CELL MEMBRANE, CHANNELS
AND TRANSPORTER
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LO
• Memahami membran sel
• permeabilitas sel
• Imemahami lingkungan intrasel
MEMBRAN SEL
 MEMBRAN : membatasi lingk
intrasel dg ekstrasel
terdiri atas : LIPID dan
PROTEIN,KH
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MEMBRAN SEL
• * Tebal : 7,5 – 10 nm
* 3 garis paralel
- Electron dense layer :
2 garis tebal, hitam
lapisan
padat electron : 2,5 – 3 nm
- Electron-lucent layer :
1 lapisan diantaranya
jernih :
3,5– 4 nm
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Komposisi membran sel
1. Lipid (40%) : - Phospholipid :
* Phosphatidylcholine (lecithin)
* Phosphatidylethanolamine (cephalin)
- Sphingomyelin
- Cholesterol
2.
Proteins (55%) : a. Integral proteins  usually they are insoluble
in water solutions, are associated with lipids,
this proteins may be attached to
oligosaccharides  forming glycoproteins
b. Peripheral proteins are soluble in aqueous
solutions, and are usually free of lipids
3. Carbohydrates (5%) → oligosaccharide : - glycoproteins
- glycolipids
- glycocalyx
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Gambaran struktur membran sel
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Struktur membran
Molekul protein – lemak penyusun membran
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Molekul fosfolipid pada Membran
 Gambaran molekul
fofsfolipid yang merupakan
komponen penting dari
membran sel dan
menentukan bentuk
membran sel
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Struktur fosfolipid
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Protein
1. Protein integral ; menembus dan tertanam dlm
2. lapisan ganda, terikat pd bagian ekor nonpolar
a. Protein transmembran; membentuk saluran
(pori-pori) → transport zat yg melewati membran
b. peranannya:
● Berikatan dng karbohidrat dpt membentuk sisi
reseptor untuk menerima pesan kimia dr sel lain :
kelenjar endokrin
● Sebagai pemberi tanda, atau antigen, yg menjadi
identitas jenis sel
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2. Protein perifer : terikat pada permukaan
membran, dapat dng mudah terlepas dr
membran.
Fungsi : - Protein ini mungkin terlibat dlm
struktur pendukung dan
perubahan bentuk membran
saat pembelahan atau
pergerakan
sel
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Karbohidrat
 Karbohidrat juga berkaitan dng molekul lipid dan
protein.
dalam bentuk:
* Glikolipid dan glikoprotein → mrpk sisi
pengenal permukaan untuk interaksi antar sel
mempertahankan sel-sel darah merah :
- agar tetap terpisah
- atau memungkinkan penggabungan sel-sel
yg sama untuk membentuk sebuah jaringan.
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Fungsi membran sel:
1.
2.
3.
Protective function:
The cell membrane protects the
cytoplasm
and the organelles of the cytoplasm.
As a semipermeable membrane:
The cell membrane permits only some
selective substances to pass through it
and acts as a barrier for other
substances.
Absorptive function:
The nutrients are absorbed into the cell
through the cell membrane.
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4.
5.
6.
Excretory function:
The metabolites and other waste products
from the cell are excreted out through the
cell membrane.
Exchange of gases:
Oxygen enters the cell from the blood and
carbon dioxide leaves the cell and enters
the blood trough the cell membrane.
Maintenance of shape and size of the cell:
The cell membrane is responsible for the
maintenance of shape and size of the cell.
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Sitoskeleton membran
Cytoskeletal network
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Type of transport
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Transpor melalui
membran sel
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Pergerakan materi menembus
membran sel
 Prinsip dasar : * TRANSPORT PASIF
* TRANSPORT AKTIF
* Mekanisme transport pasif :
● difusi bebas
● osmosis
● difusi terfasilitasi
● filtrasi
* Mekanisme transport aktif : - memerlukan energi,
- enzim
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Mekanisme transport aktif
 1. Transport aktif diperantarai carrier
Carrier : protein integral yg disebut pompa
→ pompa ion natrium/kalium yg aktif
dlm sel hidup.
→ Pompa kalsium : - kontraksi otot
 2. Transport massa berukuran besar : vesikel
(vakuola) → * Fagositosis
* Pinositosis
* Endositosis
* Eksositosis
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Transport protein, mekanisme
