Objectives

• To discuss how the structure and properties of water relate to the role
that water plays as a medium of life.
• To explain the relationship between the structure and function of
glucose.
• To explain the relationship between the structure and function of
sucrose.
• To discuss how the molecular structure of starch, glycogen and
cellulose relate to their functions in living organisms.
Aspects of Biochemistry • To describe the molecular structure of a triglyceride and its role as a
source of energy.
MODULE 1: CELL AND MOLECULAR BIOLOGY

Objectives cont’d Introduction

• To describe the structure of phospholipids and their role in membrane • All life on Earth shares a common chemistry. This provides indirect
structure and function. evidence for evolution.
• To describe the generalised structure of an amino acid, and the formation
and breakage of a peptide bond. • Despite their great variety, the cells of all living organisms contain only a
• To explain the meaning of the terms: primary, secondary, tertiary and few groups of carbon-based compounds that interact in similar ways.
quaternary structures of proteins.
• To outline the molecular structure of haemoglobin, as an example of a • There are 4 major classes of biomolecules:
globular protein, and of collagen, as an example of a fibrous protein. • Carbohydrates
• To carry out tests for reducing and nonreducing sugars, starch, lipids and • Lipids
proteins. • Proteins
• To investigate and compare quantitatively reducing sugars and starch. • Nucleic acids
 Introduction cont’d
Introduction cont’d
• Carbohydrates are commonly used by cells as
respiratory substrates. They also form structural
components in plasma membranes and cell • Nucleic acids carry the genetic code for the
walls.
production of proteins. The genetic code is
common to viruses and to all living organisms,
• Lipids have many uses, including the bilayer of providing evidence for evolution.
plasma membranes, certain hormones and as
respiratory substrates.
• The most common component of cells is water;
• Proteins form many cell structures. They are hence our search for life elsewhere in the universe
also important as enzymes, chemical involves a search for liquid water.
messengers and components of the blood.

Structure of water

Solvent Properties

pH properties

Water and Heat capacity

Temperature Regulation Heat of fusion
Heat of vaporization
Mixtures
Surface Tension

Capillarity
Water and Mixtures
Solutions
Dispersions: Colloids
Aspects of Biochemistry – Part A suspensions
 Objectives Water
• To describe with diagrams the structure of water molecule. • Abundant on earth.

• To describe how water molecules are affected by pH and temperature.

• Covers ~3/4 of the earth’s surface
• To explain the terms surface tension, capillarity and solvent. • Molecular structure
• ~70% of human body weight. • 1. size
• To explain the relationship between the properties of water and its role in living
organisms. • 2. polarity
• Makes life possible. • 3. angle of the bonds
• To differentiate homogenous & heterogenous dispersions systems
• 4. forms hydrogen bonds
• To define colloid and emulsion. • Structure facilitates function

Elements, Size, Ability to form Hydrogen bonds

Polarity &
Angle of bonds
• Molar mass = 18.01528 g/mol
• A partially +ve charged H atom
lies between two partially -ve
• Composed of 2 elements – charged O atoms
Oxygen and Hydrogen
• O more electronegative than
H • the H atom is attracted to both O
• So - electrons stay closer to atoms and is considered to be
nucleus of O atom than of H acting as a bond between them
atom
• Therefore - H has partial
positive charge & O has • H bonding influences
partial negative charge.
arrangement of water molecules
 Water’s influence Properties - Affecting Non-polar
on life Compounds
• Solvent •
• ionic salts
• polar compounds
• Effect on nonpolar compounds
• Fluidity
• Surface tension
• Capillarity
• Temperature Regulation
• Specific Heat Capacity
• Heat of Vaporization
• Heat of Fusion
• pH properties

Properties of water Solvent Properties - Dissolving ionic salts

• •
 Solvent properties of water – dissolving
Properties of water - Fluidity
polar compounds
• •

Properties – Surface Tension Properties – Surface Tension cont’d

• "The property of the surface of a liquid that • Cohesive forces at the surface of a liquid result in
allows it to resist an external force, due to the surface tension.
cohesive nature of its molecules.” • the surface of the liquid occupies the least possible
surface area & behaves as if a film is present which
• The molecules at the surface of a glass of water resists being separated.
do not have other water molecules on all sides
of them. • Water has a higher surface tension than any
other liquid due to hydrogen bonding.
• Consequently, they cohere more strongly to
those directly associated with them (in this case,
next to and below them, but not above). • It takes force to overcome this molecular attraction
and break the water’s surface.
 Properties – Surface Tension cont’d Properties – Surface Tension cont’d

• Many small organisms rely on

surface tension to settle on water
or to skate over its surface.

