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The Living Body 1 - The Basics.docx
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Department
Natural Science
Course
NATS 1610
Professor
Barbara Czaban
Semester
Winter

Description
NATS 1610 WINTER TERM L20 – Forming the 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 fertilized egg – zygote – cleaves to increase cell numbers − Human adults  10 to 65 to 100 trillion living cells The METABOLIC REQUIREMENTS set 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) − Smaller objects have a greater ratio of surface area to volume • The SA of a cell is its cell membrane − Want to have more cell membrane (SA) for efficient nutrient waste diffusion Cells divide instead of growing larger to LIMIT their Surface Area to Volume Ratios • As cells gets larger, Volume increases faster than SA (of cell membrane) − Less surface area per unit volume, thus, less cell membrane for nutrient/waste diffusion • Cells get around this problem by: − Dividing (SA increases as Volume stays constant) − Getting thinner (SA increases as Volume stays constant) − Forming microvilli − Storing nutrients – i.e., chicken egg can be bigger The CELL CYCLE describes the life events of a cell • Stages (phases) of the Cell Cycle − Interphase: G1 + S + G2 o G1 – period of cell growth before the DNA is duplicated (Interphase begins in daughter cells) o S – period when the DNA is duplicated (that is when chromosomes are duplicated) o G2 – period after DNA is duplicated; cell prepares for division (Interphase ends in parent cell) − M – cytoplasm divided (mitosis) o Prophase-> Metaphase-> Anaphase-> Telophase Inside the cell, DNA molecules associate with various proteins • Not dividing – chromatin − DNA is long, thin − Wrapped around histone proteins • When dividing –
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