General Biology
WEEK 1-2
Cell Membrane and Transport Mechanisms
WHAT IS CELL
MEMBRANE?
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Also known as plasma membrane
- Cell’s flexible outer limitating barrier
(semi-preamble) that seperates the cell’s
internal environment from the external
(extracelullar) environment.
Present in prokaryotes and eukaryotes.
Follows a fluid mosaic model.
Amphipathic – has hydrophilic and
hydrophobic regions.
It controls what goes in and out of the cell.
cell membrane helps regulate homeostasis.
PHOSPHOLIPID
 polar (head)
hydrophilic
it does not take any energy to force
these molecules (oxygen and carbon
gas)
Moves with the flow.
It moves with the concentration
gradient; molecules move from a high
concentration to low concentrarion.
 FACILITATED DIFFUSION
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Moves with the flow.
It does not require energy.
Proteins are facilitating or helping
things pass.
Helps molecules that maybe too big to
cross the membrane on their own.
 nonpolar (tail)
hydrophobic
Phospolipids are amphiphilic.
CELL TRANSPORT
PASSIVE TRANSPORT
 SIMPLE DIFFUSION
COMPARISON
OSMOSIS
TYPES OF ACTIVE
TRANSPORT (PUMP)
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PRIMARY ACTIVE
TRANSPORT
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movement of water
through a semi
permeable
membrane
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SECONDARY ACTIVE
TRANSPORT
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ACTIVE TRANSPORT
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Requires energy; because it moves from
low concentration to high concentration
meaning its against the flow therefore it
requires energy.
Requires ATP energy (adenosine
triphosphate)
It has three phosphate and when the
bond for the last phosphate is broken; it
releases a great amount of energy.
• also called direct active transport,
directly uses chemical energy (such as
from ATP in case of cell membrane) to
transport all species of solutes across a
membrane against their concentration
gradient.
Example: sodium-potassium pump
(Na+/K+). The Sodium Potassium
Pump
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Essential for nutrient uptake and the
maintenance of ion gradients in various
cell types.
It does not directly consume ATP but
relies on the energy generated by
primary active transport processes,
like the sodium-potassium pump.
This interplay of primary and secondary
active transport ensures proper cell
function and homeostasis.
TYPES OF ACTIVE
TRANSPORT (VESICLE)
Vesicle: Small, spherical sac that has budded off from
an existing membrane.
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 ENDOCYTOSIS
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Endo – “in”
These vesicles are involved in the
process of endocytosis, where cells
engulf (eat or swallow) particles or
substances from their external
environment.
There are different types of endocytosis
vesicle:
is nonspecific in the substances it
transports.
 EXOCYTOSIS
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Exo – “exit”
Reverse direction of endocytosis
Can be used to get rid of cell waste.
Important for getting important
materials out that the cell has made.
For example: For example,
neurotransmitters are released from nerve
cells through exocytosis vesicles to signal
neighboring cells or tissues.
PHAGOCYTOSIS
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“Cell eating”
Ingests and destroys solid particles.
It stretches out around they want to
engulf and then it pulled into vacuole.
RECEPTOR-MEDIATED
ENDOCYTOSIS
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Very picky about whats coming in
because the incoming substances must
bind to receptors to even get in.
cells take up specific ligands, molecules
that bind to specific cell receptors
(membrane proteins).
imports materials that are needed by the
cells (example: lipoproteins, transferrin,
some vitamins, antibodies, certain
hormones).
INSIDE THE CELL
MEMBRANE?
 COMPONENTS OF THE
CELL MEMBRANE
 MEMBRANE PROTEINS
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Cholesterol – can actually function kind of
like space between these phospolipids
keeping them from being too packed – or
vice versa, cholesterol can function to
connect phospholipids to keep them from
being fluid in warm temperatures.
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Peripheral Proteins- not imbedded in the
membrane. (exterior area of the
PINOCYTOSIS
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“Cell drinking”
The cell “gulps” droplets of
extracellular fluid (containing
molecules), forming a vesicle around
them.
Allows cell to take in fluids.
membrane) tends to be in peripheral area of
the membrane.
- Tends to be more loosely attached since
theyre generally not stuck in the
membrane.
- Acting as enzyme to speed up reactions
or attaching to the cystoskleton
structures to help with the cell shape.
o Integral proteins – goes inside through the
membrane.
- Transporting method for all kinds of
materials
site exposed to substances in the adjacent
solution.
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Signal transduction – a protein built into the
membrane may have a binding site with a
specific shape that fits the shape of a
chemical messenger, such as a hormone.
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Cell to Cell recognition- It refers to a cell's
capacity to recognize and engage with
another cell through molecular signals.
Some glycoproteins serve as identification
tags that arespecifically recognized be
membrane proteins of other cells.
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Intercellular Joining - m embrane proteins
act as adhesion molecules, connecting and
joining adjacent cells together. They are
essential for maintaining tissue structure and
facilitating cell signaling and
communication.
Both protein types can have carbohydrates inbound to
them which can be considered as a glycoprotein
If the carbohydrate atach to the phospholipid, you
have a glycolipid.
 MEMBRANE
CARBOHYDRATES
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Glycoprotein - sugar chains covalently
bonded to proteins.
Glycolipid - sugar chains covalently
bonded to lipids.
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These proteins act as a kind of adhesive,
linking adjacent cells and keeping them
in position to create tissues.
Structural Support - some membrane
proteins provide structural support to the cell
membrane by anchoring it to the
cytoskeleton or extracellular matrix. This
helps maintain the membrane's stability
and shape.
Classification of
Transport proteins
Functions of Membrane
Proteins and
Carbohydrates
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Transport – a protein that spans the
membrane may provide a hydrophilic
channel across the membrane.
Enzymatic Activity - protein built into the
membrane may be an enzyme with its active
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Uniporter – (one), transports substances in a
unidirectional manner depending on the
concentration gradient.
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Symporter – (two molecules, same
direction), Transports different types of
molecules in the cell membrane at the same
time.
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Antiporter – (two molecules, opposite
direction), Transport different types of
molecules in the cell membrane in opposite
direction at the same time
Discovery of Cell
Membrane
References
https://drive.google.com/file/d/1Y8wgoYsi6
A7wQVlzohHwZoNuKAZGVyLn/view?pli=1
https://youtu.be/qBCVVszQQNs?si=g3I9cJ4
2P52WKAKQ
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In 1890’s the existence of plasma membrane
was discovered, and its chemical
components was discocverd in 19 1 5.
Hugh Davson and James Danielli (1935) –
theorize that the structure of plasma
membraen resembles a sandwich.
Seymour Singer and Gath L. Nicolson
(1972) proposed the fluid mosaic model
(which are we using now)
https://www.youtube.com/watch?v=Ptmlvt
ei8hw&ab_channel=AmoebaSisters