Respiration, BIO (Pt1)
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What is respiration?
The process whereby energy stored in complex organic molecule (carbohydrates, fats and proteins) is used to make ATP - occurs in living cells.
What is ATP?
A phosphorylated nucleotide and is the universal energy currency.
What is metabolism?
All the reactions that take place are collectively known as metabolism.
Metabolic reactions that build large molecules are described as ____, and those that break large molecules into smaller ones are ____.
List some metabolic processes that need energy. (8)
- Active transport: moving molecules across membrane against conc gradient. Much of organism's energy used for this. (eg. sodium-potassium pumps).
- Secretion: large molecules made in some cells are released by exocytosis.
- Endocytosis: bulk movement of large molecules into cells.
- Synthesis of large molecules from smaller ones, (such as proteins from amino acids; steroids from cholesterol and cellulose from beta-glucose. these are all anabolic)Replication of DNA and synthesis of organelles before cell division.
- Movement: bacterial flagella, eukaryotic cilia, muscle contraction and microtubule motos that move organelles around inside of cell.
- Activation of chemicals: glucose phosphorylated at beginning of respiration to make is more unstable and easier to break down.
- Some catabolic reactions (like in liver) release energy in form of heat.
How does energy from respiration manifest itself?
- Thermal energy
- Chemical potential in ATP. Respiration releases the chemical energy in large organic molecules and this is used to phosphorylate ADP, making ATP. This phosphorylation also transfers energy to ATP molecule.
Describe the role of ATP.
- The standard intermediary between energy-releasing and energy-consuming reactions in both prokaryotic and eukaryotic cells.
- It provides immediate source of energy for biological processes.
How can ATP provide immediate source of energy for metabolic processes? And how is it adapted for its purpose?
- It can be hydrolysed to ADP and Pi, releasing 30.6 kJ of energy/mol.
- So energy immediately available to cells in small manageable amounts that will not damage the cell and will not be wasted.
- This hydrolysis of ATP is coupled with a reactionthat needs energy , such as DNA replication or protein synthesis, so energy is immediately available.
- Small and soluble, so easily transported around cell.
Describe the structure of a molecule of ATP. Also imagine it.
- Adenosine (adenine and ribose sugar)
- And 3 phosphate groups/molecules. (that's why it is triphosphate).
What is the role of coenzymes in respiration in general?
- During glycolysis, link and Krebs, hydrogen atoms are removed from substrate molecules in oxidation reactions, catalysed by dehydrogenase enzyme.
- But coenzymes (like NAD and FAD) are needed to help with the reaction, and they accept hydrogen and are reduced.
- They carry the hydrogen to cristae, where H+ and electrons are involved in oxidative phosphorylation.
- Delivery of hydrogen reoxidises the coenzymes so they can combine with more hydrogen atoms from first three stages of respiration.
What is NAD? Name and imagine structure. Also, how many hydrogen atoms can one NAD accept?
- Nicotinamide adenine dinucleotide (NAD)
- Made of 2 linked nucleotides. Made in body from nicotinamide (Vit B3), 5-carbon ribose sugar, adenin and 2 phosphate groups. Nicotinamide ring can accept 2 hydrogen atoms with their electrons, and it is then reduced.
What is the role of NAD and FAD?
- Accept hydrogen and are reduced (from Glycolysis, link and Krebs)
- Reduced NAD and FAD carry electrons to electron transport chain for oxidative phosphorylation.
- Reduced NAD and FAD carry hydrogen ions for chemiosmosis/oxidative phosphorylation.
- [Be careful tho, say they carry hydrogen atoms first, which later becomes proton and electrons).
What is the role of conenzyme A in respiration?
It carries acetate to Krebs cycle.
Glycolysis occurs all cells that respire, in their ____.
We can split glycosis into 4 stages. (instead of more complicated 10 stages). Describe the first stage, phosphorylation.
- 1. An ATP molecule is hydrolysed and phosphate released is attached to glucose at C-6 - to form glucose 6-phosphate.
- 2. Glucose 6-phosphate is changed to fructose 6-phosphate.
