1 / 23

Revision questions

Revision questions. What do you understand by supplementary/complementary value of proteins? (Give an example) Give an account of the properties of protein (with a culinary use where possible). Outline the biological functions of protein. What is the RI value of protein?

dacia
Download Presentation

Revision questions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Revision questions What do you understand by supplementary/complementary value of proteins? (Give an example) Give an account of the properties of protein (with a culinary use where possible). Outline the biological functions of protein. What is the RI value of protein? What is the energy value of protein? What do you understand by the deamination of protein? Outline the digestion and absorption of protein. • Outline the basic chemical structure of an amino acid. • Explain the formation of a protein. • Classify proteins according to their chemical structure. • Describe the classification of protein. • Name a food source for the following proteins: albumin caseinogen, collagen, actin, gluten, myosin, gelatin. • Differentiate between an essential and non-essential amino acid (give four examples of each). • What do you understand by the biological value of protein?

  2. Q1. Outline the basic chemical structure of an amino acid Proteins are made up of chains of small molecules called amino acids. There are 20 different amino acids, but each has the same basic structure. C = carbon atom H= Hydrogen atom NH2= Amino group (basic) COOH = Carboxyl group (acidic) R = Variable group (changes for every amino acid)

  3. The amino acid glycine: The R group = H (one hydrogen atom) Glycine

  4. Q2. Explain the formation of a protein • The bond that links one amino acid to another is called a peptide link or bond. • Each time two amino acids link together, a water molecule is taken away. The linking process is therefore called condensation. • The reverse of condensation is called hydrolysis ̶ water molecules are added to protein chains and split the amino acids apart. This happens during protein digestion. • The amino group (NH2) of one amino acid links with the carboxyl group (COOH) of another amino acid. • The amino group (NH2) loses one H and the carboxyl group (COOH) loses an OH group. • The H and OH bond together to form a water molecule (H2O). • The remaining CO and NH bond together to form a peptide link. • Two amino acids joined is called a dipeptide. • Many amino acids joined in a chain is called a polypeptide.

  5. 1. Acid reacts with the NH2 of another amino acid. 2. The amino group (NH2) loses one H and the carboxyl group (COOH) loses an OH group. 3. The remaining CO and NH join together to make a dipeptide.

  6. Q3. Classify proteins according to their chemical structure Primary structure The number and sequence of amino acids in a protein chain. For example, the protein insulin has over 50 amino acids in its chain, arranged in a definite order.

  7. Involves the folding of the protein chain into a spiral or zigzag shape. This structure is caused by cross-links that form between different chains or within the one chain. There are different types of cross-links: Hydrogen links –where a hydrogen atom in one chain bonds Disulfide links –when two sulphur atoms bond with an oxygen atom in another chain. Secondary structure A hydrogen link A disulfide link

  8. This refers to the three-dimensional folding of the chain. This structure can be globular or fibrous. The shapes give certain properties to the protein. Fibrous: In these the protein chain takes on a straight, coiled or zigzag shape. These shapes make the protein insoluble and stretchy or tough. Gluten in wheat and elastin in meat have a coiled structure. Collagen in meat has a zigzag structure. Tertiary structure

  9. Q4. Describe the classification of protein SIMPLE CONJUGATED DERIVED These proteins are formed due to a chemical or enzyme action on a protein, i.e. rennin acts on caseinogen and makes casein PROTEIN + NON-PROTEIN Protein + lipid = lipoprotein (lecithin) Protein + phosphate = phosphoprotein (casein) Protein + nucleic acid = nucleoprotein (DNA) Protein + colour pigment = chromoprotein (haemoglobin) ANIMAL PLANT Classified Classified GLUTENINS: Soluble in acids & alkali according according Glutenin in wheat to shape to solubility PROLAMINES: Soluble in alcohol FIBROUS GLOBULAR gliadin in wheat Collagen Albumin

  10. Albumin = Egg/meat Caseinogen = Milk/cheese Collagen = Meat/fish Actin = Meat/fish Gluten = Wheat/cereals Myosin = Meat/fish Gelatin = Meat/fish Q5. Name a food source for the following proteins

  11. Q6. Differentiate between an essential and non-essential amino acid (give four examples of each) • There are over 20 different amino acids. • Eight are essential amino acids that cannot be made by the body and must be eaten, e.g. valine, leucine, isoleucine, lysine, phenylalanine, tryptophan, threonine and methionine. • There are two extra essential amino acids for children, i.e. arginine and histidine. • The rest are non-essential amino acids. These can be made by the body, e.g. cysteine, alanine, asparagine, glutamine, glycine, proline and tyrosine.

