Biological processes that require ATP:
- Active transport
- Endocytosis
- Exocytosis
- Synthesis of large molecules such as proteins
- DNA replication
- Cell division
- Movement e.g. motor proteins walking along cytoskeleton threads
- Activation of chemicals
How much energy is released from each phosphate ion hydrolysed from ATP?
Outer two: 30.5kJ
Inner one: 13.8kJ
Glycolysis definition:
- First stage of respiration
- Converts glucose to pyruvate
What are the stages of glycolysis:
- Phosphorilation of glucose to hexose bisphosphate
- Splitting of each hexose bisphospahte molecule into two triose phosphate molecules
- Oxidation of triose phosphate to pyruvate
What does NAD in glycolysis?
- It is a coenzyme that helps dehydrogenease enzymes to carry out oxidation reactions
- Oxidises molecules during glycolysis, the link reaction and the Krebs cycle
Structure of NAD:
Contains:
- Adenine
- Nicotinamide (vitamin B3)
- Ribose
- Two phosphoral groups
What can the nicotinamide ring of NAD accept?
Two hydrogen atoms to become reduced NAD
What does reduced NAD do?
Carries proteins and electron to the cristae of mitochondria and delivers them to be used in oxidative phosphorilation for the generation of ATP
What happens in the first stage of glycolysis (phosphorilation)?
- One molecule of ATP is hydrolysed and the released phosphoryl group is added to glucose to make hexose monophosphate
- Another molecule of ATP is hydrolysed and the phosphoryl group is added to the hexose monophosphate molecule to make hexose bisphosphate
- The sugar has one phosphate group at carbon 1 and one at carbon 6
- The energy from the hydrolysed ATP molecules activates the hexoses sugar and prevents it from being transported out of the cell
What happens in the second stage of glycolysis (Splitting the hexose bisphosphate)?
- Each molecule of hexose bisphosphate is spit into two threee-carbon molecules, triose phosphate
- Each has a phosphate group attached
What happens in the third stage of glycolysis (oxidation of triose phosphate to pyruvate)?
- Dehydrogenase enzymes (and NAD) remove hydrogen from triose phosphate
- The two molecules of NAD accept the hydrogen atom and become reduced NAD
- Two moleules of NAD are reduced for every molecule of glucose undergoing this process.
- Four molecules of ATP are made for every two triose phosphate molecules undergoing oxidation
- This makes 2 pyruvate molecules. Each has 3 carbons
Why is oxidation of triose phosphate to pyruvate an oxidation reaction if it is anearobic?
It involves the removal of hydrogen atoms
What are the products of glycolysis?
- Two molecules of ATP, (four have been made but two are used to start the reaction so the net gain is two)
- Two molecules of reduced NAD
- Two molecules of pyruvate
What are the stages of respiration?
-Glycolysis
-The link reaction
-The Krebs cycle
-Oxidative phosphorilation
The last three stages only take place under aerobic conditions. In the absence of oxygen, pyruvate is converted, in the cytoplasm, to lactate or ethanol.
Cristae definition:
Inner, highly-folded mitochondrial membrane. The intrusions
Mitichondrial matrix definition:
Fluid-filled inner part of the mitichondria
What is the shape of mitochondria?
Rod shaped, thread-like, or spherical
What is the diameter of a mitochondrion?
0.5-1um
What is the length of a mitichondrion?
2-5um but occasionally up to 10um
What kind of membrane do mitochondria have?
- Outer and inner phospholipid membrane
- Makes an envelope
- Inner membrane folded into cristae to give a large surface area
What are embedded in the inner membrane of mitochondria?
- Proteins that transport elections
- Protein channels associated with ATP synthase enzyme that allows protons to diffuse through them
What is between the inner and outer membranes of the mitochondria?
Intermembrane space
What is in the mitichondrial matrix?
- Enzymes that catalyse stages of the link reaction and the Krebs cycle
- Molecules of NAD and FAD
- Oxaloacatate (4 carbon compound that accepts the acetyl group in the link reaction)
- Mitochondrial DNA
- Mitochondrial ribosomes
What is he structure of the outer mitichondrial membrane?
