Biology Chapter on Proteins

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Questions and Answers

Which of the following amino acids is considered conditionally essential?

Tyrosine (correct)

Methionine

Glutamic Acid

Lysine

What type of bond connects amino acids in a protein?

Ionic bond

Peptide bond (correct)

Hydrogen bond

Disulfide bond

Which structure provides strength and rigidity to a protein?

Primary structure

Quaternary structure

Tertiary structure

Secondary structure (correct)

Which type of amino acid side chain is hydrophilic?

Attracts water Signup and view all the answers

What is the final structure of a protein that involves interactions among multiple polypeptides?

Quaternary structure Signup and view all the answers

What is the primary function of hemoglobin in the body?

Carries oxygen from lungs to cells Signup and view all the answers

How do antibodies function in the immune response?

They bind to and neutralize specific invaders Signup and view all the answers

What happens to protein metabolism during starvation?

Tissue proteins break down to free amino acids for energy Signup and view all the answers

What role do transport proteins play in the body?

They facilitate the movement of compounds across cell membranes Signup and view all the answers

Which of the following statements about protein turnover is correct?

The amino acid pool remains constant despite degradation rates Signup and view all the answers

What role do proteins play in the formation of bone?

They are the primary components of collagen. Signup and view all the answers

How do proteins function as hormones in the body?

They act as messenger molecules to elicit responses. Signup and view all the answers

Which of the following best describes the role of enzymes as proteins?

They remain unchanged during chemical reactions. Signup and view all the answers

What is the primary goal of proteins as acid-base regulators?

To prevent acidosis or alkalosis. Signup and view all the answers

During critical illness, how can proteins affect fluid balance?

They leak into tissues causing swelling. Signup and view all the answers

In the context of protein roles, what does catabolic mean?

To break down substances. Signup and view all the answers

What condition can result from inadequate dietary protein intake?

Reduced ability of cells to function. Signup and view all the answers

Which of the following proteins plays a role in blood glucose control?

Insulin Signup and view all the answers

What is a potential negative health aspect of a vegetarian diet?

Low quality protein Signup and view all the answers

Why might vegetarians enjoy better cardiovascular health?

Increased fiber and reduced saturated fat intake Signup and view all the answers

What nutrient might be low or lacking in a vegan diet?

Vitamin B12 Signup and view all the answers

Which aspect is correlated with a decreased incidence of cancer in vegetarians?

Higher fiber intake from fruits and vegetables Signup and view all the answers

What is one of the main reasons some individuals choose a vegetarian diet?

Concerns over animal cruelty Signup and view all the answers

What can vegetarians do to combat potential nutrient deficiencies?

Ensure a balanced diet and consider supplementation Signup and view all the answers

How does a vegetarian diet typically affect body weight?

May result in lower body weight Signup and view all the answers

What type of fatty acids do vegetarians typically have more of in their diet?

Monounsaturated and polyunsaturated fatty acids Signup and view all the answers

What is the state of nitrogen balance in healthy individuals?

Nitrogen equilibrium Signup and view all the answers

Under what circumstances is a positive nitrogen balance likely to occur?

During pregnancy Signup and view all the answers

Which amino acid is a precursor for the neurotransmitter serotonin?

Tryptophan Signup and view all the answers

Which process involves stripping amino acids of their nitrogen-containing amino group?

Deamination Signup and view all the answers

Excess ammonia in the blood is primarily a result of which organ's failure?

Liver Signup and view all the answers

What is the purpose of converting ammonia to urea in the body?

To eliminate nitrogenous waste Signup and view all the answers

Which characteristic defines high-quality protein?

Contains all essential amino acids Signup and view all the answers

What is the recommended maximum protein intake for optimal urea production?

250g/day Signup and view all the answers

Which group of proteins cannot support protein synthesis by itself?

Low-quality proteins Signup and view all the answers

Which method enhances the quality of plant proteins?

Complementary proteins Signup and view all the answers

What is the recommended dietary ratio for non-heme iron intake compared to usual recommendations?

1.8 times the usual recommendation Signup and view all the answers

Which factor is known to negatively impact the absorption of zinc?

Soy products Signup and view all the answers

Which vitamin is only found in animal-derived foods and fermented soy products?

