Components Of Eukaryotic Cells And Their Functions

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Components Of Eukaryotic Cells And Their Functions

Components Of Eukaryotic Cells And Their Functions

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Different Parts Of A Cell

Eukaryote, any cell or organism with a clearly defined nucleus. The eukaryotic cell has a nuclear membrane that surrounds the nucleus, where the chromosomes (bodies containing the hereditary material) are well defined. Eukaryotic cells also contain organelles, including mitochondria (cellular energy exchangers), Golgi apparatus (secretory apparatus), endoplasmic reticulum (a canal-like system of membranes within the cell), and lysosomes (digestive apparatus within many types of cells). There are several exceptions to this, however; for example, the absence of mitochondria and nucleus in red blood cells and the lack of mitochondria in the oxymonad

Eukaryotes are thought to have evolved between about 1.7 billion and 1.9 billion years ago. The earliest known microfossils that resemble eukaryotic organisms date to about 1.8 billion years ago. Have you ever heard the phrase “form follows function?” It is a philosophy used in many industries. In architecture, this means that buildings should be built to support the activities that will take place inside them. For example, a skyscraper should be built with several elevator shafts; a hospital should be built so that its emergency room is easily accessible.

Our natural world originates from the principle of form following function, especially in cell biology, and this becomes clear as we examine eukaryotic cells. Unlike prokaryotic cells, eukaryotic cells have: (1) a membrane-bound nucleus; (2) numerous membrane-bound organelles – such as the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria, and others; and (3) several rod-shaped chromosomes. Because the nucleus of a eukaryotic cell is surrounded by a membrane, it is often said to have a “true nucleus.” The word “organelle” means “small organ,” and, as already mentioned, organelles have specialized cellular functions, just as the organs of your body have specialized functions.

Figure 1. These figures show the main organelles and other cell components of (a) a typical animal cell and (b) a typical eukaryotic plant cell. The plant cell has a cell wall, chloroplasts, plastids, and a central vacuole – structures not found in animal cells. Plant cells do not have lysosomes or centrosomes.

What Is Prokaryotic And Eukaryotic Cell?

Before we start looking at individual organelles, we need to briefly address the matrix in which they sit: the cytoplasm. The part of the cell referred to as cytoplasm is slightly different in eukaryotes and prokaryotes. In eukaryotic cells, which have a nucleus, the cytoplasm is everything between the plasma membrane and the nuclear envelope. In prokaryotes, which do not have a nucleus, cytoplasm simply means everything found inside the plasma membrane.

A major component of the cytoplasm in prokaryotes and eukaryotes is the gel-like cytosol, a water-based solution containing ions, small molecules, and macromolecules. In eukaryotes, the cytoplasm also contains membrane-bound organelles, which are suspended in the cytosol. The cytoskeleton, a network of fibers that supports the cell and gives it shape, is also part of the cytoplasm and helps organize cellular components.

Although the cytosol is mostly water, it has a semi-solid, Jello-like consistency due to the many proteins it contains. The cytosol contains a rich soup of macromolecules and smaller organic molecules, including glucose and other simple sugars, polysaccharides, amino acids, nucleic acids, and fatty acids. Ions of sodium, potassium, calcium and other elements are also found in the cytosol. Many metabolic reactions, including protein synthesis, take place in this part of the cell.

Components Of Eukaryotic Cells And Their Functions

Figure 2. The nucleus stores chromatin (DNA plus proteins) in a gel-like substance called the nucleoplasm. The nucleolus is a condensed region of chromatin where ribosome synthesis takes place. The border of the nucleus is called the nuclear envelope. It consists of two biphospholipid layers: an outer membrane and an inner membrane. The nuclear membrane is continuous with the endoplasmic reticulum. Nuclear pores allow substances to enter and exit the nucleus.

Cell Structure And Function

) houses the cell’s DNA and directs the synthesis of ribosomes and proteins. Let’s look at it in more detail (Figure 2).

The nuclear envelope is a double-membrane structure that represents the outer part of the nucleus (Figure 2). The inner and outer membranes of the nuclear envelope are bilayers of lipids.

