SNS Biology - Respiration Flashcards
Glycolysis
Occurs in cytoplasm
- Glucose + ATP > glucose-6-phosphate + ADP
- > fructose-6-phosphate
- +ATP > fructose-1,6-diphosphate
- > glyceraldehype-3-phosphate (PGAL) + dihydroxyacetone phosphate
- dihydroxyacetone + NAD+ > PGAL + NADH
- 2 x PGAL > 2 x 1, 3-diphosphoglycerate
- 2 x ADP > 2 x 3-phosphoglycerate + 2 x ATP
- > 2 x 2-phosphoglycerate
- > 2 x phosphoenolpyruvate
- 2 x ADP > 2 x pyruvate + 2 x ATP
Glycolysis
Net Reaction
One molecule glucose used, two molecules pyruvate formed
Two ATP used, 4 generated - net production of two ATP per glucose
Two NADH per glucose
Glucose + 2ADP + 2Pi + 2NAD+ > 2Pyruvate + 2ATP + 2NADH + 2H+ + 2H2O
Glycolysis
Substrate Level Phosphorylation
ATP synthesis directly coupled to degradation of glucose without participation of an intermediate molecule such as NAD+
Glycolysis
Fermentation
For glycolysis to continue in the absence of oxygen, NAD+ must be regenerated, accomplished by reducing pyruvate into ethanol or lactic acid
Fermentation therefore produces only 2ATP per glucose
- Ethanol - yeast, some bacteria. Pyruvate converted into ethanol regenerating NAD+
- Lactic acid - fungi, bacteria, human muscle during strenous activity. Pyruvate reduced to lactic acid regenerating NAD+
Cellular Respiration
Aerobic
- Pyruvate decarboxylation
- Citric acid cycle
- Electron transport chain
Cellular Respiration
Pyruvate Decarboxylation
- Transported from the cytoplasm into the mitochondrial matrix
- Is decarboxylated (loses CO2) and remaining acetyl group is transferred to coenzyme A to form acetyl CoA
- In the process NAD+ is reduced to NADH
Cellular Respiration
Citric Acid Cycle
- Begins when 2C acetyl group from acetyl-CoA combines with 4C oxaloacetate to form 6C citrate
- Via complex series of reactions, 2CO2 are released and oxaloacetate regenerated
- For each cycle, 1ATP produced by substrate level phosphorylation via GTP intermediate.
- Additionally electrons are transferred to FAD and NAD+ to form FADH2 and NADH. These conenzymes transport the electrons to the electron transport chain
Cellular Respiration
Citric Acid Cycle
Net Reaction
For each molecule of glucose, 2 pyruvates enter the cycle, so 6 NADH, 2FADH2, 2ATP formed.
2 Acetyl CoA + 6NAD+ + 2FAD +2GDP + 2Pi +4H2O > 4CO2 + 6NADH + 2FADH + 2GTP(ATP) +4H+ + 2CoA
Cellular Respiration
Electron Transport Chain
- Electrons transferred from NADH to FADH2 to oxygen via series carrier molecules located on the inner mitochondrial membrane, most of which are cytochromes
- Functional unit of the cytochrome consists of central iron atom, capable of undergoing reversible redox reaction
- Final electron acceptor is O2 which also picks up 2H+ to form water
Anaerobic and Cellular Respiration
Total Energy Produced per Glucose
- Anaerobic (substrate level phosphorylation) = 2ATP
- Citric Acid Cycle = 2ATP
- Oxidative Phosphorylation = 32 ATP
Sum = 36 ATP
Cellular Respiration
Electron Transport Chain
Net Reaction
• Each glucose molecule produces 2NADH via glycolysis, 2NADH via pyruvate decarboxylation and 6NADH and 2FADH2 via the TCA cycle.
• Each FADH2 generates 2ATP
• Each NADH generates 3ATP, except the two of glycolysis which generate 2ATP
32ATP total therefore produced via the electron transport chain
Alternative Energy Sources
• In order of preference:
- Carbohydrates
- Fats
- Proteins
Alternative Energy Sources
- Disaccharides are hydrolysed to monosaccharides most of which can be converted into glucose or glycolytic intermediates.
- Glycogen stored in liver can be converted when needed to a glycolytic intermediate
Alternative Energy Sources
Fats
- Fat molecules stored in adipose tissue as triglycerides. When needed, converted by lipases to Fas and glycerol - Carried by blood to other tissues for oxidation
- Glycerol can be converted to PGAL, a glycolytic intermediate
- Fas must first be activated in the cytoplasm, requiring 2ATP, before transport into mitochondria and taken through cycles of beta oxidation to form 2C fragments which are converted to Acetyl-CoA. This then enters the TCA cycle.
