Question

1. What are the three components of a nucleotide? (HINT: What were the three components used in putting the model together? Remember that Adenine, Guanine, Cytosine, and Thymine are all Nitrogen Bases!) Refer to your DNA article if you are still unsure.
2. What is the name of the sugar molecule in the DNA helix?

3. Suppose you know that the sequence of bases on one DNA strand (one side of the DNA ladder) is AGCTCAG. What is the sequence of the bases on the opposite strand?

4. Assume that a 100-bair pair DNA double helix contains 45 cytosines. How many adenines are there?

Answer 1

Answer:

1) Nitrogenous bases, Pentose (ribose) sugar and the phosphate group

2) Deoxyribose sugar

3)CTGAGCT

4) 55

Explanation:

1) A nucleotide (DNA/RNA) comprises of the following

• Nitrogenous bases: which are adenine, thymine (only found n DNA), cytosine  and uracil (only found in RNA).
• Pentose sugar: A five carbon sugar called ribose is also one of the components of a nucleotide
• Phosphate group: made up of phosphorus and oxygen

2) Deoxyribose sugar: It is also a pentose but it is one oxygen atom lesser than the ribose sugar found in the RNA.

3) In base pairs of DNA, Adenine binds to Thymine while Cytosine binds to Guanine. Also, the DNA is read in the 5' to 3' direction for both the forward and reverse strand. Hence when forward strand is written from left to right, the reverse strand will be written from right to left.

The explanation above provides the reason for writing the opposite strand as CTGAGCT.

4) From the explanation in the previous answer, it can also be deduced that the total number of adenine is equal to the total number of thymine in a DNA base pair while the total number of guanine is equal to the total number of cytosine in a base pair. Hence when cytosine is 45 in a base pair of 100, guanine is also 45 while adenine is 55 and thymine is also 55. Hence, the 45 cytosine will bind to 45 guanine while the 55 adenine will bind to 55 thymine to form the 100 base pairs.

NOTE: 45 + 55 = 100 base pairs

Answer 2

1. a sugar, a phosphate, and a base (such as Adenine.)

2. Deoxyribose 

3. TCGAGTC, A pairs with T and G pairs with C

4. 55 adenines, 100-45=55