Nutrition of Proteins

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Questions and Answers

What distinguishes proteins from carbohydrates and lipids in their chemical composition?

Proteins contain sulfur atoms.

Proteins lack carbon atoms.

Proteins contain nitrogen atoms. (correct)

Proteins only contain oxygen atoms.

What are essential amino acids?

Amino acids that do not contain nitrogen.

Amino acids that can be synthesized by the body.

Amino acids required only during exercise.

Amino acids that must be consumed through diet. (correct)

How can high-quality proteins be differentiated from low-quality proteins?

High-quality proteins have a higher PDCAAS score. (correct)

High-quality proteins do not yield energy.

High-quality proteins contain fewer amino acids.

High-quality proteins are only found in animal products.

What is protein turnover?

The breakdown and synthesis of proteins in the body. (C) Signup and view all the answers

What is the implication of a negative nitrogen balance?

The body is losing more nitrogen than it is consuming. (B) Signup and view all the answers

Which of the following best explains the concept of mutual supplementation in the context of protein consumption?

Combining different incomplete protein sources to obtain all essential amino acids. (A) Signup and view all the answers

Why are legumes and grains considered complementary proteins?

Because the amino acids they lack are different and thus can supplement each other when combined. (A) Signup and view all the answers

Which role of body proteins is most directly involved in maintaining the body's resistance to disease?

Antibodies. (A) Signup and view all the answers

How do proteins contribute to the body's fluid and electrolyte balance?

By attracting and retaining water in different body compartments. (A) Signup and view all the answers

What is the primary function of proteins acting as buffers in the body?

To maintain the acid-base balance of body fluids. (B) Signup and view all the answers

Which of the following exemplifies the role of proteins in providing structural support for the body?

The formation of collagen in scar tissue. (C) Signup and view all the answers

What is the immediate requirement provided by amino acids during protein turnover?

To build proteins for new tissues. (B) Signup and view all the answers

Besides providing structural components and enabling chemical reactions, what is another function of protein related to energy?

They can be converted to glucose for energy when needed. (A) Signup and view all the answers

What structure is formed when three amino acids are bonded together?

Tripeptide (B) Signup and view all the answers

Which factor contributes to the incomplete or low-quality protein source in diets?

Improper combination of essential amino acids (B) Signup and view all the answers

What is the main site of amino acid absorption into the blood?

Small intestine (D) Signup and view all the answers

What happens to proteins when they are denatured?

They lose function but maintain primary structure (A) Signup and view all the answers

What determines the unique sequence of proteins?

Genes (DNA) (B) Signup and view all the answers

What is the role of pepsin in protein digestion?

Cleaving proteins into smaller polypeptides (D) Signup and view all the answers

Excess dietary protein typically leads to which metabolic response for amino acids?

They are metabolized and nitrogen is excreted (B) Signup and view all the answers

How many different kinds of proteins can potentially exist in the human body?

10,000-50,000 (B) Signup and view all the answers

Which amino acids must be obtained through diet as they cannot be synthesized by the body?

Histidine (D) Signup and view all the answers

What is the main function of transamination in amino acid metabolism?

To transfer the amine group from one amino acid to another (A) Signup and view all the answers

Under what condition does a nonessential amino acid become conditionally essential?

When the body's ability to produce it is impaired (D) Signup and view all the answers

Which of the following amino acids is classified as essential?

Leucine (C) Signup and view all the answers

What role do transaminases play in amino acid synthesis?

They facilitate the transfer of amine groups (A) Signup and view all the answers

What is released during the condensation reaction that forms a peptide bond?

Water (A) Signup and view all the answers

In the context of amino acids, what is the significance of phenylketonuria (PKU)?

It prevents the conversion of phenylalanine to tyrosine (C) Signup and view all the answers

How are dipeptides formed?

By linking two amino acids through a peptide bond (C) Signup and view all the answers

What type of protein does not contain all nine essential amino acids?

Incomplete protein (D) Signup and view all the answers

Which factor does NOT determine the quality or completeness of protein?

Source of protein (B) Signup and view all the answers

What effect can high supplementation of one amino acid have on absorption?

Inhibit absorption of other amino acids (D) Signup and view all the answers

In the context of protein quality, what does PDCAAS stand for?

Protein digestibility-corrected amino acid score (A) Signup and view all the answers

Which of the following foods typically has the highest protein digestibility?