- With each cycle of beta oxidation of a saturated FA, 1NADH and 1FADH2 produced
Alternative Energy Sources
Proteins
- Only degraded when insufficient carbs and fat available
- Most AAs undergo transamination
- Carbon atoms of most AAs converted to acetyl-CoA, pyruvate or another of the intermediates of the TCA cycle
- Alternatively, AAs may be converted to keto acids via oxidative deamination
Alternative Energy Sources
Proteins
Transamination
• Amino group of an AA exchanged for a ketone group of another acid to form an alpha-keto acid
Alternative Energy Sources
Proteins
Oxidative Deamination
- Removes an ammonia molecule from an AA directly
- Ammonia is toxic to vertebrates – fish can excrete it, insects and birds convert it to uric acid for excretion, and mammals to urea
Photosynthesis
Net Reaction
6CO2 + 12H2O + light energy > C6H12O6 + 6O2 + 6H2O
Photosynthesis
Reactions
- Light reaction – photolysis. Convert solar energy to chemical energy (ATP and NADP).
- Dark reaction – or reduction synthesis – carbs produced by reducing CO2. Coupled to the light reactions. Incorporate CO2 into organic molecules by carbon fixation
Photosynthesis
Reactions
Light Reactions
- Cyclic
- Non-cyclic – key pathway
Photosynthesis
Reactions
Light Reactions
Cyclic
- Photon of light is absorbed by chlorophyll a P700,
- Electrons excited to a higher energy level
- Move along a series of carriers and a series of redox reactions take place which ultimately return them to P700 whilst cyclic phosphorylation occurs to generate ATP
Photosynthesis
Reactions
Light Reactions
Non-Cyclic
- Photon of light is absorbed by chlorophyll a P700,
- Electrons excited to a higher energy level
- Transferred to NADP+ to form NADPH instead of returning to P700 along electron transport chain
- When light strikes P680, excited electrons travel down same electron carrier chain as for cyclic reaction until reach P700 where replace lost electrons, producing ATP by noncyclic phosphorylation
- P680 is strong enough oxidising agent to oxidise water to replace lost electrons, producing 2H+, 2e- and O2
Photosynthesis
Reactions
Dark Reactions
- Use NADPH and ATP generated by light reactions to reduce CO2 to carbohydrates
- CO2 is the source of carbon for carb production by the Calvin cycle
Photosynthesis
Reactions
Dark Reactions
Calvin Cycle
- CO2 fixed to 5C ribulose bisphosphate (RBP)
- Resulting 6C molecule splits to form 2 x 3C phosphoglyceric acid (PGA)
- PGA phosphorylated and reduced by ATP and NADPH to PGAL
- Most PGAL recycled to RBP via complex series of reactions
- PGAL considered prime end product
Photosynthesis
Reactions
Dark Reactions
PGAL
Used as:
- Intermediate food nutrient
- Combined and rearranged to form monosaccharides such as glucose
Photosynthesis
Reactions
Dark Reactions
Calvin Cycle
Net Reaction
• In 6 turns, 12 PGAL former from 6CO2 and 6 RBPThe 12 PGAL combine to form 6 RBP and 1 molecule glucose (end product)
Respiration
Invertebrates
Protozoa and Hydra
- Every cell in contact with external environment
- Respiratory gases can be exchanged by simple diffusion across the cell membrane
Respiration
Invertebrates
Annelids
- Mucous secreted by cells on the external surface provides a moist surface for gaseous exchange by diffusion
- The circulatory system brings O2 to the cells and returns waste products to the skin for excretion
- Vascularity of the skin makes cutaneous respiration very efficient
- Aquatic annelids use branchial respiration via gills or parapodia for gas exchange
Respiration
Invertebrates
Arthropods
- Respiratory system of the grasshopper consists of series of respiratory tubules – tracheae – whose branches reach to almost every cell
- Access the surface by spiracles (openings)
- Permits intake, distribution and removal of respiratory gases by diffusion
- No O2 carrier needed and its efficiency allows insects to have relatively effortless open circulatory system
Respiration
Humans
Alveoli number and surface area
- ~3 million
- 100m2 surface
Ventilation
• Process by which air is inhaled and exhaled from the lungs
- Muscular diaphragm contracts and flattens
- External intercostal muscles contract pushing the rib cage and chest wall up and out
- Thoracic cavity increases in volume, reducing pressure in the lungs
- Lungs expand and fill
Ventilation
Exhalation
• Generally a passive process - Lungs and chest wall are highly elastic and tend to recoil to original positions
- Diaphragm and intercostal muscles relax
- Chest wall moves inward
- Decrease in thoracic volume, increase in pressure
- Lungs deflate
Ventilation
Control
- Regulated by collections of neurons – respiratory centres – located in the medulla oblongata
- Rhythmic discharges from the medulla stimulate the intercostal muscles and/or diaphragm to contract
- When partial pressure CO2 rises, medulla stimulates increase in rate of ventilation
Ventilation
Pulmonary Surfactant
- Water molecules coat the walls of the alveoli
- Pulmonary surfactant is secreted by alveolar cells in order to prevent surface tension between water molecules from causing collapse of alveoli
- Coats alveolar walls reducing surface tension, permitting easier gas exchange and better pulmonary compliance 9lung elasticity)
Respiration In Plants
- Plants undergo aerobic respiration similar to animals
- Glycolysis produces 2ATP and pyruvic acids, 36ATP per glucose
- Anaerobic respiration takes place in simple plants in a similar manner to animals
