Lesson 2: Review: Organic Compounds

Question 1

Carbon

Answer 1

Carbon is unique in several
ways;

Carbon has 4 available
binding sites

Carbon can form single,
double or triple covalent
bonds

Carbon is able to bond
covalently with a large
number of elements

Carbon can form both long
chains and rings of atoms

Tetrahedral structure
when bound allows for
isomerism

Question 2

Organic Compounds

Answer 2

Compounds containing carbon found in living organisms

Not including carbonates, hydrogen carbonates, CO2 or CO

Often based upon a skeleton of carbon

Evolution has chosen a few for use in living organisms

There are four principal groups: sugars, fatty acids, amino acids and nucleotides

Question 3

Carbohydrates

Answer 3

Organic molecules commonly referred to as
sugars.

Made up of carbon, hydrogen and oxygen. The
general formula is C(H2O)n

There are three types of carbohydrates

Monosaccharides

Disaccharides

Polysaccharides

Question 4

Monosaccharides

Answer 4

Monosaccharides are the simplest form of carbohydrates.

Contain a carbonyl group and at least two hydroxyl groups.

Empirical formula is CH2O.

6 carbon monosaccharides include glucose, fructose and galactose. (hexose
sugars)

5 carbon monosaccharides include ribose and deoxyribose (pentose sugars)
All hexose sugars have the
molecular formula C6H12O6.
However, there are many
isomers.

Question 5

Straight Chain and Cyclic
Structure

Answer 5

The previous slide contained the straight chain structure of three
monosaccharides.

The carbons are numbered starting at the carbonyl group.

However, in aqueous solution monosaccharides adopt a ring structure.

This occurs as a result of an intermolecular reaction between the
aldehyde group on C1 and the OH group on C5

Question 6

Ring Structure Isomers

Answer 6

The intermolecular reaction that
causes the ring structure to from
in aqueous solution produces an
asymmetric carbon at C1.

Therefore, there are two ring
structure isomers of glucose called
α-glucose and β-glucose.

The difference has an effect on the
properties of their polymer.

Question 7

Condensation Reactions

Answer 7

Monosaccharides undergo condensation reactions in order to from
disaccharides and polysaccharides.

Hydroxide groups on adjacent monosaccharides react to form a bond, known as
a glycosidic link, and a molecule of water.

Two molecules of α-glucose condense to form a 1-4 glycosidic link which
produces the disaccharide maltose.

Question 8

Disaccharides

Answer 8

Disaccharides are composed of two monosaccharides joined together.

Combining different monosaccharides produces different disaccharides.

Disaccharides are soluble molecules that can be broken down into their
component monosaccharides through acid hydrolysis or by enzyme catalysed
reactions (digestion)

Question 9

Polysaccharides

Answer 9

Polysaccharides are long chains of monosaccharides held together by glycosidic
bonds.

Have large molar mass, are not sweet, are insoluble or slightly soluble in water
and are non-reducing.

Polysaccharides differ in the nature of their recurring monosaccharide, their
bonds, the length of their chains and the degree of branching.

Question 10

Glucose Based Polysaccharides

Answer 10

There are three common glucose based polysaccharides.

Starch

Glycogen

Cellulose

Question 11

Starch

Answer 11

Starch is a polymer of α-glucose and is the
main form of carbohydrate storage in
plants.

Starch can form a compact spiral structure
and is stored in the starch granules of
plants.

There are two forms of starch

Amylose – a straight chain polymer of
α-glucose with 1-4 glycosidic bonds.

Amylopectin – a branched polymer of
α-glucose with both 1-4 and 1-6
glycosidic bonds.

Question 12

Glycogen

Answer 12

A polymer of α-glucose.

Main form of carbohydrate storage in
animals, found in the liver and muscle
tissue.

Similar to amylopectin but with more 1-6
glycosidic branches.

Question 13

Cellulose

Answer 13

A polymer of β-glucose.

It is the structural material
in the cell walls of plants

A linear polymer with 1-4
β-glycosidic linkages

This forms an uncoiled
structure with alternate
glucose molecules upside
down.

This allows cellulose to
form cables known as
microfibrils that give a rigid
structure.

