Chapter 6

Question 1

Describe how proteins differ from carbohydrates and fat.

Answer 1

Proteins contain nitrogen

Genetic material dictates the structure of each protein molecule

Question 2

Describe the process of protein synthesis.

Answer 2

Proteins are long chains of amino acids. Amino acids bond to form a variety of peptides.

Amino acids join together by means of a peptide bond.
    The amine group of one amino acid binds to the acid group of another
When amino acids join together, they form peptides.
    Dipeptide:  2 amino acids joined together
    Tripeptide:  3 amino acids joined together
    Oligopeptide:  4 to 9 amino acids joined together
    Polypeptide:  10 or more amino acids joined together
Genes regulate amino acid bonding.
    The structure of each protein is dictated by the DNA of a gene.
        Gene expression:  The process of using a gene to make a protein.
    Transcription:  use of the genetic information in DNA to make RNA.
        mRNA copies (transcribes) information from DNA in nucleus and carries to ribosomes in cytoplasm
    Translation:  conversion of genetic information in mRNA to the amino acids sequence of a protein.
        Information from the mRNA is translated into a growing strand of amino acids that bind together to form a specific protein.
Protein turnover involves synthesis and degradation of body proteins.

Question 3

What are the building blocks of protein?

Answer 3

Amino Acids

Question 4

Identify the parts of an amino acid molecule.

Answer 4

1. an alpha carbon, which is the central, asymmetric carbon
2. a carboxyl group at the right end of the alpha carbon
3. an amino group at the left end of the alpha carbon
4. an R group
5. a hydrogen atom

Question 5

Which part of an individual amino acid distinguishes it from other amino acids?

Answer 5

The R Group/side chain

Question 6

What is an essential amino acid and how many are there?

Answer 6

A complete protein contains all 9 essential amino acids.

The most complete protein food sources include meat, poultry, fish, egg whites, milk, and soybeans.
    These foods are considered to be “high quality protein” foods.

Question 7

How many non-essential amino acids are there?

Answer 7

11, these can be made by the body

Question 8

Discuss how proteins are digested and absorbed by our bodies.

Answer 8

Stomach acids and enzymes break proteins into short polypeptides.

    Hydrochloric acid (HCl) in the stomach begins protein digestion by denaturing the protein.
    HCl also converts inactive pepsinogen to its active form, pepsin.
    Pepsin begins breaking the peptide bonds between amino acids.

Enzymes in the small intestine break polypeptides into single amino acids.

Proteases from the pancreas and small intestine continue the breakdown of polypeptides in the small intestine.
Amino acids, dipeptides, and tripeptides are absorbed into the cells of the intestinal wall.
Enzymes in the intestinal cells further break down dipeptides and tripeptides into single amino acids.
Amino acids are transported into the bloodstream.

Protein digestibility affects protein quality.

Digestibility of a protein refers to how well our bodies can digest it.
Animal protein sources are highly digestible.

Question 9

Proteins contribute to cell growth, repair, and maintenance.

Answer 9

Cells are constantly being broken down, repaired, and replaced.
When proteins in the cells are broken down, the amino acids are recycled into new proteins.
Examples: skin cells, hair cells, burn recovery

Question 10

Proteins act as enzymes and hormones.

Answer 10

Enzymes are compounds (usually proteins) that speed up chemical reactions, without being changed by the chemical reactions themselves.
Some hormones are made from amino acids.
Hormones are substances that act as chemical messengers in the body.
Examples: glucagon, insulin, thyroid hormone

Question 11

Proteins help maintain fluid and electrolyte balance.

Answer 11

Proteins attract fluid.
When protein intake is deficient, it can cause edema (swelling).
Transport proteins in the cell membrane help to maintain the proper balance of sodium and potassium inside and outside the cell.

Question 12

Proteins help maintain acid-base balance.

Answer 12

Proteins are excellent buffers and help to maintain a proper blood pH.

acidosis- blood becomes acidic; level of hydrogen (H+) in blood is excessive
alkalosis - blood becomes basic (alkaline); level of H+ in blood is deficient
buffers - proteins that help maintain proper acid-base balance by attaching to, or releasing H+ ions

Question 13

Proteins help maintain a strong immune system.

