Chapter 6: BiomoleculesLong Questions with Answers

Carbohydrates are organic compounds in which the ratio of H and O is 2 : 1. They are also called saccharides; general formula Cₙ(H₂O)ₙ.

1. Monosaccharides

Made of single sugar molecule; easily soluble in water; sweet taste; 3 to 7 carbon atoms. Pentoses: ribose (C₅H₁₀O₅), deoxyribose (C₅H₁₀O₄). Hexoses: glucose, fructose, galactose (C₆H₁₂O₆).

Roles: glucose is the main fuel of cellular respiration; ribose and deoxyribose are parts of RNA and DNA.

2. Disaccharides

Made of two monosaccharide units; less soluble; less sweet. Sucrose = glucose + fructose; maltose = glucose + glucose; lactose in milk.

Roles: plants transport sugar between body parts as sucrose; lactose is the sugar of milk.

3. Polysaccharides

Hundreds to thousands of monosaccharide units; insoluble; tasteless.

Proteins are the polymers of amino acids and the most abundant biomolecules in cell. They participate in everything organisms do:

Structural

Catalysis and control

Transport and movement

Protection

Good sources: meat, fish, eggs, milk, pulses and beans.

1. Saturated fatty acids

Their internal carbon atoms are bonded with maximum number of hydrogen atoms. They do not have double bonds between carbon atoms. They are solid at room temperature, e.g. in animal fats (ghee, butter).

2. Unsaturated fatty acids

They have one or more double bonds between carbon atoms. They are liquid at room temperature, e.g. in plant oils such as olive and corn oil.

Structure

Fats and oils are the most familiar lipids. They contain one glycerol and three fatty acids. Each of the three OH groups of glycerol is joined to one fatty acid.

Role in energy storage

DNA is made of deoxyribonucleotides; each has deoxyribose sugar, a phosphate group and a base: adenine (A), thymine (T), cytosine (C) or guanine (G).

Double helix model (Watson and Crick, 1953)

Base pairing

Watson and Crick received the Nobel prize in 1962 for this discovery.

The DNA molecule in a chromosome consists of thousands of nucleotides. Along its length are specific segments called genes. Each gene consists of specific sequence of nucleotides that carries information for the synthesis of a specific protein.

Step 1: Transcription (in the nucleus)

During the working of a gene, the specific sequence of DNA nucleotides is copied in the form of a molecule of messenger RNA (mRNA). The process of making mRNA copy of DNA is called transcription.

Step 2: mRNA moves to the cytoplasm

The mRNA carries the sequence of its nucleotides to the ribosome.

Step 3: Translation (at the ribosome)

The ribosome reads this sequence and joins specific amino acids to form a protein. This step is known as translation. tRNA transfers the specific amino acids to the ribosome in the correct sequence; rRNA forms the ribosome.

The molecules produced by organisms are called biomolecules; they are mostly large and called macromolecules. They make 93 % of the dry mass of protoplasm.

An amino acid is an organic molecule made of an amino group (NH₂), a carboxyl group (COOH), a hydrogen and a side group (R) attached to a central carbon atom.