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Ch 4: Energy and Cellular Metabolism

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Ch 4: Energy and Cellular Metabolism Energy as it relates to Biology Chemical reactions Enzymes and how they speed rxs Metabolism and metabolic pathways – PowerPoint PPT presentation

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Title: Ch 4: Energy and Cellular Metabolism


1
Ch 4 Energy and Cellular Metabolism
  • Energy as it relates to Biology
  • Chemical reactions
  • Enzymes and how they speed rxs
  • Metabolism and metabolic pathways
  • Catabolism (ATP production)
  • Anabolism (Synthesis of biologically important
    molecules)

2
Energy in Biological Systems
  • Review on your own!

3
Chemical Reactions
  • Transfer energy
  • or use energy to do work

A B C D
Bioenergetics Study of energy flow through biol.
systems Reaction rate speed of reaction
4
Activation Energy Starts Reaction
Fig 4-3
  • Reversible (most biol. rxs.) vs. irreversible
    reactions

5
Endergonic vs. Exergonic Reactions
  • Coupling endergonic and exergoinic rxs
  • Direct coupling vs. indirect coupling

Which kind?
6
Enzymes are Proteins acting as Biological
Catalysts
4 important characteristics of enzymes
  1. ? chemical reaction rate by lowering activation
    energy
  2. are not changed themselves
  3. do not change nature of rx nor result
  4. are specific

Fig 4-8
7
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8
Enzymes lower activation energy
All chemical reactions in body must be conducted
at body temp.!!
How do enzymes lower activation energy ?
9
  • Enzymes bind to reactant molecules and bring them
    together in best position for rx.

10
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 Fig 2-16
11
Enzyme-substrate interaction The old and the
new model
12
Naming of Enzymes
Not in book
mostly suffix -ase first part gives info on
function
  • Kinase
  • Phosphatase
  • Peptidase
  • Dehydrogenase

examples
13
Isozymes different models of same enzyme
(differ in 1 or few aa)
Catalize same reaction under different conditions
and in different tissues/organs
  • Examples
  • Amylase
  • LDH ? importance in diagnostics

Review Table 4-3
14
Enzyme Activity depends on
  1. proteolytic activation (for some)
  2. cofactors coenzymes (for some)
  3. temperature
  4. pH
  5. other molecules interacting with enzyme

15
1) Proteolytic Activation
  • Also
  • Pepsinogen Pepsin
  • Trypsinogen Trypsin

16
2) Cofactors Coenzymes
structure ___________ molecules (e.g.
?) 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
17
Cofactors bind to active site
18
3)
Breakage of intramolecular bonds lead to ?
19
Siamese Cats
  • Tyrosine Melanin
  • Tyrosinase is temperature sensitive ?? does not
    function at cats core body temperature (101.5
    F)

tyrosinase
20
4)
21
5) Molecules interacting with enzyme Allosteric
Modulators bind to enzyme away from active site
changing shape of active site for better or for
worse
Allosteric Activator
Fig 2-20
Allosteric Inhibitor
22
5) Molecules interacting with enzyme cont.
  • Competitive inhibitors
  • reversible binding to active site

Fig 2-19
block active site
  • Also possible irreversible binding via covalent
    bonds, e.g.
  • Penicillin
  • Cyanide

23
Reversible Reactions follow the Law of Mass Action
Fig 4-9
24
Three Major Types of Enzymatic Reactions
  • Oxydation - Reduction reactions
  • (transfer of ?)
  • Hydrolysis - Dehydration reactions
  • (breakdown synthesis of ?)
  • Addition-Subtraction-Exchange reactions

25
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26
?
27
Metabolism
Anabolism
Catabolism
?
?
28
  • Metabolism definition ___________
  • Metabolic pathways network of linked
    reactions
  • Cells regulate metabolic pathways via
  • Control of enzyme concentration
  • Modulator production (allosteric modulators,
    feedback inhibition, Fig 4-11)
  • Different enzymes for reversible rxs, Fig 4-12)
  • Compartmentation of enzymes
  • ATP / ADP ratio