Vitamin B12 Signup and view all the answers

For individuals avoiding milk products, which vitamin is a significant concern, particularly for specific age groups?

Vitamin D Signup and view all the answers

What is a key practice when planning a vegetarian meal?

Choosing whole foods over processed ones Signup and view all the answers

What does nutrigenomics focus on?

Interaction between diet and gene expression Signup and view all the answers

In genetics, what term describes the addition of a methyl group to DNA that can affect gene expression?

Methylation Signup and view all the answers

What distinguishes single-gene disorders from multi-gene disorders?

Single-gene disorders involve mutations affecting only one gene. Signup and view all the answers

Which of the following is a common type of genetic variation associated with complex diseases?

Single-nucleotide polymorphisms (SNPs) Signup and view all the answers

Why do some individuals respond differently to dietary interventions?

Genetic differences affect metabolism and nutrient absorption. Signup and view all the answers

Study Notes

Protein Overview

Proteins are made of 20 different amino acids (AA).
Amino acids are composed of C, H, O, and N atoms.
They have an amine group (NH2), an acid group (COOH), and a unique side chain.
The side chain differentiates one AA from another in size, shape, and electrical charge. These differences create unique chemical structures.
Amino acids join via peptide bonds to form proteins.
The peptide bond is between the amine group of one amino acid and the acid group of the next.
Each AA has an electrical charge affecting its shape (e.g., globular, strips, coiled).
Shape enables specific tasks; like acting as catalysts (enzymes), transporting oxygen (hemoglobin), and forming connective tissue (collagen).

Essential, Non-essential, and Conditionally Essential Amino Acids

Non-essential amino acids: The body can synthesize these.
Dispensable amino acids: Alanine, asparagine, aspartic acid, glutamic acid, and serine are examples.
Essential amino acids: These are not made by the body and must be obtained from the diet.
- Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine are essential.
Conditionally essential amino acids: These are normally non-essential but become essential under certain conditions (e.g., disease or stress). An example would be tyrosine.

Amino Acid Chains & Structures

Proteins consist of linked amino acids with various sequences.
These amino acids are connected by peptide bonds.
Dipeptide: two linked amino acids.
Tripeptide: three linked amino acids.
Polypeptide: multiple amino acids linked together.
Primary Structure: The sequence of amino acids in a protein.
Secondary Structure: The shape that a polypeptide chain takes, determined by weak electrical attractions within the chain. The patterns, like helices (coils) and sheets (folds) give the protein part of its three-dimensional structure. This creates stability.
Tertiary Structure: The unique, three-dimensional shape of a protein, determined by interactions between the amino acid side chains.
Quaternary Structure: The arrangement of multiple polypeptide chains in a protein. These chains are stabilized via the interactions between their side chains.

Protein Digestion and Absorption

Protein digestion begins in the mouth with chewing.
Saliva prepares the food for swallowing.
In the stomach, hydrochloric acid (HCl) denatures proteins, exposing peptide bonds for enzymes to break down proteins.
HCl activates pepsin from pepsinogen, crucial for the breakdown.
The small intestine and pancreas contain enzymes that further break down polypeptides & dipeptides, into single amino acids.
Proteases, peptidases digest peptides into individual amino acids.
Intestinal cells absorb amino acids into the bloodstream, carrying them to the liver and then the body for use.
Enzymes are optimal functioning in specific pH environments inside the body.
Their denaturation occurs outside of their ideal range which affects digestion.

Protein in the Body

The human body has more than 1 million kinds of proteins, but only a few thousand have been studied well.
Each protein has a specific function determined during protein synthesis based on an amino acid sequence specified by heredity.

Protein Synthesis

Protein synthesis relies on adequate dietary protein and essential amino acids.
DNA serves as the template to produce messenger RNA (mRNA).
Messenger RNA (mRNA) carries instructions to the cell's protein-making machinery (ribosomes).
Transfer RNA (tRNA) collects amino acids from the body's pool/cell fluid and brings them to the ribosomes.
Ribosomes use the information in mRNA to arrange amino acids in a specific sequence forming the protein.
Transcription: The mRNA is created from the DNA template.
Translation: The mRNA, using the information on the nucleotide sequence, is used by the ribosome to create the protein.

