BIOCHEMISTRY
The study of chemical constituents of living organisms.
Organic Molecules - Materials that are formed in the metabolism of living things.
The wide range of Organic compounds in living organisms may be conventionally divided into 5 major groups:
1 Carbohydrates
2 Lipids (Fats)
3 Amino Acids and Proteins
4 Nucleotides and Nucleic Acids
5 Group of complex organic molecules including Porphyrins (eg Haemaglobin, Chlorophyll)
CARBOHYDRATES
Defn: Containing Carbon, Hydrogen and Oxygen. Where the ration of H : O is 2 : 1 as in H2O (water)
General Formula CnH2nOn or C(h2O)n where n = whole No
There are a few exceptions eg Pentose (5C) sugars in DNA has a molecular formula C5H10O4, also Chitin has N as well as C,H,O.
Simple classification of C/H
Mono
Simple Oligo (mainly Di) Saccharides
(Sugar)
Carbohydrates
Poly
Complex ------Carbohydrate derivatives eg Chitin, Pectic Acid
Biological Importance
1 Energy Source Carbohydrates are principal respiratory substrates
2 Structural Compounds eg Cellulose (CW of all plant cells)
Lignin
3 Storage Compounds eg 1. Starch
(common plant storage never in animals)
Plants
2. Sucrose ( eg sugar cane, sugar beet)
3. Inulin
Animals - 4. Glycogen (eg mammalian liver
4 Glycoside Formation Wide variety of compounds/ functions eg colouration in flowers (see later )
CLASSIFICATION
The basic sugar unit = the saccharide . The group is classified according to the No of units
1 sugar unit = Monosaccaride
2 sugar units = Disaccharide
Many sugar units = Polysaccharide
NB The Di and Tri saccharides are also called Oligosaccharides. DES (Oligo = ‘Few’)
Nomenclature (naming C/H) - commonly used is the suffix (ending) OSE to indicate a C/H ie:
Gulcose Cellulose Fructose etc
C/H in more detail…….
A Monosaccharides
General There are the building blocks of other important C/H’s n in the general formula is 2-8. All monosaccharides are:
a Sweet tasting
b Soluble in water
c Form crystals
d Reducing sugars (see below)
e Are subdivide according to C atom No
Nomenclature 3C atom M/S = Triose sugars (occur in resp. glycolysis)
4C atom M/S = Tetrose sugars (photosynthesis)
5C atom M/S = Pentose sugars
6C atom M/S = Hexose sugars
7C atom M/S = Heptose suagars
Chemical Nature
Aldose sugars ~ process ALDEHYDE gp. (-CHO)
Monosaccharides
are either
Ketose sugars ~ process KETO gp. (-C=O)
These chemical groups affect fundamentally the Chemical properties of a C/H
eg Aldose M/S = glucose
Ketose M/S = fructose
Reducing Sugar Properties (all M/S are reducing sugars). Both Aldose anmd Ketose M/S are capable of REDUCING Cu III (Cuprous) ® Cu II (Cuprous) in HOT, ALKALINE solution. When this reduction occurs as Cu II is insoluble it PRECIPITATES ® Brick Red/Orange Red ppt.
NB Benedicts Solution - Alkaline solution of Copper Acetate (Fehling solution also produces similar results)
NOTE Polymerised C/H’s have a free -OH (Hydroxyl group) and -H group on C, to be reducing sugars
General Chemical Test for all C/H = Barfoeds test (see separate note practical file.
HEXOSE MONOSACCHARRIDES
Here n = 6 \ subs in general formula C6 H12 O6 = molecular formula
Structural Isomeration
There are however a number of different ways of arranging molecules (configurations) for C6H12O6 ie 2 different structural versions of C6H12O6 are:
Fischer projections
CHO CHO
HO OH
HO
HO
HO
OH
OH OH
CH2OH CH2OH
2 More common sugars are:
CHO CH2OH
2 OH = O
HO 3 HO
4 OH OH
5 OH OH
OH2OH OH2OH
(Aldose sugar) glucose (Ketose sugar) fructose
The carbon atoms C2 C3 C4 C5 with 4 different groups attached are called asymetric carbon atoms allowing 24 different just 6 common.
Stereo - Isomerism
As with structural isomerism of the presence of asymmetric C atoms it is possible to have chemical groups attached to the 4 central C atoms in different positions so that minor images result.
This is -D- glucose ( form is called TRANS form) This is -D-glucose ( form is called CIS form)
The & form is fundamentally important when the sugars enter into combination with other sugars (polymerisation) to form molecules like starch and cellulose.
Polymerisation of ® cellulose Polymerisation of -D- glucose ® starch
NOTE THE 5C RING FORM
= The PYRANOSE Ring
GLYCOSIDE FORMATION
A very important monosaccharide characteristic is the ability to form compounds called glycosides where the OH group attached to 1C reacts with other groups (radicals or molecules) eg1 Phosphate Group ® Sugar Phosphates.
In more detail…..