Animal foods (D) Signup and view all the answers

What is an amino acid score?

A comparison of essential amino acids in food against a reference (D) Signup and view all the answers

Which essential amino acid is considered limiting if present in the shortest supply in dietary protein?

Methionine (D) Signup and view all the answers

How is the PDCAAS calculated?

Amino acid score multiplied by protein digestibility (A) Signup and view all the answers

Which of the following examples is considered a complete protein source?

Eggs (C) Signup and view all the answers

What percentage of protein digestibility is typically seen in plant foods compared to animal foods?

80-90% (C) Signup and view all the answers

What occurs in the body during a negative nitrogen balance?

The body degrades more protein than it synthesizes. (C) Signup and view all the answers

Which of the following is true regarding protein needs?

They vary based on activity, age, and health status. (B) Signup and view all the answers

During protein turnover, what percentage of available amino acids is typically stripped of nitrogen for energy?

25% (A) Signup and view all the answers

What characterizes a positive nitrogen status in the body?

The body synthesizes more protein than it degrades. (A) Signup and view all the answers

How can protein needs be effectively assessed?

By measuring nitrogen balance. (D) Signup and view all the answers

Which of the following amino acids is considered conditionally essential?

Arginine (A) Signup and view all the answers

What process involves linking amino acids to form proteins?

Condensation reaction (C) Signup and view all the answers

Which amino acid must be obtained from the diet if phenylalanine cannot be converted into it due to a metabolic disorder?

Tyrosine (D) Signup and view all the answers

Which of the following describes an essential amino acid?

It must be obtained through dietary sources. (A) Signup and view all the answers

Which enzyme group catalyzes the transamination process?

Transaminases (A) Signup and view all the answers

Why are there nine essential amino acids that cannot be synthesized by the body?

The body lacks the necessary enzymes for their synthesis. (A) Signup and view all the answers

Which amino acid undergoes transamination to become an essential amino acid in certain conditions?

Tyrosine (D) Signup and view all the answers

What is formed when two amino acids are joined together?

Dipeptide (A) Signup and view all the answers

What is the role of hydrochloric acid (HCl) in the digestion of proteins?

Denatures proteins (C) Signup and view all the answers

What happens to proteins when they undergo denaturation?

They lose their function (D) Signup and view all the answers

Which statement best describes a limiting amino acid?

An essential amino acid in the shortest supply for protein synthesis (D) Signup and view all the answers

In protein synthesis, what primarily determines an individual's protein structure?

Amino acid sequence (A) Signup and view all the answers

Where do absorbed amino acids go after entering the bloodstream?

Transported to the liver (A) Signup and view all the answers

Which agents can potentially cause protein denaturation?

Acids and heat (A) Signup and view all the answers

How many amino acids are typically needed to form a polypeptide?

Ten or more (D) Signup and view all the answers

What is the primary benefit of mutual supplementation in protein consumption?

It enables complete amino acid profiles from incomplete sources. (B) Signup and view all the answers

Which amino acids are legumes particularly low in, making them a complementary source when paired with grains?

Methionine and tryptophan (A) Signup and view all the answers

In what way do proteins contribute to the body's acid-base balance?

By functioning as buffers. (D) Signup and view all the answers

Which role of proteins is essential for transporting substances around the body?

Transporters (A) Signup and view all the answers

What happens during protein turnover in the body?

Proteins are continuously synthesized and degraded. (B) Signup and view all the answers

Which of the following purposes is NOT served by body proteins?

Regulating water intake (A) Signup and view all the answers

What is an important factor in maintaining nitrogen balance in the body?

Availability of amino acids (C) Signup and view all the answers

What role do antibodies, which are proteins, play in bodily functions?

Inactivating disease-causing agents (A) Signup and view all the answers

What is a characteristic of incomplete proteins?

They do not contain all nine essential amino acids. (C) Signup and view all the answers

Which two factors determine the protein quality or completeness?

Amount of essential amino acids and protein digestibility. (A) Signup and view all the answers

What does the Protein Digestibility-Corrected Amino Acid Score (PDCAAS) evaluate?

The amino acid score corrected for protein digestibility. (C) Signup and view all the answers

Which type of amino acid is present in the shortest supply relative to protein synthesis needs?

Limiting amino acid. (C) Signup and view all the answers

Which food source is typically associated with high protein digestibility?

Soy foods. (C) Signup and view all the answers

What can excessive consumption of one amino acid due to supplementation lead to?

