Bio_Lecture_4

Bio_Lecture_4 - Lecture 4: Cell structure The Organization...

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Unformatted text preview: Lecture 4: Cell structure The Organization of Life Characteristics of life Life: You know it when you see it, but it is hard to define life (like beauty) Characteristics of life 1. Complexity and organization 2. Respond to environment (homeostasis) 3. Growth and metabolism 4. Reproduction/heredity (passing on genetic information) 5. Evolve (organisms slowly change/adapt to the environment) None of these alone defines life, but together, they are not a bad definition Cell theory Simple statements, powerful concept: First proposed in 1838: o All living things are made of cells o Cells are the smallest living things the basic unit of life Can take a cell out of an organism, and culture it to maintain life o Processes inherent to life occur within cells Metabolism Heredity (ancestors/descendents) o All existing cells come from preexisting cells The size of cells How big is a cell? o Which cell though? o Average range: from 1 m to 1mm In humans o Largest human cell = ovum o Smallest human cell = sperm Cell size limits What limits size? Transport substances into and out of cells Read pages o Transport limited by surface area of cell o Need for energy etc. determined by volume Surface area to volume ration Decreases as size increases Consequence? o Limits the size of the cell Figure 4.1 10 fold increase in radius (r), 100 fold increase in surface area (4 r 2 ), 1000 increase in volume (4/3 r 3 ) What keeps cells small Cell types There are two basic cell types: o Prokaryotic o Eukaryotic These have vastly different architecture Simple definition: o Prokaryotic absence of a membrane bound nucleus (DNA just compacted into a specific region, not surrounded) o Eukaryotic: presence of a membrane bound nucleus Prokaryotic cells Lack nucleus, and no internal membrane system Divided into two Domains: o Bacteria (also called Eubacteria) o Archaea (formerly called Archaebacteria) Tend to be small (1-10 m) Dominant life forms on the planet o Biomass (very great mass when added together) o Diversity Consider similarities of structure briefly Prokaryotic cell structures Circular DNA compacted into nucleoid o Not contained in membrane bounded structure Cytoplasm : semi-fluid matrix that fills cell o Soluble cytosol and suspended particles No membrane bounded organelles Ribosomes the universal organelle (every/any form of life has ribosomes!) Cell wall made of carbohydrates Plasma membrane phospholipid bilayer o Regulates what goes in/out of the cell Pili (looks like hair)...
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Bio_Lecture_4 - Lecture 4: Cell structure The Organization...

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