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Genetics 101

Genetics is a fascinating topic that affects every aspect of life on earth.

The following pages, which I loving refer to as “Genetics 101″, is a brief overview of genetics. I hope to explain each topic in a way that is easy to understand, so that anyone can read it and understand how genetics works.

Lesson 1: Nucleic Acids

What is DNA?

Every living thing on earth, from the smallest bacteria to the largest whale, contains DNA (short for deoxyrobonucleic acid). What’s it’s purpose? DNA is not only a way to store genetic information, but it also allows us to transmit that information from one generation to the next.

Structure:

  • DNA is a double-helical structure that is often likened to a ladder that has been twisted into a spiral shape.
    • The ‘backbone’ of DNA (think of the uprights of the ladder) are made of alternating sugar and phosphate groups. The sugar in the backbone is deoxyribose (hence its name). The backbone doesn’t carry any information, it just holds the ladder together (blue area in image below).
    • The two uprights run in an ‘antiparallel’ fashion, meaning that one pole goes in one direction, while the other pole faces in the opposite direction.
    • The rungs of the twisted ladder consist of paired organic bases called nucleosides (see image below). There are 4 of them: Adenine (A), Guanine (G), Thymine (T), Cytosine (C).
      • The way they pair up is always the same: A -T; G - C
      • These4 bases are combined in countless ways and make up what we call the ‘genetic code’.
      • A nucleoside + a phosphate = nucleotide

DNA structure

 

  • DNA is a huge molecule that is divided into smaller strands called CHROMOSOMES. In humans, there are 46 chromosomes inside the nucleus of each cell (except red blood cells, which don’t have nuclei and gametes which only have 23 chromosomes. More about this later…)
  • Sequences of DNA that occupy specific locations on chromosomes are called GENES. There are many definitions of genes, but I like to think of them as sequences of DNA that contain instructions on how to make a specific protein or perform a specific task.

How does DNA fit into tiny cells?  SUPERCOILING!  To fit into each cell, sections of DNA are wrapped up around proteins called histones, with ‘linker DNA’ in between the wrapped areas. This makes it look like beads on a string. This string is then coiled up many times and finally twisted around itself so thightly that over six feet of DNA is compressed into only a few thousandths of an inch.  (I like to think of a phone cord that has been twisted around and around on itself… that is kind of how supercoiling works.)

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What is RNA?

Lesson 2: Proteins

Proteins function in nearly every aspect of cellular life. There are thousands of different proteins inside each cell. Knowing about proteins is important in understanding how mutations and environmental conditions can modify proteins and interrupt their functions.

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