Teaching DNA By Analogies

Teaching Biotechnology by Analogies

Biotechnology, particularly genetic engineering, focuses on manipulating tiny structures in the cell. While carrying out the procedures, many concepts and standard techniques can be difficult to comprehend. Students may not understand the main idea of the procedure if they are not familiar with the technique beforehand. Short analogies, stories, and/or models have been developed to help students visualize the overall concept or technique. These analogies are designed to stand alone, and may or may not include a laboratory activity
Recombinant DNA Analogies



Enzyme Function Analogy

Mrs. Busybody Story

The following is a very dramatic story to help students remember why enzymes are so special to the functioning of a cell. First tell them the actual definition as it relates to a chemical change while you write the definition on the board or overhead.

An enzyme is a special substance (protein ) that brings about (speeds up) a chemical change but does not change itself.

As you tell your story with as much flamboyance as you can generate, ask them to be listening for which character in the story would best represent the role of the enzyme.

Setting: Eastern Europe. The time is the mid 1800's. Life is different than today. People were born, lived and died in the same area. Families were large and extended. Travel and long distance communication were difficult. People within a community were dependent upon one another. Male and female roles were very established and traditional. Modern medicine was not around and people died at early ages and women often died during childbirth. People often married out of necessity rather than for love. This was a time before there were TV's, computers, microwaves, dry cleaners, fast foods, frozen foods, birth control, antibiotics, modern plumbing, women's lib, etc.

Plot: Mr. and Mrs. Schmidt are very concerned that Mildred, their "lovely" eldest daughter (one of 10 children) is not yet married and out of the house since another child is on the way. They decide to consult the town matchmaker Mrs. Busybody who makes it her business to know everyone else's business. In fact, her ears are "soooo" big that she makes it her business not only to know all her village's gossip but the gossip of the neighboring villages along the rail line. As a matchmaker arranging marriages, she will be paid for her services. If she can find a husband for Mildred there will be money in her pocket for the effort, so of course, she tells the Schmidts that she has just the man for their Mildred.

Since there are no "eligible" men in this town she takes the train the next day to another village to hunt up some fine man for Mildred. Any eligible man will do. And who should she find but Mortimer, who happens to be a 40 year-old man with six children whose wife has just died. Out of necessity he is in need of a wife and agrees to marry Mildred, sight unseen.

A wedding is arranged between Mildred and Mortimer. It is the day of the wedding and present at the wedding are Mom and Dad Schmidt, "lovely" Mildred, Mortimer and his six children, the justice of the peace, and of course, Mrs. Busybody, who is happiest of all. Mildred Schmidt and Mortimer Jones change their relationship and become Mr. and Mrs. Jones as they are united in heavenly matrimony and live happily ever after.

Now let's look at this a little closer. Mrs. Busybody is Mrs. Busybody before Mildred met Mortimer, Mrs. Busybody is Mrs. Busybody when she attends the wedding, and she is Mrs. Busybody three years later when she visits them when their child is born. If Mrs. Busybody had not set up Mildred and Mortimer their chance of getting together and changing their relationship may never have occurred.

Now which character in the story acts like an enzyme?

Some enzymes bring about "marriages" like Mrs. Busybody and some bring about divorces and cause things to split up. All enzymes are proteins and all enzymes are very, very picky (specific). Some enzymes even get assistance (coenzymes and vitamins) in order to accomplish their work.

Remember: A cell is a very busy place, and most of what it does is to move molecules around or change molecules into other kinds of molecules (chemical change) by either making smaller molecules bigger or bigger molecules smaller. Each and every one of these chemical changes occurring in a cell is controlled by one or more enzymes.



Biotechnolgy Recipe Analogy

Biotechnology Recipe Analogy

The following is a good way to show the relationships among cell, nucleus, gene, 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:

  1. Tell the story leaving out scientific words that appear in parentheses.
  2. Place scientific terms on paper or board and have students insert them as you or they retell the story.

