Cell biology or cytology is a branch of biology that studies the structure, function, and behavior of cells.
All living organisms are made of cells.
Cell are the basic unit of life that is responsible for the living and functioning of organisms.
Cell biology involves both prokaryotic and eukaryotic cells
It includes the study of cell metabolism, cell communication, cell cycle, biochemistry, and cell composition.
The study of cells is performed using several microscopy techniques, cell culture, and cell fractionation.
Cell biology is interconnected to other fields such as genetics, molecular genetics, molecular biology, medical microbiology, immunology, and cytochemistry.
All cells come from the division of pre-existing cells.
Viruses are not considered in cell biology – they lack the characteristics of a living cell, and instead are studied in the microbiology subclass of virology.
Techniques commonly used to study cell biology:
Cell culture: Utilizes rapidly growing cells on media which allows for a large amount of a specific cell type and an efficient way to study cells.
Cell culture allows for studying the normal physiology and biochemistry of cells, the effects of drugs and toxic compounds on the cells, and mutagenesis, carcinogenesis, drug screening and development, and large scale manufacturing of biological compounds – vaccines, therapeutic protein.
Fluorescence microscopy is used to label a specific component of the cell, and a certain light wavelength is used to excite the fluorescent marker which can then be visualized.
Phase-contrast microscopy uses the optical aspect of light to represent the solid, liquid, and gas-phase changes as brightness differences.
Confocal microscopy combines fluorescence microscopy with imaging by focusing light and shooting instances to form a 3-D image.
Transmission electron microscopy: Involves metal staining and the passing of electrons through the cells, which will be deflected upon interaction with metal.
Cytometry technique places cells that scattered cells based on different aspects and can therefore separate them based on size and content.
Cells may also be tagged with GFP-fluorescence and can be separated that way as well.
Cell fractionation requires breaking up the cell using high temperature or sonification followed by centrifugation to separate the parts of the cell allowing for them to be studied separately.
There are two classifications of cells: prokaryotic and eukaryotic.
Prokaryotic cells are distinguished from eukaryotic cells by the absence of a cell nucleus or other membrane-bound organelle.
Prokaryotic cells are much smaller than eukaryotic cells, making them the smallest form of life.
Prokaryotic cells include Bacteria and Archaea, and lack an enclosed cell nucleus.
Eukaryotic cells are found in plants, animals, fungi, and protists.
They range from 10 to 100 μm in diameter, and their DNA is contained within a membrane-bound nucleus.
Eukaryotes are organisms containing eukaryotic cells.
The four eukaryotic kingdoms are Animalia, Plantae, Fungi, and Protista.
Bacteria, the most prokaryotic prominent type, have several different shapes, although most are spherical or rod-shaped.
Bacteria can be classed as either gram-positive or gram-negative depending on the cell wall composition.
Gram-positive bacteria have a thicker peptidoglycan layer than gram-negative bacteria.
Bacterial structural features include a flagellum that helps the cell to move, ribosomes for the translation of RNA to protein, and a nucleoid that holds all the genetic material in a circular structure.
There are many processes that occur in prokaryotic cells that allow them to survive. In prokaryotes, mRNA synthesis is initiated at a promoter sequence on the DNA template comprising two consensus sequences that recruit RNA polymerase.
The prokaryotic polymerase consists of a core enzyme of four protein subunits and a σ protein that assists only with initiation.
A fertility factor allows the bacteria to possess a pilus which allows it to transmit DNA to another bacteria which lacks the F factor, permitting the transmittance of resistance allowing it to survive in certain environments.
Eukaryotic cells are composed of the following organelles:
Nucleus: The nucleus of the cell functions as the genome and genetic information storage for the cell, containing all the DNA organized in the form of chromosomes.
It is surrounded by a nuclear envelope, which includes nuclear pores allowing for the transportation of proteins between the inside and outside of the nucleus.
This is also the site for replication of DNA as well as transcription of DNA to RNA.
