Thymine is exclusive amongst the four bases as it only occurs in DNA molecules. Adenine, cytosine and guanine are also found in nucleotides that make up ribonucleic acid, or RNA. Inside an RNA molecule, thymine is replaced by uracil.he order that the bases appear is insignificant in the DNA molecule. This means that there can be four different cross rungs â adenine with thymine, thymine with adenine, cytosine with guanine, and guanine with cytosine.
The pituitary gland hangs from the base of the brain by a stalk and is enclosed by bone. It consists of a hormone-producing glandular portion (anterior pituitary) and a neural portion (posterior pituitary), which is an extension of the hypothalamus.
The average human brain weighs about 1360 grams, or 3 lbs. Thatâs about four times lighter than an elephant brain. The heaviest mammalian brain is found in the sperm whale â weighing 7711 grams (17 lbs). Larger brains are needed, in part, to control larger muscles. At the other end of the scale is the owl brain that weighs just over two grams. A bullfrog's brain is about one-tenth smaller than that.