Cell structure

1. Unit 1
BASIC ELEMENTS OF HUMAN BODY

2. UNIT -1
Cell
Cell Structure and organelles
Functions of each component in the cell
 Cell membrane
Transport across membrane
Action potential (Nernst, Goldman equation),
Homeostasis
Tissue:
Types, functions

3. Cell- Defined as the structural and functional
unit of the living body.

4. Structure of cell

5. Thus, the structure of the cell have
1. Cell membrane
2. Cytoplasm
3. Nucleus.
CELL MEMBRANE
Cell membrane is a protective envelop of the cell
body. It is also known as plasma membrane

6. • This membrane separates the fluid outside
the cell called extracellular fluid (ECF) and the
fluid inside the cell called intracellular fluid
(ICF).
• The cell membrane is a semipermeable
membrane. So, there is free exchange of
certain substances between ECF and ICF.
• Thickness of the cell membrane varies from 75
to 111Å

7. COMPOSITION OF CELL MEMBRANE
Cell membrane is composed of three types of
substances:
1. Proteins (55%)
2. Lipids (40%)
3. Carbohydrates (5%).

8. Structural Model of the Cell
Membrane
Fluid mosaic model
Later in 1972, SJ Singer and GL Nicholson
proposed ‘The fluid mosaic model’. According
to them, the membrane is a fluid with mosaic of
proteins
(mosaic means pattern formed by arrangement
of different colored pieces of stone, tile, glass or
other such materials).

10. Lipid Layers of the Cell Membrane
• The central lipid layer is a bi-layered
structure.

11. • Phospholipid molecules -arranged in two
layers
• The outer part of the phospholipid molecule is
called the head portion and the inner portion is
called the tail portion
• Head portion is the polar end -soluble in
water and has strong affinity for water
(hydrophilic)-outside cell memb-ECF
• Tail portion is the non-polar end. It is insoluble
in water and repelled by water (hydrophobic)-
inside cell memb-ICF

13. Cholesterol
• Cholesterol molecules are arranged in
between the phospholipid molecules.
• Phospholipids are soft and oily structures and
cholesterol helps to ‘pack’ the phospholipids
in the membrane.
• So, cholesterol is responsible for the
structural integrity of lipid layer of the cell
membrane.

14. Functions of Lipid Layer in Cell Membrane
• Lipid layer of the cell membrane is a
semipermeable membrane and allows only the
fat-soluble substances to pass through it.
eg:oxygen, carbon dioxide and alcohol

15. Protein Layers of the Cell Membrane
• Protein layers of the cell membrane are
electron-dense layers.
• These layers cover the two surfaces of the
lipid layer. Protein layers give protection to
the lipid layer.
• The protein substances present in these layers
are mostly glycoproteins.

16. Protein molecules are classified into two
categories:
1. Integral proteins or transmembrane proteins.
2. Peripheral proteins or peripheral membrane
proteins.
1. Integral proteins
• Integral or transmembrane proteins are the
proteins that pass through entire thickness of cell
membrane from one side to the other side.
• These proteins are tightly bound with the cell
membrane.

17. Examples of integral protein:
i. Cell adhesion proteins
ii. Cell junction proteins
iii. Some carrier (transport) proteins
iv. Channel proteins
v. Some hormone receptors
vi. Antigens
vii. Some enzymes.

18. 2.Peripheral proteins
• Peripheral membrane proteins are the proteins
which are partially embedded in the outer and
inner surfaces of the cell membrane and do
not penetrate the cell membrane.
• Examples of peripheral proteins:
i. Proteins of cytoskeleton
ii. Some carrier (transport) proteins
iii. Some enzymes.

19. Functions of Proteins in Cell Membrane
• Integral proteins provide the structural integrity of
the cell membrane
• Channel proteins help in the diffusion of water
soluble substances like glucose and electrolytes
• Carrier or transport proteins help in the transport
of substances across the cell membrane by means
of active or passive transport
• Pump: Some carrier proteins act as pumps, by
which ions are moved.

20. • Receptor proteins serve as the receptor sites for
hormones and neurotransmitters
• Enzymes: Some of the protein molecules form the
enzymes and control chemical (metabolic) reactions
within the cell membrane
• Antigens: Some proteins act as antigens and induce
the process of antibody formation
• Cell adhesion molecules or the integral proteins are
responsible for attachment of cells to their neighbors
or to basal lamina.

21. Carbohydrates of the Cell Membrane
• carbohydrate +proteins =glycoproteins
(proteoglycans).
• Carbohydrate+ lipids =glycolipids.
• Carbohydrate molecules form a thin and loose
covering over the entire surface of the cell
membrane called glycocalyx.