1 Sugar Phosphates (Phosphate = PO2-4) P = Phosphate
* Glucose-1-phosphate is important in respiration see later.
Other glycoside include:
a Coloured compounds like ANTHOCYANINS ie RED ® PURPLE compound eg beetroot juice. ANTHOXANTHINS ie YELLOW ®CREAM eg Daffodil Petals.
b Toxic compounds (plant protection compounds - natural anti fungicide eg Cyanophoric* glycosides in cherry laurel, hawthorn (* give off -H HCN) Saponin glycoside eg digitalin (foxgloves).
Summary: Glycosides are
a A protective, reducing herbivore attack and fungal attack - toxic glycosides
b Play important part in pollination, coloured petals etc
c Play an important part in dispersal, coloured trunks etc
2 Oligosaccharides
These include C-H’s which on hydrolysis yields a small No of saccharide units ie 2,3 or 4 sugar units.
a Disaccharides These are a form of glycoside. The general formulae is (CnH2nO+CnH2nOn) - H2O
* Glycoside Nature
All Disaccharides are a form of glycoside as the 2nd sugar unit attaches (by condensation) to the OH group of sugar unit 1. see below:
Examples of D/S
1 Maltose (Malt sugar)
2 Cellobiose (not naturally occuring but the “monomer” of cellulose
3 Sucrose (cane sugar)
4 Lactose (milk sugar)
1 Maltose
Molecular formula C12H22O11 (ie n= 6 in the general formula)
formation - formed by CONDENSATION of 2 units of -D-glucose
Linkage is 1:4
Eqn:
Hydrosis of Maltose
1 By boiling in solution (v.slow)
2 By boiling with dil HC1 (fairly rapid)
3 Enzymatic hydrosis via maltose (fastest)
NB Maltose is usually synthesised by hydrolysis of starch
General Properties
1 Free OH and -H group attached to 1C \ REDUCING SUGAR
2 Maltose is the repeating unit (MONOMER) of Starch
3 Maltose (Milk Sugar) is produced in the “Malting” stage of brewing (1st step)
2 Sucrose
Molecular formula C12H22O11
Formation - formed by CONDENSATION of -D-fructose and -D-glucose (usually as a sugar phosphate)
Lineage 1:2
Eqn
Synthesis In PLANTS only. Made form glucose 1-P (glycoside) + fructose via enzyme SUCROSE PHOSPHORYLASE.
Hydrolysis of Sucrose
1 Boil in solution with dil HC1 (fairly rapid)
2 Enzymatic hydrolysis via SUCRASE
General Properties
1 NON-REDUCING sugar ie no free OH and -H group on 1C
2 Important as (a) Main TRANSLOCATE in the phloem of higher plants (b) storage carbohydrate in sugar beet and sugar cane.
3 Cellobiose
Molecular formulae C12H22O11
Formation - Formed by CONDENSATION of -D-glucose
Lineage 1:4
Eqn
Hydrosis of Cellobiose
1 Hot acid (very slow)
2 Enzymatic (cytase)
General Properties
1 Reducing sugar
2 Monomer - repeating units of cellulose
3 Does not occur naturally as the free sugar
4 LACTOSE
Molecular formulae C12H22 O11
Formation - by CONDENSATION of 1 unit of -D galactose and
1 unit of -D-glucose
Lineage 1:4
Eqn
Hydrolysis
1 Hot acid (very rapid)
2 Enzymatic
General Properties
1 REDUCING SUGAR
2 Forms 6% by dry weight of human milk
General Summary
1 May be reducing or non-reducing
2 Sweet tasting
3 Water soluble
4 Form crystals
POLYSACCHARIDES
General Introduction
These are an important group of carbohydrates. Two main divisions:
a Structural Polysaccharides eg Cellulose, Chitin, Lignin (wood)
b Storage Polysaccharides eg Starch, Glycogen and Insulin
General Formula
(CnHzn-2 On-1)x
Where n = 4-6
x = 100’s (sometimes 1000’s)
Genral Properties of P/S
Sugar properties lost all are:
1 Non sweet tasting
2 Non truly soluble in H2O (form collodial sols not crystaloid sols)
3 Non Cyrstaline
Structural P/S
In these polysaccharides the sugar unit residues present in the form the long chain molecules of the polymer are straight, and cross-linkages between chains occur giving the material its strength.
A Cellulose
From general formula n=6 (C6H10O5) 100’s
Formation the monomer is cellabiose which condense together in a 1:4 linkage.
Representation of a portion of celluboise molecule:
MACROSTRUCTURE
Each cellulose chain is thought to be at least 500 celluboise residues long and can be up to 5000.
H-bonding occurs between chains due to projecting OH groups forming a 3D lattice called a microfibril.
The long chain polymers of cellulose, may X-link due to H bonding between projecting -OH groups creating a 3D lattice arrangement which has considerable mechanical strength, the lattice arrangement creates a ‘bundle’ of cellulose polymers which is called a Microfibril.