Question 14

Digestion

Answer 14

Polysaccharides are broken down into their monosaccharide units during the
digestive process.

The human body has enzymes that digest starch and glycogen through a series
of enzyme controlled reactions (hydrolysis) during which the glycosidic links are
broken.

The human body does not produce enzymes that work on cellulose.

Question 15

Carbohydrate Functions

Answer 15

Sugars (mono and disaccharides) small molecules soluble in water:

Maintenance of osmotic balance (e.g. salts in blood plasma, plant cell turgidity);

transport of energy reserves (e.g. glucose in blood or sucrose in sap);

energy substrate (respiration and photosynthesis);

energy store (sugar cane);

flavouring (fruits); reward (nectar);

precursors (building blocks) of polysaccharides, nucleotides and amino acids

Polysaccharides Large molecules insoluble in water:

Osmotically inactive carbohydrate storage, (seeds, roots, chloroplasts);

Structural (cellulose in plants)

Question 16

Lipids

Answer 16

Lipids contain carbon, hydrogen and oxygen

More hydrogen (more reduced) than carbohydrates.

Lipids are insoluble in water but they are soluble in polar solvents (organic
solvents such as alcohols, acetone, chloroform etc.)

The most common lipids are fats, oils, steroids and phospholipids.

Question 17

Fats and Oils

Answer 17

The major component of fats and oils are glycerides.

Glycerides are composed of glycerol and fatty acids.

Glycerol is a molecule of three carbons, each of which contains an
alcohol group.

Fatty acids are long chain carboxylic acids.

An esterification reaction takes place between the carboxyl group of a
fatty acid and each of the hydroxide groups of the glycerol.

This forms an ester link

A glycerol condenses with three fatty acids to form a triglyceride.

The three fatty acids that form a triglyceride do not have to be the
same.

Question 18

Fatty Acids

Answer 18

Fatty acids differ in the length of
the carbon chain (14-22) and the
position and number of double
bonds between carbons.

Fatty acids with no double
bonds are called saturated

Fatty acids with one double
bond are called
monounsaturated

Fatty acids with more than
one double bond are called
polyunsaturated

Question 19

Saturated Fatty Acids

Answer 19

Saturated fatty acids have high
melting points, are solid at room
temperature.

These are known as fats and are
derived from animals.

These properties are the result
of the carbon –carbon single
bond angles being tetrahedral
(109.5) which allows them to
pack closely together which
leads to significant van der
Waals forces between
molecules.

Question 20

Unsaturated Fatty Acids

Answer 20

Unsaturated fatty acids have
lower melting points and are
liquid at room temperature.

These are known as oils and are
derived from plants.

The properties are caused by
the carbon-carbon double bond
having a bond angle of 120
which creates kinks in the chain
that make packing close
together difficult which leads to
lower intermolecular forces.

Question 21

Essential Fatty Acids

Answer 21

The human body can synthesize all of the fatty acids it requires except two:

Linoleic acid (omega-6-fatty acid)

Linolenic acid (omega-3-fatty acid)

The terms omega-6 and omega-3 indicate the position of the first double bond
in the molecule relative to the terminal -CH3 group to represent its distance
from the carboxyl group.

These fatty acids must be obtained in the diet.

They are found in plants and fish.

These essential fatty acids play a role in prostaglandin production and help
lower LDL cholesterol.

Question 22

Digestion of Fats and Oils

Answer 22

Since fats and oils are insoluble they must be broken down into fatty acids and
glycerol in order to be transported.

This is done through the process of hydrolysis which is controlled by a group of
enzymes known as lipases.

These are the slowest molecules to break down in the digestive system as
lipases act sequentially in different parts of the digestive system.

Question 23

Phospholipids

Answer 23

Similar to triglycerides but
they only have two fatty
acids condensed onto the
glycerol.

The remaining hydroxide
group condenses with a
phosphate group.

Phospholipids vary in the
fatty acids attached and
the group that binds with
the phosphate.

The most common
phospholipid is lecithin.
Similar to triglycerides but
they only have two fatty
acids condensed onto the
glycerol.

The remaining hydroxide
group condenses with a
phosphate group.

Phospholipids vary in the
fatty acids attached and
the group that binds with
the phosphate.

