The Nucleus Of The Eukaryotic Cell Functions – Home / A level / Biology / OCR / Revision notes / 2. Basics of biology / 2.1 Cell structure / 2.1.6 Eukaryotic cells under the microscope
The ultrastructure of an animal cell shows a densely packed cell – the ER and RER and ribosomes form extensive networks in reality throughout the cell.
The Nucleus Of The Eukaryotic Cell Functions
TEM electron micrograph of a plant cell showing key features. Note the presence of the cell wall and vacuole.
Lesson Video: Eukaryotic Cell Structure
Mucus-producing goblet cells (found in the lining of the trachea, bronchi, and larger bronchi) are shown in a photomicrograph.
Be sure to learn the most important identifying characteristics of animal cells and plant cells! It can also help to learn the shape and size of important structures and organelles in cells by finding additional micro and electron micrographs.
LΓ‘ra graduated from the University of Oxford with a degree in Biological Sciences and is currently working as a science teacher in the UK for several years. LΓ‘ra has a special interest in infectious diseases and epidemiology, and enjoys creating original educational materials that develop self-confidence and facilitate learning.
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The Nucleus And Cell Functions
Β© Copyright 2015-2023 Save My Exams Ltd. All rights reserved. The IBO was not involved in the production of, and does not endorse, the resources created by Save My Exams. Eukaryotic organisms include protozoa, algae, fungi, plants, and animals. Some eukaryotic cells are independent unicellular microorganisms, while others are part of multicellular organisms. The cells of eukaryotic organisms have many properties. First, eukaryotic cells are defined by the presence of a nucleus surrounded by a complex nuclear membrane. In addition, eukaryotic cells are characterized by the presence of membrane-bound organelles in the cytoplasm. Organelles such as mitochondria, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and peroxisomes are held in place by the cytoskeleton, an internal network that supports the transport of intracellular components and helps maintain cell shape (Figure 1 ). The genomes of eukaryotic cells are packaged into multiple rod-shaped chromosomes, as opposed to the single, circular chromosome that characterizes most prokaryotic cells. Table 1 compares the characteristics of eukaryotic cell structures with those of bacteria and archaea.
Figure 1. Click for larger image. Illustration of a generalized unicellular eukaryotic organism. Note that cells in eukaryotic organisms vary widely in structure and function, and a given cell may not have all of the structures shown here.
Eukaryotic cells exhibit a variety of cell morphologies. Possible shapes are spherical, ovoid, rectangular, cylindrical, flat, lenticular, fusiform, disk-shaped, crescent, ring, and polygonal (Figure 2). Some eukaryotic cells are irregular in shape, and some are able to change shape. The shape of a particular type of eukaryotic cell can be influenced by factors such as its primary function, the structure of the cytoskeleton, the viscosity of its cytoplasm, the stiffness of its cell membrane or cell wall (if any), and the physical pressure exerted on it by the surrounding environment and/or neighboring cells.
. (a credit: NOAA work modification; b, e credit: Centers for Disease Control and Prevention work modification)
Balance Of Osmotic Pressures Determines The Nuclear To Cytoplasmic Volume Ratio Of The Cell
Figure 3. Eukaryotic cells have a well-defined nucleus. The nucleus of this mammalian lung cell is the large, dark, oval-shaped structure in the lower half of the image.
Unlike prokaryotic cells, in which DNA is loosely located in the nucleoid region, eukaryotic cells have a nucleus surrounded by a complex nuclear membrane containing the DNA genome (Figure 3). The nucleus, which contains the cell’s DNA, ultimately controls all of the cell’s activities and plays a vital role in reproduction and heredity. The DNA of eukaryotic cells is typically organized into several linear chromosomes. The DNA in the nucleus is highly organized and condensed to fit inside the nucleus, which is accomplished by wrapping the DNA around proteins called histones.
Although most eukaryotic cells have only one nucleus, there are exceptions. For example, protozoa in the genus Paramecium typically have two complete nuclei: a small nucleus used for reproduction (micronucleus) and a large nucleus that controls cell metabolism (macronucleus). In addition, some fungi temporarily form cells with two nuclei, called heterokaryotic cells, during sexual reproduction. Cells that have a dividing nucleus but no cytoplasm are called coenocytes.
Figure 4. In this fluorescence microscopy image, all intermediate filaments are stained with bright green fluorescent dye. The nuclear lamina is an intense light green ring around pale red nuclei.
