Structure of human cell, detials of structure and function of cell organelles

1. CELL: Structure and Function
Dr. Poonam Kharb Janghu

2. CELLS
•Cells are the basic structural and
functional units of the human
body.
•Each cell has the capacity to
perform all essential functions of
life.
•Cells of different tissues and
organs have functional
specialization.

3. The Cell Theory
• Cells were discovered by Robert
Hook
• The cell theory proposed by
Theodore Schwann (1810-1882)
holds that all living things are
composed of cells.
• Rudolf Virchov stated that and
that cells can only arise from pre-
existing cells.

4. NUMBER AND SIZE OF HUMAN CELLS
• An average person is estimated to contain roughly 30 trillion
human cells.
• There are approximately 200 different types of cells in the human
body which have different shape and size.
• Cells lie in the range of 5 -50µm dia.
• Lymphocyte- 6µm
• RBC – 7.5µm
• Columnar epithelium cell
• Ovum - .12mm
• Sperm - 50µm

5. THE CELL
• A cell is the smallest unit of life
capable of independent existence.
• Each cell contains protoplasm and
is enclosed by a cell membrane.
• Protoplasm includes two
components:
• Cytoplasm - (Metabolic
machinery).
• Nucleus - (Hereditary
material)
 Within the cytoplasm lie hundreds or even thousands of
miniscule but distinct structures called organelles.
 All cells except mature RBC contain nucleus

6. Cytoplasmic organelles
• Cytoplasmic organelles are "little organs" that are suspended in
the cytoplasm of the cell.
• Each type of organelle has a definite structure and a specific role in
the function of the cell

7. THE CELL
• As each organelle is bounded by
membrane, therefore cell is
divided into number of membrane
bound compartments each with
its on biochemical environment.
• Membranes also contain enzymes
and are sites of biochemical
reactions.
• Organelles are suspended in A
fluid medium called cytosol.
• Within cytosol is network of
microfilaments and microtubules
which provide structural support.

8. 1. Nucleus
2. Mitochondria
3. Rough endoplasmic reticulum (RER)
4. Smooth endoplasmic reticulum (SER)
5. Golgi complex
6. Lysosomes
B. Organelles not bounded by a membrane :
11. Microtubules
2. Microfilament
3. Centriole
4. Ribosomes
A. Membrane-Bound Organelles

9. CELL ORGANELLES

10. • It encloses the cell & separates the contents of the cell from the
external environment.
• Cell membrane ( plasma membrane) is a double layer of
phospholipids and associated proteins that surrounds a cell.
• As the various components of the bilayer (phospholipids, proteins,
carbohydrates) are able to move around, it is referred to as a fluid-
mosaic model ( by Singer & Nicholson).
Cell Membrane – Plasmalemma

11. Cell Membrane – Plasmalemma
40% lipid – E.g. phospholipid molecules and cholesterol
60% protein – E.g. channel proteins and carrier proteins
1-10% carbohydrate – Often found attached to proteins/lipids
on the outside of the cell membrane.

12. • Intrinsic proteins: they are incorporated within the cell
membrane.
• Extrinsic/peripheral proteins: are attached to outer or inner
surface of cell membrane.
• Transmembrane proteins: span entire thickness of cell
membraneans function as ‘pores’

13. Functions Of Cell Membrane
1. Acts as a barrier, is selectively permeable and regulates ion and
macromolecule movement in and out of the cell.
2. Surface carbohydrate molecules allows cell to cell communication.
3. Is the recognition sites for immunologic reaction.
4. Has receptors proteins to receive chemical messages (e.g. for
hormones).
5. Transport proteins serve as channels or pumps to move materials in
and out of cells.
6. Generates membrane potential in nerve transmission and muscle
contraction.

14. Transport Across Cell membrane
Plasma membrane allows e passage of molecules between
internal and external environment of the cell via following
ways:
• Passive Diffusion: it is dependent on concentration
gradient of molecules , ions and gases across the membrane.
• Active transport: it is independent of concentration gradient
and requires energy provided in the form of ‘ATP’.

