Biological Molecules: Proteins  Links to GCSE  Bonding  Balanced diet & food tests  Hormones & immunity  Haemoglobin

Give the functions of some proteins. Give the functions of some proteins. Describe the structure of an amino acid. Describe the structure of an amino acid. Explain what is meant by ‘essential’ and ‘non essential’ amino acids. Explain what is meant by ‘essential’ and ‘non essential’ amino acids.

Key definition: Amino acids  Amino acids are the monomers of all proteins. All amino acids have the same basic structure. The 20 different amino acids involved in protein synthesis differ only in the R-group bonded to the central carbon

Amino acid structure showing R-group (side chain)‏

Basic amino acid structure - glycine © Pearson Education Ltd 2008 This document may have been altered from the original Week 14

Amino acids  There are about 20 standard amino acids.  Around 8 of these are known as ‘essential amino acids’ because they are required in the diet.  The rest can be synthesised by the body.  Most are found in meat.  Soya is a good source for vegetarians.  The amino group makes an amino acid toxic when too much is present so we do not store excess amino acids.  The removal of the amino group by the liver is called DEAMINATION.  It produces UREA, removed by urination.

Describe the formation and breakage of peptide bonds in the synthesis and hydrolysis of dipeptides and polypeptides. Describe the formation and breakage of peptide bonds in the synthesis and hydrolysis of dipeptides and polypeptides. Explain the term primary structure. Explain the term primary structure. Explain the term secondary structure with reference to hydrogen bonding. Explain the term secondary structure with reference to hydrogen bonding. Explain the term tertiary structure with reference to hydrophobic and hydrophilic interactions, disulfide bonds and ionic interactions. Explain the term tertiary structure with reference to hydrophobic and hydrophilic interactions, disulfide bonds and ionic interactions.

Condensation and hydrolysis © Pearson Education Ltd 2008 This document may have been altered from the original Week 14

Key definition  The primary structure of a protein is given by the specific sequence of amino acids that make up the protein.

Primary structure of insulin © Pearson Education Ltd 2008 This document may have been altered from the original Week 14

Four-amino-acid structure © Pearson Education Ltd 2008 This document may have been altered from the original Week 14

Forming different proteins  In a polypeptide that is 4 amino acid residues long,  any of the 20 amino acids may be present at any position in the chain.  Therefore there are 20x20x20x20 possible combinations.  This equals 160,000 different sequences with a mere 4 amino acids.  A small protein may be 100 amino acids long.  Therefore, in theory, the number of different possible proteins is immense!

Enzymes  Covalent bonds are VERY strong and do not simply form nor fall apart. -Protease enzymes break peptide bonds not just in the digestive system e.g. hormones must be broken down when their effect is no longer required  Skin loses elasticity because it is difficult to rebuild collagen in older skin when it is broken down.  Other (complex!) reactions involve anabolic enzymes e.g polymerase to build molecules up.

Key definition: secondary structure  Refers to the coiling and pleating of parts of the polypeptide molecule.  The specific order of the amino acids is determined by the DNA.  Hydrogen bonds stabilise the long molecules as they are produced and so is dependent on the primary structure.  This may be an alpha helix or beta pleated sheet

Alpha helix and polypeptide chain © Pearson Education Ltd 2008 This document may have been altered from the original Week 14

Key defintion: tertiary structure  Refers to the overall 3D structure of the final polypeptide or protein molecule.  This is vital to its function.

The bonds responsible for maintaining tertiary structure © Pearson Education Ltd 2008 This document may have been altered from the original Week 14

Individual student presentations  Title: Denaturation  5-8 slides to explain the science behind the term.  Use images.  No more than 15 words per slide.  Work alone or in pairs.  BEWARE only 1 of pair will be randomly selected to present!

Explain the term quaternary structure with reference to the structure of haemoglobin. Explain the term quaternary structure with reference to the structure of haemoglobin. Describe the structure of a collagen molecule. Describe the structure of a collagen molecule. Compare the structure and function of haemoglobin and collagen. Compare the structure and function of haemoglobin and collagen. © Pearson Education Ltd 2008 This document may have been altered from the original Week 14

Key definition: Quarternary structure  Refers to the fact that some proteins are made up of more than one polypeptide subunit joined together, or a polypetide and an inorganic component.  These polypeptide units may be identical or not.

Globular vs fibrous proteins  There are 2 categories of 3d shapes  Globular proteins roll up into a compact globe -Hydrophobic r groups tend to turn inwards towards the centre -Hydrophilic r groups tend to be on the outside -This makes the protein water soluble  Fibrous proteins from fibres. -Most have regular repetitive sequences of amino acids and are usually insoluble -Collagen fibres consist of 3 alpha helix coils, coiled around each other to form a superhelix!

Haemoglobin  Present in red blood cells  2 α and 2 β chains  Haem group with an Iron ion to carry O 2  Coloured bright red in combination with O 2

Collagen: structural molecule

Collagen structure © Pearson Education Ltd 2008 This document may have been altered from the original Week 14

Give the functions of some proteins.Give the functions of some proteins. Describe the structure of an amino acid.Describe the structure of an amino acid. Explain what is meant by ‘essential’ and ‘non essential’ amino acids.Explain what is meant by ‘essential’ and ‘non essential’ amino acids. Describe the formation and breakage of peptide bonds in the synthesis and hydrolysis of dipeptides and polypeptides.Describe the formation and breakage of peptide bonds in the synthesis and hydrolysis of dipeptides and polypeptides. Explain the term primary structure.Explain the term primary structure. Explain the term secondary structure with reference to hydrogen bonding.Explain the term secondary structure with reference to hydrogen bonding. Explain the term tertiary structure with reference to hydrophobic and hydrophilic interactions, disulfide bonds and ionic interactions.Explain the term tertiary structure with reference to hydrophobic and hydrophilic interactions, disulfide bonds and ionic interactions. Explain the term quaternary structure with reference to the structure of haemoglobin.Explain the term quaternary structure with reference to the structure of haemoglobin. Describe the structure of a collagen molecule.Describe the structure of a collagen molecule. Compare the structure and function of haemoglobin and collagen.Compare the structure and function of haemoglobin and collagen.