1.4. Cell nucleus

Cell nucleus

The nucleus is the characteristic structure of the eukaryotic cell, being its largest component. Within the nucleus is DNA, with the genetic information and instructions necessary for the cell to carry out its vital functions.

Remember that the prokaryotic cells does not have its DNA wrapped by any membrane.

Although the nucleus is characteristic of eukaryotic cells, and they usually have only one nucleus, there are some exceptions, such as red blood cells, which do not have a nucleus, and others, such as muscle cells, have many nuclei (polynucleated).

Animation: Cell nucleus.

By Mariana Ruiz Villarreal (LadyofHats), translation by Kelvinsong. [CC0], via Wikimedia Commons

The structure of the nucleus

The cell nucleus does not always have the same structure, but can be found in two different states, depending on the state of division in which the cell is:

Nucleus in interphase. DNA duplication occurs.
Nucleus in cell division. DNA that was in the form of chromatin, condenses to form chromosomes.

This section describes the nuclear structure in the interphase state. In the section "cell cycle" we will deal with the characteristics of the nucleus in a state of division.

The cell nucleus, during the interphase, is a spherical structure that is located in the central zone of animal cells. In plant cells, due to the large size of the vacuole, it moves to one side along with the other organelles.

In the interphase nucleus, when the cell is not dividing, one can distinguish:

Nuclear envelope.
Nucleoplasm.
Nucleolus.
Chromatin.
Chromosomes.

Nuclear envelope

The nuclear envelope is made up of two membranes separated by an intermembrane space. The outer membrane carries ribosomes attached to it and continues with the membranes of the endoplasmic reticulum. These membranes are interrupted by nuclear pores that allow the exchange of substances between the nucleus and the cytoplasm.

Nucleoplasm

The nucleoplasm is the internal aqueous environment of the nucleus, in which the nuclear components are immersed.

Nucleolus

The nucleolus is a spherical structure, without a membrane, that appears in the interphase nucleus. It has the function of synthesizing ribosomes.

Chromatin

In the interphase nucleus, the genetic material is made up of chromatin. Chromatin consists of long strands of DNA associated with proteins called histones. When the cell is about to divide, the chromatin filaments condense and form the shorter and thicker chromosomes.

In eukaryotes, each chromosome is made up of a single linear DNA molecule.

Remember that the prokaryotic cell has circular DNA and the eukaryotic cell has linear DNA .

Interactive activity. The core.

Chromosomes

The chromosomes are filaments of genetic material (DNA and protein) displayed on the cell when in division. Chromatin is condensed to be able to divide the genetic information of the mother cell between the two daughter cells.

A chromosome has the following structure:

Two sister chromatids. The DNA of each chromatid is identical, which is why they are called sister chromatids.
Centromere. Place where the two sister chromatids meet.
Arms. Each chromatid is made up of two arms that can have the same or different length, depending on the chromosome. Each arm is the part of the chromatid that goes from the centromere to the telomere.
Telomeres. They are the ends of the arms.

Alejandro Porto [CC BY-SA 3.0], via Wikimedia Commons

Number of chromosomes

The number of chromosomes that a species has is the same for all cells (except gametes) of all individuals of that species. This number is characteristic of the species and its chromosomes always have a constant size and shape. The number of chromosomes does not have a direct relationship with the complexity of the living being. For example, humans have 46 chromosomes, flies 12, dogs 78, and chimpanzees 48 chromosomes.

Most of the cells of organisms are diploid (or 2n), with two sets of chromosomes that are identical in shape and size, although possibly different genetic information, since one comes from the father and the other from the mother. These chromosomes are called homologous chromosomes.

Gametes or reproductive cells (and some other organisms) are haploid cells (or n), and they do not have homologous chromosomes. They have half the chromosomes because it will unite with another gamete to form the new individual that will be diploid. For example, human eggs and sperm have 23 chromosomes, which when fertilization occurs will give rise to a zygote (diploid) of 23 pairs of homologous chromosomes.

Rarer, but there are also polyploid organisms , with several sets of chromosomes (3n, 4n, etc.).

