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 H o-H

C c c c c

H-o H 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 ACIDSFatty Acid Structure Eg’s

Saturated • 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.

Animals: Lard, butter, fats, blubber

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.

Plants: oils of olives, canola, sunflower, aromatic oils of

plants

SATURATED & UNSATURATED FATTY ACIDS

Saturated Fatty Acids

O H H H H H H H H H H H H H H H H

C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-H

H H H H H H H H H H H H H H H H

Unsaturated Fatty Acids

O H H H H H H H H H H H H H H H H

C-C-C-C-C-C-C-C-C=C-C-C=C-C-C-C-C-H

H H H H H H H H H H H H

Examples of Lipids1 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 “5-carbon” 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

Deoxyribonucleicacid – 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.

Deoxyribonucleicacid – 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 structure2. Cytosine & Thymine – the

pyrimidines having a double ring structure

Deoxyribonucleicacid – 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. Ribonucleic Acid

• RNA is used to make Proteins• RNA is single stranded.• Thymine is replaced by Uracil. Bases

• RNA is formed in the nucleus,but passes into the cytoplasm for protein synthesis.

• Three main forms are – Ribosomal, Messenger and Transfer.

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 AcidsPolypeptide

Peptide Bonds Amino Acids

Amino Acid (General Structure)

HH O

N C CH 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 StructureThere 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 Structure4. 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 StructureSummary

BiomacromoleculesSummary