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Ch 4: Cellular Metabolism - Part 2
Energy as it relates to Biology
Enzymes
Metabolism
Catabolism (ATP production)
Glycolysis and the TCA Cycle
Anabolism (Synthetic pathways)
Protein Synthesis
Developed by
John Gallagher, MS, DVM
Metabolism
Definition = “All chemical reactions that take place within an organism.”
Metabolic pathways = network of linked reactions
Basic feature: coupling of exergonic rxs with endergonic rxs. (direct vs. indirect coupling)
Review:
Energy = capacity to do work
Usually from ATP
Enzymes = biological catalyst
Lower activation energy
Return to original state
Opportunity for control
Metabolism p 101
Anabolism
Synthesis
Energy transferred commonly measured in calories:
1 cal = 1 g of H2O by 1° C
1 Kcal = temp. of 1L H2O by 1o C.
= Calorie (capital C)
Energy released in catabolic reactions is trapped in
1) Phosphate bonds
2) Electrons
Catabolism
Energy
Metabolic pathways: Network of
interconnected chemical reactions
Linear pathway
Circular pathway
Branched pathway
Intermediates
Control of Metabolic Pathways
1. Enzyme concentration (already covered)
2. Enzyme modulators - Feedback- or end product
inhibition - Hormones - Other signaling molecules
3. Different enzymes for reversible reactions
4. Enzyme isolation
5. Energy availability (ratio of ADP to ATP)
(Chapter 6)
Catabolic Pathways: ATP-Regeneration
Amount of ATP produced reflects on
usefulness of metabolic pathways: Aerobic pathways
Anaerobic pathways
Different
biomolecules enter
pathway at
different points
ATP Cycle
ATP = Energy Carrier of Cell (not very useful
for energy storage)
ATP : ADP ratio determines status of ATP synthesis reactions
Glycolysis
From 1 glucose (6 carbons) to 2 pyruvate (3 carbons) molecules
Main catabolic pathway of cytoplasm
Does not require O2 common for (an)aerobic catabolism
Starts with phosphorylation of Glucose to Glucose 6-P
(“Before doubling your money you first have to invest!”)
Anaerobic catabolism: Pyruvate
Lactate
Aerobic catabolism: Pyruvate
Citric Acid Cycle
Pyruvate has 2 Possible Fates:
Citric Acid Cycle
Other names ?
Takes place in ?
Energy Produced: 1 ATP
3 NADH
1 FADH2
Waste – 2 CO2
Electron transport
System
Final step: Electron Transport System
Chemiosmotic theory / oxidative phosphorylation
Transfers energy from NADH and FADH2 to ATP (via e- donation and H+ transport)
Mechanism: Energy released by movement of e- through 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 4-25
Cellular
Respiration
Maximum potential
yield for aerobic
glucose metabolism:
30-32 ATP
synthesized from
ADP
H2O is a byproduct
Summary of
CHO catabolism
Protein Catabolism??
Proteases
Peptidases
Deamination (removal
of the NH3)
NH3 becomes urea
Pyruvate, Acetyl CoA,
TCA intermediates are
left.
Lipid Catabolism??
Lipolysis
Lipases break lipids
into glycerol (3-C)
Glycerol enters the
glycolytic pathway
Called β-oxidation
Synthetic Pathways
Unit molecules Macromolecules
Polysaccharides
Lipids
DNA
Protein
nutrients &
energy required
Anabolic reactions synthesize large
biomolecules
Glucose
Amino Acids
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
Proteins are necessary for cell functions
Protein synthesis is under nuclear direction
DNA specifies Proteins
Protein Synthesis
DNA mRNA Protein ? ?
1 start codon
3 stop codon
60 other codons for
19 aa
Redundancy of Genetic Code (p 115)
A combination of three bases forms
a codon
Transcription
DNA is transcribed into
complementary mRNA
by
RNA Polymerase
+ nucleotides
+ Mg2+
+ ATP
Gene = elementary
unit of inheritance Compare to Fig. 4-33
Translation mRNA is translated into string of aa (= polypeptide)
mRNA + ribosomes + tRNA meet in cytoplasm
Anticodon pairs with mRNA
codon aa determined
Amino acids are linked via
peptide bond.
2 important components ??
Protein Sorting
No signal sequence protein stays in cell
Signal sequence protein destined for translocation
into organelles or
for export
Post – Translational protein modifications:
Folding, cleavage, additions glyco- , lipo- proteins
Modifications in ER
Transition vesicles to
Golgi apparatus for further modifications
Transport vesicles to cell membrane
For “export proteins”: Signal sequence
leads growing polypeptide chain across ER
membrane into ER lumen