Phospholipid composition similar to that of other organelles in eukaryotic cells
What is the structure of the inner mitochondrial membrane?
- Less permeable to small ions such as H+ than the outer membrane
- The cristae give a large surface area for the electron carriers and ATP synthase enzymes all arranged in electron transport chains
What are electron transport chains involved in?
The final stage of aerobic respiration, oxidative phosporilation
Why can iron ions accept and donate electrons?
Because it can accept them, (becoming Fe2+), or donate them, (becoming Fe3+)
What type of enzyme are electron carrier proteins?
Oxido-reductase enzymes
How does the electron transport chain work?
- The electron carriers have a coenzyme that uses energy released from electrons to pump protons from the matrix into the intermembrane space.
- Protons accumulate in the intermembrane space and a gradient forms across the membrane
- This causes a flow of flow of protons through the channels in the ATP synthase enzymes to make ATP
What is a ATP enzyme?
- Protons pass through from the intermembrane space to the matrix
- This produces ATP
- The ATP enzymes protrude from the inner membrane into the matrix
Decarboxylation definition:
Removal of a carboxyl group from a substrate molecule
Dehydrogenation definition:
Removal of hydrogen atoms from a substrate molecule
Substrate-level phosphorylation definition:
Production of ATP from ADP and Pi during glycolysis and the Krebs cycle
What happens to pyruvate after glycolysis?
It is transported across the outer and inner mitochondrial membranes vie specific pyruvate-H+ symports. There are transport proteins that transport two ions or molecules i the same direction
Brieft overview of link reactions and Krebs cycle:
- Pyruvate is converted into a two-carbon acetyl group
- The acetyl group is oxidised
What happens in the link reaction?
- Pyruvate (3C) is decarboxylated and dehydrogenated (catalysed by pyruvate dehydrogenase)
- This forms an acetyl group which combines with coenzyme A to form acetyl CoA(2C), (reduced NAD and CO2 are produced)
What is the equation for the link reaction?
2pyruvate + 2NAD + 2CoA -> 2CO2 + 2NADH + 2 acetylCoA
What happens in the Krebs cycle
- Acetyl group (2C) released from acetylCoA (2C) combines with oxaloacetate (4C) to form citrate (6C)
- This is decarboxylated and dehydrogenated to produce a 5 carbon compound, one CO2 and one NADH
- 5 carbon compound is further decarboxylated and dehydrogenated, producing a 4 carbon compound, one CO2 and one NADH
- The 4 carbon compound bind temporarily with and is then released from coenzyme A. Substrate level phosphorylation takes place, which produces one ATP
- 4 carbon compound is dehydrogenated, producing a different 4 carbon compound and one FADH
- Rearrangement of atoms produces one oxaloacetate (4C) so the cycle can continue
Krebs cycle molecules:
- Acetyl group (2C) + oxaloacetate (4C) ->citrate (6C)
- Citrate (6C) -> 5C (CO2, NADH)
- 5C -> 4C (CO2, NADH)
- 4C -> 4C (ATP)
- 4C -> 4C (FADH)
- 4C -> oxaloacetate (4C) (NADH)
How many molecules of everything are produced in the link reaction from one molecule of glucose?
- 2 NAHD
- 0 FADH
- 2 CO2
- 0 ATP
How many of everything are produced in the Krebs cycle from one molecule of glucose?
- 6 NADH
- 2 FADH
- 4 CO2
- 2 ATP
What other substrates besides glucose can be respired aerobically?
- Fatty acids are broken down into molecules of acetate that enter the Krebs cycle via acetyl CoA
- Glycerol may be converted to pyruvate and enter the Krebs cycle via the link reaction
- Amino acids may be deaminated and the rest of the molecule can enter the Krebs cycle directly or be changed to pyruvate or acetyl CoA
Chemiosmosis definition:
Flow of protons, down their concentration gradient, across a membrane, through a channel associated with ATP synthase
Oxidative phosphorilation definition:
The formation of ATP using energy released in the electron transport chain and in the presence of oxygen. It is the last stage of aerobic respiration
What is the final electron acceptor?
Oxygen
What is the equation for when oxygen is used as the final electron acceptor?
