to
membranes.
$I**!R!#C!S "IH MIOCHO#$RIA
hloroplast /itochondria
chloroplasts are shaped like minute biconvex /itochondria are usually rod-shaped, about
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lenses, 1-' mm in diameter and 0-2 mm thick
'-0 mm long and .2-.+ mm wide. # few
species may have spherical or spiral shaped
mitochondria%.
chloroplasts contain many double membranes
called lamellae. "hese form disc like structures
called thylakoids which are piled on top of eachother, making the structures known as grana. 3ranaare joined to each other by intergranal lamellae.
"he thylakoids contain many small and large
particles which can only be seen under the highest
powers of the electron microscope. "hese are the
(uantosomes and house the photosystem systems
of pigments
"he innermost membranes of mitochondria
are called christae and are extensions of the
inner membrane of the mitochondrialenvelope. "he christae and inner membrane
are covered with thousands of small spherical
bodies called oxysomes which are attached to
the membranes by short stalks #oxysome 4
stalk 5 stalked particle%.
chloroplasts may contains temporary stores of
starch and lipids
mitochondria do not contains temporary
stores of starch and lipids
chloroplasts contain the photosynthetic pigments,
chlorophyll a, chlorophyll b, b-carotene andsometimes xanthophyll. "hese are situated in the
(uantosomes of the thylakoids and make up the
photosystems
/itochondria do not contain photosyntheticpigments.
chloroplasts are concerned with the process of
photosynthesis only operates in light
mitochondria are concerned with aerobic
respirationoperate all the
time, whether light or dark.
chloroplasts absorb carbon dioxide, for use inphotosynthesis during light periods, and release
oxygen
mitochondria continually absorb oxygen for
respiration and release carbon dioxide
it also absorb pyruvic acid, the final product
of glycolysis, which occursin the cytoplasm of cells.
the light dependent stage of photosynthesis #light
reaction% occurs in the (uantosomes of the
thylakoids. "he small and large (uantosomes
are thought to house the pigment systems of
photosystem & and photosystem && respectively.yclic photophosphorylation involves only
photosystem & but non-cyclic photophosphorylation
involves both photosystems & and &&.. "he light
independent stage of photosynthesis #dark reaction
or alvin pathway% occurs in the stroma of the
chloroplast and uses ") and ND)H, generatedby the light reaction, to fix carbon dioxide onto the
acceptor, ribulose bisphosphate. "his results in the
synthesis of sugars.
"he en!ymes of the 6ink *eaction and 7rebs
cycle, for metaboli!ing pyruvic acid, #and the
en!ymes for the b-oxidation of fatty acids%,are present in the matrix of the mitochondria.
"he bases of the stalked particles house the
coen!ymes of the respiratory chain, including
the electron transport chain. "he spherical
heads of the stalked particles contain the
en!ymes, such as ")ase, which link the
respiratory chain to oxidativephosphorylation, which occurs in the
spherical heads. ") is thus generated in the
spherical heads.
the coen!yme used for hydrogen transfer in the
process of photosynthesis, in the chloroplasts, is
ND) #nicotinamide adenine dinucleotide
phosphate%
"he initial coen!yme used for hydrogen
transfer in the process of respiration, in the
mitochondria, is ND #nicotinamide adenine
dinucleotide%.
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2. In what ways is photosynthesis the reverse of respiration
P+otosy't+esis Res)ir%tio'
Productio' o, AP- 8es
8es9 theoretical yield is 2: ")
molecules per glucose but actualyield is only about 2-20.
Re%ct%'ts-;lectron "ransport hain
#oxidative phosphorylation%.
"+%t )oers AP
sy't+%se-
H4 gradient across thylakoid
membrane into stroma. High
H4 concentrationin the
thylakoid lumen
H4 gradient across the inner
mitochondria membrane into matrix.
