Exam1 - Chapter 2: Cell Chemistry and Biosynthesis The...

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Chapter 2: Cell Chemistry and Biosynthesis The chemical components of a cell Cells are made form a few types of atoms o Atomic weight/molecular weight = its mass relative to H atoms o Mass of an atom/molecule is specified in Daltons (~mass of 1 H atom) o Avogadro’s number 6x10 23 o Living organisms are only made out of C, H, N and O The outer most electrons determine how atoms interact o Protons and neutrons are found tight bound in the center, only when radioactive decay (an extreme condition) is when it can change o Electron shell – laws dictate that electrons in an atom can exist only in a certain states [orbitals] and the strict limitation to the number of electrons can be accommodated in an orbital Electrons closest on average to the (+) nucleus are attracted the most strongly to it and occupy the inner most 2 nd shell – holds 8 electrons 3 rd shell – holds 8 electrons 4 th / 5 th shells – holds up to 18 electrons o H only has 1 electron and half of its shell filled Highly reactive o Unfilled shell is less stable than a filled one Atoms with incomplete outer shells tend to interact with other atoms This forms 2 different type of chemical bonds Ionic bond – electrons are donated by one atom to another Covalent bond – electrons is shared unequally, with partial transfer btwn atoms o One is more electronegative than the other o H atom tends to form covalent bonds with other atoms (polar) o Valence – the number of electrons that an atom must acquire or lose to fill its outer shell Covalent bonds form by sharing of electrons o A molecule is defined as a cluster of atoms held together by covalent bonds o Bond strength is measured by the amount of energy that can break the bond kcal/mole Amount of energy to raise the temperature of one liter of water by 1*C
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o Breaking/making covalent bonds are extremely violent and it needs to be controlled by highly specific catalyst enzymes o Noncovalent bonds are much weaker o O - 2 covalent bonds o N- 3 covalent bonds o C- 4 covalent bonds There are different types of covalent bonds o Single bonds – sharing of 2 electrons, 1 donated by each atom, can rotate o Double bonds – sharing of 2 + electrons, shorter and stronger than single bonds, prevents rotation o Polar covalent bonds – covalent bonds in which the electrons are shared unequally (H2O) Permanent dipoles – allows molecules to interact through electrical forces Electrostatic interaction – molecule encounters a second molecule with a complementary setoff charges Atoms often behaves as if it has a fixed radius o Van der waal radius – radius of the electron cloud at which strong repulsive forces prevent a closer approach of any 2 nd non-bonded atom Amount of repulsion increase very steeply as 2 atoms approach each other closely o Van der waal attraction – very weak! Once it pass the radius it has a small weak attractive force where the forces are balanced to
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This note was uploaded on 04/09/2010 for the course BIO 57290 taught by Professor Huke during the Spring '10 term at University of Houston.

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Exam1 - Chapter 2: Cell Chemistry and Biosynthesis The...

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