Welcome to

Chapter 6

Dr. Joseph Silver

major topics are

-what is energy-what is thermodynamics-how do enzymes work- how does ATP work

-multienzyme complexes-what is metabolism-the role of feedback

thermodynamicsis

that branch of chemistrywhich deals with

changes of energy

why is this important to biology

becauseyou cannot live without

a constant inputof energy

where does our energy come from

from the sunwhich

allows for the productionof

the plant and animalfood we eat

energy is described as

kinetic (motion)or

potential(position)

energy can bemechanical, sound, electrical, light,

radioactiveand

all forms of energy can generate heat

heat is usually described as a calorie

one calorie is the amount of heatneeded to raise the temperatureof one gram of water one degree

Celsius

since the source of all energy on our earthis from the sun

then the energy chemically locked

in the ionic and covalent bondsof all plants and animals

comes from heat from the sun

when we break down the food we eatwe release the heat locked into

the chemical bonds

when an atom releases or losesan electron

it is said to be oxidized (more positive)

when an atom gains an electronit is said to be reduced (more negative)

these reactions are very importantin the movement of energythrough biological systems

anabolic = use energy to build upcatabolic = use energy to breakdown

heat = energy moves from one item to anotherchemical energy = potential energy available from

chemical reactions pathways = steps from raw material to finished

product metabolism = chemical reactions of an organism

1st law of thermodynamicsknown as

conservation of energy

energy cannot be created or destroyedit

can only change from one form to anotherand

during each changesome energy is lost as heat

0

what is heat

energy caused by the random movement of molecules

or caused by the kinetic energy of atoms

the faster the atoms move the more heat is generated

2nd law of thermodynamicssates that

disorder in the universe (entropy) is increasing

the universe is becoming more disorganized (less order)

every energy transfer increases the entropy

of the universe

spontaneous = increases entropy

nonspontaneous = decreases entropy

in order to do workenergy must be available

where does it come form

in biological systemsit comes from breaking chemical bonds

the energy available to do work is calledfree energy

andit comes

from breaking chemical bonds

free energy = energy in - temperature x change inavailable for a chemical absolute entropy work bond (enthalpy)

G = H - TS

-G = spontaneous

+G or zero G = nonspontaneous

every spontaneous process decreasesthe systems free energy

endergonic = needs energy to proceed (+G)

exergonic = reaction gives off energy (-G)

endergonic reactionsrequire

an input of energy to start the chemical reaction

this is known as the

energy of activation

enzymesbiological catalysts

lower the energy of activation (fig 8.14)

an enzyme makes 1 biological chemical reaction

proceed millions of times faster anda cell

makes 1000s or 1000000 of the same enzyme

where does the energy come fromto do biological work

from

ATP

adenosine tri phosphateand also from GMP

ATP has 3 phosphate bondseach is a positive functional group

to keep a 2nd group in place requires some energy

but to keep a 3rd positive bond attachedrequires

a large amount of energywhen

the energy of the 3rd bond (high energy bond)

is released it is used to do work

enzymes are not destroyedwhen they are used to do work

theyare used over and over

until they are not neededthen

they are recycled

enzymes have an active sitewith

the correct shape

substrates (chemicals)fit into the enzyme

causing changes whichactivate a chemical reactionwhich changes the substrate

most biological chemical reactionsare part of a

series of stepsleading to the breakdown or building up

of various chemicals

in order to make the chemistry of cells more efficient

enzymes needed to accomplish a specific task are

part of amultienzyme complex

all of the enzymes needed for one job areright next to each other so that the

individual steps needed to form a producttake place right next to each other

it was once believed thatall enzymes were proteins

but scientists have now identified

RNA enzymes (ribozymes)

there are thousands of different RNAs inour cells and for most we have yet to

determine their function

many enzymes are activatedby molecules called activators

activators can activate an enzymeor

they can inhibit an enzyme

an enzyme can be inhibitedby

binding to the activation siteand not allowing the substrate access to the

enzymecompetitive inhibition

ora chemical can bind to the enzyme changing

the shape of the activation sitenoncompetitive inhibition

see fig. 8.18

the chemical reactions of an organismis known as metabolism

anabolism = use of energy to build up molecules

catabolism = getting energy by breaking up molecules

our bodies do 1000s of chemical reactions

production of a product usually involves multiple steps

the sequence of steps are known as a biochemical pathway

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when a cell no longer needs to keep making a product

the cell muststop making the product

how does this happen?

allosteric regulation

a molecule binds to an enzymeand

changes it’s shapeto activate or inhibit the enzyme

It happens byfeedback inhibition

the end product of a biochemical pathway

acts on the first step of the pathwayto stop the pathway

the opposite also happenswhen the end product

level drops to a low amountthen

the pathway begins to make more end product