Science Current Events | Science News | Brightsurf.com
 
Email a Friend Send to a friend
Printer Friendly Print New models question old assumptions about how many molecules it takes to control cell division

New models question old assumptions about how many molecules it takes to control cell division

February 25, 2009

Blacksburg, Va. -- A single cell - whether a yeast cell or one of your cells - is exquisitely sensitive to its surroundings. It receives input signals, processes the information, makes decisions, and issues commands for making the proper response. As with any control system, noise - errors, slip-ups, mis-reads - can get in the way of correct decision making. Virginia Tech biologists and engineers have created a mathematical model to explore the roles of noise in controlling the basic events of the cell cycle - DNA replication and cell division.

Their work will appear the week of February 23 in the Online Early Edition of the Proceedings of the National Academy of Sciences (PNAS) and later in the print version of the special feature issue on complex systems. The article, "Exploring the Roles of Noise in the Eukaryotic Cell Cycle," is by postdoctoral associate Sandip Kar; William Baumann, professor of electrical and computer engineering; Mark Paul, professor of mechanical engineering; and John Tyson, University Distinguished Professor of biological sciences.




Their efforts to accurately calculate the effects of noise in a yeast cell revealed flaws in two accepted notions about information processing in single cells: about the numbers of messenger RNA (mRNA) molecules in a cell, and about how long they live.

A fundamental challenge of systems biology is trying to understand the molecular basis of decision making in a single cell. "Information processing is done by a molecular network consisting of interacting genes and proteins," Tyson said. "You could compare it to a computer that is based on integrated circuits or to a mechanical control system based on sensors, wires and servomotors -- except that information processing in cells is unique in two ways. First, the cell is a sloppy, liquid environment, with molecules bouncing around and reacting with one another. Second, cells are extremely tiny; therefore sensitive to random fluctuations in the number of molecules being created or destroyed at any given moment."

Nonetheless, the ebb and flow of molecules in a cell must reliably convey instructions for such essential processes as DNA replication and cell division.

How big are the molecular fluctuations expected in a single yeast cell? Physicists estimate molecular fluctuation using a rule-of-thumb that the size of typical fluctuations is the square root of the average number of molecules. "If there are on average 900 molecules of a particular protein in a cell, then we can expect fluctuations of plus or minus 30 molecules, or 3.3 percent," said Tyson. "That is not too bad."

For DNA there might be a severe problem, Tyson noted, "because there is only one copy of every gene in a yeast cell. But cells are equipped with an elaborate and expensive mechanism to replicate DNA molecules and not allow the random fluctuations predicted by statistical physics."

The weak link in the is mRNA: the molecule that carries information from the gene to the cell's ribosomes, where proteins are made.

The literature reports that there is on average only 1 mRNA molecule per gene per cell, in yeast, and that each mRNA molecule lives, on average, for 15 to 20 minutes before it is degraded. "This is intriguing," said Tyson, "because the physicist's rule-of-thumb would predict very large fluctuations in mRNA abundance - sometimes 1, sometimes 0, sometimes 2 or 3 or 4 -- which means the noise among mRNA molecules is huge, and it propagates to the level of the encoded protein."

The noisy fluctuations in protein level may be 50 percent instead of 3 percent. "There is no way the control system can work in the face of such large fluctuations," Tyson said. "It would be completely unreliable."

Progression through the cell cycle is indeed a noisy process, with typical flucutations of 15 to 20 percent for the time taken to complete the process. To achieve this level of control, the Virginia Tech researchers conclude, in their PNAS paper, that 1) the average number of specific mRNA molecules must be 5 to 10 times larger than the generally accepted value, or 2) the half-life of mRNA molecules must be 10 to 20 times shorter than the reported value, or 3) the cell must have specific mechanisms for noise reduction in its mRNA populations. Or some combination of these strategies.

"At least we have an accurate model that tells where the questions are," Tyson said. "Computational cell biologists address puzzles like this one by building reliable mathematical models, based on basic principles of physics and chemistry, that address the roles of noise and noise reduction mechanisms in living cells."

