Download Cell cycle

GRE Exam
Biochemistry, Cell and Molecular Biology
Preparation course
Cell Biology – Membrane bilayer
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
The membrane determines the
interaction between the cell and
its environment.
The membrane is
composed from a
mix of various
types of
phospholipids
and cholesterol
molecules
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
Cholestrol
 Amphipatic
 Four Fused rings
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
Sphingomyelin (SPH) is a type
of sphingolipid found in animal cell membranes,
especially in the membranous myelin sheath that
surrounds nerve cell axons.

Phosphatidylcholine is more commonly found in
the exoplasmic or outer leaflet of a cell
membrane. It is thought to be transported
between membranes within the cell
by Phosphatidylcholine Transfer Protein (PCTP).
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
Phosphatidylserine – during apoptosis phosphatidyl serine is no longer
restricted to the cytosolic part of the membrane, but becomes exposed on
the surface of the cell. Many cells maintain asymmetric distributions of
phospholipids between their cytoplasmic and exoplasmic membrane
leaflets.The loss of asymmetry, in particular the appearance of
the phosphatidylserine on the exoplasmic face, can serve as an early
indicator of apoptosis

Phosphatidylinositol is a negatively charged phospholipid and a minor
component in the cytosolic side of eukaryotic cell membranes.
The inositol can be phosphorilated to form phosphatidylinositol phosphate
(PIP), phosphatidylinositol biphosphate (PIP2) and phosphatidylinositol
triphosphate (PIP3). PIP, PIP2 and PIP3 are collectively called
phosphoinositides.

Phosphatidylethanolamine (cephalin) is found in all living cells, although
in human physiology it is found particularly in nervous tissue such as
the white matter of brain, nerves, neural tissue, and in spinal cord.
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
Phospholipids movement
 Lateral movement and rotation are done without
the usage of energy or enzymatic activity.
 Flip-Flop movement is aided by flippasses
(Phospholipid translocators).
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Different factors, with different physical qualities have a different ability
to cross the membrane.
The ones that cannot cross the membrane in a direct way – do it via
transport proteins
Water can:
• Enter the cell via osmosis
• Enter the cell via channels called aquaporins
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
Proteins can be bounded to the
membrane in different ways;
direct or indirect (integral &
peripheral respectively)
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
Membrane proteins have various roles in the
living cell
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passive transport
fig. 12-4/9
active transport
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Coupled transport - gradients provide energy
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
Example – the
mechanism of
glucose intake
via digestive
system.
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The Na+/K+-ATPase helps maintain resting potential, avail transport, and
regulate cellular volume. It also functions as signal transducer/integrator to
regulate MAPK pathway, as well as intracellular calcium. For most animal
cells, the Na+/K+-ATPase is responsible for 1/3 of the cell's energy expenditure.
For neurons, the Na+/K+-ATPase is responsible for 2/3 of the cell's energy
expenditure
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
What fact is correct concerning transport
proteins:
 a. In sodium - potassium ATPase pump – the same




number of ions is transferred from each side
b. There is more than one way in which water can get
into the cell
c. Ions channels control the direction of ion migration
and allow ions to cross the membrane only in one
direction
d. Transporters and channels are ligand independent
e. Phosphorilation never effect transporters
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