physiology of the cell

7/31/2019 Physiology of the Cell

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Physiology of the Cell

By

Imelda A. Ygan


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The Laws of Thermodynamics

Describe the Basic Properties of

Energy The laws of thermodynamics define he basic

properties and behavior of energy. The first law of

thermodynamics states that, assuming there is no

influx of energy, the total amount of energy within a

given system remains constant. Although nuclear

reactions convert matter into energy, energy can

neither be created nor destroyed by ordinaryprocesses. Thus, the first law is otherwise called as

the law of conservation of energy.


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The second law of thermodynamics states that when

energy is converted from one form to another, the

amount of useful energy decreases. In other words, allspontaneous changes result in a more uniform

distribution of energy, reducing the energy differences

that are essential for doing work; energy is

spontaneously converted from more useful into lessuseful forms. We can also phrase the second law in terms

of the organization of matter: unless energy is added to

the system, processes that proceed spontaneously result

in an increase in randomness and disorder. This tendencytoward loss of orderliness and high-level energy and an

increase in randomness, disorder, and low-level energy is

called entropy.


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PHYSIOLOGY

Is the study of the

vital life processes of

organisms.

Animal

Physiology concerns

with the vital life

processes of animals.


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ENZYMES

ENDOENZYMESenzymes produced within a cell that remainwithin the cellto catalyze reactions within the cell.

EXOENZYMEproduced within a cell that are then released fromthe cellto catalyze extracellular reactions.

HYDROLASESbreakdown macromolecules by the addition of

water. POLYMERASESinvolved in the formation of large polymers like

DNA and RNA.

APOENZYMESare proteins, cannot on their own catalyze achemical reaction if not linked up with a co-factor. Co-factors areeither mineral ions (Mg, Ca, Fe cations) or coenzymes.

COENZYMESare small organic, vitamin-type molecules such asFAD and NAD. Like enzymes, they do not have to be present inlarge amounts because they are not altered during chemicalreactions, that they help catalyze. They are available for use overand over.


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Factors that affect the efficiency of

enzymes

TEMPERATURE (limited range)

pH (limited range)

Appropriate concentration of enzyme

Appropriate concentration of substrate


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Points to remember

The energy in a system available for doing work istermed asfree energy.

The energy that is released (exergonic) during

catabolic reactions is used to drive anabolic reactions. Some important reactions, however, in cells require

the addition of free energy and are said to beendergonic.

The energy required by a cell may be trapped fromthe rays of the sun (photosynthesis), or it may beproduced by certain catabolic reactions. Then theenergy can be temporarily stored within high-energy

bonds in special molecules, called ATP.


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ATP molecules Most important high-energy

compounds within a cell. The major energy-storing

molecules in the cell.

Found in all cells.

Are used to transfer energyfrom energy-yielding molecules

like glucose, to an energy-requiring reaction.

If not used shortly after it isformed, it is soon hydrolyzed toADP, a more stable molecule.

If not available, ADP can be

used as an emergency energysource by the removal ofanother phosphare group toproduce AMP.


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Biochemical Pathways

Is a series of linked

biochemical reactions

that occur in a step-wise

manner, leading from astarting material to an

end product.


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Glycolysis Also known as glycolytic

pathway, the Embden-Meyerhof

pathway, and the Embden-Meterhof-Parnas pathway.

Is a nine-step biochemicalpathway, involving nine separatebiochemical reactions.

Each reaction requires a specificenzyme.

In this pathway, a six-carbonmolecule glucose is ultimatelybroken down into two three-carbon molecules of pyruvic acid

(also called pyruvate). Can occur in either the presence

or absence of oxygen.


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KREBS CYCLE

Is a biochemical pathway

consisting of eight separatereactions, each of which iscontrolled by a differentenzyme.

Othername names are citric

acid cycle and tricarboxylicacid cycle or TCA cycle.

Referred to as a cyclebecause at the end of the eightreactions,it ends up back at its

starting point. Located within the

mitochondria (in eucaryotes)or at the inner surface of thecell membrane (in

procaryotes).


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ELECTRON TRANSPORT CHAIN

Also called the electrontransport system or respiratorychain.

Consists of a series ofoxidation-reduction reactions,whereby energy is released aselectrons aare transferred from

one compound to another. The compounds involve in the

transfer are: flavoproteins,quinones, nonheme ironproteins, and cytochromes.

Oxygen is at the end of the

chain; it is referred to as thefinal or terminal electronacceptor.

A large number of ATP areproduced in the process knownas oxidative phosphorylation.


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Oxidation-Reduction (REDOX) Reactions

Are reactions in which electrons are transferred from onecompound to another.

Whenever an atom, ion, or molecule loses one or moreelectrons in a reaction, the process is called oxidation, and the

molecule is said to be oxidized. The electrons that are lost do not float about at random, but

since they are reactive, they attached immediately to anothermolecule.

The resulting gain of one or more electrons by a molecule iscalled reduction, and the molecule is said to be reduced.


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Aerobic respiration of Glucose

Glucose is the favorite food or nutrient of cells,includingmicroorganisms.

The complete catabolism of glucose by the process known asaerobic respiration (or cellular respiration) occurs in threephases mentioned earlier. Each of which is a biochemicalpathway: glycolysis, Krebs cycle, and electron transport chain.

Although the first phaseglycolysisis an anaerobic process,the other two phases require aerobic conditions; hence thename, aerobic respiration.

Aerobic respiration is a very efficient system. It produces 18times (procaryotes) or 19 times (eucaryotes) as much energythan does fermentation of glucose.


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The chemical equation representing

aerobic respiration is:

C6H12O6 + 6O + 38ADP + 38P6H2O +6CO2 + 38ATP

Number of ATP molecules produced from one glucose:

Procaryotes Eucaryotes

Glycolysis 2 2

Krebs cycle 2 2

Electron transport 32 34

Total ATP molecule 36 38


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physiology of the cell

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