Cell RespirationIB Topic 3.7

Cell respiration is used by all cells to produce ATP • Every living cell must carry out cell respiration• Converts energy into a form that can be used

within the cell• Cells require energy for: • Synthesizing large molecules like DNA, RNA, and proteins • Pumping molecules or ions across membranes by active

transport• Moving things around inside the cell, such as

chromosomes, vesicles or in muscle cells the protein fibers that cause muscle contraction

Cell respiration is used by all cells to produce ATP• The energy for these processes is supplied by ATP

(adenosine triphosphate) • When ATP is split into ADP (adenosine

diphosphate) and phosphate, energy is released

ADP + phosphate ATP

Cell respiration

Active cell processes

Cell respiration is used by all cells to produce ATP • ATP cannot usually be absorbed through the

plasma membrane• So, every cell must produce its own supply• Organic compounds containing energy are broken

down by enzymes• Very controlled • So that as much as possible of the energy released can be

used to form ATP from ADP• Cell respiration defined as the controlled release

of energy from organic compounds to form ATP

What is cell respiration? • A: taking air into the lungs

• B: removing carbon dioxide from the lungs

• C: Use of ATP in cells

• D: Controlled release of energy in cells

Glycolysis • Cell respiration can release energy form a variety

of organic compounds, but carbohydrates and lipids are the usual substrates

• If glucose is being used, almost all organisms begin cell respiration the same way

• Before we get to the process, think about what the word means … • Glyco = sugar • Lysis = split

Glycolysis • Overview: •A chain of reactions takes place in the cytoplasm of the cell•Converts glucose to pyruvate •This chain of reactions is called glycolysis

Glycolysis – Deeper Look • Glucose enters the cell through the plasma

membrane (into the cytoplasm)• An enzyme modifies the glucose (slightly)• A second enzyme modifies the molecule even

more • Followed by a series of reactions (biochemical …) • Which you do not need to know

• Ultimately, the reactions cleave the 6-carbon glucose molecule into 2, 3-carbon molecules called pyruvate

Glycolysis – A Deeper Look (cont.) • Some of the covalent bonds in the glucose were

broken• Some of the energy that was released from the

breaking of these bonds was used to form a small number of ATP molecules

• 2 ATP molecules are needed to get the reaction started

• A total of 4 ATP molecules are produced• So there is a net gain of 2 ATP molecules

Glycolysis – Recap • No oxygen is used in glycolysis • A small amount of ATP is produced • If no oxygen is available, then this is the only ATP

that can be produced • Anaerobic conditions • Alcoholic fermentation • Lactic acid fermentation

What are the products of glycolysis?• A: glucose

• B: glucose and ATP

• C: ATP and pyruvate

• D: glucose, ATP, and pyruvate

Glycolysis Animation & Quiz • http://highered.mcgraw-hill.com/sites/0072507470

/student_view0/chapter25/animation__how_glycolysis_works.html

Let’s check in … • Cell respiration variety of biochemical pathways

that metabolize glucose • All of the pathways start with glycolysis • Common to all organisms

• Some organisms derive all of their ATP completely without oxygen (anaerobic)• Also called fermentation • Two main anaerobic pathways • Alcoholic fermentation • Lactic acid fermentation

Alcoholic Fermentation • Yeast – common, single-celled fungus that uses

alcoholic fermentation for ATP generation • Use glycolysis• Produce 2 net ATP molecules• Produce 2, 3-carbon pyruvate molecules

• Yeast then converts the pyruvate molecules to ethanol

• Ethanol is a 2-carbon molecule• So a carbon molecules is “lost” • Given off as carbon dioxide

• Baking – helps dough rise • Ethanol is drinking alcohol

Alcoholic fermentation

Glucose 6C

Pyruvate 3C Ethanol 2C

CO2Glycolysis (net gain 2 ATP)

Which substances are produce by yeast in anaerobic cell respiration? • A: carbon dioxide and lactate

• B: carbon dioxide and ethanol

• C: Lactate and ethanol

• D: carbon dioxide, lactate, and ethanol

Lactic Acid Fermentation • Organisms that use aerobic respiration sometimes

find themselves in a metabolic situation where they cannot supply enough oxygen to their cells

• Example: a person pushing beyond their physical limits; their pulmonary & cardiovascular systems supply as much oxygen to their cells as is physically possible

• If a person’s exercise rate exceeds their capability of supplying oxygen, then some of the glucose entering the cell respiration will follow lactic acid fermentation

Lactic Acid Fermentation (cont.)• Low-oxygen setting (not a normal setting) • Excess pyruvate molecules are converted into

lactic acid molecules• Lactic acid molecules • 3-carbon molecules • No production of carbon dioxide

• What’s the benefit? • Allows glycolysis to continue with the small gain of ATP

generated in addition to the ATP which is being generated through aerobic respiration

Lactic Acid Fermentation

Glucose 6C

Pyruvate 3C Lactate 3C

Glycolysis (net gain 2 ATP)

Aerobic pathway

(Reaction reversible when oxygen available)

If a blood sample from a person contains a high concentration of lactate, what is the conclusion? • A: the person has been drinking too much milk and

ingested large amounts of lactose

• B: the person is lactose intolerant and should change to drinking lactose-free milk

• C: the person has eaten live yogurt, containing bacteria that have carried out anaerobic cell respiration

• D: the person has exercised vigorously and carried out anaerobic cell respiration

Summary Equations • Cell Respiration = glucose pyruvate

• Occurs in almost all organisms • Aerobic or anaerobic respiration

• Lactic Acid Fermentation = pyruvate lactate • Occurs in humans• Occurs in some bacteria• Anaerobic respiration

• Alcoholic Fermentation = pyruvate ethanol + CO2• Occurs in yeast• Anaerobic respiration

ADP ATP

Aerobic Cell Respiration • The most efficient pathway • Takes place in the mitochondria • Begins with glycolysis• 2 net ATP & 2 pyruvate molecules • Enter the mitochondrion • Further metabolized

Aerobic Respiration – A Deeper Look • Each pyruvate first loses a carbon dioxide

molecule • Becomes a molecule called acetyl-CoA • Each acetyl-CoA enters into a series of reactions

called the Krebs cycle • During this series, two more CO2 molecules are

produced from each original pyruvate that enter • See Figure 3.24 in your textbook (page 82)

Aerobic Respiration – A Deeper Look• Some ATP is directly generated during the Krebs cycle• Some ATP is indirectly generated through a later

series of reactions directly involving oxygen • Aerobic respiration breaks down (completely oxidizes)

a glucose molecule and the end product are carbon dioxide and water • In most organisms, carbon dioxide is a waste product that

must be excreted • The water is useful – in humans, about ½ a liter of water is

produced per day • Some desert animals never have to drink water and eat only

dry foods because cell respiration supplies almost all their water needs

What is the main source of energy in aerobic cell respiration? • A: oxygen

• B: ATP

• C: Heat

• D: organic compounds

Why is aerobic respiration more effective than anaerobic respiration? • Anaerobic respiration does not completely oxidize

the glucose molecule • Ethanol and lactic acid are generated because

they represent portions of the original glucose that were not oxidized

• Aerobic respiration leaves no such by-products • Aerobic respiration results in a much higher yield

of ATP

Khan Academy – Helpful Link/Tutorial • https://

www.khanacademy.org/science/biology/cellular-respiration/v/introduction-to-cellular-respiration

Cell Respiration – Khan Academy