Cellular Respiration part 2 Citric Acid Cycle, ETC, and Anaerobic Processes

In eukaryotes, if O2 is present, pyruvate enters the…

mitochondrion (matrix) to finish oxidizing glucose

Before entering the citric acid cycle, pyruvate is converted to…

acetyl coenzyme A (acetyl CoA)

What is released when pyruvate is converted to acetyl CoA?

CO2

Products of pyruvate oxidation (per pyruvate)?

1 acetyl CoA, 1 CO2, 1 NADH

Pyruvate oxidation makes ____ NADH per pyruvate and ____ NADH per glucose

1; 2

Where does pyruvate oxidation happen?

Mitochondrial matrix

The citric acid cycle is also called the…

Krebs cycle

The citric acid cycle completes the breakdown of pyruvate to…

CO2

Each turn of the citric acid cycle oxidizes molecules from…

one pyruvate

How many times does the citric acid cycle turn per glucose?

Twice (one glucose makes 2 pyruvates)

Citric acid cycle products per glucose?

2 ATP, 6 NADH, 2 FADH2 (plus 4 CO2)

Citric acid cycle products per pyruvate (one turn)?

1 ATP, 3 NADH, 1 FADH2, 2 CO2

Where does the citric acid cycle happen?

Mitochondrial matrix

How many steps are in the citric acid cycle?

Eight, each with its own enzyme

The acetyl group of acetyl CoA combines with ____ to form ____

oxaloacetate; citrate

Why is the citric acid cycle a "cycle"?

The last steps turn citrate back into oxaloacetate, which is reused

Which molecules capture energy from the citric acid cycle's redox reactions?

NADH and FADH2 (and a little ATP)

How is ATP made in the citric acid cycle?

Substrate-level phosphorylation

Where do the electrons from the citric acid cycle go?

NADH and FADH2 carry them to the electron transport chain

Total CO2 released per glucose (pyruvate oxidation + citric acid cycle)?

6 (2 + 4)

How many ATP do glycolysis and the citric acid cycle make by substrate-level phosphorylation?

Only 4 total (2 + 2)

What accounts for most of the energy extracted from glucose?

NADH and FADH2

Role of NADH and FADH2?

Carry electrons from glycolysis/citric acid cycle to the ETC (they link those stages to oxidative phosphorylation)

Where is the ETC in eukaryotes?

Inner mitochondrial membrane

Where is the ETC in prokaryotes?

Plasma membrane

How does ETC location support the endosymbiotic theory?

The inner mitochondrial membrane matches the plasma membrane of the bacteria mitochondria came from

Most ETC components are…

protein complexes (numbered I to IV) with electron carriers

Role of cofactors/coenzymes in the ETC?

They're attached to proteins and actually carry the electrons (like heme groups and iron-sulfur)

Most ETC proteins are ____ with attached ____ groups

cytochromes; heme

Role of cytochromes?

Proteins with heme groups that pass electrons down the chain

The only non-protein electron carrier in the ETC?

Ubiquinone (Q), a small lipid that moves in the membrane

NADH drops off its electrons at Complex…

I

FADH2 drops off its electrons at Complex…

II

Which gives more energy for ATP synthesis: NADH or FADH2?

NADH (FADH2 enters lower in the chain, so it makes less ATP)

Electron carriers in the ETC switch between…

reduced and oxidized states (accepting and donating electrons)

"Electron flow down the chain" means…

electrons drop in free energy with each transfer between carriers until they reach O2

Each carrier in the ETC is more ____ than the one before it

electronegative

"Less electronegative" means…

weaker pull on electrons (it gives them away more easily)

Why release energy in small steps down the ETC?

So energy comes out in manageable amounts instead of one big explosion

What is the final electron acceptor of the ETC?

O2

What is formed when O2 is reduced at the end of the ETC?

H2O

Does the ETC make ATP directly?

No

What does the ETC use the energy from electron transfer for?

Pumping H+ into the intermembrane space

Where does the ETC pump H+?

From the matrix into the intermembrane space

The ETC creates an H+ ____ across the inner mitochondrial membrane

gradient (concentration gradient)

How does H+ get back into the matrix?

By diffusing down its gradient through ATP synthase

ATP synthase is located in the…

inner mitochondrial membrane (plasma membrane in prokaryotes)

Function of ATP synthase?

Uses the flow of H+ to make ATP from ADP + phosphate

Power source for ATP synthase?

The H+ gradient (H+ flowing down its concentration gradient)

Is the flow of H+ through ATP synthase exergonic or endergonic?

Exergonic

ATP synthase vs an ion pump?

