Sept. 20, 2013

Harvesting Chemical Energy from Sugar, Part 2

Agenda• Administrative Stuff• A Quick Review: ATP, Glycolysis,

Enzymes, NAD+/NADH• Oxidation and Reduction• Breaking Down Sugar Further

(Citric Acid Cycle)• Harvesting High-Energy Electrons

(Electron Transport Chain)• Wrap-up

Test YourselfOn your index card, briefly answer the following:

What is the function of glycolysis?

Does glycolysis happen inside or outside of the mitochondria?

What is ATP, and what is it for?

ATP: A Cellular “Battery”

Understanding Glycolysis

Glycolysis: Inputs and Outputs

Input (molecules

)

Output (molecules

)1 Glucose 2 Pyruvic

Acid2 ATP 2 ADP4 ADP 4 ATP

2 NAD+ 2 NADH4 P 2 P

?????

NAD+: An Electron Carrier

NAD+ is a molecule that can be used to carry electrons and store chemical energy.

Not as generally useful as ATP, though.

Two electrons are transferred together with an H+ to turn NAD+ into NADH.

FYI: The “A” in NADH is adenine, the “A” DNA base (in GTAC) and the A in ATP! Evolution re-uses chemicals a lot!

Getting the Most out of Glucose

At the end of glycoysis, we were left with two molecules each of NADH and pyruvic acid. In bacteria, fermentation might follow to get rid of the NADH.

But eukaryotic cells can harvest more energy by pulling electrons off of these molecules. Which substance is used to grab electrons from these molecules? Make a guess!

Burn the Pyruvic Acid with Oxygen!

… but don’t burn it suddenly.

Respiration is a kind of “slow burn,” a gradual transfer of electrons to oxygen.

By passing electrons from glucose and its pieces to oxygen gradually, we can harvest the chemical energy it stores. We use NADH to pass these electrons!

Two Useful Terms for “Electron Grabbing”

If something gains an electron, will its charge become more positive or negative?

Its charge becomes negative, so we say it is reduced.

If something loses electrons (like sugar being burned in oxygen), we say it is oxidized.Oxygen is good at oxidizing nutrients!

GER…

Mnemonic: LEO says GER

Loss of Electrons = OxidationGain of Electrons = Reduction

Examples of Oxidation + Reduction

Iron + Oxygen -> Iron Oxide (Rust)

Batteries use the oxidation of metal to move electrons!

Practice!Loss of Electrons = OxidationGain of Electrons = Reduction

GER…

1) Is NAD+ oxidized or

reduced during glycolysis?

2) Which atom is oxidized here?

Respiration = A Reduction + Oxidation Reaction

Don’t Forget the Big Picture:

Oxidizing Some Carbon (and harvesting NADH)

Follow the carbon! This is the first place where we released any CO2 waste!

The Citric Acid Cycle: Don’t Panic!

The Citric Acid Cycle: Don’t Panic!

What are the most important things to know about the citric acid cycle?

A two-carbon compound (acetyl CoA) goes into the mitochondrion. Two carbons are oxidized to CO2. Carbon is balanced!It only makes a little ATP compared to later stages.

Makes NADH and FADH2!

FAD is an electron carrier… just like NAD+.

How are these processes similar?

How are these processes different?

Harvesting Electrons

When substances move from higher concentration to lower concentration, we call that “moving down a concentration gradient.”

This movement releases energy, which can be used to do work! In mitochondria, differences in H+

across the “folds” are used to drive the making of ATP from ADP.

The Electron Transport Chain: A Molecular “Waterwheel”

Simplified Version:

How Much ATP Do We Get from One Molecule of Glucose?

On Wednesday:Essay due!

Lab practical for Wednesday section!

Special class: Putting It All Together – real-world research and applications of what we’ve done so far. Review + Activities + Real Science.

Lecture exam on Friday the 27th.