ORGANIC
MOLECULES
Carbohydrates, Lipids,
Proteins & Nucleic Acids
CARBOHYDRATES
Carbohydrates are the most common
organic compounds in nature. They
 Are an important source of chemical energy for living
organisms
 Are used as energy reserves in plants and animals
 Form structural components such as cellulose cell
walls in plants and chitin cell walls in fungi
 Form part of both DNA and RNA
 Combine with proteins and lipids to form
glycoproteins and glycolipids as in cell membranes
Monosaccharides
Meaning single sugars.
• These are the basic subunit of carbohydrates.
• They contain carbon, hydrogen and oxygen in a 1 : 2 : 1 ratio, eg. Glucose C6 H12 O6
The 3 types of monosaccharides are:
Triose
Pentose
Hexose
H
H-c-o-H
C
c
c
o
c
o-H
c
H-o
H
H
C
C
c
c
c
c
c
c
H
Glyceraldehyde
Ribose, Deoxyribose
Glucose, Galactose
Disaccharides – Meaning 2 sugars.
• Formed when 2 sugars bond together by a
condensation or dehydration synthesis
reaction.
• Two single sugars (monomers) join by 1 losing a
hydrogen (H+) ion and the other losing a
hydroxide (OH-) ion that go into the formation of
a water molecule.
• The remaining part of the monomer is called the
residue.
• The common disaccharide, sucrose, consists of
a glucose and a fructose residue bonded
together.
Sucrose = glucose and fructose
Glucose
Fructose
O
Glycosidic Bond
Condensation reactions can be
reversed.
• If a molecule of water is added to a
disaccharide between the monosaccharide
residues, the disaccharide will split into the
original monosaccharides.
• This is a hydrolysis reaction.
Polysaccharides – Meaning many sugars.
These are formed through a series of condensation
reactions where many monosaccharides are joined
together.
Common examples include:
• Starch – Used to store excess sugar molecules in plants as an
energy store.
• Cellulose – A structural polysaccharide used to support cell walls
and stiffen the bodies of plants. This is the most abundant organic
compound found in nature.
• Glycogen – Made and stored in animal liver or muscle tissue, where
it is readily available as an energy reserve.
These 3 polysaccharides are all composed of a series of glucose
residues, however their arrangement differs. See page 14 of text.
Complex polysaccharides are those that consist of different
monosaccharide subunits in the same molecule, eg. Murein – found
in the cell walls of bacteria.
Carbohydrate structure
• Monosaccharide
• Disaccharide
• Polysaccharides
Starch
Glycogen
Cellulose
LIPIDS
• Fats (solids) & oils (liquids), used as long term energy
storage molecules.
• Fats are composed of glycerol and 3 fatty acid
molecules and are insoluble.
• Fatty substances that store about twice the energy
carbohydrates do.
• They contain Carbon, Hydrogen and Oxygen but a
much higher proportion of Hydrogen atoms to Carbon
and Oxygen atoms than carbohydrates.
• Some lipid molecules contain atoms of phosphorous –
forming phospholipids which are the major component
of cell membranes. Others contain nitrogen.
• They are non-polar, hydrophobic molecules. This
allows them to form an effective barrier between 2
watery environments.
• They also include steroids (hormone and vitamins).
In cells, lipids have 3 important
functions.
1. energy storage: they have twice the amount
of energy as carbohydrates
2. structural components of cells
3. specific biological functions, such as the
transmission of chemical signals both within
and between cells.
SATURATED & UNSATURATED FATTY ACIDS
Fatty Acid
Saturated
Structure
• Single bonds between carbon atoms.
• The max. number of hydrogen atoms are attached to
each carbon atom.
• Therefore chains of fatty acids pack tightly together.
• Therefore more bonding b/w chains
• Therefore need more energy to “move apart”.
•Therefore have a higher melting point.
• Therefore tend to be solid at room temp.
Unsaturated • Double bonds between some carbon atoms.
• Don’t have the max. number of hydrogen atoms per
carbon atom.
• Therefore the chains don’t pack together as tightly.
• Therefore less bonding b/w chains.
• Therefore need less energy to move apart.
• Therefore have a lower melting point.
•Therefore tend to be liquid at room temp.
Eg’s
Animals:
Lard,
butter,
fats,
blubber
Plants: oils
of olives,
canola,
sunflower,
aromatic
oils of
plants
SATURATED & UNSATURATED
FATTY ACIDS
Saturated Fatty Acids
OHHHHH HHHH HHHHHH H
C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H
HHHHH HHHH HHHHHH H
Unsaturated Fatty Acids
OHHHHH HHH H HH HHHH H
C-C-C-C-C-C-C-C-C=C-C-C=C-C-C-C-C-H
HHHHH HH
H
HHH H
Examples of Lipids
1 Triglycerides
• Most abundant lipids
• Economical store of energy
- eg. as oils in plant seeds
- as fat deposits under animals skin
Glycerol
Fatty Acids
Examples of Lipids
2 Phospholipids
• Form cell membranes
• The phosphate end is attracted to water (hydrophillic) while the
fatty end is repelled, (hydrophobic).
