Protein, a Primer

Proteins are large molecules made out of one or more long chains of amino acids. They differ mainly in their sequence of amino acids. They usually fold into a specific three-dimensional structure that determines its activity. Proteins are active in all kinds of functions in an organism. They catalyze reactions, replicate DNA, provide structure in cells, transport molecules etc. All the proteins in all the species are commonly made out of 20 standard amino acids, even though more amino acids exist in nature. Plants can synthesize all these amino acids. Animals can not do this but these amino acids are still essential for life so they must get them from the outside, for example through eating meat.

Proteins have different structures. The primary structure is the linear chain of amino acids. The secondary structure is the regular folding of regions of the chain. The most common folds are the α-helix and the β-pleated sheet. The tertiary structure is between regions that are further apart as well as between adjacent residues. The final structure, the quaternary, is a spatial arrangement between the polypeptide subunits. Under the appropriate conditions, proteins fold spontaneously in their native structure. In cells this is aided by accessory proteins. This allows them to fold faster. One class of these accessory proteins is the molecular chaperones. Molecular chaperones include heat shock proteins 70. These help to prevent incorrect folding and aggregation of proteins. Later on we will refer back to heat shock proteins 70, or HSP70, when we talk about heat therapy or sauna use. Remember that animals have to ingest some proteins, that proteins have a three-dimensional structure, and HSP70.

Examples of proteins and their functions

Function Description Example
Antibody These proteins fight foreign substances in the body. Immunoglobulins
Enzyme These proteins regulate the many complex reactions in organisms. Fructokinase
Messenger These proteins help regulate activities and balances in the body. Growth hormone
Structure These proteins provide structure. They are also found in muscle and thus allow bodies to move. Collagen
Transport These proteins ferry atoms and molecules throughout the body. Hemoglobin

Further Reading

Protein. Encyclopedia Britannica. https://www.britannica.com/science/protein

Fat, a Primer

Humans store fat in specialized cells called adipose cells (or simply, fat cells). Adipose cells are almost entirely made out of triacylglycerols. They specialize in the synthesis, storage and mobilization of triacylglycerides. Triacylglycerols are also known as triglycerides or fats. They are made out of three fatty acid chains attached to a glycerol backbone. Large lipid-protein particles called lipoproteins ferry triacylglycerol around the body. Simple triacylglycerols have three identical fatty acids attached to their glycerol backbone. Mixed triacylglycerols have two or three different fatty acids.

Fatty acids are made of a hydrocarbon chain (a chain of hydrogen and carbon) and a terminal carboxyl acid group. The chains found in biology are usually unbranched and have an even number of carbon atoms, commonly having 16 or 18 carbon atoms. A fatty acid is saturated when all carbon atoms in its chain have a hydrogen atom. Fatty acids are unsaturated when there is at least one double bond in its structure. There are two types of unsaturated fatty acids: monounsaturated and polyunsaturated. Monounsaturated means there is one double bond in the structure of the fatty acid. It is polyunsaturated when there are two or more double bonds in the structure. The double bonds of polyunsaturated fatty acids are separated by at least one methylene group. The length of the chain and the number of double bonds determines the properties of the fatty acid. Fatty acids have four major biological roles:

  1. They act as fuel molecules, as in triacylglycerols as described above.
  2. They make up essential parts of biological membranes.
  3. They modify numerous proteins.
  4. Fatty acid derivatives act as hormones and intracellular second messengers.

The importance of fat for an organism is not to be underestimated. When it is ingested, it needs to be processed (metabolized). For fat metabolism, remember its structure, the backbone containing three strands.

Further Reading

Lipid. Encyclopedia Britannica. https://www.britannica.com/science/lipid

Triglyceride. Encyclopedia Britannica. https://www.britannica.com/science/triglyceride

Carbohydrate, a Primer

Some people are surprised to learn that the pasta and cookies they eat are carbohydrate, and basically sugar. Others talk about slow and fast sugars. Here slow sugars are the stuff like bread and waffles, and fast sugars are found in things like soda and glucose tablets. It’s especially interesting when talking to someone about diabetics and their diet. Diabetics are allowed, by their doctor, to eat pasta or fries with the associated insulin shot. Diabetics have a problem with carbohydrate metabolism. They can’t metabolize sugar properly because they have a problem with insulin production. It’s strange to me that one may eat something that causes such problems. But that is something to go into deeper when we talk about carbohydrate metabolism. Here’s a short overview of what carbohydrate is.

A carbohydrate is made up of carbon (hence, carbo-), hydrogen and oxygen (hence, -hydrate). The simplest ones are called monosaccharides, also known as a simple sugar. The word saccharide comes from the Greek meaning “sugar”. They have the general formula (CH2O)n where n is 3 or more. They consist of a carbon chain and a number of hydroxyl (OH) groups and, either an aldehyde group or a ketone group. The sugar with an aldehyde group is called an aldose. The sugar with a ketone group is called a ketose. For example: glyceraldehyde is an aldose with the formula C3H6O3, or (CH2O)3.

The aldehyde and the ketone group can react with a hydroxyl group to form a bond. This allows these simple sugars to become complex sugars. If two monosaccharides combine they form a disaccharide, also known as a double sugar. The names of monosaccharides and disaccharides end very often in the suffix -ose. For example: the monosaccharides glucose and fructose, and the disaccharides sucrose and lactose. Note here that sucrose is a bond between glucose and fructose. This will be come back when we talk about carbohydrate metabolism.

Polysaccharides are chains of many sugars joined together. These chains can be linear or branched. Glycogen is a large, chained polysaccharide that is found in animals as a way to store excess glucose. The numerous branches allow for greater accessibility when the molecule needs to be broken down. This allows for rapid use in time of need. Note these long chains and their breakdown for when we talk about carbohydrate metabolism. Most plants store excess glucose in the polysaccharide called starch. In plants it exists as insoluble starch granules in chloroplasts. These granules contain a mix of two polysaccharides, amylose and amylopectin. Polysaccharides can also be used for structure, as is the case for cellulose, which makes up the cell walls of plants. Cellulose is an unbranched polysaccharide of glucose units. Long chains are formed that form fibrils. Mammals, including humans, lack enzymes to digest cellulose linkages and cannot digest plant cell walls. However, some bacteria can.

The last group is oligosaccharides. These are short chains of monosaccharides. They can be linked to proteins (glycoproteins) or lipids (glycolipids).

Class

Component

Found in

Monosaccharides

Glucose

Many fruits

Fructose

Disaccharides

Sucrose

Table sugar

Lactose

Milk

Polysaccharides

Glycogen

In humans it is stored primarily in the cells of the liver and skeletal muscle

Starch (amylose, amylopectin)

Cereals, potatoes, foods based on cereals (bread, pasta)

Cellulose

Plant cell walls, main part of insoluble dietary fiber

Further Reading

Carbohydrate. Encyclopedia Britannica. https://www.britannica.com/science/carbohydrate