High H4 concentration in the
intermembrane space
Products-; H'0 lectron transport chain
electrochemical gradient created
energy that the protons use to flow
passively synthesi!ing atp
Occurs i' +ic+
org%'elle/-hloroplasts /itochondria 3lycolysis #cytoplasm%
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*i'%l electro' rece)tor- ND)4 #forms ND)H %
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. In general terms! how do the light-independent reactionsdiffer from the light " dependent reactions# $hat are theprimary products of the two types of reactions
refers to the use of light energy fromphotosynthesisto ultimately provide the energy to
convert D) to "),thus replenishing the universal energy currency in living things.
&n the simplest systems in )ro%ryotes3 )+otosy't+esis is used 4ust ,or t+e )roductio' o,
e'ergy3and not for the building of any biological molecules. &n these systems there is a
process called cyclic )+oto)+os)+oryl%tio' %cco&)lis+es t+e A$P to AP )rocess ,or
i&&edi%te e'ergy ,or t+ese cells5
&n the process called 'o'cyclic )+oto)+os)+oryl%tio'3 % )l%'tmust accomplish the
s)litti'g o, %ter3 t+e co'6ersio' o, A$P to AP3 %'d t+e )ro6isio' o, t+e reduced
coe'y&e #A$PH to power the synthesis of energy storage molecules.
#O#CYCLIC PHOOPHOSPHORYLAIO#
;
http://hyperphysics.phy-astr.gsu.edu/hbase/biology/psyncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/biology/atp.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/biology/atp.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/biology/etcyc.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/biology/etnoncyc.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/biology/psyncon.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/biology/atp.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/biology/etcyc.html#c1http://hyperphysics.phy-astr.gsu.edu/hbase/biology/etnoncyc.html#c1 -
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consists of two sets of pigments to excite.
)', or photosystem ' )- +
)0, or photosystem 0 )- ;:.
Process
>nergy enters the system when )0 becomes excited by light.
>lectrons are shed by the excited )0 #oxidation%, which grabs electrons from
water, producing a molecule of oxygen gas for every two waters split.
"he electron then travels from the excited reaction center of ) 0 to
plasto(uinone #E%, to the b;-f complex, to plastocyanine #pc% and finally to the
reaction center of ) '
"his electron transport system generates a proton motive force that is used to
produce ") Bhen photosystem & absorb a photon of light, it ejects a high-energy electron.
"he energy from this light absorption is used to generate reducing powder in the
form of ND)H
"he ejected electron is replaced by an electron from photosystem &&
CYCLIC PHOOPHOSPHORYLAIO#
Process
6ight of the photons is captured by the antenna complexand transferred to the
)hotosystem & reaction center, which contributes two high energy electrons to the
primary electron receptor. >lectrons are passed to ferrodoxin #Ad%, an iron containing protein which acts as
an electron carrier.
second electron carrier plasto(uinone #)(% carries the electrons to a complex of
two cytochromes.
&n the process, energy is provided to produce a proton gradient across the
membrane which can be used for the D) to ") conversion.
+
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"he electrons are returned by plastocyanin #)c% to the )+ pigment in the
reaction center to complete the cycle.
%. How does the proton gradient lead to the formation of &'(#
C+e&ios&osis
is the process of using )roton movement to join D) and )i
accomplished by en!ymes called ") synthases or ")ases as protons pass through
this en!yme D) and )i are joined to make "). "he movement of the )rotons through
this en!yme provides the >nergy needed to make ").
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). Describe the basic plan of the *alvin cycle! indicating thereactions that re+uire energy input. $hy is it described as acycle#
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"he alvin cycle is a series of reactions that results in conversion of carbon dioxide
into the organic molecules needed to build new cells.
