Explains the functions of cells in the body

1. 1.01.Fishing Trip
Session 1
Cell Physiology
By
Dr. Mudassar Ali Roomi (MBBS, M.Phil.)
Assistant Professor Physiology

2. Cell Components
– cell membrane
– nucleus
– cytoplasm
• cytosol
• organelles

3. CELL MEMBRANE
• The cell membrane (plasma membrane), envelops the
cell as a thin, pliable, elastic structure
• It is only 7.5-10 nm thick.
• It is composed of proteins, lipids and carbohydrates.
Composition of cell membrane is:
 Proteins, 55%;
 Lipids: 40-45 %
phospholipids,
cholesterol
other lipids
 carbohydrates, 3 %.

4. PLASMA MEMBRANE- FLUID MOSAIC MODEL
• lipid bilayer is made of
phospholipids and is fluid in
nature.
• Phospholipids molecules make the
‘backbone’ of cell membrane and
each molecule has two ends:
– Polar end: hydrophilic.
– Non-polar end: hydrophobic.
• Proteins are embedded in lipid
bilayer.
• Cholesterol Molecules:
– Are between phospholipids.
– Contributes to fluidity and
stability of cell membrane.

5. Membrane Proteins
1. INTEGRAL PROTEINS
These are the proteins which
Penetrate completely or partially
into the phospholipid bilayer.
2. PERIPHERAL PROTEIN
Are attached to inner and outer
surface of membrane

6. MEMBRANE PROTEINS CAN ACT AS
1. Transport Proteins:
2. Membrane-bound enzymes.
3. Receptor sites.
4. Cell adhesion molecules (CAMs) which perform the function of
intercellular joining.

7. Carbohydrates
GLYCOCALYX:
The loose carbohydrate coat on the outer
surface of cell. It is made of
• Glycoproteins = Carbohydrate +
protein
• Glycolipids = Carobhydrate + lipid.
IMPORTANT FUNCTIONS OF GLYCOCALYX:
(1) Many of them have a negative
electrical charge, that repels other
negative objects e.g. bacteria.
(2) The glycocalyx of some cells attaches
to the glycocalyx of other cells
(3) Many of the carbohydrates act as part
of the receptors for binding hormones,
(4) Some carbohydrate moieties enter into
immune reactions.

8. General functions of Plasma membrane
1. It separates the ICF from ECF.
2. It provides protection to the cell
3. Regulation of cell contents: It allows for different conditions between inside
and outside of cell.
– Selective permeability of plasma membrane is the basis of differential
concentration of electrolytes in ECF and ICF.
4. It acts as material exchange gateway (transport function).
5. It allow selective receptivity and signal transduction by providing
transmembrane receptors that bind signaling molecules
6. It provide anchoring sites for cytoskeleton components. This allows the cell
to maintain its shape.
7. It provides physical and functional connections with other cells or the
extracellular matrix so that the cells group together to form tissues.

9. Cytoplasm
• Network of membranes
and organelles are
suspended in a clear gel
called cytosol.
• Protein rods and
tubules form the
cytoskeleton, a
supportive framework.
• Organelles perform
specific cellular
functions.

10. Cell
Organelles

11. Nucleus
• Large, spherical
structure
• Enclosed in a double-
layered nuclear
envelope
• Layers are joined at
openings, the nuclear
pores, channels that
allow movement in and
out of the nucleus

12. Nucleoli and Chromatin
• Nucleolus (pl. Nucleoli)
are small, dense bodies
composed of RNA and
protein.
– It is the site of ribosome
production.
• Chromatin fibers are
composed of continuous
DNA molecules wrapped
around histone proteins.
Chromatin
fibers

13. Mitochondria
• Fluid-filled sacs that contain
their own DNA and can
divide on their own.
• There are two layers, an
outer membrane and an
inner membrane.
• The inner membrane is
folded into cristae.
• Enzymes of the
mitochondrion control the
energy releasing reactions
• Function: Power house of
cell-ATP synthesis.