• Basilisk ‘Jesus’ lizard, Pond

skaters, Water Striders.

Properties of water - Temperature

Properties of water
regulation
Capillarity • Water has high thermal capacity due to H bonding
• the rise of water in narrow tubes due to H bonds.
• Raising the temperature of a liquid involves increasing the average
• Water is attracted to hydrophilic substances such as glass (adhesion). kinetic energy (rate of motion) of its molecules; rate of motion is
• The force is greater than gravity and water ‘crawls’ up the tube. resisted by H bonds.
• As it moves it pulls along adjacent molecules to which they are H-bonded (cohesion).
• Eventually, the water in the centre of the tube also rises.
• Prevent large fluctuations of temperature in cells and in environment
• Movement of water along cell walls, through soil, and through the xylem in
(keeping the temperature relatively constant) thus making it ideal for
plants. animal and plant life.
 Properties of water - Heat capacity Properties of water - Heat capacity cont’d

• Much heat energy absorbed by water is therefore used to break H • Constant temperature environment important for enzymes which
bonds before molecular motion of water molecules can be increased catalyze chemical reactions.
and temperature raised.
• Readily absorbs heat generated by metabolic activity without greatly
• Therefore, it takes a lot of heat to raise temperature of a given increasing the cell’s temperature.
amount of water.

• Biochemical processes in organisms can tolerate small temperature

ranges; are affected by extremes & even a little fluctuation in may be
detrimental.

Properties of water - Conductivity

•

Phase of
Matter
 Properties of water Properties of water - Heat of vaporization

•
•

Properties of water Properties of water

Temp: Heat of Fusion •
• With its high heat capacity, ice requires relatively large amounts of
heat energy to thaw.
• Liquid water must also lose a relatively large amount of heat energy
to freeze.
• Contents of cells and their environments are also less likely to freeze
since it requires so much heat loss to convert liquid water to solid
water.
• Ice crystals cause great damage to plasma membrane and organelles if
they develop inside cells.
 Properties of water - Freezing properties Properties of water - Freezing properties
• The fact that ice floats, facilitates aquatic life during winter.
•
• Solid ice floats on liquid water; frozen crust provides insulation
against additional heat loss; water beneath ice stays warm enough to
remain liquid; aquatic life live in liquid instead of freezing death in
ice.

• If ice was dense it would sink to the bottom of lakes and rivers and
force more water to the surface, to in turn freeze and sink; most of our
planet’s water supply would be solid & unavailable.

Properties of water Properties of water – pH

Acids and Bases •
• The pH of a solution is measured by the conc. of H+
• The pH scale ranges from 0 to 14; Below pH 7 is acidic; above pH 7
basic
• A base/alkaline is a H+ (Proton) acceptor; An acid is proton donor
• Pure water has a pH of 7 (neutral); produces equal amounts of H+ and
OH– ions.
• Intracellular spaces of most organisms range from pH 7.2 to 7.4
• Water dilutes acids or bases
 Dispersion systems - Mixtures Mixtures/ Dispersion systems
Mixtures •

• May be of variable composition (differ from

molecules & compounds).

• Common in nature; most materials found in

nature are not pure.

• Separated by physical processes (as opposed to a

chemical reaction).