22. Functions of Carbohydrates in Cell
Membrance
• Carbohydrate molecules - negatively charged
and do not permit the negatively charged
substances to move in and out of the cell
• Glycocalyx from the neighboring cells helps in
the tight fixation of cells with one another
• Function as the receptors for some hormones.

23. FUNCTIONS OF CELL MEMBRANE
1.Protective function
2. Selective permeability
3. Absorptive function
4. Excretory function
5. Exchange of gases
6. Maintenance of shape and size of the cell

24. CYTOPLASM
• Jellylike material formed by 80% of water
• clear liquid portion called cytosol
• It contains proteins, carbohydrates, lipids or
electrolytes in nature.
• Cytoplasm also contains many organelles

25. Cytoplasm is made up of two zones:
1. Ectoplasm: Peripheral part of cytoplasm,
situated just beneath the cell membrane
2. Endoplasm: Inner part of cytoplasm,
interposed between the ectoplasm and the
nucleus.

26. ORGANELLES IN CYTOPLASM
• Some organelles are bound by limiting
membrane and
• Others do not have limiting membrane

27. ORGANELLES WITH LIMITING
MEMBRANE
ENDOPLASMIC RETICULUM
• Endoplasmic reticulum is a network of tubular
structures.
• Contains limiting membrane-proteins and
bilayered lipids
• Lumen of endoplasmic reticulum contains a
fluid medium -endoplasmic matrix.

28. • video

29. • diameter of the lumen is about 400 to 700Å.
• Forms link between nucleus and cell
membrane.
Types of Endoplasmic Reticulum
• Rough endoplasmic reticulum
• smooth endoplasmic reticulum

30. Rough Endoplasmic Reticulum
• Rough appearance is due to the attachment of
granular ribosomes to its outer surface-
granular endoplasmic reticulum
Functions of Rough Endoplasmic Reticulum
1. Synthesis of proteins
2. Degradation of worn-out organelles

31. Smooth Endoplasmic Reticulum
• formed by many interconnected tubules.
• So, it is also called tubular endoplasmic
reticulum.
Functions of Smooth Endoplasmic Reticulum
1. Synthesis of non-protein substance
2. Role in cellular metabolism
3. Storage and metabolism of calcium
4. Catabolism and detoxification

32. GOLGI APPARATUS

33. • Involved in the processing of proteins.
• 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.

34. • 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

35. Functions of Golgi Apparatus
• Processing, packing, labeling and delivery of
proteins and other molecules like lipids to
different parts of the cell.

36. Lysosomes
• The lysosomes are formed by Golgi apparatus.
• The enzymes synthesized in rough
endoplasmic reticulum are processed and
packed in the form of small vesicles in the
Golgi apparatus.
• Then, these vesicles are pinched off from
Golgi apparatus and become the lysosomes.
• lysosomes have the thickest covering
membrane-bilayered lipid material.

37. Types of Lysosomes
Two types:
1. Primary lysosome, which is pinched off from
Golgi apparatus. It is inactive in spite of having
hydrolytic enzymes
2. Secondary lysosome, which is the active
lysosome. It is formed by the fusion of a primary
lysosome with phagosome or endosome.

38. Functions of Lysosomes
.
• Lysosomes are often called ‘garbage system’ of
the cell because of their degradation activity.
Important lysosomal enzymes
• Proteases, which hydrolyze the proteins into
amino acids
• Lipases, which hydrolyze the lipids into fatty
acids and glycerides
• Amylases, which hydrolyze the polysaccharides
into glucose
• Nucleases, which hydrolyze the nucleic acids into
mononucleotides.

39. Mechanism of lysosomal function
Lysosomal functions involve two mechanisms:
1. Heterophagy: Digestion of extracellular
materials
2. Autophagy: Digestion of intracellular materials
(worn-out cytoplasmic organelles)

40. Specific functions of lysosomes
1.Degradation of macromolecules
2. Degradation of worn-out organelles
3. Removal of excess secretory products in the
cells
4. Secretory function – secretory lysosomes

41. PEROXISOMES
Peroxisomes are pinched off from endoplasmic
reticulum.
Functions of Peroxisomes
• Breakdown the fatty acids by betaoxidation
• Degrade the toxic substances such as hydrogen
Peroxide (produced by alcohol) and other metabolic
products by means of detoxification.

42. • Form the major site of oxygen utilization in the
cells
• Accelerate gluconeogenesis from fats
• Degrade purine to uric acid
• Participate in the formation of myelin
• Play a role in the formation of bile acids.

43. 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.

44. SECRETORY VESICLES
• Contain the secretory substances.
• Formed in the endoplasmic reticulum and are
processed and packed in Golgi apparatus.
• Present throughout the cytoplasm.
• When necessary, these vesicles are ruptured
and secretory substances are released into the
cytoplasm

45. MITOCHONDRION

46. • Concerned with production of energy.
• 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
• This membrane contains various enzymes such
as acetyl-CoA synthetase and
glycerolphosphate acetyltransferase.