Everything About Biotech β β’πππππππ The Nucleus Contains Most Of The Genes In
The nucleus is bounded by a complex nuclear membrane, often called the nuclear envelope, which consists of two distinct lipid bilayers adjacent to each other (Figure 4). Despite the connections between inner and outer membranes, each membrane contains unique lipids and proteins on its inner and outer surfaces. The nuclear envelope contains nuclear pores, which are large, rosette-shaped protein complexes that regulate the movement of materials into and out of the nucleus. The general shape of the nucleus is determined by the nuclear lamina, a network of intermediate filaments located directly within the nuclear envelope membranes. In addition to the nucleus, additional intermediate fibers form a looser mesh and help anchor the nucleus inside the cell.
The nucleolus is a dense region in the nucleus where ribosomal RNA (rRNA) biosynthesis takes place. Also, the nucleolus is where the assembly of ribosomes begins. Preribosomal complexes are composed of rRNA and proteins in the nucleus; they are then released into the cytoplasm, where ribosome assembly is completed (Figure 5).
Figure 5. (a) The nucleus is the dark, dense region within the nucleus. It is the site of rRNA synthesis and preribosome assembly. (b) Electron micrograph showing the nucleus.
Ribosomes found in eukaryotic organelles such as mitochondria or chloroplasts have 70S ribosomesβthe same size as prokaryotic ribosomes. However, in eukaryotic cells, ribosomes not associated with organelles are 80S ribosomes, which consist of a 40S small subunit and a 60S large subunit. In terms of their size and composition, this distinguishes them from the ribosomes of prokaryotic cells.
What Is The Nucleolus?
Two types of non-organelle-associated eukaryotic ribosomes are determined by their location in the cell: free ribosomes and membrane-bound ribosomes. Free ribosomes are found in the cytoplasm and are used to synthesize water-soluble proteins; Membrane-bound ribosomes are associated with the rough endoplasmic reticulum and produce proteins for incorporation into the cell membrane or proteins that are exported from the cell.
The differences between eukaryotic and prokaryotic ribosomes are clinically relevant because certain antibiotics are designed to target one or the other. For example, cycloheximide targets eukaryotic action while chloramphenicol targets prokaryotic ribosomes.[1] Because human cells are eukaryotes, they are generally not harmed by antibiotics, which destroy the prokaryotic ribosomes of bacteria. However, sometimes negative side effects can occur because the mitochondria in human cells contain prokaryotic ribosomes.
The endomembrane system, unique to eukaryotic cells, is a series of membranous tubules, sacs, and flattened discs that synthesize many cellular components and move materials within the cell (Figure 6). Because of their larger cell size, eukaryotic cells need this system to transport materials that cannot be dispersed by diffusion alone. The endomembrane system consists of several organelles and the connections between them, including the endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles.
Figure 6. The endomembrane system consists of a series of membranous intracellular structures that facilitate the movement of substances across the cell to the cell membrane.
Facts About The Cell Nucleus
The endoplasmic reticulum (ER) is a continuous assembly of tubules and cisternae (flattened sacs) with a single lipid bilayer (Figure 7). The spaces inside the cisternae are called the lumen of the ER. There are two types of ER, rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). These two different types of ER are clearly sites for the synthesis of different types of molecules. The RER is lined with bound ribosomes on the cytoplasmic side of the membrane. These ribosomes produce proteins destined for the plasma membrane (Figure 7). After synthesis, these proteins are incorporated into the membrane of the RER. Small sacs from the RER containing newly synthesized proteins then bud as transport vesicles and are either transported to the Golgi apparatus for further processing, directly to the plasma membrane, to the membrane of another organelle, or from the cell. Transport vesicles are lipid bilayered membranous spheres with a hollow interior that carry molecules. SER has no ribosomes, so it appears ‘smooth’. It participates in lipid biosynthesis, carbohydrate metabolism and detoxification of toxic compounds within the cell.
Figure 7: The rough endoplasmic reticulum is lined with ribosomes for the synthesis of membrane proteins (which gives it its rough appearance).
The Golgi apparatus was discovered in the endomembrane system in 1898 by the Italian scientist Camillo Golgi (1843-1926), who developed a new staining technique that revealed stacked membrane structures in cells.
, the causative agent of malaria. The Golgi apparatus consists of a series of membrane discs called dictyosomes, each with a single lipid bilayer, which are stacked on top of each other (Figure 8).
Ultrastructure Of Cells 1.2
Figure 8. Transmission electron micrograph (left) of the Golgi apparatus in a white blood cell. The image (right) shows cup-shaped, stacked discs and several transport vesicles. The Golgi apparatus modifies lipids and proteins, thus producing glycolipids and glycoproteins, which are often incorporated into
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