Dispersion systems- Solutions Dispersion systems- Solutions

• Common in nature Solutions
• Solutions = solvent + ≥ 1 solutes
• Solvent – dispersing medium in which the solutes are dissolved. H2O in
• Extremely important for life processes. biological systems
• Body fluids of all life forms are solutions: • Solutes - usually molecules or ions. dispersed phase
• intracellular, circulatory, tissue, excretory. (cytoplasm, blood, haemolymph,
sap, urine) • Proportions of solute and solvent vary from one solution to another
(whereas pure substances have fixed composition).
• Concentrations of the solutes give valuable clues on the state of health • Liquids, solids, or gases can act as either a solvent or solute.
of organisms. • Liquids - most common solvent – water in biological systems
 Dispersion systems - Homogenous
Dispersion systems- heterogeneous mixture
mixtures.
True solutions Suspensions
Solute molecules relatively small in comparison to the solvent molecules and • Solute-like particles are large and immediately settle out after mixing with the
dissolve.
solvent.
• E.g., Sand stirred into water; sand solute does not dissolve in water solvent.
• Non-liquid solvents of homogenous mixtures:
• Gases – in which other gases are dissolved
• air solutions. Colloids
• Solid metals - in which a non-metal may be dissolved • Solute-like particles are suspended in the solvent-like phase Intermediate kind
• Dental fillings: silver, copper & mercury. of mixture (between homogenous solution & heterogeneous, suspension.
• Steel: iron & graphite (C)
• Solid metals - in which other solid metals may be dissolved to form alloys • E.g., clay in water; clay particles disperse throughout the water, but are visible,
• Brass: copper & zinc and eventually settle out.
• Bronze: copper & tin

Dispersion systems - Colloids Dispersion systems- Colloids

• Particles of dispersed solute are large compared to solvent but small Hydrophobic Colloids
enough to remain suspended; settling is negligible. • Hydrophobic solutes need emulsifying agents in order to exist in polar
• Solute neither dissolves nor sediments solvents (to form colloids).
Emulsions
• Solute particles large enough to make mixture appear cloudy (or • Two liquids are immiscible and there do not dissolve in each other. E.g.,
opaque) because light is scattered as it passes through. Suspension oil in water. – hydrophobic interaction. both liquids separate. How to form a
colloid?
therefore heterogenous.
• Emulsifiers coat the solute to prevent its coagulation into a separate phase.
• Eg., Mayonnaise: vegetable oil (hydrophobic solute) emulsified in water (polar
solvent) by egg yolk (emulsifying agent).
• If left for a long time, flocculation occurs, that is, the particles come • Eg. Milk: fat emulsified in water by casein.
together then settle out.
 Colloids
• Colloidal particles suspended in a solution may adsorb much of
the solvent.
• E.g., Charcoal mixture; used in industry to remove colors from solutions, since
it adsorbs many dyes and carry these with it when separated from the solution.

• Adsorption - Adhesion of the molecules of liquids, gases and Carbohydrate Structure

dissolved substances to the surfaces of solids
• (as opposed to absorption, in which the molecules actually enter the absorbing
medium). and Function
Aspects of Biochemistry Part B

Objectives – On successful learning of Carbohydrates

this topic you will be able to:
•
• Levels of organization
• Monosaccharides e.g., glucose
• Disaccharides e.g., sucrose
• Polysaccharides e.g., starch, cellulose,
glycogen
• Isomerism – structural & stereoisomeris
• Roles in energy transfer, structural
frameworks, storage
 Carbohydrates cont’d Carbohydrates cont’d
• In biochemistry, carbohydrates are often referred to as ‘saccharides’ (= ‘sugars’)
• Saccharides comprise a group that includes sugars, starch, and cellulose.
• The saccharides are divided into three chemical groups:
• monosaccharides, e.g., glucose
• disaccharides, e.g., sucrose
• polysaccharides, e.g., starch, cellulose.

Functions of carbohydrates:
• Monosaccharides and disaccharides, the smallest (lower molecular weight)
carbohydrates, are commonly referred to as ‘sugars’. 1. Storage and release of energy
2. Structural roles within the cell

Monosaccharides Monosaccharides cont’d

• Carbohydrate molecule containing one sugar unit • Classified according to the number of carbon atoms in each molecule.

• Simple, sweet sugars

No. of Category Name
• Soluble in water Carbons
3 Triose
• Cannot be broken down into smaller carbohydrate units by 4 Tetrose
hydrolysis (splitting of a larger molecule into smaller ones by the 5 Pentose
chemical addition of water). 6 Hexose
7 Heptose
• No. C atoms range from 3 to 7.
 Monosaccharide Structure Monosaccharide Structure cont’d

•
Structural isomers

• Glucose: Aldehyde or aldose sugar.

• Carbonyl group on C #1.

• Fructose: Ketone or keto sugar.

