Amino acids - Defination, Function, Benifits
Amino acids are the building blocks of proteins, vital for life processes like enzyme activity, hormone production, and tissue repair. Learn their structure, classification, and sources with easy mnemonics for NEET and CBSE. Includes exam-weightage, FAQs, and MCQs.
This Story also Contains
- What Are Amino Acids?
- Structure of Amino Acids
- Types Of Amino Acids
- Classification Of Amino Acids
- How Many Amino Acids Are There?
- Food Sources of Amino Acids
- Functions Of Amino Acids
- Preparation Tips
- Weightage of Amino Acids in Exams
- Types Of Questions Asked in Exams
- Amino Acids NEET MCQs
- FAQs on Amino Acids
- Recommended Video On Amino Acids
Amino acids are among the basic components of biomolecules, which play a significant role in the biochemical processes of life. These organic compounds, as they are considered to be the building blocks of proteins, play an essential physiological role in such functions as enzymatic activity, hormone production, and tissue repair. Amino acids can be classified into two major types: essential amino acids and non-essential amino acids, which the body can synthesize.
What Are Amino Acids?
Amino acids are organic compounds containing carbon, hydrogen, nitrogen, oxygen, and sometimes sulfur. They have an amino group (-NH₂), a carboxyl group (-COOH), and a unique side chain, or R group, that determines the unique characteristics of each amino acid.
Commonly Asked Questions
Amino acids are organic compounds that serve as the building blocks of proteins. They are crucial for life because they form the structural components of cells, catalyze biochemical reactions as enzymes, and play vital roles in metabolism, growth, and repair of body tissues.
The general structure of an amino acid consists of a central carbon atom (alpha carbon) bonded to four groups: an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom (H), and a unique side chain (R group) that determines the specific properties of each amino acid.
Structure of Amino Acids
Apart from proline, all of the 20 aminoacids found in proteins have a common structure in which a carbon atom is linked to a carboxyl group, a primary amino group, and a side chain (R) which is different in each amino acid. Amino acids are dipolar ions (zwitterions) in aqueous solution. They behave as both acids and bases, amphoteric. The side chains differ in size, shape, charge and chemical reactivity, and are responsible for the differences in the properties of different proteins.
Each amino acid has the following general structure:
Amino group: -NH₂
Carboxyl group: -COOH
Hydrogen atom: -H
R group: Variable side chain that defines the amino acid
Types Of Amino Acids
Amino acids can be divided on the basis of the requirement of human health and chemical characteristics. The primary classification is as follows:
Essential Amino Acids
There are several amino acids that the human body cannot produce and must obtain from the diet. This is listed in the essential amino acids list:
Essential Amino Acids |
Histidine |
Isoleucine |
Leucine |
Lysine |
Methionine |
Phenylalanine |
Threonine |
Tryptophan |
Valine |
Non-Essential Amino Acids
Non-essential amino acids can be synthesized by the body. Some common examples are:
Non-Essential Amino Acids |
Alanine |
Asparagine |
Aspartic acid |
Glutamic acid |
Serine |
Tyrosine |
Semi-Essential Amino Acids
These amino acids are generally non-essential but may become essential under certain circumstances, such as illness or stress. Examples include:
Arginine
Cysteine
Glutamine
Glycine
Proline
Tyrosine
Commonly Asked Questions
Amino acids play multiple roles in exercise response. They are used to repair and build muscle tissue after exercise. During prolonged exercise, they can be used as an energy source. Some amino acids, like beta-alanine, can enhance exercise performance by buffering lactic acid buildup. Post-exercise, amino acids are crucial for recovery and adaptation.
Amino acid racemization is the conversion of L-amino acids to their D-form counterparts. This process occurs slowly over time and is considered a marker of protein aging. Accumulation of D-amino acids in tissues has been associated with various age-related conditions and diseases, such as cataracts and Alzheimer's disease.