In the primary and secondary cell walls of higher plants ,highly visible under the EM (usually heavy metal shadowed), are the Microfibrils, often arranged with bundles of microfibrils = MICROFIBRILS (Ref see handout - Cytology)
Diagram of a Microfibril of Cellulose
Commercial Importance of Cellulose
See Roberts p68 (Old Roberts)
Synthesis
2 enzymes involved
Cellobiose Cytose
-D glucose Cellobiose Cellulose
Photosynthesis (or from storage P/S)
Hydrolysis
1 Hot acid hydrolysis (very slow)
2 Enzymatic enzyme cellulose
Cellulose ,D - glucose and F
NB Cellulose is exclusive to the invertabrates (ie No Vertabrate makes cellulose) only larhe invertabrates = snail (in UK) eg Cellulose secreted by protazoan Trichonympha found in the gut of termites. Relation of trichonympha found in the gut of RUMINANTS (animals with Rumen - which acts as a fermentation chamber in the gut)
Test for Cellulose
Zinc-chlor-iodide solution (SHULTZES SOLUTION) deep blue colour = the result
Hemicellulose
A mixed bag. Hemicelluloses are present in the Primary and Scenondary cell walls of the plants they fill in the spaces between the cellulose microfibrils and the macrofibrils.
H Celluloses are polymers of (usually -D) sugars, OTHER than glucose eg PENTOSE (5C) sugars including - Xylose, Arabinose
HEXOSE (6C) sugars including - Galactose, Mannose
Hemicellulose molecules unlike cellulose may be branched.
Structural Carbohydrate - Derivatives
A derivative in this case is a molecule that has some C/H qualities but is not a C/H.
a PECTIC COMPOUNDS
Consist of Polymers of Sugar-acids, most common sugar acid is PECTIC ACID = a polymer of -D-galacturanic acid.
The Carboxyl (-COOH) or acid groups of pectic acid combine readily to form salts with divalent ions like Ca2+ or Mg2+ - The Ca/Mg acting as X-links between polymers ® very strong adhesive substances. Ca/Mg Pectates = the substance of the middle lamalla in plant cells.
Diagram of Ca/Mg Pectate
b CHITIN
Located in the exoskeletons of anthropods found in the cell walls of some fungi. Chitin is a polymer of acetyl glucosmine - this is the acetyl derivative of the N containing amino-sugar glucosamine. The linkages between monomers is 1:4
Lignin Tests
Chemical Test:
Macroscopic - acidified phloroglucinol ® red colour indicates lignin.
Microscopic - amiline chloride/sulphate ® yellow colour indicates lignin.
c LIGNIN (wood)
Closely related to the C/H’s but strictly speaking not a C/H.
Lignin is the chemical term for wood - the principal strengthening material for the Zudary cell wall in plant material. Lignin is a 3D polymer made up of Phenyl Propane residues.
Occurance lignified plant tissue are : a Xylem vessels
b Fibre cells eg sclerenchyma
collenchyma
Food Storage in C/H
In these polymers the sugar monomers are assembled in the alpha configuration. The linkages, principally 1-4 are all on thje same side of chains, the chains are \ not straight.
a Starch
Molecular formula (C6H10O5)x where x = 300-1000
There mare two natural forms of starch 1 is Amylose starch (35% of starch is soluble) the other is Amylopectin Starch.
Occurance: 1 Pea seeds = 100% Amylose Starch
2 Maize Seeds = 100% Amylopectin Starch
3 Most plants = mixture of both
1 Amylose (soluble starch)
Structure: This is a HELICALLY coited molecule which is made up of unbranched chain of 300-1000 -D-glucose residues the linkage is 1:4 (sometimes the odd -D-glucose residue is present)
Representation of Amylose Molecule
The average Mr is approx 60,000
Chemical test for amylose:
Reagent = Iodine (I2) Potassium Iodide (KI) solution - deep blue/black colouration + indicates amylose. + due to starch iodine complex.
Note: 1 Amylose + water ® Colloidal sol
2 Ideal storage/food reserve a Insoluble
b Low OP
c HEC (high energy compound)
d Large molecules (can’t escape)
3 AMYLOPECTIN
Structure This is a 2D branched chain of -D-glucose residues. Linkages are 1:4 & 1:6.
Representation of Amylopectin molecule:
Starch Synthesis
Starch phosphorylase
glucose - 1 - P Starch + X P1
(glycoside)
Starch Hydrolysis
Amylose - A
Amylopectin -B
1 Heating to 2000C A ® Shorter chains ® Maltose
B ® Shorter chains (dextrins)
2 Boil A/B with oil HCI ® dextrins ® Maltose ® glucose
3 Enzymatic hydrolysis
In animals -2 step process:
Step One Salivery AMYLASE Pancreatic AMYLASE
Amylase
Starch Maltose
(1 or 2)
Step Two Maltase (in pancreatic juice)
Maltose Glucose (-D)
In plants - enzyme complex - = DIASTASE completly hydrolyses starch
DIASTASE contains following enzymes Amylase
Amylase
R Enzyme
Maltase
AMYLOSE Hydrolysed by (& ) Amylase then Maltase in Diastase to