Respiration Flashcards
Why do living organisms need to respire
-respiration is process that occurs in living cells and released energy stored in organic molecules
-the energy is immediately used to synthesise molecules of ATP from ADP and inorganic phosphate (Pi)
-ATP in cells can be hydrolysed to release energy needed to drive biological processes
-microorganisms (both prokaryotes and eukaryotes), plants, animals, fungi and protoctists all respire to obtain energy
Why do living organisms need energy
-energy is the capacity to do work
-the energy that is stored in complex organism molecules - e.g. fats, proteins, carbohydrates - is potential energy
-it is also chemical energy converted from light energy during process of photosynthesis
-when this energy is released from organic molecules via respiration, it can be used to make ATP to drive biological processes:
-active transport
-endocytosis/exocytosis
-activation chemicals
-cell division
-DNA replication etc
Describe the different metabolic reactions
-anabolic reactions are metabolic reactions where large molecules are synthesised from smaller molecules
-catabolic reactions are metabolic reactions involving hydrolysis of large molecules to smaller ones
Importance of kinetic energy
-within living cells atoms, ions and molecules have kinetic energy and this allows them to move
-for example when molecules diffuse down concentration gradient, moving from one place to another, they use kinetic energy to do so
Describe the structure of ATP
-ATP is standard intermediary between energy-releasing and energy-consuming metabolic reactions in both eukaryotic and prokaryotic cells
-structure of ATP is phosphorylated nucleotide
-each molecule of ATP consists of adenosine, which is the nitrogenous base adenine plus five-carbon sugar ribose and three phosphate (phosphoryl) groups
Describe ATP in solution
-ATP is relatively stable (it does not break down ADP and Pi) when in solution but is readily hydrolysed by enzyme catalysis
-However, whilst in solution, it can easily be moved from place to place within a cell
How efficient is the release of ATP
-energy-releasing hydrolysis of ATP is coupled with an energy-consuming metabolic reaction
-when ATP is hydrolysed to ADP and Pi a small quantity of energy is released for use in cells
-cells can therefore obtain energy they need for process in small manageable amounts that will not cause damage or be wasteful
-ATP is referred to as universal energy currency as it occurs in all living cells and is source of energy that can be used by cells in small amounts
Describe the release of ATP as heat
-some energy is released from hydrolysis of ATP as heat
-the release of heat, both in respiration and during ATP hydrolysis, may appear to be inefficient and wasteful
-heat however helps keep living organisms ‘warm’ and enables their enzyme catalysed reactions to proceed at or near optimum rate
What is glycolysis
-glycolysis is a biochemical pathway that occurs in cytoplasm of all living organisms that respire, including many prokaryotes
-the pathway involves a sequence of 10 reactions, each catalysed by a different enzyme, some with help of coenzyme NAD
What are the three main stages of glycolysis
1) phosphorylation of glucose to hexose biphosphate
2)splitting each hexose biphosphate molecules into two triose phosphate molecules
3)
oxidation of triose phosphate to pyruvate
What is NAD
-enzymes that catalyse oxidation and reduction reactions need help of coenzymes that accept hydrogen atoms removed during oxidation
-NAD is non protein molecule that helps dehydrogenase enzymes to carry out oxidation reactions
-NAD oxidises substrate molecules during glycolysis, the link reaction and Krebs cycle
How is NAD made
-NAD is synthesised in living cells from nicotinamide (B3 vitamin) , the five-carbon sugar ribose, the nucleotide base adenine and two phosphoryl groups
-the nicotinamide ring can accept two hydrogen atoms, becoming reduced NAD
Role of reduced NAD
-reduced NAD carries the protons and electrons to cristae of mitochondria and delivers them to be used in oxidative phosphorylation for generation of ATP from ADP and Pi
-when reduced NAD gives up the protons and electrons that it accepted during one of first three stages of respiration, it becomes oxidised and can be reused to oxidise more substrate, in process, becoming reduced again
Describe the process of phosphorylation
-glucose is a hexose sugar which means it contains 6 carbon atoms
-it molecules are stable and need to be activated before they can be split into two three carbon compounds
1) one molecule of ATP is hydrolysed and released phosphoryl group is added to glucose to make hexose monophosphate
2) another molecule of ATP is hydrolysed and the phosphoryl group added to the hexose phosphate to form a molecules of hexose biphosphate. This sugar has one phosphate group at carbon atom number one and another at carbon atom six
