B.1.9 – Genetic Activities

Defined Words: DNA, nucleotides, genetics, replication, chromatid, chromosome, genes, allele, dominant, recessive, RNA, ribosomes, mutation

 

In every one of your cells, you have a double stranded molecule called “Deoxyribonucleic Acid,” or DNA. It exists within a protected section of each cell called the nucleus. The two strands of DNA are held together by the attraction between specific pairs of molecules called nucleotides.

Nucleotides are the letters that make up the genetic alphabet; we represent them as A, G, C, and T. Each letter will pair with a specific complementary letter: A’s go with T’s, G’s go with C’s. Unlike English, which has 26 letters, the language of life only has four letters. Those four letters spell out the instructions of creating you and me and every other living thing. The only difference between you and a seahorse is the sequence of just four letters in your genetic story.

Genetics describes the instructions of how to make the pieces that make up you. DNA is the main player of genetics and it’s constantly being used for various activities. This section will describe the genetic activities of DNA and its importance for life.

The first activity we’ll talk about is replication, one of the main qualifiers of life. First, an enzyme will “unzip” the double stranded molecule. Free-floating nucleotides, attached to a backbone molecule, will pair up with both strands of the unzipped DNA.

The nucleotides will pair based on the A-T and G-C combinations. Another enzyme seals up all the gaps in the backbones of the newly formed strands until two identical molecules of DNA have formed. Each new molecule will have one strand from the original and one that’s completely new.

After replicating, the two strands will condense themselves, wrapping back and forth until they have formed a single larger fiber that we call a chromatid. We now have two identical copies of our DNA condensed into chromatids. A protein binds them together near the center to form an X shaped structure called a chromosome.

Each chromosome has a pair that is roughly the same size and contains roughly the same genes, or codes for a trait. Chromosomal pairing was an adaptation to lessen the effects of a mutation on a single gene; the organism could just use the other copy to get the right information. Each copy of a gene is called an allele. Some alleles are more likely to be used and are therefore called dominant. Others tend to be ignored, we call these recessive alleles and they are only used when the gene has no dominant allele.

While it might seem redundant, having backups for the instructions to keep you alive is a very advantageous trait in nature. Your genetic code is made up of pairs of similar chromosomes which are each made up of two identical chromatids which are made up of DNA with basically two identical strands (each strand is the complement of the other). DNA plays it safe; it’s holding precious information, after all.

When most cells divide, they will split the chromosome at the center protein and pull the two identical chromatids to opposite sides of the cell. The cell will then split to finish the process and end with two identical cells. Your sex cells pair up the chromosomal pairs to pull apart so that it can pull the chromatids apart during a second division process. The pairs of chromosomes have the opportunity to trade genetic material, a scrambling of genes that leads to greater diversity in the offspring. Sex cell division ends with four different cells.

The second genetic activity is to send instructions to the cell to create proteins. This is done by unzipping the portion of the DNA that contains the specific instructions. Your DNA has over 3 billion nucleotides, so finding the right “page” is an important process. The DNA will not use both sides, but rather nucleotides with a different backbone will pair to only one side. This molecule is called RNA and it’s basically a single stranded DNA molecule that replaces T with U (slightly different structure), though they both pair with A. The RNA molecule is glued together by an enzyme and the DNA zips back up, ready for its next task.

The RNA messenger leaves the nucleus and heads to structures in the cell called ribosomes. Fun fact: those ribosomes are not actually made by your genetic material; they are made by the genetic material of the nucleolus which lives inside your nucleus. I guess an argument can be made that they are your nucleoli, but that’s beside the point here.

The RNA heads to the ribosomes where it is met with free-floating RNA nucleotides that are attached to amino acids in the cell. The pairing process takes place again but this time, an enzyme forms bonds between the amino acids to form a long chain; we call this chain a protein. Remember, proteins are the building blocks of cells which are the building blocks of you.

As I said earlier, your DNA has over 3 billion nucleotides. The huge amount of nucleotides gives an opportunity for mistakes when copying. Those mistakes can occur when replicating the DNA or in any of the steps of making proteins. When a mistake is made, big or small, we call it a mutation. Sometimes those mutations were helpful, other times they weren’t. Natural selection kept the beneficial traits and killed off the harmful ones.

It was microscopic mistakes, compounded over millions of years among (probably) trillions of organisms that led to you. The lesson to take here is to not be afraid to take chances and make mistakes; they could accidentally lead to something wonderful.

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