Afterwards, the RNA is modified and transported out to the cytosol to be translated to protein.
Nucleolus: This structure is within the nucleus, usually dense and spherical in shape.
It is the site of ribosomal RNA (rRNA) synthesis, which is needed for ribosomal assembly.
Endoplasmic reticulum (ER): This functions to synthesize, store, and secrete proteins to the Golgi apparatus.
Structurally, the endoplasmic reticulum is a network of membranes found throughout the cell and connected to the nucleus.
The membranes are slightly different from cell to cell and a cell’s function determines the size and structure of the ER.
Mitochondria are known as the powerhouse of the cell is a double membrane bound cell organelle that functions for the production of energy or ATP within the cell.
Specifically, the mitochondria is where the Krebs cycle or TCA cycle for the production of NADH and FADH occurs, producing within the electron transport chain (ETC) and oxidative phosphorylation for the final production of ATP.
The Golgi apparatus functions to process, package, and secrete the proteins to their destination.
The proteins contain a signal sequence that allows the Golgi apparatus to recognize and direct it to the correct place.
Golgi apparatus also produce glycoproteins and glycolipids.
The lysosome functions to degrade material brought in from the outside of the cell or old organelles.
The lysosome contains many acid hydrolases, proteases, nucleases, and lipases, which break down the various molecules.
Autophagy is the process of degradation through lysosomes which occurs when a vesicle buds off from the ER and engulfs the material, then, attaches and fuses with the lysosome to allow the material to be degraded.
Ribosomes: Functions to translate RNA to protein, and serve as a site of protein synthesis.
Cytoskeleton is a structure that helps to maintain the shape and general organization of the cytoplasm.
The cytoskelon anchors organelles within the cells and makes up the structure and stability of the cell.
The cytoskeleton is composed of three principal types of protein filaments: actin filaments, intermediate filaments, and microtubules.
These proteins are held together and linked to subcellular organelles and the plasma membrane by a variety of accessory proteins.
Cell membrane is a phospholipid bilayer and is also consisted of lipids and proteins.
The inside of the cell membrane’s bilayer is hydrophobic and in order for molecules to participate in reactions within the cell, they cross this membrane layer to get into the cell via osmotic pressure, diffusion, concentration gradients, and membrane channels.
Centrioles: Function to produce spindle fibers which are used to separate chromosomes during cell division.
Eukaryotic cells are composed of the following molecular components:
Chromatin: This makes up chromosomes and is a mixture of DNA with various proteins.
Cilia: They help to propel substances and can also be used for sensory purposes.
Cell metabolism is required for the production of cell energy and survival.
For cellular respiration, glycolysis occurs within the cytosol of the cell to produce pyruvate.
Pyruvate undergoes decarboxylation by the multi-enzyme complex to form acetyl coA.
Acetyl coA is used in the TCA cycle to produce NADH and FADH2, involved in the electron transport chain to ultimately form a proton gradient across the inner mitochondrial membrane.
This gradient drives the production of ATP and H2O during oxidative phosphorylation.
Cell signaling/ cell communication is important for cell regulation and for cells to process information from the environment and respond accordingly.
Signaling occurs through direct cell contact or endocrine, paracrine, and autocrine signaling.
Ion channels: voltage or ligand gated ion channels allow for the outflow and inflow of molecules and ions.
G-protein coupled receptor (GPCR): Is widely recognized to contain seven transmembrane domains.
The ligand binds on the extracellular domain and once the ligand binds, this signals target other proteins such as adenyl cyclase or phospholipase C, which ultimately produce secondary messengers such as cAMP, Ip3, DAG, and calcium.
These secondary messengers function to amplify signals and can target ion channels or other enzymes.
Receptor tyrosine kinases: Bind growth factors, further promoting the tyrosine on the intracellular portion of the protein to cross phosphorylate.
Cells are the foundation of all organisms.
Cells are the fundamental units of life.
The growth and development of cells are essential for the maintenance of the host its survival.
