Unit 3; Energy Pathways Flashcards Preview

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Flashcards in Unit 3; Energy Pathways Deck (57):
1

redox reactions

the transfer of one or more electrons from one reactant to another in a chemical reaction

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oxidation

the loss of electrons from one substance

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reduction:

the addition of electrons to another substance

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reducing agent

electron donor

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oxidizing agent

electron acceptor
-oxygen is highly electronegative and so is one of the most potent oxidizing agents.

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Fuels

-compounds that can participate in exergonic reactions and be broken down to simpler wast products
-most common is glucose
-organic molecules with high H content are good fuels

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NAD+

-an electron carrier, it accepts electrons from H atom
-can easily cycle between oxidized (NAD+) and reduced (NADH) states
-functions as an oxidizing agent during respiration

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Process by which NAD+ acts as an electron carrier

1. Dehydrogenases enzymes remove a pair of hydrogen atoms (total of 2 electrons and 2 protons) from the fuel
2. 2 electrons plus 1 proton are delivered to the NAD+, neutralizing it, the other proton is released as an H+

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electron path in cellular respiration

glucose- NADH- electron transport chain-oxygen

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Three Metabolic Stages of Cellular Respiration

1. Glycolysis
2. Pyruvate Oxidation and the citric acid cycle
3. Oxidative phophorylation

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Overview of Cellular respiration

1.glycolysis occurs in cytosol,
-begins degradation process by breaking glucose into two molecules of pyruvate
2.pyruvate oxidized to acetyl CoA in Mitochondria
3. citric acid cycle completes breakdown of glucose to carbon dioxide
4. oxidative phosphorylation: electron transport chain accepts electrons form breakdown product of first two stages. Electrons are later combined with oxygen, water is produced

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substrate-level phosphorylation

enzyme transfers a phosphate group from a substrate molecule to ADP

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Formula of cellular respiration

Organic Compounds+Oxygen-- Carbon Dioxide + Water+ Energy

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Glycolysis in short

-In energy investment phase, two ATP are used and glucose is split into two 3-carbon sugars
-IN energy payoff phase, the smaller sugars are oxidized, (forming 2NADH and 2H+) and atoms are rearranged to form 2 pyruvate. (2 H20 is released in process)

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Glycolysis: Energy Investment phase

1. Phosphate group from ATP is transferred to glucose, forming Glucose 6-phosphate
2.This is converted to its isomer, Fructose 6-phosphate
3. Another phosphate group from ATP is attached to the opposite end of sugar forming Fructose 1,6 -biphosphate
4. Aldolase cleaves sugar molecule into 2 three carbon chains
5. Reversible reaction between the two isomers, Glyceraldehyde 3-phosphate is used in the next reaction

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Glycolysis: Energy Payoff Phase

6. Glyceraldehyde-3 phosphate is oxidized, producing 2NADH and 2H+, energy released is used to attach a P to the substrate, forming 1,3-Biphosphoglycerate
7. P is transferred to ADP in a exergonic reaction (2ATP are formed )
8. Phosphate group is relocated, forming 2 phosphoglycerate
9. Water is extracted forming a double pond in the substrate, phosphoerol pyruvate (PEP)
10. Phosphate group is transferred from PEP to ADP

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Oxidation of Pyruvate to Acetyl CoA

1. Pyruvate's carboxyl group is removed and given off as a molecule of CO2
2. Remaining 2-carbon fragment is oxidized, forming acetate. Extracted electrons are transferred to NAD+
3. CoA is bonded to acetyl, forming acetyl CoA which has a high potential energy

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Summary of Citric Acid Cycle

-pyruvate is broken down to 3 CO2 molecules
-one ATP is generated per turn
-3 NADH and one FADH2 are produced which carry electrons into the electron transport chain

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electron transport chain

a collection of molecules embedded in the inner membrane of the mitochondria
-mos are proteins with prosthetic groups bound tightly to them
-electrons are reduced then oxidized as they pass electrons down the chain
- a major function is to establish the H+ gradient

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prosthetic groups

non protein components essential for catalytic functions of certain enzymes

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Electron Transport chain process

electrons carried by NAD+ are transferred to the first molecule of the electron transport chain in complex I
-passed from a flavoprotein, to an iron-sulfur to ubiuinane to cytochromes then to oxygen
-water us formed at end
-FADH2 add electrons at Complex II

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ATP Synthase

the enzyme that actually makes ATP from ADP and inorganic phosphate
-uses energy of an existing ion gradient to power ATP synthesis
-power source is the difference in H+ on opposite sides of the membrane

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chemiosmosis

the process in which energy stored in the form of a H+ gradient across a membrane is used to drive cellular work

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proton-motive force:

potential energy generated by pumping of H+ along with electrons

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Cellular Respiration and ATP