29
Metabolic pathways Network of interconnected
chemical reactions
Linear pathway
Intermediates
Circular pathway
Branched pathway
30
Special case
end product inhibition
Fig 4-11
31
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32
Catabolic Pathways ATP-Production
  • Amount of ATP produced reflects on usefulness of
    metabolic pathways
  • Aerobic pathways
  • Anaerobic pathways

Different biomolecules enter pathway at different
points
33
ATP Energy Carrier of Cell (not very useful
for energy storage)
ATP ADP ratio determines status of ATP
synthesis reactions
34
Glycolysis
  • From 1 glucose to 2 pyruvate molecules
  • Main catabolic pathway of cytoplasm
  • Does not require O2 ? part of _________ and
    ____________ catabolism
  • Starts with phosphorylation (Before doubling
    your money you first have to invest!)

Fig 4-13
35
Pyruvate has 2 Possible Fates
Anaerobic catabolism Pyruvate
lactate
Aerobic catabolism Pyruvate Citric
Acid Cycle
36
Citric Acid Cycle
  • Other names ?
  • Takes place in ?
  • Energy Produced
  • 1 ATP
  • 3 NADH
  • 1 FADH2
  • Waste 2 CO2

Fig. 4-16
37
Energy Yield of Krebs Cycle
Compare to Fig. 4-16
38
Final step Electron Transport System
  • Chemiosmotic theory / oxydative phosphorylation
  • Transfers energy from NADH and FADH2 to ATP (via
    e- donation and H transport)
  • Mechanism Energy released by movement of e-
    trough transport system is stored temporarily in
    H gradient
  • NADH produces a maximum of 2.5 ATP FADH2
    produces a maximum of 1.5 ATP
  • 1 ATP formed per 3H shuttled through ATP
    Synthase

Fig 4-17
39
Cellular Respiration
Maximum potential yield for aerobic glucose
metabolism 30-32 ATP synthesized from ADP H2O is
a byproduct
40
Synthetic Pathways
Anabolic rxs synthesize large biomolecules
Unit molecules Macromolecules
nutrients energy required
Polysaccharides Lipids DNA Protein
41
Glycogen Synthesis
  • Made from glucose
  • Stored in all cells but especially in
  • Liver (keeps 4h glycogen reserve for between
    meals)
  • Skeletal Muscle ? muscle contraction

Gluconeogenesis
Glycolysis in reverse From glycerol, aa and
lactate All cells can make G-6-P, only liver and
Kidney can make glucose
42
Protein Synthesis
Proteins are the key to cell function ? necessary
for all cell functions Protein synthesis is under
nuclear direction ? DNA specifies Proteins
DNA mRNA Protein
?
?
43
How can only 4 bases in DNA encode gt 20 different
aa in protein?
  • 1 letter word 1 base 1 aa ? how many
    possibilities?
  • 2 letter word 2 bases 1 aa? how many
    possibilities?
  • 3 letter word 3 bases 1 aa ? how many
    possibilities?
  • 3 letter words base triplets or codons

44
Redundancy of Genetic Code
  • 1 start codon (AUG Met)
  • 3 stop codons
  • 60 other codons for 19 aa

45
Transcription
  • DNA is transcribed into complementary mRNA

by RNA Polymerase nucleotides Mg2 ( ?) ?
Gene elementary unit of inheritance
Compare to Fig. 4-25 and review Fig 4-26
46
Translation
mRNA is translated into string of aa (
polypeptide)
2 important components ??
mRNA ribosomes tRNA meet in
cytoplasm Anticodon pairs with mRNA codon ?
aa determined Amino acids are linked
via ______________ bond.
Fig 4-27
47
Protein Sorting
Post Translational protein modifications
Folding, cleavage, additions ? glyco- , lipo-
proteins
  • Due to signal/targeting sequence
  • No targeting sequence ? protein stays in
    cytoplasm
  • Targeting sequence ? protein destined for
    translocation into organelles or for export from
    cell

48
For export proteins Signal sequence leads
growing polypeptide chain across ER membrane into
ER lumen
  • Modifications in ER
  • Transition vesicles to
  • Golgi apparatus for further modifications
  • Transport vesicles to cell membrane

Compare to Fig 4-28
49
DNA Replication
  • Semi- conservative
  • DNA polymerase

50
the end
Running problem Tay-Sachs Disease
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