Learning about Cells. First thing to show you are two beautiful pictures of a Cell. Imagine all of this is in something so small we cannot see it with our naked eyes. About 10,000 average-sized human cells can fit on the head of a pin. There are a few exceptions, but the average cell is very tiny.
Here are a few beautiful examples of a cell structure to kind of give you an idea of its beauty, and how they fit together.
Plasma Membrane (cell membrane) First we are going to learn about the Plasma membrane, it is also called the cell membrane. No, it is not the same thing as the Plasma Tv.
The Plasma membrane, positioned on the outer side of the cell as depicted in the picture above, acts as a boundary between the cell's interior and the outside environment. It operates like an orange peel, allo
...wing specific ions and organic molecules to pass through while controlling substance movement into and out of cells. Essentially, it serves as a protective fence for the cell while still enabling passage of substances such as carbon dioxide, oxygen, and water.
The cell membrane is responsible for several functions, including giving the cell its shape and connecting it to the cytoskeleton. It also plays a role in tissue formation by attaching to the extracellular matrix and neighboring cells. In terms of composition, biological membranes can be seen as a two-dimensional liquid, with lipid and protein molecules able to move freely within it. Although lipid bilayers alone create this liquid property, the plasma membrane contains many proteins that help maintain its structure.
Below is an illustration of the Cell Membrane or Plasm
membrane, which acts as the control center for eukaryotic cells. The Nucleus, situated in the middle of the cell, contains a substantial amount of the cell's DNA that determines our traits and how they are expressed. Enclosed within organelles, the Nucleus plays a crucial role in cellular functions.
The nucleus, which is the largest organelle in animals and accounts for about 10% of the cell volume, plays a crucial role in maintaining the cell's structure and regulating its functions through gene expression. This intricate process involves various proteins, such as histones, combining to form chromosomes that carry the cell's nuclear genome. Acting as the central command center, the nucleus ensures genetic stability. Additionally, it contains nucleoplasm, a dense fluid with a composition similar to that of cytosol found outside of the nucleus.
The nuclear envelope is a dense spherical organelle that encloses the nucleus. It comprises an inner and outer membrane, serving as a barrier against the unrestricted movement of macromolecules between the nucleoplasm and cytoplasm. Furthermore, the outer membrane links to the rough endoplasmic reticulum (RER) and contains ribosomes.
The area between the membranes is called the pronuclear space. In this image, HeLa cells are stained with Blue Hoechst dye to emphasize the DNA in the cell nucleus. The central and rightmost cells are in interphase, meaning their entire nuclei are labeled. On the left, a cell is going through mitosis and its DNA has condensed for division. Now, let's discuss chromosomes, which most people know about. Our chromosomes dictate our physical appearance, inherent personality traits, and body development. Chromosomes consist of structured arrangements of DNA and protein found in cells.
The composition of chromosomes consists of coiled
DNA chains that contain genes, regulatory elements, and other nucleoid sequences. Moreover, proteins bound to the DNA govern its function and packaging. Chromosome structure varies across organisms, with the DNA molecule being circular or linear and comprising 100,000 to 10,000,000,000 nucleotides. Eukaryotic cells possess substantial linear chromosomes due to their nuclei while prokaryotic cells generally have smaller circular chromosomes due to the lack of defined nuclei. However, there are exceptions to this overall trend.
Cells can contain various types of chromosomes, including mitochondria in eukaryotes and chloroplasts in plants, which have their own compact chromosomes. In humans, there are two primary types: autosomes and sex chromosomes. Sex-related genetic characteristics are passed down through sex chromosomes, while autosomes carry the remaining hereditary information. Both types of chromosomes play similar roles in cell division, with each species having a specific number of them. Humans possess 23 pairs of chromosomes, and changes to these chromosomes lead to different genetic abnormalities.
The cell contains various helper components, including ribosomes. Ribosomes are often referred to as the "black boxes" in molecular biology and play a crucial role. In a single human cell, there are numerous ribosomes that carry the genetic information from DNA. These ribosomes also serve as sites where different chemicals can be utilized by antibiotics and viruses to either fight against or enhance diseases. Notably, certain viruses like polio and hepatitis C have the ability to hijack human ribosomes for their own benefit, using them to produce proteins that support viral growth.
Extensive research has been conducted on ribosomes, which are vital cell components responsible for protein chain synthesis. Although our knowledge of ribosomes is not complete, they play a crucial
role in combining specific amino acids to form proteins based on RNA nucleotide sequence. Ribosomes constitute 25% of a cell's mass and consist of two subunits that work together to convert mRNA into polypeptide chains during protein synthesis.
In bacterial sub-units, there are ribosomal RNA (rRNA) and protein molecules. On the other hand, eukaryotic sub-units have larger rRNA molecules and protein molecules. Recent crystallographic studies indicate that ribosomal proteins do not directly contribute to polypeptide synthesis but rather facilitate rRNA's ability to do so. The endoplasmic reticulum functions as an intracellular transportation system.
