Cellular Respiration

Question 1

Why is the basic overview of cellular respiration and its two types of cellular respiration

Answer 1

• Can utilize carbohydrates, lipids, and proteins
• Converts energy in fuel molecules into ATP
• Allows the cell to do work
• Two types of phosphorylation
  i. Substrate-level (inefficient.)
  ii. Oxidative

Question 2

What are the first two stages of cellular respiration?

Answer 2

• Stage 1: glycolysis → happens in cytoplasm
• Glucose is partially broken down → small amount of energy is released
• Note - fatty acids and amino acids may also be broken down by different pathways
• Stage 2: pyruvate oxidation → mitochondria (pyruvate created in mitochondrial matrix)
• Pyruvate is produced from the breakdown of glucose in glycolysis → converted to acetyl-CoA and CO2

Question 3

What are the last two stages of cellular respiration?

Answer 3

• Stage 3: citric acid cycle → happens in mitochondria
• Acetyl-CoA from the end of step 2 is broken down
• This releases: CO2, small amount of energy and electron carriers
• Stage 4: oxidative phosphorylation → happens in mitochondria
• All the electron carriers from stages 1-3 release their high-energy electrons to the electron transport chain
• This produces ATP

Question 4

Overview of ATP generation

Answer 4

• ATP is generated using several mechanisms:
• Substrate-level phosphorylation is the process by which ATP is synthesized by a hydrolysis reaction involving an enzyme/substrate complex
• A small amount of ATP is generated
• The energy is transferred to electron carriers → carry energy from one reaction to another
• The electron carriers transport electrons to the respiratory electron transport chain → which transfers electrons along membrane-associated proteins to final acceptor
• These proteins harness the energy released to produce ATP → process called oxidative phosphorylation
• The majority of ATP is produced using oxidative phosphorylation

Question 5

Oxidation reactions in Cellular Reactions

Answer 5

• NAD* and FAD are important electron carriers in cellular respiration
• In cellular respiration → the energy stored in glucose is harnessed in electron carriers as glucose is oxidized into COz
• In the breakdown of glucose, glucose is oxidized to COz and Oz is reduced to H2O
• Remember → oxidation is the loss of electrons & reduction is the gain of electrons
• Recall that the carbon atoms of glucose are bonded to other carbon atoms, hydrogen atoms, and oxygen atoms

Question 6

OIL RIG and LEO the lion says “GER”

Answer 6

OIL RIG
Oxidation Is Loss of electrons
Reduction Is Gain of electrons

LEO the lion says “GER”
Loss Electrons is Oxidation
Gain of Electrons is Reduction

Question 7

Reduction Reactions in Cellular Respiration

Answer 7

• Oxygen is the final electron acceptor in cellular respiration
• When O2 is reduced → water is formed.
• The original electron donor in cellular respiration is glucose
• But the electrons move from one molecule to the next during cellular respiration via reduction reactions

Question 8

Electron Carriers

Answer 8

• Two important electron carriers in cells are NAD+/NADH & FAD/FADH2
• The oxidized forms of these carriers are NAD+ and FAD; the reduced forms are NADH and FADH2
• Through glycolysis, pyruvate oxidation, and the citric acid cycle, the form of the electron carrier accepts electrons and becomes reduced
• The reduced form of the electron carriers has high potential energy
• This is used to synthesize ATP in the final stage of cellular respiration

Question 9

Basics of Glycolysis

Answer 9

• Catabolic pathway → Glycolysis
• The sum of ten chemical reactions that breakdown glucose
• Goes from six-carbon glucose → to two three-carbon pyruvates
• Occurs in cytosol in presence or absence of O2
• Considered an anaerobic process because no oxygen is consumed

Question 10

The three phases of glycolysis

Answer 10

• There are three different phases of glycolysis:
  1. Preparatory → where energy is consumed
  2. Cleavage → where glucose is split into two
  3. Pay off → where ATP is one of the products

Question 11

Glycolysis Phase 1: Prepratory

Answer 11

Phase 1 are energy consuming reactions

• Events in Phase 1 include:
• The preparation of glucose for the next two phases → addition of two phosphate groups, producing fructose 1,6-bisphosphate
• This process requires an input of energy in the form of two molecules of ATP
• The phosphorylation of glucose traps the molecule inside the cell and destabilizes it so that it is ready for phase 2

Question 12

Glycolysis Phase 2: Cleavage

Answer 12

Phase 2 splits glucose

• Events in Phase 2 include:
• Cleavage of fructose 1,6-bisphosphate into two molecules:
  i. Glyceraldehyde 3-phosphate
  ii. Dihydroxyacetone phosphate → converted into another molecule of glyceraldehyde 3-phosphate
• Thus, at the end there are two molecules of glyceraldehyde 3-phosphate at the end of phase 2

Question 13

Glycolysis Phase 3: Pay Off

Answer 13

Phase 3 are energy producing reactions

• Events in Phase 3 include:
• Two molecules of pyruvate are formed
• Two molecules of the electron carrier NADH are produced
• Four molecules of ATP are produced

Question 14

End of Glycolysis

Answer 14

• After glycolysis → there is a net gain of two ATP
• Phase 3 produced four ATP → but two were consumed in phase 1
• Phase 3 also produces two NADH
• These will be used in the last reaction of cellular respiration

Question 15

Mitochondria membrane

Answer 15

• A mitochondrion has an inner membrane and an outer membrane → this defines the two spaces
• The space between the two membranes → intermembrane space
• The space inside the inner membrane → mitochondrial matrix