Answer 13

Antibodies are proteins that defend the body against foreign substances.
Each antibody is designed to defend against a specific invader.

Question 14

Proteins serve as an energy source.

Answer 14

In healthy people, protein contributes little to energy needs.
When proteins are needed for energy, they are taken form the blood and body tissues.
To use proteins for energy, deamination is required.

deamination - amine group is removed from amino acid and nitrogen is transported to the kidney for excretion, while carbon and other components are metabolized for energy

To protect our body tissues, it is important to eat an adequate amount of fat and carbohydrate.
Our body cannot store excess protein. Excess protein intake results in nitrogen excretion; remaining components are used for energy or converted to fat for later use.

Question 15

Calculate the AMDR and the recommended dietary allowance for protein.

Answer 15

The RDA for sedentary people is 0.8 gram per kilogram of body weight per day.
Example: 150 pound sedentary adult / 2.2 = 68.2 kg
68.2 kg x 0.8 grams/kg = 55 grams protein per day
Protein needs depend on many factors including age, activity level, etc.
The recommended percentage of energy that should come from protein is 10 to 35% of total energy intake.
Protein needs are higher for some groups, such as children, adolescents, pregnant or lactating women, vegetarians, and athletes.

Question 16

Identify the potential health risks associated with high-protein diets.

Answer 16

High protein intake is associated with high cholesterol.
High protein intake may contribute to bone loss.
High protein intake can increase the risk for kidney disease.

Question 17

Describe cycle cell anemia.

Answer 17

Sickle cell anemia is a disease passed down through families. The red blood cells which are normally shaped like a disc take on a sickle or crescent shape. Red blood cells carry oxygen to the body.

Question 18

Identify the best food sources of complete proteins.

Answer 18

Complete protein sources come from animal sources

Question 19

What are peptides and peptide bonds?

Answer 19

Amino acids join together by means of a peptide bond.

The amine group of one amino acid binds to the acid group of another

Question 20

Describe the process of denaturation.

Answer 20

Denaturation is the loss of shape of protein.

A denatured protein loses its function.
Exposure to heat, acids, bases, heavy metals, alcohol can denature proteins.

Question 21

What is an incomplete vs. a complete protein?

Answer 21

A complete protein contains an adequate amount of all of the essential amino acids that should be incorporated into a diet. Some protein contains all the amino acids needed to build new proteins, which generally come from animal and fish products. A complete protein must not lack even one essential amino acid in order to be considered complete.

Question 22

What are the risks of excess OR inadequate protein intakes?

Answer 22

Too much dietary protein can be harmful.

High protein intake is associated with high cholesterol.
High protein intake may contribute to bone loss.
High protein intake can increase the risk for kidney disease.

Protein-energy malnutrition can lead to debility and death.

Marasmus is a disease that results from grossly inadequate intakes of protein, energy, and other nutrients.
    It is most commonly seen in young children living in impoverished conditions.
    Consequences of marasmus include:
        wasting and weakening of muscles, including the heart muscle.
        stunted brain development and learning impairment.
        depressed metabolism and little insulation from body fat, causing a dangerously low body temperature
        stunted physical growth and development
        deterioration of the intestinal lining, which further inhibits absorption of nutrients
        anemia
        a severely weakened immune system
        fluid and electrolyte imbalances
Kwashiorkor results from a low-protein diet.
    It is typically seen in young children who no longer drink breast milk.
    Consequences of kwashiorkor include:
        weight loss and muscle wasting, with some body fat retention
        retarded growth and development (less severe than with marasmus)
        edema, which results in extreme belly distention
        enlarged, fatty liver
        loss of appetite, sadness, irritability, apathy
        development of skin sores
        dry, brittle hair

Question 23

Describe nitrogen balance and give examples of those who would be in positive and negative states of nitrogen balance.

Answer 23

Positive nitrogen balance occurs when a person consumes more nitrogen than is excreted.
Negative nitrogen balance occurs when a person excretes more nitrogen than is consumed.
Nitrogen balance occurs when nitrogen intake equals nitrogen excretion.