Biomolecules Class 11 NCERT Notes & NEET MCQs

 

Biomolecules Class 11 NCERT Notes & NEET MCQs

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

  1. Introduction to Biomolecules
  2. Carbohydrates
  3. Proteins
  4. Lipids
  5. Nucleic Acids
  6. Enzymes
  7. NEET Practice MCQs

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

  1. Which of the following is a disaccharide?
    a) Glucose
    b) Fructose
    c) Sucrose
    d) Ribose
    Answer: c) Sucrose
  2. 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
  3. Which lipid is a major component of the cell membrane?
    a) Triglyceride
    b) Cholesterol
    c) Phospholipid
    d) Steroid
    Answer: c) Phospholipid
  4. The sugar present in RNA is:
    a) Deoxyribose
    b) Ribose
    c) Glucose
    d) Fructose
    Answer: b) Ribose
  5. 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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