Genetics in 10 Minutes

LESSON 1: What is the Genetic Code?

The genetic code contains the information for the creation of life. This information is found in the nucleic acid, DNA. Biological characteristics are determined by the DNA molecular plan which is passed from cell to cell and from generation to generation. DNA is the common material for inheritance in all living things.

LESSON 2: The Basic Units of DNA

The basic unit from which DNA is made is the NUCLEOTIDE. A nucleotide consists of three parts -

1. the sugar deoxyribose (D)

2. a phosphate group (P)

3. one of four nitrogenous bases; the four possible bases are: adenine (A), guanine (G), cytosine (C) and thymine (T)

When these three subunits are joined together they make a nucleotide. There is only one form of deoxyribose in DNA, and one form of phosphate group, so the only variation comes from the different bases. So there are only four types of nucleotides.

LESSON 3: Linking Nucleotides Together

All we have to do to make a DNA molecule is to join lots of nucleotides together. In joining them together it is the sugar part of one nucleotide that connects up to the phosphate of the next.

LESSON 4: Linking Strands

So now you know how a single strand of DNA is formed by linking nucleotides together. However, DNA doesn't just have a single strand - DNA has two such strands of nucleotides running side by side. The two strands are held together by bonding between the bases.

In DNA, the pairing of bases is specific: Adenine (A) only pairs with Thymine (T) and vice versa, while Guanine (G) only pairs with Cytosine (C) and vice versa. The rule of specific base pairing is crucial to the function of DNA. Whenever there is the base Adenine in one strand there must be the base Thymine in the other and vice versa. Whenever there is Guanine there must be Cytosine opposite it and vice versa. If the base sequence of one strand is known the base sequence of the other can be worked out. The two strands are said to be complementary.

So DNA resembles a LADDER. The rungs of the ladder are formed by the bases pairing together. The sides of the ladder are formed by the phosphate and deoxyribose that bond to each other linking the rungs into a ladder. The important thing to remember is that Adenine always bonds with Thymine, and Guanine always bonds with Cytosine - forming the A-T and G-C base pairs.

LESSON 5: A Spiral Ladder

The genetic ladder twists to form a spiral ladder, just like a spiral staircase. There are 10 base-pairs (rungs) per single complete twist.

LESSON 6: Where is the "Information" in DNA?

All of the information in the genetic code is conveyed in the sequence of the bases, A, T, G and C, because these are the only units that vary from nucleotide to nucleotide. The base pairs form the rungs of the genetic ladder.  The ribose sugar and phosphate groups are exactly the same in each nucleotide, so they do not carry any genetic information. Rather they simply act as the "sides of the ladder", a backbone for holding the successive rungs in place.

LESSON 7: How Does DNA Copy Itself?

The genetic material must be able to make exact copies of itself. The rule of specific base pairing in double stranded DNA is the key to the molecule being able to do this. DNA replication can be summarised in one sentence:

"The two strands of the molecule separate and a new partner is made for each one, following the rule of specific base pairing"

So we see that DNA replication is only possible because of the bonding between A and T, and between G and C.

LESSON 8: Key Numbers to Remember

DNA is made up of 2 strands each consisting of a sequence of bases.

There are 4 different bases..

The 2 strands in DNA are bonded to each other by the A-T base pair and the G-C base pair