Group translocation
Group translocations is a process in which an organic molecule such
as glucose is transported into the cell while being chemically
modifed. The PEP phospotranserase system is an example o group
translocation.
In this process, the phosphate rom high energy rom high-energy
compound phospoenol-pyruate or PEP, is transerred to !Pr by en"yme
I and the product, pyruate, is release.
The phosphate is then transerred rom !Pr to En"yme II # by
En"yme II $.
The membrane-bound En"yme II % then carriers the glucose
across the membrane and the glucose becomes phosporylated as it
enters the cell.
&odium-potassium pump wor's
The sodium potassium pump is an actie transport
mechanism.
Three spdium ions bind to the protein channel and an $TP
proides the energyto change the shape o the channel that in turn
driers the ions through the channel.
(ne phosphate group rom the $TP remains bound with the
channel.
The sodium ions are release on the other side o the membrane
outside o the cell and the new shape o the channel has a high
a)nity or potassium ions and two o these ions now bind to the
channel.
This binding again causes a change in the shape o the protein
channel and this conormational change release the phosphate group
on the cytoplasm side.
This release allows the channel to reert to its original
shape and as the result, the potassium ions are release inside the
cell.
In its original shape the channel has a high a)nity or sodium ions
and when these ions bind again, they initiate another cycle.
The important characteristic o this pump is that both sodium
and potassium ions are moing rom areas o low concentration to areas
o high concentration i.e., each in ion is moing against its
concentration gradient.
This type o moement can only be achieed by the constant
expenditure o $TP energy.
%otransport*$ntiport and symport+
&mall molecules such as sugars and amino acids can be
transported up a
concentration gradient.
The sugar moe ia membrane transport protein rom outside o the
cell where the
sugar concentration is low to the inside o the cell where the sugar
concentration is
high.
The transport o the sugar through a coupled transport protein
is drien by the
moement o counterions such as sodium ions or protons, that are
moing down their
concentration gradient, rom a region o high to low
concentration.
&odium ions and the specifc sugar or amino acid simultaneously
bind to the same
transmembrane protein on the outside o the cell, called a
symport.
hen the counterion is sodium, the low concentration o sodium on the
inside o the
cell reuired to transport the sugar is maintained by
sodiumpotassium pump, which
is powered by $TP.
In related process, called counter transport, the inward moement o
sodium ions is
coupled with the outer moement o another substance such as calcium
ions.
$s in co-transport, the sodium ions and another substance bind to
the same transport
protein, called the antiport, but in this case, they bind on
opposite sides o the
membrane and are moed in opposite directions.
The low internal sodium ion concentration is maintained by
the sodiumpotassium
pump.
Endositosis dan E'sositosis
The substances ta'en in by single celled organism are oten
particles or large, polar molecule that cannot cross the
hydrophobic plasma membrane.
/any single-celled eu'aryotes employ endocytosis to ingest such ood
particles. In this process, the plasma membrane extends outward and
surround the ood particle.
%ells use three ma0or type o endocytosis1 phagocytosis, pinocytosis
and receptor- mediated endocytosis.
I the material the cell ta'es in is particulate, such as a
bacterium or a ragment o organic matter, the process is called
phagocytosis.
I the material the cell ta'es in is liuid, it is called
pinocytosis.
&pecifc molecules such as low density lipoproteins *232+ are
oten transported into eucaryotic cells through receptor-mediated
endocytosis. /olecules to be transported frst bind to specifc
receptors on the plasma membrane.
The interior portion o the receptor protein is embedded in
the membrane. The protein clathrin coats the inside o the membrane
in the area o the pit.
hen an appropriate collection o molecules gathers in the coated
pit, the pit deepens and seals o4 to orm a coated esicle, ehich
carriers molecules into the cell.
Exocytosis is the reerse o endocytosis. This process result in the
discharge o material rom esicles at the cell surace to the outside
o the cell.
(smosis
3i4usion is the net moement o the molecules down a concentration
gradient. This process allow small molecules such as oxygen and
carbon dioxide to across the plasma membrane.
/ost polar molecules, as sugars and proteins cannot reely cross
this lipid membrane.
$lthough water molecules are polar, the are small enough to pass
through the membrane reely. This special case o di4usion that
inoles the moement o water molecules across the membrane is called
osmosis.
I a molecule such as urea is added to one side o the membrane, it
will not be able to di4use across the membrane because it is both
large and polar.
#ecause o its polar nature, it will interact with other polar
molecules, such as the water. This interaction reduce the number o
ree water molecules on the right hand side.
ith ewer ree water molecules on the right hand side, there is now a
net moement o water molecules, down their concentration gradient to
the side with the urea molecules.
#ecause more water molecules are moing into this area than are
leaing, the water leel on the right side will rise.
