INTRODUCTION TO THE MOLECULES FOR LIFE
All living things are made up of four classes of biological molecules:
1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic acids
● The molecular structure of something determines its function.
● When organic molecules join together, they are called macromolecules
Terminology:
● Polymers: long molecule consisting of many similar building blocks
○ Only carbohydrates, proteins and nucleic acids form polymers
● Monomers: small building blocks that make up a polymer
Synthesis of polymers (polymerisation)
● Occurs via a condensation reaction - a reaction in which two molecules are
covalently bonded to each other with the loss of a small molecule
● Condensation reactions connect monomers to polymers
○ A dehydration reaction occurs when the small molecule lost is water
1
, ○ The loss of the water molecule results in the formation of a new bond
Breakdown of polymers
● Occurs in hydrolysis (reverse of dehydration)
● Addition of a water molecule to a polymer breaks the bond between the
monomers of the polymer, resulting in a shorter polymer
The chemistry of carbon
Formation of bonds with carbon
● Carbon has 6 electrons in its outer shell and usually forms a single or double
covalent bond in organic molecules
● Molecules with carbon atoms are arranged in a tetrahedral shape
2
,Molecular diversity that arises from carbon skeletons
● A hydrocarbon only consists of hydrogen and carbon
○ They are not prevalent in living organisms however many cell’s organic
molecules have regions only consisting of hydrogen and carbon
● A fat molecule consists of a small non-hydrocarbon element joined to three
hydrocarbon tails that account for the hydrophobic behavior of fats
Isomers
● Variation in the architecture of organic molecules is seen in isomers
○ Structure all isomers differ in the covalent arrangements of their structure
○ Cis-trans isomers differ in the arrangement about a double bond. A cis
takes two elements on the same side and a trans takes tow elements on
opposite sides
○ Enantiomers differ in the spatial arrangement around an asymmetric
carbon, resulting in mirror images.
■ These can be considered ‘left and right hands’ of a molecule.
Chemical groups that are most important in the processes of life
● Chemical groups that are directly involved in chemical reactions are called
functional groups
3
, ● The 7 chemical groups important in biological processes are :
○ Hydroxyl
○ Carbonyl
○ Carboxyl
○ Amino
○ Phosphate
■ ATP is an important organic phosphate
○ Methyl
○ Sulfhydryl
● All of the above groups are hydrophilic and thus increase the solubility of
organic compounds in water
THE IMPORTANCE OF WATER IN THE FUNCTIONING OF A CELL
● Water is a polar molecule - it has polar covalent bonds between its atoms
○ Thus its overall charge is unevenly distributed
Importance of hydrogen bonds in the uniqueness of water
● Between water molecules; the positive hydrogen of one molecule is attracted to
the negative oxygen of another molecule
4
, ○ Thus there are hydrogen bonds between water molecules - hydrogen
bonds help water molecules stick together
● In liquid form, hydrogen bonds are very weak and thus break very quickly
● The breaking and reforming of hydrogen bonds occurs at a great frequency
● Therefore at any moment most water molecules are bonded to their
neighbouring molecules
● This is where the uniqueness of water comes from: the constant hydrogen
bonding organises the water molecules into a higher level of structural order
● NB: hydrogen bonds themselves are weak, but they require a great amount
of energy to overcome because there are so many hydrogen bonds between
the many water molecules
Properties of water
● The holding together of the molecule by hydrogen bonding is called cohesion
● Water has a high surface tension due to cohesion - this is why small insects can
walk on water
● Cohesion results in the transport of water from roots through the leaves of a
tree
● Adhesion helps water defy gravity
5
, Hydrophobic and hydrophilic substances
● A substance that has an affinity for water is hydrophilic
○ Note that substances can be hydrophilic but not dissolve in water (e.g.
cotton)
● A substance that does not have an affinity for water is hydrophobic
○ These substances are nonionic and nonpolar or cannot form hydrogen
bonds (e.g. oil)
Importance of water in the functioning of a cell
Water is very important for the success of the cells intracellular functioning.
