CH06_lecture

cemeterymarylandMechanics

Oct 27, 2013 (4 years and 13 days ago)

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Energetics

1

Adapted by G. Cornwall, Ph.D.

From Raven’s Biology, McGraw Hill Publishing

Chapter 6

2

Flow of Energy


Thermodynamics


Branch of chemistry concerned with energy
changes


Cells are governed by the laws of
physics and chemistry


Energy


capacity to do work


2 states

1.
Kinetic


energy of motion

2.
Potential


stored energy


Many forms


mechanical, heat, sound,
electric current, light, or radioactivity

3


Heat the most convenient way of
measuring energy.


1 calorie = heat required to raise 1 gram of water 1ºC


calorie or Calorie?


Energy flows into the biological world from
the sun


Photosynthetic organisms capture this
energy


Stored as potential energy in chemical
bonds

4

5

Redox reactions


Oxidation


Atom or molecule loses an electron


Reduction


Atom or molecule gains an electron


Higher level of energy than oxidized form


Oxidation
-
reduction reactions (redox)


Reactions always paired

Laws of thermodynamics


First law of
thermodynamics


Energy cannot be created
or destroyed


Can only change from one
form to another


Total amount of energy in
the universe remains
constant


During each conversion,
some energy is lost as
heat

6

7


Second law of thermodynamics


Entropy (disorder) is continuously increasing


Energy transformations proceed
spontaneously to convert matter from a more
ordered/ less stable form to a less ordered/
more stable form

8

Free energy


G = Energy available to do work


G = H


TS


H = enthalpy, energy in a molecule

s
chemical bonds


T = absolute temperature


S = entropy, unavailable energy

Δ
G =
Δ
H
-

TS


Δ
G = change in free energy


Positive
Δ
G


Products have more free energy
than reactants


H is higher or S is lower


Not spontaneous, Requires input
of energy


Endergonic


Neagtive
Δ
G


Products have less free energy
than reactants


H is lower or S is higher or both


Spontaneous (may not be
instantaneous)


Exergonic


9

Activation energy


Extra energy required to destabilize existing
bonds and initiate a chemical reaction


Exergonic reaction

s rate depends on the
activation energy required


Larger activation energy proceeds more slowly

10


Rate can be increased 2 ways

1.
Increasing energy of reacting molecules (heating)

2.
Lowering activation energy

11

Catalysts


Substances that influence chemical bonds
in a way that lowers activation energy


Cannot violate laws of thermodynamics


Cannot make an endergonic reaction
spontaneous


Do not alter the proportion of reactant
turned into product

12

13

ATP


Adenosine triphosphate


Chief

currency


all cells
use


Composed of


Ribose


5 carbon sugar


Adenine


Chain of 3 phosphates


Key to energy storage


Bonds are unstable


ADP


2 phosphates


AMP


1 phosphate


lowest energy form

14

ATP cycle


ATP hydrolysis drives endergonic reactions


Coupled reaction results in net

Δ
G (exergonic and
spontaneous)


ATP not suitable for long term energy storage


Fats and carbohydrates better


Cells store only a few seconds worth of ATP

Card Quiz A


Oxidation is the ____________ and reduction is the
________.


loss of electrons, gain of electrons


gain of protons, loss of protons


loss of protons, gain of protons


loss of electrons, gain of protons



Card Quiz A


The first law of thermodynamics states that energy can
be



Created


Destroyed


Converted


Lost

Card Quiz A


The energy in a system that is able to do work.


Enthalpy


Entropy


Free energy


Kinetic energy

Card Quiz A


A reaction with a positive ∆G is




Exergonic


Endergonic


Enthalpic


Energertic


Card Quiz A


Spending ATP involves hydrolyzing it into ADP and
inorganic P. The energy released can drive other
chemical reactions.


This is true


This is false


Card Quiz A


A catalyst speeds up chemical reactions. How do
catalysts do this?


