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Cell: The Unit of Life - Nucleus and Cytoskeleton

Grade 11CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The nucleus was first described by Robert Brown in 18311831. It is the control center of the cell, containing the genetic material.

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The nuclear envelope consists of two parallel membranes with a perinuclear space of 1010 to 50 nm50 \text{ nm}. The outer membrane remains continuous with the Endoplasmic Reticulum and bears ribosomes.

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Nuclear pores are formed by the fusion of the two membranes, acting as passages for the movement of RNARNA and protein molecules in both directions.

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The nucleoplasm contains the nucleolus (site for active rRNArRNA synthesis) and chromatin. Chromatin consists of DNADNA, basic proteins called histones, non-histone proteins, and RNARNA.

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Based on the position of the centromere, chromosomes are classified as: Metacentric (middle centromere), Sub-metacentric (slightly away from middle), Acrocentric (near the end), and Telocentric (terminal centromere).

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The cytoskeleton is an elaborate network of filamentous proteinaceous structures present in the cytoplasm, comprising microtubules, microfilaments, and intermediate filaments.

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Functions of the cytoskeleton include mechanical support, motility, and maintenance of the shape of the cell.

📐Formulae

Perinuclear Space=10−50 nm\text{Perinuclear Space} = 10 - 50 \text{ nm}

Chromosome Composition≈DNA+Histones+Non-histone proteins+RNA\text{Chromosome Composition} \approx DNA + \text{Histones} + \text{Non-histone proteins} + RNA

Centromere Position  ⟹  Metacentric: p arm=q arm\text{Centromere Position} \implies \text{Metacentric: } p \text{ arm} = q \text{ arm}

💡Examples

Problem 1:

Identify the type of chromosome where the centromere is situated close to its end, forming one extremely short and one very long arm.

Solution:

Acrocentric Chromosome

Explanation:

In an acrocentric chromosome, the centromere is located near one end (sub−terminalsub-terminal), resulting in one 'p' arm being significantly shorter than the 'q' arm.

Problem 2:

Explain the significance of the nucleolus in a cell with high protein synthesis requirements.

Solution:

High rRNArRNA production.

Explanation:

The nucleolus is the site for active ribosomal RNARNA (rRNArRNA) synthesis. Since ribosomes are the 'protein factories' of the cell, cells actively engaged in protein synthesis possess larger and more numerous nucleoli.

Problem 3:

Calculate the width of the perinuclear space if it is expressed as 0.01 to 0.05μm0.01 \text{ to } 0.05 \mu\text{m} in nanometers.

Solution:

10 nm to 50 nm10 \text{ nm to } 50 \text{ nm}

Explanation:

Since 1μm=1000 nm1 \mu\text{m} = 1000 \text{ nm}, then 0.01μm×1000=10 nm0.01 \mu\text{m} \times 1000 = 10 \text{ nm} and 0.05μm×1000=50 nm0.05 \mu\text{m} \times 1000 = 50 \text{ nm}.

Nucleus and Cytoskeleton - Revision Notes & Key Diagrams | CBSE Class 11 Biology