Exam 4 lecture

The two reactions involved in a redox reaction are

oxidation and reduction

Electrons that are removed from the C—H bonds of glucose during glycolysis and the Krebs cycle are donated to

electron carriers

The transfer of a high energy phosphate group from a phosphorylated organic molecule to ADP is referred to as

substrate-level phosphorylation

Redox reactions involve the

loss and gain of electrons.

During the reactions of glycolysis, one molecule of glucose is converted into how many molecules of pyruvate?

2

When one glucose molecule undergoes glycolysis, the cell generates two molecules each of (net yield):

ATP pyruvate and NADH

The citric acid cycle and glycolysis do what

used by cells to strip electrons off of the C-H bonds of a glucose molecule.

what happens during glycosis?

NAD⁺ is reduced to NADH.
Substrate-level phosphorylation of ADP occurs.

Glucose is converted to two molecules of pyruvate

During substrate-level phosphorylation, ATP is made by

transferring a phosphate group from a phosphate-bearing intermediate directly to ADP

NADH must be oxidized to _ in order for glycolysis to continue.

NAD+

What are the two ways in which a eukaryotic cell can regenerate NAD+ needed to continue carrying out glycolysis?

aerobic respiration (when oxygen is present) and anaerobic fermentation (when oxygen is absent)

Which of the following molecules is generated during the oxidation phase of glycolysis?

NADH

In the presence of oxygen, pyruvate can enter the citric acid cycle but must be converted to

acetyl-CoA first 

main changes that occur during glycolysis

• ADP is converted to ATP via substrate level phosphorylation.

• Glucose is converted to two molecules of pyruvate.

• NAD⁺ is reduced to NADH.

During the oxidation of pyruvate, which molecule is reduced?

NAD+ is the molecule that is reduced to form NADH

The complex of enzymes that removes CO₂ from pyruvate is called

pyruvate dehydrogenase

In order to continue performing glycolysis, cells regenerate NAD+ by using NADH to

reduce another molecule

Which of the following happens to the molecule formed by the addition of carbon dioxide to ribulose bisphosphate?

It is immediately split into two more stable three carbon molecules.

In order to continue carrying out glycolysis, a eukaryotic cell must regenerate NAD+ from NADH. If the cell has oxygen available to it, it uses _ respiration. If oxygen is unavailable, an organic molecule can accept electrons from NADH, i.e., the cell performs _

aerobic, fermentation

What is the function of the enzyme rubisco?

It catalyzes the addition of carbon dioxide to RuBP.

During fermentation, most of the pyruvate produced during glycolysis is used to convert NADH to

NAD+

In aerobic conditions, _ produced in glycolysis is oxidized to acetyl-CoA resulting in the formation of _ and carbon dioxide.

pyruvate, NADH

events that occur in the reaction that produces acetyl-CoA

An acetyl group is attached to coenzyme A (CoA)

CO₂ is removed from pyruvate

NAD⁺ is reduced

carbon fixation:

carbon dioxide is incorporated into a molecule of ribulose biphosphate forming an unstable 6-carbon intermediate that immediately splits into two 3-carbon molecules.

Where is rubisco located?

chloroplast stroma

pigment molecules (chlorophylls) are important to light rxns because they

capture light energy

chlorophylls are in

photosystems

photosystems are in

thylakoid membranes

1. antenna chlorophylls (AC) capture

photon energy

2. photon energy is transferred from

AC to AC

3. the energy from the ACs then goes to the

reaction center chlorophyll (RCC)

4. the energy is then absorbed by

electrons in the RCCs

5. the energized e-’s 

either leave the RCC,

are captured by an electron carrier, 

or enter into an ETC 

6. the electrons missing from the RCCs are

replaced 

PS 2 gets replacement electrons from 

H2O, the energized electrons get ejected and enter into the ETC 

the ETC carries the electrons from

PS2 to PS1

PS1 gets replacements electrons from

PS2

when electrons reach PS1, their extra energy is gone — where does it goes?

extra energy in the electrons is used to power a proton (H+) pump which creates a proton H+ gradient across the membrane

to diffuse back across the membrane, H+’s need a

channel from ATP synthase (enzyme/transport protein)

ATP synthase uses the energy of H+ flow to make

ATP (which is how the light rxns make ATP)

How is NADPH made in the light rxns?

photon energy from light is used to re-energize the e-’s in PS1. Re-energized electrons are used to reduce NADP+ to NADPH.

In both PS1 and PS2

• antenna chlorophylls capture photon energy

• photon energy is used to energize electrons within reaction center chlorophylls

only in PS2:

• energized electrons enter the ETC and are transported from PS2 → PS1

• energy from electrons in the ETC is used to produce ATP

• replacement electrons come from H2O 

only in PS1

• replacement electrons come from PS2

• those electrons are re-energized with photon energy 

• energized electrons are transferred to NADP+ (reduction) → NADPH

linear electron flow: 

• produces about 1.2 ATPs per NADPH

the linear electron flow doesn’t produce as much as teh dark rxns need 

which is 1.5 ATPs per NADPH so extra ATP is generated from the cyclic electron flow 

cyclic electron flow

re-energized electrons from PS1 are transported back to the proton pump instead of being used to reduce NADP+ to NADPH

dark rxns occur in the

stroma of the chloroplast

dark rxns need

NADPH and ATP (produced by the light rxns) and CO2

dark rxns have 3 steps

1. carbon fixation

2. reduction of PGA

3. regeneration of RuBP

carbon fixation:

converts a gaseous form of carbon (CO2) into a non-gaseous form (PGA)

reduction of PGA:

electrons are transferred from NADPH to PGA 

regeneration of RuBP:

