5B Respiration Flashcards
Where does the energy come from that is used to synthesise ATP?
- solar energy in photosynthesis
- oxidative processes eg. cell respiration breaks down organic molecules to release chemical energy that is stored as ATP
What 3 ways does the synthesis of ATP and H2O from ADP and Pi occur?
- occurs in cytoplasm by glycolysis when phosphate groups are transferred from donor molecules (SUBSTRATE-LEVEL PHOSPHORYLATION)
- occurs in mitochondria during aerobic respiration (OXIDATIVE PHOSPHORYLATION)
- occurs in chloroplasts by photosynthesis (PHOTOPHOSPHORYLATION)
What is substrate-level phosphorylation?
- the synthesis of ATP and H2O from ADP and Pi in the cytoplasm by glycolysis
- phosphate groups are transferred from donor molecules
What is oxidative phosphorylation?
- the synthesis of ATP and H2O from ADP and Pi in the mitochondria during aerobic respiration
What is photophosphorylation?
- the synthesis of ATP and H2O from ADP and Pi in the chloroplasts during photosynthesis
What are the 2 key functions of ATP within the cell?
- energy: releases energy when hydrolysed
- phosphorylation: it may transfer the released phosphate to other organic molecules (makes them less stable and more reactive)
Where does aerobic respiration occur?
in the mitochondria
What does aerobic respiration require and produce?
- requires oxygen
- produces CO2, H2O and lots of ATP
Where does anaerobic respiration take place?
- in the cytoplasm
- in the absence of oxygen
What does anaerobic respiration produce in animals, plants and fungi?
- animals: lactate and a small amount of ATP
- plants and fungi: ethanol, CO2 and a small amount of ATP
What are the 4 steps of aerobic respiration?
- glycolysis
- link reaction
- krebs cycle
- oxidative phosphorylation
Describe simply what happens in glycolysis
- the splitting of the 6 carbon glucose into 2x molecules of 3 carbon pyruvate
Describe simply what happens in the link reaction
- the 3 carbon pyruvate molecules enter into a series of reactions which lead to the formation of acetylcoenzyme A
How many carbons does acetylcoenzyme A consist of?
2
Describe simply what happens in the krebs cycle
- the introduction of acetylcoenzyme A into a cycle of redox reactions that yield some ATP and a large quantity of NAD and FAD
Describe simply what happens in oxidative phosphorylation
- the use of the electrons associated with reduced NAD and FAD, released from the krebs cycle to synthesise ATP with water produced as a by product
Where does glycolysis occur?
in the cytoplasm
What are the 4 stages of glycolysis?
- activation of glucose by phosphorylation
- splitting of phosphorylated glucose into 2x TP
- oxidation of 2x TP
- production of ATP and pyruvate
During glycolysis, what is the overall yield from one glucose molecule?
- 2x ATP (NET: 4 produced but 2 used)
- 2x reduced NAD
- 2x pyruvate
What is the purpose of the link reaction?
- the pyruvate molecules from glycolysis possess potential energy that can only be released in a process called the krebs cycle
- they must be oxidised before this in the link reaction
Where does the link reaction occur?
in mitochondria
Describe the stages of the link reaction
- pyruvate is oxidised to acetate
- 3 carbon pyruvate loses CO2 and H2
- H2 is accepted by 2x NAD to form 2x reduced NAD
- 2 carbon acetate combines with a molecule called coenzyme A to produce acetylcoenzyme A
State the equation for the link reaction
pyruvate + NAD + CoA
–>
acetylcoA + reduced NAD + CO2
Describe the krebs cycle
- involves a series of redox reactions that take place in the mitochondria
- these redox reactions donate hydrogen atoms to NAD and FAD to reduce them
Summarise the steps of the krebs cycle
- 2 carbon acetylcoA from the link reaction combines with a 4 carbon molecule to form a 6 carbon molecule
- in a series of reactions, this 6 carbon molecule loses 2 molecules of CO2 and H2 to give a 4 carbon molecule and a single molecule of ATP
- the 4 carbon molecule can now combine with a new molecule of acetylcoA to begin the cycle again
What are NAD and FAD?
- coenzymes
- coenzymes aren’t enzymes, just molecules that some enzymes require in order to function
- coenzymes are needed in photosynthesis and respiration to carry hydrogen atoms from one molecule to another
What significance does the krebs cycle have?
- breaks macromolecules into smaller ones
- produces hydrogen that is carried by NAD to the electron transfer chain and provides energy for oxidative phosphorylation (leads to production of ATP)
- regenerates the 4 carbon molecules to combine with acetylcoA which would otherwise accumulate
- source of intermediate compounds used by cells eg. fatty acids, amino acids and chlorophyll