Both functional
• Carbonyl group on C #2 groups are
Functional groups collectively called
carbonyls

Monosaccharide Structure cont’d Monosaccharide Structure cont’d

• • Straight chain structures

Structural
formulae

glyceraldehyde ribose fructose glucose

Molecular
formulae
 Monosaccharide Structure cont’d Monosaccharide Structure cont’d
• Pentose (5C) and Hexose (6C) sugars can flip into ring form, in • α-glucose: the OH group on C1 projects downwards
which the chain links up with itself. • β-glucose: the OH group on C1 projects upwards, above the plane of
• Sides branches: some terminate as H atoms; others as OH (hydroxyl) the ring.
groups. • These molecules that are nonsuperimposable mirror images of one
• α-glucose and β-glucose are stereoisomers (same formula but another, like left and right gloves.
different spatial arrangements of atoms).

Monosaccharide Structure cont’d Monosaccharide Functions

• • Monosaccharides are an energy source
• Most of them provide about 4 Calories (kilocalories) per gram, just like
other carbohydrates.
• Glucose is the main fuel for the body cells.
α-fructose • Fructose also participates in metabolism.
• Galactose is found in erythrocytes of individuals with B-type
of blood.
• Ribose is part of ribonucleic acid (DNA, RNA) in cells.
• Monosaccharides are non-essential nutrients, which means your body can
produce all of those it needs for proper functioning from other nutrients, so
you do not need to get them from food.
β-fructose
 Monosaccharide Functions cont’d Disaccharides
Absorption of Monosaccharides: Effect on Blood Sugar Levels • Two monosaccharide molecules link together form a disaccharide.
• Monosaccharides, like most nutrients are absorbed in the small intestine. • Sweet
• They can be absorbed without previously being broken down by the • Soluble in water and crystalizable
intestinal enzymes.
• Glucose and galactose are absorbed easily, completely; while fructose can • Most commonly transported carbohydrate in invertebrate animals, plants
be absorbed only slowly and incompletely. and other organisms
• After ingestion, glucose and galactose quickly raise the blood sugar (they • glucose most common in vertebrates
have high glycemic index), while fructose raises blood sugar only mildly • Formed by the action of enzymes such as amylase on starch in vertebrate
and slowly (it has low glycemic index). digestive system.
• During digestion, all carbohydrates have to be broken down into • E.g., Lactose: glucose + galactose
monosaccharides in order to be absorbed.

Disaccharides cont’d Disaccharide - Sucrose

• • Table sugar
• α glucose + β fructose =sucrose
• Main transport carbohydrate in plants, abundant in stem of sugar cane
& sugar beet.

H from C1 of
glucose and OH 1, 2 glycosidic
from C2 of fructose bond
 Disaccharide – Sucrose cont’d Disaccharide - Maltose
• Non-reducing sugar • α glucose + α glucose = maltose

• Carbonyl groups give carbohydrates their reducing property

• Sucrose’s Carbonyl group ‘tied up’ in the glycosidic bond (C #2 of

fructose combines with C #1 of glucose).

α α
• (c=o on C1 of glucose (aldehyde) but C2 of fructose (ketone)

Hydrolysis of Disaccharides Hydrolysis of Disaccharides cont’d

• • Hydrolysis of sucrose produces the
monomers.
• Sucrose α glucose + β fructose
• Sucrose is an important source of energy
for humans.
• The enzyme sucrase hydrolyses sucrose
to glucose and fructose.
• Fructose molecule is the rearranged
(isomerised) to form glucose.
• Therefore, each sucrose molecule
produces two glucose molecules that can
be used in respiration.
 Hydrolysis of Disaccharides cont’d Hydrolysis of Disaccharides cont’d
• Maltose α glucose + α glucose
• Disaccharides such as sucrose would give a negative test with
• Using the enzyme maltase Benedict’s solution
• However, if HCl is added and the solution is heated
• The glycosidic bonds will break – separating sucrose to glucose and
fructose.
• If an alkali such as NaOH is then added to neutralise the excess acid
– we will get a positive Benedict's test due to the presence of
carbonyl groups.

Polysaccharides Polysaccharides cont’d

•
• By chaining free monosaccharide molecules into an insoluble
polysaccharide, sugar can be stored in a compact form

• A polysaccharide sugar:
• Cannot diffuse out of the cell
• Exerts no osmotic action within cells.
• Can be hydrolyzed to release energy.
 Polysaccharides cont’d Polysaccharides – Starch
Starch • Starch (20% amylose and 80% amylopectin)
• Amylose
• Main food storage molecule of plants. • Alpha Glucose units linked by 1,4 glycosidic bonds
• potatoes & cereals are rich in starch. • Long and unbranched

• Not found in animals.

