BIO1140 Chapter 4 - Cells and their Organelles

BIO1140 Chapter 4 - Cells and their Organelles - Cellular...

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Cellular Biology Chapter 4 – Cells and Organelles Properties and strategies of cells All organisms are Eukaryotes, Eubacteria, Archaea Based on structural differences cells were originally divided into eukaryotes (all other living cells) and prokaryotes (bacteria) - Eukaryotes: have a true membrane bound nucleus - Prokaryotes: do not have a membrane bound nucleus (are an evolutionary earlier form of life) Based on molecular and biochemical criteria (the sequencing of rRNA’s) we know that prokaryotes can be further subdivided into Archaea and Eubacteria (includes bacteria and Cyanobacteria) - Archaea: similar to Eubacteria in structure but different in terms of molecular and biochemical composition. Archaea are modern descendants of an evolutionary ancient form of prokaryote that differed fundamentally from the ancestors of present Eubacteria. Methanobacteria - convert carbon dioxide and hydrogen into methane Sulfobacteria - can grow into salty environments Thermacidophiles - thrive in acidic hot springs They differ fundamentally and are therefore separate groups (domains) Similarities between them include - RNA polymerase - Sensitivity to specific inhibitors of protein - Nucleic acid synthesis - Presence/Absence of organelles - Differences due to rRNA’s Cells Come in Many Sizes and Shapes Come in a variety of sizes, shapes, and forms Prokaryotic cells: 1-5 um in diameter Eukaryotes (higher plants cells/ animal cells): 10 – 50 um in diameter Factors which limit cell size o Surface Area/ Volume Ratio - Main constraint - Surface area determines the amount of exchange which can occur (amount of membrane available for uptake/ excretion) - Internal volume determines the amount of nutrients that will have to be imported/ wastes that will be excreted
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Cellular Biology Chapter 4 – Cells and Organelles - As cell size increases its surface area does not keep pace with its volume Exchange therefore problematic (not enough surface area to keep up with demands of cell for nutrients/wastes) - Surface area is increased by the inward folding of cell membrane ---- Example: Microvilli Picture on pg. 75 o Diffusion Rates of Molecules - Limited by diffusion rates for molecules of various sizes within the cell - Significant for proteins an nucleic acids - Cytoplasmic Streaming: used to get around this limitation. It is a process that involves active moment and mixing of cytoplasmic contents rather than diffusion ---- Example: blood cells are smaller in order to allow for oxygen to diffuse cross fast/efficiently o Need for Adequate Concentrations of Reactants and Catalysts - Limit imposed in order to maintain adequate concentrations of the essential compounds/ enzymes for the processes which the cells must carry out - Frequency at which random collisions occur (in order for particles to bind) increases if the concentration of particles increases - As cell increases the number of particles must increase by 8 fold Eukaryotic cells use organelles to compartmentalize cell function
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This note was uploaded on 06/17/2008 for the course BIO 1140 taught by Professor Fenwick during the Winter '07 term at University of Ottawa.

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BIO1140 Chapter 4 - Cells and their Organelles - Cellular...

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