Life Sciences: DNA

Life Sciences: DNA

In this lesson, we will learn what DNA is, what its characteristics and functions are, even where it is located and what information it contains. We'll also learn how the double helix is created.

What is DNA?

Why do people look and act like people, cats look and act like cats, or frogs look and act like frogs? All of us have what is called DNA in every one of our cells. This is the genetic information we get from our parents, half from our mother, half from our father. Every time one of our cells divides, this information is passed on to the new cells to make sure the new cells look and behave like the original ones.

What is DNA?

DNA stands for deoxyribonucleic acid - that's a mouthful, isn't it? DNA is the master molecule in every cell. In eukaryotic organisms, such as animals, plants and fungi, the DNA is stored inside the cell nucleus and in the chromosomes. Prokaryotes (bacteria) store their DNA only in the cytoplasm within their cells. This master molecule, the DNA, is the perfect hiding place for biological or genetic information. This information is the instruction for the making of the DNA itself, as well as proteins, somewhat like a cookbook. If the recipe is changed even slightly, mutations will occur. DNA belongs to a class of molecules called nucleic acids (the other nucleic acid is RNA or ribonucleic acid).

Multiple Choice

DNA stands for which of the following?

• Purinic acid

• Pyrimidic acid

• Deoxyribonucleic acid

• Ribonucleic acid

Base Pairs

DNA looks very complex, but it is really pretty simple. It is just a pattern made out of four different shapes, or an alphabet with only four letters. Each side of the double helix is a long string of these shapes or letters in a specific pattern. Each of these shapes is a nucleotide.

Multiple Choice

Which of the following are the complimentary base pairs in DNA?

• adenine and thymine

  guanine and cytosine

• adenine and thymine

  guanine and cytosine

• purine and pyrimidine

  hydrogen and protein

• adenine and guanine

  cytosine and thymine

Nucleotide

A nucleotide is made of a sugar and a phosphate on the outsides, and in the middle, contains the nitrogenous bases, either purine or pyrimidine. The bases pair up, purine with pyrimidine, and are held together with hydrogen bonds.

Histones

Cells are pretty small, so how does the DNA fit inside? DNA is, after all, a very long molecule. To fit inside the cell, DNA is coiled and twisted around proteins called histones. The histones are also coiled to form chromosomes, which are located in the nucleus of the cell.

Gene

The DNA contains instructions for making proteins, which determine our physical characteristics. Each protein, or recipe, is contained within a specific gene. The pattern made by the nucleotides lists the order of ingredients or amino acids to be put together to create a protein.

Multiple Choice

In eukaryotic organisms, the DNA is stored where?

• The cell nucleus

• The capsule

• The cytoplasm

• The cell wall

DNA Characteristics

• each of its double strand is a single molecule

• each strand is a pattern made from four parts called nucleotides

• the two strands are joined together by hydrogen bonds, like rungs of a ladder

• the two strands wind around each other to create a double helix

Multiple Choice

Which of the following are characteristics of DNA?

• it is a carbohydrate

• single helix, single strand

• the strands are joined together by peptide bonds

• double helix, double strands

Creating the Helix

The four nucleotides are either purines, which are double-ringed structures, or pyrimidines, which are single-ringed structures. These are referred to as bases.

The four bases are:

adenine (A) - a purine

cytosine (C) - a pyrimidine

guanine (G) - a purine

thymine (T) - a pyrimidine

Multiple Choice

What are the functions of DNA?

• Mutation and evolution

• Replication and mutation

• Mutation and expression

• Replication and expression