14. The Use of ATP for Cellular Function
1. Membrane
transport
2. Synthesis of
chemical
compounds
3. Mechanical
work

15. Endoplasmic Reticulum
• Endo - within
• Plasmic - the cytoplasm
• Reticulum is Latin for "little net".
• Flattened, fluid-filled, membrane
enclosed sacs composed of
cisternae and tubules that
compartmentalize the cell with a
series of channels formed
between overlapping membranes.

16. Endoplasmic Reticulum
• It forms supporting skeletal framework of the cell.
• Connected to the outer membrane of the nucleus.
• Two forms:
• Rough endoplasmic reticulum (RER)
• Smooth endoplasmic reticulum (SER)

17. Rough Endoplasmic Reticulum
• Ribosomes attached on
its surface.
• Function: Synthesizes
proteins. some examples
of proteins synthesized
are:
1. For the cell membrane
2. Digestive enzymes
3. Mucus
4. Insulin, Glucagon

18. Ribosomes
• Ribosomes are found:
1. on the endoplasmic reticulum and
2. free in the cytoplasm
• Composed of protein and RNA
• Provide a structural support and enzymes
necessary for protein synthesis

19. Smooth Endoplasmic Reticulum
• Membrane enclosed
sacs that lack
ribosomes
• Membranes of SER
are embedded with
enzymes that
catalyze many
reactions and then
send products to the
Golgi apparatus.

20. Functions of SER
1. Packages proteins into vesicles for transport within the cell.
• SER is abundant in secretory cells, muscles and liver cells
2. Produces lipids like phospholipids and produces vesicles to
replace the cell membrane.
3. Produces steroid hormones in testes and adrenal cortex
4. Stores calcium ions in muscle cells.
5. Utilization of glucose for energy from glycogen
6. Detoxification by oxidation, hydrolysis, conjugation with
glucoronic acid, and in other ways.
• Why do Alcoholics have more SER?

21. Golgi Apparatus
• Usually located near
ER and nucleus.
• They are comprised
of stack of
membrane
structures known as
cisternae.

22. Golgi Apparatus
Three structural parts:
1. cis-Golgi.
• It is the section nearest to the
endoplasmic reticulum and it is
where the Golgi apparatus first
receives the cargo vesicles containing
the newly synthesized proteins.
2. medial-Golgi.
• Most of the various functions of the
Golgi apparatus occur as the cargo
proteins pass through the medial-
Golgi sections.
3. trans-Golgi.
• Eventually, they end up at the trans-
Golgi, located at the opposite end
from the cis-Golgi. This is where the
finished product is packaged for
transportation to the rest of the cell.
Trans-Golgi

23. Functions of Golgi Apparatus
1. to take the proteins from endoplasmic reticulum, process them (stored, modified,
concentrated) according to specific needs and then repackage into vesicles that
pinch off from the outer face of the Golgi body and reach on to their destinations.
– Processes such as phosphorylation and glycosylation are used to modify the various
cargo proteins received from the endoplasmic reticulum.
2. Production of polysaccharides and glycosaminoglycans (GAGs)
3. Formation of lysosomes.

24. Lysosomes
• Tiny, membranous sacs containing hydrolytic
enzymes that break down proteins,
carbohydrates, and nucleic acids
• White blood cells digest bacteria with
lysosomal enzymes
• Lysosomes also dismantle worn cells and cell
parts

25. Peroxisomes:
• similar physically to lysosomes
• two major differences:
• formed by self-replication
• they contain oxidases
Function: oxidize substances (e.g. alcohol) that may be
otherwise poisonous

26. The Cytoskeleton1. Thin/Actin
Filaments/Microfilaments/
2. Intermediate Filaments
3. Thick/Myosin Filaments
4. Microtubules