RuBP is a molecule needed for the carbon fixation step

carbon fixation begins with

RuBP and CO2

RuBP is a

5-C sugar known as the carbon acceptor

carbon fixation:

1. RuBP and CO2 form a covalent bond

2. carbon fixation is catalyzed by the enzyme Rubisco

3. the 6-C intermediate spontaneously breaks down into two 3-C molecules (PGA) 

RUBP and CO2 covalent bond:

1, RuBP + 1, CO2 → 1, 6-C intermediate

PGA molecules breakdown

1m 6-C intermediate → 2, 3-C PGA molecules

reduction of PGA uses

NADPH as an electron source and ATP as an energy source

PGA is reduced and converted into

G3P

G3P has two functions:

1. used to make glucose 

2. used to regenerate RuBP for carbon fixation 

summary of dark rxns

1. carbon fixation

2. reduction of PGA 

3. RuBP regeneration 

dark rxns make other things than glucose like

• other sugars

• amino acids

• lipids 

• nucleic acids 

glucose has energy:

686 kcal/mol

how do organisms extract energy from glucose

thru the oxidation of glucose

the oxidation of glucose has 2 phases

glycolysis and cellular respiration

phase 1 of oxidation of glucose is glycolysis

• occurs in the cytoplasm of cells

• glucose is converted into pyruvate 

phase 2 of oxidation of glucose is cellular respiration

• occurs in the mitochondria of cells 

• has 3 stages 

CR 3 stages

• oxidation of pyruvate 

• citric acid cycle (TCA, Krebs Cycle) 

• electron transport chain 

during glycolysis and cellular respiration ATP is generated _ ways

2

the flow of protons thru ATP synthase is known as

chemiosmosis

substrate level phosphorylation:

an enzyme

1) takes a phosphate from one molecule (substrate) 

2) adds the phosphate to ADP (ADP→ATP) 

glycolysis occurs in the

cytoplasm

glycolysis: glucose is converted to

pyruvate

glycolysis inputs

1 glucose (6C)

2 NAD+

2 ADP

glycolysis outputs

2 pyruvates (3C) 

2 NADH (reduction of NAD+)

2 ATP (substrate level phos.)

pyruvate steps

1. glucose to pyruvate via glysolysis

2. pyruvate to cellular respiration thru + O2 (aerobic respiration)

3. pyruvate to fermentation  thru - O2 (anaerobic respiration)

fermentation results

• incomplete oxidation 

• produces organic products 

• produces NAD+ 

• 2 ATP (from glycolysis) 

• * 2% efficiency 

cellular respiration results

complete oxidation

• produces H2O and CO2 

• can make max 36 ATP 

• around 38% efficiency max

anaerobic respiration in yeast cells (cytoplasm) inputs 

2 NADH 

2 pyruvates 

anaerobic respiration in yeast cells (cytoplasm) outputs

2 NAD+ (back to glycolysis)

2 Ethanol (fermentation)

2 CO2

purpose of glycolysis and anerobic respiration in yeast is to

regenerate NAD+ to keep glycolysis going

yield of  glycolysis and anerobic respiration

2 ATPs / glucose (2% efficiency) 

Anaerobic Respiration Muscle in cells (cytoplasm) inputs:

2 NADH

2 pyruvates

Lactate Molecules:

1) Can be converted back into pyruvate (in cells)

2) Can be converted back to glucose (by the liver)

Glycolysis + Anaerobic respiration (Muscle cells) — Purpose:

Regenerate NAD+ to keep glycolysis going

Glycolysis + Anaerobic respiration (Muscle cells) — Total Yield:

2 ATPs/glucose (2% efficiency)

Glycolysis + Anaerobic respiration (Muscle cells) Outputs:

2 NAD+ (back to glycolysis)

2 lactate (fermentation

if there is sufficient oxygen (2):

1. pyruvate will enter the mitochondria

2. cellular respiration will begin

oxidation of pyruvate occurs in the

matrix of the mitochondria

oxidation of pyruvate process

1 pyruvate → Coenzyme A (CoA) → acteyl - CoA

Citric Acid Cycle

Completes the oxidation of the acetyl group

CAC Occurs in the

matrix of the mitochondria

CAC has 

9 reactions in 3 phases

CAC steps

1) (2C) Acetyl + (4C) oxaloacetate (the Acetyl acceptor) -> (6C) citrate (citric acid)

2) The oxidation of the acetyl group is completed

3) Regeneration of oxaloacetate

and the cycle starts over with step 3 going back to step 1

CAC inputs

Acetyl group

NAD+

FAD

ADP

Oxaloacetate

CAC outputs 

CO2 (Oxidation of Acetyl group)

NADH (reduction of NAD+)

FADH2 (reduction of FAD)

ATP (substrate level phos.)

Oxaloacetate

CAC: NADH and FADH2 will

transport the electrons to the ET Chain

-Glycolysis & Anaerobic respiration :

Occur in the

cytoplasm

-Oxidation of pyruvate & the Citric acid cycle:

Occur in the

matrix