2017 Introducing proteins Proteins are a diverse group of large and complex polymer molecules made up of long chains of amino acids They have a wide range of biological roles including structural ID: 1034790
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1. ProteinsVCE Chemistry Unit 4 AOS 22017
2. Introducing proteinsProteins are a diverse group of large and complex polymer molecules, made up of long chains of amino acids.They have a wide range of biological roles, including:structural: proteins are the main component of body tissues, such as muscle, skin, ligaments and haircatalytic: all enzymes are proteins, catalyzing many biochemical reactionssignalling: many hormones and receptors are proteinsimmunological: all antibodies are proteins.
3. Proteins and amino acidsProteins are a diverse group of large and complex polymer molecules, made up of long chains of amino acids.The R group, also attached to the same carbon atom, can vary. There are 22 amino acids that are used to make proteins (proteinogenic). The simplest is glycine, where R = H.Amino acids contain both amine (NH2) and carboxyl (COOH) functional groups. In alpha amino acids, these groupsare attached to the same carbon atom.glycine (gly)
4. Proteinogenic amino acids
5. Essential Amino acids11 amino acids can be produced in the body, the other 9 must be obtained in the diet (essential aa).Essential amino acids are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine and histidine.A lack of essential amino acids in the diet can lead to serious diseases (eg kwashiorkor)
6. Zwitterions
7. Acid–base properties of amino acidsThe presence of a carboxyl group and an amine group mean that amino acids have both acidic and basic properties. NH2 group acts as a baseCOOH acid group acts as an acidWhen acting as an acid, the COOH group loses a H+ ion:When acting as a base, the NH2 group gains a H+ ion:H2NCHRCOOH + OH- ® H2NCHRCOO- + H2OH2NCHRCOOH + H+ ® H3N+CHRCOOH
8. Peptide formation
9. Peptides
10. Effect of pH on amino acids
11. Hydrolysis of peptide bondsA peptide bond can be split by refluxing with hydrochloric acid. During hydrolysis, the water molecule adds across the peptide bond, forming a mixture of the two amino acids.Peptide links can also be broken using a solution of alkali, such as aqueous sodium hydroxide at above 100°C.
12. PolypeptidesWhen more amino acids are added to a dipeptide, a polypeptide chain is formed.A protein consists of one or more polypeptide chains folded into a highly specific 3D shape. There are up to four levels of structure in a protein: primary, secondary, tertiary and quaternary. Each of these play an important role in the overall structure and function of the protein.
13. The structure of proteins
14. Protein structure
15. Bonds in proteinsThe 3D shape of a protein is maintained by several types of bond, including:hydrogen bonds:involved in all levels of structure.hydrophobic interactions:between non-polar sections of the protein. disulfide bonds: one of the strongest and most important type of bond in proteins. Occur between two cysteine amino acids.
16. Types of proteinThere are two broad classes of protein: fibrous and globular.Fibrous proteins are formed from parallel polypeptide chains held together by cross-links. These form long, rope-like fibres, with high tensile strength and are generally insoluble in water.Globular proteins usually have a spherical shape causedby tightly folded polypeptide chains with hydrophobicgroups on the inside, and hydrophilic groups on the outside. Examples of fibrous proteins include collagen, keratin and silk.Examples of globular proteins include enzymes and some hormones.
17. Denaturing proteinsIf the bonds that maintain a protein’s shape are broken, the protein will stop working properly and is denatured.Changes in temperature, pH or salt concentration can all denature a protein, although the specific conditions will vary from protein to protein.Fibrous proteins lose their structural strength when denatured, whereas globular proteins become insoluble and inactive.denaturation: bonds broken
18. Biuret test for proteins
19. Structure of enzymesAll enzymes are globular proteins. They are soluble in water due to the presence of many hydrophilic side groups on their constituent amino acids.Most enzymes are very large molecules but only a small part of them is involved in catalysis. This is called the active site and it may consist of just a few amino acids.The remainder of the amino acids maintain the precise shape of the enzyme and the active site.active site
20. Proteins: true or false?
21. Amino acids and proteins: summary
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