Cellular Respiration Chapter 9. The link between Photosynthesis and Cellular Respiration Like a...

Cellular Respiration

Chapter 9

The link between Photosynthesis and Cellular Respiration

Like a rechargeable battery, your body runs low on energy and needs to be supplied with more

You get energy from food

The energy in your food was captured from sunlight by photosynthesisTogether photosynthesis and cellular respiration form a cycle

Overview of Cellular Respiration

An introduction to the steps of cellular respiration

Cellular RespirationIs the complex process where cells make adenosine triphosphate (ATP) by breaking down organic compounds

Using Chemical Energy to Drive Metabolism

Plants, algae, & some bacteria harvest energy of sunlight through photosynthesisAutotrophs: (self-feeders) are organisms that use energy from sunlight or from chemical bonds in inorganic substances to make organic compoundsBasically: they get their energy from the sun, mostly through photosynthesis

Autotrophs vs Heterotrophs

Heterotrophs (fed by others) are animals and other organisms that must get energy from food instead of directly from sunlight95% of organisms on Earth are heterotrophs

So, Both Heterotrophs and Autotrophs

Undergo cellular respiration to break these organic compounds into simpler molecules and release energy.Some of the energy is used to make ATP.The energy is then used by cells to do work.

Cellular Respiration can be divided into 2 stages:

1. Glycolysis: organic compounds are converted into 3-carbon molecules of pyruvic (pie-ROO-vic) acid, producing s small amount of ATP and NADH (the electron carrier). Glycolysis is an anaerobic process because it does not require the presence of oxygen

Cellular Respiration can be divided into 2 stages:

2. Aerobic Respiration: if no oxygen is present in the cell’s environment, pyruvic acid is broken down & NADH is used to make a large amount of ATP through the process known as aerobic respiration

Pyruvic acid can enter other pathways

If there is no oxygen present in the cells environment.The combination of glycolysis and these anaerobic pathways is called fermentation.

Pyruvic AcidDefinition: Is the 3-carbon compound that is produced during glycolysis and needed for both the aerobic and anaerobic pathways of cellular respiration that follow glycolysis

Redox ReactionsMany of the reactions in cellular respiration are redoxPathways require oxygen, so glucose is oxidized and oxygen is reducedThe breakdown on one glucose molecule results in 38 ATP molecules

FYIOrganisms use cellular respiration to harness energy from organic compoundsGlycolysis produces a small amount of ATPMost ATP results from aerobic respiration (which is the 2nd stage of cellular respiration

Equation that summarizes cellular respiration

C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP)

Glycolysis: 1st stage of Cellular Respiration

Glycolysis: is a biochemical pathway where one 6-carbon molecule of glucose is oxidized to produce two 3-carbon molecules of pyruvic acid.catalyzed by specific enzymesAll reactions of glycolysis take place in the cytosol & occur in 4 main steps

Glycolysis Step 12 phosphate groups are attached to 1 molecule of glucose forming a 6-carbon compound that has 2 phosphate groups on its endsThe phosphate groups are supplied by 2 molecules of ATP which are converted into 2 molecules of ADP in the process

1

6-carbon sugar diphosphate

6-carbon glucose(Starting material)

2

P P

Priming reactions. Priming reactions. Glycolysis begins with the addition of energy. Two high-energy phosphates from two molecules of ATP are added to the six-carbon molecule glucose, producing a six-carbon molecule with two phosphates.

ATP

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Glucose Priming3 reactions “prime” glucose by changing it into a compound that can be cleaved into 2 3-carbon phosphorylated molecules2 of these reactions require the cleavage of ATP, so this step requires 2 ATP molecules

Glycolysis Step 2The 6-carbon compound formed in step 1 is split into two 3-carbon molecules of glyceraldehyde 3-phosphate (G3P)G3P: is also (end) produced by the Calvin cycle in photosynthesis.

Fig. 9.6b (TEArt)

2

6-carbon sugar diphosphate

P P

3-carbon sugar phosphate

P P

2

Cleavage reactions. Then, the six-carbon molecule with two phosphates is split in two, forming two three-carbon sugar phosphates.

3-carbon sugar phosphate


Glycolysis Step 3:The 2 G3P molecules are oxidized, & each receives a phosphate group.The product = 2 molecules of a new 3-carbon compound The oxidation of G3P is accompanied by the reduction of 2 molecules of (nicotinamide adenine dinucleotide) NAD+ to NADH

Fig. 9.6c (TEArt)

OVERVIEW OF GLYCOLYSIS 3

P P

3-carbon pyruvate

2

NADH

ATP 2

NADH

ATP

Energy-harvesting reactions. Finally, in a series of reactions, each of the two three-carbon sugar phosphates is converted to pyruvate. In the process, an energy-rich hydrogen is harvested as NADH, and two ATP molecules are formed.

