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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.
(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)
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)
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.