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Making DNA models can be informative, fun, and in this case tasty. Here you will learn how to construct a DNA model using candy. But first, what is DNA? DNA is a nucleic acid that contains the genetic information for the reproduction of life. Its shape is that of a double helix and its appearance is somewhat of a twisted ladder or spiral staircase. DNA is composed of nitrogenous bases (adenine, cytosine, guanine and thymine), a five-carbon sugar (deoxyribose), and a phosphate molecule.
Nucleic Acids
Nucleic acids allow organisms to transfer genetic information from one generation to the next. There are two types of nucleic acids: deoxyribonucleic acid, better known as DNA and ribonucleic acid, better known as RNA.
When a cell divides, its DNA is copied and passed from one cell generation to the next generation. DNA contains the "programmatic instructions" for cellular activities. When organisms produce offspring, these instructions, in the form of DNA, are passed down. RNA is involved in the synthesis of proteins. "Information" is typically passed from DNA to RNA to the resulting proteins.
Nucleic acids: Nucleotides
Nucleic acids are composed of nucleotide monomers. Nucleotides have three parts:
- A Nitrogenous Base
- A Five-Carbon Sugar
- A Phosphate Group
Similar to what happens with protein monomers, nucleotides are linked to each other through dehydration synthesis. Interestingly, some nucleotides perform important cellular functions as "individual" molecules, the most common example being ATP.
Polynucleotides
In polynucleotides, nucleotides are joined to one another by covalent bonds between the phosphate of one and the sugar of another. These linkages are called phosphodiester linkages
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Life is both wonderful and majestic. Yet for all of its majesty, all organisms are composed of the fundamental unit of life, the cell. The cell is the simplest unit of matter that is alive. From the unicellular bacteria to multicellular animals, the cell is one of the basic organizational principles of biology. Let's look at some of the components of this basic organizer of living organisms.
Eukaryotic Cells and Prokaryotic Cells
There are two primary types of cells: eukaryotic cells and prokaryotic cells. Eukaryotic cells are called so because they have a true nucleus. The nucleus, which houses DNA, is contained within a membrane and separated from other cellular structures. Prokaryotic cells however have no true nucleus. DNA in a prokaryotic cell is not separated from the rest of the cell but coiled up in a region called the nucleoid.
As organized in the Three Domain System, prokaryotes include archaeans and bacteria. Eukaryotes include animals, plants, fungi and protists. Typically, eukaryoitc cells are more complex and much larger than prokaryotic cells. On average, prokaryotic cells are about 10 times smaller in diameter than eukaryotic cells.
Eukaryotes grow and reproduce through a process called mitosis. In organisms that also reproduce sexually, the reproductive cells are produced by a type of cell division called meiosis. Most prokaryotes reproduce through a process called binary fission. During binary fission, the single DNA molecule replicates and the original cell is divided into two identical daughter cells.
Both eukaryotic and prokaryotic organisms get the energy they need to grow and maintain normal cellular function through cellular respiration. Cellular respiration has three main stages: glycolysis, the citric acid cycle, and electron transport. In eukaryotes, most cellular respiration reactions take place within the mitochondria. In prokaryotes, they occur in the cytoplasm and/or within the cell membrane.
The Cell-Cell Structure
There are also many distinctions between eukaryotic and prokaryotic cell structure. The following table compares the cell structures found in a typical prokaryotic cell to those found in a typical animal eukaryotic cell.
Cell Structure Comparison
Eukaryotic and Prokaryotic Cell Structure |
| Cell Structure | Prokaryotic Cell | Typical Animal Eukaryotic Cell |
Cell Wall | Yes | No |
Centrioles | No | Yes |
Chromosomes | One long DNA strand | Many |
Cilia or Flagella | Yes, simple | Yes, complex |
Endoplasmic Reticulum | No | Yes (some exceptions) |
Golgi Complex | No | Yes |
Lysosomes | No | Common |
Mitochondria | No | Yes |
Nucleus | No | Yes |
Peroxisomes | No | Common |
Cell Membrane | Yes | Yes |
Ribosomes | Yes | Yes |
