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
how many ATP can be made from 1 glucose molecule (aerobic respiration)
32
Anaerobic respiration overview
- occurs in the absence of O2 - e.g when O2 can’t be supplied fast enough to respiring cells
- doesn’t involve the link reaction, Krebs cycle or oxidative phosphorylation
- produced 2 molecules of ATP
there is no O2 to act as the final electron acceptor at the end of the electron transport chain in oxidative phosphorylation so the flow of electrons stops and the synthesis of ATP via chemiosmosis also stops
As the flow of electrons along the ETC has stopped, the NADH and FADH aren’t able to be oxidised.
This means NAD and FAD can’t be regenerated and so the decarboxylation and oxidation of pyruvate and the Krebs cycle also stop (no coenzymes to accept the H being removed)
Anaerobic respiration in eukaryotic organisms
Obligate anaerobes:
- can’t survive in the presence of O2
- include prokaryotes + some fungi
Facultative anaerobes:
- synthesise ATP by aerobic respiration if O2 is present but can switch to anaerobic respiration in the absence of O2
Obligate anaerobes:
- can only respire aerobically
Fermentation definition
The process by which complex organic compounds are broken down into simpler inorganic compounds without the use of oxygen or the involvement of an electron transport chain
the organic compounds aren’t completely broken down
ATP is produced by substrate level phosphorylation
Lactate fermentation in mammals
pyruvate can act as a H acceptor, taking the H from NADH - this is catalysed by the enzyme lactate dehydrogenase
Pyruvate is converted to lactate
NAD is regenerated and can be reused in glycolysis so a small amount of ATP can be synthesised
Lactic acid is removed from the muscles and taken to the liver via the bloodstream.
Here, lactate is converted into glucose (via gluconeogenesis) - O2 is needed for this process which is the reason for oxygen debt
why can’t lactate fermentation occur indefinitely
- reduced quantity of ATP produced isn’t enough to maintain vital processes for a long period of time
- the accumulation of lactic acid causes a fall in pH leading to proteins denaturing - respiratory proteins and muscle filaments are made from proteins and will stop functioning at a low pH
Alcoholic functioning in yeast
irreversible
CO2 is removed from pyruvate to form ethanal - catalysed by enzyme pyruvate decarboxylase
Ethanal can accept a H atom from NADH forming ethanol and NAD
regenerated NAD can be used in glycolysis
- can continue indefinitely in the absence of O2
Respiratory substrate definition
Any biological molecule that can be broken down in respiration to release energy
triglycerides
Triglycerides are hydrolysed into fatty acids which enter the Krebs cycle via acetyl coA and glycerol
Glycerol is converted into pyruvate
It undergoes oxidative decarboxylation producing an acetyl group
Acetyl is picked up by CoA forming acetyl CoA
Lipids
Lipids contain a greater proportion of C-H bonds than carbohydrates so they produce more ATP in respiration
proteins
.hydrolysed to amino acids
Amino acids are delaminated
RQ formula
CO2 produced ➗O2 consumed
Carbohydrate RQ value
1
Protein RQ value
0.9
Lipids RQ value
0.7
What does RQ tell us
High RQ - organism is short of O2 and is having to respire anaerobically and aerobicallg
Low RQ - more O2 is needed to oxidise fats and lipids