• Amylopectin
• Alpha Glucose units linked in short chains by 1,4 glycosidic bonds
• Polymer of alpha glucose
• Branched every 24-30 glucose units
• Branches formed by 1,6 glycosidic bonds
• Mixture of polymers amylose (20%) & amylopectin (80%).

Polysaccharides – Starch cont’d Polysaccharides – cont’d

 Polysaccharides – Starch cont’d Polysaccharides – Starch cont’d
• Starch molecules (Amylose) adopt a stable Testing for starch
spiral/helical configuration.
• Iodine is not very soluble in water
• 6 glucose units per turn; spiral held together
by hydrogen bonds • Therefore, the iodine reagent is made by dissolving iodine in water in
the presence of potassium iodide.
• Testing for starch
• The space in the middle of the helix (formed by • This makes a linear triiodide ion complex with is soluble. The
amylose) fits iodine molecules which form a blue- triiodide ion slips into the coil of the starch causing an intense blue-
coloured complex with starch (amylose). black color.

Testing for Starch Polysaccharides - Cellulose

• Polymer of β glucose by 1,4 glycosidic bonds
• Single chain may contain up to 10,000 sugar units with total length
5μm.
• Beta glucose forms parallel chains which interlink by H bonds to
form microfibrils, then fibers
• Different from starch whose long chain is coiled into a helix and whose OH
groups (which could form H bonds) are orientated to project inwards so there
are no cross linkages.
• Glycosidic bonds, plus H bond cross linkages between adjacent
chains makes it tough and stable.
Polysaccharides Polysaccharides - Cellulose
– Cellulose
cont’d
• Forms structures like plant cell walls

• Completely insoluble and hard to digest

• Cellulase (enzyme needed to hydrolyze cellulose) rarely in animals; they
cannot digest cellulose.

• Microscopic cellulose decomposers break down dead plant material to

re-release energy

Polysaccharide - Glycogen Polysaccharide – Glycogen cont’d

• Storage polysaccharide of animals & fungi

• Stored mainly in liver & muscle cells

• Easily converted to glucose.

• Alpha Glucose units linked in short chain by 1,4 glycosidic bonds.

• Branched every 8-12 glucose units
• Branches formed by 1,6 glycosidic bonds
 Polysaccharide - Chitin
Polysaccharide – Chitin cont’d
• Structural polysaccharide in arthropods (insects, spiders,
crustaceans), nematodes & fungi

• Polymer of N-acetylglucosamine (2-acetamido-2- deoxy-D-glucose)

• Beta 1-4 glycosidic linkage

• Structure resembles that of cellulose, except that the hydroxyl

groups on C# 2 have been replaced by acetylamino groups.

Polysaccharide Summary Polysaccharide Summary cont’d

• Carbohydrates perform numerous roles in living organisms.

• Monosaccharides e.g. glucose, fructose provide energy for living

organisms e.g. animals

• Polysaccharides serve for the storage of energy (e.g. starch and

glycogen) and as structural components e.g. cellulose in plants and
chitin in arthropods).
 Objectives

1. To describe in words & diagrams the structure of amino acids.

2. To outline how proteins are formed by peptide bonds.
Protein structure and 3. To explain how proteins are organized at primary, secondary,
tertiary, quaternary levels.
4. To state the functions of proteins
Function 5. To classify proteins according to structure/solubility, composition,
function.
Aspects of Biochemistry Part C

Introduction Proteins
Proteins
• Elements: C, H, O, N and sometimes S.
• More than 50% of the dry mass of an organism. • Monomers: amino acids.
• Numerous important functions • Made from combinations of 20 amino acids
• Regulation of movement of substances into and out of cells (channel & carrier • the same 20 amino acids, in different arrangements, are present in all living
proteins). organisms).
• Regulation of gene expression • Unique sequence of amino acids give each protein unique properties.
• Catalysis
 Amino acids - Basic structure Amino acid - Structure
•
A carbon atom (asymmetric) is bonded to:
• a carboxyl group (COOH)
• an amino group (HNH)
• a hydrogen atom and
• a variable group (‘R’)

Protein Formation
Can you • Proteins: polymers of amino acids
Identify the
four major • Amino acids join by covalent peptide bonds between the carboxyl
parts of the group of one amino acid and the amino group of the neighboring
amino acid.
20 known
amino acids?
• Dehydration Synthesis/ Condensation Reaction.

