Cell Respiration3.7 and 8.1

http://www.youtube.com/watch?v=3aZrkdzrd04

What is cell respiration?

Process by which energy in food molecules (glucose) is made available for an organism to do biological work via breakdown/being metabolized

Each redox reaction causes a small amount of energy to be released; the end goal is to convert the energy into making ATP molecules

Typically we discuss in terms of glucose, but other organic molecules can also be broken down; fats very important in making ATP and contribute to energy used in muscles, heart, liver, kidneys

OIL RIG• An easy way to remember redox reactions is

O – oxidation

I – is

L – loss

R – reduction

I – is

G - gain

Note: This is true when dealing with electrons and/or Hydrogen atoms

It is thought that aerobic respiration evolved after anaerobic respiration; possibly ~ 2.4 bya when O2 accumulated on Earth

The breakdown of glucose via respiration must be done in small steps in a controlled manner so that the heat produced does not destroy the cell/organism

3 steps in aerobic cellular respiration:

1)Glycolysis

2) Kreb’s cycle

3) electron transport system (ETS)

Step 1: Glycolysis

• Glucose enters the cell through the plasma membrane (via facilitated diffusion) and goes into the cytoplasm

• Process activated by 2 ATP molecules breaking down into ADP and phosphate (phosphate goes to energize glucose)

• A series of enzymes modifies and splits the 6-carbon glucose into two 3-carbon molecules of pyruvate

From the series of reactions in Glycolysis the following are produced:

2 Pyruvate

Net 2 ATP

2 molecules NADH

Let’s Review what happened in Glycolysis!

But first, what if NO oxygen is available:

Plants and Fungi alcohol fermentation

Animals lactate fermentation

Alcohol Fermentation

• Converts the pyruvate molecules to ethanol (ethyl alcohol) and CO2; these are waste products that are given off to environment

• No further yield of ATP• Ex: yeast for breads/beer

C6H12O6 2C2H5OH + 2CO2

Glucose Ethanol Carbon Dioxide

Lactic Acid Fermentation

• Used by human muscle cells when oxygen is scarce

• Converts pyruvate molecules to lactate• After strenuous exercise, you can feel the

build up of lactic acid as muscle fatigue/pain; it will gradually be carried to liver via bloodstream

C6H12O6 2C3H6O3

Glucose Lactate

And now, what if oxygen IS available:

Aerobic Respiration

• Cells with mitochondria and sufficient O2 use aerobic respiration

• Takes place in the mitochondria• Formula below:

C6H12O6 + 6O2 6CO2 + 6H2O + Energy (energy is ATP + heat)• Most efficient pathway to produce ATP

(net 36 ATP per 1 glucose)

The Link Reaction

1. Pyruvate enters matrix of mitochondria via active transport

2. Each pyruvate is converted to acetyl-CoA; this conversion involves the removal of: one CO2 molecule and Hydrogen (oxidation) to make NADH

• Acetyl-CoA sends acetyl group (2 carbon molecule) into Kreb’s cycle to start reactions and detaches to be used again

• For each glucose broken down in glycolysis (2 pyruvate were made) so the cycle occurs twice

Kreb’s Cycle**Occurs in matrix of mitochondria**

Main purpose of Kreb’s Cycle:

• Feed electrons into the next stage of aerobic respiration via NADH and FADH2

From the breakdown of one glucose (2 turns of the cycle):

• 2 ATP molecules produced

• 6 molecules of NADH produced

• 2 molecules of FADH2 produced

• 4 molecules of CO2 releasedLet’s Review The Kreb’s Cycle!

Electron Transport System (ETS)**occurs on inner membrane of mitochondria**

• Uses molecules that are electron carriers (easily reduced and oxidized) that are close together and vary in electronegativity (stronger pull as you go down the line)

• ATP produced from molecules NADH and FADH2 as they shuttle their electrons to electron carriers and their Hydrogen into the intermembrane space

NADH enters system before FADH2, therefore NADH makes 3 ATP and FADH2 makes 2 ATP

O2 is final electron acceptor…making H20

• The electron carriers use some of the energy from the redox reactions to pump H+ across mitochondrial membrane so that ATP synthase can use the H+ energy gradient to convert ADP + Phosphate to ATP

• Note: The ETS has allowed for Chemiosmosis and Oxidative Phosphorylation

Chemiosmosis – the movement of H+ ions to provide energy

Oxidative Phosphorylation – using an electron transport chain to make ATP

Let’s Review the Electron Transport System!

Summary of ATP Production in Cell Respiration

Process ATP used ATP produced Net ATP gain

Glycolysis 2 4 2

Kreb’s Cycle 0 2 2

ETS and Chemiosmosis

0 32 32

Total 2 38 36