Inhibition of absorption of another amino acid. (A) Signup and view all the answers

What is the method to assess protein quality based on both amino acid requirements and digestibility called?

Protein Digestibility-Corrected Amino Acid Score. (A) Signup and view all the answers

Which of the following describes an animal food's protein digestibility compared to plant foods?

Animal foods are highly digestible, often upwards of 90%. (D) Signup and view all the answers

What indicates that a protein could be considered of low quality?

When it is derived from plant sources. (A) Signup and view all the answers

What is the purpose of having an amino acid score for a protein?

To evaluate the protein quality based on essential amino acid amounts. (A) Signup and view all the answers

What is the recommended daily protein intake for infants and children?

0.95-1.5 g/kg/day (A) Signup and view all the answers

Which group of individuals has the highest protein requirement per body weight?

Infants (B) Signup and view all the answers

What percentage of total calorie intake should protein represent to meet dietary recommendations?

20%-35% (B) Signup and view all the answers

What is a possible risk associated with diets high in protein from animal sources?

High cholesterol and heart disease (A) Signup and view all the answers

Which vegetarian diet excludes only meat but allows dairy and eggs?

Lacto-ovo vegetarian (B) Signup and view all the answers

What is the risk associated with high protein diets leading to excess calcium excretion?

Bone loss (B) Signup and view all the answers

Which type of vegetarian diet only includes plant-based foods?

Vegan (A) Signup and view all the answers

What is a consequence of protein-energy malnutrition?

Utilization of protein for energy (D) Signup and view all the answers

What is a key benefit of a vegetarian diet related to health risks?

Reduced risk of cardiovascular disease (A) Signup and view all the answers

Which factor does NOT increase the protein requirements of individuals?

Vegetarianism (C) Signup and view all the answers

Study Notes

Proteins

Proteins are macronutrients that contain carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) atoms.
Proteins are essential for energy production, particularly when fat and carbohydrate stores are low.
Proteins are synthesized in the body based on a genetic code.

Learning Goals

Proteins are compared and contrasted with other energy-containing macronutrients (carbohydrates and lipids).
A list of essential amino acids, and how they are quantified is covered (PDCAAS).
Low-quality protein deficiencies can be overcome through mutual supplementation.
Roles of body proteins, protein turnover, and nitrogen balance are identified.
Health Canada's recommendations for total protein intake and challenges for vegetarians are explored.

Comparison to Lipids and Carbohydrates

Similar to carbohydrates and lipids, proteins contain carbon, hydrogen, and oxygen atoms, but proteins also contain nitrogen.
Proteins produce energy when there is a shortage of other energy sources like fats and carbohydrates.
Proteins are synthesized in the body by following the instructions encoded in genes.

Base Unit - Amino Acids

Proteins are composed of amino acids.
Amino acids share a common structure, a backbone composed of a central carbon atom bound to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R-group).
The unique R-group gives each amino acid its distinctive properties.

Amino Acids

There are 20 different amino acids involved.
9 of these are essential amino acids, meaning the body cannot produce them and they must be obtained from the diet.
The 9 essential amino acids are: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine.

Transamination

Transamination is a process that converts one amino acid into another.
It transfers an amino group (-NH2) from one amino acid to a keto acid, converting the keto acid into a new amino acid.
Transamination primarily occurs in the liver, and it plays a crucial role in converting essential amino acids into nonessential amino acids.

Amino Acids (Conditionally Essential)

Some amino acids are considered conditionally essential. This means they are normally non-essential but become essential during certain circumstances.
An example is phenylalanine and tyrosine. The body normally converts phenylalanine to tyrosine, but if the conversion process is impaired (as seen in phenylketonuria), phenylalanine becomes essential.

How are Proteins Made?

Amino acids are linked together through condensation reactions to form peptide bonds.
A dipeptide is formed when two amino acids are bonded together.
When multiple amino acids are bonded together, they form a polypeptide, which is a chain of amino acids. Most proteins are 30-300 amino acids in length.
The sequence of amino acids determines the protein's unique shape and function.

Protein Synthesis

The sequence of amino acids in a protein is determined by the genetic code in DNA.
This process begins with transcription, where DNA is copied into mRNA.
The mRNA then travels to ribosomes, where translation takes place.
During translation, the ribosomes use the mRNA code to assemble amino acids into a polypeptide chain.

