Cellular Respiration: Process and Breathing Rate

• Respiration, in biochemistry, is the process of metabolizing nutrients, making energy as adenosine triphosphate (ATP), and releasing waste products.
• Aerobic cellular respiration uses oxygen.
• Anaerobic respiration does not use oxygen.
• Breathing is the first step to cellular respiration.
• Without oxygen, the body cannot convert food into usable cellular energy.
• Breathing rate is measured in breaths per minute.
• Breathing rate is an important indicator of overall health.

Respiration Rate by Age

• Newborn: 30-60
• Infant: 30-60
• Toddler: 24-40
• 3-5 years: 22-34
• 6-12 years: 18-30
• 13-17 years: 12-16
• Adult: 12-18
• Elderly Adult: Higher than adult

Cellular Respiration Process

• Eukaryotic organisms contain a nuclear envelope that protects genetic information.
• Prokaryotic organisms have free-floating genetic information.
• All organisms use respiration, regardless of type, location, or internal structures.
• Glucose is broken down with oxygen into energy, water, and carbon dioxide.
• Prokaryotic organisms start respiration in their cytoplasm and finish through their cellular membrane.
• Eukaryotic cells start respiration in their cytoplasm, then move to the mitochondrion.

Aerobic and Anaerobic Respiration

• Waste products in anaerobic respiration differ based on what the cell uses instead of oxygen and is less efficient than aerobic respiration.
• Two common modes of anaerobic respiration are lactic acid fermentation and alcoholic fermentation.

Aerobic Respiration Equation

• C6H12O6 + 6O2 --> 6CO2 + 6H2O + Energy (ATP)

Cellular Respiration Divisions

• Glycolysis
• Krebs cycle/citric acid cycle/TCA cycle
• Oxidative phosphorylation
• All cellular respiration starts with glycolysis, whether aerobic or anaerobic.

Glycolysis

• The breakdown of glucose.
• Glucose is a hydrocarbon, meaning it has a carbon and hydrogen backbone.
• Anything with the ending "lyse" means "to split".

Krebs Cycle

• Called a cycle because it uses and creates oxaloacetate
• Water and carbon dioxide are made.

Oxidative Phosphorylation

• The last step which uses oxygen to create a positive potential that drives ATP production through chemiosmosis.

Glycolysis Respiration Equation

• Glucose + 2ATP --> Pyruvate + Water + ATP
• Glycolysis occurs in the cytoplasm.
• Glucose, a six-carbon simple sugar, is broken down into two molecules of pyruvate, a 3-carbon compound, with two ATP produced.
• The breaking of the chemical bonds is used to add a phosphate group to the already present ADP (adenosine diphosphate).
• Pyruvate can be used to make acetyl coenzyme A, or acetyl CoA and NAD+, which is an electron carrier.

Lactic Acid Fermentation Equation

• Glucose + ADP + NAD+ --> Lactic acid + ATP + NADH
• Pyruvate and lactic acid are 3-carbon molecules. During lactic acid fermentation, pyruvate is changed into lactic acid instead of acetyl CoA.
• NAD+ and two molecules of ATP are still made, making glycolysis possible again
• Muscles that need energy fast can switch from aerobic respiration to lactic acid fermentation.
• Lactic acid is stored in the muscles and leads to stiffness and soreness.

Alcoholic Fermentation Equation

• Glucose + ADP --> Ethyl Alcohol + CO2 + 2 ATP + H2O
• Pyruvate is then transformed into carbon dioxide and ethyl alcohol
• Brewers use alcoholic fermentation to make alcoholic drinks: yeast metabolizes sugar/glucose into carbon dioxide and alcohol
• The carbon dioxide gives beer the bubbles and carbonation.

Steps in Cellular Respiration

• The cellular respiration process starts in the cytoplasm and then finishes up in the mitochondria.

Step 1: Glycolysis

• Glucose is a simple sugar or monosaccharide that is absorbed directly into the bloodstream from food
• Glycolysis can also use glycogen that is stored by the liver that can be broken down to get glucose.
• Glycolysis makes many products that the body uses elsewhere.
• Glucose's carbon ring is broken by ATP and the enzyme hexokinase to form a six-carbon chain glucose-6-phosphate and ADP
• Fructose-6-phosphate is formed when the enzyme phosphoglucose isomerase breaks a carbon-hydrogen bond and forms a carbon-oxygen double bond.
• The enzyme phosphofructokinase and ATP are used to attach another phosphate group to the other side of fructose-6-phosphate to make fructose 1,6-biphosphate.
• Fructose 1,6-biphosphate is split into two three-carbon molecules by fructose biphosphate aldolase, dihydroxyacetone phosphate (DHAP), and glyceraldehyde-3-phosphate (G3P).
• An enzyme called triose phosphate isomerase can convert one into the other and vice versa.
• Glyceraldehyde-3-phosphate dehydrogenase enzyme removes an H+ from G3P and transfers it to NAD+ to make NADH (an electron transport compound).
• A phosphate molecule is added to G3P to create 1,3-bisphosphoglycerate.
• One of the phosphate groups of 1,3-bisphosphoglycerate is transferred to an ADP molecule to create ATP
• Phosphoglycerate can have the phosphate group on either the third or second carbon, with the help of the enzyme phosphoglycerate kinase.
• Phosphoglycerate will then shed a water molecule with the enzyme enolase to become phosphoenolpyruvate.
• With pyruvate kinase, this last compound loses one more phosphate group to become pyruvate, and one more ATP molecule is made.
• Four ATP have been made along with two molecules of water and two pyruvates.

