# CH06_lecture

Mechanics

Oct 27, 2013 (4 years and 6 months ago)

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Energetics

1

From Raven’s Biology, McGraw Hill Publishing

Chapter 6

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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,

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

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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

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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

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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

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ATP

Chief

currency

all cells
use

Composed of

Ribose

5 carbon sugar

Chain of 3 phosphates

Key to energy storage

Bonds are unstable

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

Green

Red

Red

Red

Green

Red

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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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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

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Inhibitors

Inhibitor

substance
that binds to enzyme
and decreases its
activity

Competitive inhibitor

Competes with substrate
for active site

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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

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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

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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

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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

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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