Biochemistry of Proteins and Amino Acids

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Questions and Answers

What distinguishes amino acids from carbohydrates and lipids at a chemical level?

Amino acids are made of simpler structures.

Amino acids are not involved in protein synthesis.

Amino acids contain additional nitrogen atoms. (correct)

Amino acids have only carbon and hydrogen.

How many different amino acids are used to make proteins in the body?

20 (correct)

Which type of amino acids cannot be synthesized in sufficient quantities by the body?

Essential amino acids (correct)

Conditionally essential amino acids

Nonessential amino acids

Categorically essential amino acids

Under what circumstances can a nonessential amino acid become conditionally essential?

When the body cannot synthesize it due to health issues Signup and view all the answers

What is the function of peptide bonds in proteins?

To link amino acids together Signup and view all the answers

What happens to dietary proteins during digestion?

They supply amino acids for body protein synthesis. Signup and view all the answers

Which of the following amino acids is considered essential?

Phenylalanine Signup and view all the answers

Which of the following is a consequence of protein deficiency?

Slowed growth Signup and view all the answers

Which condition causes tyrosine to become a conditionally essential amino acid?

Phenylketonuria Signup and view all the answers

What characterizes acute protein-energy malnutrition (PEM) in children?

Thinness for height Signup and view all the answers

Marasmus is primarily a result of which of the following?

Severe deprivation of energy and protein Signup and view all the answers

What condition is primarily associated with inadequate protein intake in children?

Kwashiorkor Signup and view all the answers

What is a potential health risk of overconsumption of protein?

Heart disease Signup and view all the answers

How does high dietary protein affect calcium levels in the body?

Increases calcium excretion Signup and view all the answers

Which food sources may help reduce the risk of some cancers?

Protein-rich legumes Signup and view all the answers

What role do vegetable proteins play in heart health?

Improve blood pressure Signup and view all the answers

What is the primary consequence of missing an essential amino acid during protein synthesis?

The body dismantles its own proteins to obtain it. Signup and view all the answers

Which type of dietary protein is considered high quality?

Animal-derived proteins. Signup and view all the answers

Which proteins can be combined to create complementary proteins?

Legumes and grains. Signup and view all the answers

What happens to protein synthesis when there is too little dietary protein?

Protein synthesis decreases and degradation increases. Signup and view all the answers

Which factor does NOT influence protein quality?

Protein color. Signup and view all the answers

When is protein deficiency most likely to develop?

When the diet consistently supplies too little protein. Signup and view all the answers

What defines a low-quality protein?

A protein limiting in one or more essential amino acids. Signup and view all the answers

Which of the following foods is considered a source of low-quality protein?

Gelatin. Signup and view all the answers

Which of the following correctly describes the role of specific carriers in protein absorption?

They actively transport amino acids and some peptides into the intestinal cells. Signup and view all the answers

What are possible fates for amino acids once they enter intestinal cells?

They can be used for energy or to synthesize needed compounds. Signup and view all the answers

How do amino acids that are not utilized by intestinal cells reach the liver?

They are transported across the cell membrane into surrounding fluid and then enter capillaries. Signup and view all the answers

Which of these factors significantly influences protein quality in a diet?

Protein digestibility and amino acid composition. Signup and view all the answers

Which of the following statements about protein digestibility is accurate?

Animal proteins generally have a higher digestibility rate than plant proteins. Signup and view all the answers

Why is protein quality important for children and adults?

It influences growth and health maintenance. Signup and view all the answers

What characteristic of soy and legumes contributes to their protein digestibility?

They have a digestibility rate over 90 percent. Signup and view all the answers

Which role is not typically associated with proteins in the body?

Act as neurotransmitters. Signup and view all the answers

Study Notes

Protein: Amino Acids

Proteins are made up of amino acids
Amino acids contain nitrogen atoms, alongside carbon, hydrogen, and oxygen
These nitrogen atoms give amino acids their name.
Different side chains distinguish different amino acids
There are 20 different amino acids.
Some amino acids are essential, while others are non-essential.

