Biocompuestos Atomos y Biomoleculas

8/6/2019 Biocompuestos Atomos y Biomoleculas

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Biocompuestos, atomos y

biomoleculas







Difieren en el número de

neutrones



















A living cell is composed of a restricted set of

elements, four of which (C, H, N, and O) makeup nearly 99% of its weight.

Nearly all of the molecules in a cell are carbon compounds,

which are the subject matter of organic chemistry.



CARBONO

Carbon is outstanding among all the elements on earth for itsability to form large molecules; silicon is a poor second.

The carbon atom, because of its small size and four outer-shell

electrons, can form four strong covalent bonds with other atoms.

it can join to other carbon atoms to form chains and rings and

thereby generate large

and complex molecules with no obvious upper limit to their size.

The other abundant atoms in the cell (H, N, and O) are also small

and able to make very strong covalent bonds.







The best evidence for this comes from laboratory

experiments.

If mixtures of gases such as CO2, CH4, NH3, and H2 are

heated with water and energized by electrical discharge or

by ultraviolet radiation.

Among these products are compounds, such as hydrogen

cyanide (HCN) and formaldehyde (HCHO), that readily

undergo further reactions in aqueous solution

Most important, representatives of most of the major

classes of small organic molecules found in cells are

generated, including amino acids, sugars, and the

purines and pyrimidines required to make nucleotides.



As competition for the raw materials for

organic syntheses intensified, a strong

selective advantage would have beengained by any organisms able to utilize

carbon and nitrogen atoms (in the form of

CO2 and N2) directly from the

atmosphere.

But while they are abundantly available,

CO2 and N2 are also very stable. It

therefore requires a large amount of

energy as well as a number of

complicated chemical reactions to convert

them to a usable form - that is, intoorganic molecules such as simple sugars.



In the case of CO2 the major mechanism that evolved toachieve this transformation was photosynthesis, in which

radiant energy captured from the sun drives the

conversion of CO2 into organic compounds.

The interaction of sunlight with a pigment molecule,

chlorophyll, excites an electron to a more highly energized

state. As the electron drops back to a lower energy level,

the energy it gives up drives chemical reactions that arefacilitated and directed by protein molecules.



One of the first sunlight-driven reactions was probably the

generation of "reducing power." The carbon and nitrogen

atoms in atmospheric CO2 and N2 are in an oxidized and

inert state.

A typical covalent bond in a

biological molecule has an energy

of 15 to 170 Kcal/mole, depending

on the atoms involved. Since the

average thermal energy at body

temperature is only 0.6 kcal/mole,even an unusually energetic

collision with another molecule will

leave a covalent bond intact.

Certain simplecombinations of atoms -

such as the methyl (-CH3),

hydroxyl (-OH), carboxyl (-

COOH), and amino (-NH2)

groups - recur repeatedly

in biological molecules.



The atomic weights of H, C, N, and O are 1, 12, 14, and

16, respectively. The small organic molecules of the cell

have molecular weights in the range 100 to 1000 and

contain up to 30 or so carbon atoms.

They are usually found free in solution, where some of

them form a pool of intermediates from which large

polymers, called macromolecules, are made. They are

also essential intermediates in the chemical reactions

that transform energy derived from food into

usable forms (discussed below).



The most abundant substance of the living cell

is water. It accounts for about 70% of a cell'sweight, and most intracellular reactions occur

in an aqueous environment.

Life on this planet began in the ocean, and the

conditions in that primeval environment put a

permanent stamp on the chemistry of living

things.

All organisms have been designed around the

special properties of water, such as its polar

character, its ability to form hydrogen bonds,

and its high surface tension.

Water will completely surround polar

molecules, for example, while tending to push

nonpolar molecules together into larger

assemblies.

El Agua



















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Biocompuestos Atomos y Biomoleculas