Protein - Definition , Structure and Functions
Definition
Proteins are complex organic molecules composed of long chains of amino acids that are folded into specific three-dimensional shapes. They are one of the fundamental building blocks of life, and are involved in a wide range of biological processes, including catalyzing chemical reactions, transporting molecules within cells, and providing structural support to cells and tissues. Proteins can be found in every cell of every organism on Earth and perform a wide range of functions essential to life.
History of protein
The study of proteins has a long and fascinating history, dating back to the 18th century. Here are some key milestones in the history of protein:
In 1728, the British chemist Stephen Hales published a book that described the preparation of protein from animal and plant sources, which he called "vegetable acid."
In 1838, the Dutch chemist Gerardus Johannes Mulder coined the term "protein" to describe the nitrogen-containing substances found in animal tissues.
In 1902, the British biochemist Archibald Garrod showed that some diseases are caused by defects in the production or breakdown of proteins, which laid the groundwork for the field of biochemical genetics.
In 1926, the American biochemist James Sumner was the first to isolate and crystallize an enzyme (urease) from a natural source, which provided proof that enzymes are proteins.
In 1949, the British biochemist Frederick Sanger developed a method for determining the amino acid sequence of a protein, which was a major breakthrough in the study of protein structure.
In 1953, the American biochemists Linus Pauling and Robert Corey proposed a model for the secondary structure of proteins, which was later refined by others to become the alpha helix and beta sheet models.
In the 1960s, the American biochemist Marshall Nirenberg, together with his colleagues, deciphered the genetic code, which allowed scientists to understand how the sequence of nucleotides in DNA specifies the sequence of amino acids in proteins.
Since then, many more discoveries have been made about the structure, function, and properties of proteins, leading to new technologies and applications in fields such as medicine, biotechnology, and agriculture.
Composition of Protein
Proteins are composed of long chains of amino acids, which are linked together by peptide bonds. The general composition of proteins is as follows:
Amino acids: Proteins are made up of 20 different amino acids, which are joined together in a specific sequence to form the protein chain. Each amino acid consists of a central carbon atom, an amino group (-NH2), a carboxyl group (-COOH), and a side chain (-R) that varies between different amino acids.
Peptide bonds: The amino acids in a protein chain are linked together by peptide bonds, which form between the carboxyl group of one amino acid and the amino group of another amino acid.
Secondary structure: Proteins can fold into regular patterns, such as alpha helices or beta sheets, through hydrogen bonding between the amino acids. These patterns form the secondary structure of the protein.
Tertiary structure: The overall three-dimensional shape of the protein is determined by the interactions between the amino acid side chains and the environment. The tertiary structure of a protein is critical to its function.
Quaternary structure: Some proteins are composed of multiple chains of amino acids, which are linked together to form the quaternary structure of the protein.
The specific sequence of amino acids in a protein determines its primary structure, which in turn determines its higher-order structure and function. Proteins are essential components of living organisms and have a wide range of functions, including catalyzing chemical reactions, providing structural support, and transporting molecules.
Types of protein
There are many different types of proteins, each with their own unique functions and structures. Here are some examples of different types of proteins:
- Enzymes - catalyze chemical reactions in the body
- Hormones - chemical messengers that regulate bodily functions
- Antibodies - part of the immune system that helps to defend against foreign invaders
- Structural proteins - provide support and shape to cells and tissues
- Transport proteins - carry molecules such as oxygen and nutrients throughout the body
- Contractile proteins - responsible for muscle contraction and movement
- Storage proteins - store molecules such as iron and oxygen for later use
- Regulatory proteins - control gene expression and other cellular processes
These are just a few examples of the many types of proteins found in the body. Each type of protein has a unique structure that allows it to carry out its specific function in the body.
Protein synthesis
Protein synthesis is the process by which cells create new proteins. It involves two main stages: transcription and translation.
Transcription: The first stage of protein synthesis is transcription, which takes place in the nucleus of the cell. During transcription, DNA is used as a template to create a complementary RNA strand called messenger RNA (mRNA). The enzyme RNA polymerase catalyzes the formation of the mRNA strand by linking nucleotides together according to the DNA sequence.
