Week 5: cellular respiration

Question 1

What are the two ways to make ATP?

Answer 1

You can make ATP via…

• Substrate phosphorellation (glycolisys and Kreb’s Cycle)
• Oxidative phosphorylation (ATPase driven by e- transport chain.

Question 2

What is produced by glycolysis?

Answer 2

• Partially oxidises one molecule of 6C glucose to two molecules of 3C pryuvate. Pyruvate then used in Kreb’s cycle (after being broken into acetyl coA).

NAD+ is reduced to 2 molecules NADH

4 ATP produced but 2 inputted (net gain of 2).

What happens next depends if oxygen is present. If aerobic moves into krebs (via intermediate phase). If anaerobic moves into fermentation (to produce lactic acid or ethanol).

Question 3

Where does the Kreb’s cycle take place?

Answer 3

Kreb’s cycle occurs in mitochondria: begins with pyruvate entering mitochondria and going through intermediate phase to produce acetyl coA.

Question 4

What happens after glycolysis?

Answer 4

Depending whether oxygen is present, pyruvate will either move into the Kreb’s cycle (aerobic) or undergo fermentation (anaerobic).

Question 5

Kreb’s cycle vs fermentation?

Answer 5

Kreb’s:

• Complete oxidation
• Aerobic
• Waste products: H2O and CO2
• Net energy trapped: 32 ATP per glucose
• Cellular respiration
• Necessary for larger life forms.

Fermentation:

• Incomplete oxidation
• Anaerobic
• Waste products: lactic acid or ethanol and CO2.
• Net energy trapped: 2 ATP per glucose.
• Not cellular respiration per se.
• Good for small microbes
• NADPH to NAD+

Question 6

Two types of fermentation?

Answer 6

Fermentation can produce either ethanol (in bacteria + fungi) or lactate (lactic acid) depending what sort of organism you are.

Question 7

Process numbers overview?

Answer 7

Glycolysis

Glucose + 2 ATP&raquo_space; 2 Pyruvates + Energy.
This energy is used for making 4 ATP (net profit of 2 ATP) and 2 NADH from 2 ADP, 2 NAD+ and 2 hydrogen (probably H+).

Fermentation

Pyruvate&raquo_space; Energy + Lactic Acid.

Krebs Cycle

2 Pyruvates + 2 O₂&raquo_space; 2 Acetyl Coenzyme A + 2 CO₂ + Energy.
This energy is used to form 2 NADH from NAD+ and hydrogen.
2 Acetyl Coenzyme A + 2 Oxaloacetic Acid&raquo_space; 2 Citric Acid.
2 Citric Acid + 4 O₂&raquo_space; 2 Oxaloacetic Acid + Energy + 4 CO₂.
This energy is used to make 2 ATP, 6 NADH and 2 FADH₂.
So after the Krebs Cycle we now have 10 NADH, 2 FADH₂ and 4 ATP (or 6 if you count the ATP spent in Glycolysis).

Electron Transport Chain

10 NADH&raquo_space; Energy + 10 NAD+ + 10 Hydrogen.
This energy is used to pump some protons out of the inner membrane of the mitochondria. They went back through the ATP synthase creating at most 3 ATP for each NADH, for a total of 30 ATP (at most).
2 FADH₂&raquo_space; Energy + 2 FAD+ + 4 Hydrogen.
This energy is also used to pump some protons. This creates, at most, 2 ATP each FADH₂, for a total of 4 ATP.

Conclusion:
Total ATP created: 38 molecules, if the cell is very efficient.
2 ATP is spent in glycolysis so there would be at most 40 ATP that went through the steps.
10 NAD+ were used, and probably reused.
2 FAD+ were used, and also probably reused.
6 O₂ were used and they became 6 CO₂ in the Krebs Cycle.
2 Oxaloacetic Acid were used and reused.

Question 8

Energy production process in a simple nutshell?

Answer 8

Basically oxidation of glucose powers one of two forms of ATP phosphorylation: substrate phos in glycolysis and krebs, and oxidative phos in e- transport chain. Side plot, energy stored in e- carriers which ultimately power oxidative phos.

1) Breakdown of energy-rich compounds such as glucoose in the cytoplasm -> glyocolysis into pyruvate and ATP.
2) Partial degredation products of glycolysis (pyruvate) enters mitochondria and moves through Kreb’s cycle to make more ATP + interact with e- transport chain.
3) Citric acid cycle takes place in fluids of matrix
4) e- transport chain + oxidative phosphorylation takes place across cristae membranes.

Question 9

Kreb’s cycle completes the oxidation of_____?

Answer 9

Krebs cycle completes the oxidation of glucose to CO2

Question 10

What is the key reaction of carbon molecules that occurs in the Kreb’s cycle?

Answer 10

In the Krebs cycle 2C acetyl CoA and 4C oxaloacetate make 6C citrate.

Citrate is then broken down (catabolised) gradually back into 4C oxaloacetate, with the 2C lost forming into 2 CO2 molecules.

So…
Acetyl coA + oxaloacetate => citrate
Citrate + O2 => oxaloacate + 2CO2

Question 11

How many NAD+, FAD, ADP, and O2 as inputs in a single turn of Kreb’s cycle?

Answer 11

3 NAD+
1 FAD
2 ADP
2 O2

Question 12

How many NADH, FADH2, ATP, CO2 as outputs in SINGLE turn of krebs cycle?

