BIOLOGICAL MOLECULES

All living organisms are made from biological molecules

Polymer --->hydrolysis --> monomer
monomer ---> condensation ---> polymer


CARBOHYDRATES: CxCH2Oy
i) monosaccharide     = only one unit ------ sugar
ii) disaccharide          = 2 units ----- sugar
iii) polysaccharide     = ∞ units ------ non- sugar

all mono and disaccharides are reducing except sucrose

(Sucrose: not reducing sugar, contains hexose sugar)


-hydrolysis of the glycosidic bond gives a gradual release of monosaccharide, releasing reducing sugars and using water



Monosaccharides: (CH2O) general formula
   glucose, fructose and galactose



                                                               Hexose sugars

1- Glucose: (C6H12O6) contains C=O bond

properties:
- small molecules
- water soluble
- 1 gram releases 16 KJ of energy
- disturbs osmotic balance
- can easily cross through plasma membranes
- can be used for release of energy
- can be stored in form of starch and glycogen


Structure of glucose:
- glucose molecules can be formed in 3 forms,
1) straight chain
2) α- glucose
3) β- glucose
- both alpha and beta glucose have 5 carbons present in the hexagon while the 6th carbon lies outside, attached to carbon 5
- in alpha glucose, C-1 hydroxyl (-OH) group is bellow the plain. while in beta glucose (-OH) is placed above the plain



2- Fructose:
 It is monosaccharide and a hexose sugar








α Fructose










  β Fructose





    2CH12O6---------> C12H22O11+ H2O

glycosidic bond between them

Polysaccharides:
*many monomers bound together in glycosidic units
*all polysaccharides are made from repeated same monomers
*present in human muscle
*glycosidic bonds


Example
1- starch
2- glycogen
3- cellulose


1) Starch: unbranched component
- final amylose/ amylopectin complex is insoluble and doesn't affect the osmotic properties of the cell


*starch and glycogen are both storage carbohydrates while cellulose is a structural carbohydrate






Amylose:

- linear helix
- alpha helix
- (1-4) links

Amylopectin:
- (1-4 & 1-6) links






- Starch is a polysaccharide made from 2 molecules, amylose and amylopectin


Amylose                                                                        Amylopectin
- α- glucose                                                                   - 1-4 and 1-6 link
- glycosidic bond                                                           - branched
- α helix
- 1-4 link
- unbranched
- is the reason for blue/black
   colour change



2) Glycogen: 
- glycogen and amylopectin both have 1-4 glycosidic bonds, glycogen contains more 1-6 branches than amylobectin
- it is a storage polysaccharide for animal cells and fungi
- exactly like amylopectin, but branching is more extensive

(cellulose and amylopectin both have C-O-C)

3) Cellulose: dependent on hydrogen bond
- structural polysaccharide
- made from β-glucose to form a straight chain
- has 1-4 links (β 1-4 only)
- these links are formed alternately bellow and above the plain thus cancelling out the effect of coiled shape and resulting in a straight chain
- being a straight chain it attains strength
- many cellulose molecules are linked together to form a micro fibril this enhances the strength
- many micro fibrils are arranged together to form  fibres
- cell wall is made from a mesh like arrangement of these fibres
- because of cellulose the cell wall is able to give a definite shape to the plant cell and helps in maintaining turgidity of cell
- synthesized from identical sub-units 




PROTEINS: 20 different amino acids
when a peptide bond is formed 1 amino acid loses a hydroxyl group from its carboxyl group
- weak H+ bond, strong disulfide bond and weak ionic bond hold a molecule of protein in shape
- the functional group 'R' defines its chemical nature
- they can be polar, non-polar, hydrophilic or hydrophobic
- there can be the presence of the sulfide group


Significance of proteins:
- make up a large component of the living body, for example: enzyme, cells etc.


Primary structure of proteins: (peptide bond)
- made by sequencing of specific amino acids
- bonded by peptide bond (covalent bond)
- all polysaccharides joined by peptide bonds are covalent. for example, a polypeptide chain is made from 200 amino acids



Secondary structure of protein: (hydrogen bond)
- a secondary structure results from many -H bonds made among the amino acids of same polypeptide chain
- there are different coiling which results due to -H bonds
- most common are α helix and β pleats sheets
- α helix reults due to more organized hydrogen bonds when they are between the oxygen of carboxylic group with H of amino group of amino acids placed 4 distance apart



Tertiary structure of protein: (disulfide bond)
- less organised beta pleats from folds
- defined by formation of different bonds among functional group of different amino acids
for example:
1- hydrogen
2- ionic
3- hydrophobic interactions
4- disulfide