  12. Q7. What do you understand by the biological value of protein? The biological value of a protein is a measure of the quality of the protein and is expressed as a percentage. It is decided by the number of essential amino acids a protein contains, in proportion to how much of them the body needs. There are two types of protein foods: 1. High biological value: contain all essential amino acids, complete proteins, animal sources. 2. Low biological value: lack some essential amino acids, incomplete protein, plant sources.

  13. Q8. What do you understand by supplementary / complementary value of proteins? (give an example) When low biological value foods that lack essential amino acids are eaten together they can provide all the essential amino acids. The essential amino acids missing in one food can be made up for by being present in the other food and vice versa. This complementary value of protein means that vegans can get all their essential amino acids without eating animal food Example: Bread is lacking lysine but is high in methionine. Beans are lacking methionine but are high in lysine. By eating beans on toast, both essential amino acids are included in the meal.

  14. Q9. Give an account of the properties of protein (with a culinary use where possible) Denaturation Denaturation is caused by: a) heat b) chemicals c) agitation It is often an irreversible process. Denaturation is a change in the nature of the protein. The protein chain unfolds, causing a change to the structure.

  15. Heat– Most proteins coagulate/set when heated, e.g. egg white coagulates at 60°C; egg yolk coagulates in the stomach at 68°C. Chemicals – Acids, alkali, alcohol and enzymes cause changes to the protein structure, e.g. lemon juice added to milk causes the milk protein caseinogen to curdle. Agitation – This is also known as mechanical action. It involves whipping or whisking the protein. This results in the protein chain unfurling and partial coagulation. 2. Solubility Proteins are generally insoluble in water. There are two exceptions: egg white in cold water connective tissue, which is converted to gelatine in hot water.

  16. 3. The Maillard reaction • The Maillard reaction is also known as non-enzymic browning. It occurs when food is roasted, baked or grilled. Examples include roast potatoes and toast. • Amino acid + carbohydrates + dry heat = brown colour. • Elasticity • Certain proteins have an elastic property, e.g. gluten, the protein found in flour, enables bread to rise during cooking • 5. Foam formation • When egg white is whisked, air bubbles are formed as the protein chains unravel. Whisking also produces heat, which slightly sets the egg white. This foam will collapse after a while, unless it is subjected to heat. This property is used to make meringues.

  17. Gel formation Collagen, when heated, forms gelatine. Gelatine can absorb large amounts of water and, when heated, forms a sol. On cooling, this becomes solid and a gel is formed. A gel is a semi- solid viscous solution. All gels have a three-dimensional network whereby water becomes trapped. This property is used in making cheesecakes and soufflés.

  18. Q10. Outline the biological functions of protein

  19. Q11. What is the RI of protein?Q12. What is the energy value of protein? RI 1 g of protein per kilogram of body weight. Child 30 ̶ 50 g/day Teenager 60 ̶ 80 g/day Adults 50 ̶ 75 g/day Pregnant or lactating 70 ̶ 85 g/day Energy value 1 g of protein gives 4 kcal or 17 kJ energy

  20. Q13. What do you understand by the deamination of protein? This is the process by which excess protein is used for energy. Leftover amino acids are brought to the liver. The NH2 group is broken off, changed to ammonia, then to urea and then excreted. The rest of the molecule is converted to glucose and used for releasing energy.

  21. Q14. Outline the digestion and absorption of protein

  22. Key words to revise • Agitation • Amino acid • Condensation • Conjugated proteins • Deamination • Denaturation • Dipeptide • Disulfide links • Elasticity • Foam formation • Gel formation • Hydrogen links • Hydrolysis • Maillard reaction • Polypeptide • Solubility

More Related