Lecture 4 - Nucleus | Cell Biology- Botany PDF Download

 Page 1


Nucleus 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
 
Lesson: Nucleus 
Lesson Developer: Manju A. Lal 
College/ Department: Department of Botany, Kirori Mal College, University 
of Delhi 
 
  
Page 2


Nucleus 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
 
Lesson: Nucleus 
Lesson Developer: Manju A. Lal 
College/ Department: Department of Botany, Kirori Mal College, University 
of Delhi 
 
  
Nucleus 
Institute of Lifelong Learning, University of Delhi 1 
Table of Contents 
Chapter: Nucleus 
? Introduction 
? Functions  
? Nuclear organization in eukaryotes 
? Nuclear envelope 
? Exchange of molecules in between nucleoplasm and 
cytoplasm 
? Import of nucleoplasmic proteins into the nucleus 
? Export of nucleoplasmic proteins into the nucleus 
? Nuclear matrix and nuclear lamina 
? Nucleoplasm 
? Chromosome territories 
? Nuclear sub compartments 
? Nucleolus: ribosome factory of the cell 
? Chromatin 
? Chromosome organization in eukaryotes 
? Chromatin 
? Metaphase chromosomes 
? Chromosome organization in prokaryotes 
? Nuclear organization in mesokaryotes 
? Summary  
? Exercises 
? Glossary 
? References  
 
 
 
 
 
Page 3


Nucleus 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
 
Lesson: Nucleus 
Lesson Developer: Manju A. Lal 
College/ Department: Department of Botany, Kirori Mal College, University 
of Delhi 
 
  
Nucleus 
Institute of Lifelong Learning, University of Delhi 1 
Table of Contents 
Chapter: Nucleus 
? Introduction 
? Functions  
? Nuclear organization in eukaryotes 
? Nuclear envelope 
? Exchange of molecules in between nucleoplasm and 
cytoplasm 
? Import of nucleoplasmic proteins into the nucleus 
? Export of nucleoplasmic proteins into the nucleus 
? Nuclear matrix and nuclear lamina 
? Nucleoplasm 
? Chromosome territories 
? Nuclear sub compartments 
? Nucleolus: ribosome factory of the cell 
? Chromatin 
? Chromosome organization in eukaryotes 
? Chromatin 
? Metaphase chromosomes 
? Chromosome organization in prokaryotes 
? Nuclear organization in mesokaryotes 
? Summary  
? Exercises 
? Glossary 
? References  
 
 
 
 
 
Nucleus 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
Nucleus is the ‘brain’ of the cell. Robert Brown had first used this term in 1831 for the 
opaque spots, which he had observed while studying epidermis of orchids.  
 
 
 
 
 
 Figure: The image as seen by Robert Brown in 1928 of the peel of orchid leaf showing a 
epidermal cells with prominent nucleus. Also seen are three stomata.  
Source:  http://www.brianjford.com/porchida.jpg 
 
In 1866 Haeckel proposed that nucleus was responsible for storing and transmission of 
hereditary characters. Every eukaryotic cell possesses one or more nuclei during their life 
cycle at some stage of their existence. For example, in mammals red blood cells have nuclei 
when they are young, however they lose it when they are mature. In flowering plants, the 
sieve cells of phloem, which are involved in conduction of food, also lose their nuclei at the 
time of maturity. The number of nuclei also varies. More than one nucleus may be present 
in lower organisms.  
 
Nucleus is characterized by the presence of hereditary material i.e. DNA. In addition nucleus 
is the site where DNA gets duplicated (replication) before it gets divided equally into 
daughter cells. The genetic information stored in DNA has to reach cytoplasm, where this 
information gets translated to proteins. The molecules, which carry this information from 
nucleus to cytoplasm, are messenger RNA (mRNA). Nucleus is the place in the cell, where 
mRNAs are synthesized (transcription), before they carry the genetically encoded 
information of DNA to cytoplasm.  
Nucleus 
Page 4


Nucleus 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
 
Lesson: Nucleus 
Lesson Developer: Manju A. Lal 
College/ Department: Department of Botany, Kirori Mal College, University 
of Delhi 
 