47. • The inner membrane is folded in the form of
shelf-like inward projections called cristae
• synthesis of adenosine triphosphate (ATP).
Functions of Mitochondrion
1. Production of energy
2. Synthesis of ATP
3. Apoptosis
4. Other functions- storage of calcium and
detoxification of ammonia in liver.

48. ORGANELLES WITHOUT
LIMITING MEMBRANE
• Ribosomes are the organelles without limiting
membrane.
• These organelles are granular and small dot-like
structures with a diameter of 15 nm.
• 35% of proteins 65% of ribonucleic acid(RNA).
• RNA present in ribosomes is called ribosomal
RNA (rRNA).
• Ribosomes are concerned with protein synthesis
in the cell.

49. Types of Ribosomes
• Ribosomes that are attached to rough
endoplasmic reticulum
• Free ribosomes that are distributed in the
cytoplasm.

50. Functions of Ribosomes
• Ribosomes are called ‘protein factories’
because of their role in the synthesis of
proteins.

51. • Ribosomes attached to rough endoplasmic
reticulum -synthesis of proteins such as the
enzymatic proteins, hormonal proteins,
lysosomal proteins.
• Free ribosomes -synthesis of proteins in
hemoglobin, peroxisome and mitochondria

52. CYTOSKELETON
• Cytoskeleton is the cellular organelle present
throughout the cytoplasm.
• It determines the shape of the cell and gives
support to the cell.
• It is also essential for the cellular movements and
the response of the cell to external stimuli.

53. Cytoskeleton consists of three major
1. Microtubule
2. Intermediate filaments
3. Microfilaments

54. Microtubules
• straight, hollow and tubular structures of the
cytoskeleton.
• Each tubule has a diameter of 20 to 30 nm.
• Structurally, the microtubules are formed by of
globular protein called tubulin.
• Tubulin has two subunits, namely αsubunit
and βsubunit.

56. Functions of microtubules
• Determine the shape of the cell
• Give structural strength to the cell
• Act like conveyer belts which allow the movement
of granules, vesicles, protein molecules and some
organelles like mitochondria to different parts of the
cell
• Form the spindle fibers which separate the
chromosomes during mitosis
• Are responsible for the movement of centrioles and
the complex cellular structures like cilia.

57. Intermediate Filaments

58. • Intermediate filaments are the structures that
form a network around the nucleus and extend
to the periphery of the cell.
• Diameter of each filament is about 10 nm.
• The intermediate filaments are formed by
made up of fibrous proteins

59. Functions of intermediate filaments
• Intermediate filaments help to maintain the
shape of the cell.
• These filaments also connect the adjacent
cells through desmosomes.

60. Microfilaments

61. • Microfilaments are long and fine thread like
structures with a diameter of about 3 to 6
nm.
• These filaments are made up of non-tubular
contractile proteins called actin and myosin

62. Functions of microfilaments
i. Give structural strength to the cell
ii. Provide resistance to the cell against the
pulling forces
iii. Are responsible for cellular movements like
contraction, gliding and cytokinesis (partition of
cytoplasm during cell division).

63. Cell Nucleus

64. Structure of the Nucleus
the nuclear
envelope
nucleoplasm
chromatin
the nucleolus
] the two major
types of materials
The Nucleus

65. Features
The nucleus is the genetic control center
of a cell.
In most cells, there is only one nucleus. It
is spherical, making up 10% of the cell’s
volume.

66. Nuclear Envelope
The nuclear envelope is a double-layered
membrane perforated with pores, which
control the flow of material going in and
out of the nucleus.
The outer layer is connected to the
endoplasmic reticulum, communicating
with the cytoplasm of the cell. The
exchange of the large molecules (protein
and RNA) between the nucleus and
cytoplasm happens here.

67. Nucleoplasm
A jelly-like (made mostly of water) matrix
within the nucleus
All the other materials “float” inside
Helps the nucleus keep its shape and serves
as the median for the transportation of
important molecules within the nucleus

68. Chromatin &
Chromosomes
Chromosomes contain DNA in a condensed form
attached to a histone protein.
Chromatin is comprised of DNA. There are two types
based on function.
Heterochromatin: highly condensed,
transcriptionally inactive mostly located
adjacent to the nuclear membrane
Eurochromatin: delicate, less condensed
organization of chromatin, located in a
transcribing cell
* Transcribing means equivalent RNA copies are being made from the DNA to create proteins.

69. Functions
The nucleus is “command center,” as it
controls all functions of the cell.
It regulates the actions of the cells.
It has message to synthesis the cell’s
proteins.