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o a biochemical barrier
o a medium for$
extracellular communication that is assisted by /s
the stable positioning of cells in tissues through cell matrix adhesion
the repositioning of cells by cell migration during cell development and
wound repair
!CM )ro6ides-
o tensile strength for tendons
o compressive strength for cartilage
o hydraulic protection for many types of cells
o elasticity to the walls of blood vessels
A$$IIO#AL #O!S 8lycoc%lyx 9cell co%t: &edi%tes cellcell ; cellsu(str%tu& i'ter%ctio'sxperiment$ digest >/ surrounding cultured cartilage or mammary
gland epithelial cells with en!ymes J= get decrease in secretory @
synthetic activities of cells
dd back >/ materials into culture J= restores differentiated state @
cells produce usual products
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?. /ay consist of ill-defined, amorphous associations of proteins @
polysaccharides #like loose connective tissue% or may be in the form of a
distinct structure
!CM t%es di6erse ,or&s i' di,,ere't tissues ; org%'is&s3 (ut is co&)osed
o, si&il%r )rotei's
/ost proteins in cells are compact @ globular9 those of extracellular space
are extended @ fibrous
mong their diverse functions, >/ proteins serve as scaffolds, girders,
mortar @ wire
lterations in amino acid se(uence of extracellular proteins can lead to
serious disorders
!CM 6ery )ro&i'e't i' co''ecti6e tissues 9c%rtil%ge3 (o'es3 te'do's3 cor'e%l
stro&%:
&n connective tissue, cells occupy a small fraction of tissue volume
>/, not cells, gives tissues their identifiable properties$ bone matrix
hardness, cartilage matrix toughness @ flexibility, tendon matrix tensile
strength, corneal stroma matrix transparency
Co&)o'e'ts o, t+e !CM &e&(ers o, % s&%ll 'u&(er o, &olecul%r ,%&ilies
ollagens G one of most important @ ubi(uitous >/ molecules9 fibrous
glycoprotein family Aunctions only as part of >/ @ only found there
)roteoglycans - protein-polysaccharide complex
Aibronectin, 6aminin, >/ )roteins
'0
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"he >xtracellular pace$ ?asement /embrane as an >xample of >/ B%se&e't &e&(r%'e 9(%s%l l%&i'%:< % co'ti'uous =>0 200 '& t+ic
s+eet< o'e o, (est de,i'ed ex%&)les< ,ou'd i' t+e ,olloi'g )l%ces-
&t surrounds muscle @ fat cells
&t underlies basal surface of epithelial tissues #skin epidermis, digestive
@ respiratory tract linings%
&t underlies the inner endothelial lining of blood vessels
*u'ctio's o, (%se&e't &e&(r%'e
)rovides mechanical support for the attached cells
3enerates signals that maintain cell survival
/aintains epithelial cell polarity
erves as a substratum for cell migration @ determines cell migration
path
eparates adjacent tissues within an organ #compartmentali!ation%
cts as barrier to passage of macromolecules @ errant cancer cells -
prevents passage of proteins out of blood as it flows through porous-
walled body capillaries #kidney G good example%
7idney glomerulus - blood filtered under high pressure through
double-layered basal lamina separating glomerular capillaries
from kidney tubule wall
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?asal lamina around glomeruli may thicken abnormally in
long-term diabetics J= kidney failure
omponents of the >xtracellular /atrix$ ollagens
Co&)rise % ,i(rous glyco)rotei' ,%&ily< )rese't o'ly i' !CMs< ,ou'd
t+roug+out %'i&%l i'gdo&
#oted ,or +ig+ te'sile stre'gt+ 9resist%'ce to )ulli'g ,orces:< it
is esti&%ted t+%t % 1 && di% coll%ge' ,i(er c%' sus)e'd % 10 g
?22 l(@ eig+t it+out (re%i'g
It is t+e si'gle &ost %(u'd%'t )rotei' i' +u&%' (ody
9co'stitutes 2> o, %ll )rotei':< re,lectsides)re%d
occurre'ce o, extr%cellul%r &%teri%ls
Coll%ge' &olecules )ro6ide t+e i'solu(le ,r%&eor t+%t
deter&i'es &%'y !CM &ec+%'ic%l )ro)erties
M%de &ostly (y ,i(ro(l%sts 9,ou'd i' 6%rious co''ecti6e
tissue ty)es:3 s&oot+ &uscle ; e)it+eli%l cells
=0 distinct types identified9 each restricted to
particular sites in body9 0 or more can be present
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together in same >/9 get functional complexity by