The endoplasmic reticulum is a cellular organelle found in eukaryotic organisms. It forms a complex network of tubules, vesicles, and cisternae. Rough endoplasmic reticula are involved in protein synthesis and act as a production site for membranes. Smooth endoplasmic reticula function in the synthesis of lipids like oils, phospholipids, and steroids. They also metabolize carbohydrates, regulate calcium levels, and detoxify drugs and poisons. Sarcoplasmic reticula have a specific role in regulating calcium levels.
The endoplasmic reticulum, a vast membrane network, is composed of interconnected sac-like structures called cisternae. These cisternae are connected by the cytoskeleton. The phospholipid membrane surrounds the space within the cisternae, known as the lumen. This lumen is connected to the perinuclear space but separate from the cytosol. Depending on its type and location within a cell, the endoplasmic reticulum performs various functions. There are three types: rough endoplasmic reticulum, smooth endoplasmic reticulum, and sarcoplasmic reticulum.
The cell can rapidly exchange the quantity of RER and SER, depending on metabolic needs. This involves various changes including the incorporation of new proteins into the membranes. Additionally, significant alterations in protein content can occur without
any apparent structural modifications, depending on the cell's enzymatic requirements. The Golgi apparatus acts as the cell's suitcase, where proteins are packaged for transportation. Its main role is protein storage. Cells produce numerous different macromolecules through synthesis.
The Golgi apparatus plays a crucial role in modifying, sorting, and packaging macromolecules for either cell secretion or internal use. Vesicles originating from the rough endoplasmic reticulum journey to the cis face of the Golgi apparatus, where they merge with the Golgi membrane and release their contents into the lumen. Within the lumen, the molecules undergo modifications before being organized for transportation to their respective next locations. Cells that produce and secrete substantial quantities of substances typically possess larger and more abundant Golgi apparatuses.
Lysosomes are referred to as the stomach of the cell because they function as the cell's digestive system. They are cellular organelles that contain acid hydrolase enzymes, which break down waste materials and cellular debris. While they are found in animal cells, yeast and plants perform similar roles with lytic vacuoles. Lysosomes digest excess or worn-out organelles, food particles, and also eliminate viruses or bacteria. The digestive enzymes within a lysosome require a pH of 4.5 to work effectively.
Lysosomes are organelles that combine with vacuoles and release their enzymes into the vacuoles, causing the digestion of their contents. These structures form when hydrolytic enzymes are introduced to early endosomes from the Golgi apparatus. The term lysosome originates from the Greek words lysis, which means separation, and soma, which means body. Lysosomes acquire this name due to a process known as Autolysis, which denotes self-digestion or self-destruction. The interior of lysosomes possesses an acidic
environment in comparison to the slightly alkaline cytosol. To maintain this pH difference, lysosomes employ proton pumps and chloride ion channels to transport protons (H+ ions) across their membrane.
The lysosomal membrane serves as a protective barrier, separating the cytosol from the enzymes contained within the lysosome. This barrier prevents the degradation of biological molecules and safeguards against pH-sensitive lysosomal acid hydrolases entering into the cytosol, which is an alkaline environment that is not suitable for these enzymes to function properly. As a result, this protective mechanism ensures that cytosolic molecules and organelles are not destroyed in case there is any leakage of hydrolytic enzymes from the lysosome. Here is an illustration demonstrating this process:
Additionally, I will now present you with an image representing the appearance of a Lysosome.
The centrosome serves as the main microtubule organizing center and a regulator of cell-cycle progression in animal cells. It plays a critical role in cell cycle advancement. Made up of two centrioles arranged orthogonally, encompassed by protein-rich pericentriolar material (PCM), the centrosome aids in microtubule nucleation and anchoring. The examination of centrosomes is highly significant because they often undergo changes in cancer cells. Thus, comprehending the centrosome is crucial for grasping cancer.
Centrosome abnormalities have been linked to cancer and benign tumors, typically occurring when the structure becomes abnormally large, leading to structural aberrations. Notably, the centrosome is replicated just once during the cell cycle, resulting in each daughter cell inheriting one centrosome comprising two centrioles. Animal cells feature centrosomes that consist of two centrioles. Interestingly, although centrioles are not essential for mitosis progression, centrosomes play a crucial role.
The diagram below shows how mitochondria, also known as "cellular power
plants," work. Mitochondria are responsible for producing most of a cell's adenosine triphosphate (ATP), which is used as an energy source. They are the second largest organelles and have their own unique genetic structure. In addition to generating energy, mitochondria play roles in signaling, cellular differentiation, cell death, and regulating the cell cycle and growth. The cristae within mitochondria help with chemical reactions that generate energy.
The mitochondrion is responsible for various tasks such as protein, fat, and carbohydrate breakdown. Additionally, it synthesizes urea. Composed of phospholipid bilayers and proteins, the mitochondrion consists of an outer membrane and an inner membrane. These membranes possess unique qualities that create five distinct compartments within the mitochondrion: the outer mitochondrial membrane, inter-membrane space (situated between the outer and inner membranes), inner mitochondrial membrane, cristae space (formed by folding of the inner membrane), and matrix (the area enclosed by the inner membrane).
