Diagram of nucleus

What is Nucleus? The cell nucleus​ is a membrane-bound structure that contains the cell’s hereditary information and controls the cell’s growth and reproduction. It is the command center of a eukaryoticcelland is commonly the most prominentorganellein a cell accounting for about 10 percent of the cell’s volume. In general, a eukaryotic cell has only one nucleus. However, some eukaryotic cells are enucleated cells (without a nucleus), for example, red blood cells (RBCs); whereas, some are multinucleate (consists of two or more nuclei), for example, slime molds. The nucleus is separated from the rest of the cell or the cytoplasm by a nuclear membrane. As the nucleus regulates the integrity of genes and gene expression, it is also referred to as the control center of a cell. Figure: Diagram of Nucleus. Nucleus Structure The structure of a nucleus encompasses the nuclear membrane, nucleoplasm, chromosomes, and nucleolus. Nuclear Membrane • The nuclear membrane is a double-layered structure that encloses the contents of the nucleus. The outer layer of the membrane is connected to the endoplasmic reticulum. • Like thecell membrane, the nuclear envelope consists ofphospholipidsthat form a lipid bilayer. • The envelope helps to maintain the shape of the nucleus and assists in regulating the flow of molecules into and out of the nucleus throughnuclear pores. The nucleus communicates with the remaining of the cell or the cytoplasm through several openings called nuclear pores. • Suc...

The Nuclear Atom The precise physical nature of atoms finally emerged from a series of elegant experiments carried out between 1895 and 1915. The most notable of these achievements was Ernest Rutherford's famous 1911 alpha-ray scattering experiment, which established that: • Almost all of the mass of an atom is contained within a tiny (and therefore extremely dense) nucleus which carries a positive electric charge whose value identifies each element and is known as the atomic number of the element. • Almost all of the volume of an atom consists of empty space in which electrons, the fundamental carriers of negative electric charge, reside. The extremely small mass of the electron (1/1840 th the mass of the hydrogen nucleus) causes it to behave as a quantum particle, which means that its location at any moment cannot be specified; the best we can do is describe its behavior in terms of the probability of its manifesting itself at any point in space. It is common (but somewhat misleading) to describe the volume of space in which the electrons of an atom have a significant probability of being found as the electron cloud. The latter has no definite outer boundary, so neither does the atom. The radius of an atom must be defined arbitrarily, such as the boundary in which the electron can be found with 95% probability. Atomic radii are typically 30-300 pm. The nucleus is itself composed of two kinds of particles. Protons are the carriers of positive electric charge in the nucleu...

h ν = Δ E = ( 1 n l o w 2 − 1 n h i g h 2 ) ⋅ 13.6 eV h\nu =\Delta E = \left(\dfrac h ν = Δ E = ( n l o w ​ 2 1 ​ − n h i g h ​ 2 1 ​ ) ⋅ 1 3 . 6 eV h, \nu, equals, delta, E, equals, left parenthesis, start fraction, 1, divided by, n, start subscript, l, o, w, end subscript, squared, end fraction, minus, start fraction, 1, divided by, n, start subscript, h, i, g, h, end subscript, squared, end fraction, right parenthesis, dot, 13, point, 6, start text, e, V, end text At the beginning of the 20th century, a new field of study known as quantum mechanics emerged. One of the founders of this field was Danish physicist Niels Bohr, who was interested in explaining the discrete line spectrum observed when light was emitted by different elements. Bohr was also interested in the structure of the atom, which was a topic of much debate at the time. Numerous models of the atom had been postulated based on experimental results including the discovery of the electron by J. J. Thomson and the discovery of the nucleus by Ernest Rutherford. Bohr supported the planetary model, in which electrons revolved around a positively charged nucleus like the rings around Saturn—or alternatively, the planets around the sun. By the early 1900s, scientists were aware that some phenomena occurred in a discrete, as opposed to continuous, manner. Physicists Max Planck and Albert Einstein had recently theorized that electromagnetic radiation not only behaves like a wave, but also sometimes like particles ca...

