Nutrition - Chapter 6

Proteins Made of Amino Acids

"Nonessential" amino acids are made in the body (can also get them from food; also called dispensible) "Essential" amino acids are those the body cannot make in significant quantities to meet needs (also called indispensible) "Conditionally essential" amino acids are those that are usually nonessential but, under certain conditions, must be supplied by the diet (inadequate dietary intake of precursor amino acid; inability to convert to from precursor to amino acid)

Proteins contain

- Carbon, hydrogen, oxygen, nitrogen - arranged into Amino acids Central Carbon - Hydrogen - Amino group (NH2) - Acid group (COOH) - Side group or side chain (unique) All amino acids have a central carbon with an amino group (NH2), an acid group (COOH), a hydrogen (H), and a side group attached. The side group is a unique chemical structure that differentiates one amino acid from another Amino acids linked into chains of about 20 different amino acids

1. The protein RDA for adults is ___ g/kg/day, assuming the diet contains sufficient carbohydrates and fat to provide adequate energy. 2. Calculate your protein requirements.

1. 0.8 2. Convert pounds to kilograms (divide by 2.2). Multiply your weight (kgs) by 0.8 grams In the United States, the average intake is 80 g/day. For infants and children, the RDA is slightly higher. Use 6-1 "How To" to check your protein RDA. When using a percentage to assess protein, ensure calorie intake is adequate

______ and a carbon structure are the products of amino acid breakdown. The carbon structures are used to make nonessential amino acids or _____. The answer to question 1 is a _____ compound. The liver converts it to _____. It is then filtered from the blood by the ______. Excretion of this compound occurs in the _____.

1. Ammonia 2. Energy 3. Toxic; urea; kidneys; urine The carbon structures can also make glucose, ketone bodies, cholesterol, and fat. Urea production increases as protein intake increases.

When nitrogen intake and output are equal, a person is in nitrogen _____. Infants, children, and pregnant women are in a state of _____ nitrogen balance. If protein is being lost and nitrogen excretion is greater than intake, a person is in a state of ______ nitrogen balance.

1. Equilibrium 2. Positive 3. Negative When the body synthesizes more protein than it degrades during periods of growth, a person has a positive nitrogen balance. Examples of people in negative nitrogen balance include those in periods of starvation, or suffering from severe burns

If a nonessential amino acid is needed, the body can make it from a/an ____ acid. The liver can synthesis nonessential amino acids through the process of _______. The process ______ occurs when amino acids are broken down. This must occur before they are used for _____.

1. Keto 2. Transamination 3. Deamination; energy Explanation: Nitrogen must be available in addition to the keto acid. Transamination involves moving the amino group from an amino acid to its corresponding keto acid. Deamination occurs before amino acids are used to make glucose or ketone bodies.

1. When an essential amino acid isn't supplied in the amount needed to support protein synthesis, it is called a ______ amino acid. 2. Combining low-quality proteins provide adequate essential amino acids, this concept is called _________ (two words).

1. Limiting 2. Complementary proteins Combining plant proteins at each meal isn't necessary, as was long believed. Vegetarians, for example, can receive all the essential amino acids they need throughout the course of the day.

1. Protein quality is influenced by which two factors? 2. Explain the difference between animal and plant protein quality. 3. High-quality proteins are named this because:

1. The protein's digestibility and its amino acid composition. 2. Animal proteins tend to have a higher digestibility (90 to 99 percent) compared to plant proteins (70 to 90 percent). 3. They supply all the essential amino acids in the proportions required by the body.

Urea Synthesis

Ammonia is produced when amino acids are deaminated. The liver detoxifies ammonia by combining it with another waste product, carbon dioxide, to produce urea.

More Protein Roles

Antibodies - Defend body against disease - Antigen and antibody - Specificity - Immunity—memory Source of energy and glucose - Starvation and insufficient carbohydrate intake Other roles - Blood clotting, vision

Proteins as Structural Materials and Enzymes

Building blocks for most body structures - Collagen matrix - Filled with mineral crystals for bones or teeth Replacement of dead or damaged cells Enzymes - Break down, build up, and transform substances - Catalysts

Protein and Amino Acid Supplements

Building muscle - Protein powders - Popular and convenient - Athletic performance - Whey protein Amino acid supplements - Potential risks associated with intake

Protein Denaturation

Denaturation is the process when a protein uncoils or loses its shape and function - Heat, acid, base, agitation, alcohol, etc. - Cooked eggs - Acid and milk = curdling - Whipped egg whites stiffen - Stomach acid during digestion

Protein Absorption

During absorption, amino acids are transported by specific carriers to intestinal cells. Amino acids unused by these cells are transported to the liver. Whole proteins are handled better by the body compared to "Predigested" amino acid supplements - Body dismantles and absorbs them at optimal rate for body

Excreting Urea

Effect of liver disease Effect of kidney disease Protein intake and urea production - Water consumption When amino acids are deaminated (stripped of their nitrogen), ammonia is released. The liver converts ammonia to urea, and the kidneys excrete urea. In this way the body disposes of excess nitrogen.