Tyson, Baumann, and Paul are lead investigators on an NIH National Institute of General Medical Sciences funded research project that also includes Yang Cao, assistant professor; Cliff Shaffer, professor; Layne Watson, professor; and Adrian Sandu, associate professor, all of Virginia Tech's computer science department in the College of Engineering.

The group is continuing to build more elaborate and accurate models of molecular noise in the cell cycle control system of yeast cells and to compare these models to the latest experimental measurements of molecular fluctuations in single cells.

Virginia Tech



Related Cell Division Current Events and Cell Division News Articles Cell Division Current Events and Cell Division News RSS Cell Division Current Events and Cell Division News RSS
Researchers discover mechanism that prevents two species from reproducing
Cornell researchers have discovered a genetic mechanism in fruit flies that prevents two closely related species from reproducing, a finding that offers clues to how species evolve.

Common weed could provide clues on aging and cancer
A common weed and human cancer cells could provide some very uncommon details about DNA structure and its relationship with telomeres and how they affect cellular aging and cancer, according to a team led by scientists from Texas A&M University and the University of Cincinnati (UC).

Boston University scientists first to see RNA network in live bacterial cells
Scientists who study RNA have faced a formidable roadblock: trying to examine RNA's movements in a living cell when they can't see the RNA. Now, a new technology has given scientists the first look ever at RNA in a live bacteria cell-a sight that could offer new information about how the molecule moves and works.

Texas A&M researchers find new mechanism for circadian rhythm
Molecules that may hold the key to new ways to fight cancer and other diseases have been found to play an important role in regulating circadian rhythm, says Liheng Shi, a researcher in Texas A&M's Department of Veterinary Integrative Biosciences.

Checkered history of mother and daughter cells explains cell cycle differences
When mother and daughter cells are created each time a cell divides, they are not exactly alike. They have the same set of genes, but differ in the way they regulate them.

Eutrophication affects diversity of algae
Eutrophication of the seas may have an impact on genetic variation in algae, research at the University of Gothenburg shows.

MDC scientists show how hematopoietic stem cell development is regulated
During cell division, whether hematopoietic stem cells (HSCs) will develop into new stem cells (self-renewal) or differentiate into other blood cells depends on a chemical process called DNA methylation.

The amazing maze of maize evolution
Understanding the evolution and domestication of maize has been a holy grail for many researchers. As one of the most important crops worldwide and as a crop that appears very different from its wild relatives as a result of domestication, understanding exactly how maize has evolved has many practical benefits and may help to improve crop yields.

Draft potato genome based on unique potato variety
The Potato Genome Sequencing Consortium (PGSC), an international team of scientists from industry and academia in 14 countries, has released a draft sequence of the potato genome with the help of a Virginia Tech researcher.

Novel 'on-off switch' mechanism stops cancer in its tracks
A tiny bit of genetic material with no previously known function may hold the key to stopping the spread of cancer, researchers at Yale School of Medicine and Sichuan University in Chengdu, China report in two papers in the September 7-11 issue of Proceedings of the National Academy of Sciences.
More Cell Division Current Events and Cell Division News Articles
The Cell Cycle: Principles of Control (Primers in Biology) (Primers in Biology)

The Cell Cycle: Principles of Control (Primers in Biology) (Primers in Biology)
by David O. Morgan (Author)

The Cell Cycle is an account of the mechanisms that control cell division, beginning with a description of the phases and main events of the cell cycle and the main model organisms in cell-cycle analysis, including Xenopus, Drosophila, and yeasts. Later chapters focus on the molecules and mechanisms of the cell-cycle control system, including the cyclin-dependent kinase family of protein kinases, the cyclins that activate them, and the signaling molecules that regulate them, and discuss cell-cycle control in development and the failure of controls in cancer.

