We are searching data for your request:
Upon completion, a link will appear to access the found materials.
I was thinking that even though I know how generally the cell works, I don't really have a feeling of how volatile it is. I want to know what is the lifetime/turnover rate of different constituents of the cell.
On the molecular level what are the lifetimes for various proteins, for ribosome, lipids, carbohydrates, DNA and RNA. What about aminoacids, nucleotides?
On the organelle level what are the lifetimes of the mitochondria, golgi apparatus. Does nucleus or ER ever change if not during meiosis.
I understand that the lifetime depends on the context. For example, for DNA, cells that replicate, half-life is about one replication as a whole new strand is generated. In neurons, that don't replicate for decades it's not the case. But the DNA can't just sit there. It is constantly unraveled, transcribed, damaged and repaired. So it has a different time constant.
I am still very interested to know any specific numbers.
Your question has several parts to it so I will attempt to address them one-by-one.
In terms of protein stability and turnover, this is a nice paper describing how human cell (HeLa) line, although this is a cancerous cell line, is used to measure the turnover of proteins (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3316722/?report=classic). They have used labelled amino acid technique and mass spectrometry (SILAC) to make measurements of protein turnover. It is concluded that on average the turnover is 20 hours, which is correct in my experience when doing gene knockdowns in Drosophila (S2) cells using RNAis as we incubate the RNAi with cells for 72 hours to ensure most proteins that we targeting are degraded and we can see the desired effects in cells.
Now getting to your questions regarding organelle turnover, you have to consider that cellular organells are very precious to the cells as most of them consume a lot of energy to build hence they are maintained unless they suffer critical damage, and they would become detrimental to the cellular integrity. In that case organells such as mitochondria undergo a specific type of degradation called mitophagy, which is a subtype of autophagy. Now I'm sure there are specific average times for the so called turn-over of cellular organelle under "normal" conditions but thats a slightly misleading view since the turnover can be tipped through reactive oxygen species (ROS) or ageing leading to less efficient cellular maintenance and buildup of toxic aggregated proteins or ROS.
Now just to clarify the use of the word half-life in you last paragraph, half-life normally refers to the time it takes for half the molecules in a given system to degrade (or to be more correct Half-life is the amount of time required for a quantity to fall to half its value as measured at the beginning of the time period) so I do not agree with your use of the word half-life in the last paragraph of above question although human DNA does have a replication limit (Hayflick limit) of roughly 40-60 due to telomer shortening and afterwards the cells (due to the DNA) that no longer replicates will enter senescence and eventually die.
Now getting to non-replicating, highly differentiated cells such as neurons, it still remains a mystery as to how neuronal DNA remains so highly stable (although DNA is a highly stable molecule (compared to RNA) and its further stabilised through histones), while undergoing many dynamic processes such as transcription (since if anything goes wrong the cells cannot be replaced at least in CNS) and how axons of some neurone that can reach over a meter in length are maintained so well for decades. There is a lively argument amongst the scientific community about this, which you can find out about if you simply search for axonal maintenance in a search engine.
Hope this answers some of your questions.
Cell Theory is a basic principle in biology that was formulated by Thodor Schwann, Matthias Schleiden and Rudolph Virchow.
According to the Cell Theory:
- All the living things (organisms) are made up of cells
- The cell is the basic unit of life
- Living cells come from existing/living cells
Recently, the theory was modified to include the following ideas:
- Energy flow takes place within cells
- Heredity information passes from one cell to another
- All cells have the same basic chemical composition
For Students & Teachers
For Teachers Only
Living systems are organized in a hierarchy of structural levels that interact.
Explain how subcellular components and organelles contribute to the function of the cell.
Describe the structural features of a cell that allow organisms to capture, store, and use energy.
Organelles and subcellular structures, and the interactions among them, support cellular function-
- Endoplasmic reticulum provides mechanical support, carries out protein synthesis on membrane-bound ribosomes, and plays a role in intracellular transport.
- Mitochondrial double-membrane provides compartments for different metabolic reactions.
- Lysosomes contain hydrolytic enzymes, which are important in intracellular digestion, the recycling of a cell’s organic materials, and programmed cell death (apoptosis).
- Vacuoles have many roles, including storage and release of macromolecules and cellular waste products. In plants, it aids in the retention of water for turgor pressure.