  
Nucleus 
Institute of Lifelong Learning, University of Delhi 1 
Table of Contents 
Chapter: Nucleus 
? Introduction 
? Functions  
? Nuclear organization in eukaryotes 
? Nuclear envelope 
? Exchange of molecules in between nucleoplasm and 
cytoplasm 
? Import of nucleoplasmic proteins into the nucleus 
? Export of nucleoplasmic proteins into the nucleus 
? Nuclear matrix and nuclear lamina 
? Nucleoplasm 
? Chromosome territories 
? Nuclear sub compartments 
? Nucleolus: ribosome factory of the cell 
? Chromatin 
? Chromosome organization in eukaryotes 
? Chromatin 
? Metaphase chromosomes 
? Chromosome organization in prokaryotes 
? Nuclear organization in mesokaryotes 
? Summary  
? Exercises 
? Glossary 
? References  
 
 
 
 
 
Nucleus 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
Nucleus is the ‘brain’ of the cell. Robert Brown had first used this term in 1831 for the 
opaque spots, which he had observed while studying epidermis of orchids.  
 
 
 
 
 
 Figure: The image as seen by Robert Brown in 1928 of the peel of orchid leaf showing a 
epidermal cells with prominent nucleus. Also seen are three stomata.  
Source:  http://www.brianjford.com/porchida.jpg 
 
In 1866 Haeckel proposed that nucleus was responsible for storing and transmission of 
hereditary characters. Every eukaryotic cell possesses one or more nuclei during their life 
cycle at some stage of their existence. For example, in mammals red blood cells have nuclei 
when they are young, however they lose it when they are mature. In flowering plants, the 
sieve cells of phloem, which are involved in conduction of food, also lose their nuclei at the 
time of maturity. The number of nuclei also varies. More than one nucleus may be present 
in lower organisms.  
 
Nucleus is characterized by the presence of hereditary material i.e. DNA. In addition nucleus 
is the site where DNA gets duplicated (replication) before it gets divided equally into 
daughter cells. The genetic information stored in DNA has to reach cytoplasm, where this 
information gets translated to proteins. The molecules, which carry this information from 
nucleus to cytoplasm, are messenger RNA (mRNA). Nucleus is the place in the cell, where 
mRNAs are synthesized (transcription), before they carry the genetically encoded 
information of DNA to cytoplasm.  
Nucleus 
Nucleus 
Institute of Lifelong Learning, University of Delhi 3 
 
Figure: In eukaryotes the DNA is replicated and transcribed in the nucleus. The mRNA 
synthesized is then transported into the cytoplasm for translation. 
Source: http://m.cdn.blog.hu/mo/molbiol/image/images/i201008/transzkripcio.gif 
 
In a eukaryotic cell, all the nuclear activities are separated from the activities of the 
cytoplasm because of the presence of nuclear envelope. Presence of well-organized pores in 
the nuclear envelope indicates that the exchange of molecules between the nucleus and 
cytoplasm is highly regulated. Nucleoli are also present in the nucleus, which are the site of 
ribosome assembly. However, in a prokaryotic cell no such membranes separate the 
hereditary material from the cytoplasm. The region of prokaryotic cell in which the DNA is 
present is called nucleoid.  
 
 
Figure: The Prokaryotic and eukaryotic cell differ primarily in the presence and absence of 
Page 5


Nucleus 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
 
Lesson: Nucleus 
Lesson Developer: Manju A. Lal 
College/ Department: Department of Botany, Kirori Mal College, University 
of Delhi 
 
  
Nucleus 
Institute of Lifelong Learning, University of Delhi 1 
Table of Contents 
Chapter: Nucleus 
? Introduction 
? Functions  
? Nuclear organization in eukaryotes 
? Nuclear envelope 
? Exchange of molecules in between nucleoplasm and 
cytoplasm 
? Import of nucleoplasmic proteins into the nucleus 
? Export of nucleoplasmic proteins into the nucleus 
? Nuclear matrix and nuclear lamina 
? Nucleoplasm 
? Chromosome territories 
? Nuclear sub compartments 
? Nucleolus: ribosome factory of the cell 
? Chromatin 
? Chromosome organization in eukaryotes 
? Chromatin 
? Metaphase chromosomes 
? Chromosome organization in prokaryotes 
? Nuclear organization in mesokaryotes 
? Summary  
? Exercises 
? Glossary 
? References  
 
 
 
 
 
Nucleus 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
Nucleus is the ‘brain’ of the cell. Robert Brown had first used this term in 1831 for the 
opaque spots, which he had observed while studying epidermis of orchids.  
 
