Cell Structure and Functions

Topics: Cell, Organelle, Cell membrane Pages: 6 (1156 words) Published: August 7, 2013
CELL STRUCTURE AND FUNCTOIN

* The Cell Theories 3 major principles:
* Cell is the basic unit of life
* All organisms consist of one or more cells
* New cells are created when existing cells divide
* Most cells contain 4 common features:
* A flexible plasma membrane that surrounds the cell
* A thick fluid called cytosol that fills their interior * The nucleic acid DNA
* Protein structures called ribosomes, which are responsible for making other proteins important for various cell functions * Plasma membranes:
* Consist of a phospholipid bilayer-
* Two layers of phospholipids arranged so that the hydrophilic heads” in each layer face outwards
* Are fluid: phospholipids are able to move, usually side to side, within a layer * Plasma membranes contain many other macromolecules:
* A variety of proteins, lipids, and carbohydrates are embedded in a plasma membrane * Proteins have many functions in the membranes:
* Channels that help the passage of ions or molecules
* Enzymes, which control chemical reactions
* Anchors for other cell structures, such as the cytoskeleton * Receptors, which bind molecular signals that are important for cell-to-cell communication * Cholesterol helps maintain membrane fluidity

* Carbohydrates are usually attached to membrane proteins or lipids * They often act as markers that aid in cell recognition * Human ABO blood types are determined by carbohydrates present on red blood cell membranes * Plasma membranes are selectively permeable

* Only certain substances can pass through a membrane
* Generally, a small and uncharged substance can cross unaided * Substances can diffuse across a plasma membrane
* Atoms and molecules are in constant motion
* Diffusion is the net movement of atoms or molecules from an area of high to an area of low concentration * Thus, the direction of net movement follows the concentration gradient * The diffusion of water across a selectively permeable membrane is called osmosis * Two basic cell types:

* Prokaryotic
* Simply organized because they lack internal structures call membrane bound organelles * Lacks a nucleus which is a membrane bound organelle * Generally unicellular
* Ex) bacteria
* Main structures:
* Cell wall- additional covering for cell besides plasma membrane. Also more rigid than membrane * Nucleoid: where DNA is located. Not a true nucleus because DNA is not enclosed in plasma membrane * Flagellum: protein structure used for cell movement. Different structures than a eukaryotic flagellum * Eukaryotic

* True nucleus
* More complex organization because they each contain a nucleus an a variety of other organelles * Can be uni-cellular or multicellular
* Ex) animals, plants, and fungi
* Function: store and protect most of the DNA present in the cell * Basic structure:
* Surrounded by a nuclear envelope consisting of two layers of plasma membrane * Within the nuclear envelope is a layer of protein fibers called the nuclear lamina * Nuclear pores assist with transport into or out of the nucleus * The Endomembrane System:

* Group of membrane-bound organelles that often work together to make and transport biological macromolecules, like a molecule factory * Some organelles help to break down macromolecules * Organelles in the endomembrane system include: * Smooth endoplasmic reticulum

* Consists of plasma membrane folds that are smooth looking in appearance * Makes lipids such as phospholipids and steroids * In muscle cells: store calcium ions to aid muscle contraction...
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