Topic 5: Respiration Flashcards
What is the word equation for respiration?
Glucose + oxygen -> carbon dioxide + water
What is oxidation?
The loss of electrons/ hydrogen atoms
The release of energy
What is reduction?
Gain of electrons/ hydrogen atoms
Energy is required
The process of respiration is a series of what kind of reactions?
A series of chemical reactions but they are oxidation reactions
Glucose is oxidised into carbon dioxide and water, releasing stored energy & making it available for use by the organism
Name the stages of respiration
- Glycolysis
- Link reaction
- Krebs cycle
- The electron transfer chain
Where does glycolysis occur?
In the cytoplasm
Where does the link reaction occur?
In the mitochondrial matrix
where does the Krebs cycle occur?
In the mitochondrial matrix
Where does the electron transfer chain?
In the Cristae of the mitochondrion
Which reactions in respiration produce ATP and how much?
Glycolysis: 2 ATP
Krebs cycle: 2 ATP
ETC:32 ATP
Which stage of respiration doesn’t release ATP?
The link reaction
Summarise what Glycolysis is
When Glucose (6-carbon) is oxidised by the removal of hydrogen producing 2 pyruvate molecules (3C)
What type of respiration does glycolysis occur in and why?
It is common to both aerobic and anaerobic because it doesnt require oxygen
What catalyses glycolysis?
Enzymes
Explain how in glycolysis the 6-carbon compound glucose is inverted to 2 molecules of triose phosphate
- glucose is phosphorylated to from golucse phosphate
- done by 2 phosphate molecules being added from the hydrolysis of 2 ATP
- means it is more chemically reactive so can be split into 2
Each phosphorylated glucose is split into 2 molecules of triose phosphate (3C)
How does triose phosphate form pyruvate and what is the role of NAD in this process?
- each triose phosphate (3C) is oxidised to form a pyruvate (3C)
- a hydrogen is removed in oxidation, from the triose phosphate and transferred to NAD so it forms reduced NAD or NADP
True or false: NAD is an enzyme
False, it is a coenzyme
What is the total ATP made in glycolysis?
4
Why is the net yield of ATP in glycolysis not 4- which is the total produced?
- when each Triose phosphate is converted to pyruvate, 2 ATP are produced. Hence the total of 4
- however 2 ATP are hydrolysed in the phosphorylation of glucose
- so net yield is 2
What is a coenzyme?
A molecule that aids the function on an enzyme by transferring a chemical group from one group to another
Name the co-enzymes in respiration
- NAD
- Coenzyme A
-FAD
How are the coenzymes NAD & FAD used in respiration?
They transfer hydrogen from one molecule to another, they reduce or oxidise a molecule (give or remove hydrogen
Give one reason that NAD, a coenzyme is not an enzyme
It is a non protein and enzymes are proteins
It does still need to be present in order for the enzyme to work
How does phosphorylation occur?
Any molecule can be phosphorylated by the addition of an inorganic phosphate (Pi) from the hydrolysis of ATP
What does phosphorylation do to a molecule?
The addition of Pi makes molecules more chemically reactive
What is substrate level phosphorylation?
The direct phosphorylation of ADP via enzymes, using energy from a coupled reaction
What happens to energy in a coupled reaction?
Energy is moved from one side of the reaction to the other via an intermediate molecule
Use glycolysis as an example of substrate level phosphorylation
The chemical energy from glucose is used to phosphorylate ADP to form ATP
Glucose phosphate is the intermediate molecule
Compare substrate-level phosphorylation and oxidative phosphorylation
- substrate level phosphorylation is the direct phosphorylation of ADP using the energy from a coupled reaction
Oxidative phosphorylation is the phosphorylation of ADP from oxidised NADH & FADH2 by the transfer of electrons/redox reactions and pumping of protons
What is decarboxylation?
A chemical reaction that removes a carboxyl group and releases CO2
What is dehydrogenation?
Process by which hydrogen is removed from an organic compound to form a new chemical
What does the link reaction do?
Connects glycolysis and the Krebs cycle
What product of glycolysis is moved from cytoplasm into the mitochondrion?
Pyruvate
How does pyruvate move from the cytoplasm to the mitochondrial matrix where the link reaction occurs?
It is actively transported
What happens to pyruvate in the link reaction and what is the end result?
-pyruvate is oxidised to form acetate (2C) which then combines with coenzyme A and forms acetyl-coenzyme A
What is the chemical equation for the link reaction?
Pyruvate (3C) + NAD + Coenzyme A -> Acetyl CoA (2C) + reduced NAD + CO2
What happens in the Krebs cycle?
- Acetylcoenzyme A reacts with a 4C compound to form a 6C compound
- The 6C compound is oxidised to release hydrogen
What are the products of the Krebs cycle?
- reduced NAD and reduced FAD: the hydrogen released is accepted by them forming the reduced versions
- carbon dioxide is released
- small amount of ATP is generated
What part of the Krebs Cycle makes it a cycle?
The fact that the 6C compound is reformed to a 4C compound so it can be reused to react with Acetyl-coenzyme A
Why is the Krebs cycle important?