The Spanish Omelet

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, "xeroxing" (replicating) is out of the question as the xeroxing 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 the 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 come out with 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 and a lousy ingredient (environmental problem) and also come out with a defective omelet. You could have a great recipe, perfect ingredients and no heat energy source (environmental problem) and also have a defective omelet. Many factors account for successfully completed omelets.



Genotype / Phenotype Aanalogies

Another analogy that works well to help students understand the relationship of genotype (genetic coding) to phenotype (expression of coding) is to compare a computer to a computer program or a Nintendo machine to a Nintendo game cartridge.

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 use the code. If the game cartridge was placed in an incompatible machine (a Nintendo cartridge in a Sega machine) the game cannot be played.

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 are played (expressed) when placed in the machine and accessed (turned on by cell).



Virus Analogy

A virus is like an M & M -- protein on the outside and nucleic acid (either RNA or DNA ) on the inside.

It is not a cell; it does not do all the life processes; it is not alive.



Gene / DNA Relationship Analogies

Gene / Chromosome - Gene / DNA Relationship Analogies

The following demonstration shows a very simple way to show the relationship between DNA and a chromosome using a large spool of light colored thread.

A Spool of Thread

Hold the spool in your hand and ask the students to describe what you have in your hand. Ask them what substances (cotton and wood) are present and what structures (thread and spool) are present. Conclude that the thread of cotton is wound around the spool made of wood. Equate the substance DNA (one molecule per one spool) to thread and the substance wood to the protein (histone) it's wound around (even though DNA is not actually wound around the histone in this manner.)

After this is established, unwind a fair amount of thread which accumulates in your hand and proceed to throw it at a student in the second row. Of course, it does not quite get there. Ask them why? It's not a convenient way to transfer the thread (DNA). Rewind the thread (DNA) and then throw the spool of thread (chromosome) to a student in the back row. Why was the spool of thread easier to catch?

Then discuss the importance of "wrapped" DNA (coiled and supercoiled into chromosomes only when DNA needs to be transferred to another part of the cell which happens during mitosis or meiosis after replication.) Stress that when the thread (DNA) is being used (during interphase) it is not so tightly coiled or wound and this is analogous to DNA in a working cell.

Next, take a colored marker and color over a two foot section of the thread. Equate this to the DNA nucleotide sequence for a particular gene. If you are using red ink, tell them this might be an instruction (gene) for the cell to make a red pigment (protein). Continue to unwind another two or three feet of thread and color it blue to represent a gene that might code for the cell to make a blue pigment (protein). Then rewind this thread around the spool so that the blue and red sections appear as part of the linear order of the thread on the spool (linear order of genes on a chromosome).

This adequately conveys the concepts that:

  1. The gene is a segment of a chromosome that codes for one protein.
  2. A gene is a linear sequence on the DNA molecule.
  3. DNA must be unwound to be able to be transcribed much like thread must be unwound to be used.



Polymerase Chain Reaction (PCR) Analogy

The Perpetual Cassette Recording (PCR)

Let's consider the following scenario. A master recording by (insert name of favorite recording artist) is produced in a sound studio. You purchased one of millions of cassettes that was an exact duplicate, song for song, of the original. Let's say you want to find a specific song on this audio tape and you wish to tape it over over and over again so you have many copies of your "targeted song". You place it into the left side of your dual cassette player and press the "seek" button which will find the section immediately preceding the targeted song. This is analogous to the primer which locates the beginning of your targeted sequence in PCR methodology. Now take a blank tape and place it into the right (dubbing) side of your dual cassette player. Pressing "record" allows the the music from your targeted song to be recorded, and the magnetic coding sequences that are being copied onto new tape is comparable to the elongation process in PCR according to the original DNA template for that particular sequence. The "stop" button is analogous to the second primer which signals the end of the targeted sequence.

Even though this is not an exact analogy of the PCR process which will allow exponential replication of a DNA sequence, the purpose of this analogy is to show how a linear ordered sequence can be targeted and duplicated over and over in an ordered manner. Remember that the magnetic coding on the audio tape is just coded information that gets copied over and over again. In order for this coded information to be expressed the tape has to be placed in a cassette player and translated into music just like the cell's coded DNA sequence has to be ultimately translated into protein in a cell environment.