I the osmotic concentrations o two solutions are eual, the
solutions are isotonic.
!oweer, when the solution hae uneual osmotic concentrations, the
solution with the higher concentration o solute is hypertonic and
the solution with the lower concentration o solutes is
hypotonic.
3iusi
/olecules dissoled in a solutions are in constant random motion due
to their 'inetic
energy. (ne result o this motion is that dissoled molecules become
eenly
distributed throughout the solution.
This tendency o molecules to spread out is an example o
di4usion. #ut how do these
molecules come to eenly distributed5 2et6s start with the ba'er o
plain water.
hat will happen i we now add a lump o sugar to the water5 $ lump o
sugar is
composed o many indiidual o sugar molecules and, een as a solid
lump, the
indiidual sugar molecules are in motion.
hen the lump is dropped into the water, it begins to dissole.
Indiidual sugar molecules moe randomly and constantly rom the area
where they
are common to the area where they are scarce.
This type o motion when molecules moe rom areas o their
higher concentration to
areas o their lower concentrations is called di4usion.
3i4usion continues until all the sugar molecules become eenly
dispersed throughout
the bea'er. The rate o di4usion is a4ected by temperature, si"e o
molecules, and the
steepness o the concentration gradient.
$lthough not specifcally shown in this animation, this is one o the
processes whereby
Translo'asi 'elompo'
Translo'asi Group adalah proses di mana sebuah mole'ul
organi' seperti glu'osa diang'ut 'e dalam sel saat sedang
dimodif'asi secara 'imia. &istem PEP phospotranserase adalah
contoh dari 'elompo' translo'asi.
3alam proses ini, osat dari energi tinggi dari energi tinggi
senyawa phospoenol- piruat atau PEP, ditranser 'e !P7 oleh en"im I
dan produ', piruat, adalah rilis.
8osat tersebut 'emudian ditranser dari !P7 'e En"im II # oleh En"im
II $.
/embran-teri'at en"im II % ma'a operator glu'osa melintasi membran
dan glu'osa men0adi phosporylated 'arena memasu'i sel.
&odium-'alium 'arya pompa
9atrium 'alium pompa me'anisme transpor a'ti.
Tiga ion spdium mengi'at saluran protein dan $TP menyedia'an
energyto mengubah bentu' saluran yang pada gilirannya drier ion
melalui saluran tersebut.
&atu 'elompo' osat dari $TP tetap teri'at dengan saluran.
Ion-ion natrium yang rilis di sisi lain dari membran luar sel dan
bentu' baru dari saluran memili'i afnitas tinggi untu' ion 'alium
dan dua ion ini se'arang mengi'at saluran.
Ini mengi'at lagi menyebab'an perubahan bentu' saluran protein dan
pelepasan perubahan 'onormasi ini 'elompo' osat di sisi
sitoplasma.
7ilis ini memung'in'an saluran untu' 'embali 'e bentu' aslinya dan
sebagai hasilnya, ion 'alium adalah rilis dalam sel.
3alam bentu' aslinya saluran memili'i afnitas tinggi untu' ion
natrium dan 'eti'a ion ini mengi'at lagi, mere'a memulai si'lus
lain.
:ara'teristi' penting dari pompa ini adalah bahwa 'edua natrium dan
'alium ion bergera' dari daerah 'onsentrasi rendah 'e daerah
'onsentrasi tinggi yaitu, masing- masing ion bergera' melawan
gradien 'onsentrasi.
;enis gera'an hanya dapat dicapai dengan pengeluaran 'onstan
energi $TP.
%otransport *antiport dan symport+
/ole'ul 'ecil seperti gula dan asam amino dapat diang'ut sebuah
gradien 'onsentrasi.
Gula 2ang'ah ia protein transport membran dari luar sel di mana
'onsentrasi gula rendah 'e bagian dalam sel di mana 'onsentrasi
gula yang tinggi.
Transportasi gula melalui protein transpor ditambah didorong
oleh gera'an ion lawan seperti ion natrium atau proton, yang
bergera' turun gradien 'onsentrasi mere'a, dari daerah tinggi 'e
'onsentrasi rendah.
:eti'a ion lawan adalah natrium, 'onsentrasi rendah natrium di
dalam sel yang dibutuh'an untu' mengang'ut gula di'elola oleh
natrium pompa 'alium, yang didu'ung oleh $TP.
3alam proses ter'ait, yang disebut 'ontra transportasi, gera'an 'e
dalam ion natrium digabung'an dengan gera'an luar "at lain seperti
ion 'alsium.
&eperti dalam co-transport, ion natrium dan mengi'at "at lain
untu' protein transport yang sama, yang disebut antiport, tetapi
dalam 'asus ini, mere'a mengi'at di sisi berlawanan dari membran
dan dipindah'an dalam arah yang berlawanan.