-for every glucose molecule oxidized, 4 ATP are produced directly by substrate-level phosphorylation
-Each NADH contributes enough to protein-motive force to generate around 3 ATP
-about 34% of potential energy in glucose is transferred to ATP, the rest is lost as heat

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anaerobic respiration

-uses another electronegative substance besides oxygen to serve as the final electron acceptor

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Fermentation

-glycolysis plus reactions that regenerate NAD+ by transferring electrons from NADH to pyruvate and its derivative
-allows generation of ATP by substrate-level phosphorylation

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alchohol fermentation

-pyruvate releases CO2 and is converted to acetaldehyde. This is then reduced by NADH to ethanol, which regenerates the supply of NAD+

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lactic acid fermentation

- pyruvate is reduced directly by NADH to from lactate as an end product with no release of CO2

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obligate anaerobes

organisms that carry out only fermentation or anaerobic respiration
-cannot survive in the presence of oxygen

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facultative anaerobes

organisms that can make enough ATP to survive using either fermentation or respiration

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Glycolysis can accept a wide range of fuels

- starch and glycogen can by hydrolized to glucose
- proteins can be used once they are broken down to amino acids, and their amino groups are removed (deamination)
-fatty acids

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beta oxidation

a metabolic sequence that breaks down fatty acids to 2-carbon fragments which enter citric acid cycle as acetyl CoA
-generates NADH and FADH2

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Biosynthesis

-cells need substances to make their own molecules
-some organic monomers obtained from digestion can be used directly
-compounds formed as intermediates of glycolysis and the citric acid cycle can be diverted into anabolic pathways as precursors from which the cell can synthesize required molecules

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feedback inhibition

shuts off anabolic pathways . End product of the anabolic pathway inhibits the enzyme that catalyzes an early step of the pathway
-cellular respiration can slow or speed up depending on ATP concentrations by inhibiting or stimulating phosphofructokinase ( in 3rd step of glycolysis)

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thermoregulation

the process by which animals maintain an internal temperature within a tolerable range
-most internal processes are sensitive to changes in body temperature
-organisms must maintain equal rates of heat gain and heat loss

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endotherms

organisms, such as birds and mammals, that warmed mostly by heat generated by metabolism

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ectotherms

organisms like amphibians, lizards, snakes, turtles etc that gain heat from external sources
-need to consume less food
-mainly use behavior to regulate body temp

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poikilotherm

an animal whose body temp varies with its environment

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homeotherm

an animal with a relatively constant body temp

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organisms exchange heat by

-radiation (emission of electromagnetic waves)
-evaporation
-convection (transfer of heat by movement of air or liquid past a surface
-conduction (heat transfer between touching objects)

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integumentory system

outer covering of the body consisting of skin, hair, and nails

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Insulation

hair, feathers, fat which reduce flow of heat between an animal and its environment
-very important for marine mammals

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vasodilation

nerve signals relax muscles of the vessel walls, widening superficial blood cells.
-blood flow in the skin increase, warming skin and increasing transfer of body heat to environment

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vasoconstriction

reduces blood flow and heat transfer by decreasing diameter of superficial vessels

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countercurrent exchange

transfer of heat between fluids that are flowing in opposite directions
-as blood moves from body core, it transfers heat to colder blood returning from extremities

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Adjusting Metabolic Heat Production

-endotherms can vary heat production to match changing rates of heat loss
-increased by muscle activity or nonshivering thermogenesis

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nonshivering thermogenesis

in mammals, certain hormones can cause mitochondria to increase metabolic activity and produce heat instead of ATP

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brown fat

a tissue in some mammals that is specialized for rapid heat production

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hypothalamus

a region in the brain that contains the sensors for thermoregulation
- groups of nerve cells act as thermostat, activating mechanisms when temp is outside a certain range

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metabolic rate

the sum of all the energy used in biochemical reactions over a given time interval
-can be measured by monitoring an animal's rate of heat loss, or O2 consumed or CO2 produced by an animal, or food and waste

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basal metabolic rate

minimum metabolic rate of a nongrowing endotherm that is at rest and has an empty stomach

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standard metabolic rate

the minimum metabolic rate of a fasting, nonstressed ectotherm at rest at a particular temp

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Size and Metabolic Rate

-larger animals have more body mass and require more chemical energy
-energy it takes to maintain each gram of body mass is inversely related to body size

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Activity and Metabolic Rate

-activity increases metabolic rate
-maximum metabolic rate an animal can sustain is inversely related to duration of activity

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torpor

a physiological state of decreased activity and metabolism
-enables animals to save energy while avoiding difficult and dangerous conditions
-small mammals may exhibit daily torpor

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hibernation

a long-term torpor that is an adaptation to winter cold and food scarcity
- body temp declines allowing huge energy savings