A Tour of the Cell

Topics: Cell, Organelle, Eukaryote Pages: 6 (1287 words) Published: May 26, 2013
Chapter 6: A Tour of the Cell
Cell fractionation – cells are taken apart using a centrifuge (differential centrifugation) and separated into their sub cellular structures Point of Difference| Eukaryotic| Prokaryotic|
Shape/Size| Larger| Smaller|
Complexity| Membrane bounded organelles| No membrane bound organelles| Nucleus| Bounded membrane with DNA| DNA in a region (nucleoid) | Kingdom| Plants, animals, fungi, protists| Bacteria and archaea | Reproduction| Sexual reproduction – mitosis| Asexual reproduction – binary fission| * Similarity: plasma membrane, cytosol, chromosomes, ribosomes|

Surface Area to Volume Ratio
* Metabolic requirements imposes limits on the size of a practical cell * Cells need a large enough surface area to adequately exchange materials * As any cell increases in size, its volume grows proportionately more than its surface area * Area – n2

* Volume – n2
* Where n = linear dimension
* Need for surface area explains the elongated nerve cells * Microvilli – long, thin projections (animal only) that increases SA and not volume Nucleus
* Contains most of genes (other genes are located in mitochondria and chloroplast) * Nuclear envelope (lipid bilayer, double membrane): encloses nucleus and separates its contents from the cytoplasm * Pore complex: regulates entry/exit of proteins, RNAs and macromolecules * Nucleoplasm: the cytoplasm of the nucleus

* Nuclear lamina: a netlike array of protein filaments that maintains the shape of the nucleus * Nuclear matrix: fibres extending throughout the nuclear interior * Nucleolus: rRNA is synthesized from instruction of DNA, proteins imported from the cytoplasm are assembled with rRNA into large and small ribosomal subunits, these subunits exist and assemble into a ribosome Ribosomes

* Complexes made of rRNA and protein and carry out protein synthesis * Pancreas has a lot of ribosomes because these cells specialize in protein secretion * Free ribosomes: in cytosol, proteins that are made function within cytosol (e.g. enzymes that catalyze the first steps of sugar breakdown) * Bound ribosomes: attached to nuclear envelope or ER, the proteins they make are inserted into the membranes, used for packaging within certain organelles such as lysosomes or for export from the cell Endomembrane system

* Synthesis of proteins and their transport into membranes and organelles or out of the cell, metabolism and movement of lipids and detoxification of poisons * Transport via vesicles
* Movement of lipids and proteins through vacuoles and organelles * Includes: nuclear envelope, ER, Golgi apparatus, lysosomes, vacuoles, plasma membrane Endoplasmic reticulum
* Extensive network of membranes that accounts for more than half the total membrane in eukaryotes * Network of membranous tubules and sacs called cisternae * ER lumen: inside the ER and separated from cytosol

* Smooth ER: lacks ribosomes
* Synthesis of lipids (oils, phospholipids and steroids), produces sex hormones (e.g. testes and ovaries are rich in SER), metabolism of carbohydrates, detoxification of drugs and poisons, stores calcium ions * Rough ER: studded with ribosomes on cytoplasmic side

* Cells secrete proteins produced by ribosomes attached to the RER * Glycoproteins – a secretory protein that is synthesized in the RER that has a carbohydrate/sugar covalently bonded to a protein * Secretory proteins depart from ER in transport vesicles * Membrane factory for the cell; adds membrane proteins and phospholipids to its own membrane Golgi Apparatus

* Transport vesicles buds from ER and travel to Golgi
* Centre of manufacturing, warehousing, sorting and shipping * Products of the ER are modified and stored and then exported * Flattened membranous sacs called cisternae which separates internal space from cytosol and has a polarity * Cis face – faces the ER,...
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