1. Proteins
Describe what a protein is and give examples of what they are used for.
Describe the structure and shape of the different types of proteins.
Explain, in terms of bonding, what happens to proteins when they are heated.

2. Proteins

3. Protein Structures
Some proteins are composed of a single polypeptide chain, but many consist of two or more polypeptide chains.
Proteins are classified according to their shape into fibrous and globular proteins.

4. Fibrous proteins
These have their polypeptide chains interwoven. The polypeptide chains are held together by hydrogen bonding, between the N-H and the C=O groups.
This gives these proteins their properties of toughness, insolubility, and resistance to change in pH and temperature. So they are found in skin, tissue, (collagens), hair, nails (keratins).
Globular proteins
Proteins which operate within cells need to be soluble The polypeptide chains are coiled together in spherical shapes. E.g. Haemoglobin and many hormones.
e.g. Insulin, was the first protein structure to be worked out. Enzymes are globular proteins.

5. Protein Structures Silk is a typical example of a fibrous protein
This view shows the protein chains contain 2 different amino acids.
This view shows the individual atoms in the protein chains.

6. Protein Structures Albumen, in egg white, is a globular protein..
backbone view
atom view

7. Enzyme Activity, Lock and Key
The critical part of an enzyme molecule is called its active site.
This is where binding of the substrate to enzyme occurs and
where catalysis takes place.
Most enzymes have one active site per molecule.
Substrate
Enzyme

8. Enzyme Activity, Lock and Key
Substrate
Enzyme
Active site

9. Enzyme Activity, Lock and Key
The substrate becomes activated
Enzyme

10. Enzyme Activity, Lock and Key
The substrate becomes activated
Enzyme

11. Enzyme Activity, Lock and Key
The complex molecule splits
Enzyme

12. Enzyme Activity, Lock and Key
The complex molecule splits
Enzyme

13. Effect of Cooking Food
Within proteins, the long chain molecules may be twisted to form spirals, folded into sheets, or wound around to form other complex shapes.
The chains are held in these forms by intermolecular bonding between the side chains of the constituent amino acids.
When proteins are heated, during cooking, these intermolecular bonds are broken allowing the proteins to change shape (denature).
These changes alter the texture of foods.

14. Protein Structures
Enzymes are globular proteins. The structure of amylase is shown below.
Starch molecule in the enzyme’s active site.

15. Enzyme Activity
Enzymes catalyse chemical reactions in the body. Each enzyme has a unique shape held together by many weak bonds. Changes to pH and temperature can denature the enzyme. This changes the enzymes shape stops it working properly.
Temp or pH
Enzyme
activity
Narrow optimum range
The bonds that hold most biological enzymes are broken around 60oC.

16. Factors Affecting Enzyme Activity
Experiment 2.9
Aim:
16/01/2019

17. Proteins
Proteins are the major structural materials of animal tissue and are involved in the maintenance and regulation of life processes.
Proteins which fulfil different roles in the body are formed by linking differing sequences of amino acids together.
Enzymes are proteins.
Within proteins, the long-chain molecules may be twisted to form spirals, folded into sheets, or wound around to form other complex shapes.
The chains are held in these forms by intermolecular bonding between the side chains of the constituent amino acids.
When proteins are heated, during cooking, these intermolecular bonds are broken allowing the proteins to change shape (denature).
Amino Acids

18. Amino Acids
Explain what amino acids are and recognise them from their functional groups.
State what is meant by “essential amino acids”.
Describe the reaction of amino acids to form proteins to including the name of the new link produced.

19. Amino acids

20. Amino acids All proteins contain the elements C, H, O, N.
They are condensation polymers, made by amino acids linking together.
The body cannot make all the amino acids required for body proteins and is dependent on dietary protein for supply of certain amino acids known as essential amino acids.
(histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.)

22. Amino acids Amino Acids NH2CHCOOH R
Most proteins contain 20+ different amino acids H N C O
When R is Hydrogen, the amino acid is glycine (Gly)
(aminoethanoic acid)
When R is CH3, the amino acid is alanine (Ala)
(2-aminopropanoic acid)

23. Protein Polymers
Proteins are condensation polymers, made by amino acids linking together.
An amine group of one molecule links to the carboxyl group of another molecule to form an amide link or peptide link/bond.

24. Polypeptide chain can have 10000
Protein Polymers
CH3 H
CH3 H O H H + O + O
N – C - C
N – C - C
N – C - C OH H OH H OH H H H H
alanine
glycine
alanine
Tripeptide, ala-gly-ala O
N – C – C -
CH3
N – C – C - H
N – C - C
+ 2H2O OH
amide (peptide) link
Polypeptide chain can have 10000
amino acids

25. Amino Acids
Amino acids are the building blocks from which proteins are formed, are relatively small molecules which all contain an amino group (NH2), and a carboxyl group (COOH).
The body cannot make all the amino acids required for body proteins and is dependent on dietary protein for supply of certain amino acids known as essential amino acids.
Proteins are made of many amino acid molecules linked together by condensation reactions.
In these condensation reactions, the amino group on one amino acid and the carboxyl group on a neighbouring amino acid join together, with the elimination of water.
The link which forms between the two amino acids can be recognised as an amide link (CONH) also known as the peptide link.

26. Hydrolysis of protein 16/01/2019
During digestion, enzyme hydrolysis of dietary proteins can produce amino acids
The structural formulae of amino acids obtained from the hydrolysis of proteins can be identified from the structure of a section of the protein.

27. Protein hydrolysis Proteins are broken down during digestion.
Digestion involves the hydrolysis of proteins to form amino acids
+ 2H2O
Protein
Amino
acids

28. Identifying amino acids by chromatography
In the lab a protein can be hydrolysed back to its constituent amino acids by refluxing with concentrated hydrochloric acid for several hours.
Amino acids can be identified by the use of paper (or thin layer) chromatography.
A piece of chromatography paper is spotted with some amino acids suspected as being present and also with the hydrolysed protein.

29. Identifying amino acids by chromatography
By comparing the position of the spots of the known amino acids with that of the hydrolysed protein, the amino acids in the protein can be identified.