Question 16

Pyruvate Oxidation

Answer 16

• When oxygen is present → pyruvate can be oxidized to produce carbon dioxide and NADH
• Ultimately to acetyl-CoA
• These reactions occur in the mitochondrial matrix
• Pyruvate is converted to acetyl-CoA
• Then it is further broken down in the citric acid cycle
• The pyruvate is initially oxidized to form CO2 and an acetyl group
• The acetyl group is then transferred to coenzyme A → carries the acetyl group to the citric acid cycle
• These reactions are catalyzed by a group of enzymes called the pyruvate dehydrogenase complex

Question 17

One molecule of pyruvate produces:

Answer 17

• One molecule of COz
• One molecule of NADH
• One molecule of acetyl-CoA
• But remember! At the end of glycolysis, there are two molecules of pyruvate
• Thus, at the end of this entire process, for each glucose molecule there are:
• Two molecules → CO2
• Two molecules → NADH
• Two molecules → Acetyl-CoA

Question 18

Citric Acid cycle additional names:

Answer 18

Krebs cycle and the tricarboxylic acid cycle

Question 19

what happens during the citric acid cycle

Answer 19

• The citric acid cycle completes the oxidation of glucose → CO2
• Substrate-level phosphorylation is used to produce ATP
• Additional energy management molecules → NADH and FADH2 are also produced

Question 20

Use of Intermediates

Answer 20

• some organisms can use products from different steps in the citric acid cycle as intermediates in other metabolic pathways
• E.g. a-Ketoglutarate can be modified to form other amino acids and purine bases

Question 21

Carbon dioxide production

Answer 21

• Have you ever thought about why we exhale CO2?
• The oxidation of acetyl-CoA produces the carbon dioxide we exhale
• There is a transfer of the potential energy stored within acetyl-CoA to be transferred and stored in NADH and FADH
• Also, the production of GTP is catalyzed by substrate-level phosphorylation

Question 22

Fate of High Energy Molecules

Answer 22

• The NADH and FADH that is produced transfers electrons to other carriers in the electron transport chain → ETC
• Recall that they are produced through redox reactions in the first three stages of cellular respiration

Question 23

Where does ETC take place

Answer 23

• The ETC is in the mitochondrial inner membrane → electrons enter & move from donors to acceptor (exchange between proteins)
• Until they reach the final electron acceptor → oxygen (gets two H+)
• When oxygen accepts the electron → reduced to H2O

Question 24

What is the role of the Electron Transport Chain (ETC)?

Answer 24

• Electrons from energy storage molecules (NADH/FADH2) move through ETC proteins via redox reactions.
• This process pumps protons (H+) across the inner mitochondrial membrane.
• It creates a proton gradient with high [H+] in the intermembrane space and low [H+] in the matrix.
• This gradient stores potential energy for ATP synthesis.

Question 25

How is the proton gradient used to make ATP?

Answer 25

- The proton gradient powers ATP synthase. - Protons flow down their concentration gradient back into the matrix through a channel in ATP synthase. -This flow rotates a protein subunit within ATP synthase. - The rotation converts the energy of the gradient into chemical bond energy in ATP.

Question 26

Overall summary of oxidative phosphorylation

Answer 26

- Overall, the energy of glucose is released slowly in a series of reactions - Some of the energy is released by substrate-level phosphorylation - Some is generated through redox reactions that transfer energy to the electron carriers NADH and FADH2 - These carriers donate electrons to the ETC → forms the proton gradient to drive ATP synthase. This is oxidative phosphorylation - Thus, the complete oxidation of glucose forms → 30-32 ATP

Question 27

What happens if oxygen is not available in bacteria and animal cells?

Answer 27

The pyruvate produced from glycolysis can be reduced by a fermentation process - In bacteria and animal cells the pyruvate is reduced to → lactic acid - This regenerates NAD+ → which can then be reduced in glycolysis - ATP is still synthesized in small amounts for use by the cell Glucose + 2 ADP + 2 P → 2 lactic acid + 2 ATP + 2H2O

Question 28

What happens if oxygen is not available for plants and fungi

Answer 28

In the absence of oxygen, plants & fungi undergo → ethanol fermentation - The pyruvate releases CO2 to form acetaldehyde → the electrons from NADH are transferred to acetaldehyde to produce ethanol and NAD+ - Regeneration of NAD+ is important so that small amounts of ATP can be generated during ethanol fermentation Glucose + 2 ADP + 2 P → 2 ethanol + 2CO2 + 2ATP+ 2H2O

Question 29

Excess sugar storage (glucose)

Answer 29

- Plants and animals can store excess glucose for use in glycolysis later → as branched polymers of glucose - Glucose monomers are cleaved one at a time → enter glycolysis as an intermediate - Plants store as → Starch - Animals store as → glycogen - Stored in muscle cells for energy to power contraction - Stored in liver for the whole body

Question 30

Excess sugar storage (other sugars)

Answer 30

- The carbohydrates that are digested can produce a variety of disaccharides & monosaccharides - May produce glucose or other glycolysis intermediates

Question 31

Other energy sources

Answer 31

- Lipids are an excellent energy source → rich in C-C and C-H bonds - Fatty acids absorbed after a meal, or produced from excess glucose, can be used by cells (not all cells can take lipids) - They are shortened through Beta-oxidation - In Beta-oxidation, lipids are broken down into glycerol and acetyl-CoA - Note: ATP is not produced directly - NADH and FADH2 are produced → can enter the ETC

Question 32

What are the 4 stages of cellular respiration?

Answer 32

1. Glycolysis 2. Pyruvate oxidation 3. Citric acid cycle 4. Oxidative phosphorylation ATP is the key end product