Ch 4: Cellular Metabolism, Part 1

1
Ch 4 Cellular Metabolism, Part 1

• Energy as it relates to Biology
• Energy for synthesis and movement
• Energy transformation
• Enzymes and how they speed reactions
• Metabolism and metabolic pathways
• Catabolism (ATP production)
• Anabolism (Synthesis of biologically important
  molecules)

2
Energy in Biol. Systems

• General definition of energy Capacity to do
  work
• Chemical, transport, movement
• First Law of Thermodynamics Energy can neither
  be created nor destroyed
• Ultimate source of energy Sun!

2 types of energy
Kinetic energy motion examples ? Potential
energy stored energy examples ?
Fig 4-2
3
Energy (E) Transfer Overview
Figure 4-1
4
Potential Energy
heat ( 70 of energy used in physical exercise)
Kinetic Energy
WORK
5
Bioenergetics study of energy flow
through biol. systems

• Chemical reactions transfer energy
• A B C D

Products
Substrates or reactants
Speed of reaction Reaction rate Initial force
Activation Energy
6
Potential Energy Stored in Chemical Bonds of
Substrate can be . . .

• transferred to the chemical bonds of the product
• released as heat (usually waste)
• used to do work ( free energy)

7
Chemical Reactions p 93

• Activation energy
• Endergonic vs. exergonic reactions
• Coupled reactions
• Direct coupling vs. indirect coupling
• Reversible vs. irreversible reactions

8
Activation Energy
Fig 4-3
9
Endo- and Exergonic Reactions
Which is which??
ATP H2O ADP Pi H Energy
10
Enzyme ( Biol. Catalyst)
Some important characteristics of an enzyme

• Enzymes are proteins
• ? rate of chemical reaction by lowering
  activation energy
• is not changed itself
• It may change DURING the reaction
• does not change the nature of the reaction nor
  the result
• is specific

Fig 4-6
11
(No Transcript)
12
Enzymes lower activation energy
All chemical reactions in body must be conducted
at body temp.!!
How do enzymes lower activation energy ?
13

• Enzymes bind to reactant molecules and bring them
  together in best position for rx.

14
Some more characteristics of enzymes

• Usually end in ase
• Inactive form -ogen
• in few cases RNA has enzymatic activity (eg rRNA
  ? peptide bond)
• Isoenzymes may be produced in different areas of
  the body
• E.g., LDH

15
Active Site

• Small region of the complex 3D structure is
  active (or binding) site.
• Enzymes bind to substrate

Old Lock-and-key model / New Induced-fit model
16
Enzyme-substrate interaction The old and the
new model
Lock and Key
Induced fit
17
Enzyme Specificity

• Often reaction with only one substrate
• Sometimes reaction with group of similar
  substrates

18
Naming of Enzymes
mostly suffix -ase first part gives info on
function

• Kinase
• Phosphatase
• Peptidase
• Dehydrogenase

examples
19
Isoenzymes different models of same enzyme
(differ in 1 or few aa)
Catalyze same reaction but under different
conditions and in different tissues/organs

• Examples
• Amylase
• LDH ? importance in diagnostics

20
Enzyme Activity depends on

• Proteolytic activation (for some)
• Cofactors coenzymes (for some)
• Temperature
• pH
• Other molecules interacting with enzyme
• Competitive inhibitors
• Allosteric modulators

21
1) Proteolytic Activation

• Also
• Pepsinogen Pepsin
• Trypsinogen Trypsin

22
2) Cofactors Coenzymes
structure Inorganic molecules
(?) function conformational change of
active site
structure Organic molecules (vitamin
derivatives, FADH2 ....) function act as
receptors carriers for atoms or
functional groups that are removed from
substrate
23
Cofactors bind to active site
24
3)
Breakage of intramolecular bonds lead to ?
25
Siamese Cats

• Tyrosine Melanin
• Tyrosinase is temperature sensitive ?? does not
  function at cats core body temperature (101.5
  F)

tyrosinase
26
3)
27
4) Molecules interacting with enzyme

• Competitive inhibitors bind to active site

Fig 4-13
block active site
E.g. Penicillin binds covalently (
irreversibly to important bacterial enzyme active
site)
28
4) Molecules interacting with enzyme, contd

• Allosteric modulators (fig 4-14) bind to enzyme
  away from active site change shape of active
  site (for better or for worse)

Special case
end product inhibition
29
Allosteric Modulation
30
Reaction Rate Depends on Enzyme Substrate
Concentration
31
Reversible Reactions follow the Law of Mass Action
32
Three Major Types of Enzymatic Reactions

• Oxydation - Reduction reactions
• (transfer of electrons or protons (H))
• Hydrolysis - Dehydration reactions
• (breakdown synthesis of water)
• Addition-Subtraction-Exchange (of a functional
  group) reactions

33
(No Transcript)
34
?
35
Metabolism
next time
Anabolism
Catabolism
36
(No Transcript)