The document summarizes the structure and functions of the plasma membrane in transporting substances into and out of cells. It discusses that the plasma membrane is semi-permeable and allows movement of substances through passive transport mechanisms like simple diffusion, facilitated diffusion, and osmosis as well as active transport powered by ATP. Active transport and bulk transport use vesicles and carrier proteins to move substances against their concentration gradient.

1. MIC 102
2. Movement in and out of the cell
Prepared by: Hajar

2. Structure of Plasma Membrane
• All the substances required by the cell and
waste products have to be transported across
the plasma membrane of the cell.
• However, the plasma membrane is semi-
permeable as it allow certain substances to
move across it.
• This is due to the structure of the plasma
membrane which comprises the phospholipid
bilayer and protein molecules

4. • Each phospholipid molecule consists of
hydrophilic head (attracted to water) and a
hydrophobic tail (repelled by water).
• The protein molecules are the transport
proteins such as pore proteins and carrier
proteins

6. Phospholipid
bilayer
Small uncharged
molecule; water,
oxygen, carbon
dioxide
Lipid-soluble
molecule; fatty acids,
glycerol, vitamins A,
D, E, and K
Protein
molecule
Pore proteins; Small
charged ions
Carrier proteins;
Glucose and amino
acids
* Move through by simple diffusion * Pass through by facilitated diffusion

7. Transport of substances across plasma membrane
Passive transport Active transport
• occurs down the
concentration gradient
• does not require
energy
1. Simple
diffusion
Across the
phospholipid
bilayer
2. Facilitated
diffusion
With the help
of protein
molecules
3. Osmosis
Diffusion of
water
molecules
only
• occurs against the
concentration gradient
• requires energy
Require carrier
proteins
Bulk transport
substances in vesicles
2. Exocytosis
1. ATP Binding
Cassette
(ABC)
2. Group
translocation
a. Phagocytosis
b. Pinocytosis
c. Receptor- mediated
1. Endocytosis

9. Passive transport
Three types:

10. a) Simple diffusion
• Small molecules (water), dissolved gases (oxygen and carbon dioxide) and fat-soluble substances
(fatty acids, glycerol, vitamin A, D, E and K) diffuse across the plasma membrane
• Down the concentration gradient through the phospholipid bilayer in the membrane
• The molecules continue to diffuse across the membrane until an equilibrium is reached.
• There is no net change in concentration on either side of the membrane.
• Simple diffusion occurs during gaseous exchange between the body cells and blood capillaries,
alveolus and blood capillaries.

12. b) Facilitated diffusion
• A carrier or transport protein is
needed to allow a molecule to
diffuse.
• move from an area of high
concentration to an area of low
concentration across the cell
membrane
• cell energy is not used.
• Small charged ions (mineral ions)
move across pore proteins.
• Pore proteins have specific shapes
and charges to allow specific ions to
pass through.
• Larger uncharged water soluble
molecules (glucose, amino acids)
move with the help of carrier
proteins.
• The carrier proteins have specific
binding sites to combine with
specific molecules
Eg; transportation of glucose, amino acids
and mineral ions from the ileum into the
villus of the ileum.

13. c) Osmosis
• Diffusion of water molecules from a
dilute solution to a more concentrated
solution across a semi-permeable
membrane.
• Water molecules move across the
phospholipid bilayer and pores in the
membrane by osmosis until a dynamic
equilibrium is reached.
• The concentration on both sides is the
same.
• Then the water molecules move in both
directions at the same rate.
• Eg: absorption of water by root hair of a
plant

14. Movement of substances across the plasma membrane
in everyday life

17. • The movement of substances
across the plasma membrane
• From a region of low
concentration to a region of
high concentration
• Against the concentration
gradient
• It requires energy
• It needs carrier proteins to
transport the substances across
the membrane
Active transport

18. Active Transport: Carrier Protein molecules aid in movement of
molecules against a concentration gradient

19. • The energy is provided by proton motive force, the
hydrolysis of ATP, or the breakdown of some other high-
energy compound such as phosphoenolpyruvate (PEP).
• Proton motive force is an energy gradient resulting from
hydrogen ions (protons) moving across the membrane from
greater to lesser hydrogen ion concentration.
• ATP is the form of energy cells most commonly use to do
cellular work.
• PEP is one of the intermediate high-energy phosphate
compounds produced during glycolysis.

