Chapter 18 - Respiration Flashcards
Respiration
Carbon framework of glucose is broken down and the carbon-hydrogen bonds are broken ; the energy released is then used in the synthesis of ATP by Chemiosmosis ; ATP is constantly synthesised and used in energy-requiring reactions and processes
Prokaryotic cells respiration
They do not have mitochondria ; so many of the reactions take place on cell membranes - process is continuous in cells but broken down into stages
Glycolysis
Occurs in the cytoplasm of the cell ; does not require oxygen and is an anaerobic process… glucose, a six carbon sugar, is split into two smaller 3 carbon pyruvate molecules ; ATP and reduced NAD are also produced
First step of glycolysis
Phosphorylation - first step of glycolysis requires two molecules of ATP ; 2 phosphates, released from the two ATP molecules, are attached to a glucose molecule forming hexose bisphosphate
Second step of glycolysis
Lysis - destabilises this unstable molecule and causes it to split into two Triose phosphate molecules
Third step of glycolysis
Phosphorylation - another phosphate is added to each Triose phosphate forming two Triose bisphosphate molecules ; these phosphate groups come from free inorganic phosphate ions present in the cytoplasm
4th step of glycolysis
Dehydrogenation and formation of ATP ; the two Triose bisphosphate molecules are then oxidised by the removal of hydrogen atoms (dehydrogenation) and they form two pyruvate molecules ; NAD coenzymes accept the hydrogen atoms and are reduced forming two reduced NAD molecules
From the removal of the two phosphates from each Triose bisphosphate - 4 ATP molecules are formed
What form of phosphorylation is glycolysis?
Substrate level - formation of ATP without the involvement of an electron transport chain ; ATP is formed by the transfer of a phosphate group from a phosphorylated intermediate to ADP
Overall net yield of Glycolysis
Two ATP molecules are used to prime the process
4 ATP molecules are produced so overall net yield = 2 ATP molecules
Where does glycolysis take place?
Cytoplasm of the cell
Where do the remaining aerobic reactions take place?
Mitochondria
Where is the electron transport chain/ATP synthase?
Inner mitochondrial membrane
Where does oxidative phosphorylation take place?
In the cristae - projections of the inner membrane with a high SA
Where are proteins pumped into by electron transport chain?
Intermembrane space - very small, concentration builds up quickly
Where are the enzymes for the Krebs cycle and link reaction?
In the matrix - also contains mitochondrial DNA
Purpose of outer mitochondrial membrane?
Separates the contents of the mitochondrion from the rest of the cell ; creating a cellular compartment with ideal conditions for aerobic respiration
Purpose of link reaction?
To link anaerobic glycolysis (cytoplasm) with the aerobic steps of respiration, occurring in the mitochondria
First step is oxidative decarboxylation
Link reaction
Pyruvate enters matrix by active transport via carrier proteins ; pyruvate then undergoes oxidative decarboxylation where carbon dioxide is removed along with hydrogen (oxidation) ; hydrogen atoms removed are accepted by NAD which is reduced to form NADH
THE RESULTING 2 CARBON ACETYL GROUP IS BOUND BY COENZYME A FORMING ACETYLCOENZYME A (acetyl CoA)
Purpose of products of link reaction
ACETYL CoA delivers the ACETYL group to the next stage of aerobic respiration known as the Krebs Cycle ; reduced NAD is used in oxidative phosphorylation to synthesise ATP
Carbon dioxide produced
Either diffuse away and be removed as metabolic waste or in autotrophic organisms it may be used as a raw material in photosynthesis
What to remember about link reaction?
HAPPENS TWICE - once for each Pyruvate molecule
Krebs cycle
Takes place in the mitochondrial matrix - each complete cycle results in the breakdown of an ACETYL group
Purpose of coenzymes produced during Krebs?
Reduced NAD and reduced FAD produced are used in the final, oxygen-requiring step of aerobic respiration to produce large quantities of ATP by Chemiosmosis
Krebs 1
ACETYL CoA delivers an acetyl group to the Krebs cycle ; the acetyl group combined with 4 carbon oxaloacetate to form 6-Carbon citrate
Krebs 2
Citrate molecule undergoes decarboxylation and dehydrogenation producing one reduced NAD and carbon dioxide - a 5 carbon molecule is formed
Krebs 3
5 carbon compound undergoes further decarboxylation and dehydrogenation eventually regenerating OAA
NAD and FAD
Coenzymes that accept protons and electrons released during breakdown of glucose