Cells go through a cell cycle, a development which involves cell growth, DNA replication, cell division, regeneration, and cell death.
The cell cycle is divided into four distinct phases: G1, S, G2, and M.
The G phase, the cell growth phase, makes up approximately 95% of the cycle.
The cell cycle is a four-stage process that a cell goes through as it develops and divides.
It includes Gap 1 (G1), synthesis (S), Gap 2 (G2), and mitosis (M).
The G1, G2, and S phase (DNA replication, damage and repair) are considered to be the interphase portion of the cycle, while the M phase (mitosis) is the cell division portion of the cycle.
Mitosis is composed of many stages which include, prophase, metaphase, anaphase, telophase, and cytokinesis, respectively.
The ultimate result of mitosis is the formation of two identical daughter cells.
Cells begin in an identical form and can essentially become any type of cells.
Cell signaling influences nearby cells to determinate the type of cell it will become.
Cell signaling allows cells of the same type to aggregate and form tissues, then organs, and ultimately systems.
The cell cycle is regulated in cell cycle checkpoints, by a series of signaling factors and complexes such as cyclins, cyclin-dependent kinase, and p53.
When cells are damaged or altered, it undergoes cell death, either by apoptosis or necrosis, to eliminate the threat it can cause to the organism’s survival.
The immortality of a cell lineage depends on the maintenance of cell division potential.
This potential for immortality of a cell lineage may be lost in any particular lineage because of cell damage, terminal differentiation as occurs in nerve cells, or programmed cell death apoptosis.
Maintenance of cell division potential over generations depends on the avoidance and the accurate repair of cellular damage, particularly of DNA.
The continuity of the germline depends on the effectiveness of processes for avoiding DNA damage and repairing those DNA damages that do occur.
Effective repair of DNA damages in the germ line occurs by homologous recombination.
Cell cycle phases:
The cell cycle is a four-stage process that a cell goes through as it develops and divides. It includes Gap 1 (G1), synthesis (S), Gap 2 (G2), and mitosis (M).
The cell can restart the cycle from G1 or leaves the cycle through G0 after completing the cycle.
The cell can progress from G0 through terminal differentiation.
The interphase refers to the phases of the cell cycle that occur between one mitosis and the next, and includes G1, S, and G2.
G1 phase The size of the cell grows.
The contents of cells are replicated.
S phase Replication of DNA
The cell replicates each of the 46 chromosomes (23 pairs).
G2 phase The cell multiplies.
In preparation for cell division, organelles and proteins form.
M phase After mitosis, cytokinesis occurs-cell separation
Formation of two daughter cells that are identical
G0 phase
These cells leave G1 and enter G0, a resting stage.
A cell in G0 is doing its job without actively preparing to divide.
Cytopathology is a scientific branch that studies and diagnoses diseases on the cellular level.
Cytopathology is used on samples of free cells or tissue fragments, in contrast to the pathology branch of histopathology, which studies whole tissues.
Cytopathology is commonly used to investigate diseases involving a wide range of body sites, to aid in the diagnosis of cancer but also in the diagnosis of some infectious diseases and other inflammatory conditions.
A common application of cytopathology is the Pap smear, a screening test used to detect cervical cancer and precancerous cervical lesions.
The cell cycle is composed of a number of consecutive stages that result in cellular division.
Cells do not begin the next stage until the last one is finished, is a significant element of cell cycle regulation.
Cell cycle checkpoints are a monitoring strategy for accurate cell cycle and divisions.
Cell cycle checkpoints associated cyclin counterparts, protein kinases, and phosphatases regulate cell growth and division from one stage to another.
Cellular DNA repair reaction is a cascade of signaling pathways that leads to checkpoint engagement, that regulates the repairing mechanism in DNA, cell cycle alterations, and apoptosis.
The cell cycle is a sequence of activities in which cell organelles are duplicated and subsequently separated into daughter cells
Cell cycle processes include cell development, replication and segregation of chromosomes.