● Water is a solvent which helps cells transport substances around it
● It is required for many reactions in the cell
● It transports nutrients, waste products etc. around the cell
6
All living things are made up of four classes of biological molecules:
1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic acids
● The molecular structure of something determines its function.
● When organic molecules join together, they are called macromolecules
Terminology:
● Polymers: long molecule consisting of many similar building blocks
○ Only carbohydrates, proteins and nucleic acids form polymers
● Monomers: small building blocks that make up a polymer
Synthesis of polymers (polymerisation)
● Occurs via a condensation reaction - a reaction in which two molecules are
covalently bonded to each other with the loss of a small molecule
● Condensation reactions connect monomers to polymers
○ A dehydration reaction occurs when the small molecule lost is water
1
, ○ The loss of the water molecule results in the formation of a new bond
Breakdown of polymers
● Occurs in hydrolysis (reverse of dehydration)
● Addition of a water molecule to a polymer breaks the bond between the
monomers of the polymer, resulting in a shorter polymer
The chemistry of carbon
Formation of bonds with carbon
● Carbon has 6 electrons in its outer shell and usually forms a single or double
covalent bond in organic molecules
● Molecules with carbon atoms are arranged in a tetrahedral shape
2
,Molecular diversity that arises from carbon skeletons
● A hydrocarbon only consists of hydrogen and carbon
○ They are not prevalent in living organisms however many cell’s organic
molecules have regions only consisting of hydrogen and carbon
● A fat molecule consists of a small non-hydrocarbon element joined to three
hydrocarbon tails that account for the hydrophobic behavior of fats
Isomers
● Variation in the architecture of organic molecules is seen in isomers
○ Structure all isomers differ in the covalent arrangements of their structure
○ Cis-trans isomers differ in the arrangement about a double bond. A cis
takes two elements on the same side and a trans takes tow elements on
opposite sides
○ Enantiomers differ in the spatial arrangement around an asymmetric
carbon, resulting in mirror images.
■ These can be considered ‘left and right hands’ of a molecule.
Chemical groups that are most important in the processes of life
● Chemical groups that are directly involved in chemical reactions are called
functional groups
3
, ● The 7 chemical groups important in biological processes are :
○ Hydroxyl
○ Carbonyl
○ Carboxyl
○ Amino
○ Phosphate
■ ATP is an important organic phosphate
○ Methyl
○ Sulfhydryl
● All of the above groups are hydrophilic and thus increase the solubility of
organic compounds in water
THE IMPORTANCE OF WATER IN THE FUNCTIONING OF A CELL
● Water is a polar molecule - it has polar covalent bonds between its atoms
○ Thus its overall charge is unevenly distributed
Importance of hydrogen bonds in the uniqueness of water
● Between water molecules; the positive hydrogen of one molecule is attracted to
the negative oxygen of another molecule
4
, ○ Thus there are hydrogen bonds between water molecules - hydrogen
bonds help water molecules stick together
● In liquid form, hydrogen bonds are very weak and thus break very quickly
● The breaking and reforming of hydrogen bonds occurs at a great frequency
● Therefore at any moment most water molecules are bonded to their
neighbouring molecules
● This is where the uniqueness of water comes from: the constant hydrogen
bonding organises the water molecules into a higher level of structural order
● NB: hydrogen bonds themselves are weak, but they require a great amount
of energy to overcome because there are so many hydrogen bonds between
the many water molecules
Properties of water
● The holding together of the molecule by hydrogen bonding is called cohesion
● Water has a high surface tension due to cohesion - this is why small insects can
walk on water
● Cohesion results in the transport of water from roots through the leaves of a
tree
● Adhesion helps water defy gravity
5
, Hydrophobic and hydrophilic substances
● A substance that has an affinity for water is hydrophilic
○ Note that substances can be hydrophilic but not dissolve in water (e.g.
cotton)
● A substance that does not have an affinity for water is hydrophobic
○ These substances are nonionic and nonpolar or cannot form hydrogen
bonds (e.g. oil)
Importance of water in the functioning of a cell
Water is very important for the success of the cells intracellular functioning.
● Water is a solvent which helps cells transport substances around it
● It is required for many reactions in the cell
● It transports nutrients, waste products etc. around the cell
6
