Cellular Respiration

Question 1

How do cells obtain energy?

Answer 1

By breaking down complex molecules and

harvesting the energy released by the reaction

Question 2

What is Fermentation?

Answer 2

Partial breakdown of sugars and other organic fuels

without the use of oxygen to provide energy for a cell.

Question 3

What is Aerobic respiration

Answer 3

A cell obtains energy via a thorough breakdown of organic fuels in which oxygen is consumed

Question 4

What happens during Aerobic respiration?

Answer 4

Organic compound + O2 → CO2 + H2O + energy

- Organic compounds = carbo’s, fats and protein molecules … can all be used as fuel!

Question 5

What is an oxidisation-reduction reaction?

Answer 5

-Transfer of electrons during chemical reactions releases energy stored in chemical molecules, which is used to synthesise ATP
- Transfer of electrons from one reactant to another is called oxidation-reduction reaction (= “redox reaction”)
» Gain of electron = “reduction” (remember: e-)
» Loss of electron = “oxidation”
- Oxygen is highly electronegative (loves electrons), so it strips electrons away from other compounds

Question 6

Oxidation is when you…

Answer 6

lose electrons

Question 7

Reduction is when you

Answer 7

gain electrons

Question 8

What happens if energy is released too fast? How does Cellular respiration combat this?

Answer 8

It cannot be efficiently harvested so Cellular respiration breaks down glucose (and other organic fuels) in a series of small steps instead of a single explosive step
- NAD+ slowly harvests H (and e-) from glucose and passes it down the electron transport chain

Question 9

What are the stages of Cellular Respiration?

Answer 9

Glycolysis ->Pyruvate Oxidation->Citric Acid Cycle-> Oxidative Phosphorylation

Question 10

Draw the cellular respiration diagram

Answer 10

in workbook, answer is in the back.

Question 11

What is substrate level phosphorylation?

Answer 11

Some ATP is made by direct transfer of a phosphate group from an organic substrate to ADP by an enzyme, where the substrate has a phosphate group in it and, via the enxyme, it is transfered to ADP to create ATP and a product.

Question 12

What is Glycolysis?

Answer 12

• Sugar splitting
• Substrates: Glucose & 2 ATP
• Products:
  » 2 pyruvate
  » 4 ATP (so net = 2)
  » 2 NADH + 2 H+
  » 2 H2O

Question 13

What are the first three products in the cellular respiration cycle?

Answer 13

Pyruvate → Acetyl CoA → Citric Acid Cycle

Question 14

What is the Citric Acid Cycle and how does it work?

Answer 14

If oxygen is present, pyruvate enters mitochondria, is
converted to Acetyl CoA, which then fuels the CAC
- Substrates
» Pyruvate (Acetyl CoA)
- Products
» 3 CO2
» 4 NADH + 4 H+ and 1 FADH2
» 1 ATP

Question 15

How many ATP’s are produced from substrate level phosphorylation?

Answer 15

4 ATPs, produced by substrate-level phosphorylation
» Glycolysis: 2 ATP
» Citric Acid Cycle: 2 ATP

Question 16

ATP production from substrate level phosphorylation accounts 4% of the total energy, where does the rest come from?

Answer 16

Most of the energy recovered is in electron carriers (NADH and FADH2)

Question 17

What is the Electron Transport chain?

Answer 17

ETC is series of molecules (mostly proteins) embedded in inner membrane of mitochondria
» Step-wise harvest of G from “falling” electron
» Doesn’t produce ATP, but uses the energy to push
H+ from the mitochondrial matrix to the intermembrane space

Question 18

What is ATP synthase?

Answer 18

An enzyme that created ATP from the proteins that are tying to enter the mitochondria. It allos them in and takes a phosphate group from the protein to creat ATP.

Question 19

What is Chemiosmosis?

Answer 19

ETC produces a H+ gradient across the mitochondrial membrane, which provides the energy to power the enzyme ATP synthase

Question 20

During respiration, energy flows from…

Answer 20

» Glucose → NADH → ETC → proton gradient → ATP

Question 21

How much ATP is made for each section of respiration and how much is made in total? What happens to the rest?

Answer 21

Glycolysis + Citric Acid Cycle: 4 ATP
» ETC & chemiosmosis: 26-28 ATP
» Total = 30-32 ATP (ie, ΔG = 219-234 kcal)
» So cellular respiration recovers ≈34% of the total energy in glucose
• Compare with 25% for internal combustion engine!
• The rest is lost as heat

Question 22

Draw the final electron yield diagram

Answer 22

In back of workbook

Question 23

What is the final electron acceptor of the ETC and what happens if there is none?

Answer 23

The final electron acceptor of the ETC is O2 … if there’s no O2, the ETC (and ATP production) stops!

Question 24

Certain cells can still generate energy without O2, how?

Answer 24

via anaerobic respiration or fermentation

Question 25

What is Anaerobic respiration and how does it work?

Answer 25

Anaerobic respiration is just respiration except without oxygen. Some prokaryotes can live in environments without O2 by using a different final electron acceptor in ETC - “anaerobic respiration”
» eg, sulfate ion (SO4^2-), nitrate (NO3-), sulfur (S) etc …

Question 26

What does fermentation do and why?

Answer 26

• Glycolysis produces 2 ATP and does not need O2!
• Not very efficient reaction (≈2% of energy in glucose),
• However, need a mechanism to recycle the NAD+ from NADH (which normally occurs in ETC)
• Fermentation regenerates NAD+ by transferring electrons from NADH to pyruvate (or derivative of pyruvate)

Question 27

What kind of feuls can a living system use?

Answer 27

Living systems can use all kinds of organic fuels, incl.
» Carbohydrates
» Proteins
» Fats

Question 28

What can organic molecules do to make ATP?

Answer 28

Organic molecules can enter cellular respiration at various stages of glycolysis or the citric acid cycle to make ATP