mixing several types in same fiber #heterotypic%
Heterotypic fibers are biological e(uivalent of metal
alloys
Different structural @ mechanical properties result from
different mixtures of collagens in fibers
M%'y di,,ere'ces %&o'g coll%ge' ,%&ily &e&(ers3 (ut %ll
s+%re 2 i&)ort%'t structur%l ,e%tures-
All coll%ge' &olecules %re tri&ers co'sisti'g o,
)oly)e)tide ?D@ c+%i's &%y (e ide'tic%l or 2 or di,,ere't
c+%i's
Alo'g %t le%st )%rt o, le'gt+3 t+e c+%i's i'd %rou'd e%c+
ot+er< ,or& u'i.ue3 rodlie tri)le +elix
So&e %re ,i(rill%r coll%ge's 9I3 II3 II: %sse&(le i'to rigid3
c%(lelie ,i(rils< t+e' i'to t+icer ,i(ers 6isi(le i' lig+t
&icrosco)e
&ndividual collagen molecules of a fibril are not in
register but are staggered K'L1 length relative to their
neighbors
"he staggered arrangement adds to the mechanical
strength of the complex @ causes banding patterns
characteristic of collagen fibers
*i(rils %re stre'gt+e'ed ,urt+er (y co6%le't crossli's
(etee' lysi'e ; +ydroxylysi'e residues o' %d4%ce't
coll%ge' &olecules i, disru)ted e%e'ed
ross-linking process continues through life
/ay contribute to decreased skin elasticity @ increased
brittleness of bones among elderly
Coll%ge' )ro6ides i'solu(le ,r%&eor t+%t deter&i'es
&%'y o, t+e !CM &ec+%'ic%l )ro)erties ; $
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"ype & collagen mutations - osteogenesis imperfecta,
potentially lethal condition characteri!ed by extremely fragile
bones, thin skin @ weak tendons
"ype && collagen mutations - alter cartilage properties9 causes
dwarfism @ skeletal deformities
number of collagen gene mutations - cause various distinct
but related collagen matrix structure defects #>hler-Danlos
syndromes% G one causes hyperextendable joints @ highly
extensible skin
"ype &I collagen gene mutations - lport syndrome, an
inherited kidney disease in which the glomerular basement
membrane is disrupted
omponents of the >xtracellular /atrix$ )roteoglycans
B%se&e't &e&(r%'es ; ot+er !CMs co't%i' l%rge %&ou'ts o, disti'cti6e
ty)e o, )rotei')olys%cc+%ride co&)lex c%lled %proteoglycan
onsist of core protein to which glycosaminoglycan #33% chains are
covalently attached
33s - repeating disaccharides #0 different sugars9 --?--?-%9 very
acidic due to both carboxyl @ sulfate groups on their component sugar
rings
>/ proteoglycans may assemble into gigantic complexes by linking
core proteins to hyaluronic acid #a nonsulfated 33%9 can occupy very
large volumes #e(uivalent to that of bacterial cell%
$ue to sul,%ted 8A8 'eg%ti6e c+%rges3 )roteoglyc%'s (i'd l%rge 'u&(ers
o, c%tio's3 +ic+3 i' tur'3 %ttr%ct lots o, H2O "hey form porous hydrated gel9 that fills extracellular space @ acts
like packing material to resist crushing #compression% forces
"his complements adjacent collagens, which resist pulling forces @
provide scaffold for proteoglycans
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"ogether they give cartilage @ other >/s strength @ resistance to
deformation #wiggle your ears%
"he >/ of bone is also made of collagen @ proteoglycans but it is
hardened by impregnation with calcium phosphate salts
omponents of the >xtracellular /atrix$ Aibronectin, 6aminin @ /
)roteins
/atrix implies a structure made up of a network of interacting components9
this is apt for >/
&t contains a number of proteins, in addition to collagen @
proteoglycans that interact with one another in highly specific ways
/any >/ proteins occur in families #more than ' form9 each formed
by alternate m*N splicing%
Different family members made in different tissues @ at
different times during development
Different protein forms may have different properties
#characteristics may not apply to all forms%
*i(ro'ecti' 9,i(rous: o'e o, (est studied !CM )rotei's< +%s ,e%tures
co&&o' to &ost ot+er &%trix co&)o'e'ts ; !CM )rotei's< co'sists o,
li'e%r %rr%y o, disti'ct (uildi'g (locs 9% &odul%r co'structio':
>ach fibronectin polypeptide is constructed from a se(uence of K2
independently folding An modules of 2 distinct types #An&, An&& @ An&&&%
An modules were first found in fibronectin, but they are part of many other
proteins.