20. Movement of Materials across
Membranes
For the majority of substances a cell needs for metabolism to
cross the cytoplasmic membrane, specific transport
proteins (carrier proteins) are required. Transport proteins
involved in active transport include:
• ATP-binding cassette (ABC) system: Requires a transporter
protein and ATP
• Group translocation: Requires a transporter protein and PEP

21. ATP-binding cassette (ABC) system
• An example of an ATP-dependent active transport
found in various gram-negative bacteria is
the ATP-binding cassette (ABC) system. This
involves substrate-specific binding proteins
located in the bacterial periplasm, the gel-like
substance between the bacterial cell wall and
cytoplasmic membrane
• In E.coli, the maltose (a dissacharide sugar)
transport system is an example of ABC system.

22. Step 1
• . The periplasmic-
binding protein picks up
the substance to be
transported and carries
it to a membrane-
spanning transport
protein

23. Step 2
• The molecule to be
transported across the
membrane enters the
transporter protein
system and a molecule of
ATP enters the ATP
binding site of the ATP-
hydrolyzing protein.

24. Step 3
• Energy provided by the
hydrolysis of ATP into ADP,
phosphate, and energy
moves the molecule across
the membrane

25. Step 4
• The carrier protein
releases the molecule
being transported and the
transporter system is ready
to be used again.

26. Group translocation
• another form of active transport that can occur in
prokaryotes. In this case, a substance is
chemically altered during its transport across a
membrane so that once inside, the cytoplasmic
membrane becomes impermeable to that
substance and it remains within the cell.
• Bacteria apply phosphotransferase system for the
uptake of sugars (glucose, mannose and fructose)

27. Step 1
• When bacteria use the
process of group
translocation to transport
glucose across their
membrane, a high-energy
phosphate group from
phosphoenolpyruvate (PEP)
is transferred to the glucose
molecule to form glucose-6-
phosphate.

28. Step 2
• A high-energy phosphate
group from PEP is
transferred to the glucose
molecule to form glucose-
6-phosphate.

29. Step 3
• The glucose-6-phosphate is
transported across the
membrane.

30. Step 4
• Once the glucose has
been converted to
glucose-6-phosphate
and transported across
the membrane, it can
no longer be
transported back out.

31. Bulk transport materials across the
membrane in vesicles
• Requires energy to occur (ATP)
• Move a large substance or large amount of a
substance in vesicles
• Transport in vesicle lets substances enter or
exit a cell without crossing through the
membrane
• Example: Occurs in the digestive system
moving nutrients into our bodies

32. 1. Endocytosis
• A form of active transport moving substances into
the cell using cellular energy.
• The substances that are particles or large and
polar molecules that cannot cross the
hydrophobic plasma membrane taken in by
single-celled organisms.
• Eg: Employ endocytosis to ingest food particles.
• In this process, the plasma membrane extends
outward and surrounds the food particle

33. Three major types of endocytosis:

34. a) Phagocytosis
• Known as cellular eating
• This process apply when the material the cell takes in is
particulate, such as bacterium or a fragment of organic
matter.
• Overview:
1. The cell’s plasma membrane surrounds a macromolecule
or even entire cell from the extracellular environment.
2. Bud off to form food vacuole or phagosome.
3. The newly-formed phagosome then fuses with a
lysosome.
4. Hydrolytic enzymes digest the “food” inside.

36. b) Pinocytosis
• Known as cellular drinking
• The material the cell takes in is liquid.
• Overview:
1. The cell engulfs drop of fluid with dissolved
solutes.
2. Cell membrane pinching in
3. Forming vesicles that are smaller than
phagosomes.

38. c) Receptor-mediated endocytosis
• Involves specific molecules such as low density lipoproteins
(LDL).
• Overview:
1. Molecules to be transported bind to specific first bind to
specific receptors on the plasma membrane.
2. The interior portion of the receptor protein is embedded
in the membrane.
3. The protein clathrin coats the inside of the membrane in
the area of the pit.
4. When an appropriate collection of molecules gathers in
the coated pit, the pit deepens and seals off to form a
coated vesicle, which carries the molecules into the cell.

40. 2. Exocytosis
• The reverse of endocytosis.
• This process results in the discharge of
material from vesicles at the cell surface to
the outside of the cell.