The most common
phospholipid is lecithin.

Question 24

Other Lipids

Answer 24

Steroids: multiple ring structures (e.g. cholesterol)

Functions: cell membrane structure, digestion (help to emulsify fats), hormones
(testosterone etc), vitamins (e.g. Vitamin D), poisons

Waxes: long chain alcohol + fatty acids

Water proof coating to leaves, fur feathers, insect exoskeletons.

Used by bees to construct their honey combs.

Question 25

General Lipid Function

Answer 25

STRUCTURAL: biological membranes (phospholipids, steroids, glycolipids), cushioning
(fat deposits round the kidneys)

ELECTRICAL INSULATION: myelin sheath round axons

THERMAL INSULATION: subcutaneous fat deposits.

WATER PROOFING: waxes and oils

ENERGY STORE AND SUBSTRATE: very condensed form of energy (37 kJ g-1) used by
animals and seeds.

HORMONES: steroids

VITAMINS: precursor to Vitamin D

BUOYANCY: oil droplets in plankton

Question 26

Lipids in the Diet

Answer 26

The food industry uses addition reactions to
chemically modify the fats that we eat.

This decreases the degree of unsaturation across
the fat.

This creates a fat with a higher melting point
which allows it to be solid at room
temperature for easy transport and storage.

This also gives the fat a longer shelf life.

Hydrogenation requires the fat to be exposed to
heat and pressure which affects the remaining
double bonds by altering the position of the groups.

The groups are altered from a cis position to a trans
position.

These are known as trans fats.
Trans fats are present in many processed foods and are always present if the
food is labelled “partially hydrogenated”

Consuming trans fats raises the level of LDL cholesterol which is a risk factor for
heart disease and reduces HDL cholesterol which protects against heart disease.

Question 27

Effects of Excess Lipids

Answer 27

Atherosclerosis is caused by lipid deposits on the walls of major blood vessels.

The low solubility of lipids allows this deposit to occur. The deposits lead to
high blood pressure and heart disease.

Obesity is caused by the storage of excess lipids in adipose tissue.

Linked to many health issues such as diabetes, cancer and heart disease.

Question 28

Proteins

Answer 28

These are organic compounds
that contain N,C, H, and O.

Proteins are responsible for
most of the chemical functions
that take place in the cells of the
body.

Proteins are polymers of Amino
Acids

An amino acids contain an
amine functional group at
one end and a carboxylic
acid functional group at the
other end

Amino acids bond together
in long chains to form
proteins

There are 20 naturally occurring
amino acids

Question 29

Types of Amino Acids

Answer 29

Amino end and carboxyl end can be ionised
NH3+ and COO- to give acidic and basic
characteristics

Most amino acids are “neutral” as they
contain one acid group and one alkaline
group.

The residues are side chains which give the
individual properties to the amino acid
(acidic, basic, neutral and nonpolar)

Some amino acids contain side chains
(R groups) that contain –NH2 groups
which makes them basic amino acids;
while others contain –COOH in their
side chains which makes them acidic
amino acids.

Question 30

Functions of Amino Acids

Answer 30

Protein synthesis, energy reserve, hormones (thyroxin)

20 different amino acids used in protein synthesis though others do occur in
nature.

Essential amino acids cannot be synthesised by the organism and must form part
of their diet

Question 31

The Formation of Proteins

Answer 31

Amino acids undergo
condensation reactions to
form substituted amides in
the presence of enzymes.

Example:

Glycine and alanine can
combine to form two
possible dipeptides.
A dipeptide is a substituted amide
made up of two amino acids joined by
a peptide bond or peptide linkage.

Water is formed in this enzyme
controlled reaction.

If a compound contains many peptide
bonds it is considered a polypeptide,
and after some folding, a protein.

Question 32

Protein Conformation

Answer 32

A functional protein is not just a polypeptide chain but one or more polypeptide
chains twisted, folded and coiled into a molecule of unique shape. This
three-dimensional shape is known as the protein conformation.

Protein conformation determines the function of the protein.

Question 33

Four Levels of Protein Structure

Answer 33

When a ribosome synthesizes polypeptide the chain folds spontaneously to
assume the functional conformation of that protein.