Translation: The second stage of protein synthesis is translation, which takes place in the cytoplasm of the cell. During translation, the mRNA strand is read by ribosomes, which are protein-making machines. The ribosomes use the mRNA sequence as a template to create a chain of amino acids, which will form the protein. Each group of three nucleotides on the mRNA strand, called a codon, specifies a particular amino acid. The transfer RNA (tRNA) molecule brings the appropriate amino acid to the ribosome and adds it to the growing chain. This process continues until the ribosome reaches a stop codon, signaling the end of the protein.
Once the protein is complete, it may undergo further modifications, such as folding or addition of other molecules, to achieve its final functional form.
Structure of proteins
Proteins are composed of long chains of amino acids that are linked together by peptide bonds. The sequence of amino acids in the chain determines the primary structure of the protein. The primary structure then determines the way the protein folds into its three-dimensional structure, which is essential for its function.
Proteins can have four levels of structure:
Primary structure: the linear sequence of amino acids in the protein chain.
Secondary structure: the way the protein chain folds into regular patterns, such as alpha helices or beta sheets, through hydrogen bonding between the amino acids.
Tertiary structure: the overall three-dimensional shape of the protein, determined by the interactions between the amino acid side chains and the environment.
Quaternary structure: the arrangement of multiple protein subunits, if the protein is composed of more than one chain.
The specific three-dimensional shape of a protein is critical to its function, and any changes in the protein structure can affect its activity. Protein folding is a complex process that is aided by molecular chaperones, which help to prevent misfolding and aggregation.
Application of protein
Proteins have a wide range of applications in various fields due to their diverse functions and properties. Here are some examples of applications of proteins:
Biotechnology: Proteins are used in biotechnology for a variety of purposes such as production of recombinant proteins, gene therapy, and drug development.
Food industry: Proteins are used in the food industry for their functional properties such as emulsification, gelation, and foaming. Examples include the use of egg white protein in cake making or the use of casein in cheese production.
Medical industry: Proteins are used for therapeutic purposes such as insulin for diabetes, antibodies for cancer treatment, and clotting factors for hemophilia.
Agriculture: Proteins are used in agriculture for crop improvement, such as the development of genetically modified plants that express proteins to resist pests or increase yield.
Environmental applications: Proteins are used in environmental applications such as bioremediation, where enzymes are used to degrade pollutants in the environment.
Forensic science: Proteins are used in forensic science for DNA analysis and identification.
These are just a few examples of the many applications of proteins. The versatility of proteins and their diverse properties make them valuable in a wide range of fields.
Most Important Questions -
Q: What are proteins made of?
A: Proteins are made of long chains of amino acids, which are linked together by peptide bonds.
Q: How many different types of amino acids are there?
A: There are 20 different types of amino acids.
Q: What is the primary structure of a protein?
A: The primary structure of a protein is the sequence of amino acids in the protein chain.
Q: What is the function of proteins in the body?
A: Proteins have many functions in the body, including catalyzing chemical reactions, providing structural support, and transporting molecules.
Q: How are proteins synthesized in cells?
A: Proteins are synthesized in cells through a process called protein synthesis, which involves two main stages: transcription and translation.
Q: What is the role of enzymes in protein metabolism?
A: Enzymes are proteins that catalyze chemical reactions in the body, including those involved in protein metabolism.
Q: What are the consequences of protein deficiency?
A: Protein deficiency can lead to a variety of health problems, including stunted growth, weakened immune system, and impaired mental function.
Q: What is the difference between a complete and incomplete protein?
A: A complete protein contains all of the essential amino acids in the right proportions, while an incomplete protein lacks one or more essential amino acids.
Q: What is denaturation of a protein?
A: Denaturation of a protein refers to the disruption of its three-dimensional structure, which can occur due to changes in pH, temperature, or exposure to certain chemicals.
Q: What is the recommended daily intake of protein for an adult?
A: The recommended daily intake of protein for an adult is about 0.8 grams per kilogram of body weight.