Aound in proteins from blood clotting factors to membrane receptors @ other
>/ proteins >ach of the two polypeptide chains making up fibronectin contains$
?inding sites for other >/ components #collagen, proteoglycans,
etc.%9 link these molecules into stable, interconnected networks
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?inding sites for cell surface receptors #form stable >/-cell
attachments%9 endothelial cell will adopt shape unlike it does in body
when it spreads over a s(uare surface coated with fibronectin
*i(ro'ecti' ; ot+er !CM )rotei's %re i&)ort%'t +e' tissues %re
i'6ol6ed i' dy'%&ic %cti6ities 9e&(ryo'ic de6elo)&e't:
Development involves waves of cell migration over pathways
containing >/ proteins9 different cells follow different routes from
one part of embryo to another
/igrating cells guided by proteins like fibronectin contained in
landscape over which they pass
Neural crest cells follow fibronectin pathways from early nervous
system throughout embryo9 antibodies to fibronectin bind @ block
recognition sites on fibronectin J= inhibit cell movements
L%&i'i'also has specific domains G family of extracellular glycoproteins9
consist of 2 different polypeptide chains linked by disulfide bonds9 organi!ed
into a cross with 2 short arms @ ' long arm
>xtracellularly, it greatly influences cellMs potential for migration,
growth @ differentiation
3uides embryonic axon tips as grow outward from central
nervous system to distant targets
ritical role in primordial germ cell #)3% migration G )3s
follow laminin paths from yolk sac #outside embryo% through
blood @ embryonic tissues to developing gonad, become eggs
or sperm
During migration, )3s traverse surfaces particularly
rich in laminin
ertain cells migrate over laminin-containing matrix that they
secrete #keratinocytes G skin cells%
&solate keratinocytes from mice genetically engineered
to lack genes for this type of laminin
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lso binds tightly to other laminins, proteoglycans,
basal lamina components, cell surface receptors
?asal lamina type &I collagens @ laminin may form
separate, but interconnected, networks
"hese interwoven networks give basal lamina
both strength @ flexibility
?asal lamina with this structure are not restricted
to vertebrates9 seen throughout animal kingdom
/. ist two characteristic that distinguish hemidesmosomesfrom local adhesions
&nteractions of ells with Noncellular ubstrates$ Aocal dhesions @ Hemidesmosomes
Aocal contacts anchor cells to their substratum G it is much easier to study cell adhesion
to a surface in vitro #in a culture dish% than with an extracellular matrix inside an animal
/uch of our knowledge of cell-matrix interactions is derived from studies of
cells adhering to various substrates in vitro
teps in cell adhesion to culture dish
ell initially has rounded morphology like most animal cells suspended
in a(ueous medium
s cell contacts substratum, it sends out projections that make
increasingly stable attachments
/ @ cytoskeleton
#actin%9 cytoskeleton attachment seems necessary for cell adhesion
ctin filaments along with myosin molecules are part of cellMs contractile
machinery, which can create or respond to mechanical forces
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Aocal adhesions form in cells grown in vitro, but similar types of adhesive contacts are
found in certain tissues, like muscle @ tendon
&n body, the tightest attachment between a cell @ >/ is at epithelial cell basal surface
where they are anchored to underlying basement membrane by speciali!ed adhesive
structure #hemidesmosome%
"hey contain dense pla(ue on membrane inner surface with filaments coursing outward
into cytoplasm
Ailaments are thicker than actin of focal adhesions @ made of keratin
#intermediate filaments%
)rimarily supportive rather than contractile9 keratin-containing filaments of
hemidesmosome are linked to >/ by membrane-spanning integrins #;O1%
?ullous pemphigoid G rare autoimmune disease #people make antibodies against
hemidesmosome pla(ue proteins, bullous pemphigoid antigens%9 demonstrates
importance of hemidesmosomes
utoimmune disorders are caused by production of antibodies #autoantibodies%
directed against oneMs own tissues9 responsible for a wide variety of conditions
)resence of autoantibodies causes lower epidermal layer to lose attachment to
underlying basement membrane @ thus to underlying connective tissue layer of
dermis
auses severe blistering of skin when fluid leaks into space under epidermis
>pidermolysis bullosa #a similar inherited blistering disease% - found in patients with
genetic alterations in any one of a number of hemidesmosomal proteins #; or O1 integrin
subunit or laminin%
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I8H FG#CIO#
also referred to as a !onula occludens
is a site where the membranes of two cells come very
close together.
