Biomolecules are organic compounds essential for life, forming the structural and functional basis of living organisms. This chapter delves into the various types of biomolecules, their structures, functions, and significance, aligning with the Class 11 NCERT curriculum and NEET syllabus.
Table of Contents
Introduction to Biomolecules
Biomolecules are organic molecules present in living organisms, playing crucial roles in maintaining life processes. They are primarily composed of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Biomolecules are categorized into:
- Micromolecules: Low molecular weight compounds like amino acids, sugars, nucleotides, and lipids.
- Macromolecules: High molecular weight polymers such as proteins, polysaccharides, and nucleic acids.
Carbohydrates
Carbohydrates are polyhydroxy aldehydes or ketones, serving as the primary energy source for living organisms. They are classified based on the number of sugar units:
- Monosaccharides: Single sugar units (e.g., glucose, fructose).
- Disaccharides: Two monosaccharide units linked by a glycosidic bond (e.g., sucrose, lactose).
- Polysaccharides: Long chains of monosaccharide units (e.g., starch, glycogen, cellulose).
Functions:
- Provide energy (glucose metabolism).
- Serve as structural components (cellulose in plants).
- Participate in cell recognition and signaling.
Proteins
Proteins are polymers of amino acids linked by peptide bonds, exhibiting diverse structures and functions.
Structure:
- Primary Structure: Linear sequence of amino acids.
- Secondary Structure: Alpha-helices and beta-sheets formed by hydrogen bonding.
- Tertiary Structure: Three-dimensional folding due to interactions among R-groups.
- Quaternary Structure: Assembly of multiple polypeptide chains.
Functions:
- Enzymatic activity (e.g., amylase).
- Structural support (e.g., collagen).
- Transport (e.g., hemoglobin).
- Defense (e.g., antibodies).
Lipids
Lipids are hydrophobic molecules, including fats, oils, phospholipids, and steroids.
Types:
- Simple Lipids: Esters of fatty acids with alcohols (e.g., triglycerides).
- Compound Lipids: Contain additional groups (e.g., phospholipids).
- Derived Lipids: Substances derived from simple and compound lipids (e.g., steroids).
Functions:
- Energy storage.
- Structural components of cell membranes.
- Insulation and protection.
- Precursor for hormones.
Nucleic Acids
Nucleic acids, DNA and RNA, are polymers of nucleotides responsible for genetic information storage and transfer.
Components of Nucleotides:
- Nitrogenous base (purines: adenine, guanine; pyrimidines: cytosine, thymine/uracil).
- Pentose sugar (deoxyribose in DNA, ribose in RNA).
- Phosphate group.
Functions:
- DNA stores genetic information.
- RNA translates genetic code into proteins.
Enzymes
Enzymes are biological catalysts that accelerate biochemical reactions without being consumed.
Characteristics:
- Highly specific to substrates.
- Operate under optimal temperature and pH.
- Can be inhibited or activated.
Mechanism:
- Substrate binds to the enzyme's active site.
- Enzyme-substrate complex forms.
- Product is released, and the enzyme is free to catalyze another reaction.
NEET Practice MCQs
- Which of the following is a
disaccharide?
a) Glucose
b) Fructose
c) Sucrose
d) Ribose
Answer: c) Sucrose - The bond linking amino acids
in a protein is called:
a) Glycosidic bond
b) Peptide bond
c) Phosphodiester bond
d) Hydrogen bond
Answer: b) Peptide bond - Which lipid is a major
component of the cell membrane?
a) Triglyceride
b) Cholesterol
c) Phospholipid
d) Steroid
Answer: c) Phospholipid - The sugar present in RNA is:
a) Deoxyribose
b) Ribose
c) Glucose
d) Fructose
Answer: b) Ribose - Enzymes increase the rate of
reaction by:
a) Increasing temperature
b) Lowering activation energy
c) Changing pH
d) Consuming substrates
Answer: b) Lowering activation energy
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