Membrane Transport Biochemistry I Unit 1

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The presentation “Membrane Transport – Biochemistry I, Unit 1” explains how substances move across cell membranes. It describes the structure of the plasma membrane and the main types of transport mechanisms: passive transport, active transport, and bulk transport. The slides cover diffusion, osmosis, facilitated diffusion, and the role of carrier and channel proteins. It also explains active transport using ATP, as well as processes like endocytosis and exocytosis. The presentation helps students understand how cells maintain balance by controlling the movement of ions, nutrients, and wastes.

1. MEMBRANE TRANSPORT
UNIT ONE
BIOCHEMISTRY ONE
BATCH: AGRICULTURE

2. MEMBRANE TRANSPORT
o Every cell is surrounded by a plasma membrane.
This membrane controls what enters and leaves the
cell. It helps the cell maintain the right balance of
nutrients, ions, and waste.
o The plasma membrane is semipermeable, meaning
some substances pass through easily, while others
are restricted.

3. FUNCTIONS OF PLASMA MEMBRANE
o Regulates passage of small molecules
across it.
o Biological membranes are semipermeable
o Certain molecules diffuse freely
o Movement of others is restricted by size,
charge, or solubility

4. TYPES OF MEMBRANE TRANSPORT
The two types of transport mechanisms are:
1.Passive Transport or Passive diffusion
2.Active Transport

5. PASSIVE TRANSPORT OR PASSIVE DIFFUSION
o Passive transport is the movement of molecules across the
cell membrane without using energy (ATP). The
molecules move from a region of higher concentration to
a region of lower concentration until balance is reached.
o This process depends on the natural movement of particles
and does not require help from the cell. The cell membrane
allows certain small or lipid-soluble molecules to move
freely through it.
o There are two types of passive transport as follows:
1.Simple diffusion
2.Facilitated diffusion.

6. SIMPLE DIFFUSION
o Simple diffusion is the movement of molecules across the cell
membrane without using energy and without help from
carrier proteins. Molecules move from a region of higher
concentration to a region of lower concentration until the
concentration is equal on both sides of the membrane.
oThe driving force for simple diffusion is the concentration
gradient. The larger the difference in concentration, the
faster the diffusion occurs.

7. KEY FEATURES OF SIMPLE DIFFUSION
o Key features of simple diffusion:
o No ATP or cell energy is used.
o No carrier or channel proteins are involved.
o Movement continues until equilibrium is reached.
o Direction of movement is always from high to low
concentration.
Molecules that pass by simple diffusion:
o Lipid-soluble molecules such as oxygen, carbon dioxide, and
steroid hormones.
o Small uncharged molecules like water (to a limited extent).

8. o The cell membrane is made of a lipid bilayer. Lipid-
soluble (nonpolar) molecules dissolve in the
membrane and move through it easily. In contrast,
charged or large molecules cannot pass freely
because the lipid layer repels them.
Example:
-Oxygen diffuses from the lungs into red blood cells.
-Carbon dioxide diffuses out of cells into the blood to
be exhaled.

9. FACILITATED DIFFUSION
o Facilitated diffusion is a type of passive transport
that helps water-soluble molecules and ions cross
the cell membrane. It does not use energy (ATP) and
always moves substances from a region of higher
concentration to a region of lower concentration.
o Because the lipid bilayer blocks large or charged
molecules, these substances need help from specific
transport proteins found in the membrane.

10. KEY FEATURES OF FACILITATED DIFFUSION
o Since it is a passive transport process, no energy is required.
o The movement occurs down the concentration gradient, from
higher to lower concentration.
o It uses carrier proteins or channel proteins to move substances
across the membrane.
o The movement stops when equilibrium is reached.
An example of facilitated diffusion is the movement of
glucose and most of the amino acids across the plasma
membrane.

11. TYPES OF TRANSPORT PROTEINS INVOLVED:
1. Carrier proteins
-Bind to a specific molecule, change shape, and release it on the other
side of the membrane.
-Example: Glucose transport into cells.
2.Channel proteins
-Form small pores or tunnels in the membrane.
-Allow specific ions like Na+, K+, or Cl– to pass through easily.
Examples of facilitated diffusion:
- Glucose moving into cells from the bloodstream.
- Amino acids entering cells.

12. Passive Transport

13. Active Transport
o Active transport is the movement of molecules across the cell
membrane from a region of lower concentration to a region
of higher concentration. This process goes against the
concentration gradient, so it requires energy in the form of
ATP.
o Active transport is vital for keeping the correct balance of ions
and nutrients inside the cell.

