Respiration💥 Flashcards
What is respiration?
The process by which the energy in food molecules is made available for an organism to do biological work - make ATP
What is ATP?
- Form of chemical energy that is used to fuel endergonic biological activities
- Universal energy source
- Covalent bond between last phosphate is unstable, so is removed during an exergonic hydrolysis reaction
What is energy needed for?
- Active transport
- Endocytosis/exocytosis
- Cell division
- DNA replication
- Synthesis of large molecules
- Movement (e.g. cilia)
Structure of ATP
- 3 phosphate groups held together by covalent bonds
- Ribose sugar
- Adenine nitrogenous base
- Phosphorylated nucleotide
Steps of glycolysis (simple)
- 6C glucose
- 6C glucose diphosphate
- 2x 3C triose phosphate (glyceraldehyde 3-phosphate)
- 2x 3C pyruvate
Glycolysis (detailed)
•6C glucose:
-Phosphorylation reaction
-2ATP->2ADP
•6C glucose-diphosphate:
-More polar (less chance to diffuse out of the cell)
-More unstable (less activation energy needed for enzymes)
-Splits…
•x2 3C TP (glyceraldehyde 3-phosphate):
-Dehydrogenation reaction (exergonic) removes 2H (from each) which reduce NAD (carrier)
-Energy released from dehydrogenation is used to synthesise 2 ATP molecules (from each) by substrate-level phosphorylation
•x2 3C pyruvate
How much ATP is used in glycolysis?
2 ATP
How many ATP molecules are gained during glycolysis?
4 ATP
What is the net gain of ATP from glycolysis?
2 ATP
How many NAD carriers are reduced during glycolysis?
2 NADred
Where does glycolysis occur?
Cytoplasm
Does glycolysis require oxygen?
No
What is NAD?
A coenzyme that acts as a hydrogen carrier
What is a dehydrogenation reaction?
- Involves removal of pairs of hydrogen atoms from a molecule
- Catalysed by a dehydrogenase enzyme
What is substrate-level phosphorylation?
Synthesis of ATP using energy released from the breakdown of a high-energy substrate molecule
What is phosphorylation?
The addition of a phosphate group (Pi)
Why is NAD regarded as a coenzyme?
It assists dehydrogenases
Link reaction (simple)
- x2 pyruvate (3C)
* Acetyl-CoA (2C)
Link reaction detailed
- Pyruvate enters mitochondrial matrix by active transport
- Oxidative decarboxylation
- Dehydrogenation reduces NAD
- Forms acetate
- Acetate combines with coenzyme-A to form acetyl coenzyme-A
Where does the link reaction occur?
Mitochondrial matrix - pyruvate is transported by protein
Where does the Krebs cycle occur?
Mitochondrial matrix
-Requires O2
What is the Krebs cycle?
- Involves a series of decarboxylation and dehydrogenation reaction
- CO2, ATP, NADred, FADred
- 2 cycles per glucose molecule
How can the Krebs cycle be continuous?
- Carriers are regenerated
* If more acetyl-CoA is available, the cycle can start again
Krebs cycle process (simple)
•4C + 2C (acetyl-CoA) -CoA is removed •6C -dehydrogenation removes 2H (NADred) -decarboxylation •5C -decarboxylation of CO2 -substrate-level phosphorylation of ATP -dehydrogenation removes 2H (NADred) •4C -dehydrogenation removes 2H (FADred) •4C -dehydrogenation removes 2H (NADred) •4C (oxaloacetate)
How much NADred is produced from the Krebs cycle per one glucose molecule?
6 NADred
These go on to form 18 ATPs
How much FADred is produced from the Krebs cycle per one glucose molecule?
2 FADred
These go on to form 4 ATPs
How much ATP is directly made from the Krebs cycle per one glucose molecule?
2 ATPs
How much CO2 is produced from the Krebs cycle per one glucose molecule?
4 CO2
What is the main purpose of the Krebs cycle?
- To feed electrons into the next stage of aerobic respiration
- Electrons come from reduced NAD and FAD molecules which carry hydrogen atoms
What are cytochromes?
- Iron-containing pigmented molecules
- Embedded in inner membranes of mitochondria where they form an ETS
- Each redox reaction in the ETS releases energy which can be used to synthesise ATP
What is oxidative phosphorylation?
Oxygen dependent synthesis of ATP within mitochondria using energy released from redox reactions
What is chemiosmosis?
