The Start of Cell Respiration

Electronegativity

• The Sharing Game– Some are better at sharing and others are not– Elements are the same way– Atoms sharing electrons is what is creating the bond– Some atoms want to give away their electrons,

some will share equally, and some will have unequal sharing

– Electronegativity: the ability an atom has to attract other electrons

• You don’t necessarily want to play with the kid who didn’t want to share their toys because it brought up a negative feeling of losing something you liked

• What makes one atom more electronegative than another?– Atomic structure

As you move down a group, what happens to size of atom?

Gets bigger…valence electrons are getting farther away from nucleus

The nucleus is positive and will pull electrons in. If an electron is far away the pull is not as strong to keep it in.

Which has a higher electronegativity? Why?

So therefore as you move down a group, the less electronegative the atom is

As you move across a row, what happens to the electronegativity?

The atom is not getting bigger…all have the same outer electrons BUT the number of protons in the nucleus INCREASES so it will attract electrons more and will want electrons from other atoms

Li FWhich is more electronegative?

Noble Gases are the exception because their outer electron shell is FULL!

Free Energy• Life requires free energy…but where do we

get that?

• How do we utilize that free energy?

COVALENT BONDS!!!! (Chemical Energy Potential energy)

Metabolism

Free Energy

• Why do some bonds have more stored energy than others?

• When the difference in electronegativity is high bond energy is high– C-H bond– C-O bond

Electronegativity between atoms bonded

Free Energy and Bonds

• Atoms do whatever they can to reduce their energy (be stable)

• Reach this best by sharing (or transferring) electrons…but not being too clingy (the 2 nuclei repel each other) or too distant (not sharing enough)

High and Low Free Energy Bonds

• Which has higher free energy/transfer of electrons:

Harvesting stored energy

• Glucose is the model– catabolism of glucose to produce ATP

C6H12O6 6O2 ATP 6H2O 6CO2+ + +

RESPIRATION = making ATP (& some heat)by burning fuels in many small steps

CO2 + H2O + ATP (+ heat)

ATP

glucose

glucose + oxygen energy + water + carbondioxide

resp

iratio

n

O2

+ heat

enzymesATP

How do we harvest energy from fuels?

• Digest large molecules into smaller ones– break bonds & move electrons from one

molecule to another• as electrons move they “carry energy” with them• that energy is stored in another bond,

released as heat or harvested to make ATP

e-

+ +e-

+ –loses e- gains e- oxidized reduced

oxidation reduction

redox

e-

How do we move electrons in biology?

• Moving electrons in living systems– electrons cannot move alone in cells

• electrons move as part of H atom• move H = move electrons

pe

+

H

+H

+ –loses e- gains e- oxidized reduced

oxidation reduction

C6H12O6 6O2 6CO2 6H2O ATP+ + +

oxidation

reductionH e-

Coupling oxidation & reduction• REDOX reactions in respiration

– release energy as breakdown organic molecules• break C-C bonds• strip off electrons from C-H bonds by removing H atoms

– C6H12O6 CO2 = the fuel has been oxidized

• electrons attracted to more electronegative atoms

– in biology, the most electronegative atom? – O2 H2O = oxygen has been reduced

– couple REDOX reactions & use the released energy to synthesize ATP

C6H12O6 6O2 6CO2 6H2O ATP+ + +

oxidation

reduction

O2

Oxidation & reduction• Oxidation

– adding O– removing H – loss of electrons– releases energy– exergonic

• Reduction– removing O– adding H – gain of electrons– stores energy– endergonic

C6H12O6 6O2 6CO2 6H2O ATP+ + +

oxidation

reduction

REDOX REACTIONS

• LEO says GER– (lose electrons oxidized)– (gain electrons reduced)

REDOX

• Side Note: Oxygen is one of the best oxidizing agents

Moving electrons in respiration• Electron carriers move electrons by

shuttling H atoms around– NAD+ NADH (reduced)

– FAD+2 FADH2 (reduced)

+ Hreduction

oxidation

PO–

O–

O

–O

PO–

O–

O

–O

CC

O

NH2

N+

H

adenine

ribose sugar

phosphates

NAD+

nicotinamideVitamin B3niacin

PO–

O–

O

–O

PO–

O–

O

–O

CC

O

NH2

N+

HNADH

carries electrons as a reduced molecule

H

Cellular Respiration

• In each step, glucose will lose electrons (redox reactions)

• Each e- travels with a H passed to NAD+

– NAD+ is an e- carrier– NAD+ easily cycles from reduced to oxidative

state– DEHYDROGENASES remove H atoms

(oxidize) and add the H to NAD+

What do you remember?

• What in the equation is oxidized and reduced?

• Fe + Cu2+ Fe2+ + Cu

What do you remember?

• What are the 2 electron carriers and why are they used?

• NAD and FAD• Easily cycles between being oxidized and

reduced (good at carrying electrons)

What do you remember?

• What is the function of dehydrogenases?

• Remove H and add H to NAD+