• The Hydrophobic ends turn inwards in the membrane to form a
double lipid layer as found in cell membranes.
3 Steroids
• Different structure to other lipids.
• 3 rings of “6-carbon” atoms each and a fourth ring containing “5carbon” atoms.
• Examples include cholesterol, testosterone and oestrogen.
NUCLEIC ACIDS
• Very, very large
molecule
• Always contains
carbon, hydrogen,
oxygen, nitrogen and
phosphorus
• Made up of long chains
of molecular units
called NUCLEOTIDES.
• Eg’s. Deoxyribonucleic
Acid (DNA), &
Ribonucleic Acid (RNA)
• FUNCTION – Store
and transfer genetic
information
RNA & DNA
NUCLEOTIDE
Deoxyribonucleic
acid – DNA 1
• In Prokaryotes – DNA found in cytoplasm
• In Eukaryotes – DNA found in nucleus & also
mitochondria & chloroplasts
• Organised into segments called genes
• Genes code for production of proteins,
determining inherited characteristics.
• GENOME is all of an organisms genes
• Genes are the recipe, the proteins do the work.
• The products of the genome is called the
PROTEOME –the entire collection of proteins in
an organism.
• There are 20-25 000 genes in humans.
• There are more than 200 000 proteins.
Deoxyribonucleic
acid – DNA 2
DNA is a macromolecule made
of many nucleotides.
Each nucleotide is made of:
• a phosphate group
• a deoxyribose sugar – a 5 carbon
sugar, and a base
• There are 4 types of bases.
1. Adenine & Guanine – the purines
having a double ring structure
2. Cytosine & Thymine – the
pyrimidines having a double ring
structure
Deoxyribonucleic
acid – DNA 3
DNA is double stranded
with bases bonding in the
centre.
• Adenine always bonds
with Thymine
• Cytosine always bonds
with Guanine
• This is due to the
Complementary Base
Pairing rules.
Ribonucleic Acid –
RNA
•
•
•
•
•
DNA is used to make RNA.
RNA is used to make Proteins
RNA is single stranded.
Thymine is replaced by Uracil.
RNA is formed in the nucleus,
but passes into the cytoplasm
for protein synthesis.
• Three main forms are – Ribosomal,
Messenger and Transfer.
Ribonucleic Acid
Base
sugar phosphate backbone
PROTEINS
 These are very complex molecules that make up 50% of our dry
weight.
 They all contain carbon, hydrogen, oxygen, and nitrogen and many
also contain sulphur.
 There are thousands of different types of proteins with varied
functions.
 Some form structural components, others are enzymes, hormones or
carrier molecules, (Eg haemoglobin), and some form channels in
membranes.
 They consist of chains of smaller subunits called amino acids (AA’s).
There are 20 amino acids commonly found in proteins.
 Each organism has it’s own unique AA’s, where as carbohydrates and
lipids are similar in plants & animals.
 AA’s are linked by Peptide Bonds, hence the proteins are called
Polypeptides (meaning many bonds)
Polypeptides and
Amino Acids
Polypeptide
Peptide Bonds
Amino Acids
Amino Acid (General Structure)
H
H
O
N
C
H
C
OH
R
Proteins
• Each different protein has a different
number and sequence of AA’s
• The sequence of AA’s determines the
shape (structure) of the protein.
• The structure of the protein
determines it’s properties (how it
behaves) and therefore its function
(job) in life.
Protein Structure
There are 4 levels of
Protein structure:
1. Primary structure
•
The actual sequence of amino acids in the
polypeptide
Protein Structure
2. Secondary Structure
• Hydrogen bonding between some AA’s causes the
Primary polypeptide to fold or pleat in some places
or to undergo coiling into helix structures in other
parts of the chain.
Protein Structure
3. Tertiary Structure
• Hydrophobic R groups are attracted to each other.
Hydrophilic R groups are also attracted to each other.
These interactions between R groups of the amino acids
cause the polypeptide chains to become folded, coiled or
twisted into the proteins functional shape or
conformation
• All protein molecules with the same sequence of amino
acids will fold into the same shape.
• Changing 1 amino acid will alter the shape.
• It is the tertiary shape that determines the biological
functionality.
Protein Structure
Tertiary Structure continued.
Protein Structure
4. Quaternary Structure
•
Sometimes 2 or more separately created
polypeptide chains join together.
1. (eg. Heamoglobin consists of 4 polypeptide chains,
joined by a variety of hydrogen bonds, ionic bonds
and covalent bonds, which gives the molecule it’s
overall shape).
Protein Structure
Summary
Biomacromolecules
Summary