Introduction To Cell Biology: Prokaryotes And Eukaryotes

There are 2 basic kinds of cells that make up all living things, primitive Prokaryotes, (Fig.1) and advanced Eukaryotes. (Fig.2). All bacteria and bacteria-like Archaea are prokaryotic, these are single-celled organisms that reproduce through binary fission, duplicating their genetic material. These cells lack certain features compared to the eukaryotic cell.

Prokaryotes don’t have a real nucleus as the DNA is not contained within a membrane, it is coiled up in a region of the cytoplasm called the nucleoid, a nucleoid may be a thin, transparent region of cells that contains primary DNA. Nucleoids are the main Centre of DNA transcription and replication. The Cytoplasm is a fluid of cells inside the semipermeable membrane composed of water, proteins, lipids, minerals, and enzymes, their function is the place where metabolic reactions happen and store food reserves in the form of insoluble granules. Other structures inside a prokaryotic cell include Ribosomes, Ribosomes are nano-machines for protein synthesis. The function of ribosomes is to translate in the synthesis of proteins that convert the genetic code of DNA into proteins. Which in turn are essential for carrying out the cell’s activities. Plasmid DNA are smaller than chromosomes and are circular in shape, their function is to carry the non-essential properties of DNA that give prokaryotic cells, such as antibiotic resistance, virulence (the ability to cause disease), and conjugation (sharing plasmids with other prokaryotic cells). Plasma/cell membranes are thin semi-permeable biological membranes consisting of two layers of phospholipids and embedded with proteins. The function of plasma membranes is a cell protector against extracellular environments and regulates the traffic of substances in and out of cells. Cell wall is the outer coating structure between the capsules and the plasma membrane which contain pores for the entry and exit of molecules. The function of the cell wall is to shape and protect the internal organelles of the cell. The Capsule is the thick layer composed of glycoproteins and it is usually found in disease-carrying bacteria (pathogenic). The function of the capsule is as a cell protector, preventing cell dryness, helping to attach itself to other bacteria or in other organisms, and protecting pathogenic bacteria from the influence of host cell antibodies. Attached to the outside of the cell is a whip-like structure that allows cells to move called Flagella, flagella function is a motion tool.

Eukaryotic cells are more complicated, having evolved from a prokaryote-like predecessor. Most of the living things that we are typically familiar with are composed of eukaryotic cells, animals, plants, fungi, and protists. Eukaryotic cells are those cells that contain a nucleus and organs encircled by a plasma membrane. Most of the eukaryotes are multicellular organisms having complex forms. The main organelle that differentiates between a eukaryotic and prokaryotic cell is a nucleus. This is the largest organelle present in the centre of eukaryotic cell and is the control centre of the cell. Inside the nucleus, DNA is coiled to form chromosomes. Inside Eukaryotes, there are 2 endoplasmic reticulum areas, one side rough, that is because of the presence of ribosomes that are connected in the form of dots. The opposite side lack ribosomes and appear smooth when studied underneath a microscope. They play a significant role in the synthesis of proteins, e.g., lipids, cholesterol, and steroid hormones as the Golgi complex, A Golgi apparatus is the organ that processes and transports proteins and other materials out of the cell. Lysosomes are the spherical membrane-bound vesicles found abundantly in the eukaryotic cells. They contain digestive enzymes that may digest any type of substance getting into the vesicle. It’s necessary to keep these digestive enzymes apart from the rest of the cytoplasm to prevent autodigestion of the cells. Peroxisomes are small, spherical organelles encircled by single membranes; they perform chemical reactions that break down fatty acids and amino acids, additional detoxify many poisons that may enter the body. One of the most vital organelles found in Eukaryotes is Mitochondria, these are oval-shaped, double membrane organelles that have their own ribosomes and DNA, they break down food molecules to create ATP. These organelles are usually known as the powerhouse of the cell. The cytoskeleton of eukaryotic cells is the network of protein filaments: these give support. The 3 components can easily assemble and dismantle to help in many functions performed by the cytoskeleton. the whiplash like structures that project from the plasma membrane of some eukaryotic cells are known as flagellates Their primary function is to assist the cell in locomotion, trying to find food and avoiding danger. The basal body of eukaryotic flagella is anchored to the cell body; however, the flagellum lacks a rod and disks. Instead, the filament is solid and is created of pairs of microtubules. Centrioles are created in pairs of structures held tight at an angle to 1 another act as organisers in preparation for the separation of chromosomes throughout the nuclear division. All these organelles are found in every eukaryotic cell.

