Easy NEET Notes – Biomolecules Types
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| CBSE Class 11 Biomolecules: Amino acids, lipids, and nucleic acids explained with clear diagrams for easy exam preparation. |
- Dr.Sanjaykumar Pawar
1. Proteinaceous Amino Acids
What is an Amino Acid?
- Amino acids are the building blocks of proteins.
- Every amino acid contains:
- Amino group (–NH₂)
- Carboxyl group (–COOH)
- Hydrogen atom (H)
- R group (Side chain) → makes each amino acid different.
R Group (Side Chain)
- The R group decides the type and properties of an amino acid.
Examples:
- Glycine (Gly) → R = Hydrogen (H) → Simplest amino acid.
- Alanine (Ala) → R = Methyl group (–CH₃).
- Serine (Ser) → R = Hydroxymethyl group (–CH₂OH).
NEET Tip: R group is responsible for the unique nature of every amino acid.
Types of Amino Acids (Based on Amino & Carboxyl Groups)
1. Acidic Amino Acids
- Have more carboxyl (–COOH) groups than amino groups.
- Carry a negative charge.
- Example: Glutamic acid.
Easy Trick: Acidic = More COOH.
2. Basic Amino Acids
- Have more amino (–NH₂) groups than carboxyl groups.
- Carry a positive charge.
- Example: Lysine.
Easy Trick: Basic = More NH₂.
3. Neutral Amino Acids
- Equal number of amino and carboxyl groups.
- No overall charge.
- Example: Valine.
Aromatic Amino Acids
These amino acids contain a benzene (aromatic) ring.
Examples:
- Tyrosine
- Phenylalanine
- Tryptophan
NEET Remember: "Try Phenyl Tyre"
- Try → Tryptophan
- Phenyl → Phenylalanine
- Tyre → Tyrosine
Zwitterion (Very Important for NEET ⭐⭐⭐)
- Amino acids can exist as zwitterions in solution.
- A zwitterion has:
- Positive charge on NH₃⁺
- Negative charge on COO⁻
- Overall charge = Zero
Why? Because amino acids contain both acidic and basic groups.
Definition: A molecule having both positive and negative charges but overall electrically neutral is called a zwitterion.
2. Lipids
Definition
- Lipids are water-insoluble organic compounds.
- They store energy and form cell membranes.
Fatty Acids
Definition
A fatty acid contains:
- One carboxyl group (–COOH)
- One long hydrocarbon chain (R group)
The R group may contain:
- Methyl (–CH₃)
- Ethyl (–C₂H₅)
- Long chain of CH₂ groups
Examples
Palmitic Acid
- Total carbon atoms = 16
Arachidonic Acid
- Total carbon atoms = 20
Types of Fatty Acids
1. Saturated Fatty Acids
- No double bond (C=C).
- Contain only single bonds.
- Usually solid at room temperature.
Examples:
- Butter
- Ghee
2. Unsaturated Fatty Acids
- One or more double bonds (C=C).
- Usually liquid at room temperature.
Examples:
- Mustard oil
- Sunflower oil
- Gingelly (Sesame) oil
Easy Trick:
- Saturated = Single bonds
- Unsaturated = Double bonds
Glycerol
- Glycerol is a 3-carbon alcohol.
- Chemical name = Trihydroxy propane.
- Contains three –OH groups.
Types of Glycerides
When fatty acids combine with glycerol, they form glycerides.
Monoglyceride
- 1 fatty acid + glycerol
Diglyceride
- 2 fatty acids + glycerol
Triglyceride
- 3 fatty acids + glycerol
NEET Fact: Triglycerides are the main storage form of fats.
Fats vs Oils
Fats
- Higher melting point.
- Solid at room temperature.
Examples:
- Butter
- Ghee
Oils
- Lower melting point.
- Liquid at room temperature.
Example:
- Gingelly (Sesame) oil
Phospholipids ⭐⭐⭐
- Lipids containing a phosphate group are called phospholipids.
- Main component of the cell membrane.
Example:
- Lecithin
NEET Fact: Cell membrane is mainly made of phospholipids.
3. Nitrogen Bases
These are nitrogen-containing compounds found in nucleic acids.