• OH from the carboxyl end of one amino acid and H from the amino
end of another.
 Dipeptide

Protein
Formation
• Continued condensation
leads to the addition of
further amino acids
resulting in the formation
of a long chain called a
polypeptide.

Levels of Protein Structures Primary structure

• The specific linear sequence of amino acids in a polypeptide.
• Formed by:
• the linear chain of amino acids of which the polypeptide is composed, plus
• any disulphide bridges formed by the presence of >1 cysteine molecule
 Primary structure Secondary structure
• The organization of portions of the polypeptide chain based
• Different proteins have different sequences on how amino acids react with each other.

• Sequence • Three major types of secondary structure:

• determines function.
• alpha helix,
• is dependent on the genetic code in the DNA of the cell.
• beta-pleated sheet
• a random coil.

Secondary structure - Alpha helix

Secondary
• Formed by a polypeptide chain or part of a chain.
structure - Beta
• Formed when hydrogen bonding occurs between pleated sheet
the amino group in one peptide bond and the • Formed by a polypeptide chain or
carbonyl (C═0) group (of the COOH) of another parts of the chain.
close by peptide bond. • Formed when two or more
sections of a polypeptide chain lie
side by side and hydrogen
bonding occurs, holding them
• Found in alpha keratin; the major protein of together.
• Found in Fibroin (silk protein)
wool, hair, nails, feathers, horns.
• Less stretchable than alpha helix.
 Tertiary structure Tertiary structure cont’d
• Formed by further folding & coiling of the secondary structure of the • Hydrogen bonds – forms between CO (of carboxyl) and NH (of
polypeptide
amino group).
• Strongly influenced by the interactions of R groups in different parts of the • Ionic bonds – formed between R groups with positive and negative
chain. charges.
• Disulphide bonds – links the S atoms of the sulphydryl group of two
• Formed by hydrogen, ionic, disulphide, and covalent bonds or by cysteine amino acids.
hydrophobic interactions between R groups.
• Hydrophobic interactions –protein folds in such a way as to shield
• Results in the final compact 3D shape. hydrophobic groups while exposing hydrophilic groups to aqueous
• E.g., myoglobin, enzymes. surroundings.

Tertiary Interactions cont’d Quaternary structure

• The secondary, tertiary and quaternary structures are not random, but • Interaction of more than one polypeptide chain
highly specific, and precisely dictated by the primary structure that • Quaternary structures may be held together by a variety of bonds
is by the sequence of amino acids in the chain. (similar to tertiary structure)
• E.g., haemoglobin consists of four polypeptide chains (two alpha and
two beta).
 Biuret test
Summary of
the Four
• Biuret test - testing for proteins
Levels of using copper (II) sulfate
Protein solution in an alkaline
Structure environment (NaOH).

• The copper ions reflect off

closely clustered amide groups
of proteins casting a violet color
to a solution with proteins.

Properties of proteins Classification of Proteins

• Anything that affects the specific 3D structure of a protein will affect
its properties. Structure and solubility:

• Disruption of structure is called denaturation • fibrous

• Globular
• The protein unfolds, losing its tertiary & secondary structure. Primary • intermediate
structure is unaffected.
• Under suitable conditions, reforming of the structure can occur
(renaturation).
 Classification of Proteins cont’d Fibrous and Globular Proteins
There are two main classes of protein tertiary structure:

• Fibrous proteins are generally composed of long and narrow strands

and have a structural role (they are something)

• Globular proteins generally have a more compact and rounded shape

and have functional roles (they do something)

Fibrous and Globular Proteins cont’d Globular Protein - Haemoglobin

• Globular - These tend to form ball-like structures where •
hydrophobic parts are towards the centre and hydrophilic are
towards the edges, which makes them water soluble. They usually
have metabolic roles, for example: enzymes in all organisms, plasma
proteins and antibodies in mammals.

• Fibrous - They proteins form long fibres and mostly consist of

repeated sequences of amino acids which are insoluble in water. They
usually have structural roles, such as: Collagen in bone and cartilage,
Keratin in fingernails and hairɂ

 Fibrous Protein- collagen Fibrous Protein- collagen cont’d
• Composed of three polypeptide • This strength is increased as collagen molecules form further chains
chains wound around each other. with other collagen molecules
• Each of the three chains is a coil
itself. • Collagen molecules also form Covalent Cross Links with each other
• Hydrogen bonds form between
these coils, which gives the • Collagen molecules wrapped around each other form Collagen
structure strength. Fibrils which themselves form Collagen Fibres.
• This is important given collagen’s
role, as structural protein.