Prokaryotic Eukaryotic Similarities

• Have No Nuclei Have nuclei Enclosed by Plasma Membrane
• Lack some organelles Do Not lack organelles Contain ribosomes.
• Not found in humans
• Always unicellular
• Reproduce by binary fission.
• Circular DNA Structure Found in humans.
• Often unicellular
• Reproduce via mitosis/meiosis.
• Linear DNA structure Have DNA.
• Filled with cytoplasm

Multicellular organisms contain a wide variety of different cells, every cell is specialized to perform its job as best as possible. Cells may have different shapes, different contents, or different numbers of an organelle.

Eukaryotic cells differentiate to partake in specific functions. As an organism develops, new cells are produced, which can grow and alter to become specialized for certain functions. These are referred to as specialized cells. Some of the examples of these cells are: The spermatozoon Cell and Root hair cell

The sperm/ spermatozoon cells are the male cells. Their job is to mix with the female cell and make a completely new organism. spermatozoon Cells are specialized in manyl ways. They need a tail that moves by energy generated by several mitochondria and propels the cell. Spermatozoon Cells are also very little and thin, which aids their movement. spermatozoon cells are the only human cell that contains flagella. They are created of 3 basic parts: the head, the middle piece, and the tail. The head is an oval-shaped structure, which size ranges from 5 to 8 µm. It consists of 2 sections: Acrosome, which has 40% to 70% of total sperm head area and is found at one end of the sperm cell. It contains proteolytic enzymes that facilitate to destroy the outer layer of the egg cell, thereby permitting the sperm to enter it easily. This is the only part of the sperm cell that enters the egg cell. The neck and the middle piece are the parts that will be found between the head and the tail. Their job is to attach each end of the sperm cell.

There are 5 organelles found inside a root hair cell. These are the: nucleus, cytoplasm, cell membrane, semi-permeable membrane & vacuole. Root hair cells have elongated projections that increase the area for quicker absorption of water and minerals, The Nucleus manages many of the functions of the cell and contains DNA, the cell membrane is the semipermeable membrane surrounding the cytoplasm of a cell. The cytoplasm is a thick solution that fills every cell and is closed by the cell membrane, surrounding the membrane is the semi-permeable cell Wall this is a tough and flexible wall that surrounds some varieties of cells and supplies cells with structural support and protection. Vacuoles will store food or any form of nutrients a cell may need to survive. A root hair cell is tailored 3 ways, 1) they need an extension that will increase the surface area for a lot of water intake. 2) they have several mitochondria for respiration to become more active. 3), a concentrated vacuole to assist in absorbing water by osmosis. They are located within the root of the plants. They do not contain chloroplasts.

Despite the variations in cells seen so far, all cells have a cell membrane, The cell membrane is an especially pliable structure composed primarily of back-to-back phospholipids, One phospholipid molecule has a phosphate group on one end, called the “head,” and 2 hydrophobic chains of fatty acids that structure the lipid tails. Peripheral proteins are a bunch of biologically active molecules formed from amino acids that act with the surface of the lipid bilayer of cell membranes. Channel proteins job is to transfer water molecules and tiny polar molecules across the semipermeable biological membrane. The job of the carrier proteins is to transfer several of each polar and non-polar molecule across the semipermeable biological membrane. This does not have an exact structure; however, it has many key aspects which make it a peripheral protein. Movement through the plasma membrane happens in 2 ways, Active & Passive, substances penetrate the membrane with no energy input from the cell. With active processes, the cell provides the metabolic energy to maneuver the transport process to move the substance across the membrane. Lipid-soluble molecules and a few tiny molecules will permeate the membrane, This process is termed ‘Osmosis’ diffusion but the lipid bilayer effectively repels the many large, water-soluble molecules and electrically charged ions that the cell must import or export in order to live, instead, they move quickly through the membrane by a process referred to as facilitated diffusion. Recently, a few protein channels have been discovered which facilitate in the transport of water. These channels are called Aquaporins, Aquaporins are a family of membrane water channel proteins that osmotically modulate water fluid homeostasis in several tissue

The purpose of the cell membrane is to hold the different components of the cell together and to safeguard it from the atmosphere outside the cell. The cell membrane also regulates what enters and exits the cell so that it does not lose a lot of nutrients or absorb too many ions. It also does a fairly smart job of keeping harmful things out. The fluid mosaic model describes the plasma membrane of animal cells. The cell membrane that surrounds these cells has 2 layers (a bilayer) of phospholipids (fats with phosphorous attached. Every phospholipid molecule includes a head that is attracted to water and a tail that repels water. Proteins and substances such as cholesterol become embedded within the bilayer, giving the membrane the design of a mosaic, the proteins and other substances will move across it. That is why the plasma membrane is explained using the fluid-mosaic model. Carbohydrate chains attach to the outer surface of the plasma membrane on every cell. These carbohydrates are specific to each person, and they offer characteristics such as your blood type.

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