The folding of the inner membrane increases the surface area, which allows for more ATP to be synthesized.
Within the chloroplast are thylakoids and the stroma.
The thylakoids are organized in stacks, called grana.
Membranes contain chlorophyll pigments and electron transport proteins that comprise the photosystems.
The light-dependent reactions of photosynthesis occur in the grana.
The stroma is the fluid within the inner chloroplast membrane and outside of the thylakoid.
The carbon fixation (Calvin-Benson cycle) reactions of photosynthesis occur in the stroma.
The Krebs cycle (citric acid cycle) reactions occur in the matrix of the mitochondria.
Electron transport and ATP synthesis occur on the inner mitochondrial membrane.
Cellular & Molecular Biology
Molecular biology is the study of biology at the molecular level. It involves the study of DNA, RNA, proteins and other molecules that affect cellular processes. The field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry.
The field of cell biology investigates multiple aspects of cells including their physiological properties, structure, and the organelles they contain. Cell biology also includes the study of a cell's interactions with its environment, its life cycle, division and death. Molecular and cellular biology are related, as most of the properties and functions of a cell can be described at the molecular level.
The two areas of study encompass many different sub-fields including microbiology, genetics and developmental biology. Alfa Aesar provides a wide range of high quality reagents for cellular and molecular biology, especially for the study of apoptosis and signal transduction.
NotesAccess-restricted-item true Addeddate 2020-12-11 03:07:49 Boxid IA1983708 Camera Sony Alpha-A6300 (Control) Collection_set printdisabled External-identifier urn:oclc:record:1244500879 Foldoutcount 0 Identifier cellmolecularbio0002karp Identifier-ark ark:/13960/t7kq7jk61 Invoice 1652 Isbn 0471192791
9780471192794 Lccn 97053198 Ocr tesseract 4.1.1 Ocr_detected_lang en Ocr_detected_lang_conf 1.0000 Ocr_detected_script Latin Ocr_module_version 0.0.4 Ocr_parameters -l eng Old_pallet IA18193 Openlibrary_edition OL703809M Openlibrary_work OL3269846W Page_number_confidence 79.27 Pages 904 Partner Innodata Pdf_module_version 0.0.3 Ppi 300 Rcs_key 24143 Republisher_date 20201024203119 Republisher_operator [email protected] Republisher_time 869 Scandate 20201022104404 Scanner station24.cebu.archive.org Scanningcenter cebu Scribe3_search_catalog isbn Scribe3_search_id 9780471192794 Tts_version 4.0-initial-155-gbba175a5
Cells are the fundamental unit of living organisms. Biologists have studied cells for centuries in order to understand their physiological properties, their structure, the organelles they harbour, interactions between cells and with their extracellular environment, their life cycle, how they divide and how they die.
Modern cell biologists use a multitude of techniques from whole organism microscopy rightdown to the molecular level investigating the proteins and the genetics of cellular components and cell functions. Cell biology research encompasses both the great diversity of single-celled organisms like bacteria and protozoa, as well as the myriad specialised cells in multicellular organisms such as humans and plants. Cell biology is at the core of developmental biology and stem cell research as well as immunology and cancer biology.
This page is the start point for your journey into cell biology. We hope you enjoy learning about the life of cells!
Cell and Molecular Biology – general information
Cells unpacked – a look inside at cell inclusions
Take a look around the cell components by exploring the links below – you can also visit CELLpics from these pages this is our interactive sister site based around research-level microscope images.
- Lysosomes are small, round, membranous vesicles formed by Golgi bodies. They contain a group of digestive enzymes. The lysosomes’ function is to get rid of worn and senile cells and organelles which no longer have benefits. Furthermore, lysosomes digest the large molecules of nutrients engulfed by the cell and change them into structurally simpler substances to enable the cell to benefit from them. For example, white blood cells use the digestive enzymes present inside the lysosomes to digest and destroy the pathogens which invade the cell.
- The cell is not affected by the lysosome enzymes because these enzymes are surrounded by a membrane, isolating them from the cell’s components.
