Golgi Body Diagram
Chanelle Kirksey
Ideas about cell structure have changed considerably over the years. Early biologists saw cells as simple membranous sacs containing fluid and a few floating particles. Today's biologists know that cells are infinitely more complex than this.
There are many different types, sizes, and shapes of cells in the body. For descriptive purposes, the concept of a "generalized cell" is introduced. It includes features from all cell types. A cell consists of three parts: the cell membrane, the nucleus, and, between the two, the cytoplasm. Within the cytoplasm lie intricate arrangements of fine fibers and hundreds or even thousands of miniscule but distinct structures called organelles.
Every cell in the body is enclosed by a cell (Plasma) membrane. The cell membrane separates the material outside the cell, extracellular, from the material inside the cell, intracellular. It maintains the integrity of a cell and controls passage of materials into and out of the cell. All materials within a cell must have access to the cell membrane (the cell's boundary) for the needed exchange.
The cell membrane is a double layer of phospholipid molecules. Proteins in the cell membrane provide structural support, form channels for passage of materials, act as receptor sites, function as carrier molecules, and provide identification markers.
The nucleus, formed by a nuclear membrane around a fluid nucleoplasm, is the control center of the cell. Threads of chromatin in the nucleus contain deoxyribonucleic acid (DNA), the genetic material of the cell. The nucleolus is a dense region of ribonucleic acid (RNA) in the nucleus and is the site of ribosome formation. The nucleus determines how the cell will function, as well as the basic structure of that cell.
The cytoplasm is the gel-like fluid inside the cell. It is the medium for chemical reaction. It provides a platform upon which other organelles can operate within the cell. All of the functions for cell expansion, growth and replication are carried out in the cytoplasm of a cell. Within the cytoplasm, materials move by diffusion, a physical process that can work only for short distances.
Cytoplasmic organelles are "little organs" that are suspended in the cytoplasm of the cell. Each type of organelle has a definite structure and a specific role in the function of the cell. Examples of cytoplasmic organelles are mitochondrion, ribosomes, endoplasmic reticulum, golgi apparatus, and lysosomes.
The golgi apparatus is a stack of smooth cisternae (membrane-bound spaces) piled on each other. These flattened plate-like membrane-bound sacs contain tubules and have vesicles protruding from their margins. Vesicles bud off from the tubules and contain materials for cell wall construction. There is a maturing face and a forming face to the golgi body. New cisternae are added to the forming face and as they mature they move progressively across the stack. At the mature face, cisternae are swollen and secretory vesicles are shed. Once the vesicle detaches from the Golgi body (presumably after reaching a critical size) they move across the cytoplasm to the cell membrane and the material is discharged. The membrane of the vesicle ruptures and becomes continuous with the plasmalemma and the contents are released outside of the cell. Vesicles may also fuse with vacuoles.
In this talk, we discuss buckling of an extensible, semi-flexible rod embedded in two and three dimensions. We systematically examine the problem both analytically, using a momentum-space renormalization procedure, and numerically, using Monte Carlo simulations, to determine the topology of the phase diagram containing the unbuckled and buckled states. We determine that thermal fluctuations tend to stabilize the straight-rod state over the buckled state in both two and three dimensions and that this stabilization increases with temperature. We also analyze the mechanical response of the rod in order to study the differing scaling regimes of the system.
Abstract: Emergence of different nanoscopic and microscopic manufacturing techniques facilitates synthesizing nanoparticles with different shapes and sizes, including but not limited to tripod, prism, polyhedral, cubs, and elliptical nanoparticles in nano and micron sizes. Due to the presence of simple entropic forces self- assembly of these building blocks are limited to simple FCC, BCC, diamond crystal structures. Therefore, to obtain more complicated and complex self-assembled structures one requires to introduce specificity and directionality on the surface of nanoparticles in order to induce anisotropic interactions between those constituents. One way to create patchy particles is by spontaneous self-assembly of the physisorbed supramolecules layer on the surface of a nanoparticle. Those nanoparticles protected by the supramolecular shell is known as monolayer protected nanparticles (MPNs). Although there are limited literatures available on the self-assembly of monolayer protected nanoparticles, most of them revolve around surfaces with uniform curvatures, e.g. spheres and cylinders. In this presentation we studied self-assembly of alkathiol surfactants on the surface of gold nanoparticles with spheroid geometries. Owning to the fact that Oblate and Prolate geometries possess non-uniform curvature, phase separation will be altered by the geometry of the substrate which leads to observation of new phases that are absent in the case of systems with uniform curvature. For this purpose we used Dissipative Particle Dynamics (DPD) as a mesoscale simulation technique to study phase separation of alkathiol molecules with different length and miscibility. On the road to understand the physics of phase separation we also address the effect of geometry on the brush-mushroom transition of those mobile surfactants.