The nuclear envelope is punctuated with pores that control the passage of ions, molecules, and RNA between the nucleoplasm and cytoplasm. The nucleoplasm is the semi-solid fluid inside the nucleus, where we find the chromatin and the nucleolus.

To understand chromatin, it is useful to consider chromosomes first. Chromosomes are structures within the nucleus that contain DNA, the hereditary material. In prokaryotes, DNA is organized into a single circular chromosome. In eukaryotes, chromosomes are linear structures. Each eukaryotic species has a certain number of chromosomes in the nucleus of its body cells. For example, in humans, the chromosome number is 46, while in fruit flies, it is eight. Chromosomes are only visible and distinguishable when the cell is preparing to divide. When the cell is in the growth and maintenance stages of its life cycle, proteins are attached to chromosomes, and they are like a bunch of uninhabited, tangled threads. These unwound protein-chromosome complexes are called chromatin (Figure 3); chromatin describes the material that makes up the chromosomes when they are condensed and decondensed. We will focus on chromatin and chromosomes in more detail later.

Plant Cell Diagram, Structure, Types And Functions

Figure 3. (a) This image shows various levels of chromatin organization (DNA and protein). (b) This image shows paired chromosomes. (b credit: adaptation of work by NIH; scale bar data by Matt Russell)

We already know that the nucleus directs the synthesis of ribosomes, but how do we do this? Some chromosomes have sections of DNA that encode ribosomal RNA. A darkly stained area within the nucleus called the nucleolus (plural = nucleoli) aggregates the ribosomal RNA with associated proteins to assemble the ribosomal subunits which are then transported out through the pores in the nuclear envelope into the cytoplasm.

Figure 4. Ribosomes consist of a large subunit (top) and a small subunit (bottom). During protein synthesis, ribosomes assemble amino acids into proteins.

Components Of Eukaryotic Cells And Their Functions

Ribosomes are the cellular structures responsible for protein synthesis. When viewed through an electron microscope, ribosomes appear either as clusters (polyribosomes) or as small, single dots that float freely in the cytoplasm. They can be attached to the cytoplasmic side of the plasma membrane or the cytoplasmic side of the endoplasmic reticulum and the outer membrane of the nuclear envelope. Electron microscopy has shown us that ribosomes, which are large complexes of protein and RNA, consist of two subunits, appropriately called large and small (Figure 4). Ribosomes receive their “orders” for protein synthesis from the nucleus where the DNA is transcribed into messenger RNA (mRNA). The mRNA travels to the ribosomes, which translate the code provided by the sequence of nitrogenous bases in the mRNA into a specific sequence of amino acids in a protein. Amino acids are the building blocks of proteins.

Endosymbiotic Theory: How Eukaryotic Cells Evolve

Since the synthesis of proteins is an essential function of every cell, ribosomes are found in almost every cell. Ribosomes are particularly abundant in cells that synthesize large amounts of protein. For example, the pancreas is responsible for creating a number of digestive enzymes and the cells that produce these enzymes contain many ribosomes. So, we see another example of function following form.

) are often called the “powerhouses” or “energy factories” of a cell because they are responsible for making adenosine triphosphate (ATP), the cell’s main energy-carrying molecule. ATP represents the cell’s short-term storage energy. Cellular respiration is the process of making ATP using the chemical energy found in glucose and other nutrients. In mitochondria, this process uses oxygen and produces carbon dioxide as a waste product. In fact, the carbon dioxide you exhale with each breath comes from the cellular reactions that produce carbon dioxide as a by-product.

In keeping with our theme of function following form, it is important to note that muscle cells have a very high concentration of ATP producing mitochondria. Your muscle cells need a lot of energy to keep your body moving. When your cells don’t get enough oxygen, they don’t make much ATP. Instead, the production of lactic acid is accompanied by the small amount of ATP they make in the absence of oxygen.

Figure 5. This electron micrograph shows a mitochondrion as seen with a transmission electron microscope. This organelle has an outer membrane and an inner membrane. The inner membrane contains folds, called cristae, which increase its surface area. The space between the two membranes is called the intermembrane space, and the space inside the inner membrane is called the mitochondrial matrix. ATP synthesis occurs on the inner membrane. (credit: adaptation of Matthew Britton’s work;

Plant Cell: Parts • Microbe Online

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