~Ionic bond: when 'R' group has a polar group then an ionic bond is formed
~hydrophobic interactions: takes place between non- polar groups
~Disulfide bonds: (glycoprotein) very strong and can only be broken down by using reducing agents like urea

- ionic bonds break due to change in pH and temperature
- hydrophobic interaction are broken down by a change in temperature
-- Hydrogen can be broken by both --

*tertiary structure is formed as a 3D structure of a polypeptide chain




Quaternary structure of protein:
- if a protein is made of 2 or more polypeptide chains then it is said to have quaternary structure
- protein can be of 2 types

           Fibrous                                                                  Globular 
- linear structure                                                         - spherical structure
- structural                                                                  - functional protein
- keratin, collagen                                                       - haemoglobin
- they are all water insoluble                                      - always hydrophobic groups present
                                                                                      clustered on the inside while
                                                                                      hydrophilic groups are on
                                                                                      the outside
                                                                                    - all water soluble

*Keratin: forms hair, nail, and the outer
 layer of skin, making these structure water proof.



Haemoglobin: (depends on hydrogen bond)
- globular protein
- has a quaternary structure
- made from a 4 polypeptide chains of which 2 are identical α chains and 2 β chains
- each chain has amino acids with hydrophobic -R- groups contained in the centre shielded by hydrophilic -R- groups on the outer sides
- each chains contain a haem as a prosthetic group (made from IRON) [non protein part]
- haem can be bind with an oxygen molecules
- 4O2 molecules can bind with 4 haem groups
- consists of 4 polypeptide, each with a prosthetic group




Collagen:
- insoluble fibrous protein
- found in skin, tendons, cartilage, bones teeth and walls of blood vessels
- structural protein
- has a quaternary structure
- consist of 3 polypeptide chain each in shape of a loose helix [not alpha helix]
- almost every third amino acid in each polypeptide is glycine
- it can with stand large pulling forces without structure or breaking and is also flexible
- many collagen molecules are laid close together to enhance the strength and make covalent bonds among C-N of 2 different chains
- the molecules don't start and end at the same point rather have staggered ends so that there is not a weak point in the structure

[collagen and deoxyribonucleic acid contains, carbon, hydrogen, oxygen and nitrogen]





Lipids: (contains C=O bonds)
- fats and oil
- fats are solid at room temperature whereas oils are liquid at room temperature
- lipid is a polymer made from condensation of 3 fatty acids and 1 glycerols releasing 3 water molecules
- high energy density (38KJ/mol)
- helps in insulation
- make up blubber
- used as energy storage molecules






Fatty acids:
they can be saturated when they have all single bonds in the hydrocarbon chains

[ a kink is a bend shown due to a bend in hydrocarbon chain]

Triglyceride: 
- they have lower ratio of O2 to carbon compared with carbohydrates
- they are non- polar
- less denser than water
- higher energy value than carbohydrates
- higher proportion of H+ than in carbohydrates



Phospholipids:
- phospholipid molecule is a polymer made from replacement of 1 hydrogen chain by 1 phosphate
- make plasma membrane
- cell membrane/ plasma membrane are made from a bi-layer of phospholipids in such a way that the hydrocarbon tails [hydrophobic] are sandwiched between the phosphate heads
- in such an arrangement the phosphate heads being hydrophilic stay compatible with water on the outside and inside
- the placement gives cell membrane their property of partial permeability
- since much of the width of the membrane is hydrophobic so small and non- polar molecules can easily pass through the small gaps formed in the phospholipid molecules

Water: (dependent on hydrogen bond)
- because of partial positive and partial negative charges on the hydrogen and oxygen, water acts as solvent for charged ions
- it also act as solvent for transport of dissolved glucose and urea
- it has a high specific heat capacity needed to change state, either into vapour or into ice
- water shows an odd quality at 4°C thus ice floats on water
- ice insulates the water underneath due to convection current which maintain the aquatic life even in cold temperature, water molecules have strong inter molecular attraction due to which cohesion and adhesion results in water bodies so that small insects can walk on
- due to Cohesion forces, water molecules make a column to be pulled up through the xylem vessels
- Adhesion means water molecules tend to cling on to the surface along which they pass and this property helps in movement of water molecules along the cell wall of the plant calls




sodium(Na)/ potassium(K)= needed for maintaining electrolyte 
                                               balance and stability of membrane
Magnesium(Mg)= control of chlorophyll 
Iron(Fe)= red blood cells
Calcium(Ca)= 1- bones and teeth
                        2- at synapses 
Chloride ions(Cl−)= needed to dilute the mucus formed in respiratory tract