Amino acids play complex roles in neurodegenerative diseases. Some amino acids, like glutamate, can be neurotoxic in excess. Others, like glycine and D-serine, are important for proper neurotransmission. Imbalances in amino acid metabolism have been implicated in diseases like Alzheimer's, Parkinson's, and Huntington's disease.
Classification Of Amino Acids
Amino acids can also be classified based on their chemical properties that influence their function in proteins and metabolism.
Basic Amino Acids
These are amino acids whose side chains consist of basic (alkaline) groups. They include;
Lysine
Arginine
Histidine
Acidic Amino Acids
These are the amino acids whose side chains contain acidic groups. They include:
Aspartic acid
Glutamic acid
Aromatic Amino Acids
These are amino acids that possess an aromatic ring in their side chains. They include:
Phenylalanine
Tyrosine
Tryptophan
Commonly Asked Questions
Essential amino acids cannot be produced by the body and must be obtained from food, while non-essential amino acids can be synthesized by the body from other compounds. However, some non-essential amino acids may become conditionally essential in certain situations, such as illness or stress.
Most amino acids exist in two forms that are mirror images of each other, called L-form and D-form (chiral molecules). In nature, almost all amino acids used in proteins are L-form. This chirality is crucial for the proper folding and function of proteins.
Branched-chain amino acids (leucine, isoleucine, and valine) are particularly important for muscle metabolism. They can be oxidized in muscle tissue for energy and play a crucial role in promoting muscle protein synthesis. BCAAs are often used as supplements by athletes to support muscle growth and recovery.
Creatine, an important compound for energy metabolism in muscles, is synthesized from three amino acids: glycine, arginine, and methionine. The liver and kidneys are the primary sites of creatine synthesis. Understanding this process has led to the development of creatine supplements popular among athletes.
Amino acids contribute to acid-base balance through their amphoteric nature (ability to act as both acids and bases). They can accept or donate protons, helping to buffer changes in blood pH. Additionally, the metabolism of sulfur-containing amino acids can produce acid, while the metabolism of other amino acids can produce bases.
How Many Amino Acids Are There?
20 standard amino acids coded by the genetic code and used in protein synthesis exist. The particular sequence of these then goes to form proteins into their appropriate shapes and functions.
Commonly Asked Questions
There are 9 essential amino acids in humans. They are called "essential" because the human body cannot synthesize them, so they must be obtained through diet. These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Food Sources of Amino Acids
Amino acids can be obtained from a variety of foods. Foods that are rich in amino acids are;
Animal products: Chicken
Fish: Salmon and tuna
Milk products: Milk, cheese, yoghurt
Legumes and Lentils: Good source of amino acids
Nut and seed products: Almonds, pumpkin
Eggs: Source of complete amino acids
Functions Of Amino Acids
Amino acids perform some key functions:
They are used as the building blocks for proteins.
They act as precursors to hormones.
They participate in enzyme activity.
Some of the amino acids are involved in the formation of neurotransmitters.
Commonly Asked Questions
Amino acids join together through peptide bonds to form long chains called polypeptides. These polypeptides then fold and interact with other polypeptides to create the three-dimensional structure of proteins. The sequence and number of amino acids determine the protein's structure and function.
Amino acids can act as buffers in the body, helping to maintain a stable pH. They can accept or donate hydrogen ions (protons) through their amino and carboxyl groups, which allows them to neutralize small changes in pH and keep the body's acid-base balance within a narrow range.
Several amino acids serve as precursors for neurotransmitters, which are chemical messengers in the nervous system. For example, tryptophan is used to produce serotonin, tyrosine is used to make dopamine and norepinephrine, and glutamate itself acts as a neurotransmitter.
When carbohydrates are not available, amino acids can be broken down and used for energy production through a process called gluconeogenesis. The amino group is removed (deamination), and the remaining carbon skeleton can enter the citric acid cycle to produce ATP.