3-carbon sugar phosphate 3-carbon sugar phosphate

3-carbon pyruvate


Glycolysis Step 4The phosphate groups added in step 1 & step 3 are removed from the 3-carbon compoundsThis reaction produces 2 molecules of pyruvic acidEach phosphate group combines with ADP to make ATPA total of 4 Phosphate groups were added in step 1 & 3—4 ATP are made

Step 4 ContinuedNotice that 2 ATP molecules were made in step 1, but 4 were produced in step 4.Therefore, glycolysis has a net yield of 2 ATP molecules for every molecule of glucose that is converted into pyruvic acid.

GlucoseNew 6-carboncompound

2 molecules of G3P

2 ATP 2 ADP

1 2

3 4

c-c-c-c-c-c P-c-c-c-c-c-c-P P-c-c-cc-c-c-P

P-c-c-c-PP-c-c-c-P c-c-c

c-c-c

2 Phosphate

2 NAD+ 2 NADH+ 2H+

2 molecules of new

3-carbon compound

4 ADP 4 ATP2 H2O

2 molecules of pyruvic acid

Glycolysis Video

http://www.youtube.com/watch?v=x-stLxqPt6E

In Aerobic conditionsWhen oxygen is present, cellular respiration continues as pyruvic acid enters the pathways of aerobic respiration

In Anaerobic conditionsDuring heavy exercise, when your cells are without oxygen for a short period of time, an anaerobic process called fermentation follows glycolysis and provides a means to continue producing ATP until oxygen is available again

FermentationIn anaerobic conditions, some cells can convert pyrvic acid into other compounds through additional biochemical pathways that occur in the cytosol Glycolysis & these pathways regenerate NAD+

Fermentum meaning “leaven” or anything that causes baked goods to rise

The Processes of Fermentation

The additional pathways do not produce ATPWithout the cellular process that recycled NAD+ from NADH, glycolysis would quickly use up all the NAD+ in the cellGlycolysis would then STOP!ATP production through glycolysis would also STOP!The fermentation allows the process to continue

Many fermentation pathways

There are many fermentation pathwaysThey differ in terms of the enzymes that are used & the compounds that are made from pyruvic acid2 common fermentation pathways result in the production of1. Lactic acid2. Ethyl Alcohol

2 common fermentation pathways

Lactic Acid: an enzyme that supplies energy when oxygen is scarce, they make pyruvic acidTwo molecules of pyruvic acid use NADH to form two molecules of lactic acid This releases NAD+ to be used in glycolysis, allowing two ATP molecules to be formed for each glucose molecule

• The lactic acid is transferred from muscle cells, to the liver that converts it back to pyruvic acid.

Lactic Acid Fermentation

2 common fermentation pathways

Alcoholic Fermentation1. A CO2 molecule is removed from pyruvic acid leaving 2-C. 2. 2-H atoms are added to the 2-C to form ethyl alcoholH-atoms come from NADH & H+, regenerating NAD+ for use in glycolysis

used by yeast cells and some bacteria to produce CO2 and ethyl alcohol

Alcoholic Fermentation

NADH

PyruvateWith oxygen Without oxygen

Acetyl-CoA

Lactate

Ethanol

NAD+

NAD+

NADH

NAD+

NADH

CO2

Acetaldehyde

H20

Krebscycle

O2


Aerobic Respiration

2 major stages:1. Krebs cycle2. Electron Transport Chain

(chemiosmosis)

Where the Krebs cycle Happen

In Prokaryotic Cells: the Krebs cycle takes place in the cytosolIn Eukaryotic Cells: the Krebs cycle takes place in the mitochondrial matrix

Mitochondrial MatrixThe mitochondrial matrix is the space inside the inner membrane of the mitochondrionIt contains the enzymes needed to catalyze the reactions of the Krebs cycle

Acetyl CoAWhen pyruvic acid enters the mitochondrial matrix, it reacts with a molecule called coenzyme A to form acetyl coenzyme A (acetyl CoA)

Pyruvic acid Acetyl CoAThe acetyl part of acetyl CoA: 2-C atoms(but remember that) Pyruvic acid: 3-C atomThe C-atom is lost in the conversion from pyruvic to acetyl CoA & released as CO2

Reaction reduces a molecule of NAD+ to NADH

Glycolysis yields 2 molecules of pyruvic acid

Pyruvic Acid

Acetyl Co A

c-c-cCoA

CO2

NAD+

NADH + H+

c-c

The Krebs CycleIs a biochemical pathway that breaks down acetyl CoA, producing CO2, H+, & ATP

The Krebs Cycle has 5 main partsAll occur in the mitochondrial matrixAKA: The Citric Cycle

A Little Krebs Cycle History

Discovered by Hans Krebs in 1937He received the Nobel Prize in physiology or medicine in 1953 for his discoveryForced to leave Germany prior to WWII because he was Jewish

The Krebs Cycle: Step 1A 2-carbon molecule of acetyl CoA combines with a 4-carbon compound, oxaloacetic (AHKS-uh-loh-uh-SEET-it) acid, to produce a 6-carbon compound, citric acid.{the reaction regenerates coenzyme A}

OVERVIEW OF THE KREBS CYCLE

1

6-carbon molecule4-carbon molecule(Starting material)

CoA-(Acetyl-CoA) CoA

The Krebs cycle begins when a two-carbon fragment is transferred from acetyl-CoA to a four-carbon molecule (the starting material).


