Transport and structure of membranes – 2
Membranes are not permeable, specially to charged molecules, the size plays too a role, but this is also about the polarity. Some steroid hormones are larger then ions, but ions are charged and cannot go through the membranes. However there are some way...
transport and structure of membranes – 2 membranes are not permeable
specially to charged molecules
the size plays too a role
but this is also about the polarity some steroid hormones are larger
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Concepts in Molecular Biology
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11 LC Concepts in Molecular Biology 21.10.2022
Transport and structure of membranes – 2
Membranes are not permeable, specially to charged molecules, the size plays too a role, but this is also
about the polarity. Some steroid hormones are larger then ions, but ions are charged and cannot go
through the membranes. However there are some ways to transport things though the membrane, this
could be through membrane embedded proteins, channels or transporter.
There are two different types of transports: facilitated diffusion along the concentration gradient and the
other against the concentrated gradient.
→ in the latic case the transport molecules are called pumps and the transport against the concentration
gradient is actually coupled to ATP hydrolysis.
There are several types of transporters: symporters, transport molecules in the same direction or very
often the cells utilize transporters as antiporters coupling molecules in opposite direction.
- PUMP → actively move ions or other molecules against their concentration gradient using atp
hydrolysis and they can also create the concentration gradients across the membrane
- ION CHANNELS → in this case this gradient is already there and the channel can open an let the
gradient to equilibrate.
TRANSLOCASES
They could be called atp-ases, hydrolases, but the atp hydrolysis was part of the mechanism to transport
solid from one side of the membrane ton an other.
- ATP synthase
Present in the mythocondria, is a rotatory transporter that transports protons according to the
gradient and couples the protons transport into the atp sysnthesis (oxidative phosphorylation final
, 11 LC Concepts in Molecular Biology 21.10.2022
step).
- Na+/N+ ATPase sodium Potassium antiporter
- Flippase (is ABC transporter)
Atp binding cassette transporter that helps to transfer lipids from one site of the membrane to the
other.
There are many different transporters and these molecules are responsible for making sure what actually
the cells take s from the outside.
SERCA
It is important for pumping calcium into
the lumen of the ER → it’s a
transmembrane molecule which has
binding sites for the atp and for the
calcium.
- Once calcium binds it increases the
affinity for the atp up to a micro
molar range, and then essentially
the atp phosphorylates the trasporter itself resulting in huge conformational rearrangement
induced by one of the aa
- The entrance gate on the cytoplasmic site is closed and calcium ions are released into the ER
lumen.
- Once calcium is released, two protons can bind to the transport on the other side and as they bind,
conformation is changed to release these protons into the cytoplasmic site.
Btu Trasporter
Transports vitamin B12 from one side to another across the plasma membrane. there are everal subunits,
a transmembrane part which forms a channel, the cytosolic part and the extracellular part.
- Once atp binds to the BtuD subunit, there is a conformational change in the transmembrane part
that now is able to bind the vitamin b12, BtuF
- Hydrolysis of atp in cytosolic subunits results in the transfer od B12 into the antechamber, into the
vestibule of the trasmamber complex, and disassociation of the outside subunit and change of
conformation of this one with actually releases the b12 into the cytoplasm.
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