1. Dr. Salman Ul Islam
Unit#1 BASIC CELL FUNCTIONS
Topic: Cell Organelles
Physiology-A
2. Cell
All the living things are composed of cells. A single cell is the smallest unit that has all the
characteristics of life. Cell is defined as the structural and functional unit of the living body.
3. Cell
General Characteristics of Cell
Each cell in the body:
1. Needs nutrition and oxygen
2. Produces its own energy necessary for its growth, repair and other activities
3. Eliminates carbon dioxide and other metabolic wastes
4. Maintains the medium, i.e., the environment for its survival
5. Shows immediate response to the entry of invaders like bacteria or toxic substances into
the body
4. Cell under microscope
(A) This chart lists sizes of cells and
their component parts, the units in
which they are measured, and the
instruments needed to visualize them.
(B) Drawings convey a sense of scale
between living cells and atoms. Each
panel shows an image that is magnified
by a factor of 10 compared to its
predecessor—producing an imaginary
progression from a thumb, to skin, to
skin cells, to a mitochondrion, to a
ribosome, and ultimately to a cluster of
atoms forming part of one of the many
protein molecules in our bodies. Note
that ribosomes are present inside
mitochondria (as shown here), as well
as in the cytoplasm. Details of
molecular structure, as shown in the
last two bottom panels, are beyond the
power of the electron microscope.
5. Cell organelles
Organelles are considered as small organs of the cell. Some organelles are bound by
limiting membrane and others do not have limiting membrane.
Each organelle is having a definite structure and specific functions.
6.
7. Cell organelles
Double membrane-bound organelles: Nucleus and mitochondria are double membrane-
bound organelles.
Single membrane-bound organelles: Lysosome, Golgi Apparatus, Endoplasmic Reticulum
are single membrane-bound organelles.
Organelles without membrane: Ribosomes, and Cytoskeleton are non-membrane-bound
cell organelles.
8. Cell organelles
Nucleus
The nucleus is a double-membraned organelle found in all eukaryotic cells. It is the largest
organelle, which functions as the control center of the cellular activities and is the
storehouse of the cell’s DNA. Nucleus is covered by a membrane called nuclear membrane
and contains many components. Major components of nucleus are nucleoplasm, chromatin
and nucleolus.
Chromosomes are thin and thread-like structures which carry another important structure
called a gene. Genes are a hereditary unit in organisms i.e., it helps in the inheritance of
traits from one generation (parents) to another (offspring). Hence, the nucleus controls the
characters and functions of cells in our body. The primary function of the nucleus is to
monitor cellular activities including metabolism and growth by making use of DNA’s
genetic information. Nucleoli in the nucleus are responsible for the synthesis of protein and
RNA.
10. Cell organelles
Mitochondria
Mitochondrion (plural = mitochondria) is a membrane-bound cytoplasmic organelle
concerned with production of energy.
It is a rod-shaped or oval-shaped structure with a diameter of 0.5 to 1 μ.
It is covered by a bilayered membrane. The outer membrane is smooth and encloses the
contents of mitochondrion. This membrane contains various enzymes such as acetyl-CoA
synthetase and glycerolphosphate acetyltransferase.
The inner membrane is folded in the form of shelf-like inward projections called cristae and
it covers the inner matrix space.
12. Cell organelles
Mitochondria
Cristae contain many enzymes and other protein molecules which are involved in
respiration and synthesis of adenosine triphosphate (ATP).
Enzymes and other proteins of respiratory chain
i. Succinic dehydrogenase
ii. Dihydronicotinamide adenine dinucleotide (NADH) dehydrogenase
iii. Cytochrome oxidase
iv. Cytochrome C
v. ATP synthase.
13. Cell organelles
Mitochondria
Inner cavity of mitochondrion is filled with matrix which contains many enzymes.
Mitochondrion moves freely in the cytoplasm of the cell. It can reproduce itself.
Mitochondrion contains its own deoxyribonucleic acid (DNA), which is responsible for
many enzymatic actions. In fact, mitochondrion is the only organelle other than nucleus,
which has its own DNA.
14. Cell organelles
Functions of Mitochondria
1. The most important function of mitochondria is to produce energy. Mitochondria
produce the molecule adenosine triphosphate (ATP), one of the cell’s energy currencies
that provide the energy to drive a host of cellular reactions and mechanisms.
2. Mitochondria help the cells to maintain the proper concentration of calcium ions within
the compartments of the cell.
