lect20_Essential_cell

lect20_Essential_cell - The Essentials of a Cell Chromosome...

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1 The Essentials of a Cell 1 μ m Chromosome •But first more features of cell membranes! How do large / charged materials enter cells? ± Passive transport (diffusion) through a membrane protein – Channels: ion channels, aquaporins – Facilitated Diffusion : specific carriers for amino acids, sugars. • Carrier changes tertiary shape as it moves substance across. Hydrophilic interior. • Solute is still moving down its concentration gradient! Rate of entry into cell Solute concentration on outside of membrane Which of the drawings above represents the results you’d expect if the material were moving by simple diffusion? A. B.
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2 Cells can concentrate materials inside themselves ± Diffusion REDUCES differences between the inside and outside of cells – Entropy (disorder) is favored (2nd law of thermodynamics), and is increased by diffusion. ± Passive transport via a membrane protein also reduced concentration gradients. ± So how does a cell maintain specialized internal conditions that differ from the external environment? Active Transport: ± Requires energy input ± Moves solute from Low to High concentration. – A transmembrane protein can be used as a “pump” – An integral protein can act as a “shuttle” moving materials across the membrane ± The cell must expend energy to organize solutes! * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ******* ************ ************ *** **** ******** **** ***** **** What transport method could account for the pattern observed below? * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ******* ************ ************ *** **** ******** **** ***** **** What transport method could account for the pattern observed below? A. Simple diffusion
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lect20_Essential_cell - The Essentials of a Cell Chromosome...

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