pembawa, dan poros tetap
 Transport molekul-molekul berbeda
melewati membran memperlihatkan
spesifitas tinggi
 Permeabilitas molekul berkaitan dengan
susuna kimianya.
 Macam selektifitas ini berkaitan dengan
transport protein → carrier / pembawa
 Ada 2 hipotesis :
1. mekanisme carrier
2. mekanisme poros tetap
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 Mekanisme poros tetap
 Mekanisme Carrier
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Difusi
 Water*
 Gases
- CO2
- N2
- O2
 Small uncharged polar molecules
- ethanol
- urea*
 Hydrophobic molecules
- steroid hormones
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Must be transported !
 Ions
- K+, Na+, Mg2+, Ca2+, Cl-,
HCO3-,
HPO42 Large uncharged polar molecules
- glucose
 Charged polar molecules
- amino acids
- ATP
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Hypothetical diagram of simple diffusion through the cell membrane.
A = Diffusion through lipid layer. B = Diffusion through ungated channel.
C - Diffusion through gated channel.
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Transport of Small Molecules
selectively permeable to small molecules.
melalui phospholipid bilayer, membran plasma membentuk
barrier yang menghalangi pertukaran molekul
antarastiplasma dg lingk eksternal sel
Specific transport proteins (carrier proteins and channel
proteins) then mediate the selective passage of small
molecules across the membrane, allowing the cell to control
the composition of its cytoplasm.
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Mobility of phospholipids in a membrane
Individual phospholipids can rotate and move laterally within a
bilayer.
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Permeability of phospholipid bilayers
Small uncharged molecules can diffuse freely through a phospholipid
bilayer. However, the bilayer is impermeable to larger polar molecules (such
as glucose and amino acids) and to ions.
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Permeability of phospholipid bilayers :
Gases, hydrophobic molecules, and small polar can diffuse through
phospholipid bilayers. Larger polar molecules and charged molecules cannot
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Hypothetical diagram of facilitated diffusion from higher concentration (ECF) to
lower concentration (ICF). through the cell membrane.
Stage 1. Glucose binds with carrier protein. Stage 2. Conformational change
occurs in the carrier protein and glucose is released into ICF.
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Ion channels
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 Conduct ions 10 ions/sec
 Recognize & select specific ions
 Open and close in response to specific
signals
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Channel and carrier proteins
(A) Channel proteins form open pores through which molecules of the
appropriate size (e.g., ions) can cross the membrane.
(B) Carrier proteins selectively bind the small molecule to be transported
and then undergo a conformational change to release the molecule
on the other side of the membrane.
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Model of active transport
Energy derived from the hydrolysis of ATP is used to transport H+ against the
electrochemical gradient (from low to high H+ concentration).
Binding of H+ is accompanied by phosphorylation of the carrier protein, which
induces a conformational change that drives H+ transport against the electrochemical
gradient.
Release of H+ and hydrolysis of the bound phosphate group then restore the
carrier to its original conformation.
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 Uniporter
- The facilitated diffusion of glucose is
an example of uniport, the transport
of only a single molecule.
 Symporter - The coordinate uptake of glucose
and Na+ is an example of symport,
the transport of two molecules in the
same direction.
 Antiporter - Active transport can also take place by
antiport, in which two molecules are
transported in opposite directions.
Model of an ion channel
In the closed conformation,
the flow of ions is blocked by
a gate.
Opening of the gate allows
ions to flow rapidly through
the channel. The channel
contains a narrow pore that
restricts passage to ions of
the appropriate size and
charge.
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Examples of uniport: Model for the facilitated diffusion of glucose

