Chapter 7: Proteins

What are 2 examples of when it is beneficial for proteins to be denatured?

1. While being digested, food proteins are denatured by the HCl in our stomachs, which increases their exposure to digestive enzymes. 2. The heat in cooking denatures proteins and makes them safer to eat (if bacterial proteins are denatured) and more pleasing to eat (when eggs solidify during cooking)

Out of the ____ amino acids our bodies need, ____ of them can be made in our bodies, so they are called ____. The other ____ amino acids that we can't make are called ____ and must be obtained from our diets.

20; 11; nonessential amino acids; 9; essential amino acids

T/F Protein synthesis is "cheap," meaning that it doesn't require much energy input from the body.

F. Every amino acid added requires energy input from ATP, so protein synthesis is actually very costly to the body.

T/F The majority of our amino acid pool comes from recycled body proteins and not from our diet.

T. We make and degrade about 250 to 300 grams of protein each day, but we only get between 65 and 100 grams of protein from our diets daily.

What is a limiting amino acid?

The amino acid in shortest supply from the diet. It limits the amount of body proteins that can be synthesized.

How do you calculate a chemical score?

The amount of each amino acid in the food being evaluated is divided by the amount of that amino acid found in a reference food (usually egg protein). The lowest ratio will be found in the limiting protein for the evaluated food, and that ratio is its chemical score (ranges from 0 to 1)

What does Protein Efficiency ration measure (PER)?

The amount of weight gained in a laboratory animal/ the amount of protein consumed in comparison to the same ration in terms of a reference protein (casein, which is milk protein)

What is the most widely used method for determining protein quality?

The protein digestibility corrected amino acid score (PDCAAS)

Some amino acids can lose an amino group in a process called by ____ without transferring it to another carbon skeleton. The nitrogen is taken to the liver and then excreted by the kidneys in the form of ____. These amino acids are now just a ____, and can be used for _____ or _____ (ex. for making ____).

deamination; urea; carbon skeleton; energy; synthesis; glucose

If the R group on an amino acid is a hydrogen the amino acid is ____. If the R group on an amino acid is a methyl group, the amino acid is ____.

glycine; alanine

What does translation entail?

mRNA enters a ribosome, which reads the codons on the mRNA and translates them to produce a specific protein.

What does chemical score measure?

mg limiting amino acid per g of protein/ mg of limiting amino acid per g of "ideal" protein

What is the general treatment plan for sickle-cell anemia? List 3 aspects.

1. Blood transfusions 2. Medications to enhance RBC synthesis 3. Bone marrow transplants

Why can essential amino acids be made in our bodies (list 3 reasons)?

1. Body cells can't make the carbon skeleton of the amino acid 2. Can't attach the amino group to the carbon skeleton 3. Can't synthesize the amino acid fast enough to meet the body's needs

List the 5 elements that are found in amino acids

1. Carbon 2. Hydrogen 3. Oxygen 4. Nitrogen 5. Sulfur

List 4 conditions that will denature a protein.

1. Heat 2. Acid or alkaline solutions 3. Enzymes 4. Agitation

What are the 9 essential amino acids?

1. Histodine 2. Isoleucine 3. Leucine 4. Tryptophan 5. Lysine 6. Methionine 7. Phenylalanine 8. Threonine 9. Valine

What are the health problems associated with sickle-cell anemia? List 6.

1. Severe bone and joint pain 2. Abdominal pain 3. Headache 4. Convulsions 5. Paralysis 6. Possible death when the sickled cells clump in capillary beds and impede blood flow.

What is an oligopeptide?

A protein consisting of 4-10 peptides bound together.

What codon(s) act/s as a start codon?

AUG

How are dietary proteins classified? What are meat and plant proteins referred to?

According to their amino acid composition. Meat (except gelatin) = complete protein; plant proteins (except quinoa and soy) = incomplete protein

Alanine donates its ____ to the ____ of _____ to become the nonessential amino acid ____.

Amino group; carbon skeleton; pyruvic acid; glutamic acid

What food groups contain all 9 essential amino acids? And what food is an exception to this rule?

Animal proteins (meat, poultry, fish, eggs, and milk). Gelatin does not have all 9 because it loses an amino acid during processing and it doesn't contain ample amounts of the other 9.

What foods have a high BV?

Animal proteins. BV is high when all 9 amino acids are present, and when the amino acid composition of the food is similar to that of the human body.

What happens when protein synthesis is completed?

As signaled by the stop codon. The ribsome releases the polypeptide and the mRNA. The polypeptide folds into a complex 3D structure.

Where does translation begin and end on an mRNA molecule?

At the start codon on the mRNA (AUG), and at the stop codon (UAA, UAG, UGA)

If a food has a high ___, it will also have a high ____.

BV; PER

What happens when a diet doesn't contain complete proteins, or enough incomplete proteins to create a full protein pool?

Body proteins can not be made, and the ingested amino acids are used as energy or converted to carbohydrate or fat and stored.