Objectives
• Describe (in words and diagrams) the structure of triglycerides and
their components

• Differentiate between saturated and unsaturated fatty acids

Lipid structure and • Describe the structure of phospholipids, steroids

Function • State the function and properties of different types of lipids.
Aspects of Biochemistry Part D
 Lipids Testing for Lipids
• Elements: C, H and O; Sudan Test
• less O, more C-H bonds than carbohydrates.
• Sudan IV is insoluble in water but soluble in lipids.
• Non-polar; doesn’t dissolve in water
• vital component of membranes which separate aqueous compartments • Sudan IV Test for lipids: Dark red Sudan IV is added
to a solution along with ethanol to dissolve any
• Will dissolve in non-polar substances possible lipids.
• alcohols, acetone, ether and chloroform.
• Positive test: Sudan IV will stain any lipids present
reddish-orange.

Lipids: Fats and Oils

Fats & Oils are esters
Testing for
Lipids cont’d
Emulsion
Test

• In organisms, lipids are usually made from glycerol (a 3C alcohol)

and fatty acids.
 Lipid components: Glycerol Lipid components: Fatty Acids
Glycerol • Fatty acids:
• 3C molecule. • methyl group at one end
• C atoms form the ‘backbone’ of the lipid. • hydrocarbon chain
• carboxyl group

• Each C bears an OH (hydroxyl) group. • The shorthand chemical formula for a fatty acid is
• 3 sites available to form ester linkages with fatty acids. RCOOH
• Glycerol + 1 FA= monoglyceride (monoacylglycerol) • Fatty acids can vary in two ways:
• Glycerol + 2 FA = diglyceride (diacylglycerol) • Length of the hydrocarbon chain
• Glycerol + 3 FA = triglyceride (triacylglycerol)
• The fatty acid may be saturated (mainly in animal fat) or
unsaturated (mainly vegetable oils, although there are
exceptions e.g., coconut and palm oil)

Lipid components: Fatty Acids cont’d Lipid components: Fatty Acids cont’d
Saturated fatty acids: Unsaturated fatty acids
• No double bonds between any C atoms. • Have ≥ 1 double bonds. Triglycerides have many.
• All possible bonds are used. • Tend to be oils at room temperature because
• Has maximum no. of H atoms possible • They have a lower melting point
• The chains are harder to pack closer together due to
• Usu
Usuallyy solid
so d at room e pe u e.
oo temperature. kinks in the tail.
 Lipid components: Fatty Acids cont’d Monoglycerides
• 1 fatty acid + glycerol = Monoglyceride.
• FA are Amphipathic
• The fatty acid can be joined on any of glycerol’s 3C

• Carboxyl end of molecule is hydrophilic

• will dissolve in aqueous solutions in the cell

• Hydrocarbon chain is hydrophobic

• will attach to or dissolve in nonpolar organic
compounds

Diglycerides Triglycerides/ Triacylglycerols

• Formed when two fatty acid are joined to glycerol. •
• The fatty acids can be the same or different.
 Triglycerides
• Solid or liquid at normal room temp.
• Solids are called “fats” or “butters” - Animals
• Liquids are called “oils” – Plants

• Less dense than water

• Animals in cold habitats usually have less saturated triglycerides to

Diagrammatic representations of prevent their bodies becoming rigid at the low temperatures.
Triglycerides

Triglyceride - Energy Storage Functions of lipids

• As triglycerides are hydrophobic - they do not cause osmotic water • Energy source & storage
uptake in cells so more can be stored. • Cell membrane structure
• Shock absorbers for internal organs
• Plants store triglycerides, in the form of oils, in their seeds and fruits. • Structural support
If extracted from seeds and fruits these are generally liquid at room • Accentuates the body
temperature due to the presence of double bonds which add kinks to • Insulation
the fatty acid chains altering their properties • Waterproofing
• Carries fat soluble vitamins (A,D,E,K)
• Mammals store triglycerides as oil droplets in adipose tissue to help • Supplies essential fatty acids
them survive when food is scarce (e.g., hibernating bears) • Hormones