 
 
 
 
 Figure: The image as seen by Robert Brown in 1928 of the peel of orchid leaf showing a 
epidermal cells with prominent nucleus. Also seen are three stomata.  
Source:  http://www.brianjford.com/porchida.jpg 
 
In 1866 Haeckel proposed that nucleus was responsible for storing and transmission of 
hereditary characters. Every eukaryotic cell possesses one or more nuclei during their life 
cycle at some stage of their existence. For example, in mammals red blood cells have nuclei 
when they are young, however they lose it when they are mature. In flowering plants, the 
sieve cells of phloem, which are involved in conduction of food, also lose their nuclei at the 
time of maturity. The number of nuclei also varies. More than one nucleus may be present 
in lower organisms.  
 
Nucleus is characterized by the presence of hereditary material i.e. DNA. In addition nucleus 
is the site where DNA gets duplicated (replication) before it gets divided equally into 
daughter cells. The genetic information stored in DNA has to reach cytoplasm, where this 
information gets translated to proteins. The molecules, which carry this information from 
nucleus to cytoplasm, are messenger RNA (mRNA). Nucleus is the place in the cell, where 
mRNAs are synthesized (transcription), before they carry the genetically encoded 
information of DNA to cytoplasm.  
Nucleus 
Nucleus 
Institute of Lifelong Learning, University of Delhi 3 
 
Figure: In eukaryotes the DNA is replicated and transcribed in the nucleus. The mRNA 
synthesized is then transported into the cytoplasm for translation. 
Source: http://m.cdn.blog.hu/mo/molbiol/image/images/i201008/transzkripcio.gif 
 
In a eukaryotic cell, all the nuclear activities are separated from the activities of the 
cytoplasm because of the presence of nuclear envelope. Presence of well-organized pores in 
the nuclear envelope indicates that the exchange of molecules between the nucleus and 
cytoplasm is highly regulated. Nucleoli are also present in the nucleus, which are the site of 
ribosome assembly. However, in a prokaryotic cell no such membranes separate the 
hereditary material from the cytoplasm. The region of prokaryotic cell in which the DNA is 
present is called nucleoid.  
 
 
Figure: The Prokaryotic and eukaryotic cell differ primarily in the presence and absence of 
Nucleus 
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nucleus and other membrane bound organelles. 
Source: http://ap-bio-patrick-steed.wikispaces.com/Eukaryotic-Prokaryotic-Cells 
Dinoflagellates are unicellular microscopic protists that represent a unique group of 
eukaryotes. These lack histones and nucleosomes. Interestingly the cells of dinoflagellates 
(which are a type of algae) have the nucleus, which has the nuclear envelope, but the 
chromosomes remain permanently condensed even during the interphase of cell cycle. The 
dinoflagellates were therefore considered to be mesokaryotes with a lineage in between that 
of the prokaryotes and eukaryotes. The nucleus of dinoflagellates is called ‘mesokaryotic’. 
 
After studying this unit you will learn, 
? The role of nucleus in eukaryotic cell 
? Structure of nucleus in eukaryotes 
? Structure and role of nuclear envelope and nuclear pores. 
? How and where are ribosomes synthesized? 
? What is chromatin and its distribution within nucleus of eukaryotic cell? 
? How enormously big DNA molecules gets fitted in a eukaryotic cell nucleus? 
? How is DNA packed to form chromosome in prokaryotes? 
? How is nuclear organization in eukaryotic cell is different from that of prokaryotes and 
mesokaryotes? 
 
Functions  
The functions of nucleus are:  
? It stores genetic information in the form of DNA 
? DNA is duplicated (replication) before it can be distributed equally into the daughter 
cells during the cell division. 
? mRNAs are synthesized (transcription) in the nucleus. These carry the genetic 
information from DNA in the nucleus to cytoplasm where the message is translated 
to proteins. 
? Ribosomes are synthesized in nucleolus, which are then transported to the cytoplasm.