Transcript An Introduction to Metabolism

METABOLISM
Chapter 8
Energy of Life

Metabolism is the combination of all the chemical
reactions in an organism
 Arises
from interactions of molecules within an orderly
cell

Facilitated by metabolic pathways which are
altered series of steps that create new products
 Often
catalyzed by enzymes
 Balances supply and demand of the cell (think traffic
lights)
Types of Metabolic Pathways

Catabolic (C
A + B)
 Release
energy by breaking down complex molecules
into simpler ones; degradation
 E.g cellular respiration: fuels and O2 to energy, H20,
and CO2

Anabolic (A + B
C)
 Use
energy to make more complex molecules by
consuming simpler ones; biosynthetic
 E.g amino acids to form proteins

Energy from catabolic (downhill) reactions can be
stored to drive anabolic (uphill) ones
A Review of Energy

The capacity to cause change or rearrange matter;
to do work
 KE
is energy of movement or objects in motion
 Thermal
energy (heat) is KE from random movement of
atoms or molecules
 PE
is stored energy; energy due to structure or location
 Chemical
energy is the PE available for release in a
chemical reaction


Necessary for all metabolic processes
Organisms are energy transformers

Energy forms include: heat, light, and sound
Energy Moves Around

Energy enters the world (light E)
 Sunlight

is the ultimate source of all energy
Harnessed or captured by plants (converts to
chemical E)
 Photosynthesis

Energy transfer between organisms (converts to
kinetic E)
 Organisms
 Some

produces sugars stored in plants
that consume plants can use for metabolism
lost as heat
Energy transfer again
 Organisms
that eat what ate plants
Thermodynamics

1st Law of Thermodynamics
 Energy
can not be created or destroyed, it is
transferred or transformed

2nd Law of Thermodynamics
 During
conversion of energy from one form to another,
some is lost as heat
 Makes
universe more disorderly
 An input of energy is needed to maintain order
Order vs. Disorder

Living systems create ordered structures from less
ordered starting materials
 Amino
acids ordered into polypeptide chains
 Living organisms are organized and complex

Take in ordered forms of matter and energy and
replace them with less ordered forms
 Consume
food to catabolize into CO2 and H20
 Organisms’ orderly state converted to disorder upon
death
Classifying Reactions
Exergonic: ‘energy outward’



Net release of energy
Magnitude is max
work that can be done
Are spontaneous, no
energy needed
Endergonic: ‘energy inward’



Absorbs free energy
Magnitude is energy
needed to drive reaction
Stores free energy,
nonspontaneous
Metabolic Equilibrium

Matter that doesn’t interact with
environment will reach equilibrium
and stop reacting


Cell at metabolic equilibrium is
dead (can’t work)
Cells maintain constant flow of
materials in and out of cell
Keeps metabolic pathways from
reaching equilibrium
 Continues if product don’t
accumulate


C6H12O6 and O2 available and ways
to excrete waste ≠ equilibrium
Energy Coupling

Use exergonic processes to drive endergonic
 ATP
mediates most processes
 Immediate source of energy to power cellular work

3 main types of cellular work
 Chemical:
endergonic reactions, synthesizing polymers
 Transport: pumping substances across membrane
against [gradient]
 Mechanical: beating of cilia or contraction of muscle
cells
Adenosine Triphosphate (ATP)


Nucleotide consisting of
sugar ribose, nitrogenous
base adenine, and 3
phosphate groups
Bonds can be hydrolyzed
 ATP
ADP + Pi + E
 Exergonic:

-7.3 kcal/mol
Phosphate groups have (-)
charge grouped together
 Repulsion
like a spring
Hydrolysis of ATP

Can heat cells when sole reaction
 Shivering
to generate heat from muscle contraction =
inefficent

Proteins actually harness E to perform cellular work
 Use
exergonic to drive endergonic reactions
 Involves transfer of Pi from ATP to another molecule,
called phosphorylation
 Molecule

becomes more reactive
Can change protein shape and binding
Activation Energy (EA)


Amount of energy needed to
‘push’ reactants toward
products
Barrier that determines the
rate of a reaction

Enzymes, proteins that act as
catalysts, act to lower EA so
reactions occur faster
Often end in ‘-ase’
 Reaction specific


Reactants absorb E until
unstable, allowing bonds to
break
Enzyme Activity
* Specific to a substrate, based
on 3D shape
Enzyme Function Effects

Temperature: increase rate b/c molecules move faster



pH: optimal 6-8, but exceptions exist (pepsin and trypsin)
Cofactors/coenzymes: inorganic or organic helpers


To a point, above will denature
i.e. vitamins
Inhibitors: weak bonds = reversible, covalent bonds aren’t

Competitive inhibitors: prevents substrate from binding to
active site b/c binds first or stronger (CO vs O2)

Counter by increasing substrate
Non-competitive inhibitors: binds to an alternate spot and
changes active site so intended substrate can’t bind
 i.e. sarin gas and DDT