Protein Synthesis Limiting Factors

The synthesis of proteins may be limited by the availability of specific essential amino acids present in lower concentration in dietary protein than needed
Inadequate energy intake can also limit protein synthesis, as amino acids might be used for alternative metabolic processes, such as gluconeogenesis.

Protein Organization

The unique sequence of amino acids in a protein determines its three-dimensional structure.
The structure then determines its function.
Proteins vary in complexity ranging from around 10,000-50,000 different kinds.

Protein Denaturation

Proteins can be denatured by various agents such as heat, acid, changes in pH, and changes in salinity.
Denaturation results in a loss of protein function and the proteins' three-dimensional structure is disrupted.

Protein Digestion

Protein digestion begins in the mouth with mechanical breakdown and mixing with saliva.
In the stomach, hydrochloric acid denatures proteins and activates pepsin, an enzyme that breaks down proteins into smaller polypeptides.
In the small intestine, tripeptidases and dipeptidases further break down these smaller polypeptide chains into amino acids.

Protein Absorption

Intestinal cells absorb amino acids and some di- and tripeptides from the small intestine's lining.
Amino acids are transported directly to the liver through the portal vein to be utilized for multiple processes.
Excess amino acids are rapidly metabolized, and nitrogen is excreted if exceeding body need.

Protein in Foods

Complete proteins contain all essential amino acids and are typically animal-derived.
Incomplete proteins are lacking one or more essential amino acids and are mostly plant-derived.
Protein quality is determined by the amount and digestibility of essential amino acids.
PDCAAS, the Protein Digestibility-Corrected Amino Acid Score, is a method to quantify protein quality.

Mutual Supplementation

Mutual supplementation involves combining incomplete protein sources, providing needed essential amino acids missing from each other.
For example, legumes provide abundant isoleucine and lysine but are deficient in methionine and tryptophan, while grains offer the opposite profile.

Roles of Body Proteins

Proteins have many roles in the body, including forming structures (tendons and ligaments), facilitating chemical reactions (enzymes), transporting molecules, regulating fluid balance, and maintaining acid-base balance.
They also create blood clots (fibrin), form scars (collagen) and participate in vision (opsin).
Antibodies help protect the body and hormones regulate bodily processes.

Protein Turnover and Nitrogen Balance

Protein turnover is the continuous process of protein synthesis and breakdown within the body's cells.
Amino acids released during protein breakdown can be recycled, or used as energy.
Nitrogen balance is the difference between nitrogen intake (from proteins) and nitrogen excretion (primarily in urine).
Positive nitrogen balance indicates growth or tissue repair, whereas negative nitrogen balance can occur in situations of starvation, injury, or illness.

How Much Protein Should We Eat?

The Acceptable Macronutrient Distribution Range (AMDR) for protein intake in adults is usually 10% to 35% of daily caloric needs.
Individual needs vary based on factors such as age, activity level, and health status. Based on body weight, estimated requirement rates for proteins are higher for athletes, and children and adolescents. Lactating and pregnant women require even more than the normal daily requirements.
There are differences in the exact amounts required based on specific factors.

Calculation of Energy Content

The method for converting grams of nutrients to kilocalories is provided and the calculation of percentages is shown for an example.

Dietary Protein Risks

Too little dietary protein results in protein-energy malnutrition (PEM), often affecting children most severely.
Signs of PEM can include stunted growth and weakened immunity.
Too much dietary protein may contribute to risks such as high cholesterol, heart disease, and possible bone loss, particularly if excessive saturated fat from animal products is consumed. This risk is especially higher for those with a family history of kidney disease.

Vegetarianism

Vegetarianism involves restricting the diet to exclude meat or other animal products.
Several types of vegetarianism exist, each with different restrictions. Vegetarians may avoid red meat, poultry, seafood, eggs, and dairy.
Vegetarians may need to carefully plan protein intake and supplement diets to ensure they obtain nutritional requirements as complete proteins are hard to obtain through plant-based proteins alone. Protein sources such as beans, tofu, and nuts should be prioritized to maintain optimal health.
Health advantages of vegetarianism include generally reduced fat and calorie intake, and therefore a reduced risk of obesity, heart disease, and certain cancers.

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Description

This quiz explores key concepts in biochemistry, focusing on the distinct chemical compositions of proteins, carbohydrates, and lipids. It covers essential amino acids, differences between high and low-quality proteins, protein turnover, and the implications of a negative nitrogen balance.