Author: Lynn Gordon
Woodrow Wilson Biology Institute
The following is a good way to show the relationships among cell, nucleus, genes, chromosome, ribosome, replication, mitosis, transcription, translation, DNA, RNA, amino acids and proteins, genotype, phenotype, and genetic vs. environmental causes of cell defects.
There are a number of ways the following can be used.
(!) Tell story leaving out scientific words that appear in parentheses. Place scientific terms on paper or board and have students insert as you or they retell the story.
Let's pretend that you have a yen for a homemade Spanish omelet. The only recipe you know for that omelet is found in the Library of Spanish Cookery. There are many volumes of books in this specialized library and that recipe occurs on one page of one of those books. You locate the library (nucleus), the volume (chromosome) and page (gene) on which the recipe DNA coded sequence) is found.
The librarian refuses to let you check out the book as all reference material must stay in the library. (DNA does not leave the nucleus.) According to the rules of this library, "Xerox"ing (replicating) is out of the question as the "Xerox"ing process in this library is only used if they have to recreate a duplicate library (mitosis or meiosis.).
You are free to transcribe the recipe (from DNA to mRNA) for the omelet (a particular protein) in your own handwriting on a piece of paper that is able to leave the library (mRNA leaving the nucleus). (Same information, different format.) Remember you only used one opened page (gene) in the book (unwound strand of DNA molecule) which was closed (DNA zips back together) after you wrote the recipe in your own handwriting (transcription).
You take this transcribed recipe (mRNA) for this omelet (protein) to a kitchen (ribosome) where you also bring your ingredients (amino acids) to be assembled (translation) into an omelet (protein) according to the directions (DNA via mRNA). Not until your omelet is assembled in final form has your recipe (genotype) been expressed (phenotype).
The different ingredients are to be assembled in a particular order to result the desired product. All omelets are always made in the kitchen and a mistake in the recipe can result in a lousy omelet (genetic problem). Likewise, you can have a great recipe (genetic) and a lousy ingredient (environmental) and also come out with a defective omelet. You could have a great recipe, perfect ingredients and no heat energy source (environmental) and also have a defective omelet. Many factors account for completed omelets.
For years my son (neighbor, nephew etc.) had two Nintendo games that Uncle Fred had sent him for his birthday. There was only one "small" problem. He had a couple of cartridges, each with coded information for one game (DNA molecules coding for one gene) but was only able to play (express) them when they were in the environment of a machine (cell) that could express the information. If the game cartridge were placed in an incompatible machine (a Nintendo cartridge in a Sega machine) the game could not be expressed.
Phenotype can be equated to the expression of the game that shows up on the screen. (If more than one game is found on one cartridge, each game represents a gene on a chromosome.) The game program represents the genotype. Other cartridges (chromosomes) contain other games (genes) which express themselves when placed in the machine and accessed (turned on by cell).