Cell Respiration 3.7 and 8.1

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 O 2 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

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 CO 2 ; these are waste products that are given off to environment No further yield of ATP Ex: yeast for breads/beer C 6 H 12 O 6  2C 2 H 5 OH + 2CO 2 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 C 6 H 12 O 6  2C 3 H 6 O 3 Glucose Lactate

And now, what if oxygen IS available:

Aerobic Respiration Cells with mitochondria and sufficient O 2 use aerobic respiration Takes place in the mitochondria Formula below: C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + 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 CO 2 molecule and an electron which goes to NAD + to make NADH

1.Acetyl-CoA sends acetyl group (2 carbon molecule) into Kreb’s cycle to start reactions and it recycles itself back to be used again 2.After many steps the products of the reactions are: CO 2, NADH, FADH 2, ATP Kreb’s Cycle

Main purpose of Kreb’s Cycle: Feed electrons into the next stage of aerobic respiration via NADH and FADH 2 From the breakdown of one glucose (2 turns of the cycle): 2 ATP molecules produced 6 molecules of NADH produced 2 molecules of FADH 2 produced 4 molecules of CO 2 released

Electron Transport System (ETS) 1.ATP produced from molecules NADH and FADH 2 as they shuttle their electrons to electron carriers 2.The electron carriers use some of the energy from the redox reactions to pump H + (hydrogen ions/protons) across mitochondrial membrane so that ATP synthase can use the H + energy gradient to convert ADP + Phosphate to ATP 3.Products of ETS are H 2 0, ATP, NAD, and FAD (NAD and FAD recycled back into Kreb’s cycle)

Note: ETS located on inner membrane Note: Formation of ATP at this stage called oxidative phosphorylation

matrix Intermembrane space

Lab Tie-In The rate of cellular respiration in an aerobic organism is measured by a respirometer It works by measuring the O 2 intake of an organism while the CO 2 output is eliminated by the use of a chemical This causes the respirometer, when under water to show the amount of O 2 consumed via the rate at which water enters the respirometer