often occur in a belt completely encircling the cell
material cannot pass from one side of the sheet to the
other by s(uee!ing between cells. &nstead, it must go
through a cell, and hence the cell can regulate its
passage. uch an arrangement is found in the gut, to regulate absorption of digested
nutrients.
*G#CIO#S
o "hey prevent the passage of molecules and ions through the space between cells.
o materials must actually enter the cells #by diffusionor active transport% in
order to pass through the tissue. "his pathway provides control over what
substances are allowed through.
o "hey block the movement of integral membrane proteins#red and green ovals%
between the apical and basolateral surfaces of the cell. "hus the special functions
of each surface, for example receptor-mediated endocytosisat the apical
surface and exocytosisat the basolateral surface can be preserved.
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8AP FG#CIO#
there is a channel between the membranes of contacting cells in the gap junction so that
the cyto)l%s& of the two is connected
"he basic building block of each gap junction is the connexin subunit lipid bilayers
are penetrated by protein assemblies called connexons. "wo connexons join across the
intercellular space to form a continuous a(ueous channel that links the two cells
?ecause ions can flow through them, gap junctions permit changes in membrane potential
to pass from cell to cell.
*u'ctio'
o "heaction potentialin heart #cardiac% muscle flows from cell to cell through the
heart providing the rhythmic contraction of the heartbeat.
o t some so-called electrical synapsesin the brain, gap junctions permit the
arrival of an action potential at the synaptic terminals to be transmitted across to
the postsynaptic cell without the delay needed for release of a neurotransmitter.o s the time ofbirthapproaches, gap junctions between the smooth muscle cells
of the uterus enable coordinated, powerful contractions to begin.
o everal inherited disorders of humans such as certain congenital heart defects
and certain cases of congenital deafnes have been found to be caused by mutant
genes encoding co''exi's.
A$H!R!#S FG#CIO#S A#$ *OCAL CO#ACS
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sometimes called !onula adherens
are found at sites of cell-cell interaction.
Aocal contacts mediate association of cells with the extracellular matrix.
?oth associate with the actin cytoseleto' and both are involved in adhesion #sticking
cells together or sticking cells to surfaces%.
Aocal contacts possess specific transmembrane receptors of the integrin family that link
the cell to the extracellular matrix on the outside of the cell and the microfilament system
on the inside. onversely, members of a family of calcium ion-dependent cell adhesion
molecules, called cadherins, mediate attachment between cells at adherens junctions.
dherens junctions and focal contacts not only tether cells together or to the extracellular
matrix, but they also tr%'sduce signals into and out of the cell, influencing a variety of
cellular behaviors including proliferation, migration, and differentiation. &n fact some
protein components of these junctions can shuttle to and from the nucleus where they are
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thought to play a role in regulating gene expression.
$!SMOSOM!S A#$ H!MI$!SMOSOM!S
Desmosomes #the macula adherens% and hemidesmosomes are distinguished by their
association with the keratin -based cytoskeleton
?oth are primarily involved in adhesion
"he desmosome, like the adherens junction, possesses calcium ion-dependent cell
adhesion molecules that interact with similar molecules in the adjacent cell.
integrins at the core of the hemidesmosome mediate its interaction with the extracellular
matrix.
