Molecular Genetics. Genetics is the study of how genes bring about traits in living things and how those characteristics are inherited.

Transcription

1 DNA

2 Molecular Genetics Genetics is the study of how genes bring about traits in living things and how those characteristics are inherited. During the 1950s, an explosion of biological research occurred. The knowledge generated during this period helped explain how genes function, and it gave rise to the science of molecular genetics. This science is based on the activity of deoxyribonucleic acid (DNA) and how this activity brings about the production of proteins in the cell.

3 The DNA Structure DNA is made up of a series of units called nucleotides Each nucleotide is made of three parts: 1) a sugar called deoxyribose (composed by 5 ) hosphate group = 2 2) a phosphate group (also called phosphoric acid) 3) a nitrogen-containing bases. The 4 nitrogen bases are adenine (A), guanine (G), thymine (T), and cytosine () Sugar (deoxyribose) Nitrogen base Each nitrogen base is attached to a sugar, and each sugar is then attached to a phosphate group to form a single nucleotide. Each nucleotide is named for the base it contains.

4 The DNA Structure DNA is made up of a series of units called nucleotides Therefore, in DNA there are four possible nucleotides, each containing one of four bases. For example, Figure 6.5 shows an adenine nucleotide. Therefore, in DNA there are four possible nucleotides, each containing one of four bases. Note that adenine and guanine have a double-ring structure. They belong to a group of nucleotides called purines. Thymine and cytosine have a single-ring structure. Single-ring nucleotides are called pyrimidines. LINK Note that adenine and guanine have a double-ring structure. They belong to a group of Now that you know what DNA is made of and where DNA is nucleotides called purines. found, why do you think scientists called this chemical deoxyribonucleic acid? Thymine and cytosine have a single-ring structure. Single-ring nucleotides are called pyrimidines hosphate group = 2 Sugar (deoxyribose) Figure 6.5 ne DNA nucleotide, the adenine nucleotide. Like athletes, scientists can be very competitive. As the evidence mounted, scientists knew they were very close to determining N the structure of DNA. Many people were vying to be the first to make this important N discovery. The Nrace was on! ere are the N facts the scientists knew at the time. DNA is made of nucleotides. N 3 Nucleotides N are linked Ntogether in a string. The Thymine (T) N sugar Adenine of one (A) nucleotide is attached N to the N phosphate group of the next, and the nitrogen bases stick out from one side of this sugarphosphate backbone. N N In each DNA molecule, the number Guanine of (G) adenine nucleotides equals the number of thymine Figure nucleotides, 6.4 The nitrogen and bases the number of DNA are of cytosine adenine, guanine, thymine, and cytosine. nucleotides equals the number of guanine nucleotides. Nucleotides are joined together trough hydrogen bonds to form the long DNA chains Further studies showed that nucleotides are joined together to form long chains, much like beads in a necklace. The phosphate group of one nucleotide is bonded to the deoxyribose sugar of an adjacent nucleotide, as shown in Figure 6.6. The phosphate groups and deoxyribose molecules form Nitrogen base Word Discovering the Double elix If the nucleotides are strung in a straight line, a typical DNA molecule would be over a metre long. Somehow, the DNA molecule must be compressed. N ytosine ()

5 The DNA Structure 4' 2' 1' The is a five-carbon sugar (carbohydrate). The carbons are numbered 1' (read one prime ), 2',, 4', and to distinguish from the the atoms of the nitrogen bases rings. The carbon links to the phosphate group The phosphate group of one nucleotide is bonded to the of the deoxyribose sugar of an adjacent nucleotide. The phosphate groups and deoxyribose molecules form the backbone of the DNA chain.

6 The DNA Structure 4' 1' 2' The nitrogen bases are attached to the deoxyribose molecules, and the purine and pyrimidine bases are opposite one another on the two nucleotide chains.

7 The DNA Structure 4' 1' 2' The nitrogen bases are attached to the deoxyribose molecules, and the purine and pyrimidine bases are opposite one another on the two nucleotide chains.

8 The DNA Structure A T T G G A The nitrogen bases are attached to the deoxyribose molecules, and the purine and pyrimidine bases are opposite one another on the two nucleotide chains.

9 The DNA Double elix Structure As resulted from the studies of Rosalind Franklin and Maurice Wilkins and proposed by James Watson and Francis rick in 1953, DNA consists of two long nucleotide chains. The two nucleotide chains twist around one another to form a double helix, a shape resembling a spiral staircase. Weak chemical bonds (hydrogen bridge) between the chains hold the two chains of nucleotides to one another. Furthermore, the DNA molecule had a constant diameter of 2 nm