Decreasing entropy


Altering ∆G


Consuming reactants


Lowering activation energy

Card Quiz Answers


Green


Red


Red


Red


Green


Red



22

Enzymes


Most enzymes are protein


Some are RNA


Shape of enzyme stabilizes a temporary
association between substrates


Enzyme not changed or consumed in reaction


Carbonic anhydrase


200 molecules of carbonic acid per hour made without enzyme


600,000 molecules formed per second with enzyme

Active site


Pockets or clefts for substrate binding


Forms enzyme
-
substare complex


Precise fit of substrate into active site


Applies stress to distort particular bond to lower
activation energy


Induced fit

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24


Enzymes may be suspended in the
cytoplasm or attached to cell membranes
and organelles


Multienzyme complexes


subunits work
together to form molecular machine


Product can be delivered easily to next
enzyme


Unwanted side reactions prevented


All reactions an be controlled as a unit


25

Nonprotein enzymes


Ribozymes


1981 discovery that certain reactions
catalyzed in cells by RNA molecule itself

2 kinds

1.
Intramolecular catalysis


catalyze reaction
on RNA molecule itself

2.
Intermolecular catalysis


RNA acts on
another molecule

Enzyme function


Rate of enzyme
-
catlyzed reaction depends on
concentrations of substrate and enzyme


Any chemical or physical condition that affects
the enzyme

s 3 dimensional shape can change
rate


Optimum temperature


Optimum pH

26

27

Inhibitors


Inhibitor


substance
that binds to enzyme
and decreases its
activity


Competitive inhibitor


Competes with substrate
for active site

28


Noncompetitive inhibitor


Binds to enzyme at a site
other than active site


Causes shape change
that makes enzyme
unable to bind substrate

Cofactors & Coenzymes


Cofactors
: assist in enzyme function


Often metal ions found in active site


Zinc in corboxypeptidase


Required in the diet in small amounts


Coenzymes
: a cofactor that is an organic
molecule (non
-
protein)


Many are vitamins essential in our diets


Often coenzymes and cofactors are involved in
capturing and transferring electrons


29

30

Allostery


Allosteric enzymes


enzymes exist in active
and inactive forms


Most noncompetitive inhibitors bind to allosteric
site


chemical on/off switch


Allosteric inhibitor


binds to allosteric site and
reduces enzyme activity


Allosteric activator


binds to allosteric site and
increases enzyme activity

31

Metabolism


Total of all chemical reactions carried out
by an organism


Anabolic reactions / anabolism


Expend energy to build up molecules


Catabolic reactions/ catabolism


Harvest energy by breaking down molecules

32

Biochemical pathways


Reactions occur in a
sequence


Product of one reaction
is the substrate for the
next


Many steps take place
in organelles

Feedback inhibition


End
-
product of pathway binds to an
allosteric site on enzyme that catalyses
first reaction in pathway


Shuts down pathway so raw materials and
energy are not wasted

33

Card Quiz B


Small organic molecules that assist in enzymatic
functions are



Coprolites


Cofactors


Activators


Coenzymes

Card Quiz B


Feedback inhibition occurs when the final product acts
as an inhibitor to the first enzyme in the pathway.


This is true


This is false


Card Quiz B


Carbon monoxide (CO) binds to the hemoglobin protein
at the oxygen binding site. Once the CO binds, the
oxygen can no longer be transported. What does this
describe?


Non
-
competitive inhibition


Feedback inhibition


Allosteric inhibition


Competitive inhibition



Card Quiz B


Increasing the temperature increases the rate of an
enzyme
-
catalyzed reaction. Once a critical temperature
is reached, the reaction stops. Why does this happen?


The concentration of reactants drop


The enzymes have all been consumed in the
reaction


The increase in temperature alters the pH


The polypeptide chains in the enzyme denature



Card Quiz Answers


Yellow


Blue


Red


Red