Cell Structure and Function The Development of Cell Theory Hooke's original microscope, that he used at Oxford University, in 1665. Robert Hooke first examined a thin piece of cork (see below), and coined the term "cells" because they looked like Monk's cells.
An Overview of Cell Structure & Function
The plasma membrane isolates the cell but allows interactions with the environment. The genetic material provides a cellular "blueprint. " Cytoplasm fills each cell and surrounds the nucleus.
Cell Function Limits Cell Size Link to MODELING LIMITS TO CELL SIZE from Genetech's Access Excellence Types of Cells: Prokaryotic & Eukaryotic Characteristics of Prokaryotes and Eukaryotes
There are two general classes of cells: prokaryotic and eukaryotic. The evolution of prokaryotic cells preceded that of eukaryotic cells by 2 billion years. Streptococcus pyogenes, the bacterium that causes strep throat, is an example of a prokaryote. Yeast, the organism that makes bread rise and beer ferment, is an example of an unicellular eukaryote. Humans, of course, are an example of a multicellular eukaryote. The major similarities between the two types of cells (prokaryote and eukaryote) are: 1.They both have DNA as their genetic material. 2.They are both membrane bound. 3.They both have ribosomes. 4.They have similar basic metabolism 5.They are both amazingly diverse in forms. The major and extremely significant difference between prokaryotes and eukaryotes is that eukaryotes have a nucleus and membrane-bound organelles, while prokaryotes do not. The DNA of prokaryotes floats freely around the cell; the DNA of eukaryotes is held within its nucleus. The organelles of eukaryotes allow them to exhibit much higher levels of intracellular division of labor than is possible in prokaryotic cells. Additional obvious differences between prokaryotes and eukaryotes include: Size Eukaryotic cells are, on average, ten times the size of prokaryotic cells. Genomic composition and length The DNA of eukaryotes is much more complex (in both size and organisation) and than the DNA of prokaryotes.
Cell Wall Prokaryotes have a cell wall composed of peptidoglycan, a single large polymer of amino acids and sugar. Many types of eukaryotic cells also have cell walls, but none made of peptidoglycan. Prokaryotic cells are relatively simple. Staphylococcus aureus Eukaryotic cells are more complex.
The Nucleus: Control Center of the Cell The nuclear envelope allows selective exchange of materials.
Chromatin consists of DNA and its associated proteins. The nucleolus is the site of ribosome assembly.
The Membrane System of the Cell Membranes consist of a double layer of phospholipids in which proteins are embedded. The cell's membrane system includes the plasma membrane, endoplasmic reticulum, the Golgi complex, and lysosomes.
Chloroplasts & Mitochondria:
Energy Capture and Extraction Chloroplasts are the site of photosynthesis.
Mitochondria produce ATP using energy stored in food molecules.
Vacuoles: Storage and Elimination Many types of plastids store food in plants. Vacuoles serve many functions, including: o support o storage o and elimination of food and wastes. The Cytoskeleton: Shape, Support, and Movement Microfilaments allow cells to change shape and guide the movement of organelles. Helicobacter pylori
Intermediate filaments provide a supportive framework. Association of plectin with myosin II. (a) REF-52 cytoskeleton with actin filaments decorated by myosin S1 (black arrow). An intermediate filament (white arrow) associates with an actin filament bundle via plectin sidearms (10 nm immunogold labeling, white arrowheads). (b-e) Gelsolin-treated cells immunogold labelled for plectin (b,e) or myosin II (d). After actin depletion, intermediate filaments (white arrows) with plectin sidearms (white arrowheads) remain associated with myosin-rich remnants of stress fibers (b, black arrowhead), and also bind to clusters of myosin filaments (c, black arrowheads) and individual myosin bipolar filaments (d, black arrowheads). (e) Nocodazole-treated cell with actin depleted by gelsolin. Individual plectin molecules in lamella (white arrowheads) cross-link myosin filaments (black arrowheads) and their clusters. Some plectin molecules bind to each other (asterisk). Bars, 0.1 µm.
Microtubules help position, anchor, and move organelles and alter the shapes of cells. Microtubules & Mitotic Spindles The mitotic spindle is the structure responsible for the segregation of chomosomes at mitosis. How is the spindle assembled? What factors regulate the dynamics of microtubules during the cell cycle? Microtubules in Cells The following images show the localization of microtubules and DNA in interphase and mitotic Xenopus XL-177 cells. Tubulin (detected with an anti-tubulin antibody) is shown in green; DNA (detected with DAPI) is shown in blue. Images by Claire Walczak.
Microtubules In Vitro This image shows the localization of microtubules and DNA in a mitotic spindle assembled in vitro in a cytoplasmic extract from Xenopus laeviseggs. Tubulin (detected with an anti-tubulin antibody) is shown in red; DNA (detected with DAPI) is shown in blue. Image by Claire Walczak.
People and Projects Claire Walczak and Ann Yonetani are studying the role of kinesin-like proteins in spindle assembly. Lisa Belmont is characterizing a protein that regulates the catastrophe rate of microtubules. Heather Deacon is looking for novel factors that regulate microtubule dynamics. Mimi Shirasu is looking for novel factors involved in spindle assembly. Jennifer Frazier is looking for molecular and structural evidence of microtubules in prokaryotes and Archae. Last updated: March 27, 1996 Questions or comments?? Send mail to swedlow@cgl.ucsf.edu Link to the Mitchison Lab Home Page. Cilia and flagella move the cell or move fluid past the cell.
Cilia from a Hamster's throat The direction of rotation determines whether the bacterial flagella swims or tumbles. Cross-section of cilia