Why Our Food Rots II

This is the second edition of “Why our Food Rots.” To get you up to speed, last week’s article described what causes food to rot: MICROBES! I also mentioned the basic methods of food preservation and that changing the temperature of a food can either slow the growth of microbes or kill them. This week’s article will describe how various chemical treatments help in preserving food. The means of preserving food and the chemicals used to preserve the food are as follows:

  • pickling (salt or sugar; vinegar, a weak acid)
  • salting/sugaring
  • fermentation (alcohol)
  • chemical preservation (lots of compounds too long and hard to pronounce for now)

When people think of chemicals they usually think of compounds with long names that are poisonous to life. That is not really true. We are made up of chemicals. Salt and sugar are chemicals that are commonly found in our bodies. There are other chemicals that are not commonly found in us that can be deadly. Lead is a chemical that you don’t want in your body because it is very poisonous.

Unlike lead, chemicals like salt, and sugar are only poisonous in very very very high concentrations. Salt and sugar are also poisonous to microbes when in high concentrations. High concentrations of salt and sugar actually suck the water out of our cells and out of microorganism’s cells. When water levels get too low in a cell the cell will die because the enzymes in the cell can’t do their work. No enzymes working means no energy being produced. No energy leads to cell death.

There are a lot of examples of people using high concentrations of salt or sugar to preserve food. Beef jerky is one example. The meat is dried and salted to preserve it. Pickles are preserved in a salt brine that prevents the growth of microbes in and on the cucumbers. Vinegar is also used in salt brine to increase the acidity of the brine. Microbes are killed by acidic conditions because acid will also destroy the enzymes that make microbes grow. Jams, jellies and sweet pickles are examples of the use of sugar to preserve food.

These preservation techniques don’t kill us because we can lower the concentration of the salt or sugar by diluting them out with other foods we eat and because of the large mass of our bodies compared to the amount of salt or sugar we eat. Unfortunately for the microbes, their cell body mass is very small and as a result concentrations of salt and sugar that have little effect on us are deadly to them.


Functions and Structure of Ribosomes: Small Organelles that Carry Out the Process of Translation

Ribosomes are small organelles made of RNA and protein that carry out the important work of translating mRNA templates into proteins.

Ribosome Structure – Subunits of RNA and Protein

Ribosomes in eukaryotes are made up of two subunits, a large subunit, called 60-S, and a small subunit, named 40-S. In prokaryotes, the subunits are 50-S and 30-S.

These two subunits are made in the nucleus and join together in the cytoplasm to create the ribosome whenever mRNA is present and proteins need to be made. The two subunits join together, hook onto the mRNA and start protein synthesis. During the production of proteins, the larger subunit binds to tRNA and amino acids and the small subunit binds to the mRNA template. When the ribosome finishes reading the mRNA and making the protein, the two subunits break apart again.

Function of Ribosomes – Protein Construction

The function of ribosomes is to make proteins in a process called protein synthesis. The ribosomes combine amino acids, the building blocks of proteins, in the order specified by a messenger RNA (mRNA) template.

As the ribosome moves along the mRNA and reads the sequence, amino acids are attached to and organized by transfer RNA (tRNA), a special type of RNA that can bind to both the ribosome and amino acids.

Location of Ribosomes in the Cell – Free and Attached Ribosomes

Ribosomes come in two types, free ribosomes and membrane bound ribosomes, which can be found in different places within the cell and carry out slightly different versions of protein synthesis.

Free ribosomes are found floating in the cytosol of the cell, the liquid that fills the cell interior. Free ribosomes can move around in the cytosol and they generally make proteins for use inside the cell.

Membrane bound ribosomes, also called attached ribosomes, attach to the endoplasmic reticulum, creating rough endoplasmic reticulum, RER. These rough ER ribosomes make proteins that will be exported for use outside the cell or used in cell membranes. The proteins generated by ribosomes in the rough ER travel into the ER and are then packaged for transport to the plasma membrane to be incorporated there or sent outside the cell.

Ribosomes are capable of chaning between one type and another. Free ribosomes can become membrane-bound ribosomes and vice-versa depending on what the cell needs at any given time.

It is important for students of biology to understand the function and structure of ribosomes, since these important organelles carry out the steps of protein synthesis that create all of the proteins in the body. Without ribosomes, there would be no protein construction and no work could ever get done inside or out of the cell.