- 3. Another ATP is hydrolysed and phosphate group released is attached to fructose 6-phosphate at C-1.
- 4. Energy released from hydrolysis of ATP activates hexose sugar and prevents it from being transported out of cell. This is now hexose 1,6-bisphosphate.
What is important about this first stage?
- Glucose is a stable hexose sugar, so it must be activated before it can be split into two to make triose phoshpate.
- Hexose 1,6-bisphosphate is activated and phosphrylated sugar at the end which can be split into two.
- Use of 2 ATP for each molecule of glucose for this stage.
Describe the second stage in glycolysis. (Mind you, this is just artificially made stages to break up glycolysis to remember better. In revision guide, it has just 2 steps - phosphorylation and oxidation).
Each molecule of hexose 1,6-bisphosphate is split into 2 molecules of triose phosphate (3C, each with one phosphate group attached).
Describe our third stage of glycolysis.
- Oxidation of triose phosphate.
- 1. 2 hydrogen atoms (with electrons) are removed from each triose phosphate, involving dehydrogenase enzymes.
- 2. Aided by coenzyme NAD. NAD combines with the hydrogen atoms, becoming reduced NAD.
- 3. So, 2 molecules of NAD are reduced per molecule of glucose.
- 4. At this stage, 2 molecules of ATP are formed. Called substrate-level phosphorylation.
Describe stage 4.
- After stage 3, 2 intermediate compounds (3C) are left.
- 1. Four enzyme-catalysed reactions convert each triose phosphate molecule to a molecule of pyruvate (3C).
- 2. In this process, another 2 molecules of ADP are phosphorylated to 2 molecules of ATP.
What products are left at the end of glycolysis for each molecule of glucose?
- 2 x ATP: 4 were made but 2 were used at stage 1 (phosphorylation) to phosphorylate and activate the glucose. So net gain is 2 ATP.
- 2 x reduced NAD: These carry H atoms to inner mitochondrian membranes and used for more ATP production during oxidative phosphorylation.
- 2 x pyruvate: actively transported into mitochondrial matrix for next stage of aerobic respiration. In absense of oxygen (anaerobic respiration), it will be changed in cytoplasm, to lactate or ethanol.
Remember, pyruvate is ___ ___ into mitochondria.
So let's summarise in brief terms about glycolysis.
- Phosphorylation of glucose to hexose 1,6-bisphosphate.
- Splitting hexose bisphosphate into 2 triose phosphate molecules.
- Oxidation of each triose phosphate to pyruvate.
- [Also producing 2 net ATP, 2 reduced NAD]
How is the matrix of the mitochondria adapted for its function? (6)
- Is where link reaction and Krebs cycle take place. Contains...
- Enzymes that catalyse the stages of these 2 reactions.
- Molecules of coenzyme NAD
- Oxaloacetate - 4C compoundthat accepts acetate from link reaction.
- Mitochondrial DNA - some of which codes for mitochondrial enzymes and other proteins.
- Mitochondrial ribosomes (structurally same as prokaryote ribosomes) where proteins are assembled.
How does the structure of the outer membrane enable it to carry out its function.
Contains proteins, some enzymes, and some of which form channels or carriers that allow passage of molecules such as pyruvate.
How does the structure of the inner membrane enable it to carry out its function?
- Has different lipid composition from outer membrane and is impermeable to most small ions, including H+ ions.
- Folded into many cristae to give large surface area.
- Has embedded in it many electron carriers and ATP synthase enzymes.
- High protein-to-phospholipid ratio.
The electron carriers in the inner membrane are protein complexes, arranged in electron transport chains. How is electron transport chain adapted to its function?
- Most carrier has Fe3+ ion (cofactor), which become reduced to Fe2+ by accepting electron, and then donate them again to next electron carrier to become oxidised again.
- Many oxidoreductase enzymes - involved in oxidation and reduction reactions.
- Some carriers also have co-enzymes that pump (using energy from passage of electrons) protons from matrix to intermembrane space.
- FAD, which becomes reduced during one stage of Krebs, bound to dehydrogenase enzyme in inner membrane, deos not pump hydrogen atoms into intermembrane space, but instead pass back into matrix.
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