Chapter Outline

Chemists' view of proteins
Digestion and absorption of proteins
Protein in the body
Protein in foods
Health effects and recommended intakes of protein

The Chemists' View of Proteins

Chemically, proteins contain nitrogen atoms, in addition to carbon, hydrogen, and oxygen atoms.
The nitrogen atoms give amino acids their name.
Amino acids form links in protein chains.
Proteins have four structural levels
- Primary: The sequence of amino acids
- Secondary: Folding patterns (alpha helix or beta sheet) created by hydrogen bonding
- Tertiary: 3D structure of the polypeptide chain
- Quaternary: Structure formed by multiple polypeptide chains

Amino Acids

All amino acids have the same basic structure
The side chains vary, contributing to the diversity of proteins
The side chains distinguish one amino acid from another

Essential Amino Acids

Nine essential amino acids are not produced by the body.
They must come from food.
- Ex: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine

Nonessential Amino Acids

These are produced by the body
- Ex: Alanine, Arginine, Asparagine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Glycine, Proline, Serine, Tyrosine

Conditionally Essential Amino Acids

Sometimes a non-essential amino acid becomes essential
This usually occurs when the body cannot produce a required amino acid due to a diet lacking the precursor, or a hereditary condition
Ex: Tyrosine

Proteins

Cells link amino acids end-to-end in various sequences, forming thousands of different proteins
Peptide bonds unite amino acids

Digestion of Proteins

Dietary protein does not directly become body protein.
Enzymes break down polypeptides into smaller peptides, then into individual amino acids
- Ex: Polypeptide chains -> Tripeptides -> Dipeptides -> Individual amino acids

Protein Digestion and Absorption Process

Digestive enzymes hydrolyze proteins (break them down)

Protein Absorption

Special carriers transport amino acids and di/tripeptides into intestinal cells
Amino acids are used for energy or building new proteins

Proteins in the Body

Protein synthesis occurs in the cytoplasm.
Genes provide information for creating proteins

Roles of Proteins

Structural materials
Enzymes
Hormones
Regulators of fluid balance
Regulators of acid-base balance
Transporters
Antibodies
Source of energy (glucose)

Protein Functions in the Body

Proteins form part of body tissues
Facilitate chemical reactions (enzymes)
Regulate body processes and maintain body fluid
Function as buffers (Acid-base balance)
Transport molecules around the body (lipids, vitamins, etc)
Inactivate foreign invaders
Provide energy to the body
Participate in vision
Involved in blood clotting, scar tissue formation

Protein in Foods

Protein quality depends on the amino acid composition and digestibility
Animal protein tends to have high digestibility
Plant protein, while important, has potentially lower digestibility.
Two factors that influence Protein Quality are digestibility and amino acid composition.

Two Factors Influence Protein Quality

Protein digestibility: the measure of amino acids absorbed from a protein source.
Animal proteins generally have high digestibility (90-99%)
Plant proteins usually have lower digestibility (70-90%)
Soy and legumes are notable exceptions

Amino Acid Composition

To create proteins, a cell needs all the required amino acids
The liver produces several essential amino acids that are in short supply
If an essential amino acid is missing, protein synthesis is limited, potentially causing a partial or complete deficiency.
Dietary protein must contain all essential amino acids, or the diet must contain complimentary food sources to cover the missing amino acids to prevent protein breakdown and synthesis limitations.

High Quality Proteins

Dietary proteins containing all essential amino acids relatively equally
Primarily from animal sources, but can also come from soy and legumes

Low Quality Proteins

Dietary proteins limiting in one or more essential amino acids
Primarily from plants, but can also come from some animal sources

Complementary Proteins

Two or more proteins that contain different essential amino acid profiles
Combining those foods provides the full complement of essential amino acids

Health Effects of Protein

Protein deficiency can have devastating health consequences
Deficiencies develop when the diet doesn't supply sufficient or balanced amino acids
Protein deficiency involves reduced protein synthesis and elevated protein degradation
Serious deficiency may become life threatening, due to the essential functions proteins serve in the body.
Protein excess also presents possible risks.

Consequences of Protein Deficiency

Slowed growth and impaired brain/kidney function
Weakened immune function and reduced nutrient absorption
PEM (Protein-energy malnutrition) includes kwashiorkor, and marasmus.
- Kwashiorkor: Edema, swollen belly, malnutrition, and increased infection risk
- Marasmus: Muscle and fat loss, starvation, and stunted growth

Overconsumption of Protein

High-protein diets may present health risks
Possible links to chronic diseases such as:
- Heart disease
- Cancer
- Osteoporosis
- Kidney stones

Recommended Intakes of Protein

RDA (Recommended Dietary Allowance) for protein is 0.8 grams/kg body weight/day
Protein intake should constitute 10-35% of total daily energy intake

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Description

This quiz explores the fundamental aspects of proteins and amino acids, including their chemical distinctions from carbohydrates and lipids. It covers essential amino acids, the role of peptide bonds, and the impact of protein deficiency. Test your knowledge on protein digestion and dietary implications.