Answer 12

3 NADH (from 3 NAD+)
1 FADH2 (from 1 FAD)
2 ATP (from 2 ADP)
2 CO2 (from 2 O2)

Question 13

What are the three main steps of cellular respiration?

Answer 13

The three main phases of cellular respiration are

1) Glycolysis
1. 5: intermediate phase
2) Kreb’s cycle
3) Electron transport chain

Question 14

Catabolism vs anabolism?

Answer 14

Catabolism: breakdown of large molecules for energy (e.g. cellular respiration)

Anabolism: use of energy to build larger molecules

Question 15

What is the purpose of the oxidation of glucose?

Answer 15

As glucose molecules are broken into simpler carbon compounds throughout cellular respiration pathways electrons are released by oxidation of these compounds. These electrons are then used to enable phosphorylation of ADP to ATP so that energy can be stored in the form of ATP.

Question 16

What are the two key electron carriers used in cellular respiration pathways?

Answer 16

NADH and FADH2 act as electron carriers, moving electrons between glycolysis, krebs cycle and the e- transport chain to supplement energy needed to drive these processes where necessary.
-> NAD+ and FAD are reduced into NADH and FADH2 forms that store energy as electrons. NADH stores more energy than FADH2.

Ultimately electrons pass to oxygen at the end of the electron transport chain.

Question 17

What are the two types of ADP phosphorylation and where do they occur?

Answer 17

Substrate phosphorylation occurs in glycolysis and the kreb’s cycle (using enzymes). From transferring phosphate from substrate to ADP.

Oxidative phosphorylation occurs in e- transport chain in mitochondria (using ATPase). Makes >90% of ATP. Aerobic. Occurs in two steps: 1) e- transport chain where protons power an electron pump 2) chemiosmosis; when protons move back across membrane and drive ATPase to produce ATP.

Question 18

Where does glycolysis occur?

Answer 18

Glycolysis occurs in the cytosol (cytoplasm).

Question 19

What are the phases of glycolysis?

Answer 19

1) Glucose => fructose biphosphate (uses ATP
2) fructose biphosphate => 2X glyceraldehyde phosphate (from 6C=>3C)
3) Each glyceraldehyde converted to pyruvate over a series of steps we don’t need to worry about

Question 20

What causes glycolysis to stop (reach equlibrium; not exactly stopped but not producing a net gain)?

Answer 20

Glycolysis stops when pyruvate is no longer being removed + used.

Question 21

Why is fermentation useful?

Answer 21

Fermentation doesn’t make as much ATP as cellular respiration (it makes 2ATP, Kreb’s cycle pathway etc makes more like 30 both w substrate phosphorylation) but if oxygen isn’t present then it’s still better than nothing.

Endergonic: uses some energy

It recycles NADH back to NAD+ by adding these e- to make ATP

Because it doesn’t produce much energy means that small organisms (bacteria etc) who rely solely on fermentation for energy are constrained on how big they can do and how complex systems they can run.

Question 22

What happens in the intermediate phase?

Answer 22

In the intermediate phase pyruvate is converted into acetyl coA (3C => 2C + CO2) using coenzyme A + catalysed by pyruvate dehydrogenase complex, over several steps we don’t need to worry about. Exergonic: produces some energy to charge electron carriers

Occurs in membrane of mitochondria. There is an energy cost in crossing membrane, uses transport protein which needs ATP.

Recyles NAD+ to NADH. Produces 1 CO2.

Question 23

What is the initiation of the citiric acid cycle?

Answer 23

The initiation of the citric acid cycle is 2C acetyl coA + 4C oxaloacetate.

Question 24

What are the two steps of oxidative phosphorylation?

Answer 24

The steps of oxidative phosphorylation are

1) e- transport chain
2) Chemiosmosis

Question 25

How are e- transport chains different in prokaryotes and eukaryotes?

Answer 25

Prokaryotes have no mitochondria so the e- transport chain occurs in proteins in the plasma membrane.

In eukaryotes it occurs in the mitochondrial inner membrane.

Question 26

What happens at the e- transport chain phase of cellular respiration if there’s no oxygen?

Answer 26

If anaerobic conditions then e- transport chain can’t occur, so pyruvate is diverted to fermentation.

Question 27

What chemical changes and movements are driven by the e- transport chain?

Answer 27

in the e- transport chain e- are stripped off NADH and FADH2 and driven back across the inner mitochondrial membrane which drives the flow of protons in the other direction (pushes protons to outside of membrane from mitochondrial matrix to intermembrane space).

Lipid bilayer doesn’t allow H+ ions to cross so over time concentration of H+ builds up in the intermembrane space, creating a concentration gradient and building electrochemical potential. This triggers chemiosmosis: these protons then flow through ATPase (ATP synthase), an enzyme complex built of multiple proteins. This essentially turns a rotor and central rod like an engine and drives the production of ATP through oxidative phosphorylation (as catalytic sites are activated to phosphorylate ADP to ATP).

Sooooo

1) e- transport from NADH and FADH2 pumps H+ across membrane, creating a gradient and electrochemical potential.
2) Chemiosmosis: ATP synthesis powered by the flow of H+ back across the membrane.

Question 28

What are Q and Cyt c?

Answer 28

Q and cyt c are components of the oxidation of electron carriers chain, mobile within the membrane, used to drive e- and H+ flow

Question 29

Where is the krebs cycle?

Answer 29

The krebs cycle is in the mitochondrial matrix.

Intermediate phases happens at the mitochondrial membrane.