Sequencing Errors

Genetic errors altering protein AA sequences can cause disorders like sickle cell anemia.
Sickle cell anemia arises when valine replaces glutamic acid in the hemoglobin protein resulting in unusual hemoglobin function.
This affects the ability of red blood cells to carry oxygen effectively due to shape alterations.

Roles of Protein

Building Materials: Proteins are crucial for building & repairing tissues (blood, muscle, skin, etc.) and replacing damaged cells. Collagen is particularly important in bone, ligaments, tendons.
Hormones: Some hormones, like insulin and glucagon (regulating blood sugar) and thyroxine (regulating metabolism), are proteins.
Enzymes: Proteins act as catalysts, speeding up chemical reactions in the body.
Acid-Base Regulators: Proteins help maintain the proper balance of acids and bases in body fluids.
Fluid Balance: Proteins help regulate fluid balance within cells and tissues. Leaking of proteins leading to edema.
Transporters: Proteins transport nutrients and other molecules throughout the body. Hemoglobin transports oxygen; lipoproteins carry lipids.
Antibodies: Proteins that defend the body against disease. They recognize and neutralize foreign invaders (antigens). Memory underlies immunizations.
Energy Source: Proteins can be broken down to provide energy if carbohydrate & total energy intake is insufficient.
Other roles: proteins also involved in blood clotting, vision, and other critical bodily functions.

Protein Metabolism and Turnover

Protein turnover: Proteins within cells are continuously being made and broken down.
An amino acid pool exists where amino acids are constantly changing.
Amino acids used to make new body proteins or other nitrogen-containing compounds.
Amino acids can be used directly for energy production and the rest stored as fat.
Nitrogen balance: Healthy individuals are in a state of equilibrium (protein synthesis = protein degradation).
People in growing stages or pregnancy have positive nitrogen balance (protein intake greater than excretion).

Using Amino Acids to Make Other Compounds

The body uses amino acids as building blocks for other molecules:
- Tyrosine: forms norepinephrine, epinephrine, melanin, and thyroxine.
- Tryptophan: forms niacin and serotonin.

Using Amino Acids to Make Fat

If energy and protein intake exceed body needs and adequate carbohydrate intake is present, amino acids are converted to fat for storage.

Deaminating Amino Acids

Deamination is the removal of the amino group to produce ammonia and a keto acid.
The keto acid can be used in energy production, glucose synthesis, or fat production.
Ammonia is converted to urea for excretion.

Using Amino Acids to Make Proteins and Essential Amino Acids

The body breaks down existing proteins to obtain missing essential amino acids. Non-essential amino acids are synthesized from available intermediates.
Essential amino acids, which can't be manufactured by the body, are obtained from the diet.
The liver is key in synthesizing non-essential amino acids. Transamination reactions and keto acids are central processes in this synthesis.

Converting Ammonia to Urea

Ammonia is a toxic waste product of protein metabolism.
The liver converts ammonia to urea, a less toxic substance.
Urea is excreted by the kidneys.

Excreting Urea

The kidneys filter urea from the blood.
Urea is part of waste products excreted in urine.

Protein in Food

Quality is influenced by digestibility and amino acid composition.
High-quality proteins contain all essential amino acids and are mostly from animal sources, and some from soy protein.
Low-quality proteins lack one or more essential amino acids and are sourced from plant products.

Protein Quality and Digestibility

Protein quality is evaluated using PDCAAS which measures the digestibility corrected amino acid score.
Protein digestibility depends on the protein source (animal vs. plant) and preparation methods (cooking with moist heat)

Food Labels: Protein

Food labels must include the quantity of protein in grams.
They might include %DV values depending on the country, including Canada or the US.
PDCAAS is used to evaluate protein quality, reflecting digestibility & amino acid composition.

Health Effects of Protein

High intake of animal protein can increase the risk of heart disease.
Replacing animal protein with plant protein may reduce this risk.
Protein, itself, doesn't directly cause cancer. However, certain protein-rich foods might have different impacts.
Increased protein intake can increase calcium excretion, potentially affecting bone health.
Protein intake and fibre can help with weight control. Individuals with kidney disease require individualized protein intake based on the disease state.