15. Nucleus
Contains
• DNA – 20%
• Nucleoproteins - Histones
Non – histones
• RNA – Newly synthesized
mRNA, tRNA , rRNA
•It is the largest organelle.
•Is covered by double layer of
membrane which has pores.
•Outer membrane contains ribosomes
and is continuous with endoplasmic
reticulum.

16. Nucleus and Nucleolus
• The nucleus is the control center of
the cell. The nucleus determines
how the cell will function, as well
as the basic structure of that cell.
• Nucleolus is a dense region in the
nucleus and is the site of ribosomal
RNA formation .
• Ribosomal proteins are imported
from cytoplasm and conjugated
with ribosomal RNA to form
ribosomal units.
• During cell division, the nucleolus
disappears.

17. EUCHROMATIN AND HETEROCHROMATIN
• Chromatin is DNA that is complexed
with proteins called histones. Histones
combined with DNA
form nucleosomes, which are the
subunit of chromatin.
• Chromatin can exist
as euchromatin or heterochromatin.
• Euchromatin is present during gene
expression, and has a characteristic
and is lightly stained.
• Heterochromatin is the ‘inactive’
form, and is densely packed.

18. MITOCHONDRION
• Are known as the ‘Powerhouse ‘ of cell.
• Mitochondria vary in size and shape but mostly are elongated and
cigar shaped. The average length of mitochondrion is 3-4 microns and
the average diameter 0.5 to 1.0 micron.
• The number of mitochondria in a cell can vary according to the cell
type. A mature red blood cell has no mitochondria, whereas a liver
cell can have more than 2000.
• Mitochondria contain DNS. Their DNA has maternal lineage which
means their DNA is passed from mother to child

19. • Mitochondria have an inner and outer membrane, with an intermembrane
space between them.
• Outer membrane contains proteins known as porins, which allow movement
of ions into and out of the mitochondrion.
• Inner membrane has many folds called Cristae. It contains ATP
synthase which generates ATP in the matrix.
• The space within the inner membrane of the mitochondrion is known
as matrix, which contains the enzymes of the Kreb cycle and DNA, RNA,
ribosomes and calcium granules.

20. Functions of Mitochondrion
• Mitochondrion is the site of ATP synthesis for the cell.
• The number of mitochondria found in a cell are therefore a
good indicator of the cell’s rate of metabolic activity; cells
which are very metabolically active, such as hepatocytes, will
have many mitochondria.
• Mitochondria store caspases responsible for triggering apoptosis.
• Are able to transiently store calcium contributing to calcium
homeostasis.
• In brown adipose tissue mitochondria have an alternative
function of heat production using the electron transport chain.

21. Endoplasmic Reticulum
• Endoplasmic reticulum is the major site of synthesis in the cell.
• It is a system of flattened sacs (cisternae) that are continuous with the outer
nuclear envelope.
• Its function is very close association with that of the Golgi apparatus and
together, they form the secretory pathway of the cell.
• The endoplasmic reticulum is classified as Rough (RER) or Smooth (SER).

22. • The rough endoplasmic
reticulum (RER) looks
rough because there are
ribosomes attached to it.
• As the ribosomes
synthesize a protein it is
internalized by the RER.
• Once inside the RER the
protein can be modified in
some way.
• Once modified the protein
will pinch off of the RER in
a membrane sac known as
a vesicle and can be
transported to other areas
of the cell as needed.

23. • Cells that produce proteins will have extensive RER .
• The RER plays an important role in the synthesis of proteins that
are destined for:
• Secretion into the extracellular matrix e.g. mucus and enzymes.
• Association with the cell membrane e.g. receptors and channels.
• Membrane bound vesicles e.g. enzymes of lysosomes.

24. Ribosomes

25. Smooth Endoplasmic Reticulum (SER)
Smooth because there are
no ribosomes attached.
• The SER is the site of lipid
synthesis and is also
involved in the
detoxification of drugs and
alcohol.
• A person with a severe
drug or alcohol problem
will have a lot of SER in
their liver cells to deal with
the toxins.
•
In muscle it is called sarcoplasmic reticulum. It
is involved in storage and release of Ca ions
which initiate muscle contraction.