This is reinforced by a variety of chemical bonds between parts of the chain

In this, three levels of structure have been identified; primary, secondary and
tertiary

A fourth level of structure known as quaternary occurs when a protein contains
two or more polypeptide chains

Question 34

Primary Structure

Answer 34

The primary structure of a protein is its unique sequence of amino acids.

Even a slight change in this primary structure can affect the its conformation and
ability to function

Ex. Sickle-cell disease is an inherited blood disorder in which one amino acid
is substituted for another in a single position in the primary sequence of
hemoglobin

Question 35

Secondary Structure

Answer 35

Most proteins have segments of
their polypeptide chain repeatedly
coiled or folded in patterns that
contribute to the overall
conformation of the protein.

This is a result of the hydrogen
bonds at regular intervals along the
polypeptide backbone

Alpha (α) Helix

A type of secondary structure

A coil held together by a
hydrogen bond every fourth
peptide bond

Pleated Sheet (β sheet)

A type of secondary structure

The polypeptide chain folds
back and forth or where two
regions are parallel to each
other

Hydrogen bonds between the
parallel regions holds this
structure together

Question 36

Tertiary Structure

Answer 36

This is a series of irregular contortions caused by bonding between the side
chains(R-groups) of the various amino acids.

Two major factors contribute to tertiary structure;

Hydrophobic interactions

Disulfide bridges

Question 37

Hydrophobic Interactions

Answer 37

As the polypeptide folds into its conformation, the amino acids with nonpolar
(hydrophobic) side chains usually move towards the core of the protein, out of
contact with water.

This keeps the hydrophobic side chains together in localized clusters

Caused by the behaviour of water molecules as they hydrogen bond to one
another and hydrophilic side chains.

Question 38

Disulfide Bridges

Answer 38

Strong covalent bonds form where two cysteine monomers (AA with sulfhydryl
groups – SH) are brought close together by the folding of the protein.

The sulfur of one cysteine bonds to the sulfur of a second and the disulfide
bridge rivets parts of the protein together.
Hydrogen bonds between
side chains and ionic bonds
(salt bridges) between
positively and negatively
charged side chains also
help stabilize tertiary
structure

Question 39

Quaternary Structure

Answer 39

When two or more polypeptide
chains aggregate to form one
functional macromolecule.

This is the overall protein
structure that results from the
aggregation of these polypeptide
subunits.

Collagen

A fibrous protein that has
helical subunits supercoiled
into a triple helix

Hemoglobin

A globular protein that
consists of two kinds of
polypeptide chains, two of
each kind for four subunits
per molecule

Question 40

Nucleotide Structure

Answer 40

DNA and RNA are made up
of nucleotides.

Each Nucleotide is made up
of 3 parts;

Phosphate group

Nitrogenous base

Pentose sugar

Question 41

The Sugar

Answer 41

In DNA the sugar is called
deoxyribose.

Deoxyribose is a pentose
sugar because it has 5 carbon
atoms in its structure.

In RNA the sugar is called ribose

Ribose is also a pentose sugar
with a 5-carbon ring structure

Question 42

The Phosphate Group

Answer 42

The acidic part of the nucleotide

Connects the 5’ carbon of one nucleotide to the
hydroxide (-OH) group on the 3’ carbon of the
neighbouring nucleotide.

Question 43

The Nitrogenous Bases

Answer 43

These are bases that contain nitrogen

The nucleotide is named for the nitrogenous base attached

There are 4 nitrogenous bases found in DNA

There are 4 nitrogenous bases found in RNA (Thymine is replaced by Uracil)

These fall into two categories:

Purines – Adenine and Guanine

Pyrimidines – Thymine and Cytosine and Uracil

Question 44

Purines

Answer 44

The nitrogenous bases that
have a double-ringed
structure

Question 45

Pyrimidines

Answer 45

The nitrogenous bases that have
a single-ringed structure

Question 46

DNA & RNA Molecular Structure

Answer 46

In DNA nucleotides form
long strands which
hydrogen bond across two
antiparallel strands to
forma double stranded
molecule in the shape of a
double helix.

In RNA nucleotides form
long chains in a single
stranded molecule.