1. CHAPTER 5
GENETIC CONTROL
Leonardus, S.Si.

2. Structure and replication of DNA Role of DNA in protein synthesis
Content
Structure and replication of DNA
Role of DNA in protein synthesis

3. Learning Outcomes
Candidates should be able to:
(a) describe the structure of RNA and DNA and explain the importance of base pairing and the different hydrogen bonding between bases;
(b) explain how DNA replicates semi-conservatively during interphase;

4. Learning Outcomes
(c) state that a gene is a sequence of nucleotides as part of a DNA molecule, which codes for a polypeptide and state that a mutation is a change in the sequence that may result in an altered polypeptide;
(d) describe the way in which the nucleotide sequence codes for the amino acid sequence in a polypeptide with reference to the nucleotide sequence for HbA (normal) and HbS (sickle cell) alleles of the gene for the β-haemoglobin polypeptide;

5. Learning Outcomes
(e) describe how the information on DNA is used during transcription and translation to construct polypeptides, including the role of messenger RNA (mRNA), transfer RNA (tRNA) and the ribosomes (for genetic dictionaries see pages 37–39);
(f) use the knowledge gained in this section in new situations or to solve related problems.

6. Summary
DNA and RNA are polynucleotides, made up of long chains of nucleotides. A nucleotide contains a pentose sugar, a phosphate group and a N-containing base. A DNA molecule consists of 2 polynucleotide chains, linked by H bonds between bases. Adenine always pairs with thymine, and cytosine with guanine. RNA, which comes in several different forms (mRNA, tRNA & rRNA), has only 1 polynucleotide chain, although this may be twisted back on itself, as in tRNA. In RNA, the base thymine is replaced by uracil

7. DNA molecules replicate during interphase
DNA molecules replicate during interphase. The H bonds between the bases break, allowing free nucleotides to fall into position opposite their complementary ones on each strand of the original DNA molecule. Adjacent nucleotides are then linked, through their phosphates and sugars, to form new strands. Two complete new molecules are thus formed from one old one, each new molecule containing one old strand and one new.
The sequence of bases (or nucleotides) on a DNA molecule codes for the sequence of amino acids in proteins (or polypeptide). Each amino acid is coded for by 3 bases. A length of DNA coding for one complete protein or polypeptide is gene.

8. During protein synthesis, a complementary copy of the base sequence on a gene is made, by building a molecule of mRNA against one DNA strand. The mRNA then moves to a ribosome in the cytoplasm. tRNA molecules with complementary triplets of bases temporarily pair with the base triplets on mRNA, bringing appropriate amino acids. As 2 amino acids are held side by side, a peptide bond forms between them. The ribosome moves along the mRNA molecule, so that appropriate amino acids are gradually linked together, following the sequence laid down by the base sequence on the mRNA

9. Structure of DNA and RNA
DNA : deoxy ribonucleic acid
RNA : Ribonucleic acid
DNA & RNA are macromolecules
DNA & RNA are polymer
The smaller molecules from which DNA & RNA are made are nucleotide ----- therefore DNA & RNA are polynucleotides
3 components of nucleotides are :
A nitrogen containing base
DNA (adenine, guanine, cytosine & thymine)
RNA (adenine, guanine, cytosine & uracil)

10. A pentose sugar
DNA (deoxy ribose)
RNA (Ribose)
A phosphate group

11. DNA components

14. Purine base

15. Pyrimidine base

16. Deoxyribose vs ribose

17. Doble helix structure of DNA

18. Two strands of DNA run antiparalel

19. DNA double stranded DNA has two strands
A phosphate-deoxyribose polymer composes the backbone of the DNA
adjacent sugars are connected by phosphodiester bonds
nitrogenous bases are convalently bonded to the 1' carbon of the deoxyribose
the two DNA strands are antiparallel
the two strands are held together by hydrogen bonds between complementary bases
adenine hydrogen bonds (base pairs) to thymine
guanine hydrogen bonds to cytosine

20. RNA structure

21. mRNA

22. tRNA

23. rRNA

24. DNA vs RNA DNA RNA Double polynucleotide chain
Single polynucleotide chain
Bases are : adenine, guanine, cytosine & thymine
Bases are : adenine, guanine, cytosine & uracil
Pentose sugar is deoxyribose
Pentose sugar is ribose
Only one type
3 types (mRNA, tRNA & rRNA)
Amount per diploid cell is constant in any one species
Amount varies from cell to cell