4H+ + 4e- + O2 -> 2H2O
How many ATP molecules are produced at each stage of respiration from one glucose molecule?
Glycolysis: 2 The link reaction: 0 The Krebs cycle: 2 Oxidative phosphorilation: 28 Total: 32
Why in reality is there probably not going to be a whole 32 molecules of ATP produced from one glucose molecule?
- Some ATP used to actively transport pyruvate into the mitochondria
- Some ATP used in shuttle system that transports reduced NAD made in glycolysis, into mitchondira
- Some protons may leak out through the mitochondrial membrane
Why can’t aerobic respiration happen in the absence of oxygen?
- Oxygen cannot act as final electron acceptor at the end of oxidative phosphorylation, so protons that have travelled through ATP synthase cannot combine with electrons and form water
- Concentration of protons in matrix increases and reduces proton gradient across inner mitochiondrial membrane
- Oxidative phosphorylation ceases
- NADH and DADH can not unload their hydrogen atoms and can’t be reoxidised
- The Krebs cycle stops and so does the link reaction
Ethanol fermentation pathway equation:
Pyruvate -> (with pyruvate decarboxylase, releases CO2) -> ethanAl -> (with ethanOl dehydrogenase, NADH becomes NAD) -> ethanOl
CH3COCOOH -> (with pyruvate decarboxylase, releases CO2) -> CH3CHO -> (with ethanOl dehydrogenase, NADH becomes NAD) -> CH3CH2OH
Lactate fermentation pathway equation:
Pyruvate -> (with lactate dehydrogenase, NADH becomes NAD) -> lactate
CH3COCOOH -> (with lactate dehydrogenase, NADH becomes NAD) -> CH3CHOHCOOH
What happens to lactate after it is produced?
- May be converted to pyruvate, which may enter the Krebs cycle via the link reaction
- May be recycles to glucose and glycogen
What would happen if lactate was not removed from the muscle tissues?
The pH would be lowered and this would inhibit the action of many of the enzymes involved in glycolysis and muscle contraction
Respiratory substrate definition:
An organic substance that can be oxidised by respiration, releasing energy to make molecules of ATP
Which cells can only use glucose for respiration?
Some mammalian cells such as brain cells and erythrocytes
What is changed about lipids so that part of it can be repsired?
Triglycerides are hydrolyses by lipase to glycerol and fatty acids. Glycerol can then be converted to triose phosphate and respired
Why are fatty acids good for respiring?
They have lots of protons
How do fatty acid chains enter the Krebs cycle?
- Energy is used to combine each fatty acid with coenzyme A
- The fatty acid- CoA complex is transported to the mitochondrial matrix, where it is broken into two-carbon acetyl groups, each attached to a CoA
- This beta-oxidation pathway generates NADH and FADH
- The acetyl groups are released from CoA and enter the Krebs cycle by combining with the four-carbon oxaloacetate
Which part of proteins can be respired?
The keto acid
How does a keto acid enter the respiratory pathway?
As pyruvate, acetyl CoA, or a Krebs cycle acid such as oxaloacetic acid
Energy value for carbohydrates:
15.8kJg-1
Energy value for lipids:
39.4kJg-1
Energy value for proteins:
17.0kJg-1
Respiratory quotient
RQ= CO2 produced / O2 consumed
Respirometer definition:
Apparatus used to measure the rate of respiration of living organisms by measuring the rate of exchange of oxygen and carbon dioxide
Setting up a respirometer:
- Place coloured liquid into manometer tube and connect the apparatus with the taps open, enabling the air in the apparatus to connect with the atmosphere
- Find mass of organism
- With the taps still open, the whole set up, including organisms is placed in a water bath for at least 10 minutes, until it reaches the temperature of the water bath
- Syringe plunger should be near the top of the scale on the syringe barrel, and its level noted
- Levels of coloured liquid should be marked
- Taps are closed and apparatus left in water bath for 10 minutes
- Change in level of manometer liquid can be measured, and the syringe barrel depressed to reset apparatus. This also enables you to measure the volume of oxygen absorbed
- Calculate the volume of oxygen absorbed per minute per gram of living organism
What does the sodium hydroxide solution in a respirometer do?
Absorbs CO2
