2–13 Polymerization of tubulin subunits into microtubules occurs with an increase in the orderliness of the subunits. Yet tubulin polymerization occurs with an increase in entropy (decrease in order). How can that be?
2–14 A 70-kg adult human (154 lb) could meet his or her entire energy needs for one day by eating 3 moles of glucose (540 g). (We do not recommend this.) Each molecule of glucose generates 30 molecules of ATP when it is oxidized to CO2. The concentration of ATP is maintained in cells at about 2 mM, and a 70-kg adult has about 25 liters of intracellular fluid. Given that the ATP concentration remains constant in cells, calculate how many times per day, on average, each ATP molecule in the body is hydrolyzed and resynthesized.
2–15 Assuming that there are 5 × 1013 cells in the human body and that ATP is turning over at a rate of 109 ATP molecules per minute in each cell, how many watts is the human body consuming? (A watt is a joule per second.) Assume that hydrolysis of ATP yields 50 kJ/mole.
2–16 Does a Snickers™ candy bar (65 g, 1360 kJ) provide enough energy to climb from Zermatt (elevation 1660 m) to the top of the Matterhorn (4478 m, Figure Q2–3), or might you need to stop at HÖrnli Hut (3260 m) to eat another one? Imagine that you and your gear have a mass of 75 kg, and that all of your work is done against gravity (that is, you are just climbing straight up). Remember from your introductory physics course that where g is acceleration due to gravity (9.8 m/sec2). One joule is 1 kg m2/sec2.
What assumptions made here will greatly underestimate how much candy you need?
Figure Q2–3 The matterhorn (problem 2–16). (Courtesy of Zermatt Tourism.) 2–17 In the absence of oxygen, cells consume glucose at a high, steady rate. When oxygen is added, glucose consumption drops precipitously and is then maintained at the lower rate. Why is glucose consumed at a high rate in the absence of oxygen and at a low rate in its presence?
PaNel 2–1: Chemical bonds and Groups Commonly encountered in biological Molecules
Carbon has a unique role in the cell because of its ability to form strong covalent bonds with other branched trees ringscarbon atoms. Thus carbon atoms can join to form: also written as also written as also written as
A covalent bond forms when two atoms come very close together and share one or more of their electrons. In a single Carbon and hydrogen combinebond, one electron from each of the two atoms is shared; in together to make stablea double bond, a total of four electrons are shared.
compounds (or chemical groups)Each atom forms a fxed number of covalent bonds in a called hydrocarbons. These aredefned spatial arrangement. For example, carbon forms four nonpolar, do not formsingle bonds arranged tetrahedrally, whereas nitrogen forms hydrogen bonds, and arethree single bonds and oxygen forms two single bonds arranged generally insoluble in water.
as shown below.
cannot rotate freely HH around the bond axis.
This restriction is a
Double bonds exist and have a different spatial arrangement.
major infuence on the three-dimensional shape of many macromolecules. methane methyl group
The carbon chain can include double Alternating double bonds in a ring bonds. If these are on alternate carbon can generate a very stable structure. CH2 atoms, the bonding electrons move within the molecule, stabilizing the structure by a phenomenon called CH2 resonance. HH
H HH H the truth is somewhere between H2C these two structures HH often written as part of the hydrocarbon “tail” of a fatty acid molecule