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.

Proteins

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.

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.

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.

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

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

Enzyme Activity, Lock and Key Substrate Enzyme Active site

Enzyme Activity, Lock and Key The substrate becomes activated Enzyme

Enzyme Activity, Lock and Key The substrate becomes activated Enzyme

Enzyme Activity, Lock and Key The complex molecule splits Enzyme

Enzyme Activity, Lock and Key The complex molecule splits Enzyme

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.

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

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.

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

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

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.

Amino acids

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.)

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)

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.

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

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.

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.

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

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.

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.