The glucose transporter
alternates between two
conformations in which a
glucose-binding site is
alternately exposed on the
outside and the inside of the cell.

In the first conformation shown
(A), glucose binds to a site
exposed on the outside of the
plasma membrane.

The transporter then undergoes
a conformational change such
that the glucose-binding site
faces the inside of the cell and
glucose is released into the
cytosol (B).

The transporter then returns to
its original conformation (C).
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Examples of symport :
 Glucose transport by
intestinal epithelial
cells

The glucose transporter
alternates between two
conformations in which a
glucose-binding site is
alternately exposed on the
outside and the inside of the cell.

In the first conformation shown
(A), glucose binds to a site
exposed on the outside of the
plasma membrane.

The transporter then undergoes
a conformational change such
that the glucose-binding site
faces the inside of the cell and
glucose is released into the
cytosol (B).

The transporter then returns to
its original conformation (C).
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Examples of antiport
 Ca2+ and H+ are
exported from cells by
antiporters, which
couple to their export to
the energetically
favorable import of Na+.
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Summary
 Membrane Structure
 Membrane models have evolved to fit




new data: science as a prosses
A membrane is a fluid mosaic of lipids,
protein, and carbohydrates
Osmosis in the passive transport of water
Cell survival depends on balancing water
uptake and loss
Specific protein facilitate the passive
transport of selective solutes
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Summary
 Traffic Across Membranes
 Active transport is the pumping of solute
against their gradiens
 Some of ion pumps generate voltage
across membranes
 In cotransport, a membrane protein
couples the transport of one solute to
another
 Exocytosis and endocytosis transport
large molecules
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NOTES:
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Overview
■ The cell membrane is mainly composed
of lipids and proteins.
■ Its frame work consists of a double layer of
phospholipids.
■ There are two major types of proteins : tightly coiled, rod
–shaped, fibrous proteins and the more compact,
globular – shaped integral proteins and peripheral
proteins.
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These are the different types of molecules of the cell membrane.
Phospholipid
Fibrous protein
Examples of globular – shaped proteins
H2O Molecule
Glycoprotein
Pore protein
Na+
Channel protein
■ Two layer of phospholipids molecules self – assemble
so that their water soluble (hydrophilic) heads form
the surface and interior of the membrane, and the
water insoluble (hydrophobic) tails face each other.
Hydrophobic tails
Hydrophilic heads
■ The fibrous proteins may span the entire membrane
and serve as receptors for the cell
■ One type of globular protein form “pores” to allow
lipid insoluble water molecules to pass through.
H2O Molecule
■ Other integral proteins serve as channel proteins
and selectively transport ions for the cell.
H2O Molecule
Na+
■ Globular proteins, which are peripheral (associated with the
surface of the cell), may be enzymes or glycoproteins (proteins
with carbohydrate associations that identify the cell.
H2O Molecule
Na+
■ Cholesterol molecules are embedded in animal cell.
Membranes but not in plant cell membranes, they help make the
membrane (along with the phospholipids) impermeable to watersoluble substances. Cholesterol also stabilized themembrane.
H2O Molecule
Na+
SPECIAL CATEGORIES OF TRANSPORT
● ENDOCYTOSIS
● EXOCYTOSIS
● FILTRATION
● OSMOSIS
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Osmosis
is the movement of water from a concentrated solution
to a dilute solution through a cell membrane.
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Permeable
Permeable is having pores or openings that
permit liquids or gases to pass through, or that
something is capable of being permeated.
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Vacuole
 A vacuole is found in both plant and animal cells,
but in the plant cells there are fewer of them yet they
are larger and in the animal cells the are small. They
have fluid filled sacs and store food, water and waste
(plants need to store large amounts of food).
Vacuoles have membrane-bound sacs for storage,
digestion and waste removal. They also contain
water solutions.
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TERIMAKASIH
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