Amino acids
Fatty acids
Nucleotides
Unit 3: Signatures of Life
Area of Study 1: Molecules of life
Chapter 1: The Chemical Nature of Cells (p. 2, Nature of Biology – Book 2)
There are many different types of molecules that are found in living cells all with various structures and functions. Some of the more significant molecules can be catagorised into groups; carbohydrates and polypeptides, proteins and amino acids, lipids and nucleic acids.
Water also plays an essential role in the structure and function of a cell. Water is the most abundant compound found in our bodies and can exist in nature in three different states: ice, liquid water and gas.
Water is the main solvent for the various organic compounds found in human cells.
Organic Molecules:
Organic molecules are generally large molecules that consist of smaller molecules, referred to as
monomers. These larger compounds are then defined as polymers.
MONOMER POLYMER
Sugars Polysaccharide
Protein
Lipid (Fats / Membranes)
Nucleic acid (DNA / RNA)

Carbohydrates:
Carbohydrates are organic compounds made up carbon, hydrogen and oxygen. The simple or basic form of carbohydrate is known as a simple sugar or monosaccharide (meaning one sugar). A disaccharide, in turn, consists of two monosaccharides. When two sugars form a bond a water molecule is released.
Carbohydrates may be classified in the following way:
Simple sugars:
Monosaccharides:
Monosaccharides consist of only one sugar and most have the same basic formula:
Glucose is an example of a monosaccharide and is the sugar that is produced during photosynthesis:
Representations of the simple carbohydrate, glucose:
Another important monosaccharide is fructose and is the simple sugar found in fruits. Fructose combines with glucose to produce sucrose – a dissacharide.
Disaccharides:
A disaccharide consists of two monosaccharides. Examples of disaccharides are fructose – the form in which carbohydrate is transported within plants, and lactose – the carbohydrate present in milk and it’s derivatives.
Formation of sucrose:

Polysaccharides (Complex sugars):
Polysaccharides are polymers of sugar molecules. The most common component of polysaccharides is glucose. NOTE: Unlike simple sugars, polysaccharides are NOT soluble in water.

Glycogen - the form of energy stored in animals and is stored in the liver (up to 100g) and in muscle tissue (around 300g). Once these storage areas are at their limit the excess is converted to fat storage. Glycogen is a circular molecule with many branches (refer figure 1.13a, p. 12,
Nature of Biology – Book 2).

Starch - In plants, sucrose is form that glucose takes to be transported and some plants can store carbohydrates in this form. However, most plants store glucose in the form of starch and can be stored in numerous areas (stems, roots, leaves and endosperm – in the case of seeds) depending on the variety of the plant. Starch is stored in small grain-like structures and can take on different shapes depending on the plant species (refer figure 1.13b, p. 12, Nature of Biology –
Book 2).
Starch is not water soluble and has little to no effect on the osmotic action of a cell. Starch also is readily converted back into sugar when required.

Cellulose - has a similar formula to that of starch however it takes on a fibrous form consisting of long and unbranched molecules which is essential for the formation of cell walls. A derivative of cellulose, chitin can be used by animals to perform structural roles.
Inulin must also be noted as a storage polysaccharide present in some plants, such as bananas, onions and asparagus. Inulin can not be digested by animals.
Pectin is also another polysaccharide that cements the material between cell walls of plant tissues.
*Q4 – 6, p. 13, Nature of Biology – Book 2
Amino acids
Amino acids are the building blocks of proteins. All amino acids and in turn, proteins contain carbon, hydrogen and oxygen like carbohydrates but also contain nitrogen. Some amino acids contain sulphur and phosphorus also.
There are 20 naturally occurring amino acids, humans are unable to make 9 of these and rely on dietary intake for their supply.
General formula for an amino acid:

When two amino acids bind together they form what is known as a peptide bond:
Proteins:
Proteins are relatively large molecules that consist of thousands of amino acids. Due to their size, the molecules fold into different shapes. This folding structure is described on four levels: primary, secondary, tertiary and quaternary.
The structure and shape of proteins:

Types of Proteins:
Enzyme
Type of Protein
Contractile
Receptor
Transport
Function
Fibrous support tissues in the skin, bone, tendons, cartilage, blood vessels, heart valves and the cornea of the eye.
Muscle movement
Regulate body activity
Carry other molecules
Antibodies
Insulin
Example
Refer to Table 1.2, p. 17, Nature of Biology – Book 2.
Conjugated proteins
Some amino acids bind with other types of molecules to form conjugated proteins. An example of this occurs in the nucleus of a cell. A chain of amino acids will form a bond with nucleic acid to produce nucleoproteins (contains protein and nucleic acid).
Another example is haemoglobin – a protein that transports oxygen through the bloodstream.
Activation of molecules:
Some proteins form two different structures according to whether they are active or non active, such as insulin.
Refer to figure 1.23, p. 20, Nature of Biology – Book 2.

Proteomes:
A proteome is the full set of proteins that is produced by a cell or whole organism. Proteomics is the study of protein interactions and the analysis of patterns of protein production within each cell or organism.
*Q7-11, p21. Nature of Biology – Book 2.
Lipids:
A lipid is the term we use to describe fats, oils and waxes. This category of molecule also includes steroids. They are hydrophobic (water-hating) molecules that cannot dissolve in water. They are composed of carbon, hydrogen and oxygen and contain a high energy per molecule ratio due to the decreased amount of water in their structure.
Fats
These molecules are an important form of energy for animals as they store double the amount of energy as the same weight of polysaccharide, thus are essential energy stores.
These molecules consist of two sorts of molecules: fatty acids and glycerol.
Common forms of fats are:

Triglycerides - which are made up of three fatty acid molecules attached to a single glycerol molecule.

Phospholipids – which are made up of two fatty acids attached to a glycerol. The glycerol has a phosphate group attached to it, which is in turn attached to a variety of other small groups according to the type of phospholipid. These molecules are a major component of cell membranes.
*Q12 – 15, p23. Nature of Biology – Book 2.
Nucleic Acids:
There are two types of nucleic acids:

Deoxyriboucleic acid (DNA) – genetic material found in chromosomes within a eukaryote cell nucleus.

Ribonucleic acid (RNA) – genetic material formed against DNA, which acts as a template.

DNA
DNA is a polymer formed by two complementary chains of nucleotides. Nucleotides are composed of sugar (deoxyribose), phosphate backbone and a nitrogen base (adenine – thymine and cytosine -
guanine). DNA forms a double helix structure held together by hydrogen bonds.
A chromosome is formed when DNA binds with certain proteins and is stored in the nucleus of a cell.
The genetic information that is contained within DNA controls all the functions of that cell.
DNA controls the functions of the cell by producing polypeptide chains containing codons which are responsible for synthesizing specific proteins that carry out various actions within the cell. Codons are groupings of 3 nucleotides in a polypeptide chain that work like a code that will determine the protein that will be synthesized.
RNA
RNA is a polymer formed by an unpaired chain of nucleotides and differs from DNA as it contains the nitrogen bases (adenine –uracil and cytosine – guanine). RNA can exist in three different forms:

Messenger RNA (mRNA) – carries the genetic message to the ribosomes where it is translated into a protein

Ribosomal RNA (rRNA) – in conjunction with certain proteins to make ribosomes in the cytosol.

Transfer RNA (tRNA) - carry amino acids to ribosome which are used to make proteins.
*Q17-19, p. 26. Nature of Biology – Book 2.
**Complete Chapter Review (p. 29-31) as revision for end of chapter test.