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Samenvatting celbiologie jaar 1 psychobiologie module 2 deel 1
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Samenvatting celbiologie jaar 1 psychobio module 2 deel 1.
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Module 2 deel 1: BioenergeticaHoofdstuk 2
Pag. 51 tot 67
Catalysis and the use of energy by cells
The cells in a living organism must perform a never-ending stream of chemical reactions.
small organic molecules >> taken apart or modified to supply the many other small molecules that the cell
requires.
small molecules >> construct an enormously diverse range of proteins, nucleic acids, and other
macromolecules that endow living systems with all of their most distinctive properties.
Cell metabolism is organized by enzymes
Normally, the chemical reactions that a cell carries out would occur at much higher temperatures. Each
reactions requires a specific boost in chemical reactivity >> catalysts. Almost always proteins (enzymes),
but RNA catalysts (ribozymes) also exist. Each enzyme catalyses one of many reactions, and they are
connected in series, so that the product of one
reaction becomes the starting material for the next.
Long linear reaction pathways >> linked to one
another, forming a maze of interconnected reactions that enable the cell to survive, grow & reproduce.
2 streams of chemical reactions
the catabolic pathways >> break down foodstuffs into smaller molecules, generating
both a useful form of energy & some of the small molecules that the cell needs as
building blocks
the anabolic pathways (biosynthetic) >> use the products of the catabolic pathways
to drive the synthesis of the many other molecules of the cell
>> together: the metabolism of the cell.
Biological order is made possible by the release of heat energy from
cells
The second law of thermodynamics >> in the universe, the degree of disorder always increases.
Systems will change spontaneously toward those arrangements that have the greatest probability. The
movement toward disorder is a spontaneous process, requiring a periodic effort to reverse it.
The amount of disorder in a system >> quantified and expressed as the entropy of the system >> the
greater the disorder, the greater the entropy.
Systems will change spontaneously toward arrangements with greater entropy
Living cells are generating order and thus might appear to defy the second law of thermodynamics. >> the
cell is not an isolated system: it takes in energy from its environment in the form of food. >> uses this
energy to generate order within itself. In the course of the chemical reactions that generate order, the cell
converts part of the energy it uses into heat. The heat is discharged into the cell’s environment and
disorders the surroundings. >> the total entropy increases, as demanded by the second law of
thermodynamics.
The first law of thermodynamics >> energy can be converted from
one form to another, but it cannot be created or destroyed. The amount
of energy in different forms will change as a result of the chemical
reactions inside the cell, but the first law tells us that the total amount of
energy must always be the same.
Coupling of heat production to an increase in order >> distinguishes the metabolism of a cell from the
wasteful burning of fuel in a fire.
, Cells obtain energy by the oxidation of organic molecules
All living cells are powered by energy stored in the chemical bonds
of organic molecules. Organisms must extract this energy in usable
form >> by a process of gradual oxidation, or controlled burning. A
cell is able to obtain energy from sugars/other organic molecules by
allowing their carbon and hydrogen atoms to combine with oxigen to
produce CO2 and H2O. >> earobic respiration.
Oxidation and reduction involve electron transfers
The cell does not oxidize organic molecules in one step. Use of enzymes
>> metabolism takes these molecules through a large number of reactions.
Oxidation: removal of electrons
Reduction: the addition of electrions
>> oxidation and reduction always occur simultaneously: if one molecule
gains and electron, a second molecule loses the electron.
>> C & O -> polar covalent bond (C gives up more than its equal share of electrons)
A + e- + H+ AH >> hydrogenation = reduction. Dehydrogenation = oxidation
>> enzymes catalyze the orxidation in small steps > to harvast useful energy
Enzymes lower the activation-energy barriers that block chemical reactions
Burning of paper >> loss of free energy. >> reduction of orderliness in the way the energy and molecules
were stored in the paper. chemical reactions proceed spontaneously only in the direction that leads to a
loss of free energy.
Molecules in a living organism are in a relatively stable state, and they cannot be changed to a stat of lower
energy without an input of energy >> a molecule requires activation energy before it can undergo a
chemical reaction that leaves it in a more stable state.
The kick over energy barriers is greatly aided by enzymes. Each
enzyme binds tightly to one or more molecules (substrates)
and holds them in a way that greatly reduces the activation
energy of a particular chemical reaction. Catalysts increase the
rate of chemical reactions >> they allow a much larger
proportion of the random collisions with the surrounding
molecules to kick the substrates over the energy barrier.
Enzymes can drive substrate molecules along specific reaction pathways
An enzyme cannot change the equilibrium point of a reaction >> when an catalyst lowers the activation
energy for the reaction Y → X, it also lowers the activation energy for the reaction X → Y by exactly the
same amount. !! no matter how much an enzyme speeds up a reaction, it cannot change its direction.
Enzymes steer all of the reactions in cells through specific reaction
paths >> enzymes are highly selective & very precise. >> catalyzing
only one particular reaction. Success of living organisms >> the
ability to make enzymes of many types, each with precisely specified
properties. Each enzyme has a unique shape containing an active
site (a pocket/groove in the enzyme into which only particular
substrates will fit). Enzymes remain unchanged after a reaction >> can function over and over again.
How enzymes find their substrates: the enormous rapidity of molecular motions
Enzymes must be able to bind a new substrate molecule in a fraction of a millisecond. But both enzymes &
substrates are present in relatively small numbers in a cell. >> rapid binding is possible because the
motions caused by heat energy are enormously fast at the molecular level. 3 classes of molecular motions:
The movement of a molecule from one place to another (translational motion)
The rapid back-and-forth movement of covalently linked atoms with respect to one another (vibrations)
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