- Energy from electrons during redox reactions is used to pump H+ protons from the matrix into the inter-membrane space
- H+ accumulate so that steep conc & electrochemical gradient are established across the inner membrane
- H+ diffuse back into matrix via stalked particles which consists of a chemiosmotic channel protein attached to ATPsynthase
- Flow of protons through ATPsythase provides energy to produce ATP from ADP and Pi
Why are stalked particles required for chemiosmosis?
- Inner membrane is impermeable to protons
* Has ATPsynthase which produces ATP
How much ATP is made from one NADred entering the chain?
3 ATP molecules
-3 proton pumps involved
How much ATP is made from one FADred entering the chain?
2 ATP molecules
-2 proton pumps involved
What is the terminal electron acceptor?
•Oxygen
-combines protons (H+) and electrons (e-) and is reduced to H2O
Why is oxygen important in aerobic respiration?
•It is the terminal electron acceptor in the ETC
-accepts H+ and e- and is reduced to H20
•Drives the ECT
•Allows NAD and FAD to return to the Krebs cycle
How can cyanide affect aerobic respiration?
•Respiratory inhibitor
•Non-competitive inhibitor of cytochrome oxidase
-an enzyme associated with the final proton pump in the ETC
•When cyanide attaches to the enzyme, the ETC cannot function and oxidative phosphorylation cannot occur
-ATP is not produced
Where does each stage of respiration take place?
- Glycolysis - cytoplasm
- Link reaction - mitochondrial matrix
- Krebs cycle - mitochondrial matrix
- ETC - inner mitochondrial membrane/cristae
What is produced at each stage of respiration?
- Glycolysis - pyruvate, ATP, NADH2
- Link reaction - Acetyl Co-A, NADH2, CO2
- Krebs cycle - CO2, ATP, NADH2, FADH2
- ETC - NAD, FAD, ATP, H2O
Where is ATP produced and how much?
•Glycolysis -2 ATP •Krebs cycle -2 ATP •ETC -34 ATP
Where in the cell does anaerobic respiration occur?
In the cytoplasm
How does anaerobic respiration occur?
•NADred and FADred are not oxidised
-become limiting factors
-dehydrogenation reactions of Krebs cycle and Link reaction cannot occur
•Glycolysis continues as the pyruvate enters a different pathway and is reduced
-oxidising NADred to NAD
What is the pyruvate converted into in animals?
Lactate (3C)
What is the pyruvate converted into in plants and fungi?
Ethanol (2C)
Respiratory quotient (RQ)
RQ =
Volume of CO2 produced/
Volume of O2 taken in
What is the RQ of glucose?
1.0
What is the RQ of a fatty acid?
0.7
What is the RQ of protein?
0.9
What is the RQ of anaerobic respiration?
> 1
Compare the breakdown of glucose in aerobic and anaerobic respiration
•Aerobic respiration
-complete breakdown to CO2 and H2O
•Anaerobic respiration
-incomplete breakdown of glucose
Compare ATP production of aerobic and anaerobic respiration
•Aerobic respiration
-38 ATP
•Anaerobic respiration
-2 ATP
Compare efficiency of aerobic and anaerobic respiration
•Aerobic respiration -40% efficient •Anaerobic respiration -2% efficient -energy remains locked up in lactate/ethanol
Why do lipids release lots of energy? (Alternative respiratory substrates)
•Longer fatty acids have more H
- more NAD reduced
- more ATP
How can lipids be used in respiration? (Alternative respiratory substrates)
•Glycerol is converted into 3C
-enters Glycolysis
•Long-chain fatty acid molecules are split into 2C acetate fragments
-enter Krebs cycle as acetyl CoA
How can proteins be used in respiration? (Alternative respiratory substrates)
•High protein diet
-excess amino acids are metabolised in the liver
•If a person is starving, tissue protein is hydrolysed into amino acids
•Amino acids are deaminated, forming ammonia and a keto-acid
-keto-acids enter glycolysis and Krebs cycle
Explain the advantages of collecting results from the whole class
- A statistical test can be used to increase confidence
* Increase reproducibility
Where is the most acidic region of the mitochondria and why?
- Intermembrane space
* H+ ions
Function of DNA in respiration
Allows coding for polypeptides
Function of ribosomes in respiration
Protein synthesis to produce ATP
Suggest a suitable tissue to examine mitochondrial function and explain why
- Muscle tissue
- Abundance of mitochondria
- Easy to extract
Why does aerobic respiration yield fewer molecules of ATP than the theoretical maximum?
- Some is used to actively transport pyruvate into the mitochondria for Link Reaction
- Some used to actively transport H+ from reduced NAD formed in glycolysis, into the mitochondria
- Not all NADH2 is used to feed the ETC
- Not all H+ is used to generate ATP through ATP synthase
