Structure & Function of Proteins

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This presentation deals with proteins, their structure and functions as regards biological systems.

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Proteins: structure & function : 

Proteins: structure & function Dr. Deryck. D. Pattron, Ph.D.

Protein Composition : 

Protein Composition Differ from carbohydrates and lipids by the presence of nitrogen atoms. Amino acids are joined by peptide bonds. Each protein has its own amino acid sequence. All amino acids have the same basic structure; a carbon with three groups attached to it; an amine group (NH2), an acid group (COOH) and a hydrogen atom (H). 2

What are proteins? : 

What are proteins? Proteos = prime importance. Proteins are composed of elements: carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorous. Proteins are composed of amino acids-the building blocks of cells and tissues. Two types of amino acids: essential amino acids (9) Non-essential amino acids (10-13) Essential amino acids must be obtained from the diet. 3

Essential Amino Acids : 

Essential Amino Acids Amino acids that cannot be synthesized by the body. Must be obtained in diet. There are nine amino acids generally considered essential for humans, including tryptophan, which is necessary for the body to create the neurotransmitters serotonin and melatonin. 4

Sources of Essential Amino Acids : 

Sources of Essential Amino Acids All essential amino acids can be found in varying levels in vegetables. Meat including chicken, beef, pork, lamb, fish, eggs, and dairy products Dried beans (black, kidney, northern, red, and white beans), peas, soy, nuts, and seeds. 5

Essential Amino Acids : 

Essential Amino Acids Adapted from the University of Arizona Biology Project 6

Essential Amino Acids : 

Essential Amino Acids Adapted form the University of Arizona Biology Project 7

Essential Amino Acids : 

Essential Amino Acids Adapted form the University of Arizona Biology Project 8

Non-essential Amino Acids : 

Non-essential Amino Acids The 10 amino acids that we can produce are alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine. 9

Sources of Non-Essential Amino Acids with noted deficiencies : 

Sources of Non-Essential Amino Acids with noted deficiencies Wheat- lysine Rice- lysine Legumes- tryptophan Maize- lysine tryptophan Pulses- methionine (or cysteine) 10

Amino Acid Interconvertibility : 

Amino Acid Interconvertibility The sulfur-containing amino acids, methionine and homocysteine, can be converted into each other but neither can be synthesized de novo in humans. Cysteine can be made from homocysteine but cannot be synthesized on its own. Likewise arginine, ornithine, and citrulline, which are interconvertible by the urea cycle, are considered a single group. Tyrosine is produced from phenylalanine, so if the diet is deficient in phenylalanine, tyrosine will be required as well. 11

Protein Functions : 

Protein Functions Structural-provides building blocks for growth and repair: Cells Tissues Organs e.g. actin, amyloid, collagen, elastin, fibrillin, lamin, reticular fiber, sclerotin, scleroprotein, spongin, viral structural protein 2. Calorific - provides 4 calories per gram e.g. meat and meat products, dairy and dairy products, eggs, fish, seafoods. 3. Enzymatic –speeds up biological reactions e.g. amylases, cellulases, pectinases, rennin, lipases, papain, glucose isomerase, xylanases, ligninases, proteases, DNA ligase, DNA polymerase 4. Immunological-protects the body against foreign invaders e.g. antibodies, T-helper cells, MHC2 receptors, CD4, B cells, macrophages, killer T cells 12

Daily Recommended Allowance for Proteins : 

Daily Recommended Allowance for Proteins Infants  0–6 mo  9.1 g/day  7–12 mo  13.5 g/day Children  1–3 years  13 g/day 4–8 years 19 g/day Males  9–13 years 34 g/day 14–18 years  52g/day 19–30 years  56g/day 31–50 years 56g/day 51–70years 56 g/day > 70 years 56g/day Females  9–13 years 34 g/day 14–18 years  46 g/day  19–30 years 46 g/day 31–50 years 46 g/day 51–70years  46 g/day > 70 years  46 g/day Pregnancy  14–18 years  71 g/day 19–30 years  71 g/day 31–50 years  71 g/day Lactation  14–18 years 71 g/day 19–30 years  71 g/day 31–50 years  71 g/day Adapted from The Food and Nutrition Board, Commission on Life Sciences, National Research Council. 13

Two Diseases caused by protein deficiency : 

Two Diseases caused by protein deficiency Marasmus condition of a wasting away of the body tissues from the lack of calories as well as protein in the diet. In Marasmus the child is fretful rather than apathetic and is skinny rather than swollen with edema. Kwashiorkor Symptoms include apathy, muscular wasting, and edema. Both the hair and the skin lose their pigmentation. The skin becomes scaly and there is diarrhea and anemia, and permanent blindness can result from this condition. 14

References : 

References http://science.jrank.org/pages/4796/NutrientDeficiency-Diseases-Marasmuskwashiorkor.html#ixzz0JMjskpEk&C Insel, Paul; Turner, R.; and Ross, Don (2001). Nutrition. Sudbury, MA: Jones and Bartlett. Whitney, Eleanor N., and Rolfes, Sharon R. (2002). Understanding Nutrition, 9th edition. Belmont, CA: Wadsworth Group. 15