Chromosome types

According to the shape of the chromosomes, several types of chromosomes are distinguished according to the position of the centromere:

Metacentric chromosomes. The centromere is located in the middle of the chromosome, so the arms are the same length.
Submetacentric chromosomes The arms are slightly unequal because the centromere is displaced to one of the extremes.
Acrocentric chromosomes. The arms have different lengths, one is much longer than the other, because the centromere is very displaced towards one end.
Telocentric chromosomes. The centromere is at one end of the chromosome, so there is only a single arm.

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Skip navigation Biology and Geology 4th ESO Biology and Geology 4º ESO 1. The cell 1.1. Levels of organization of living beings 1.2. Cell theory 1.3. The cell 1.3.1. Prokaryotic cell 1.3.2. Eukaryotic cell 1.3.2.1. Common organelles 1.3.2.2. Organelles of the animal cell 1.3.2.3. Plant cell organelles 1.4. Cell nucleus 1.5. Vital functions of cells 1.6. Cellular cycle 1.6.1. Mitosis 1.6.1.1. Cytokinesis 1.6.2. Meiosis 1.6.2.1. Meiosis I. First meiotic division 1.6.2.2. Meiosis II. Second meiotic division 1.6.2.3. Result of meiosis 1.6.3. Differences between mitosis and meiosis 1.6.4. Biological importance of mitosis and meiosis 1.7. Bibliography 2. Genetic information 2.1. Nucleic acids 2.1.1. DNA 2.1.2. RNA 2.1.3. Control of protein synthesis 2.2. DNA and molecular genetics 2.3. Gene concept 2.4. Replication of DNA 2.5. DNA to RNA transcription 2.6. Genetic code 2.7. Translation of RNA to proteins 2.8. Mutations Relations with evolution 2.9. Biotechnology 2.10. Genetic engineering: techniques and applications 2.10.1. Cloning 2.10.2. Human Genome Project 2.11. Bioethics 2.12. Bibliography 3. Biological inheritance 3.1. The inheritance and transmission of characters 3.2. Introduction and development of Mendel's Laws 3.2.1. Mendel's First Law 3.2.2. Mendel's second law 3.2.3. Mendel's third law 3.3. Chromosomal basis of Mendel's Laws 3.3.1. Exceptions to Mendel's Laws 3.3.2. Chromosomal theory of heredity 3.3.3. Genetics concepts 3.3.4. Types of inheritance 3.4. Human genetics 3.4.1. Inheritance of blood groups 3.4.2. Sex inheritance 3.4.3. Sex-linked inheritance 3.4.4. Heredity influenced by sex 3.5. Genetics problems 3.5.1. Inheritance of a character (problems solved) 3.5.1.1. Albinism (problems solved) 3.5.1.2. Rh groups (problems solved) 3.5.1.3. Eye color (problems solved) 3.5.1.4. More inheritance problems of a character 3.5.1.5. More inheritance problems of a character 3.5.1.6. More inheritance problems of a character 3.5.1.7. More inheritance problems of a character 3.5.2. Two-character inheritance (problems solved) 3.5.2.1. More two-character genetic inheritance solved problems 2 3.5.2.2. More two-character genetic inheritance solved problems 3 3.5.2.3. More two-character genetic inheritance solved problems 4 3.5.2.4. More two-character genetic inheritance solved problems 5 3.5.3. Codominance and intermediate inheritance (problems solved) 3.5.3.1. More codominance and intermediate inheritance problems 2 3.5.4. Sex-linked inheritance (problems solved) 3.5.4.1. Color blindness or daltonism (problems solved) 3.5.4.1.1. More color blindness problems or daltonism 3.5.4.2. Hemophilia (problems solved) 3.5.4.3. Sex-linked inheritance (two characters) 3.5.4.4. More sex-linked inheritance problems 3.5.5. Sex-influenced inheritance (problems solved) 3.5.6. Multiple alleles (problems solved) 3.5.6.1 AB0 blood groups (problems solved) 3.5.6.1.1. More AB0 blood group problems solved 2 3.5.6.1.2. More AB0 blood group problems solved 3 3.5.7. Genealogical trees 3.5.7.1. Family Trees 2 3.5.7.2. Family Trees 3 3.6. Bibliography 4. Origin and evolution of living beings 4.1. Hypothesis about the origin of life on Earth 4.2. Evolution of living beings 4.3. Theories of evolution 4.3.1. Lamarck 4.3.2. Darwin and Wallace 4.3.3. Neo-Darwinism 4.3.4. Other evolutionary theories 4.4. Evidences of evolution 4.4.1. Anatomical evidence of evolution 4.4.2. Embryological evidence of evolution 4.4.3. Paleontological evidence of evolution 4.4.4. Biogeographic evidence of evolution 4.4.5. Biochemical evidence