Teaching Systems Biology Module 4: Cell Division & Metabolism

Teaching Systems Biology Module 4: Cell Division & Metabolism
Starring: Standard Deviants
Directed By: Standard Deviants

The DVD features award-winning Standard Deviants School programming, which will capture your students' attention and make the subject come alive! Content includes a topic based video programming, classroom notes, graphic handouts, quiz, and answer questions plus a fact filled video segment accompanied by quiz and discussion questions. Cerebellum Teaching System equips you with everything you need to succeed where it matter most: the classroom. Topics covered: Cell division, DNA replication, prophase, metaphase, anaphase, telophase, the principle of segregation, the principle of independent assortment, metabolism, photosynthesis, oxidation & reduction.

SciEd Cell Division: Mitosis, Meiosis, and Cytokinesis VHS Video

SciEd Cell Division: Mitosis, Meiosis, and Cytokinesis VHS Video
by Neo/Sci Corporation

Cell Division Video VHS

The Dead Rose

The Dead Rose
Cell Division (Primary Contributor)



Cell Division 1: Mitosis & the Cell Cycle

Cell Division 1: Mitosis & the Cell Cycle
by iKnow

Use the power of 3-D animation to excite your students about cell division! They will learn the phases of mitosis in animal and plant cells, and the difference between mitosis and cytokinesis. Students can compare and contrast the phases of mitosis in side-by-side plant and animal cell micrographs. Video microscopy makes mitosis come alive in an amphibian lung cell and a zebrafish embryo. The eukaryotic cell cycle is presented in detail in 6 fully narrated animations. Topics covered include: DNA replication and structure, cell cycle variations, molecular control of a cell's progress through the cell cycle, and a discussion of cancer. Students will explore the anatomy of plant, animal, and bacteria cells with interactive diagrams and definitions. Prokaryotic cell division is compared to...

Midnight

Midnight
Also With: J.J. Abrams (Producer), Alex Kurtzman (Producer), Roberto Orci (Producer), Jeff Pinkner (Producer), Bryan Burk (Producer)



  MOOSE UTILITY DIVISION MUD RADIO/GPS/CELL MOUNT A710BLK-00-MOO
by MOOSE MUD ATV PARTS

MOOSE UTILITY DIVISION MUD RADIO/GPS/CELL MOUNT A710BLK-00-MOO

Mitosis, Miosis, and Cell Division Slide Set

Mitosis, Miosis, and Cell Division Slide Set

Biology Slide Set I, Bacteria (3 types), oedogonium, moss, fern, ranunculus root, leaf epidermis, lilium leaf, amoeba proteus, paramecium, grantia, hydra, and syringa leaf. Biology Slide Set II, Physarum, spirogyra, wheat rust, molds (3 types), marchantia (male),herb and woody stems, corn stem, corn root, lily ovary, euglena, obelia hydroid, and planaria. Bacteria, Fungi, and Slime Molds, Physarum, mouth smear, coccus, bacillus, spirillum, molds (3 types), saccharomyces, wheat rust, coprinus, and stemonitis. Mitosis, Meiosis, and Cell Division, Paramecium fission, allium root tip, hydra budding, saccharomyces, whitefish mitosis, ascaris mitosis, grasshopper testis, and lilium. General Botany, Stemonitis, nostoc, hydrodictyon, penicillium, polysiphonia, wheat rust, molds (3 types),...

Powerboy And The Queen

Powerboy And The Queen
Julian Snow Index (Primary Contributor)



OL Medical Division Cell-U-Less - 75 Capsules

OL Medical Division Cell-U-Less - 75 Capsules
by OL Medical Division

Cell-U-Less is a comprehensive herbal remedy consisting of standardized herbs that help to improve circulation, decrease water retention and may enhance connective tissue structures. Impaired circulation, water retention problems and the breakdown and thinning of connective tissue structures are contributing factors to the development of cellulite. The term cellulite is used to describe a condition that is related to hormonal variations and results from circulatory impairments, fluid retention, enlargement of fat cells and alterations in connective tissue. Women are most often affected by cellulite due to structural differences in subcutaneous tissue when compared to men. In women, the subcutaneous tissue contains vertical fat cells that are separated by dividing walls of connective...

© 2009 BrightSurf.com