CHAPTER 2CHAPTER 2

The Nature of Molecules

Which Elements Are Most Significant To Biologists?Which Elements Are Most Significant To Biologists?

Six of these plus a few other trace elements

Figure 2.3 Nitrogen deficiency

All plants need nitrogen to grow. Do you know why?

Heavy isotopes are used

As biological Tracers

Do you know Why?

ISOTOPESISOTOPES

3H hydrogen (tritium)

14C carbon

32P phosphorous

35S sulfur

131I iodine

Figure 2.8 The Tokaimura nuclear accident

RADIOACTIVE TRACERSRADIOACTIVE TRACERS

Examples of how biologists use isotopes to trace specific molecules

AUTORADIOGRAPHY - locate specific molecules within cells w/ X-ray film

SCINTILLATION COUNTER - follow and chart metabolic activity within cells

PET SCAN - Positron Emission Tomography reveals location of intense chemical activity

Figure 2.6 Using radioactive isotopes to study cell chemistry

Figure 2.4 Goiter

Iodine is used to trace thyroid problems

Figure 2.5 Two simplified models of a helium (He) atom

Figure 2.9 Energy levels of an atom’s electrons

Figure 2.11 Electron orbitals

Figure 2.10 Electron configurations of the first 18 elements

IONIC BONDSIONIC BONDS

the transfer of electrons loss of electron(s) cation

gain of electron(s) anion dissociate in aq. soln.

Figure 2.15 A sodium chloride crystal

COVALENT BONDSCOVALENT BONDS

sharing of electron pairs

strong bonds in aqueous solution

The most common bond in organic molecules

COVALENT BONDSCOVALENT BONDS

sharing of electron pairs strong bonds in aqueous solution

NONPOLAR COVALENT BOND

CH4

C & H equal affinity for electrons

Figure 2.12x Methane

What is the shape of this molecule?

Why does this molecule havethis shape?

COVALENT BONDSCOVALENT BONDS

POLAR COVALENT BOND

H2O

ELECTRONEGATIVITY each atom in polar bond has partial

charge creating opposite poles or polarity

remember O and N bonded to H

Figure 2.13 Polar covalent bonds in a water molecule

HYDROGEN BONDSHYDROGEN BONDS

weak bonds

bonds between polar molecules or polar parts of large macromolecules.

H-bonds give macromolecules their 3-D shape.

water forms hydration shells hydration shells around ions

HYDROGEN BONDSHYDROGEN BONDS

You must understand hydrogen interactions to understand biochemistry

You must understand hydrogen interactions to understand biochemistry

Hydrophobic InteractionsHydrophobic Interactions

nonpolar w/ nonpolar

squeeze out water

Important in shaping and organizing the molecules of life

Most Common Bond in LifeCovalent Bond

Electrons are shared Overlapping orbitals &

lack of charge strong in aqueous

solution

Covalent bonds are not all created equal

Nonpolar Covalent atoms share electrons equally

Example: O2 CH4

Polar Covalent Atoms shared electrons unequally Slightly positive and slightly negative pole

H2O NH3

Hate hanging out w/ water

Love hanging out w/ water

Why?????

Hydrogen Bonds

Hydrogen Bond

Technically these are Fake Bonds

Interactions between polar molecules

molecules with slightly charged poles can hydrogen bond

sticky

sticky

sticky

Hydrogen bonds give water many

special properties

sticky

Effects onTemperature

Great solvent

Also very important Determines 3D shape of many organic molecules!!!!!

The Medium of Life

hydrophobicVs.

hydrophilic

Biochemistry is wet chemistry

Only molecule found in all three states on the surface of the earth

Hydrogen bonds give water many

special properties

sticky

Hydrogen bonds help determine the

shape of macromolecules

Review of some helpful terms

Atoms Molecules Macromolecules

Protons Functional Groups Carb’sNeutrons Nonpolar LipidsElectrons Polar Proteins

Nucleic AcidsIons InorganicIsotopes Organic

How are these used?

How do these How do these differ?

differ?

An the most important Love/Hate Relationship

on earth

Hydrophobic

Hydrophilic

3-D shape is essential to structure/function

Unnumbered Figure (Page 38) Chemical reaction between hydrogen and oxygen

Figure 2.20 Photosynthesis: a solar-powered rearrangement of matter

The bubbles are evidence

that ????

Is taking place

Can you fill in the ?????