Step 2: Citric Acid Cycle

• Also called Krebs cycle and tricarboxylic acid cycle.
• Technically, this is the start of cellular aerobic respiration, even though ATP is not made in this process.
• Electron carrier molecules like NADH and FADH2 are produced which are important in oxidative phosphorylation
• This is a cycle, so acetyl CoA goes in, and acetyl CoA comes out to start all over again.
• In eukaryotic organisms, this takes place in the mitochondria, but in prokaryotic organisms this takes place in the cytoplasm.
• Dehydrogenation means the loss of a hydrogen proton, and decarboxylation is the loss of a carbon group.
• Pyruvate is changed into acetyl (a 2-carbon group) coenzyme A, or acetyl CoA, by oxidative decarboxylation: a carbon group is removed to produce carbon dioxide, and the CoA group is added on.
• Pyruvate can also be made into oxaloacetate by pyruvate carboxylase by the addition of a carbon group.
• acetyl CoA and oxaloacetate are combined by the enzyme citrate synthase to make citrate, a six-carbon compound + water
• Coenzyme group is removed to be reused to produce more acetyl CoA.
• Citrate changes by the enzyme aconitase into isocitrate.
• Alphaketogluterate is formed when isocitrate loses a carbon group with the help of the enzyme isocitrate dehydrogenase and NADH.
• Alphaketogluterate loses a carbon group, forming succinyl-CoA, carbon dioxide, and NADH, with the Alpha-ketoglutarate dehydrogenase enzyme complex.
• Succinyl-CoA is reformed as succinate, releasing the CoA substrate and GTP (changed into ATP) by the enzyme succinyl-CoA synthase.
• Succinate is converted into the four-carbon compound fumarate by succinate dehydrogenase with FADH2.
• Fumarate is hydrogenated into malate by the enzyme fumarase.
• Malate is formed into oxaloacetate by malate dehydrogenase, along with NADH.

Step 3: Oxidative Phosphorylation (Electron Transport Chain and Chemiosmosis)

• Takes place in the mitochondria, within the inner membrane to create a positive electron gradient: the flow of hydrogen protons powers the phosphorylation of ADP into ATP.
• Complexes within the membranes keep the flow of molecules moving.
• In complex I, NADH loses a H ion, making it NAD+. The Hydrogen proton moves from the membrane space through complex 1 into an inner-membrane space.
• Complex II, along with a mobile protein "Q" or ubiquinone, receives FADH_2, pumping protons across the membrane, it does not pass through complex I.
• Complex III has a heme group that carries electrons, passing one electron at a time to complex IV.
• The fourth complex is composed of two cytochrome proteins; the cytochromes hold an oxygen molecule tightly until completely reduced.
• Reduced oxygen picks up two hydrogen ions from the surrounding medium to make water.
• Chemiosmosis: The free energy from the proton gradient and reduction/oxidation reactions through complexes I-IV drives the addition of a phosphate group to ADP.
• In ATP synthase protein, the protons move through the complex, creating chemical potential energy
• Most of the ATP (up to 32 from one molecule of glucose) comes from this last step.

Purpose and By-Products of Respiration

• The aim is to take food and turn it into chemical energy the body can use. biproducts: water and CO_2
• Water is used by the body to regulate blood pressure, move nutrients, and helps with homeostasis.
• Plants use carbon dioxide to power photosynthesis, where they make glucose and oxygen.
• Photosynthesis' chemical equation is the opposite of cellular respiration.
• Plants and animals work together to keep an ecosystem healthy.

Types of Cellular Respiration

• Aerobic respiration
• Anaerobic respiration
• Methanogenesis: the end product is ATP and methane, CH_4.
• Anaerobic bacteria in the kingdom Archaea only do methanogenesis.
• Obligate methanogens live in all kinds of environments.
• They respire, using methane as energy.
• These organisms can convert acetate into carbon dioxide and water, and they can use hydrogen and carbon dioxide to make water and methane.

Cellular respiration metabolizes nutrients to produce energy (ATP) and waste. Aerobic respiration uses oxygen, while anaerobic does not. Breathing rate, measured in breaths per minute, indicates overall health and varies by age.