Cell biology

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Not to be confused with Cell (biology). Cell biology_sentence_0

Cell biology (also cellular biology or cytology) is a branch of biology studying the structure and function of the cell, also known as the basic unit of life. Cell biology_sentence_1

Cell biology encompasses both prokaryotic and eukaryotic cells and can be divided into many sub-topics which may include the study of cell metabolism, cell communication, cell cycle, biochemistry, and cell composition. Cell biology_sentence_2

The study of cells is performed using several techniques such as cell culture, various types of microscopy, and cell fractionation. Cell biology_sentence_3

These have allowed for and are currently being used for discoveries and research pertaining to how cells function, ultimately giving insight into understanding larger organisms. Cell biology_sentence_4

Knowing the components of cells and how cells work is fundamental to all biological sciences while also being essential for research in biomedical fields such as cancer, and other diseases. Cell biology_sentence_5

Research in cell biology is interconnected to other fields such as genetics, molecular genetics, biochemistry, molecular biology, medical microbiology, immunology, and cytochemistry. Cell biology_sentence_6

History Cell biology_section_0

Cells were first seen in 17th century Europe with the invention of the compound microscope. Cell biology_sentence_7

In 1665, Robert Hooke termed the building block of all living organisms as "cells" after looking at a piece of cork and observing a cell-like structure, however, the cells were dead and gave no indication to the actual overall components of a cell. Cell biology_sentence_8

A few years later, in 1674, Anton Van Leeuwenhoek was the first to analyze live cells in his examination of algae. Cell biology_sentence_9

All of this preceded the cell theory which states that all living things are made up of cells and that cells are the functional and structural unit of organisms. Cell biology_sentence_10

This was ultimately concluded by plant scientist, Matthias Schleiden and animal scientist, Theodor Schwann in 1839, who viewed live cells in plant and animal tissue, respectively. Cell biology_sentence_11

19 years later, Rudolf Virchow further contributed to the cell theory, adding that all cells come from the division of pre-existing cells. Cell biology_sentence_12

Although widely accepted, there have been many studies that question the validity of the cell theory. Cell biology_sentence_13

Viruses, for example, lack common characteristics of a living cell, such as membranes, cell organelles, and the ability to reproduce by themselves. Cell biology_sentence_14

Scientists have struggled to decide whether viruses are alive or not and whether they are in agreement with the cell theory. Cell biology_sentence_15

Techniques Cell biology_section_1

Modern-day cell biology research looks at different ways to culture and manipulate cells outside of a living body to further research in human anatomy and physiology, and to derive medications. Cell biology_sentence_16

The techniques by which cells are studied have evolved. Cell biology_sentence_17

Due to advancements in microscopy, techniques and technology have allowed for scientists to hold a better understanding of the structure and function of cells. Cell biology_sentence_18

Many techniques commonly used to study cell biology are listed below: Cell biology_sentence_19

Cell biology_unordered_list_0

  • 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 biology_item_0_0
  • Fluorescence microscopy: Fluorescent markers such as GFP, are used to label a specific component of the cell. Afterwards, a certain light wavelength is used to excite the fluorescent marker which can then be visualized.Cell biology_item_0_1
  • Phase-contrast microscopy: Uses the optical aspect of light to represent the solid, liquid, and gas phase changes as brightness differences.Cell biology_item_0_2
  • Confocal microscopy: Combines fluorescence microscopy with imaging by focusing light and snap shooting instances to form a 3-D image.Cell biology_item_0_3
  • Transmission electron microscopy: Involves metal staining and the passing of electrons through the cells, which will be deflected upon interaction with metal. This ultimately forms an image of the components being studies.Cell biology_item_0_4
  • Cytometry: The cells are placed in the machine which uses a beam to scatter the cells based on different aspects and can therefore separate them based on size and content. Cells may also be tagged with GFP-florescence and can be separated that way as well.Cell biology_item_0_5
  • Cell fractionation: This process 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.Cell biology_item_0_6

Cell classification and composition Cell biology_section_2

There are two fundamental classifications of cells: prokaryotic and eukaryotic. Cell biology_sentence_20

Prokaryotic cells are distinguished from eukaryotic cells by the absence of a cell nucleus or other membrane bound organelle. Cell biology_sentence_21

Prokaryotic cells are much smaller than eukaryotic cells, making them the smallest form of life. Cell biology_sentence_22

The study of eukaryotic cells is typically the main focus of cytologists, whereas prokaryotic cells are the focus of microbiologists. Cell biology_sentence_23

