L21: Cellular Respiration and Redox Reactions

Question 1

What are the 4 stages of cellular respiration?

Answer 1

• Glycolysis
• Pyruvate oxidation
• Citric Acid Cycle (TCA)
• Oxidative phosphorylation

Question 2

What is the result of CR?

Answer 2

• the complete oxidation of the carbon in glucose to carbon dioxide

Question 3

What is the purpose of CR?

Answer 3

• Capture energy released harnessed in the form of ATP

Question 4

What does the energy break down in CR look like?

Answer 4

• the energy in the carbon bonds in glucose is broken down in steps (i.e. slowly oxidized)
• the energy is captured (harnessed) in the form of ATP and other high energy intermediates (NADH, FADH2)

Question 5

CR Overview

Answer 5

• Oxidation of glucose to CO2
• Energy captured in ATP
• Production of high energy intermediates such as NADH, FADH2

Question 6

What is glycolysis?

Answer 6

• Glucose is broken down into pyruvate
• ATP and other high energy intermediates (electron carriers) are produced
• “glucose splitting”

Question 7

Where does CR occur in bacterial cells?

Answer 7

• Steps 1-3: cytoplasm/cytosol

- Step 4: cell membrane

Question 8

Where does CR occur in eukaryotic cells?

Answer 8

• Step 1: Cytoplasm

- Step 2-4: Mitochondria

Question 9

Which steps in CR is CO2 produced as a product?

Answer 9

• Pyruvate oxidation (processing)

- Citric Acid cycle

Question 10

CO2 production is significant because this indicates…

Answer 10

• carbon atoms from glucose has been completely oxidized

- these carbon atoms become waste products (i.e. released from the cell!)

Question 11

ATP in glycolysis is synthesized via…

Answer 11

• Substrate level phosphorylation

Question 12

What is the overall goal of glycolysis?

Answer 12

• break down glucose (i.e. being oxidized)
• extract the energy from the reduced form of carbon in several steps
• in the process, synthesize high energy ATP and NADH (an electron carrier)
• create pyruvate - a molecule that can be used in different pathways

Question 13

What is the first phase of glycolysis?

Answer 13

• Energy investment phase

- 2 ATP used to phosphorylate a 6 carbon sugar with 2 negatively charged phosphate groups.

Question 14

What is the second phase of glycolysis?

Answer 14

• Energy payoff phase
• 4 ATP made by substrate level phosphorylation
• 4 electrons removed to reduce 2 NAD+ to 2 NADH

Question 15

How many reactions occur in glycolysis?

Answer 15

• 10 enzyme catalyzed reactions that breakdown glucose.

Question 16

How much ATP and NADH are synthesized at the end of glycolysis?

Answer 16

• uses 2 ATP and synthesized 4 ATP
• 2 net ATP
• synthesizes 2 NADH (4 electrons -2 to each NAD+)

Question 17

What are the high energy intermediates?

Answer 17

HIGH ENERGY FORM:

• ATP and NADH
• Play a role in metabolism

LOW ENERGY FORM:

• ADP OR AMP
• NAD+

Question 18

NADH is an…

Answer 18

• electron carrier

Question 19

What is the oxidized form of NAD?

Answer 19

• NAD+
• can take up/accept 2 electrons
• “being reduced”

Question 20

What is the reduced form of NAD?

Answer 20

• NADH
• can donate 2 electrons
• “being oxidized”

Question 21

What is substrate-level phosphorylation?

Answer 21

• Enzyme catalyzes transfer of phosphate from a phosphorylated molecule (substrate) to ADP
• how ATP can be synthesized from ADP and Pi
• Occurs in cytosol/mitochondrial matrix (EUKARYOTIC) and cytosol (BACTERIA)

Question 22

SLP vs. Oxidative phosphorylation (oxphos)

Answer 22

SLP:

• Involves enzymes and substrates the phosphorylate ATP
• Enzyme removes P from substrate to phosphorylate ADP
• ATP is synthesized. Substrate has lost a phosphate

Oxphos:
-involves membrane-bound enzymes and H+ (proton) gradient drives ATP phosphorylation

Question 23

What do cells capture in a series of redox reactions?

Answer 23

• Energy
• Energy is transformed into high energy intermediates (i.e. ATP, NADH, FADH2) which are usable forms of energy for the cells

Question 24

Where does a cell get the energy from?

Answer 24

• energy is captured by oxidation and reduction reactions = REDOX
• nutrients (food) are electrons donors i.e. donate electrons to molecules in the cell
• the electron acceptor molecules capture some of the energy loss from the electron donors
• Redox reactions shift potential energy stored in chemical bonds by changing electron positioning.

Question 25

What is oxidation?

Answer 25

• loss of electrons by an atom
• and usually gains O atoms
• and/or loses H

Question 26

What is reduction?

Answer 26

• gain of electrons by an atom
• and usually also gains H atoms
• and/or loses O

Question 27

What are the 2 components of redox reactions?

Answer 27

• electron donor: loses electrons and becomes oxidized
• electron acceptor: gains electrons and becomes reduced
• electrons are always donated or accepted by atoms (that are part of molecules) electrons cannot float in the cell!