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Biological_chemistry tb notes

Biological_chemistry tb notes - J Voltzow Biol 141...

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J. Voltzow Biol. 141 BIOLOGICAL CHEMISTRY Water and its properties Water molecule Shaped roughly like a V o O is more electroneg. Than hydrogen o The electrons of the cov. Bonds spend more time closer to O than to H = Polar Bonds Polar Polar Molecule – two ends of the molecule have opposite charges - O region of the molecule has a partial (-) charge and the H have a partial (+) charge (+) H of one molec. is attracted to the slightly (-) O of a nearby molec. Polar Cov. Bond- depends on the relative electroneg. of the two atoms o Ex: Bonds b/w the O and H atoms of water molecule = polar o O is one of the most electroneg. – attract shared electrons more strongly than H o O and H – the electrons spend more time near the O nucleus than the H nucleus Have neg. charge, the unequal sharing of electrons in a H2O causes the O atom to have partial neg. charge and H atom to have partial positive charge (delta) Hydrogen bonds between molecules H bonds = fragile, form, break, re-form Structural organization Water molecs. stay close to each other Forms when H atom covalently bonded to one electroneg. atom is also attracted to another electroneg. atom Unusual properties of water Common in all three states Very cohesive H bonds hold the substance together H bonding contributes: o Transport of water o Dissolved nutrients against gravity in plants o Ex: water from the roots reaches the leaves through a network of water-conducting cells water evaporates from a leave H bonds cause water molecs. Leaving the veins to tug on molecules farther down
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the upward pull transmitted through the water-conducting cells all the way to the roots Surface tension- a measure of how difficult it is to stretch or break the surface of a liquid o Measure of how difficult it is to stretch or break the surface of a liquid o Water = greater surface tension o Ex: observe the surface tension of water by slightly overfilling a drinking glass = water will stand above the rim Moderation of Temperature o Water can absorb or release a relatively large amt. of heat with only slight change in its own temp o Calorie – amt. of heat it takes to rise the temp of 1 g of water releases when it cools by 1C Amt. of heat that 1g of water releases when it cools by 1C High specific heat Amt. of heat that must be absorbed or lost for 1 g of that substance to change its temp. by 1 C Specific heat of water – 1 calorie per gram per degree of Celsius <1 cal/g/C> o Ex: ethyl alcohol – SH of 0.6 cla/g/C; only 0.6 cal req to raise the temp of 1 g of ethyl alcohol 1C Water will change its temp. less when it absorbs or loses a given amt. of heat Water resists changing its temp. – when it does change its temp, it absorbs or loses a large quant. Of heat for each degree of change
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