-the energy from hydrolysed ATP molecules activates hexose sugar and prevents it from being transported out of cell
Describe the splitting of the hexose biphosphate
-each molecule of hexose biphosphate is split into two three-carbon molecules, triose phosphate, each with a phosphate group attached
Describe the oxidation of triose phosphate to pyruvate
-although this process is anaerobic, it involves oxidation, because it involves removal of hydrogen atoms from substrate molecules
1) dehydrogenase enzymes, added by coenzyme NAD, remove hydrogens from triose phosphate
2) two molecules of NAD accept hydrogen atoms and become reduced
3)at this stage of glycolysis, two molecules of NAD are reduced for every molecule of glucose undergoing this process. Also at this stage, four molecules of ATP are made for every two triose phosphate molecules undergoing oxidation
What are the products of glycolysis
-from each molecule of glucose, at end of glycolysis there are
-two molecules of ATP: four have been made but two used to ‘kickstart’ process so net gain is two molecules of ATP
-two molecules of reduced NAD
-two molecules of pyruvate
What are the four main stages of respiration
1)glycolysis
2)link reaction
3)Krebs cycle
4) oxidative phosphorylation
-the last three stages only take place under aerobic conditions
-under aerobic conditions pyruvate molecules from glycolysis are actively transported into mitochondria for link reaction
-in absence of oxygen pyruvate converted in the cytoplasm to lactate or ethanol
-in process, reduced NAD molecules are reoxidised so glycolysis can continue to run, generating two molecules of ATP for every glucose molecule metabolised
Discovery of mitochondria
-mitochondria are organelles that are present in all types of eukaryotic cells
-mitochondria first identified in animal cells in 1840
-identified in plant cells in 1900
-ultrastructure discovered in 1950s after using electron microscope
Describe structure of mitochondria
-all mitochondria have inner and outer phospholipid membrane making up the envelope
-outer membrane smooth and inner membrane folded into cristae giving it large surface area
-embedded in inner membrane are proteins that transport electrons and protein channels associated with ATP synthase enzymes that allow protons to diffuse through them
-between inner and outer mitochondrial membranes of envelope is inter membrane space
-mitochondrial matrix enclosed by inner membrane is semirigid and gel like
-it contains mitochondrial ribosomes, looped mitochondrial DNA and enzymes for link reaction and Krebs cycle
MITCOHONDRIA FUNCTION: the matrix
-matrix is where link reaction and Krebs cycle take place
-enzymes that catalyse stages of these reactions
-molecules of coenzymes NAD and FAD (flavine adenine dinucleotide)
-oxaloacetate - four carbon compound that accepts acetyl group from link reaction
-mitochondrial DNA- some of which codes for mitochondrial enzymes and other proteins
-mitochondrial ribosomes, structurally similar to prokaryotic ribosomes, where these proteins assembled
MITOCHONDRIA FUNCTION: outer membrane
-the phospholipid composition of outer membrane similar to that of membranes around other organelles in eukaryotic cells
-it contains proteins, some of which form channels or carriers that allow passage of molecules such as pyruvate into mitochondrion
MITOCHONDRIA FUNCTION: inner membrane
-lipid composition of inner membrane differs from outer membrane
-lipid bilayer less permeable to small ions such as hydrogen ions
-the folds, cristae, in inner membrane give large surface area for electron carriers and ATP synthase enzymes embedded in them
-electron carriers are protein complexes arranged in electron transport chains
-electron transport chains are involved in final stage of aerobic respiration; oxidative phosphorylation
MITOCHONDRIA FUNCTION: intermembrane space
-intermembrane space between outer and inner layers of mitochondrial envelope is also involved in oxidative phosphorylation
-inner membrane is in close contact with mitochondrial matrix so molecules of reduced NAD and FAD can easily deliver hydrogen to electron transport chain
MITOCHONDRIA FUNCTION: electron transport chain - cofactor
-each electron carrier proteins contains a cofactor - a non protein haem group that contains an iron ion
-the iron ion can accept and donate electrons because it can become reduced (Fe2+) by gaining electron and oxidised (Fe3+) when donating electron to next electron carrier
-electron carrier proteins are oxido-reductase enzymes
MITOCHONDRIA FUNCTION: electron transport chain - coenzyme
-electron carriers also have coenzyme that, using energy released from electrons, pumps protons from matrix to intermembrane space
-protons accumulate in intermembrane space and proton gradient forms across membrane
-proton gradient can produce flow of protons through channels in ATP synthase enzymes to make ATP
