Water is the most abundant constituent of cells and plays a critical role in biochemical reactions. It has unique physical and chemical properties due to its dipolar structure and ability to form hydrogen bonds between molecules. These hydrogen bonds allow water to solvate a wide range of molecules and influence their structure. Water also acts as a reactant and product in many metabolic reactions and helps maintain pH balance in the body. Disruptions to water balance can cause health issues.

1. 2. Chemical
Constituents of Cells
and
Water

2. Contents
• The major chemical constituents of cells
• 2.1. General chemical composition
• (Elementary composition of the human body)
• 2.2. Water
a.Chemical properties and structure
b.As a media for biochemical reaction

3. The cell and cell organelle
 The cell is the structural & functional unit of living
systems.
 Every cells have a molecular & chemical basis to
constitute the life.
 Cell is composed mainly of 6 basic biomolecules:-
water
Carbohydrates
 proteins
 lipids
 nucleotides & electrolytes
3

4.  Cells are natural reaction vessels for biochemical reactions.
 The internal organization of the cell is perfect(all events are well
coordinated)
 The cell respond to the external signals/stimuli & modifies its metabolic
activities with proper maintenance of internal environment.
 Biochemical reactions take place in a very small size of the cell through:
 Physiological mild conditions of temp, presure, pH & in aqueous
medium.
• Cells are highly organized & they are compartmentalized.
 Compartmentalization is responsible for division of works.
 Different compartments of cell are responsible for d/t biochemical
processes:
 Examples: Cell membrane for regulating of nutrients, mitochondria for
energy production, lysosomes for defense, ribosome for protein
synthesis…

5. • Basic structure of the typical human cell

9. Major biochemical function of cell organelles

11. Themajorstructuralcomponentsofthebodyareproteins,carbohydratesand
lipids
Proteins are building blocks and catalysts;
as structural units, they form the architectural framework of our
tissues;
as enzymes, together with helper molecules known as coenzymes
and cofactors.
Carbohydrates and lipids are used primarily as energy sources.
Their storage forms in the body are glycogen and triglycerides.
Carbohydrates are also present as glycoconjugates with proteins
and lipids and form the backbone of biological membranes.
Chemical variables, such as pH, oxygen tension, inorganic ion and
buffer concentration, define the homeostatic environment in
which metabolism takes place. Small changes in this environment
can be life-threatening.

12. Blood is the medium for exchange of gases, fuels, metabolites and
information between tissues.
Blood plasma is an accessible ‘window’ on metabolism and serves as
a source of clinical information for the diagnosis and management of
disease.
The blood coagulation system and immune system defend against
disturbances in this environment.
Biological membranes compartmentalize metabolic pathways. They
play a fundamental role in ion and metabolite transport, and also in
transducing signals from one cell to another. Most of the body’s
energy is consumed to maintain ion and metabolic gradients across
biological membranes; nerve and muscle function, and the red
blood cell are critically dependent on membrane potentials, which
are used for nerve transmission, muscle contraction and
maintenance of cell shape.

13. Energy released from nutrients is distributed throughout the cell in
the form of adenosine triphosphate.
Central pathways of carbohydrates and lipid metabolism are access
routes to other processes.
Pyruvate from glucose via glycolysis, in mitochondria may also
produce metabolites that are the starting points for synthesis of
amino acids, proteins, lipids and nucleic acids.
Genome and cellular signalling. The genome provides the
mechanism of conservation and transfer of genetic information,
the regulation of the expression of constituent genes and the
control of protein synthesis.
Cell growth, cellular signalling and repair mechanisms are
important for survival, and the time- dependent decline in these
systems leads to ageing and development of diseases.

14. Cell Membrane
• Contains cell contents
• Double layer of phospholipids & proteins
Polar Hydrophilic head Interacts with water, Hydrophobic tail

15. Movement Across the Plasma Membrane
• A few molecules move freely
– Water, Carbon dioxide, Ammonia, Oxygen
• Carrier proteins transport some molecules
– Proteins embedded in lipid bilayer
– Fluid mosaic model – describes fluid nature of a lipid
bilayer with proteins

16. Membrane Proteins
Channels or transporters - Move molecules in one direction
Receptors - Recognize certain chemicals

17. Membrane Proteins
Glycoproteins -Identify cell type
Enzymes -Catalyze production of substances

18. Cytoplasm
• Viscous fluid containing organelles
• components of cytoplasm
Interconnected filaments & fibers
Fluid = cytosol
Organelles (not nucleus)
storage substances

19. Nucleus
• Control center of cell
• Double membrane
• Contains
– Chromosomes
– Nucleolus

20. Nuclear Envelope
• Separates nucleus from rest of cell
• Double membrane
• Has pores

21. DNA
• Hereditary material
• Chromosomes
– DNA
– Proteins
– Form for cell division
• Chromatin

22. 22

23. Nucleolus
• Most cells have 2 or more
• Directs synthesis of RNA
• Forms ribosomes

24. 24

25. Endoplasmic Reticulum
• Helps move substances within cells
• Network of interconnected membranes
• Two types
– Rough endoplasmic reticulum
– Smooth endoplasmic reticulum