of evolution 4.5. Mechanisms of evolution 4.5.1. Genetic variability 4.5.2. Natural selection 4.5.3. Consequences of evolution 4.5.3.1. Adaptation of organisms 4.5.3.2. Speciation 4.5.3.3. Species diversification 4.6. Human evolution: process of hominization 4.6.1. Primates 4.6.2. Hominids 4.6.3. The human being 4.7. Bibliography 5. The history of the Earth 5.1. The origin of the Earth 5.2. Earth, a changing planet 5.3. Geological time: historical ideas about the age of the Earth 5.4. Dating methods 5.4.1. Relative dating 5.4.1.1. Geological history exercises - relative dating 5.4.2. Absolute dating 5.5. Fossils 5.5.1. Fossils in Aragon 5.6. Geological history of the Earth 5.6.1. Precambrian 5.6.2. Phanerozoic 5.6.2.1. Paleozoic 5.6.2.2. Mesozoic 5.6.2.3. Cenozoic 5.7. Bibliography 6. Structure and dynamics of the Earth 6.1. Earth study methods 6.1.1. Seismic discontinuities 6.2. Structure and composition of the Earth 6.2.1. Geochemical model 6.2.2. Dynamic model 6.3. Bibliography 7. Plate tectonics 7.1. From continental drift to plate tectonics 7.1.1. Wegener continental drift 7.2. Plate Tectonics and its manifestations 7.2.1. Lithospheric plates 7.2.2. Oceanic ridges 7.2.2.1. Expansion of the ocean floor 7.2.3. Ocean trenches 7.2.4. Transforming faults 7.2.5. Formation of mountain ranges 7.3. The Wilson cycle 7.4. Rock deformation 7.4.1. Folds 7.4.2. Faults 7.4.3. Joints 7.4.4. Mixed structures 7.5. Bibliography 8. Ecosystems 8.1. Ecosystem structure 8.1.1. Types of ecosystems 8.1.1.1. Aquatic ecosystems 8.1.1.2. Terrestrial ecosystems 8.1.1.2.1. Urban ecosystems 8.2. Components of the ecosystem: community and biotope 8.2.1. Biotope 8.2.2. Biocenosis or community 8.3. Habitat and ecological niche 8.4. Limiting factors and adaptations 8.5. Tolerance limit 8.6. Trophic levels 8.7. Trophic relationships: chains and networks 8.8. Ecological pyramids 8.9. Self-regulation of the ecosystem, the population and the community 8.9.1. Intra and interspecific relationships 8.10. Matter cycle and energy flow 8.11. Biogeochemical cycles 8.11.1. Carbon cycle 8.11.2. Nitrogen cycle 8.11.3. Phosphorus cycle 8.12. Ecological successions 8.13. Bibliography 9. Resources and environmental impacts 9.1. Human activity and the environment 9.2. Natural resources and their types 9.3. Environmental impacts 9.3.1. Pollution of the atmosphere 9.3.1.1. Air pollutants 9.3.1.2. Acid rain 9.3.1.3. The smog 9.3.1.4. Ozone layer hole 9.3.1.5. Increased greenhouse effect 9.3.1.6. Climate change 9.3.2. Noise pollution 9.3.3. Light pollution 9.3.4. Water contamination 9.3.4.1. Water pollutants 9.3.4.2. Water eutrophication 9.3.4.3. Aquifer reduction 9.4. Soil 9.4.1. Soil contamination 9.5. Main environmental problems of Aragon 9.6. Overpopulation and its consequences 9.7. Waste and its management 9.8. Bibliography and student work « Previous \| Next » 1.4. Cell nucleus Cell nucleus The nucleus is the characteristic structure of the eukaryotic cell, being its largest component. Within the nucleus is DNA, with the genetic information and instructions necessary for the cell to carry out its vital functions. Remember that the prokaryotic cells does not have its DNA wrapped by any membrane. Although the nucleus is characteristic of eukaryotic cells, and they usually have only one nucleus, there are some exceptions, such as red blood cells, which do not have a nucleus, and others, such as muscle cells, have many nuclei (polynucleated). Animation: Cell nucleus. By Mariana Ruiz Villarreal (LadyofHats), translation by Kelvinsong. [CC0], via Wikimedia Commons The structure of the nucleus The cell nucleus does not always have the same structure, but can be found in two different states, depending on the state of division in which the cell is: Nucleus in interphase. DNA duplication occurs. Nucleus in cell division. DNA that was in the form of chromatin, condenses to form chromosomes. This section describes the nuclear structure in the interphase state. In the section "cell cycle" we will deal with the characteristics of the nucleus in a state of division. The cell nucleus, during the interphase, is a spherical structure that is located in the central zone of animal cells. In plant cells, due to the large size of the