Autophagy pathway: Cellular and molecular mechanisms
Macroautophagy/autophagy is an essential, conserved self-eating process that cells perform to allow degradation of intracellular components, including soluble proteins, aggregated proteins, organelles, macromolecular complexes, and foreign bodies. The process requires formation of a double-membrane structure containing the sequestered cytoplasmic material, the autophagosome, that ultimately fuses with the lysosome. This review will define this process and the cellular pathways required, from the formation of the double membrane to the fusion with lysosomes in molecular terms, and in particular highlight the recent progress in our understanding of this complex process.
Keywords: ATG proteins RAB protein SNARE autophagic lysosome reformation omegasome phagophore.
Autophagy pathway in mammalian cells.…
Autophagy pathway in mammalian cells. The molecular pathway comprised of the core autophagy…
Intracellular organelles and membrane contacts…
Intracellular organelles and membrane contacts facilitating autophagosome formation. (A) The major organelles required…
Schematic illustration of autophagosome-lysosome fusion.…
Schematic illustration of autophagosome-lysosome fusion. The cytoskeleton components and related motor proteins, the…
The overview of the autophagic…
The overview of the autophagic lysosome reformation (ALR) process. mTOR reactivation trigger ALR.…
Physiology and molecular biology of petal senescence
Petal senescence is reviewed, with the main emphasis on gene expression in relation to physiological functions. Autophagy seems to be the major mechanism for large-scale degradation of macromolecules, but it is still unclear if it contributes to cell death. Depending on the species, petal senescence is controlled by ethylene or is independent of this hormone. EIN3-like (EIL) transcription factors are crucial in ethylene-regulated senescence. The presence of adequate sugar levels in the cell delays senescence and prevents an increase in the levels of EIL mRNA and the subsequent up-regulation of numerous senescence-associated genes. A range of other transcription factors and regulators are differentially expressed in ethylene-sensitive and ethylene-insensitive petal senescence. Ethylene-independent senescence is often delayed by cytokinins, but it is still unknown whether these are natural regulators. A role for caspase-like enzymes or metacaspases has as yet not been established in petal senescence, and a role for proteins released by organelles such as the mitochondrion has not been shown. The synthesis of sugars, amino acids, and fatty acids, and the degradation of nucleic acids, proteins, lipids, fatty acids, and cell wall components are discussed. It is claimed that there is not enough experimental support for the widely held view that a gradual increase in cell leakiness, resulting from gradual plasma membrane degradation, is an important event in petal senescence. Rather, rupture of the vacuolar membrane and subsequent rapid, complete degradation of the plasma membrane seems to occur. This review recommends that more detailed analysis be carried out at the level of cells and organelles rather than at that of whole petals.
If you believe that content available by means of the Website (as defined in our Terms of Service) infringes one or more of your copyrights, please notify us by providing a written notice (“Infringement Notice”) containing the information described below to the designated agent listed below. If Varsity Tutors takes action in response to an Infringement Notice, it will make a good faith attempt to contact the party that made such content available by means of the most recent email address, if any, provided by such party to Varsity Tutors.
Your Infringement Notice may be forwarded to the party that made the content available or to third parties such as ChillingEffects.org.
Please be advised that you will be liable for damages (including costs and attorneys’ fees) if you materially misrepresent that a product or activity is infringing your copyrights. Thus, if you are not sure content located on or linked-to by the Website infringes your copyright, you should consider first contacting an attorney.
Please follow these steps to file a notice:
You must include the following:
A physical or electronic signature of the copyright owner or a person authorized to act on their behalf An identification of the copyright claimed to have been infringed A description of the nature and exact location of the content that you claim to infringe your copyright, in sufficient detail to permit Varsity Tutors to find and positively identify that content for example we require a link to the specific question (not just the name of the question) that contains the content and a description of which specific portion of the question – an image, a link, the text, etc – your complaint refers to Your name, address, telephone number and email address and A statement by you: (a) that you believe in good faith that the use of the content that you claim to infringe your copyright is not authorized by law, or by the copyright owner or such owner’s agent (b) that all of the information contained in your Infringement Notice is accurate, and (c) under penalty of perjury, that you are either the copyright owner or a person authorized to act on their behalf.
Send your complaint to our designated agent at:
Charles Cohn Varsity Tutors LLC
101 S. Hanley Rd, Suite 300
St. Louis, MO 63105