Respiration Flashcards
Role of glucose in respiration
Glucose is a complex molecule containing energy absorbed from sunlight within its C-H bonds
The carbon framework of glucose is broken down and the C-H bonds are broken. The energy released is then used in the synthesis of ATP by chemiosmosis
where does respiration occur in prokaryotic cells and why
cell membranes
they do not contain mitochondria
what are the 4 stages of aerobic respiration and where do they take place
Glycolysis (cytoplasm)
Link reaction (mitochondria)
Krebs cycle (mitochondria)
Oxidative phosphorylation (mitochondria)
- the first three stages are a series of reactions. The products of these stages are used in the final stage to produce lots of ATP
Structure of the mitochondria (labelled diagram p 482)
OUTER MITOCHONDRIAL MEMBRANE:
- separates the content of the mitochondrion from the rest of the cell, creating a cellular compartment with ideal conditions for aerobic respiration
INNER MITOCHONDRIAL MEMBRANE:
- contains electron transport chains + ATP synthase
CRISTAE:
- projections of the inner membrane which increase the surface area available for oxidative phosphorylation
INTERMEMBRANE SPACE:
- Proteins are pumped into this space by the electron transport chain.
- It is a small space so the concentration builds up quickly
MATRIX:
- contains enzymes for the Krebs cycle and the link reaction
- also contains mitochondrial DNA
Glycolysis overview
- it is an anaerobic process as it doesn’t require O2
- takes place in the cytoplasm
- involves splitting oen molecule of glucose into 2 smaller 3-C molecules of pyruvate
Glycolysis process
GLUCOSE –> PYRUVATE
STAGE 1 - Phosphorylation:
- Glucose is phosphorylated by adding 2 phosphates, released from 2 molecules of ATP
- This forms 1 molecule of hexose bisphosphate and 2 molecules of ADP
- Lysis - Hexose bisphosphate is split into 2 Triose Phosphate molecules
Phosphorylation:
- Another phosphate group is added to each TP forming 2 triose bisphosphate molecule - these phosphate ions came from free inorganic phosphate ions in the cytoplasm
Stage 2 - Oxidation
- The 2 triose bisphosphate molecules are oxidised (loses H) forming 2 pyruvate molecules
- NAD coenzymes accept H ions (reduced) forming 2 reduced NAD molecules
- At the same time, 4 ATP molecules are produced using phosphate ions from triose bisphosphate
there is a net gain of 2 ATP molecules (4 ATP formed overall but 2 were used in stage 1)
OVERALL:
- 2 pyruvate molecules
- 2 ATP
2
- 2 reduced NAD
why is glycolysis an example of substrate level phosphorylation
ATP is formed without the involvement of an electron transport chain
ATP is formed by the transfer of a phosphate group from a phosphorylated intermediate to ADP
The link reaction (oxidative carboxylation)
converts pyruvate to acetyl CoA
- takes place in the matrix
- pyruvate enters the mitochondrial matrix by active transport via specific carrier proteins
Link reaction:
- Pyruvate is decarboxylated (CO2 is removed) and oxidised (H is removed)
- NAD is reduced to NADH - it accepts the H atoms from pyruvate, changing pyruvate into acetate
- acetate combines with acetyl CoA forming acetyl CoA
- No ATP is formed
- the link reaction occurs twice for every glucose molecule. 2 pyruvate molecules are made for every glucose molecule in glycolysis
2 molecules of Acetyl CoA go into the Krebs cycle
2 CO2 molecules are released as a waste product
2 molecules of reduced NAD are formed and used in oxidative phosphorylation
The Krebs cycle overview
- takes place in the mitochondrial matrix
- occurs twice for every glucose molecule
- occurs once for every pyruvate molecule
- results in the breakdown of an acetyl group
- involves decarboxylation, dehydrogenation and substrate level phosphorylation
- involves a series of oxidation-reduction reactions
- doesn’t require O2
The Krebs cycle process
- the acetyl group (2C) from acetyl CoA combines with oxaloacetate (4C) forming citrate (6C) (this is catalysed by citrate synthase)
- Co enzyme A goes back to the links reaction to be used again
- the 6C molecule (citrate) is converted to a 5C molecule via decarboxylation (CO2 is removed) + dehydrogenation (H is removed)
- The H is used to form NADH
- The 5-C molecule is converted to a 4-C molecule (Citrate is converted to oxaloacetate) via Decarboxylation and dehydrogenation, producing 1 reduced FAD molecule and 2 reduced NAD molecules
- ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP (substrate level phosphorylation)
PRODUCTS per 1 pyruvate:
1 CoA
Oxaloacetate
2CO2
1 ATP
3 NADH
1 FADH
The importance of coenzymes in respiration
- coenzymes are needed to transfer protons, electrons and functional groups between enzyme-catalysed reactions
- When NAD+ is reduced it accepts 2 protons and an electron pair forming NADH + H+. NADH then transfers the proton and electron pair to another reaction
Differences between NAD and FAD
- NAD takes part in all stages of respiration but FAD only accepts H in the Krebs cycle
- NAD accepts 1 H but FAD accepts 2 H
- NADH is oxidised at the start of the electron transport chain (releasing protons and electrons) while FAD is oxidised further along the chain
- NADH results in the synthesis of 2.5 ATP molecules but FADH results in the synthesis of 1.5 ATP molecules
Oxidative phosphorylation overview
- energy carried by the electrons from the reduced coenzymes is used to make ATP
- takes place in the inner mitochondrial membrane (membranes of the cristae)
oxidative phosphorylation process
H atoms are released from NADH and FADH and delivered to electron transport chains in the membranes of the cristae
The H atoms dissociate into H+ ions and electrons
the electrons move along the electron transport chain forming (made up of 3 electron carriers) losing energy at each carrier (energy is lost during redox reactions as the electrons reduce and oxidise electron carriers)
this energy is used by the electron carriers to pump protons from the mitochondrial matrix into the inter membrane space (space between the inner and outer mitochondrial membranes)
the concentration of protons is now higher in the intermembrane space than the mitochondrial matrix, forming an electrochemical gradient
protons move down the electrochemical gradient into the mitochondrial matrix via ATP synthase - this movement drives the synthesis of ATP from ADP + Pi
in the mitochondrial matrix, protons, electrons and O2 (from the blood) combine to form H2O
2e- + 1/2 H2O + 2H+ –> H2O
O2 is the final electron acceptor
substrate level phosphorylation definition
production of ATP involving the transfer of a phosphate group from a shortly-lived, highly reactive intermediate
