Chapter 3
Cell Transport -- Active
Slide 148-161
What is active transport?
Substances can move passively in and out of cells by diffusion until the
concentration on both sides of the cell membrane reaches an equilibrium.
Substances can continue to move in and out of a cell using a process called
active transport.
During active transport, carrier proteins in the
cell membrane
‘pick up’ particles and move them against the
concentration gradient.
As the name suggests, active transport requires
energy from the cell, which is created by
respiration.
What is active transport?
Active TransPort

Energy required for molecules to pass
across
ATP – the “battery” of the cell
 Breaking a bond in ATP releases energy
 Can “pump” molecules from low to high
concentration (against concentration gradient)


Example: Like riding a bike uphill
ATP
ATP
4
Active Transport
Active transport is the movement of molecules from LOW to HIGH
concentration.
Energy is required as molecules must be pumped against the
concentration gradient.
Proteins that work as pumps are called protein pumps.
Ex: Body cells must pump carbon dioxide out into the surrounding
blood vessels to be carried to the lungs for exhale. Blood vessels are
high in carbon dioxide compared to the cells, so energy is required
to move the carbon dioxide across the cell membrane from LOW to
HIGH concentration.
outside of cell
inside of cell
Carbon Dioxide
molecules
Active Transport

Cell must use energy

Ion Pump


Protein channels use energy to pump ions into/out of
cells against the concentration gradient.
Endocytosis

The cell membrane surrounds incoming particles to
form a vesicle inside the cell.


Exocytosis


Ex-Hormones, iron, vitamins, cholesterol,
A vesicle moves to the cell membrane, releases its
contents outside the cell, and becomes part of the cell
membrane.
Real world application
6
Active Transport
Cells cannot rely solely on passive
transport to move substances across the
plasma membrane.
 A cell may need to maintain a greater
concentration of a given substance on one
side of its membrane.
 Yet, passive transport equalizes
concentrations of substances on both sides
of the plasma membrane.

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Active Transport
To deal with such needs, cells use active
transport.
 Chemical pumps move compounds across
the plasma membrane against their
concentration gradients.
 Energy must be expended to move
compounds against their concentration
gradients, meaning from a lower to a higher
concentration.

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The Need for Energy in Active Transport






Some transport proteins, however, can move
solutes against their concentration gradients
Active transport moves substances against their
concentration gradients
Active transport requires energy, usually in the form
of ATP
Active transport is performed by specific proteins
embedded in the membranes
Active transport allows cells to maintain
concentration gradients that differ from their
surroundings
The sodium-potassium pump is one type of active
transport system
9
Active Transport

One example of such transport is the
pumping of glucose into cells that line the
small intestines.
10
Figure 7.18-6
EXTRACELLULAR [Na] high
FLUID
[K] low
Na
Na
Na
Na
Na
Na
Na
Na
CYTOPLASM Na
1
[Na] low
[K] high
P
ADP
2
ATP
P
3
K
K
K
6
K
K
K
5
4
P
Pi
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Active transport
 Cells
may need molecules to move
against concentration “hill”

need to pump “uphill”

from LOW to HIGH using energy
protein pump
 requires energy
 ATP

ATP
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Primary Active Transport

Primary active transport involves a carrier protein
that directly hydrolyzes ATP to drive the transport
process.
 In this process, ions are moved across a cell
membrane by carrier proteins that directly
couple transport with hydrolysis of ATP. Such
carrier proteins are usually called ATPases,
although they would be better described as
molecules that collect the free energy of ATP
hydrolysis to move ions up an electrochemical
gradient. The only substances transported by
carriers that directly hydrolyze ATP are positivelycharged ions - Na+, K+, Ca++ or H+.
http://arbl.cvmbs.colostate.edu/hbooks/cmb/cells/pmemb/transport_active.html
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Active Transport
https://www.youtube.com/watch?v=2-icEADP0J4
14
Structure Of The Cell Membrane Active and Passive Transport
https://www.youtube.com/watch?v=AcrqIxt8am8
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