Protein Definition and 15 Discussions

Proteins are large biomolecules and macromolecules that are comprised of 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.
A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide. Short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptides. The individual amino acid residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the genetic code specifies 20 standard amino acids; but in certain organisms the genetic code can include selenocysteine and—in certain archaea—pyrrolysine. Shortly after or even during synthesis, the residues in a protein are often chemically modified by post-translational modification, which alters the physical and chemical properties, folding, stability, activity, and ultimately, the function of the proteins. Some proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors. Proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes.
Once formed, proteins only exist for a certain period and are then degraded and recycled by the cell's machinery through the process of protein turnover. A protein's lifespan is measured in terms of its half-life and covers a wide range. They can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells. Abnormal or misfolded proteins are degraded more rapidly either due to being targeted for destruction or due to being unstable.
Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in virtually every process within cells. Many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized. Digestion breaks the proteins down for use in the metabolism.
Proteins may be purified from other cellular components using a variety of techniques such as ultracentrifugation, precipitation, electrophoresis, and chromatography; the advent of genetic engineering has made possible a number of methods to facilitate purification. Methods commonly used to study protein structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance and mass spectrometry.

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  1. M

    I need help with this math equation -- hypothetical number of unimaginable proportions

    Kurzesagt in a Nutshell said that the number of possible protein combinations the human body can have is 6.8 x 10^495. I asked GPT to multiple it by 20 million (which is the hypothetical number of possible alien civilizations in the Milky Way galaxy give or take). The chatbot gave me 1.36 x...
  2. S

    Question about antibody affinity chromatography

    I am learning about protein purification in my Biochemistry class, and I have a question about protein elution in antibody affinity chromatography. My understanding of the mechanism for the technique is that proteins that do not bind to the antibody will be separated first as it runs down the...
  3. M

    What does HC3 mean in 'His HC3'?

    My lecturer said it means: "3rd residue, C-terminal to Helix 'H'" but that makes no sense. If it's the 3rd residue then it can't be on the C-terminal, because the C-terminal is at the end of a massively long sequence of residues. Visa versa if it's on the C-terminal then it can't be the 3rd...
  4. Igor 77

    A Radioisotope-induced radioactivity in a protein molecule

    Dear Forum Members, I am a molecular biologist. One of my projects is focused on the identification of a protein that interacts with a known organic molecule. Namely, I try to chase a transmembrane protein that is known to transport one organic acid. If possible, I would like to get an idea on...
  5. I

    Different lengths of genes expressed

    I was wondering whether it can ever happen that only a certain "length" of the same gene gets expressed in different species? Or perhaps even within the same species? (Without it being a random mutation) Basically, can a part of a gene be expressed, and still have some functionality in the...
  6. P

    Protein melt temp/half life relation?

    Is anyone familiar with a way to determine the half-life of a protein from its melt temperature (Tm)? It seems like there ought to be some sort of correlation, be it theoretical or empirical.
  7. mktsgm

    Medical Are there any other Macronutrients?

    I have a few questions on energy from foods. Do we have any other macronutrients that contribute energy to the body other than carbohydrates, proteins and fats in our body? What is the role of Hydrochloric acid (HCL) in our stomach? Is the HCL involved in all three above macronutrient digestion?
  8. I

    Gene and its protein term?

    Hello again! Is there a common word/term for a gene and the protein that it codes for? I know there is signal transduction, but that would be for a whole set of genes and proteins doing a stream of functions. But would there be a name for the specific gene/protein "bundle"?
  9. C

    Other Statistical Physics and Biology

    I'm undergrad physics student and I have read some statistical physics like equilibrium statistical physics, Langevin model and Fokker-Planck equation. I have developed interest in application of statistical physics in biology like protein folding. So what are the other research topics that lie...
  10. I

    Proteins that duplicate the DNA in interphase

    For some reason, I can't seem to be able to find this answer easily on the internet. Or it is there and I somehow I can't see the wood for the trees. I know that in transcription (when DNA is read for protein production), "RNA polymerase" is the protein that creates the mRNA by creating the new...
  11. I

    Genes coding for cells?

    My understanding is that genes code for proteins that then do a certain function. Apart from mitosis in an organism, I heard that cells (in forms of stem cells) are also produced and released into the body. I guess these would be all the floating around the body cells? Or the nerve cells that...
  12. I

    What happens to a protein built from mutated RNA?

    I was wondering if anyone knew what happens to a protein that gets wrongly assembled due to a mutated RNA? Does it just do a slightly different or very destructive action in the organism, or does the organism catch it and kick it out? Also an extra side question: Speaking of mutations of RNA...
  13. I

    Genes and protein they code size relation?

    If the gene is smaller, is the protein that it codes for smaller too? Vice versa?
  14. G

    Methods of Regulating Proteins

    I have been looking into different methods of regulating protein activity for a project. I think it is pretty interesting and I want to learn more about this. I want to learn about the different methods out there, if you know of any cool or helpful regulation techniques I would certainly...
  15. G

    Biophoton Emission Outside Visible Range

    There are a lot of florescent proteins in the visible range, but why haven't we fount any above or below that range? I think a protein that emits radio waves could be very helpful both biologically and scientifically. Are we not looking for such proteins, or do they not exist?