:onsentrasi internal yang ion natrium yang rendah dipertahan'an
oleh pompa natrium 'alium.
Endositosis 3an e'sositosis
<at diambil oleh organisme bersel tunggal sering parti'el atau
besar, mole'ul polar yang tida' dapat melintasi membran plasma
hidroobi'.
#anya' eu'ariota bersel tunggal mengguna'an endositosis untu'
menelan parti'el ma'anan tersebut. 3alam proses ini, membran plasma
meluas 'e luar dan mengelilingi parti'el ma'anan.
&el mengguna'an tiga 0enis utama dari endositosis1 agositosis,
pinositosis dan endositosis reseptor-mediated.
;i'a bahan sel mengambil dalam adalah parti'el, seperti
ba'teri atau ragmen bahan organi', proses ini disebut
agositosis.
;i'a bahan sel mengambil dalam cair, hal itu disebut
pinositosis.
/ole'ul tertentu seperti lipoprotein densitas rendah *232+ sering
diang'ut 'e dalam sel eu'arioti' melalui endositosis
reseptor-mediated. /ole'ul yang a'an diang'ut mengi'at pertama
dengan reseptor spesif' pada membran plasma.
#agian interior dari protein reseptor yang tertanam dalam membran.
/antel clathrin protein dalam membran di daerah pit.
:eti'a 'ole'si yang sesuai mole'ul mengumpul'an di lubang dilapisi,
lubang memperdalam dan segel o4 untu' membentu' esi'el dilapisi,
operator ehich mole'ul 'e dalam sel.
E'sositosis adalah 'ebali'an dari endositosis. !asil proses ini
dalam mela'sana'an materi dari esi'el pada permu'aan sel 'e luar
sel.
(smosa
3iusi adalah gera'an bersih dari mole'ul menuruni gradien
'onsentrasi. Proses ini memung'in'an mole'ul 'ecil seperti o'sigen
dan 'arbon dio'sida untu' melintasi membran plasma.
/es'ipun mole'ul air polar, yang cu'up 'ecil untu' melewati membran
bebas. :asus 'husus ini diusi yang melibat'an pergera'an mole'ul
air melintasi membran disebut osmosis.
;i'a mole'ul seperti urea ditambah'an 'e salah satu sisi
membran, tida' a'an dapat berdiusi melintasi membran 'arena itu
adalah bai' besar dan 'utub.
:arena siat polar, ia a'an berintera'si dengan mole'ul polar
lainnya, seperti air. Intera'si ini mengurangi 0umlah mole'ul air
bebas di sisi 'anan.
3engan mole'ul air bebas sedi'it di sisi 'anan, se'arang ada
gera'an bersih mole'ul air, bawah gradien 'onsentrasi mere'a 'e
sisi dengan mole'ul urea.
:arena mole'ul air lebih banya' bergera' 'e daerah ini daripada
meninggal'an, ting'at air di sisi 'anan a'an nai'.
;i'a 'onsentrasi osmoti' dua solusi yang sama, solusi yang
isotoni'.
9amun, 'eti'a solusi memili'i 'onsentrasi osmoti' yang tida' sama,
solusi dengan 'onsentrasi yang lebih tinggi dari "at terlarut
adalah hipertoni' dan solusi dengan 'onsentrasi yang lebih rendah
dari "at terlarut adalah hipotoni'.
3iusi
/ole'ul dilarut'an dalam larutan berada dalam gera'an aca' 'onstan
'arena energi 'ineti' mere'a. &alah satu hasil dari gera'an ini
adalah bahwa mole'ul terlarut men0adi merata di seluruh
larutan.
Ini 'ecenderungan mole'ul untu' menyebar adalah contoh dari diusi.
Tapi bagaimana mole'ul ini datang untu' merata5 /ari 'ita mulai
dengan roti air putih.
$pa yang a'an ter0adi 0i'a 'ita se'arang menambah'an ben0olan gula
'e dalam air5 &ebuah ben0olan gula terdiri dari banya' indiidu
mole'ul gula dan, bah'an sebagai ben0olan padat, mole'ul gula
indiidu dalam gera'an.
:eti'a ben0olan di0atuh'an 'e dalam air, ia mulai larut.
/ole'ul gula indiidu bergera' secara aca' dan terus-menerus dari
daerah di mana mere'a yang umum untu' daerah di mana mere'a
lang'a.
;enis gera' 'eti'a mole'ul bergera' dari daerah 'onsentrasi
yang lebih tinggi 'e daerah 'onsentrasi yang lebih rendah disebut
diusi.
3iusi terus sampai semua mole'ul gula men0adi merata tersebar di
seluruh gelas. Ting'at diusi dipengaruhi oleh suhu, u'uran
mole'ul, dan 'ecuraman gradien 'onsentrasi.