Chapter 4: Proteins

Question 1

Proteins are built from simpler organic compounds called

Answer 1

amino acids.

Question 2

The element that is contained in proteins but not in carbohydrates or lipids is

Answer 2

nitrogen.

is present in proteins but not in carbohydrates or lipids. Amino acids, the building blocks of protein, are named for their chemical structure; amino refers to compounds containing nitrogen.

Question 3

Two types of protein in the body are _____ protein and _____ protein.

Answer 3

tissue, plasma

Two types of protein in the body are tissue and plasma protein. Amino acids are classified as indispensable, dispensable, or conditionally indispensable in the diet according to whether the body can make them.

Question 4

The number of amino acids that are indispensable for human beings is

Answer 4

9.

Nine amino acids are classified as indispensable amino acids because the body cannot manufacture them in sufficient quantity or at all.

Question 5

In the diet, the greatest proportion of indispensable amino acids are provided by

Answer 5

animal products.

Indispensable amino acids are provided mostly by animal products that contain protein.

Question 6

A protein that contains all indispensable amino acids in the correct proportion and ratio is called

Answer 6

complete.

A complete amino acid is one that is dispensable, meaning that the body can synthesize it from other amino acids.

Question 7

The number of kilocalories from protein in a sandwich that contains 24 g protein is _____ kcal.

Answer 7

96

Each gram of protein has 4 kcal, so 24 g  4 kcal = 96 kcal.

Question 8

An animal protein that has little value as a dietary protein source when eaten alone is

Answer 8

gelatin.

is a protein food of animal origin, but it lacks three essential amino acids and has only small amounts of leucine.

Question 9

Proteins from plant sources such as grains, nuts, and legumes that are classified as incomplete include

Answer 9

grains, peanuts, and corn.

Grains, peanuts, and corn are considered incomplete proteins because the food is deficient in one or more of the nine indispensable amino acids.

Question 10

To form a specific tissue protein, the order of amino acids must be

Answer 10

specific.

Once proteins are eaten and broken down into amino acids in the digestive process, they are reassembled in the body into a specific order to form a variety of different proteins, such as collagen, myosin, and hemoglobin.

Question 11

The number of common amino acids is

Answer 11

20.

There are 20 common amino acids, all of which are important to human life and health.

Question 12

An example of a protein-free body substance is

Answer 12

glycogen.

Glycogen is the storage form of carbohydrates and does not contain protein.

Question 13

The primary function of protein in the diet is to supply

Answer 13

material for growth and maintenance.

The primary function of protein is to supply material in the body for growth, maintenance, and repair.

Question 14

Protein plays an important role in the body

Answer 14

in defense against disease and infection.

Protein assists in the body’s defense against disease and infection by helping build special white blood cells called lymphocytes.

Question 15

After a piece of grilled chicken is digested by the mouth and stomach, it eventually reaches the small intestine, where which of the following enzymes are secreted by the pancreas?

Answer 15

Chymotrypsin, trypsin, and carboxypeptidase

are three enzymes produced by the pancreas to continue breaking down proteins into simper and simpler substances.

Question 16

Proteins are absorbed as

Answer 16

amino acids and peptides.

Proteins are broken down to amino acids and peptides, whereas polypeptides require enzymatic breakdown.

Question 17

Pepsinogen secreted by the gastric cells is converted into pepsin by

Answer 17

hydrochloric acid.

Question 18

Protein catabolism is increased in conditions such as

Answer 18

illness.

Protein catabolism, or the breakdown of protein, is increased during illness or disease and increases the body’s need for protein and kilocalories to rebuild tissue and meet the demands of an increased metabolic rate.

Question 19

The phase of metabolism that makes growth and repair possible is

Answer 19

anabolism.

Anabolism is the metabolic process that makes growth and repair possible in the body. It is especially necessary after an illness or disease process. Anabolism also is found during periods of rapid fetal growth during pregnancy, the first year of life, lactation during breastfeeding, and adolescent growth and development into adulthood.

Question 20

A gastric enzyme that coagulates milk and is present in infants but not in adults is

Answer 20

rennin.

Rennin is the gastric enzyme found in the gastric juice of human infants and some young animals such as calves. Rennin is important to the infant in the digestion of milk.

Question 21

A protein-digesting enzyme found in the stomach rather than in pancreatic secretions is

Answer 21

pepsin.

is the main gastric enzyme specific to proteins.

Question 22

The enzyme trypsin is activated by the enzyme

Answer 22

enterokinase.

Trypsin is activated by the enzyme enterokinase. Enterokinase is secreted from the intestinal cells on contact with food entering the duodenum.

Question 23

The enzymes aminopeptidase and dipeptidase are secreted by the

Answer 23

small intestine.

Aminopeptidase and dipeptidase are enzymes secreted by glands in the wall of the small intestine.

Question 24

Complementary proteins

Answer 24

provide higher quality protein when eaten together.

Complementary proteins are used to supply all nine indispensable amino acids for the diet. Because plant proteins are incomplete, a mixture can provide adequate amounts of amino acids. A normal eating pattern throughout the day along with the body’s reserve supply of protein ensures a complementary balance of high-quality protein. Those who follow a vegetarian eating pattern must combine proteins to meet needs.

Question 25

In the mouth, protein is

Answer 25

broken up mechanically by chewing.

Question 26

Of the following, the food with the highest quality protein is

Answer 26

egg.

Eggs are a high-quality protein food and carry a chemical score of 100. Other foods are compared to it according to their amino acid ratios.

Question 27

Which of the following conditions might result in the greatest catabolism?

Answer 27

Multiple trauma with extensive organ damage

Protein catabolism, or the breakdown of protein, is increased during illness or disease and increases the body’s need for protein and kilocalories to rebuild tissue and meet the demands of an increased metabolic rate. In this case, multiple trauma with extensive organ damage requires a greater catabolic rate compared with the other choices and would create the greatest increase in metabolic rate and need for tissue repair.

DIF: Hard REF: 48 MSC: Application

Question 28

If the excretion of nitrogen exceeds the nitrogen intake, the condition is called

Answer 28

negative nitrogen balance.

If the body takes in less nitrogen than it excretes, a negative balance occurs. This means that the body has an inadequate protein intake and is losing nitrogen by breaking down more tissue than it is building up.

Question 29

The grams of protein required daily for an individual who weighs 170 lb ideal body weight would be _____ g.

Answer 29

55.3

The Recommended Daily Allowance for both men and women is set at 0.8 g of high-quality protein per kilogram of desirable body weight per day. In this case, 170 lb/2.2 lb/kg = 77 kg. 77 kg  0.8 g/kg = 61.6 g/day of protein.

Question 30

In planning a vegetarian meal, an appropriate combination of complementary proteins would be

Answer 30

cornmeal tamales and beans.

In planning and making complementary food combinations to balance the needed amino acids, families of foods (e.g., grains, legumes, and dairy) are mixed. Grains usually are low in threonine and high in methionine, whereas legumes are the opposite. Therefore grains and legumes help balance each other in the amount of indispensable amino acids required by the body. Acceptable combinations include (1) grains and peas, beans, or lentils; (2) legumes and seeds; and (3) grains and dairy. In the choices given, cornmeal tamales and beans would be the most appropriate food choice.

Question 31

An example of a low-protein food is

Answer 31

fresh fruit salad.

Fresh fruit salad is composed mostly of carbohydrates and no protein.