3. The liver cell’s mitochondria have enzymes that detoxify ammonia.
4. The mitochondria also play an important role in the process of apoptosis or
programmed cell death.
15. Cell organelles
Lysosomes
Lysosomes are membrane-enclosed organelles that contain an array of enzymes capable of
breaking down all types of biological polymers—proteins, nucleic acids, carbohydrates, and
lipids.
Lysosomes function as the digestive system of the cell, serving both to degrade material taken
up from outside the cell and to digest obsolete components of the cell itself.
In their simplest form, lysosomes are visualized as dense spherical vacuoles, but they can
display considerable variation in size and shape as a result of differences in the materials that
have been taken up for digestion.
Lysosomes thus represent morphologically diverse organelles defined by the common function
of degrading intracellular material.
17. Cell organelles
Golgi apparatus
Golgi apparatus or Golgi body or Golgi complex is a membrane-bound organelle, involved
in the processing of proteins. It is present in all the cells except red blood cells.
It is named after the discoverer Camillo Golgi. Usually, each cell has one Golgi apparatus.
Some of the cells may have more than one Golgi apparatus. Each Golgi apparatus consists
of 5 to 8 flattened membranous sacs called the cisternae.
18. Cell organelles
Golgi apparatus
Golgi apparatus is situated near the nucleus. It
has two ends or faces, namely cis face and
trans face.
The cis face is positioned near the endoplasmic
reticulum. Reticular vesicles from endoplasmic
reticulum enter the Golgi apparatus through cis
face.
The trans face is situated near the cell
membrane. The processed substances make
their exit from Golgi apparatus through trans
face.
19. Cell organelles
Functions of Golgi apparatus
The Golgi apparatus, or Golgi complex, functions as a factory in which proteins received
from the endoplasmic reticulum are further processed and sorted for transport to their
eventual destinations: lysosomes, the plasma membrane, or secretion.
20. Cell organelles
Endoplasmic Reticulum
It is a network of tubular and flat vesicular structures in the cytoplasm.
The tubules and vesicles interconnect with one another. Also, their walls are constructed of
lipid bilayer membranes that contain large amounts of proteins, like the cell membrane.
The space inside the tubules and vesicles is filled with endoplasmic matrix, a watery
medium that is different from the fluid in the cytosol outside the endoplasmic reticulum.
Electron micrographs show that the space inside the endoplasmic reticulum is connected
with the space between the two membrane surfaces of the nuclear membrane.
21. Cell organelles
Endoplasmic Reticulum
Substances formed in some parts of the cell enter the space of the endoplasmic reticulum
and are then conducted to other parts of the cell. Also, the vast surface area of this
reticulum and the multiple enzyme systems attached to its membranes provide machinery
for a major share of the metabolic functions of the cell.
22. Cell organelles
Ribosomes and the Granular Endoplasmic Reticulum
Attached to the outer surfaces of many parts of the endoplasmic reticulum are large
numbers of minute granular particles called ribosomes.
Where these are present, the reticulum is called the granular endoplasmic reticulum. The
ribosomes are composed of a mixture of RNA and proteins, and they function to synthesize
new protein molecules in the cell.
23. Cell organelles
Agranular Endoplasmic
Reticulum
Part of the endoplasmic reticulum
has no attached ribosomes. This
part is called the agranular, or
smooth, endoplasmic reticulum.
The agranular reticulum
functions for the synthesis of lipid
substances and for other
processes of the cells promoted by
intrareticular enzymes.
24. Cell organelles
Peroxisomes
Peroxisomes are similar physically to lysosomes, but they are different in two important
ways.
First, they are believed to be formed by self-replication (or perhaps by budding off from the
smooth endoplasmic reticulum) rather than from the Golgi apparatus.
Second, they contain oxidases rather than hydrolases. Several of the oxidases can combine
oxygen with hydrogen ions derived from different intracellular chemicals to form hydrogen
peroxide (H2O2).
Hydrogen peroxide is a highly oxidizing substance and is used in association with catalase,
another oxidase enzyme present in large quantities in peroxisomes, to oxidize many
substances that might otherwise be poisonous to the cell.
For instance, about half the alcohol a person drinks is detoxified by the peroxisomes of the
liver cells in this manner.
26. Cell organelles
Centrosome and centrioles
Centrosome is the membrane-bound cellular organelle situated almost in the center of cell,
close to nucleus. It consists of two cylindrical structures called centrioles which are made
up of proteins. Centrioles are responsible for the movement of chromosomes during cell
division.
