My knowledge of proteins isn’t too good at the moment. Can someone give me a basic overview?
Take Insulin. I assume some kind of (protein) signal hit the pancreas when there is a shortage of insulin, then the DNA sequence that codes for Insulin writes it out, Insulin is built and sent out of the cell. I assume that much is true, but then what, do most proteins end up docket at receptors in the human body, do they interact with each other, do they interact with nutrients floating in the bloodstream?
A protein is a molecule composed of one or more chains of amino acids, possibly with other components (such as the iron component in hemoglobin). The “genetic code” in nucleic acids is actually a code for amino acid sequences to build proteins.
Proteins are a huge, diverse family of molecules. Some are signaling molecules. Some are receptors for signaling molecules. Some form cellular and nuclear channels, to allow materials to go in and out in a controlled way. Some are structural–hair, fingernails, wool, and silk are all protein materials, as well as muscle. Some are enzymes, which build and destroy other molecules. Some are “molecular motors,” like kinesin, which transport things from one place to another.
This is a really huge question. Proteins function in many, many capacities in the the human body. You have touched briefly on the question of how proteins are manufactured, and how proteins function as signals and receptors.
Proteins are long chains of amino acids. In particular, insulin is a chain of 51 amino acids. Different amino acids have different shapes and affinity for electrons. When you string many of them together, these differences cause the protein to fold up into a specific three-dimensional shape. Mainly it’s the shape of the protein that governs how it works… its shape enables it to interact with other molecules of a complementary shape. Additionally, the shape of a protein may change in the presence of different proteins, higher pH, or higher temperature. When you think proteins, think about “Transformers”, the shape-shifting robots from the 1980’s children’s show.
Very high level overview… Proteins are assembled by RNA, which is transcribed by DNA. mRNA codes for the protein sequence, and then tRNA actually assembles the chain of amino acids. After the protein is built, it may be secreted immediately or stored in the cell.
You asked specifically about insulin… it is stored in secretory granules in a form called “proinsulin” and is converted to insulin in response to other chemical changes. Insulin binds to a certain receptor on the surface of the target cell, activating other proteins that transport glucose into the cell.
This is a really big topic, I probably haven’t done it justice, but Google will give you an overwhelming amount of information on the subject. If you have any more specific questions I am sure anyone would be glad to help you.
Proteins fall into two fundamental classes, structural and enzymatic.
Structural proteins do just that; provide mechanical strength and structure. Examples are keratin (fingernails and hair), collagen (provides an elastic substrate for bones, skin, and arteries), and muscle protein such as actin, which can contract to provide mechanical movement.
Enzymes are proteins whose job is to catalyze and coordinate the hundreds of thousands of chemical reactions which keep you alive. Many (if not most) of these reactions ordinarily wouldn’t take place at appreciable rates under the conditions found in the human body. In a lab, a chemist typically reacts two molecules by heating them in solution; the molecules zip around and crash into each other. If they collide in just the right orientation, with enough energy, chemical bonds can be hopefully made or broken. it’s a statistical crap-shoot which relies on high temperature (more collisions over time) and long reaction time (on the order of hours).
Rather than relying on chance, enzymes act as very specific templates. For just about every reaction which occurs in your body, there is an enzyme which “grabs” the reacting compounds (and only those molecules) and holds them in a precise orientation and position such that the chemical reaction can occur almost instantaneously even at body temperature. You can almost think of them as nano-machines, each designed to facilitate a very specific reaction.
What about signaling peptides, though? Hormones and receptors? Unless you were including those in enzymes (personally I wouldn’t), you’ve missed one of the biggest roles of proteins.
Deciding which proteins to study first is crucial because many are from large “families” of proteins with up to 1,000 members, and identifying the structure of one protein will enable faster determination of the structure of other family members, said Michael Baran, a manager of the project at Rutgers.
I don’t really understand the ‘family’ part.
I was trying to keep it short and sweet, and not overstep my limited background in protein chemistry, and meant to lump them in with enzymes when I said that they catalyze and coordinate the myriad of chemical reactions.
I figured someone else would do a better job of this function, which, as you said is also rather important.
Proteins that are classified into families share broad structural and functional characteristics. For example, for my master’s thesis I studied the role of one specific member of the TNF receptor (TNFR) family in regulating T cell activation. TNFR proteins are known to be transmembrane proteins (they are at the cell surface, embedded within the cell membrane, basically with bits sticking out both sides. This is useful for signaling receptors, because it allows them to transmit information from the outside of the cell to the inside, or vice versa), they form trimers, and they all play a role in regulating immune responses. Obviously, the precise details, such as amino acid sequence, fine details of structure and so on vary with each member of a family. However, knowing that a protein X belongs to family Y is a huge help in beginning to figure out precisely what protein X does and looks like because you know sort of the basic blueprint.
Hope that helps, and if it doesn’t make sense, I’ll blame the cold medication I just took!
Basically, nature is lazy and tends to reuse the same concept over and over. For example, a family might be proteases. A protease is a protein that digests other proteins. There are a bunch of them. Some are really specific and will only cleave a specific protein at a specific place, some will cleave a specific amino acid sequence in any protein, some will cleave any available site on any protein. Once you figure out what one looks like, the rest likely will look the same. Then, since you breezed through the proteases, you can move on to Rnases and Dnases and protein transaminases and a wnole bunch of other things that end in -ases, etc, etc, etc.
