cellular respiration

Question 1

what is ATP

Answer 1

• adenosine triphosphate
• small soluble organic molecule with 3 phosphate groups
• hydrolysis of a phosphate group from an ATP molecule releases energy that can be used by the cell
• H2O + ATP–> ADP + Pi

Question 2

important features of ATP

Answer 2

• moves easily within cells and organisms by facilitated diffusion
• formed in cellular respiration
• able to transfer energy in relatively small amounts
• ATP is formed from ADP and Pi by transfer of energy during cellular respiration

Question 3

what are coenzymes in respiration

Answer 3

• molecule required for an enzyme to catalyse a reaction

- e.g. NAD

Question 4

what is cellular respiration

Answer 4

• series of enzyme-controlled reactions that takes place in cells
• energy from oxidation of complex organic molecules (e.g. glucose) is transferred to ADP to synthesis ATP, from ADP + Pi
• • respiration does not ‘produce/make’ energy

aerobic respiration
- in the presence of oxygen resulting in complete oxidation of sugar/glucose to form carbon dioxide and water (much energy is released and transferred to ATP)

anaerobic respiration

• in the absence of oxygen
• resulting in partial oxidation of sugar –> less ATP results compared to aerobic respiration

Question 5

Stage 1: glycolysis

Answer 5

• occurs in cytosol
• A series of reactions in which a
  6-carbon sugar (glucose) is
  broken down into two molecules
  of 3C (3-carbon) pyruvate.
  ◼Output #1: net gain of 2 ATP
  molecules from substrate level
  phosphorylation
  ◼Output #2: 2 molecules of NADH

Question 6

stage 2: link reaction

Answer 6

• Links glycolysis to Krebs cycle reactions
• Pyruvate diffuses from cytosol into matrix of mitochondrion
  ◼Oxidative decarboxylation of pyruvate:
• (Decarboxylation) CO2 is removed from pyruvate forming 2C acetyl compound;
• pyruvate diffuses out of mitochondrion and out of the cell
• Oxidation) Electron is transferred from pyruvate to NAD, forming NADH
• Pyruvate is converted into a 2C acetyl group that immediately
  combines with coenzyme A to produce acetyl coenzyme A

Question 7

stage 3: Krebs cycle

Answer 7

• occurs in mitochondrial matrix
  ◼Acetyl CoA (2C) combines with oxaloacetate (4C) to produce
  citrate (6C) and CoA (reused in link reaction)
  ◼Citrate (6C) converted back to oxaloacetate (4C) via a series of
  reactions

In glycolysis, each glucose molecule resulted in two molecules of
pyruvate, hence every glucose molecule metabolized results in
two rounds of Krebs cycle reactions.

Question 8

stage 4: oxidative phosphorylation

Answer 8

◼Oxidation of NADH and FADH2
- electrons are removed from NADH and FADH2
- Electrons are transported down an energy gradient through the electron transport chain (ETC) found on inner mitochondrial membrane
- Oxygen is the final electron acceptor, producing water
◼ATP synthase generates ATP by chemiosmosis
◼Thus, aerobic respiration

◼Inner mitochondrial membrane is a barrier to the movement of ions and electrons
◼Protons are actively transported into intermembrane space using energy from electrons moving down the ETC
◼Results in build up of proton gradient across inner membrane
◼Diffusion of protons down electrochemical proton gradient from intermembrane space to matrix through ATP synthase (innermitochondrial membrane)
◼energy generated results in ATP synthesis from ADP + Pi

Question 9

word equations of cellular respiration

Answer 9

aerobic:
glucose + oxygen –> carbon dioxide + water + energy
C6H12O6 + 6O2 –> 6 CO2 + 6 H2O + energy

alcoholic fermentation:
Glucose–> ethanol + carbon dioxide + energy
C6H12O6–>2C2H5OH + 2 CO2 + energy

lactic acid fermentation:
Glucose–> lactic acid + energy
C6H12O6 –> 2CH3CHOHCOOH + energy

Question 10

anaerobic respiration

Answer 10

◼In the absence of oxygen, electron transfer down the ETC is hindered due to the lack of final electron acceptor (O2)
◼NADH/ FADH2 remain reduced; Krebs cycle reactions are
hindered due to lack of hydrogen carriers (NAD/FAD)
◼However, glycolysis can still continue if products of glycolysis (i.e. pyruvate and NADH) can be removed
- In a tissue in which NAD reserves have run out, glycolysis would
cease
- In alcoholic fermentation, ethanal is the hydrogen acceptor
- In lactic acid/ lactate fermentation, pyruvate is the hydrogen
acceptor
- anaerobic respiration allows for recycling of NAD
- yields small energy

Question 11

lactic acid fermentation o2

Answer 11

After prolonged strenuous exercise, lactate builds up in
muscles
◼Lactate is carried in blood stream to liver &
converted back to glucose or oxidised to carbon
dioxide and water.
◼Processes require extra oxygen ⇒ ‘oxygen debt’ (i.e.
oxygen needed for removal of lactate)
◼When someone who has been exercising pays back
an oxygen debt, it can take from a few hours for
normal exercise, to several days after a marathon.