The Krebs Cycle: Step 2Citric acid releases a CO2 molecule & a H+ atom to form a 5-C compoundBy losing the H-atom with its electrons, the citric acid is oxidizedThe electron in the H-atom is transferred to NAD+ reducing it to NADH

The Krebs Cycle: Step 3The 5-C compound formed in step 2 also releases a CO2 & a H+ making a 4-C compoundAgain, NAD+ is reduced to NADHNote: a molecule of ATP is also synthesized from ADP


2

5-carbon molecule4-carbon molecule

NADH

CO2

NADH

CO2

ATP

6-carbon molecule

Then, the resulting six-carbon molecule is oxidized (a hydrogen removed to form NADH) and decarboxylated (a carbon removed to form CO2). Next, the five-carbon molecule is oxidized and decarboxylated again, and a coupled reaction generates ATP.


The Krebs Cycle: Step 4The 4-C compound made in step 3 releases a H+ to form another 4-C compoundThis time the H-atom is used to reduce FAD to FADH2.

FAD or flavin adenine dinucleotide is a molecule similar to NAD+; accepting electrons during redox reactions

The Krebs Cycle: Step 5The 4-C compound formed in step 4 releases a H+ to regenerate oxaloacetic acid which keeps the Krebs cycle operating.The electron in the H+ reduces NAD+ to NADHMakes 2 turns


3

NADH

FADH2

4-carbon molecule

4-carbon molecule(Starting material)

Finally, the resulting four-carbon molecule is further oxidized (hydrogens removed to form FADH2 and NADH). This regenerates the four-carbon starting material, completing the cycle.


Krebs Cycle Video

http://www.youtube.com/watch?v=lvoZ21P4JK8&feature=related

Think about this…In glycolysis…1 glucose makes 2 pyruvic molecules…which then makes 2 molecules of acetyl CoAThis 1 glucose molecule is broken down into 2 turns of the Krebs cycleThese 2 turns make 4CO2, 2-ATP, & a H+ atom…that are used to make 6-NADH & 2 FADH2

Then…The CO2 diffuses out of the cell and is given off as wasteATP can be used for energyEach glucose molecule yields only 2 molecules of ATP through the Krebs cycle…the same number as in glycolysis

Electron Transport ChainLinked with chemiosmosis, starts the 2nd stage of aerobic respirationThe electrons in the H-atoms from NADH & FADH2 are at a high energy levelIn the ETC these molecules are passed along a series of molecules embedded in the inner mitochondrial membrane

Eukaryotes vs Prokaryotes of the ETC

In Eukaryotes, ETC & ATP synthesis are found in the inner membrane of the mitochondria in the folds of the cristae

In Prokaryotes ETC is found in the cell membrane

ETC step 1NADH & FADH2 give up electrons to the ETCNADH donates electrons at the beginning and FADH2 donates them farther down the chainThese molecule also give up protons (Hydrogen ions +)

ETC step 2The electrons are passed down the chainAs they move from molecule to molecule, they lose energy

ETC step 3The energy lost from the electrons is used to pump protons from the matrix, building a high concentration of protons between the inner and outer membranesSo, a concentration gradient of protons is created across the inner membraneAn electrical gradient is also created, as the protons carry a positive charge

ETC step 4The concentration and electrical gradient of protons drives the synthesis of ATP by Chemiosmosis (same process that generates ATP in photosynthesis)ATP synthase molecules are embedded in the inner membrane near the ETC moleculeAs protons move through ATP synthase & down their concentration and electrical gradients, ATP is made from ADP + P

ETC step 5Oxygen is the final acceptor of electrons that have passed down the chain.Oxygen also accepts protons that were part of the H-atom supplied by NADH and FADH2The protons, electrons, and oxygen all combine to form water

Electron Transport Chain Animation

http://www.science.smith.edu/departments/Biology/Bio231/etc.html

What's the point of the ETC?

The ETC helps turn NADH and FADH2 into ATPTotal ATP made in glycolysis…2Total ATP made in Krebs…2Total NADH made…10. This will be used in ETC- 1 NADH makes 3 ATPTotal FADH2 made..2. This will be used in ETC – 1 FAHD2 makes 2 ATP

2

2 6 ATP

Pyruvate

Glucose

Acetyl-CoANADH

2 6 ATPNADH

2 ATP

2 ATP

6 18 ATPNADH

2 4 ATP

Total net ATP yield = 38 ATP

FADH2

Krebscycle

ATP Glycolysis


Electron Transport Chain

http://www.youtube.com/watch?v=Idy2XAlZIVA&feature=related

Fig. 9.3 (TEArt)

H+

ATP

ADP + Pi

Catalytichead

Intermembranespace

Mitochondrial matrix

Rod

Rotor

H+ H+

H+

H+ H+

H+H+H+


Date post:	04-Jan-2016
Category:	Documents
Upload:	janice-curtis
View:	213 times
Download:	1 times

Cellular Respiration Chapter 9. The link between Photosynthesis and Cellular Respiration Like a...

Documents