Proteins
- [University of Pennsylvania]
- Overview
A protein is a naturally occurring, extremely complex substance consisting of amino acid residues linked by peptide bonds. Proteins are present in all living organisms and include many essential biological compounds such as enzymes, hormones and antibodies.
Proteins are large, complex molecules that play many key roles in the body. They do most of the work in cells and are necessary for the structure, function and regulation of human tissues and organs.
Proteins are made up of hundreds or thousands of small units called amino acids, which are connected to each other in long chains. There are 20 different types of amino acids that can be combined into proteins. The amino acid sequence determines the unique 3-dimensional structure of each protein and its specific function. Amino acids are encoded by a combination of three DNA building blocks (nucleotides), determined by the gene sequence.
Proteins serve as structural support, biochemical catalysts, hormones, enzymes, building blocks, and initiators of cellular death. Proteins can be further defined by their four structural levels: primary, secondary, tertiary, and quaternary.
Please refer to the following for more information:
- Wikipedia: Protein
- Protein Functions
Proteins are made up of hundreds or thousands of smaller units called amino acids, which are connected to each other in long chains. There are 20 different types of amino acids that combine to form proteins. The amino acid sequence determines each protein's unique three-dimensional structure and its specific function. Amino acids are encoded by a combination of three DNA building blocks (nucleotides), determined by the gene sequence.
Proteins can be described according to their large range of functions in the body, listed in alphabetical order.
Examples of protein functions:
- Antibodies: Antibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the body. For example, immunoglobulin G (IgG).
- Enzymes: Enzymes complete almost thousands of chemical reactions that take place in cells. They also help form new molecules by reading genetic information stored in DNA. For example, phenylalanine hydroxylase.
- Messenger: Messenger proteins, such as certain types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs. For example, growth hormone.
- Structural components: These proteins provide structure and support to cells. On a larger scale, they also allow body movement. For example, actin.
- Transport/Storage: These proteins bind and carry atoms and small molecules within cells and throughout the body. For example, ferritin.
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another.
Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific 3D structure that determines its activity.
- [Examples of Protein Structures - The Protein Data Bank (PDB)]
- Building Blocks of Life
Inside every cell in your body, billions of tiny molecular machines called proteins are hard at work. They allow your eyes to detect light, your neurons to fire, and the unique "instructions" in your DNA to be read. Think of them as the building blocks of life.
Currently, there are over 200 million known proteins, with more being discovered every year. Each one has a unique 3D shape that determines how it works and what it is used for.
But figuring out a protein's exact structure can sometimes take years and hundreds of thousands of dollars, meaning scientists can only study a fraction of it. This slows down research to tackle the disease and find new medicines.
- How Do Genes Direct The Production of Proteins?
Most genes contain the information needed to make functional molecules called proteins. The journey from gene to protein is complex and tightly controlled within each cell. It consists of two major steps: transcription and translation.
Cells use a process called transcription to copy the nucleotide sequence of a gene from DNA into RNA, and then use a process called translation to use the RNA as a template to synthesize a protein. This process is called the central dogma of molecular biology and is used by all cells, from bacteria to humans.
Here are the steps involved in this process:
- Transcription: The DNA of a gene acts as a template for complementary base-pairing, and an enzyme called RNA polymerase II creates a pre-mRNA molecule. This pre-mRNA is then processed to form mature messenger RNA (mRNA). In eukaryotes, transcription takes place in the nucleus, where the DNA is stored.
- Translation: The mRNA is then used as a template to direct the synthesis of a protein. In eukaryotes, the mRNA must be exported from the nucleus before it can be translated into a polypeptide. The mRNA attaches to a ribosome, which is made of ribosomal RNA (rRNA), and the ribosome builds the protein. The process involves chains of amino acids being translated from the mRNA into a polypeptide, which then folds into a fully functional protein.
- Gene Regulation
Cells can turn genes on and off, a process called gene regulation. This process is important for normal development and gives cells their unique characteristics.
Different cell types have different gene regulatory proteins that direct gene expression patterns. For example, exposure to sunlight can activate genes that produce melanin, which darkens skin tone as a defense against UV radiation. Other factors that can impact gene expression include diet, stress, and lifestyle choices.
Gene regulation also plays a role in minor traits like hair color and vital functions like cancer protection. For example, most young children can digest milk because of the lactase enzyme, but this ability often decreases with age.
One way cells turn off specific genes is by adding a chemical called a methyl group to the DNA at the gene's location. This process is reversible.
The gene regulatory proteins allow the individual genes of an organism to be turned on or off specifically. Different selections of gene regulatory proteins are present in different cell types and thereby direct the patterns of gene expression that give each cell type its unique characteristics.
[More to come ...]