26. Golgi Apparatus
Golgi apparatus is a membrane bound organelle found in most cells. It is
responsible for packaging proteins into vesicles prior to secretion and therefore
plays a key role in the secretory pathway.

27. • Golgi is made of 5-8 folds
called cisternae. The cisternae
contain specific enzymes
creating five functional regions
which modify proteins passing
through them in a stereotypical
way, as follows:
• Cis-Golgi face: faces the
nucleus, forms a connection
with the endoplasmic reticulum
and is the entry point into the
Golgi apparatus.
• Trans-Golgi Face: exit point for
vesicles budding off the Golgi
surface, packages and sorts
biochemicals into the vesicles
according to their destination.

28. Golgi Apparatus - Function
Golgi apparatus modifies proteins and lipids that it receives from the
endoplasmic reticulum which leave golgi by exocytosis before delivered
to extracellular targets.
• Protein processing – carbohydrate regions of glycoproteins are
altered by addition, removal or modification of carbohydrates.
Lipid processing – adds phosphate groups and glycoproteins to lipids
from the endoplasmic reticulum (such as cholesterol) to create the
phospholipids that make up the cell membrane.

29. Golgi Apparatus - Function
Sorting, Budding and Exocytosis
Biochemicals are chemically labelled in the golgi to ensure appropriate
delivery to the correct destination.
• Lysosomal proteins – such as enzymes are packaged into specific
vesicles. These proteins are typically tagged with mannose-6-
phosphate in the Golgi
• Secretory proteins – such as hormones are packaged into secretory
vesicles ready for exocytosis.
• Cell surface proteins – such as phospholipids enter the constitutive
secretory pathway present in all cells.

30. Lysosome
• Lysosomes are spherical, membrane bound organelles that are
generated by the golgi apparatus.
• Lysosomes are the cells garbage disposal system. They also function
as part of the recycling system of the cell. They are known as ‘Suicidal
bags’.
• They contain up to 40 acidic enzymes (hydrolases) at a pH 5. The
membrane prevents the enzymes from destroying cellular
structures.
• They are capable of degrading different types of biological
material including pathogens, nucleic acids, lipids and proteins.
• Lysosomes also degrade worn out organelles such as
mitochondria.

31. Lysosome Types
There are two main types,
these include:
• Primary lysosomes - are
formed from Golgi apparatus
appearing as small vesicles.
These lysosomes are
surrounded by a single
phospholipid layer and
contain acid hydrolases.
• Secondary lysosomes - are
formed when primary
lysosomes fuse with
phagosomes.
Compared to primary lysosomes,
secondary are larger in size and
capable of releasing their content
(enzymes) outside the cells where
they degrade foreign material.

32. Centrosome
• Centrosome is microtubule-organizing centre.
• It is located near the nucleus of cell.
• It contains a pair of centrioles arranged perpendicular to each other.

33. Centrioles
Centriole is a cylindrical in shape
and has specialized arrangement of
microtubules.
• They are composed of nine triplet
microtubules that are each
connected via protein fibers.
• The centrioles, and ultimately the
centrosome, have several
important functions.
• They are involved in
chromosomal separation
during cell division.
• They are responsible for
positioning the nucleus and
other organelles within the
cell.
• They are responsible for
forming the flagella and cilia.

34. Questions
• Who discovered cells?
• Which cell organelle/s contain DNA?
• Which organelle helps in spindle formation?
• Which organelle is known as powerhouse of cell and why?
• Which cell structure regulates the entry and exit of molecules to and
from the cell?
• Which cell organelles is called a suicidal bag?

35. Questions
• ……………………… serves as a primary packaging area for molecules that will be
distributed throughout the cell?
• r RNA is synthesized by …………………………….
• During cell division centrioles take part in the formation of ………………….
• Longest cells in human body are ………………………………………
• Hydrolytic enzymes are located in …………………………..
• Functional unit of life is ………….
• ………………………. Is involved in lipid synthesis.