14. KEY FEATURES OF ACTIVE TRANSPORT:
o Active transport requires energy in the form of ATP.
o It moves substances against the concentration gradient, from
lower to higher concentration.
o It uses carrier proteins located in the cell membrane.
o This process helps maintain essential ion and nutrient levels
inside cells.
Examples of substances moved by active transport:
Sodium (Na⁺), Potassium (K⁺), Calcium (Ca²⁺), Hydrogen (H⁺),
Chloride (Cl⁻), Sugars and amino acids

15. Types Of Active Transport
Active transport is classified into two types according
to the source of energy used as follows :
1.Primary active transport
2.Secondary active transport.

16. Primary Active Transport
Primary active transport is a process in which substances are
moved across the cell membrane against their concentration
gradient using energy that comes directly from the breakdown
of ATP. This means molecules are transported from a region of
lower concentration to a region of higher concentration with
the help of specific carrier proteins.

17. SODIUM-POTASSIUM PUMP (NA ⁺-K⁺ PUMP)
o Na⁺-K⁺ Pump is a primary active transport process that pumps sodium ions
out of the cell and at the same time pumps potassium ions from outside to the
inside, generating an electrochemical gradient. The carrier protein of the
Na⁺-K⁺ pump has three receptor sites for binding sodium ions on the inside of
the cell and two receptor sites for potassium ions on the outside. The inside
portion of this protein has ATPase activity.
oThe pump is called Na⁺-K⁺ ATPase because the hydrolysis of ATP occurs only
when three sodium ions bind on the inside and two potassium ions bind on
the outside of the carrier proteins. The energy liberated by the hydrolysis of
ATP leads to conformational change in the carrier protein molecule,
extruding the three sodium ions to the outside and the two potassium ions to
the inside.

19. SECONDARY ACTIVE TRANSPORT
- In secondary active transport, a substance such as glucose is
pumped from a region of lower concentration to a region of
higher concentration. This process requires energy because
glucose molecules are transported against their concentration
gradient
- The energy that drives glucose across a membrane against
its concentration gradient does not come directly from ATP.
Rather, it comes from the energy stored in a sodium ion
gradient, which was created using ATP.

20. Because ATP does not fuel the pump directly, this process is
called secondary active transport. To pump glucose against
its concentration gradient, the pump takes up both sodium
and glucose from outside of the cell and then changes
shape, depositing both substances inside the cell.
- A pump that transports two substances in the same
direction is called a symport protein.
- The sodium ions that enter the cell are later returned to the
outside by the action of the sodium potassium pump.
- This process, called primary active transport, creates
sodium and potassium ion gradients at the expense of ATP.

23. Transport Of Macromolecules Across The
Plasma Membrane
o The process by which cells take up large molecules is called
endocytosis and the process by which cells release large molecules
from the cells to the outside is called exocytosis.
Endocytosis
There are two types of endocytosis: pinocytosis (cellular drinking) and
phagocytosis (cellular eating). Pinocytosis is the cellular uptake of
fluid and fluid contents and is a cellular drinking process. Pinocytosis
is the only process by which most macromolecules, such as most
proteins, polysaccharides, and polynucleotides can enter cells. These
molecules first attach to specific receptors on the surface of the
membrane.

24. Pinocytosis (Cellular Drinking)
Pinocytosis is a process in which the cell takes in fluids and
dissolved substances through small pits on the outer surface of
the cell membrane. These pits have receptors coated on the
cytoplasmic side with a protein called clathrin and filaments of
actin and myosin. When macromolecules bind to the receptors,
the pit folds inward, enclosing the molecules and a small amount
of extracellular fluid. The pit then pinches off from the membrane,
forming an endocytic vesicle inside the cytoplasm.

26. Phagocytosis
Phagocytosis is the ingestion of large particles such as bacteria,
viruses, tissue debris, or dead cells. It occurs only in specialized
cells like macrophages and some white blood cells. Phagocytosis
takes place in a similar way to pinocytosis. The vesicles formed
during this process fuse with lysosomes, which release enzymes
to break down proteins, carbohydrates, lipids, and other
materials. The digested products such as amino acids, sugars, and
nucleotides are released into the cytoplasm for reuse, while
undigested materials form residual bodies.

28. Exocytosis
Exocytosis is the process by which these residual bodies or
other waste materials are expelled from the cell. The
substances are enclosed in exocytic vesicles, which fuse
with the inner surface of the plasma membrane. The vesicles
then rupture, releasing their contents into the extracellular
space. The vesicle membranes are then retrieved and
reused by the cell.

29. TO BE CONTINUED….
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