- produces hydrogen atoms that are carried to the electron transfer chain by NAD and FAD. The energy transferred into the production of ATP in oxidative phosphorylation
- it breaks down larger molecules into smaller ones. E.g pyruvate into CO2
- 4C molecule accepting acetlyCoA is recycled
- intermediate molecules are produced which are used in the production of other substances
Intermediate molecules produced in the Krebs cycle are used in the production of substances.
Give examples of the substances
Chlorophyll
Fatty acids
Amino acids
What is the electron transfer chain also known as?
Oxidative phosphorylation
Summarise the electron transfer chain
- reduced NAD & FAD that are produced in glycolysis and the Krebs cycle reduce the first protein in a series of electron carriers
-The hydrogen from NAD/FAD gives an electron or proton (H+) - they pass electrons down the carriers which releases energy
how are electrons passed down the carriers in the Electron transfer chain?
Through a series of redox reactions
Explain how the movement of hydrogen ions because of the energy released in the electron transfer chain, results in the production of ATP
- energy is used to transport hydrogen ions through the inner membrane into the intermembrane space
- the hydrogen ions build up
- there is a greater concentration of hydrogen ions in the intermembrane space than the matrix
- hydrogen ions then enter the matrix by diffusion down an electrochemical gradient, and across the ATP synthase enzyme in the inner membrane
- this results in the phosphorylation of ADP to ATP
What is the terminal electron acceptor in the electron transfer chain?
Oxygen
how does the terminal electron acceptor in the electron transfer chain result in one of the products of respiration?
Oxygen combines with protons (H+) and electrons to form water
Where in the stages of respiration are the products released?
Carbon dioxide-released in the Krebs Cycle
Water-the end of the electron transfer chain when oxygen combines with protons and electrons
Why is the final stage of aerobic respiration also known as oxidative phosphorylation?
In the presence of oxygen, energy is released to allow the phosphorylation of ADP
Define chemiosmosis
The term used to describe the movement of ions across a selectively permeable membrane, down an electrochemical gradient
Where does chemiosmosis occur in respiration?
When ATP is synthesised by the movement of hydrogen ions across the mitochondrial membrane, via ATP synthase
What happens if more energy is produced in one stage of respiration than normal?
More will be lost as heat
Means less is available for other purposes like the formation of ATP
How is an energy gradient created in the Electron transfer chain and how is it used ?
- when energy is released by the transfer of electrons from reduced NAD/FAD along the ETC, each carrier molecule is at a slightly lower energy level than the one before
The energy is released down an energy gradient so it can be released more gradually
What is the first common stage in both anaerobic and aerobic respiration?
Glycolysis
In the absence of oxygen (anaerobic respiration) what stages of respiration cannot occur?
The Krebs cycle and the electron transfer chain
If both the Krebs cycle and the Electron transfer chain cannot occur is ATP still produced? How much?
Yes- only glycolysis will occur as the source of ATP
2 ATP
What must happen for glycolysis to occur?
It’s products pyruvate and hydrogen must be removed
The removal of hydrogen must be removed from reduced NAD in order to regenerate NAD
Why is it important to regenerate NAD from reduced NAD for glycolysis?
If the supplies of NAD run out, glycolysis stops
This is because there is no more NAD to accept hydrogen as glucose is oxidised
When is NAD regenerated?
When pyruvate accepts hydrogen
What happens to pyruvate in animals?
It is converted to lactate
- when oxygen is available the lactate can be converted back into pyruvate which can then be oxidised or converted to glycogen in the liver
What happens to pyruvate in plants & microbes?
Pyruvate is converted into ethanol and CO2
Compare the energy yields of aerobic and anaerobic respiration
- the energy yield of anaerobic respiration is very low in comparison with aerobic
- one molecule of glucose yields a net gain of 36 molecules of ATP in anaerobic respiration but only 2 in anaerobic respiration
Why is the energy yield lower in anaerobic respiration?
Glycolysis is the only source of ATP production- whereas ATP is produced in the Krebs cycle and ETC in aerobic
- these 2 stages can only occur in the presence of oxygen
Which stage of respiration results in the production of the most ATP?
The electron transfer chain 32 ATP
How efficient is respiration?
40% efficient
60% is lost as heat
How are other substances used in respiration?
Conversion to glycolysis or Krebs intermediate molecules
How are lipids used in respiration?
- they are hydrolysed into glycerol & long chain fatty acids
- glycerol is phosphorylated into triose phoshate, which enters glycolysis
- fatty acids are broken down to produce a series of 2 carbon compounds which are converted to AcetlylCoA
How are proteins used in respiration?
-They are hydrolysed to amino acids which can be deaminated (removing amino group)
-the acid residues enter the respiratory pathway at different points depending on the amount of carbons they contain:
-3C compounds are converted to pyruvate
- 4 & 5 carbon compounds enter the Krebs cycle
What is/was DNP?
-It is a chemical that acts as an uncoupling agent
- it makes the inner mitochondrial membrane leaky to protons
- was used as a weight loss drug until 1938
How would DNP affect the amount of ATP produced in cellular respiration?
- DNP allows protons to travel down their gradient and back into the mitochondrial matrix without passing through ATP synthase
- thus reducing ATP production in cellular respiration
- the energy of the gradient dissipated in the form of heat which raises the body temperature
Why was DNP removed from the market?
- it caused deaths due to hyperthermia ( severely elevated body temperatures)
- also because it was linked to cataracts and vision loss