The R group, or side chain, gives each amino acid its unique properties. It determines whether the amino acid is polar or nonpolar, acidic or basic, and influences its role in protein structure and function. The R group is what distinguishes one amino acid from another.
Preparation Tips
Study Aids: Draw diagrams or tables showing the functions and sources of essential and nonessential amino acids.
Mnemonics: To remember what the essential amino acids are, use "PVT TIM HLL": Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Leucine, Lysine.
Multimedia: View videos or animations showing the structures of amino acids and the function that the different kinds serve in protein synthesis.
Real-Life Example: Connect the amino acids to common foods. For example, for essential amino acids, connect it to meat and for non-essential ones to beans.
Flashcards: Use flashcards to memorize the key terms and characteristics of different amino acids.
Weightage of Amino Acids in Exams
Types Of Questions Asked in Exams
Exam Type | Types of Questions |
CBSE Board Exams |
|
NEET |
|
Nursing Entrance Exams |
|
Paramedical Entrance Exams |
|
Amino Acids NEET MCQs
Q1. Which one of the following amino acids is least likely to be in the core of a protein?
Phenylalanine
Valine
Isoleucine
Arginine
Correct answer: 1) Phenylalanine
Explanation:
An amino acid that is charged and hydrophilic, found to be on the exterior of proteins, is arginine. This allows it to interact with the aqueous environment. Amino acids such as phenylalanine, valine, and isoleucine are hydrophobic and often buried inside the protein core. Hence they contribute to structural stability by avoiding water. The proper arrangement of these different combinations of amino acids is important for maintaining the three-dimensional shape and function of the protein.
Hence the correct answer is Option (4) Arginine.
Q2. In the following question, a statement of assertion (A) is followed by a statement of reason (R)
Assertion: Covalent, peptide bonds that connect the amino acids maintain the primary structure of a protein
Reason: Bonding helps in the stability of protein structure.
Both Assertion & Reason are true and the reason is the correct explanation of the assertion.
If both Assertion & Reason are true but the reason is not the correct explanation of the assertion.
Assertion is a true statement but the Reason is false.
Both Assertion and Reason are false statements.
Correct answer: 1) Both Assertion & Reason are true and the reason is the correct explanation of the assertion.
Explanation:
The assertion and the reason are also true because the reason has explained the correct explanation of the assertion. Peptide bonds with covalency bind amino acids together in a protein to produce its primary structure. This series of amino acids is important in maintaining the final stability and activity of the protein. The power of these covalent bonds helps the protein retain its stability to fold into its active three-dimensional structure. Hence, peptide bond formation is important not only for the development of the primary structure but also for contributing to the stability of the whole protein structure.
Hence the correct answer is Option 1) Both Assertion & Reason are true and the reason is the correct explanation of the assertion.
Q3. Primary protein is a linear chain of amino acids with
N- terminal at both ends
C- terminal at both ends
N- terminal at right end and C- terminal at left end
N- terminal at left end and C- terminal at right end
Correct answer: 4) N- terminal at left end and C- terminal at right end
Explanation:
In a protein, the sequence of amino acids forms a chain, and this chain has two distinct ends. The N-terminal amino acid refers to the first amino acid in the sequence, which has a free amino group (-NH2). The C-terminal amino acid is the last amino acid in the sequence, characterized by a free carboxyl group (-COOH). The terms N-terminal and C-terminal are used to describe the orientation of the protein chain, with the N-terminal being the starting point and the C-terminal being the endpoint. This directionality is important in understanding protein synthesis and function.
Hence, the correct answer is option 4) N- terminal at the left end and C- terminal at the right end.
Also Read:
FAQs on Amino Acids
What do you mean by amino acids?
Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid contains an amino group (-NH₂), a carboxyl group (-COOH), and a variable side chain (R group) attached to the central carbon. The R group determines the chemical nature of each amino acid. They play vital roles in protein structure, enzyme activity, hormone production, and metabolic pathways. Without amino acids, protein synthesis and life processes would not be possible.