During illness, changes in ____, _____, and _____ can cause proteins to denature and loos biological function.

Body temperature; gastrointestinal pH; blood pH

How is protein quality evaluated?

By a foods digestibility (the amount of amino acids absorbed) and its amino acid profile as compared to a reference protein (usually egg whites)

How is BV determined?

By dividing retained nitrogen by the amount of nitrogen absorbed (the amount of nitrogen that is converted into body tissues/the amount that was in the original food)

How is PDCAAS found?

By multiplying the chemical score of a protein by its digestibility.

When is PER used?

By the FDA to set standards for labeling foods intended for infants.

What is/are the codon(s) for glutamic acid?

CTC and CTT

Some amino acids are only specified by one ____, but others have as many as ___.

Codon; 6

DNA has sets of 3 bases in a row called ___ that code for a specific amino acid.

Codons

A protein is considered ____ if it has ____ essential amino acids. A protein is considered ____ if it has ____ essential amino acids.

Complete; all 9; incomplete; limited amounts of at least one of the 9.

What does transcription entail?

DNA unwinds and pairs with the appropriate RNA bases to form a strand of messenger RNA which leaves the nucleus and enters the cytosol.

What food has a BV of 100?

Egg whites

What is an example of the deamination process?

Glutamic acid loses it's amino group and becomes alpha-ketoglutaric acid. The amino group is incorporated into urea in the liver and excreted by the kidneys.

Following a trauma, what amino acids would be considered "conditionally essential?"

Glutamine and arginine (shown to promote healing)

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What is an example of a protein that has quaternary structure?

Hemoglobin

What does the biological value of a protein measure?

How efficiently that protein is converted to body tissue protein

Where does protein synthesis take place?

In ribosomes in the cytosol of cells

What is an example of protein recycling in the body?

Intestinal tract cells are constantly being sloughed off. These cells are digested just like food particles, and the amino acids in the cells are absorbed, digested, and used to build new proteins.

As protein intake increases, what happens to the efficiency of protein use?

It decreases because excess amino acids can't be stored and are used for energy instead

If a protein is missing one of the 9 essential amino acids, what will its PDCAAS score be?

It will be 0, because its chemical score is 0.

How does the digestibility of plant proteins compare to that of animal proteins?

It's low. Plant digestibility is usually about 70%, while animal protein digestibility is usually around 90-100%

Acidic amino acids ____ a proton in reactions and become ____, while basic amino acids ____ a proton in reactions and become ____.

Lose; negatively charged; gain; positively charged

What essential amino acid does wheat lack?

Lysine

What is/are the limiting amino acid(s) of grains?

Lysine

What is/are the limiting amino acid(s) of nuts and seeds?

Lysine

What is/are the limiting amino acid(s) of legumes?

Methionine and tryptophan

What foods could you combine with legumes to form a complete protein? What are examples of these foods together?

Nuts and seeds or grains. Legumes are limited by methionine and tryptophan while both nuts and seeds and grains are limited by lysine. Legumes have lysine, while nuts and seeds and grains have methionine and tryptophan, so eating either of these combinations together would create a complete protein. Hummus with pita bread; pinto beans with polenta

_____ do not contain adequate amounts of essential amino acids. With the exception of ____ and ____, all other plant products are low in ____ of the 9 essential amino acids.

Plant proteins; soy; quinoa; at least 1

Most proteins are ____, ranging from ____ to ____ amino acids bound together.

Polypeptides; 50; 2000

Denaturation does not affect a proteins ____, but it often ____.

Primary structure; destroys its biological function

Describe why individuals get sickle-cell anemia, and what that causes.

They have a mutation in their DNA that causes a switch from the amino acid glutamic acid to valine in 2 of the 4 strands of hemoglobin in each RBC. This causes the RBCs to fold in on themselves becoming half-moon (sickle) shaped instead of donut shaped like healthy cells. This limits their ability to carry oxygen to tissues and causes many health problems.

What are "conditionally essential" amino acids?

They're made essential by the conditions of the individual (infancy, disease, or trauma) though they would not be considered essential for the average person. For example people with PKU can't metabolize phenylalanine due to a deficiency of the enzyme phenylalanine hydrozylase which is needed to convert phenylalanine into tyrosine. As a result individuals with PKU can't synthesize tyrosine themselves, so tyrosine becomes conditionally essential.

Non-essential amino acids are synthesized through a process called _____.

Transamination (involves the transfer of an amino group from one amino acid to the carbon skeleton of another to form a new amino acid)

What molecule is responsible for taking amino acids to ribosomes as needed during protein synthesis?

Transfer RNA. tRNA carriers have a code that is complimentary to the mRNA strand.

What codon(s) act/s as a stop codon?

UAA, UAG, or UGA

What are complimentary proteins?

When two or more incomplete protein sources are combined to form a complete protein.

Peptide bonds form between the ___ group of one amino acid and the ___ of another.

amino; carboxyl