An ion pump uses ATP to move ions against a gradient. ATP synthase works in reverse: ions flowing down a gradient make ATP

Think of ATP synthase like…

a water wheel/mill turned by H+ flowing through it

Chemiosmosis is…

using the energy in an H+ gradient across a membrane to do cellular work (like make ATP)

Chemiosmosis couples ____ to ____

the redox reactions of the ETC; ATP synthesis

Oxidative phosphorylation =

electron transport + chemiosmosis

The proton-motive force is…

the H+ gradient, emphasizing its ability to do work

How does the membrane maintain the H+ gradient?

The ETC keeps pumping H+ out, and H+ can only come back through ATP synthase

Order of energy flow in cellular respiration?

Glucose → NADH → electron transport chain → proton-motive force → ATP

About what % of glucose's energy ends up in ATP?

About 34%

About how many ATP are made per glucose?

About 32 (roughly 30–32)

What happens to the rest of glucose's energy?

It's lost as heat

ATP made by glycolysis per glucose?

2 ATP (substrate-level)

ATP made by the citric acid cycle per glucose?

2 ATP (substrate-level)

ATP made by oxidative phosphorylation per glucose?

About 26–28

Why is the exact ATP number per glucose uncertain?

Phosphorylation isn't directly coupled to redox, NADH vs FADH2 give different yields, and the proton-motive force is used for other work too

Most ATP from cellular respiration comes from…

oxidative phosphorylation

What happens to the ETC without O2?

It stops, and oxidative phosphorylation stops

2 ways cells make ATP without O2?

Anaerobic respiration and fermentation

Both anaerobic respiration and fermentation begin with…

glycolysis

Which uses an ETC: anaerobic respiration or fermentation?

Anaerobic respiration (fermentation doesn't)

In anaerobic respiration, what replaces O2 as the final electron acceptor?

Another electronegative molecule, like sulfate (SO4 2-)

Are anaerobic final electron acceptors more or less electronegative than O2?

Less electronegative

Why does anaerobic respiration make less ATP than aerobic?

Its final acceptor is less electronegative than O2, so less energy is released

How does fermentation keep making ATP?

Through substrate-level phosphorylation in glycolysis

Fermentation =

glycolysis + reactions that regenerate NAD+

Why does fermentation need to regenerate NAD+?

Glycolysis needs NAD+ to keep running

How is NAD+ regenerated in fermentation?

NADH transfers its electrons to pyruvate or a pyruvate derivative

2 common types of fermentation?

Alcohol fermentation and lactic acid fermentation

In alcohol fermentation, pyruvate is converted to…

ethanol (in two steps)

Steps of alcohol fermentation?

1) CO2 released from pyruvate → acetaldehyde 2) NADH reduces acetaldehyde → ethanol (NAD+ regenerated)

Does alcohol fermentation release CO2?

Yes

Final electron acceptor in alcohol fermentation?

Acetaldehyde

Uses of alcohol fermentation by yeast?

Brewing, winemaking, and baking (think: CO2 makes bread rise)

In lactic acid fermentation, pyruvate is converted to…

lactate (directly, no CO2 made)

Does lactic acid fermentation release CO2?

No

Final electron acceptor in lactic acid fermentation?

Pyruvate

Alcohol vs lactic acid fermentation?

Alcohol = pyruvate → acetaldehyde + CO2 → ethanol. Lactic acid = pyruvate → lactate, no CO2

When do human muscle cells use lactic acid fermentation?

When O2 is scarce (like during hard exercise)

Uses of lactic acid fermentation by fungi and bacteria?

Making cheese and yogurt (and chocolate from cacao beans)

Fermentation produces ____ ATP per glucose; cellular respiration produces about ____

2; 32

In fermentation, aerobic, and anaerobic respiration, what is the oxidizing agent in glycolysis?

NAD+

What do fermentation, aerobic, and anaerobic respiration all have in common?

All use glycolysis (net 2 ATP), use NAD+ as the oxidizing agent, and make some ATP by substrate-level phosphorylation

How do fermentation and respiration differ in oxidizing NADH?

Fermentation = gives electrons to an organic molecule (pyruvate/acetaldehyde). Respiration = gives electrons to the ETC

Final electron acceptor: aerobic vs anaerobic respiration vs fermentation?

Aerobic = O2. Anaerobic = another molecule like sulfate. Fermentation = organic molecule (pyruvate or acetaldehyde)

Fermentation vs respiration: substrate-level or oxidative phosphorylation?

Fermentation = substrate-level only. Respiration = both (mostly oxidative)

Besides glucose, what can be used for cellular respiration?

Other carbohydrates, proteins, and fats

Catabolic pathways funnel electrons from many organic molecules into…

cellular respiration

What has to happen to proteins before they're used in respiration?

Digested to amino acids and amino groups removed (deamination)

Deamination is…

removing the amino group from an amino acid

Fats are digested into…

glycerol and fatty acids