28. Cell membrane is selectively permeable

29. Types of transport Through Cell membrane
• Diffusion or passive transport:
1. Simple Diffusion
2. Facilitated Diffusion
3. Osmosis
• Active transport
– Primary Active Transport
– Secondary Active Transport
• Endocytosis
1. Pinocytosis
2. Phagocytosis
• Exocytosis

30. Simple Diffusion
• Definition: Movement of
particles of a substance
from an area of higher
concentration to an area of
low concentration (along
the gradient)
• It is through lipid bilayer or
protein channels.
• No use of ATP
Examples:
1. O2 diffuses in the lungs
from the alveoli into the
blood in the pulmonary
capillaries.
2. Inflow of Na+ through
sodium leak channels

31. Define osmosis and give an example.
• Definition: Movement of
solvent across a semi-
permeable membrane
from an area of lower to
an area of higher solute
concentration,
• Example: water
reabsorption in the distal
convoluted tubule of
kidney due to ADH
hormone increasing the
permeability of tubule.

32. facilitated diffusion
Definition: The movement
of a substance down its
concentration gradient at
a faster rate than
expected, by way of
special
carriers/transporters
present in the cell
membrane,
Example: movement of
glucose into the cell by
action of insulin.

33. What limits the rate of
facilitated diffusion:
• Saturation of carrier
molecules.
• The rate of transport cannot
be greater than the rate at
which carrier protein molecule
can undergo change back &
forth between its 2 states.

34. Factors affecting rate of diffusion
1. Effect of conc. difference across membrane (directly)
2. Effect of temperature (directly)
3. Membrane permeability (directly)
4. Lipid solubility of the substance
5. Size of molecules (inversely)
6. Effect of pressure difference across membrane (directly)

35. Active transport
• Definition: Transport of a substance from low
to high concentration (uphill) with use of
energy.
• Types of active transport:
1. Primary active transport
2. Secondary active transport

36. Primary active transport
• Uphill transport with
direct use of ATP.
– Example: Sodium-
potassium ATPase pump
– Na/K pump is electrogenic
in nature. How?
• Other examples:
– Primary active transport of
calcium ions in ER of
muscle
– Primary active transport of
hydrogen ions in gastric
parietal cells

37. Functions of Na/K pump
• The sodium pump keeps Na+ out of the cell
and K+ inside the cell, in order to maintain cell
volume.
• This creates a Na+ gradient for secondary
active transport
• Electrogenic pump→ contributes – 4 mV to
Resting membrane potential.

38. Secondary active co-transport
Sodium Co-transport of Glucose & Amino acids
• Energy for this transport is
provided by sodium gradient.
Example:
• Found at Epithelial cells of
intestinal tract.
• Found at Renal tubules of
kidneys.
Significance:
To promote absorption of Glucose
& Amino Acids into the blood.
Mechanism:
glucose / amino acid and sodium
attaches with binding sites of
carrier. Conformational change
occurs and transports both the
substances in the same direction.

39. Secondary active counter-transport
Sodium Counter-Transport of Calcium & Hydrogen Ions:
• Transport in a direction
opposite to the primary ion
(Na+).
Examples:
• Sodium-calcium counter-
transport: (sodium  in, &
calcium  out.
• Sodium-hydrogen counter-
transport (proximal tubules
of kidney)

40. Diffusion Vs Active Transport
Diffusion:
1. through lipid bilayer, protein
channels Or carrier protein.
2. Along the gradient.
3. From high to low concentration
(downhill).
4. Energy of normal kinetic motion
of matter causes diffusion.
5. Types: simple, and facilitated
diffusion.
6. Examples: transport of O2, CO2
through the cell membrane
Active Transport:
1. Through carrier proteins only
2. against the gradient.
3. Low concentration to high
concentration (uphill)
4. Kinetic energy + additional
source of energy is required.
5. Types: primary and secondary
active transport.
6. Examples: transport through
sodium-potassium ATPase
Pump.