Roles of Proteins

Hormones - Messenger molecules - Blood carries to target tissues - Insulin is a protein hormone Regulators of fluid balance - Edema Acid-base regulators - Attract hydrogen ions and act as buffers Transporters - Specificity

Amino Acid Sequence of Human Insulin

Human insulin is a relatively small protein that consists of 51 amino acids in two short polypeptide chains. Two bridges link the two chains. A third bridge spans a section within the short chain. Known as disulfide bridges, these links form between the cysteine (Cys) amino acids, whose side group contains sulfur (S)

Complementary Proteins

In general, legumes provide plenty of isoleucine (Ile) and lysine (Lys) but fall short in Methionine (Met) and tryptophan (Trp). Grains have the opposite strengths and weaknesses, making them a perfect match for legumes.

Transamination and Synthesis of a Nonessential Amino Acid

Keto acid A + Amino acid B -----> Amino acid A + Keto acid B The body can transfer amino groups (NH2) from an amino acid, forming a new nonessential amino acid and a new keto acid. Transamination reactions require the vitamin B6 coenzyme

Other Uses for Amino Acids

Making other compounds - Tyrosine and tryptophan → neurotransmitters Energy and glucose - Protein contributes 10 to 15 percent of energy needs - More with energy restriction - Starvation or fasting causes lean tissue wasting - Adequate diet

Protein Digestion

Mouth Stomach - Hydrochloric acid denatures proteins - HCl also activates pepsinogen to pepsin (cleaves proteins to small polypeptides and free AA) Small intestine - Hydrolysis reactions through intestinal and pancreatic proteases - Peptidase enzymes on surfaces of intestinal cell

Recommended Intakes of Protein

Need for dietary protein Only source of essential amino acids Only practical source of nitrogen 10 to 35 percent of daily energy intake

Sequencing Error: Sickle Cell Compared with Normal Red Blood Cell

Normally, red blood cells are disc-shaped, but in the genetic disorder sickle-cell anemia, red blood cells are sickle- or crescent-shaped. This difference in shape occurs because valine replaces glutamic acid in the amino acid sequences of two of hemoglobin's polypeptide chains. As a result of this difference in hemoglobin's shape, the capacity to carry oxygen is diminished

Proteins

Peptide bonds link amino acids together to form polypeptide chains (10 or more amino acids) - Condensation reactions Amino acid sequencing - Primary structure— sequence of amino acids connected by peptide bonds Secondary structure— polypeptide shapes made by electrical attractions within the chain - +hydrogen attract -oxygen - Form twisted helix or folded pleats - Strength and rigidity Tertiary structure— polypeptide tangles made when side groups attract or repel surrounding fluids and other amino acids - Side groups are hydrophilic or hydrophobic - Spherical (carry and store nutrients) or linear (tendons) structures Quaternary structure— mulitple polypeptide interactions form larger working complexes - Example hemoglobin in RBC carry oxygen - 4 polypeptide chains holding iron

Health Effects of Protein

Protein deficiency - Consequences - Protein-energy malnutrition - Marasmus and kwashiorkor Heart disease - Animal-protein intake - Homocysteine levels - Arginine levels Cancer - Protein not a contributing factor - Some protein foods are carcinogens - Processed meat and red meat - Soy, legumes, fish, and milk lower cancer risk Adult bone loss (osteoporosis) - Increase in calcium excretion Weight control Kidney disease

From Guidelines to Groceries

Protein foods - One ounce delivers about seven grams of protein - USDA Food Patterns - Recommended sources Milk and milk products Fruits, vegetables, and grains Read food labels - Current United States intakes - Moderation

Proteins in the Body

Uniqueness of each person because of differences in body's proteins Determined by genes, which determine these Amino acid sequences of proteins Diet must provide - Adequate protein - Essential amino acids

Match these: a) Continual production and destruction b) Used for energy c) Amino acids from protein breakdown and dietary proteins With these: a) Amino acids if nitrogen is removed b) Amino acid pool c) Protein turnover

a -> c b -> a c -> b Within cells, proteins are continually being made and broken down. Amino acids in the amino acid pool are used to make body proteins and other nitrogen-containing compounds. Amino acids can also be used for energy once nitrogen is removed

Amino acids

all amino acids have a common chemical structure but that each has a different side group

Similar to fat and carbohydrates, protein is also easily stored in the body. a) True b) False

b) False