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January 10, 2014 The basics.docx

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Natural Science
NATS 1610
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Living Body: The basics -the living body begins at fertilization when one sperm fertilizes an egg • Fertilization enables the combination of DNA from 2 parents (creating genetic diversity) • The fertilizes egg – Zygote – cleaves to increase cell numbers -the metabolic requirements set up an upper limit to the size of a single cell • As a cell increases in size its volume increases faster than its surface area (SA) • The SA of a cell is its cell membrane o Want to have more cell membrane for efficient nutrient waste diffusion -Cells divide instead of growing larger to LIMIT their surface area to volume ratios (SA/Vol ratio) • Cells get around this problem by: dividing, getting thinner, forming microvilli, storing nutrients -the cell cycle describes the life events of a cell • Stages (phases) of the cell cycle o G1: cell growth o S: duplication of the DNA o G2: forming materials required cell division o M: mitosis – nuclear – formation of 2 daughter cells, identical to parent cell • Interphase: G1 + S + G2 -Inside the cell, DNA molecules associate with various proteins • Not dividing – chromatin o DNA is long, thin o Wrapped around histone proteins • When dividing – chromosome o Coiled tightly o Shortened to form a chromosome o Both are made of the same materials, but are called different things at different times • packaging -During the S phase: duplication of DNA (one DNA molecule turns into 2) -chromosome structure and terminology • One duplic
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