Prokaryotic cells Cell biology_section_3

Prokaryotic cells include Bacteria and Archaea, and lack an enclosed cell nucleus. Cell biology_sentence_24

They both reproduce through binary fission. Cell biology_sentence_25

Bacteria, the most prominent type, have several different shapes which include mainly spherical, and rod-shaped. Cell biology_sentence_26

Bacteria can be classed as either gram positive or gram negative depending on the cell wall composition. Cell biology_sentence_27

Bacterial structural features include: Cell biology_sentence_28

Cell biology_unordered_list_1

  • Flagella: A tail-like structure that helps the cell to move.Cell biology_item_1_7
  • Ribosomes: Used for translation of RNA to protein.Cell biology_item_1_8
  • Nucleoid: Area designated to hold all the genetic material in a circular structure.Cell biology_item_1_9

There are many process that occur in prokaryotic cells that allow them to survive. Cell biology_sentence_29

For instance, in a process termed conjugation, 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. Cell biology_sentence_30

Eukaryotic cells Cell biology_section_4

Eukaryotic cells can either be unicellular or multicellular and include animal, plant, fungi, and protozoa cells which all contain organelles with various shapes and sizes. Cell biology_sentence_31

These cells are composed of the following organelles: Cell biology_sentence_32

Cell biology_unordered_list_2

  • Nucleus: This 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 transportation of proteins between the inside and outside of the nucleus. The 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.Cell biology_item_2_10
  • 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.Cell biology_item_2_11
  • Endoplasmic reticulum (ER): This functions to synthesize, store, and secrete proteins to the golgi apparatus.Cell biology_item_2_12
  • Mitochondria: This functions for the production of energy or ATP within the cell. Specifically, this is the place where the Krebs cycle or TCA cycle for the production of NADH and FADH occurs. Afterwards, these products are used within the electron transport chain (ETC) and oxidative phosphorylation for the final production of ATP.Cell biology_item_2_13
  • Golgi apparatus: This functions to further process, package, and secrete the proteins to their destination. The proteins contain a signal sequence which allows the golgi apparatus to recognize and direct it to the correct place.Cell biology_item_2_14
  • Lysosome: The lysosome functions to degrade material brought in from the outside of the cell or old organelles. This contains many acid hydrolases, proteases, nucleases, and lipases, which breakdown 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.Cell biology_item_2_15
  • Ribosomes: Functions to translate RNA to protein.Cell biology_item_2_16
  • Cytoskeleton: This functions to anchor organelles within the cells and make up the structure and stability of the cell.Cell biology_item_2_17
  • Cell membrane: The cell membrane can be described as a phospholipid bilayer and is also consisted of lipids and proteins. Because the inside of the bilayer is hydrophobic and in order for molecules to participate in reactions within the cell, they need to be able to cross this membrane layer to get into cell via osmotic pressure, diffusion, concentration gradients, and membrane channels.Cell biology_item_2_18
  • Centrioles: Function to produce spindle fibers which are used to separate chromosomes during cell division.Cell biology_item_2_19

Eukaryotic cells may also be composed of the following molecular components: Cell biology_sentence_33

Cell biology_unordered_list_3

  • Chromatin: This makes up chromosomes and is a mixture of DNA with various proteins.Cell biology_item_3_20
  • Cilia : They help to propel substances and can also be used for sensory purposes.Cell biology_item_3_21

Processes Cell biology_section_5

Main article: Cell (biology) § Cellular processes Cell biology_sentence_34

Cell metabolism Cell biology_section_6

Cell metabolism is necessary for the production of energy for the cell and therefore its survival and includes many pathways. Cell biology_sentence_35

For cellular respiration, once glucose is available, glycolysis occurs within the cytosol of the cell to produce pyruvate. Cell biology_sentence_36

Pyruvate undergoes decarboxylation using the multi-enzyme complex to form acetyl coA which can readily be used in the TCA cycle to produce NADH and FADH2. Cell biology_sentence_37

These products are involved in the electron transport chain to ultimately form a proton gradient across the inner mitochondrial membrane. Cell biology_sentence_38

This gradient can then drive the production of ATP and H2O during oxidative phosphorylation. Cell biology_sentence_39

Metabolism in plant cells includes photosynthesis which is simply the exact opposite of respiration as it ultimately produces molecules of glucose. Cell biology_sentence_40

Cell communication and signaling Cell biology_section_7

Cell communication is important for cell regulation and for cells to process information from the environment and respond accordingly. Cell biology_sentence_41

