Chemistry
Session
Session Objectives
1. The cell and energy cycle
2. Introduction to carbohydrates
3. Classification of carbohydrates
4. Preparation of glucose
5. Chemical properties of glucose
6. Proteins
7. Structure of protein
Chemical Structure of Living Matter:
An Overview
Cellular Organization
Photosynthesis
Plants convert carbon dioxide and water into
carbohydrates via photosynthesis.
– 100 sequential steps convert six moles of CO2 to
one mole of glucose.
– Carbon-14 radiolabelling helped to identify
individual steps.
Conversion of solar energy to chemical energy.
– Light reactions.
Synthesis of carbohydrates.
– Dark reactions.
Carbohydrate Metabolism
Energy Relationships in Metabolism
Carbohydrates
Hydrates of carbon: Cx(H2O)y.
Classification
Monosaccharides
The simplest carbohydrates.
Oligosaccharides
Two to ten monosaccharides
attached together.
Polysaccharides
Starch and cellulose.
Monosaccharides
Sixteen possible aldohexoses.
Three occur widely.
D-glucose, D-mannose and D-galactose.
Predominantly in the cyclic form.
Reducing sugars.
Reduce Cu2+ to Cu2O and form a brick red precipitate.
Fehling’s solution (tartrate) or Benedict’s solution (citrate).
Preparation of glucose
From sucrose (cane sugar): sucrose is boile with
dilute HCl or H2SO4 in alcoholic solution, glucose and
fructose are obtained in equal amounts,
H
C12H22O11  H2O 
 C6H12O6  C6H12O6
Sucrose
Glucos e
Fructose
Form starch: Hydrolysis of starch
H
(C6H12O5 )n  nH2O 
(C6H12O6 )n
Properties of glucose
1. Acetylation of glucose with acetic acid anhydride gives a
pentaacetate confirming the presence of five hydroxyl
groups in glucose.
2. Glucose reacts with hydroxlamine to give monoxime and
adds a molecule of hydrogen cyanide to give a cynohydrin.
3. Glucose reduces ammoniacal silver nitrate solution
(Tollen’s reagent) to metallic silver and also Fehling
solution to reddish brown cuprous oxide and itself gets
oxidised to gluconic acid.
4. On oxidation with nitric acid glucose as well as gluconic acid
both yield a dicarboxylic acid, saccharic acid. This indicates
the presence of a primary alcoholic group in glucose.
Properties of glucose
5. Glucose on prolonged heating with HI forms n-hexane, suggesting
that all the six carbon atoms in glucose are linked linearly.
6. D-Glucose reacts with phenyl hydrazine to give glucose
phenylhydrazone which is soluble. In excess of
phenylhydrazine gives osazone.
7. On heating with conc. Solution of sodium hydroxide glucose
first turns yellow, then brown and finally resignifies. With
dilute NaOH glucose undergoes a reversible isomerization and
is converted into a mixture of D-glucose, D-mannose and Dfructose.(Lobry de Bruyn-van Ekenstein reaarangement)
Ring Closure in Glucose
- and -D-glucose
Glucose doesn’t give shiff’s test and it doesn’t react with sodium
bisulphite and ammonia.
Pentaacetate of glucose doesn’t doesn’t react with hydroxylamine
indicating absence of —CHO group.
Mutarotation: the spontaneous change in specific rotation of an
optically active compound is called mutarotation.
  D  ()
Equilibrium
  D  ()
glucos e
mixture
 52.5o
Disaccharides
Made of two monosaccharides (same or different).
Hydrolysed to giving two monosaccharides.
Two Common Polysaccharides
Main sources are wheat maize, rice, potatoes, barley etc.
Chief constituent of the cell walls of plants.
Proteins – Amides from Amino Acids
Amino acids contain a basic amino group and an acidic
carboxyl group.
Joined as amides between the NH2 of one amino acid
and the CO2H the next.
Chains with fewer than 50 units are called peptides.
Protein: large chains that have structural or catalytic
functions in biology.
Structures of Amino Acids
In neutral solution, the COOH is ionized and the NH2 is
protonated.
The resulting structures have “+” and “-” charges (a
dipolar ion, or zwitterion).
They are like ionic salts in solution.
The Common Amino Acids
20 amino acids form amides in proteins
All are -amino acids - the amino and carboxyl are
connected to the same C
They differ by the other substituent attached to the
 carbon, called the side chain, with H as the fourth
substituent except for proline
Proline, is a five-membered secondary amine, with
N and the  C part of a five-membered ring.
Abbreviations and Codes
Alanine A, Ala
Leucine L, Leu
Arginine R, Arg
Lysine K, Lys
Asparagine N, Asn
Methionine M, Met
Aspartic acid D, Asp
Phenylalanine F, Phe
Cysteine C, Cys
Proline P, Pro
Glutamine Q, Gln
Serine S, Ser
Glutamic Acid E, Glu
Threonine T, Thr
Glycine G, Gly
Tryptophan W, Trp
Histidine H, His
Tyrosine Y, Tyr
Isoleucine I, Ile
Valine V, Val
Zwitterionic Form of an Amino Acid
The pH at with amino acid doesn’t move to
any electrode, called isoelectric point.
Peptides
A tripeptide
N-terminal
C-terminal
Gly-Ala-Ser
Amino Acid Sequence in Beef Insulin
Protein Classification
1. Simple proteins yield only amino acids on hydrolysis.
2. Conjugated proteins, which are much more common than
simple proteins, yield other compounds such as
carbohydrates, fats, or nucleic acids in addition to amino
acids on hydrolysis.
3. Fibrous proteins consist of polypeptide chains arranged
side by side in long filaments
4. Globular proteins are coiled into compact, roughly
spherical shapes.
Most enzymes are globular proteins.
Some Common Fibrous and Globular
Proteins
Protein Structure
1. The primary structure of a
protein is simply the amino
acid sequence.
2. The secondary structure of a
protein describes how
segments of the peptide
backbone orient into a regular
pattern.
3. The tertiary structure describes
how the entire protein
molecule coils into an overall
three-dimensional shape.
4. The quaternary structure
describes how different protein
molecules come together to
yield large aggregate
structures
Structure of Proteins: -Helix
-Keratin
A fibrous structural protein coiled into a right-handed helical
secondary structure, -helix stabilized by H-bonding
between amide N–H groups and C=O groups four residues
away a-helical segments in their chains.
Structure of Proteins: -Sheet
Linkages Contributing to Tertiary Structure
Fibroin
Fibroin has a secondary structure called a -pleated
sheet in which polypeptide chains line up in a parallel
arrangement held together by hydrogen bonds
between chains.
Myoglobin
Myoglobin is a small globular protein containing 153
amino acid residues in a single chain.
8 helical segments connected by bends to form a
compact, nearly spherical, tertiary structure.
Internal and External Forces
Acidic or basic amino acids with charged side chains
congregate on the exterior of the protein where they can be
solvated by water
Amino acids with neutral, nonpolar side chains congregate on
the hydrocarbon-like interior of a protein molecule
Also important for stabilizing a protein's tertiary structure are
the formation of disulfide bridges between cysteine residues,
the formation of hydrogen bonds between nearby amino acid
residues, and the development of ionic attractions, called salt
bridges, between positively and negatively charged sites on
various amino acid side chains within the protein
Protein Denaturation
The tertiary structure of a globular protein is the result of
many intramolecular attractions that can be disrupted by a
change of the environment, causing the protein to become
denatured
Solubility is drastically decreased as in heating egg white,
where the albumins unfold and coagulate
Enzymes also lose all catalytic activity when denatured
Thank you