How many amino acids are used in protein synthesis?
There are 20 standard amino acids that participate in the synthesis of proteins in all living organisms. These amino acids are encoded by the genetic code (codons) in DNA and mRNA. Some are essential amino acids i.e., obtained from diet) while others are non-essential i.e., synthesized in the body). They join together through peptide bonds to form long chains, which fold into functional proteins.
Which foods are rich in amino acids?
Foods rich in amino acids are those containing high-quality proteins. Animal-based sources like eggs, chicken, fish, meat, and milk provide all essential amino acids and are considered complete proteins. Plant-based sources include legumes, beans, soy, lentils, and nuts, though some may lack one or more essential amino acids. Thus, a varied diet ensures proper intake of all amino acids required for body functions.
What are essential amino acids?
The essential amino acids cannot be synthesized by the body and must be obtained through diet. These amino acids are crucial for growth, tissue repair, enzyme production, and overall metabolism. Their deficiency can lead to growth retardation, muscle wasting, and other health issues.
Phenylalanine
Valine
Threonine
Tryptophan
Isoleucine
Methionine
Histidine
Leucine
Lysine
Recommended Video On Amino Acids
Frequently Asked Questions (FAQs)
Some amino acids, such as cysteine, methionine, and taurine, have antioxidant properties. They can neutralize harmful free radicals in the body, protecting cells from oxidative stress and damage. This antioxidant action contributes to overall health and may help prevent chronic diseases.
The liver uses amino acids for various functions, including protein synthesis, glucose production, and detoxification. For example, the liver uses amino acids to produce albumin, an important blood protein. It also uses amino acids in the urea cycle to remove toxic ammonia from the body.
While amino acids are not directly used in DNA synthesis, they play supportive roles. For example, glycine, aspartate, and glutamine contribute to the synthesis of purines, which are components of DNA. Additionally, the amino acid metabolism is linked to the production of energy and reducing agents needed for DNA synthesis.
Amino acids play crucial roles in detoxification. For example, glycine and glutamine are used in Phase II liver detoxification to conjugate and neutralize toxins. Cysteine is a component of glutathione, one of the body's most important antioxidants and detoxifying agents.
Amino acids contribute to fluid balance through their role in protein synthesis. Proteins, particularly albumin, help maintain oncotic pressure in blood vessels, which is crucial for proper fluid distribution between blood and tissues. Some amino acids also act as osmolytes, helping to regulate cell volume.
Amino acids impact cardiovascular health in several ways. Arginine, for example, is a precursor to nitric oxide, which helps dilate blood vessels and improve blood flow. Taurine has been shown to lower blood pressure and reduce cholesterol levels. Additionally, amino acids are needed to produce heart muscle proteins and enzymes involved in heart function.
Amino acids are crucial in the body's response to stress. They are needed to produce stress hormones like adrenaline and cortisol. Additionally, certain amino acids like tyrosine can help mitigate the effects of stress by supporting the production of neurotransmitters that regulate mood and cognitive function under stress.
Amino acids play a role in circadian rhythms through various mechanisms. The metabolism of certain amino acids, like tryptophan, is involved in the production of melatonin, a key hormone in regulating sleep-wake cycles. Additionally, the availability of amino acids can influence the expression of clock genes that control circadian rhythms.
Certain amino acids play important roles in the body's adaptation to high altitude and low oxygen conditions. For example, branched-chain amino acids (BCAAs) may help maintain muscle mass at high altitudes. Arginine can enhance nitric oxide production, potentially improving blood flow and oxygen delivery in hypoxic conditions.
Amino acid catabolism can contribute to glucose homeostasis through gluconeogenesis, the production of glucose from non-carbohydrate sources. This process is particularly important during fasting or low-carbohydrate diets. However, excessive protein breakdown for glucose production can lead to muscle wasting in prolonged starvation or uncontrolled diabetes.