There are cell cycle checkpoint surveillance systems that keep track of the cell cycle’s integrity, accuracy, and chronology.
Each checkpoint serves as an alternative cell cycle endpoint where cell’s are examined and only when desirable characteristics are fulfilled does the cell cycle advance through the distinct steps.
The cell cycle precisely copies DNA and afterwards equally split the cell and its components between the two new cells.
Four main stages occur in the eukaryotes. In G1, the cell is usually active and continues to grow rapidly.
In stage G2, the cell growth continues while protein molecules become ready for separation.
In G2 cells gain mass, integrate growth factor receptors, establish a replicated genome, and prepare for chromosome segregation.
DNA replication is restricted to the S-phase.
During mitosis, which is also known as the M-phase, the segregation of the chromosomes occur.
Modifications in DNA’s sequence have a considerably bigger impact than modifications in other cellular constituents like RNAs or proteins because DNA acts as a permanent copy of the cell genome.
When erroneous nucleotides are incorporated during DNA replication, mutations can occur.
DNA damage is primarily fixed by removing the defective bases and then re-synthesizing the excised area.
Some DNA lesions can be mended by reversing the damage, which may be a more effective method of coping with common types of DNA damage: few forms of DNA damage are mended in this fashion, including pyrimidine dimers caused by ultraviolet (UV) light changed by the insertion of methyl or ethyl groups at the purine ring’s O6 position.
Mitochondria are commonly referred to as the cell’s power source because of their capacity to effectively produce ATP which is essential to maintain cellular homeostasis and metabolism.
Cell signaling pathways by mitochondria which are crucial for cell function regulation such as apoptosis.
Mitochondria’s physiological adaptability is linked to ongoing reconfiguration through a range of mechanisms known as mitochondrial membrane dynamics, endomembrane fusion and fragmentation, and ultrastructural membrane remodeling.
Mitochondrial dynamics regulate metabolic but also cell signaling processes such as cell pluripotent stem cells, proliferation, maturation, aging, and mortality.
Mitochondria are wrapped by two membranes: an inner mitochondrial membrane (IMM) and an outer mitochondrial membrane (OMM), each with a distinctive function and structure, which parallels their dual role as cellular powerhouses and signaling organelles.
The inner mitochondrial membrane divides the mitochondrial lumen into two parts: the inner border membrane, which runs parallel to the OMM, and the cristae, which are deeply twisted, multinucleated invaginations that give room for surface area enlargement and house the mitochondrial respiration apparatus.
The outer mitochondrial membrane, acts as a foundation for cell signaling pathways to congregate, be deciphered, and be transported into mitochondria.
The OMM connects to other cellular organelles: endoplasmic reticulum (ER), lysosomes, endosomes, and the plasma membrane.
Mitochondria can exist as independent organelles or as part of larger systems.
Mitochondria can also be unequally distributed in the cytosol through regulated mitochondrial transport and placement to meet the cell’s localized energy requirements.
Autophagy is a self-degradative mechanism that regulates energy sources during growth and reaction to dietary stress, and clears aggregated proteins, cleaning damaged structures including mitochondria and endoplasmic reticulum and eradicating intracellular infections.
Autophagy has antiviral and antibacterial roles within the cell, and it is involved at the beginning of distinctive and adaptive immune responses to viral and bacterial contamination.
Autophagy is the primary intrinsic degradative system for peptides, fats, carbohydrates, and other cellular structures, and is vital for upholding the correct cellular balance.
Autophagy instability leads to a variety of illness symptoms, including inflammation, biochemical disturbances, aging, and neurodegenerative, due to its involvement in controlling cell integrity.
Altered autophagy-lysosomal networks is a typical hallmark of many neurological and muscular illnesses.
The creation of the double membrane which would be known as nucleation, is the first step in macro-autophagy.
The phagophore approach indicates dysregulated polypeptides or defective organelles that come from the cell membrane, Golgi apparatus, endoplasmic reticulum, and mitochondria.