Protein Deficiency

Inadequate protein intake can cause slowed growth, impaired brain and kidney function, weakened immunity, and poor nutrient absorption.
Inadequate protein (and/or energy) intake leads to protein-energy malnutrition (PEM).

Protein-Energy Malnutrition (PEM)

PEM is a widespread problem due to starvation or hunger.
Two major types of PEM are Kwashiorkor and Marasmus.
Kwashiorkor is characterised by edema, skin rash (sometimes hair discoloration) and fatty liver.
Marasmus is characterized by wasting of fat reserves, weakness, and extremely low energy.

Vegetarian Diets

Several types of vegetarianism exist: vegetarian, partial vegetarian, pesco-vegetarian, lacto-ovo vegetarian, lacto vegetarian, ovo vegetarian, vegan, and fruitarian.
Motivations for choosing a vegetarian diet can include health concerns, environmental concerns, animal cruelty concerns.

Positive Health Aspects of Vegetarianism

Vegetarians often maintain a healthier body weight due to greater amounts of fiber, lower fat intake or possibly other dietary factors.
Lower SFA intake has been positively correlated with lower cardiovascular issues.
Diets with less red or processed meat appear to reduce cancer risk.

Possible Negative Aspects of Vegetarianism

Depending on the type of vegetarian diet, there can be concerns over deficiencies in nutrients like iron, B12, calcium or vitamin D. Careful planning and possible supplementation may be necessary to circumvent these issues. Fortified products can sometimes overcome these nutrient deficiencies.

Nutrients of Interest (Protein, Fat, Minerals, Vitamins)

Protein: Quality, amount, preparation (timing & technique), complete vs incomplete proteins.
Fat: Omega-3 fatty acids, EPA/DHA.
Minerals: Iron (Heme vs. Non-Heme, absorption considerations), Zinc, Calcium (for those who avoid milk products).
Vitamins: B12 and D (fortification may be crucial).

Planning a Vegetarian Meal

Emphasis on whole foods instead of processed, planning complete meals (carbohydrate, protein, and fat components).
Including fortified foods (to alleviate possible vitamin/mineral deficiencies).

Nutritional Genomics

Nutrigenomics/nutrigenetics study the relationship between nutrients & genes.
Some genomic testing is controversial due to lack of definitive clinical or scientific validity.
The goal is to personalize recommendations based on an individual's genes and environment, potentially optimizing health outcomes.

Genomics Primer

The human genome contains an estimated 20,000-25,000 protein-coding genes.
Gene expression is the process of using genetic information in DNA to make proteins.
Examining gene expression patterns may help understand disease development.
Gene expression doesn't guarantee trait expression.
Nutrients can activate or silence genetic expression.

Epi-genetics

Epi-genetics examines how environmental factors affect gene expression.
Methylation is a crucial epigenetic process in which a methyl group is added to DNA or protein. Methylation can alter gene expression, which affects protein production.
Ongoing research explores how different nutrients influence gene expression.

Genetic Variation & Disease

Individuals have different genetic variations.
Genetics can influence responses to dietary interventions (e.g., some may respond differently to the same nutritional changes).
Genetic factors contribute to diseases like heart disease.

Gene Disorders

Single gene disorders arise from mutations in a single gene.
Missing or malfunctioning proteins cause specific metabolic disorders and often require specific dietary interventions.
Examples of single-gene disorders include PKU.

Multi-gene Disorders

These disorders are influenced by multiple genes.
Many risk factors for a disease are influenced by multiple genes and/or environmental issues.
Common examples are heart disease.
Research often examines genetic variations (SNPs) to understand these issues better.

Summary

The notes above include a comprehensive summary about proteins and related concepts, drawing from the provided text. The main points regarding the role of proteins in the body, digestion, absorption, types of proteins, health implications, and implications for certain dietary choices are covered. Each concept or topic is expounded on using accurate details.

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Test your knowledge on proteins with this quiz focused on their structure, function, and metabolism. Explore key concepts like amino acids, hemoglobin, and protein turnover, and discover how proteins play crucial roles in biological processes. Perfect for students diving into biochemistry or molecular biology.