SPM Biology 4 Chemical Composition of the Cell Part 5 Organic Compounds in the Cell - Nucleic Acids

1. Macromolecules containing carbon, hydrogen, oxygen, nitrogen, and phosphorus.

2. The building blocks (monomers) of nucleic acids are called nucleotides.

3. Each nucleotide consists of three parts:

• A 5-carbon sugar or pentose
• A phosphate group
• A nitrogenous base

Structure of nucleotide

4. 2 types of pentose sugars

• ribose
• deoxyribose

5. Nitrogenous base

• adenine (A)
• guanine (G)
• cytosine (C)
• thymine (T)
• uracil (U)

6. Importance: store & transmit hereditary (genetic) information.

7. There are 2 types of nucleic acids:

• Deoxyribonucleic acid (DNA)
• Ribonucleic acid (RNA)

Deoxyribonucleic acid (DNA)

1. DNA contains deoxyribose sugar. 

2. Nitrogenous base groups for DNA - A, T, G, C

3. Consists of 2 polynucleotide strands twisted around each other in the form of a double helix.

4. DNA is found in the nucleus, mitochondrion & chloroplast.

5. Importance: carries the genetic code; to store genetic information

Ribonucleic acid (RNA)

1. RNA contains ribose sugar.

2. Nitrogenous bas groups for RNA - A, U, G, C

3. Consists of single-stranded polynucleotide chain, shorter than DNA.

4. RNA is found in nucleus & cytoplasm.

5. 3 types of RNA:

• messenger RNA (mRNA)
• ribosomal RNA (rRNA)
• transfer RNA (tRNA)

6. Importance: involve in protein synthesis

RNA and DNA structures

Formation of chromosomes

Formation of chromosomes

STPM Biology Biological Molecules Part 18 Nucleic Acids - DNA and RNA

DNA - the hereditary material of life

Structure

1. A DNA molecule consists of 2 polynucleotide chains coiled to form a double helix. 
2. The 2 chains are held together by hydrogen bonds between complementary bases. (T and A are complementary bases; while G and C are another complementary bases).
3. Each complete turn of the double helix is 3.4nm long and contains 10 pairs of bases.
4. The diameter of each helix is 1.0nm.
5. The polynucleotide chains of DNA molecule are anti-parallel (the 5'end of one chain lies next to the 3' end of the other chain).
   
6. the polynucleotide chain is made up of deoxyribonucleotides that are linked together by phosphodiester bonds.

Structure of DNA molecule

Complementary base pairing

1. Due to its structure, only purine bases can pair with pyrimidine bases.
2. Adenine (A, a purine) pairs with thymine (T, a pyrimidine) with 2 hydrogen bonds.
3. Guanine (G, a purine) pairs with cytosine (C, a pyrimidine) with 3 hydrogen bonds.

Complementary base pairing

RNA

1. RNA is a polynucleotide. The monomer of RNA is ribonucleotide.

2. RNA molecule consists of one polynucleotide chain.

3. There are three types of RNA in cells:

• ribosomal RNA (rRNA)
• messenger RNA (mRNA)
• transfer RNA (tRNA)

Ribosomal RNA (rRNA)

1. More than 80% of RNA in the cell is rRNA.

2. rRNA is found in ribosome. A ribosome is constructed from rRNA (50%) and protein (50%).

3. Functions of rRNA:

• Main component of ribosome.
• Bind mRNA molecule to ribosome during protein synthesis.

Messenger RNA (mRNA)

1. The longest RNA molecules which contains 70 to 3,000 nucleotides.

2. mRNA molecules are long uncoiled molecules.

3. Function of mRNA:

• Carry genetic information from gene into the cytoplasm for protein synthesis.

Transfer RNA (tRNA)

1. The shortest RNA molecules.

2. tRNA makes up about 10% to 15% of RNA in cells.

3. The polynucleotide chain is folded to form a 'clover-leaf'.

4. The anticodon of tRNA contains 3 bases which are complementary to the codon for the amino acid it carries.

5. Function of tRNA:

• Transfer a specific amino acid to ribosome for polypeptide synthesis.

rRNA, mRNA, tRNA

Differences between RNA and DNA

STPM Biology Biological Molecules Part 17 Nucleic Acids

1. The 2 nucleic acids in the cells are:

• DNA (deoxyribonucleic acid)
• RNA (ribonucleic acid)

2. Nucleic acids are natural polymers. Nucleic acid monomers are nucleotides.

3. A nucleotide has 3 components:

• 5-carbon sugar (pentose)
• Organic base / nitrogenous base
• Phosphoric acid

Structure of nucleotide

4. The pentose of nucleotides are ribose or deoxyribose. 

5. Nucleotide containing ribose is called ribonucleotides (RNA monomers).

6. Nucleotide containing deoxyribose is called deoxyribonucleotide (DNA monomers).

Structure of ribose and deoxyribose

7. Nucleotide has one of these five organic bases:

• adenine (A)
• guanine (G)
• thymine (T)
• cytosine (C)
• urasil (U)

8. These bases can be divided into 2 group:

• Purines (double-ringed molecule): Adenine, Guanine
• Pyrimidine (single-ringed molecule): Thymine, Cytosine, Uracil

5 organic bases

Formation of nucleotides and nucleic acid

1. In formation of nucleotide, a nitrogenous base is first linked to pentose by condensation reaction to form nucleoside.
2. Phosphate group is then added to the nucleoside to form a nucleotide.
3. Nucleic acids are polynucleotides. Polynucleotides are formed by linking nucleotides together.
4. Two nucleotides are linked together through condensation reaction to form dinucleotides.
5. Further addition of nucleotides to dinucleotides will form polynucleotides.
6. Nucleotides in polynucleotides are linked together in phosphodiester bonds.
   
   

   

   Formation of phosphodiester bond

   
   
7. A nucleotide chain has 5' end and a 3' end. The 5' end of the polynucleotide chain is the end with the free phosphate group.

5' end and 3' end of nucleotide chain