1 11/9/2015 atoms. 2 11/9/2015 major atoms in biology n c h o n s p n # of atoms in outer shell –...

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ATOMS

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Major atoms in biology

Major atoms in biology

C H O N S P# of atoms in outer shell–H, 1–C 4–N, P 5–O, S 6

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C

N P

S

Atoms are sociable

HO

HChemical bonds

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Chemical bonds.....Chemical bonds.....

CovalentNoncovalent

Strong

Puny but important

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Atoms attached via shared electrons in outer shells

H O HH HO

Covalent bonds

CC

C

C C

C

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e.g. CH3-CH3, ethane

Covalent bonds

• stable (strong)

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Covalent bond cleavage

CH3:CH3--> CH3 + CH3

Reactant Products

(Methyl radicals)

(EthaneCH3-CH3)

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Covalent bond cleavage

CH3:CH3--> CH3 + CH3Reactant Products

E = +83 kcal/mol

E is the difference between the energy of reactants and products

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Covalent bond strengths

High bond strength confers stability

0-H 110

C-H 99

C-C 83

C=C 146

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Double bonds restrict rotation

H

H

H

H

Molecule is planar (flat)

e.g. Ethylene (CH2=CH2)

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Covalent bonds are orientated in space

H

H

O104.5 deg

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Covalent Non-covalent

1-5

• 4 kinds.....

Bond strength(kcal/mol) 50-195

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Non-covalent bonds

• Hydrogen bonds

• ionic bonds

• van der Waal's interactions

• hydrophobic interactions

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Non-covalent bonds

• Hydrogen bonds

e.g. in liquid water

oxygen,

hydrogen,

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Hydrogen bond

In liquid water

Each molecule may be H-bonded to

4 others. Bonds are transient

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Typical Hydrogen bonds

H Oor

H N

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Ionic bonds

Non-covalent bonds (cont.)

Result of attraction between + and - charges of ionized atoms

e.g. Na+ Cl-

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Ionic bonds

NaCl dissolved in H2O

Na+ Cl

Note the tight shells of water molecules

Hydrated diameter of ions is important in permeability

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Van der Waals interactions

Non-covalent interactions (cont.)

Due to electron fluxes any atom can become a

transient dipole

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Van der Waals interactions

Non-covalent interactions (cont.)

2 atoms in van der Waals contact

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Van der Waals interactions

Atoms are very close

But not close enough so that their electron shells overlap. If so, they repel each other

You’re disgusting!

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Our next AttractionOur next Attraction

HydrophobiHydrophobiaaStarring a cast of thousandsof greasy characters

Hydrocarbons

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Non-covalent interactions (cont)

Hydrophobic interactions

CH

HCH

HCH

HCH

HCH

HH

Hydrocarbons

CH

HCH

HCH

HH

Combined hydrophobic and van der Waals interactions

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O

NH3 O

CH3

CH2

NH2

CH2

O H C

CH2 C

OCH2 CH2

CH2

CHCH3 CH3

CH3 CH CH2

Bonds at work, H-bonds, ionic

and vd Waals+ hydrophobic bonds

Protein

Protein

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How many water molecules in a teaspoonful?

As many as the teaspoonfuls of water present in the Atlantic Ocean

Trivia Time

A one, a two, a three...

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An everyday protein molecule, hemoglobin

All your hemoglobin alpha chains are

identical with 574 amino acids chained

together in precise sequence

In the past second you have just assembled 400 million million of them

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