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Energy management within cells
Lecture 6
Controlled Pathways
 The various compartments of the cell
(- what are they?) are populated with a very
large number of chemical reagents,
products, and enzymes.
 How does the cell control them all?
Each step in this pathway is regulated by specific enzymes this is one mechanism which allows multiple reactions to occur
in a common environment.
Pathways
A complex pathway can further be regulated by a number of
different feedback mechanisms - both up regulation and
down regulation, feedback inhibition and feedback initiation,
and other more complex interactions.
-Watch Multimedia Biochemical Pathways
 FileName: Bio10.swf
 The biosynthetic pathway for the two amino acids E and H is
shown schematically below. You are able to show that E
inhibits enzyme V, and H inhibits enzyme X. Enzyme T is most
likely to be subject to feedback inhibition by
__________________ alone.
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(a)
(b)
(c)
(d)
(e)
A
B
C
E
H
 An average cell has both general reactions
which it needs to perform to sustain life, as
well as specialized ones that make that cell
type unique, i.e. pancreatic cell.
 The general reactions are called
housekeeping reactions
 These can be many in number and their
interactions are pretty complex…
Anabolic & Catabolic
 Regardless of the complexity they are of
two types  ANABOLIC
 CATABOLIC
…
Enzymes
 Vast majority are P’s (however, some RNA)
 Increase the rate of virtually ALL chemical
reactions - fact: A reaction that takes just
milliseconds in the presence of an enzyme would
take millions of years without (some increase the
rate by as much as 1 x 1018 fold!!!)
 Enzyme pool selectively determines which
reactions shall take place inside a cell & when
Enzymes…
 Catalysts - Biological Catalysts
 2 Main Properties
 1. Increase rate without change to enzyme
 2. Do not alter chemical equilibrium
 Just speed things along by bringing
molecules together and reducing the
activation energy of the reactions too.
Random Motion
 The meeting of substrates and substrates
and enzymes is random.
 The meeting is driven by the thermal energy
of the molecules at these temperatures
 Quicktime movie (rmotion.mov) .…
Activation Energy
 An important concept that you have to learn
Enzymes mechanisms
 Enzymes are specific
 AA’s from different parts of the P’ come
together to form the active site (binding
pocket)
 ‘Lock-and-key’ model - exact fit
 Induced fit model - alteration of the
substrate by the binding process
Enzyme kinetics
 Initial binding is ionic
 Subsequent interactions may involve
covalent exchanges
 Atomic distances involved
 Prosthetic groups - small molecules that
participate in catalysis - metal ions
 Coenzymes - small molecules that enhance
rates - organic molecules - Biotin
Enzyme regulation
 Activity can be modulated - controlled to suit the
needs of the cell
 Feedback inhibition - product inhibits more
product formation
 Allosteric regulation - ‘other - site’ - molecules
which bind to the enzymes to alter its physical
properties
 Phosphorylation - adding of phosphate groups to
P’ to regulate activity - serine, threonine, or
tyrosine AA’s - : + or -
Metabolic Energy
 Cells need energy to function, grow and multiply
 A large portion of the cells resources are spent on
obtaining energy
 Most reactions utilize energy
 Gibbs FREE ENERGY = ∆G - release of energy is
-∆G
 ATP = ∆G of @ -12kcal/mol - releases energy on
hydrolysis
Glycolysis
(covered in greater detail later in this course)
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Breakdown of glucose for energy to Pyruvate
∆G = -686 kcal/mol
Nearly every cell performs glycolysis
No oxygen required - anaerobic reaction
Location - cytoplasm
Does this same reaction occur in bacteria?
Where does this same reaction occur in bacteria?
Acetyl CoA
(covered in greater detail later in this course)
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Acetyl coenzyme A
Intermediary in metabolism
Forms when Coenzyme A reacts with pyruvate
Eukaryotes - mitrochondria
Citric acid cycle
(covered in greater detail later in this course)
 Krebs cycle
 Oxidative metabolism
 Mitrochondria
Photosynthesis
(covered in greater detail later in this course)
 Sunlight is the ultimate source of energy
 Plants and bacteria produce carbohydrates
through photosynthesis
 Chlorophylls - photosynthetic pigments
Stay Current Please
 Read chapter 2 fully & visit the website.