Five nitrogen bases are:
- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T)
- Uracil (U)
Nucleoside
Definition
Nitrogen base + Sugar = Nucleoside
Examples:
- Adenosine
- Guanosine
- Cytidine
- Thymidine
- Uridine
Easy Formula: Base + Sugar = Nucleoside
Nucleotide ⭐⭐⭐
Definition
Nitrogen base + Sugar + Phosphate = Nucleotide
Examples:
- Adenylic acid (AMP)
- Guanylic acid
- Cytidylic acid
- Thymidylic acid
- Uridylic acid
Easy Formula: Base + Sugar + Phosphate = Nucleotide
DNA and RNA
- DNA and RNA are nucleic acids.
- They are made up of many nucleotides joined together.
- They store and transmit genetic information.
NEET One-Liners to Remember
- Proteins are made of amino acids.
- R group determines the identity and properties of an amino acid.
- Glycine is the simplest amino acid.
- Glutamic acid is acidic.
- Lysine is basic.
- Valine is neutral.
- Aromatic amino acids: Tyrosine, Phenylalanine, Tryptophan.
- Amino acids exist as zwitterions in solution.
- Lipids are insoluble in water.
- Fatty acids may be saturated or unsaturated.
- Palmitic acid = 16 carbons.
- Arachidonic acid = 20 carbons.
- Glycerol = Trihydroxy propane.
- Triglycerides are the main storage fats.
- Phospholipids are the main components of cell membranes.
- Lecithin is a phospholipid.
- Nucleoside = Base + Sugar.
- Nucleotide = Base + Sugar + Phosphate.
- DNA and RNA are polymers of nucleotides and act as the genetic material.
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CBSE Class 11 Biomolecules - Complete Q&A
Very Short Answer Questions
Q1. What are amino acids?
Ans: Organic compounds that form proteins.
Q2. What is a zwitterion?
Ans: A molecule having both positive and negative charges but overall neutral.
Q3. What is glycerol?
Ans: A trihydroxy alcohol (propane with three –OH groups).
Q4. Name one aromatic amino acid.
Ans: Tyrosine.
Q5. What are nucleotides made of?
Ans: Base + Sugar + Phosphate.
Short Answer Questions
Q1. Differentiate between saturated and unsaturated fatty acids.
Ans: Saturated fatty acids have no double bonds and are solid (e.g., butter). Unsaturated fatty acids have double bonds and are liquid (e.g., oil).
Q2. Difference between nucleoside and nucleotide?
Ans: Nucleoside = Base + Sugar; Nucleotide = Base + Sugar + Phosphate.
Q3. What are phospholipids?
Ans: Lipids containing phosphate group found in cell membranes. Example: Lecithin.
Q4. What is R group in amino acids?
Ans: Variable side chain that determines amino acid properties.
Long Answer Questions
Q1. Classification of amino acids.
Acidic (Glutamic acid), Basic (Lysine), Neutral (Valine), Aromatic (Tyrosine, Phenylalanine, Tryptophan).
Q2. Structure of lipids.
Lipids are made of fatty acids and glycerol. Types include simple lipids, triglycerides, and phospholipids.
Q3. Nucleic acids.
DNA and RNA are made of nucleotides. They store and transfer genetic information.
MCQs
Q1. Glycine is:
Ans: Simplest amino acid.
Q2. Lipids are:
Ans: Insoluble in water.
Q3. Nucleotide contains:
Ans: Base + Sugar + Phosphate.
Q4. Example of phospholipid:
Ans: Lecithin.
Q5. Aromatic amino acid:
Ans: Tyrosine.
Assertion & Reason
Q1. Amino acids exist as zwitterions.
Ans: True. Reason: They have NH2 and COOH groups.
Q2. Oils are solid at room temperature.
Ans: False.
Q3. DNA is made of nucleotides.
Ans: True.
Fill in the Blanks
Glycine is the ______ amino acid.
Ans: simplest
Lipids are ______ in water.
Ans: insoluble
DNA stands for ______ acid.
Ans: deoxyribonucleic
Match the Following
Glycine
Simplest amino acid
Lysine
Basic amino acid
Tyrosine
Aromatic amino acid
Lecithin
Phospholipid
DNA
Genetic material
Case Study
Q1. What is zwitterion?
Ans: Molecule with both positive and negative charge.
Q2. Why are lipids insoluble?
Ans: Because they are non-polar.
Q3. Basic unit of nucleic acid?
Ans: Nucleotide.
Q4. Genetic material?
Ans: DNA.
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