Eukaryotic organelles Living things have evolved into three categories of closely related organisms, called “domains”: Archaea, Bacteria, and Eukaryota. Life as we see it each day — including plants and animals — belongs to the third domain, Eukaryota. Eukaryotic cells are a more complex opposed to prokaryotes (simpler based cells), and the DNA is linear and found within a nucleus. Organelles are small structures within cells that perform specialized functions. They are found within the cytoplasm (a semiliquid substance that composes the foundation of a cell) Just as the name indicates, you can think of organelles as small organs.
There are a dozen different types of organelles commonly found in eukaryotic cells. Some structures of organelles are membrane bound. The Plasma Membrane is a membrane boundary of a cell, and sorts cell transport and is the outermost cell surface. It separates the cell from the external environment. The plasma membrane is made mostly of proteins and lipids, especially phospholipids. The lipids occur in two layers (a bilayer). Proteins embedded in the bilayer appear to float within the lipid, so the membrane is constantly in flux.
The membrane is therefore referred to as a fluid mosaic structure. Within the fluid mosaic structure, proteins carry out most of the membrane’s functions (prokaryote and eukaryote cell structure, 2000. ). The nucleus of eukaryotic cells is composed primarily of protein and deoxyribonucleic acid, or DNA. The DNA is organized into linear units called chromosomes. Functional segments of the chromosomes are referred to as genes. Approximately 100,000 genes are located in the nucleus of all human cells. Within the nucleus are two or more dense organelles referred to as nucleoli.
In nucleoli, submicroscopic particles known as ribosomes are put together before their passage out of the nucleus into the cytoplasm. The endoplasmic reticulum (ER) is an organelle that is a series of membranes extending throughout the cytoplasm of eukaryotic cells. In some places, the ER is studded with submicroscopic bodies called ribosomes. The endoplasmic reticulum (ER) consists of two types – the rough endoplasmic reticulum and the smooth endoplasmic reticulum. This type of ER is referred to as rough ER. In other places, there are no ribosomes.
This type of ER is called smooth ER. The ER is the site of protein synthesis in a cell. Within the ribosomes, amino acids are actually bound together to form proteins. We can take a look at another organelle called the Golgi body (also called the Golgi apparatus). The Golgi body is a series of flattened sacs, usually curled at the edges. In the Golgi body, the cell’s proteins and lipids are processed and packaged before being sent to their final destination (prokaryotic and eukaryotic cell structure, 2000. ). Lysosomes and vacuoles are membranous sacs.
The lysosome is derived from the Golgi body. It is a drop like sac of enzymes in the cytoplasm. These enzymes are used for digestion within the cell. They break down particles of food taken into the cell and make the products available for use. In other words break down old worn-out cell parts within the cell. Vacuoles Eukaryotic cells have their own internal “power plant”, called mitochondria. Mitochondria are organelles in eukaryotic cells where cellular respiration takes place. Mitochondria contain a short loop of DNA that is distinct from the DNA contained in the cell’s nucleus.
These tiny organelles in the cell not only produce chemical energy, but also hold the key to understanding the evolution of the eukaryotic cell. The mitochondria play a central role in making chemical energy available to the cell. Cells which require and expend a lot of energy typically have a lot of mitochondria (Muscle cells). Plastids are major organelles found in the cells of plants and algae. They are the site of manufacture and storage of important chemical compounds used by the cell. Plastids often contain pigments used in photosynthesis and the types of pigments present can change or determine the cell’s color.
They possess a double-stranded DNA molecule, which is circular. Microbodies are Membrane-bound organelle sacs that contain enzymes that manage many different metabolic reactions. One type of micro body, the peroxisome, regulates the conversion of fats to carbohydrates. Peroxisomes in the liver and kidney cells could also show important in the detoxifying of certain compounds such as ethanol in alcoholic beverages. Peroxisomes occur in both plant and animal cells. Organelles, which generally do not contain membranes, are ribosomes, cytoskeletal structures, centrioles, cilia, and flagella.
Centrioles are small cylindrical-shaped structures that are found just outside of the nucleus. Their purpose is to produce microtubules that help move chromosomes during cell division. The cytoskeleton gives strength and flexibility to the cell. It consists of four major components microfilaments, intermediate filaments, thick filaments, and microtubules. Each of these four components provides different functions related to the overall purpose of the cytoskeleton. Cilia, tiny hair-like structures are numerous and are found on the surface of the cell.
Their purpose is to move fluids or solids across the cell membrane. The trachea and bronchi are lined with cilia to move mucous that is secreted by the cells lining the trachea up to the pharynx (throat) where the mucous is either coughed up or swallowed. A flagellum is a long hair-like structure that performs a whip-like movement. The male sperm cell is the only cell in humans that contains a flagellum, which helps the sperm cell swim up the female oviduct. Ribosomes are small granular structures that are either attached to the endoplasmic reticulum or are free, floating in the cytoplasm.
Proteins are produced on the surface of ribosomes (Unknown, 2012. ). Every part of the cell has a function. Membranes are essential to the organization of living processes within cells because they separate the cell from the outside world. They also separate compartments inside the cell to protect the important processes and events that occur. Cellular membranes have many functions in the different regions and organelles of a cell. All membranes contain proteins and lipid. However, the amount of each may vary depending on the membrane. Cell membranes are made up of two layers of phospholipids.
Phospholipids have hydrophilic (water-loving) heads and hydrophobic (water-repelling) tails. Water exists on both the exterior and interior sides of the membrane. The hydrophobic tails hide behind the hydrophilic heads on both sides of the membrane, forming a non-rigid boundary around the inside of the cell. This non-rigid membrane is held in its shape by microfilaments (thin and solid tubes composed of protein) of cytoskeleton (Membrane structure and function, 2009. ). Proteins determine most of the membrane’s functions. One protein can have several functions.
Integral proteins – those that penetrate through the phospholipid bilayer – regulate what comes in and out of a cell. Peripheral proteins are like appendages bound to the surface of the membrane. Peripheral proteins can also act as enzymes and transporters, but they only interact with different parts within the same cell. They help transport small hydrophobic molecules, toxins, and antimicrobial peptides. A cell membrane is a great example of a super molecular structure, where many molecules are ordered into a higher level of organization with emergent properties beyond those of the individual molecules (Membrane structure and function, 2009.).
As every part of the eukaryotic cell works together to perform a task and function it seems apparent that without the team work of these components, the world would lack mammals, birds, invertebrates, fish, plants, fungi, and complex single celled organisms. The capabilities of long term functionalities are in conjunction with the growth stemming from this wondrous cell called a eukaryote, a milestone in the evolution of life. of the eukaryotic cell was a milestone in the evolution of life.
Courtney from Study Moose
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