vacuole, it moves to one side along with the other organelles. In the interphase nucleus, when the cell is not dividing, one can distinguish: Nuclear envelope. Nucleoplasm. Nucleolus. Chromatin. Chromosomes. Nuclear envelope The nuclear envelope is made up of two membranes separated by an intermembrane space. The outer membrane carries ribosomes attached to it and continues with the membranes of the endoplasmic reticulum. These membranes are interrupted by nuclear pores that allow the exchange of substances between the nucleus and the cytoplasm. Nucleoplasm The nucleoplasm is the internal aqueous environment of the nucleus, in which the nuclear components are immersed. Nucleolus The nucleolus is a spherical structure, without a membrane, that appears in the interphase nucleus. It has the function of synthesizing ribosomes. Chromatin In the interphase nucleus, the genetic material is made up of chromatin. Chromatin consists of long strands of DNA associated with proteins called histones. When the cell is about to divide, the chromatin filaments condense and form the shorter and thicker chromosomes. In eukaryotes, each chromosome is made up of a single linear DNA molecule. Remember that the prokaryotic cell has circular DNA and the eukaryotic cell has linear DNA . Interactive activity. The core. Chromosomes The chromosomes are filaments of genetic material (DNA and protein) displayed on the cell when in division. Chromatin is condensed to be able to divide the genetic information of the mother cell between the two daughter cells. A chromosome has the following structure: Two sister chromatids. The DNA of each chromatid is identical, which is why they are called sister chromatids. Centromere. Place where the two sister chromatids meet. Arms. Each chromatid is made up of two arms that can have the same or different length, depending on the chromosome. Each arm is the part of the chromatid that goes from the centromere to the telomere. Telomeres. They are the ends of the arms. Alejandro Porto [CC BY-SA 3.0], via Wikimedia Commons Number of chromosomes The number of chromosomes that a species has is the same for all cells (except gametes) of all individuals of that species. This number is characteristic of the species and its chromosomes always have a constant size and shape. The number of chromosomes does not have a direct relationship with the complexity of the living being. For example, humans have 46 chromosomes, flies 12, dogs 78, and chimpanzees 48 chromosomes. Most of the cells of organisms are diploid (or 2n), with two sets of chromosomes that are identical in shape and size, although possibly different genetic information, since one comes from the father and the other from the mother. These chromosomes are called homologous chromosomes. Gametes or reproductive cells (and some other organisms) are haploid cells (or n), and they do not have homologous chromosomes. They have half the chromosomes because it will unite with another gamete to form the new individual that will be diploid. For example, human eggs and sperm have 23 chromosomes, which when fertilization occurs will give rise to a zygote (diploid) of 23 pairs of homologous chromosomes. Rarer, but there are also polyploid organisms , with several sets of chromosomes (3n, 4n, etc.). Chromosome types According to the shape of the chromosomes, several types of chromosomes are distinguished according to the position of the centromere: Metacentric chromosomes. The centromere is located in the middle of the chromosome, so the arms are the same length. Submetacentric chromosomes The arms are slightly unequal because the centromere is displaced to one of the extremes. Acrocentric chromosomes. The arms have different lengths, one is much longer than the other, because the centromere is very displaced towards one end. Telocentric chromosomes. The centromere is at one end of the chromosome, so there is only a single arm. Licensed under the Creative Commons Attribution Share Alike License 4.0 « Previous \| Next » You can ask, comment, contribute, get in touch with other users in the forum of this course. This course is translated from https://biologia-geologia.com/BG4/
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