Podcast
Questions and Answers
What is the primary function of the centromere in a chromosome?
What is the primary function of the centromere in a chromosome?
The centrioles in a centrosome lie parallel to each other.
The centrioles in a centrosome lie parallel to each other.
False
What are the disc-shaped structures present on the sides of the centromere?
What are the disc-shaped structures present on the sides of the centromere?
Kinetochores
The chromatin contains DNA and some basic proteins called ______________.
The chromatin contains DNA and some basic proteins called ______________.
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Match the types of chromosomes with their characteristic centromere position:
Match the types of chromosomes with their characteristic centromere position:
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Who first described the nucleus as a cell organelle in 1831?
Who first described the nucleus as a cell organelle in 1831?
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The nuclear envelope is a single membrane that separates the nucleus from the cytoplasm.
The nuclear envelope is a single membrane that separates the nucleus from the cytoplasm.
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What is the function of nucleolus in the nucleus?
What is the function of nucleolus in the nucleus?
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The outer membrane of the nuclear envelope usually remains continuous with the ________________________.
The outer membrane of the nuclear envelope usually remains continuous with the ________________________.
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Match the following components of the nucleus with their descriptions:
Match the following components of the nucleus with their descriptions:
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Study Notes
Nucleus
- First described by Robert Brown in 1831
- Chromatin, a material in the nucleus, was named by Flemming
- Interphase nucleus has:
- Chromatin (nucleoprotein fibers)
- Nuclear matrix
- One or more nucleolus (spherical bodies)
- Nuclear envelope:
- Consists of two parallel membranes with a perinuclear space (10-50 nm)
- Forms a barrier between nucleus and cytoplasm
- Outer membrane is continuous with endoplasmic reticulum and bears ribosomes
- Has minute pores for movement of RNA and protein molecules between nucleus and cytoplasm
Nuclear Pores and Variations
- Nuclear pores are passages for RNA and protein molecules
- Normally, one nucleus per cell, but variations in number of nuclei are observed
- Some mature cells lack nucleus, e.g., erythrocytes of many mammals and sieve tube cells of vascular plants
Nucleolus and Chromatin
- Nucleolus:
- Spherical structure in nucleoplasm
- Site for active ribosomal RNA synthesis
- Larger and more numerous in cells actively carrying out protein synthesis
- Chromatin:
- Contains DNA, histones, non-histone proteins, and RNA
- Forms structured chromosomes during cell division
- A single human cell has approximately 2-meter long thread of DNA distributed among 46 chromosomes
Chromosomes
- Chromosomes:
- Visible only in dividing cells
- Have a primary constriction or centromere
- Centromere holds two chromatids of a chromosome
- Classification of chromosomes based on centromere position:
- Metacentric (middle centromere)
- Sub-metacentric (centromere slightly away from middle)
- Acrocentric (centromere close to end)
- Telocentric (terminal centromere)
Centrosome and Microbodies
- Centrosome:
- Organelle containing two cylindrical structures (centrioles)
- Surrounded by amorphous pericentriolar materials
- Each centriole has a cartwheel organization
- Microbodies:
- Membrane-bound minute vesicles
- Contain various enzymes
- Present in both plant and animal cells
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Description
Learn about the discovery and structure of the nucleus, including chromatin, nuclear matrix, and nucleolus. Understand the composition of the nuclear envelope and its functions.