Abstract: Hyperuniformity characterizes a state of matter for which density fluctuations vanish on large scales. Hyperuniform materials are of technological importance as they exhibit interesting photonic properties. We have shown that such materials can be obtained by assembling spheres into a disordered jammed 2D- packing. To this end, we use a binary mixture of large and small Poly(NIPAM) particles confined between two cover slips. These soft spheres have been chosen for their temperature-sensitive properties . We can locally increase or decrease the volume fraction occupied by the spheres by finely tuning the temperature. By applying various temperature patterns, we are studying the spatial arrangements of the microgels and characterizing their hyperuniform properties through reconstruction and detection algorithms. The 3D properties as well as the structure factor of the packings are investigated through a small-angle static light scattering set-up.
Abstract: Disordered solids exhibit a power-law distribution of avalanches and other critical behavior when driven slowly. We extend molecular dynamics studies1 of quasistatic shear of 2D and 3D overdamped binary LJ glasses to finite strain rate. As strain rate is increased, the deformation of the system is no longer driven by avalanches but by continuous, localized particle rearrangement. We use finite size scaling to study the critical behavior of various system properties including shear stress and diffusion which is governed by the rise in the dynamic correlation length with decreasing strain rate. 1K. M. Salerno and M. O. Robbins, Phys. Rev. E 88, 062206 (2013).
Abstract: We study the interaction of a model microswimmer (Chlamydomonas reinhardtii) against curved solid surfaces in a quasi 2D microfluidic channel. Through simulations and experiments we propose a model to describe the phenomenon and try to use it to finely control the algae spatial distribution.
Abstract: Underlying curvature is expected to non-trivially affect the behaviour of active systems due to the incompatibility of order and curvature. While active systems on a plane have been extensively studied in the past, little work has been done to understand the effects of curvature. There are a wide range of active systems that move on curved surfaces, for example, cells in crypts in the gut, vortex patterns observed in the mammalian corneal epithelium or actively driven microtubule bundles on a droplet.
Following a recent study (R. Sknepnek and S. Henkes, Phys. Rev. E 91, 022306 (2015)) of active swarms on spheres, we aim to expand the model to a range of closed surfaces, with position-dependent Gaussian curvature. We explore how curvature of the surface affects the dynamics of the collective motion of the system, coupled with the effects of alignment timescale and driving velocity. We aim to characterise the different behaviours which emerge and relate particle motion patterns to geodesics on the surface.
Abstract: In the early phase of axon outgrowth, the growth cones at the tips of axonal processes actively exert forces on their environment, thus pulling on the axonal processes and aiding extension. Evidence is accumulating that the biological processes such as growth cone migration, axon extension and the formation and regeneration of neuronal connections during nervous system development are driven in part by mechanical cues and forces.
These dynamic growth cones are responsible for guiding axons to their synaptic target by translating the different cues into signals that regulate the cytoskeleton and thereby determine the rate and direction of axonal outgrowth, but many aspects of this process are not fully understood. Our research is focused on elucidating interactions between mechanical forces and the molecular machinery that enables microtubule-actin coupling and their connections with the dynamics of ECM adhesions.
To study these connections in detail, we are combining high resolution traction force microscopy (TFM) and total internal reflection (TIRF) microscopy methods. TIRF enables us to minimize phototoxicity and photobleaching observed with the conventional TFM and thereby maintain cell viability during high resolution time lapse imaging. The widely used traction force microscopy utilizes acrylamide gel with a low refractive index as a substrate, which makes it unsuitable for TIRF. Polydimethylsiloxane (PDMS) gels were utilized to produce deformable substrates with high refractive indices matching the numerical aperture of TIRF objectives, meeting the conditions for TIRF at the cell substrate interface.
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