T6

Question 1

DNA (Deoxyribonucleic Acid)

Answer 1

1. Pentose sugar - Deoxyribose
2. Nitrogen-containing base - Adenine, Guanine, Cytosine, Thymine
3. Double stranded in the form of double helix. (Only 1 form of DNA)
4. Larger molecule
5. Found mostly in the nucleus with small amounts in the mitochondria & chloroplasts

Question 2

RNA (Ribonucleic Acid)

Answer 2

1. Pentose sugar - Ribose
2. Nitrogen-containing base - Adenine, Guanine, Cytosine, Uracil
3. Single stranded (3 types of RNA - mRNA, rRNA, tRNA)
4. Relatively small molecule
5. Synthesised in the nucleus but found mainly in the cytoplasm

Question 3

Five different types of bases

Answer 3

1. Adenine
2. Guanine
3. Cytosine
4. Thymine
5. Uracil

Question 4

Purines

Answer 4

Bases with double ring structure comprising of a six-sided ring and five-sided ring.

Example : Adenine & Guanine

Question 5

Pyrimidines

Answer 5

Bases with a single ring structure each with six sided

Examples : Cytosine, Thymine & Uracil

Question 6

Formation of Nucleotides, Dinucleotides & Polynucleotides

Answer 6

1. The 3 components (phosphoric acid, pentose sugar & nitrogen-containing base) combine together to form a nucleotide via condensation reaction.
2. Phosphoric acid is attached to the sugar molecule at carbon atom 5.
3. 2 nucleotides are joined together by covalent bonds between phosphate group of one nucleotide and the pentose sugar of the next resulting in phosphodiester bond
4. Phosphodiester bond occurs between carbon atom 3 (3’) of one sugar and carbon atom 5 (5’) of the next

Question 7

DNA Replication

Answer 7

The process by which a DNA molecule can produce an exact copy of itself

Question 8

Mechanism of DNA replication

Answer 8

1. The enzyme DNA helicase causes a region of the double helix original (parental) DNA molecule to unwind and unzip at the origin of replication by breaking the weak hydrogen bonds between the nitrogen-containing bases.
2. This causes the two (parental) strands of DNA molecule to separate and expose their bases.
3. Each single strand of DNA now acts as a template for synthesising new (daughter) DNA strands. The above mentioned specific or complementary base-pairing enables a free DNA nucleotide to find and match up against its complementary nucleotide on each of the open parental strand. (Adenine with Thymine, Cytosine with Guanine)
4. Weak hydrogen bonds are formed between these complementary base pairs
5. The enzyme DNA polymerase catalyses the formation of a phosphodiester bond between two adjacent nucleotides between the phosphate group of one nucleotide and the pentose sugar.
6. At the end of the replication, the two newly formed (daughter) molecules of DNA wind up again into double helix.