The importance of studying Mitochondria lies in their association with several human diseases, including heart disease, and their possible impact on aging. Some experts propose that cleansing Mitochondria could potentially decelerate the aging process and greatly decrease the natural degradation of the body. Furthermore, we will now explore the Cytoskeleton, which offers cellular support and enables cells to carry out their functions. Without the Cytoskeleton, cells would lack mobility and become susceptible to disintegration.
The cytoskeleton is a cell's scaffolding, offering protection and performing multiple functions. It maintains cell shape, protects the cell, facilitates cellular motion, assists in intracellular transport, and plays a vital role in cell division. Made of protein, it is present in all cells and closely interacts with cellular membranes. Moreover, it not only provides support to
the cell but also resembles our own skeletal system.
The cytoskeleton functions as a means of transportation and aids in cell movement. It plays a critical role in Cancer treatments as certain potent drugs disrupt its functionality. The Centrosome is another component associated with the cytoskeleton, consisting of paired cylindrical organelles called Centrioles that are positioned near the nucleus. Comprising nine tubes with three tubules each, Centrioles are essential for cellular division and always arranged perpendicularly to each other.
A centriole, a barrel-shaped cell structure, is present in most animal eukaryotic cells but is not found in higher plants and most fungi. In organisms with flagella and cilia, the mother centriole determines the position of these organelles, which eventually become the basal body. The failure of cells to utilize centrioles for the formation of functional cilia and flagella has been associated with various genetic and developmental disorders. Recently, the inability of centrioles to migrate properly before ciliary assembly has been identified as a cause of Meckel-Gruber syndrome.
The text focuses on plant-related information, particularly about plants and their components. To demonstrate this, an image of a plant cell is desired. One important component to be examined is the Chloroplast, which is exclusively present in plant cells and absent in animals. The Chloroplast plays a vital role in facilitating Photosynthesis and contains the green pigment Chlorophyll. Over millions of years of evolution, end symbiotic cyanobacteria have undergone both structural and functional changes while retaining their own DNA and the ability to divide through binary fission (distinct from mitosis). However, they have surrendered their autonomy by transferring some of their genes to the nuclear genome.
Within the inner membrane of
the plant cell, specifically in the region known as the stroma, there exists a network of flattened membrane compartments known as thylakoids. These thylakoids play a crucial role in light absorption and ATP synthesis. They also contain numerous proteins. Interestingly, this is exactly what Casey Anthony's mother mentioned when discussing internet searches related to chlorophyll. If they could have proven that the purpose of searching for chlorophyll was to acquire or produce it, it would have implicated her in a premeditated murder.
Chloroplasts, similar to mitochondria, are specialized organelles that originate from pre-existing organelles. These organelles possess a diverse structure comprising small granules known as "Grana," which are embedded within the stoma or Matrix. Refer to the included picture for a clearer understanding of Chloroplast structure.
Vacuoles, on the other hand, are membrane-bound sacs used for storage, digestion, and waste elimination. While primarily found in plants, they also exist in certain animals. Their main role is water storage, although they perform various other functions.
Here is a list of things it does. It isolates materials that might be harmful or a threat to the cell. It contains waste products and water in plant cells. It maintains internal hydrostatic pressure or turgor within the cell. It also maintains an acidic internal pH and contains small molecules. Additionally, it exports unwanted substances from the cell. The central vacuole allows plants to support structures such as leaves and flowers due to its pressure. In seeds, stored proteins needed for germination are kept in 'protein bodies', which are modified vacuoles.
Most mature plant cells contain a central vacuole that takes up more than 30% of the cell's volume, and can reach up
to 80% for specific cell types and conditions. Strands of cytoplasm can be found within the vacuole. I wonder if humans had vacuoles or a similar structure if we would age less like plants and potentially avoid diseases like cancer. It's just a thought though, I'm not certain. Lastly, let's discuss the cell wall, which is primarily present in plants and has some similarities to the plasma membrane.
The cell wall has various functions. It controls truguty and acts as an extracellular structure surrounding the plasma membrane. In plants, it serves as the primary cell wall and is further reinforced by a secondary wall. This layer, which can be tough and flexible or rigid in nature, protects and provides structural support to certain cell types. Additionally, it acts as a filter and prevents excessive expansion of the cell when water enters, serving as a pressure vessel.
Think of the cell wall as a wicker basket with an inflated balloon inside, exerting pressure from the inside. This rigid basket is resistant to mechanical damage and provides strength for prokaryote cells (and eukaryotic cells with a cell wall). The flexible plasma membrane pushes against the rigid cell wall, contributing to its strength. The following image illustrates the structure of the cell wall, showcasing its strength and flexibility. Thank you for joining me on this cell tour. I hope you now have a better understanding of the cell and its relevance to us.