Communication can occur through direct cell contact or endocrine, paracrine, and autocrine signaling. Cell biology_sentence_42

Direct cell-cell contact is when a receptor on a cell binds a molecule that is attached to the membrane of another cell. Cell biology_sentence_43

Endocrine signaling occurs through molecules secreted into the bloodstream. Cell biology_sentence_44

Paracrine signaling uses molecules diffusing between two cells to communicate. Cell biology_sentence_45

Autocrine is a cell sending a signal to itself by secreting a molecule that binds to a receptor on its surface. Cell biology_sentence_46

Forms of communication can be through: Cell biology_sentence_47

Cell biology_unordered_list_4

  • Ion channels: Can be of different types such as voltage or ligand gated ion channels. The allow for the outflow and inflow of molecules and ions.Cell biology_item_4_22
  • G-protein coupled receptor (GPCR): Is widely recognized to contain 7 transmembrane domains. The ligand binds on the extracellular domain and once the ligand binds, this signals a guanine exchange factor to convert GDP to GTP and activate the G-α subunit. G-α can 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. One example for amplification of a signal is cAMP binding to and activating PKA by removing the regulatory subunits and releasing the catalytic subunit. The catalytic subunit has a nuclear localization sequence which prompts it to go into the nucleus and phosphorylate other proteins to either repress or activate gene activity.Cell biology_item_4_23
  • Receptor tyrosine kinases: Bind growth factors, further promoting the tyrosine on the intracellular portion of the protein to cross phosphorylate. The phosphorylated tyrosine becomes a landing pad for proteins containing an SH2 domain allowing for the activation of Ras and the involvement of the MAP kinase pathway.Cell biology_item_4_24

Cell cycle Cell biology_section_8

Main article: Cell cycle Cell biology_sentence_48

The growth process of the cell does not refer to the size of the cell, but the density of the number of cells present in the organism at a given time. Cell biology_sentence_49

Cell growth pertains to the increase in the number of cells present in an organism as it grows and develops; as the organism gets larger so does the number of cells present. Cell biology_sentence_50

Cells are the foundation of all organisms and are the fundamental unit of life. Cell biology_sentence_51

The growth and development of cells are essential for the maintenance of the host and survival of the organism. Cell biology_sentence_52

For this process, the cell goes through the steps of the cell cycle and development which involves cell growth, DNA replication, cell division, regeneration, and cell death. Cell biology_sentence_53

The cell cycle is divided into four distinct phases: G1, S, G2, and M. The G phase – which is the cell growth phase – makes up approximately 95% of the cycle. Cell biology_sentence_54

The proliferation of cells is instigated by progenitors. Cell biology_sentence_55

All cells start out in an identical form and can essentially become any type of cells. Cell biology_sentence_56

Cell signaling such as induction can influence nearby cells to differentiate determinate the type of cell it will become. Cell biology_sentence_57

Moreover, this allows cells of the same type to aggregate and form tissues, then organs, and ultimately systems. Cell biology_sentence_58

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. Cell biology_sentence_59

Mitosis is composed of many stages which include, prophase, metaphase, anaphase, telophase, and cytokinesis, respectively. Cell biology_sentence_60

The ultimate result of mitosis is the formation of two identical daughter cells. Cell biology_sentence_61

The cell cycle is regulated by a series of signaling factors and complexes such as cyclins, cyclin-dependent kinase, and p53. Cell biology_sentence_62

When the cell has completed its growth process and if it is found to be damaged or altered, it undergoes cell death, either by apoptosis or necrosis, to eliminate the threat it can cause to the organism's survival. Cell biology_sentence_63

Pathology Cell biology_section_9

Main article: Cytopathology Cell biology_sentence_64

The scientific branch that studies and diagnoses diseases on the cellular level is called cytopathology. Cell biology_sentence_65

Cytopathology is generally used on samples of free cells or tissue fragments, in contrast to the pathology branch of histopathology, which studies whole tissues. Cell biology_sentence_66

Cytopathology is commonly used to investigate diseases involving a wide range of body sites, often to aid in the diagnosis of cancer but also in the diagnosis of some infectious diseases and other inflammatory conditions. Cell biology_sentence_67

For example, a common application of cytopathology is the Pap smear, a screening test used to detect cervical cancer, and precancerous cervical lesions that may lead to cervical cancer. Cell biology_sentence_68

Notable cell biologists Cell biology_section_10

See also Cell biology_section_11

Cell biology_unordered_list_5

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Cell biology.