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"he hemidesmosome and, most likely, the desmosome are also sites of signal
transduction
14.Describe the components that ma5e up a plant cell wall andthe role of each in the wall6s structure and function
*u'ctio' o, cell %ll
&%i't%i'i'gdeter&i'i'g cell s+%)e#analogous to an external skeleton for every cell%
Su))ort %'d &ec+%'ic%l stre'gt+#allows plants to get tall, hold out thin leaves toobtain light%
prevents the cell membrane from bursting in a hypotonic medium #i.e.,resists %ter
)ressure%
co'trols t+e r%te %'d directio' o, cell grot+ %'d regul%tes cell 6olu&e
ultimately res)o'si(le ,or t+e )l%'t %rc+itectur%l desig' %'d co'trolli'g )l%'t
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&or)+oge'esissince the wall dictates that plants develop by cell addition #not cell
migration%
has a &et%(olic role#i.e., some of the proteins in the wall are en!ymes for transport,
secretion%
)+ysic%l (%rrier to- 9%: )%t+oge's< %'d 9(: %ter i' su(eried cells. However, the
wall is very porous and allows the free passage of small molecules, including proteins up
to ;, /B.
c%r(o+ydr%te stor%ge- the components of the wall can be reused in other metabolic
processes #especially in seeds%. "hus, in one sense the wall serves as a storage repository
for carbohydrates
sig'%li'g ,r%g&e'ts o, %ll3 c%lled oligos%cc+%ri's3 %ct %s +or&o'es5 recog'itio'
res)o'ses- for example$ #a% the wall of roots of legumes is important in the nitrogen-
fixing bacteria coloni!ing the root to form nodules9 and #b% pollen-style interactions are
mediated by wall chemistry.
eco'o&ic )roducts- cell walls are important for products such as paper, wood, fiber,
energy, shelter, and even roughage in our diet.
CH!MICAL COMPOSIIO#
15 He&icellulose
(i'd to cellulose &icro,i(ril sur,%ces3 cross
li'i'g t+e& i'to % co&)lex structur%l 'etor
o ellulose
polymer of glucosetypically
consisting of ', to ', beta-
D-glucose residues
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major component of primary and secondary wall layers.
Cellulose )oly&ers %ssoci%te t+ro
ug+ H(o'ds +e H(o'di'g o,
&%'y cellulose &olecules to e%c+ ot+er results i' t+e ,or&%tio' o,
&icro ,i(ers %'d t+e &icro ,i(ers c%' i'ter%ct to ,or& ,i(ers5
branching macromolecule contstructed of - and ;-carbon sugars
generally insoluble in pH + water, but more soluble in basic solutions
classified on the basis of their component sugars. Pylose, mannose, and galactose form
the hemicellulose backbone9 arabinose, glucuronic acid, and galactose form the side
chainsaffect chemical characteristic of the hemicellulose
abundant in primary walls but is also found in secondary walls.
*u'ctio's
o li&it t+e stretc+i'ess o, t+e cell %ll (y li'i'g %d4%ce't &icro,i(rils %'d
)re6e'ti'g t+e& ,ro& slidi'g %g%i'st e%c+ ot+er ,or u'li&ited dist%'ces
involved in controlling cell enlargement
25 Pecti'
% ,%&ily o, co&)lex )olys%cc+%rides t+%t %ll co't%i' 13li'ed D$g%l%cturo'ic
%cid5
*or& exte'si6e3 +ydr%ted gel ,illi'g s)%ce (etee' ,i(rous ele&e'ts 9%ttr%ct H2O
lie %'i&%l 8A8s:
*u'ctio'
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o Bhen plant is%tt%ced (y )%t+oge's3 )ecti' ,r%g&e'ts rele%sed ,ro& %ll
trigger de,e'si6e )l%'t cell res)o'se
o Bhen purified3 )ecti' is used co&&erci%lly to )ro6ide gellie co'siste'cy o,
4%&s ; 4ellies
5 Structur%l Protei's
trucural proteins are found in all layers of the plant cell wall but they are more abundant
in the primary wall layer
*u'ctio's
o t+ey &edi%te dy'%&ic %cti6ities
expansins facilitate cell growth9 they cause locali!ed relaxation of
cell wall, which allows the cell to elongate at that site in response to
turgor pressure generated within cell
ell wall-associated protein kinases span the plasma membrane @ are
thought to transmit signals from the cell wall to the cytoplasm