Key Terms • Octet rule: A rule stating that atoms lose, gain, or share electrons in order to have a full valence shell of 8 electrons. (Hydrogen is excluded because it can hold a maximum of 2 electrons in its valence shell. ) • Electron shell: The collective states of all electrons in an atom having the same principal quantum number (visualized as an orbit in which the electrons move). Electron Shells Niels Bohr proposed an early model of the atom as a central nucleus containing protons and neutrons being orbited by electrons in shells. As previously discussed, there is a connection between the number of protons in an element, the atomic number that distinguishes one element from another, and the number of electrons it has. In all electrically-neutral atoms, the number of electrons is the same as the number of protons. Each element, when electrically neutral, has a number of electrons equal to its atomic number. An early model of the atom was developed in 1913 by Danish scientist Niels Bohr (1885–1962). The Bohr model shows the atom as a central nucleus containing protons and neutrons with the electrons in circular orbitals at specific distances from the nucleus (Figure \(\PageIndex\): The Bohr model postulated that electron orbited the nucleus in shells of fixed distance. An electron normally exists in the lowest energy shell available, which is the one closest to the nucleus. Energy from a photon of light can bump it up to a higher energy shell, but this situation is uns...

ADVERTISEMENTS: Most of the functions of the nucleus are intimately related to events that occur in the cytoplasm; for ex­ample, translation of mRNA by cytoplasmic ribosomes is the end result of the transcription of DNA in the nucleus and the processing of the resulting RNA. Structurally too, the nucleus and cytoplasm are interrelated. The outer membrane of the nuclear envelope is continuous with membranes of the endoplasmic reticulum. ADVERTISEMENTS: Events in the cytoplasm also affect nuclear function, initiating or terminating specific nuclear activities. Therefore, whereas the nucleus is perhaps the single dominant structural feature of most eukaryotic cells, it is not to be viewed as an isolated organelle. Structure of the Nucleus: The nucleus of a eukaryotic cell (Fig. 20-1) is delim­ited by a pair of membranes called the nuclear enve­lope. The outer and inner membranes of this envelope are separated by a narrow space called the peri­nuclear space but fuse with each other at the margins of pores. The fluid of the cytoplasm (the cytosol) is continuous through the nuclear pores with the fluid of the nucleus, called the nucleoplasm. Although ribosomes may be attached to the cytoplasmic surface of the outer nuclear membrane, these ribosomes are not con­sidered nuclear structures. The nucleoplasm contains a number of discrete structures including one or more nucleoli, chromosomes (as many as several hundred in some eukaryotic cells), and other structures or re­gions that ...

The nuclear envelope plays a vital role in eukaryotic cells. But what is the nuclear envelope? The nuclear envelope definition is the two-layered membrane that surrounds the nucleus and separates it from the other cell organelles. In eukaryotic cells, the nucleus contains all the genetic information. It is responsible for maintaining the integrity of DNA and for regulating gene expression, which controls cellular activities such as metabolism, growth and reproduction. As a result, it is very important to keep the nucleus protected and separate from the rest of the cell. Diagram showing the structure of a cell including the nuclear envelope. The nuclear envelope consists of two lipid bilayers: an inner nuclear membrane and an outer nuclear membrane. The gap between the two membranes is called the perinuclear space. The two membranes are connected by nuclear pores that control the movement of materials into and out of the nucleus. The inner nuclear membrane has a meshwork of protein filaments that provide support and regulate cellular processes. These are known as the nuclear lamina. What is the Nuclear Envelope? A major hallmark of eukaryotic cells is that they store their genetic material in the nucleus, a compartment that is separate from the cytosol. The nuclear envelope is the double membrane structure that surrounds the nucleus in eukaryotic cells and provides this compartmentalization. The nuclear envelope structure is made of an inner membrane, an outer membrane and ...