26. Rough Endoplasmic Reticulum
• Ribosomes attached to surface
– Manufacture protiens
– Not all ribosomes attached to rough ER
• May modify proteins from ribosomes

27. 27

28. Smooth Endoplasmic Reticulum
• No attached ribosomes
• Has enzymes that help build molecules
– Carbohydrates
– Lipids

29. Golgi Apparatus
• Involved in synthesis of plant cell wall
• Packaging & shipping station of cell

30. Golgi Apparatus Function
1. Molecules come in vesicles
2. Vesicles fuse with Golgi membrane
3. Molecules may be modified by Golgi

31. Golgi Apparatus Function (Continued)
4. Molecules pinched-off in separate vesicle
5. Vesicle leaves Golgi apparatus
6. Vesicles may combine with plasma membrane
to secrete contents

33. Lysosomes
• Contain digestive enzymes
• Functions
– Aid in cell renewal
– Break down old cell parts
– Digests invaders

35. Mitochondria
• Have their own DNA
• Bound by double membrane

36. Mitochondria
• Break down fuel molecules (cellular respiration)
– Glucose
– Fatty acids
• Release energy
– ATP

37. 37

39. Endocytosis
• Movement of large material
– Particles
– Organisms
– Large molecules
• Movement is into cells
• Types of endocytosis
– bulk-phase (nonspecific)
– receptor-mediated (specific)

40. Process of Endocytosis
• Plasma membrane surrounds material
• Edges of membrane meet
• Membranes fuse to form vesicle

41. Forms of Endocytosis
• Phagocytosis – cell eating
• Pinocytosis – cell drinking

42. Exocytosis
• Reverse of endocytosis
• Cell discharges material

43. Exocytosis
• Vesicle moves to cell surface
• Membrane of vesicle fuses
• Materials expelled

44. WATER
-Chemical properties and structure
-As a media for biochemical reaction
44

47. BIOMEDICAL IMPORTANCE
Water is the predominant chemical component of living
organisms. Its unique physical properties, which include the
ability to solvate a wide range of organic and inorganic
molecules, derive from water’s dipolar structure and
exceptional capacity for forming hydrogen bonds.
The manner in which water interacts with a solvated
biomolecule influences the structure of each.
An excellent nucleophile, water is a reactant or product in
many metabolic reactions. Water has a slight propensity to
dissociate into hydroxide ions and protons.

48. The acidity of aqueous solutions is generally reported
using the logarithmic pH scale. Bicarbonate and other
buffers normally maintain the pH of extracellular fluid
between 7.35 and 7.45.
Suspected disturbances of acid–base balance are
verified by measuring the pH of arterial blood and the
CO2 content of venous blood.
Causes of acidosis (blood pH <7.35) include diabetic
ketosis and lactic acidosis. Alkalosis (pH >7.45) may
follow vomiting of acidic gastric contents.

49. Regulation of water balance depends upon
hypothalamic mechanisms that control thirst, on
antidiuretic hormone (ADH), on retention or excretion
of water by the kidneys, and on evaporative loss.
Nephrogenic diabetes insipidus, which involves the
inability to concentrate urine or adjust to subtle
changes in extracellular fluid osmolarity, results from
the unresponsiveness of renal tubular osmoreceptors to
ADH.

50. Biological structures and processes can only be
understood in terms of the physical and chemical
properties of water.
PROPERTIES OF WATER
Water’s peculiar physical and solvent properties stem
largely from its extraordinary internal cohesiveness
compared to that of almost any other liquid.

53. Water Molecules Associate through Hydrogen Bonds
• The electrostatic attractions between the dipoles of two water
molecules tend to orient them such that the O-H bond on one
water molecule points toward a lone-pair electron cloud on the
oxygen atom of the other water molecule.
• This results in a directional intermolecular association known as a
hydrogen bond (Fig. 2-2), an interaction that is crucial both to the
properties of water itself and to its role as a biochemical solvent. In
general, a hydrogen bond may be represented as D-H------A, where D-
H is a weakly acidic “donor group” such as N-H or O-H, and A is a
lone-pair-bearing and thus weakly basic “acceptor atom” such as N or
O. Hence, a hydrogen bond is better represented as A,
where

54. the charge separation in the bond arises from the
greater electronegativity of D relative to H. The
peculiar requirement of a central hydrogen atom rather
than some other atom in a hydrogen bond stems from
the hydrogen atom’s small size: Only a hydrogen
nucleus can approach the lone-pair electron cloud of an
acceptor atom closely enough to permit an electrostatic
association of significant magnitude.