Download Chapter 4: Energy and Cellular Metabolism, Part 2

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
Catabolism
 Energy
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
Metabolic pathways: Network of
interconnected chemical reactions
Linear pathway
Intermediates
Circular pathway
Branched pathway
Control of Metabolic Pathways
(Chapter 6)
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)
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 = Energy Carrier of Cell (not very useful
for energy storage)
ATP Cycle
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!”)
The Steps of
Glycolysis
Net gain?
Pyruvate has 2 Possible Fates:
Anaerobic catabolism:
Pyruvate
Lactate
Aerobic catabolism:
Pyruvate
Citric Acid Cycle
Citric Acid Cycle
Other names ?
Takes place in ?
Energy Produced:
1 ATP
3 NADH
1 FADH2
Electron transport
System
Waste – 2 CO2
Energy Yield of Krebs Cycle
NADH
See Fig. 4-24
NADH
NADH
FADH2
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
Summary of
CHO catabolism
Cellular
Respiration
Maximum potential
yield for aerobic
glucose metabolism:
30-32 ATP
synthesized from
ADP
H2O is a byproduct
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
Anabolic reactions synthesize large
biomolecules
Unit molecules
Glucose
Amino Acids
Macromolecules
nutrients &
energy required Polysaccharides
Lipids
DNA
Protein
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
Protein Synthesis
Proteins are necessary for cell functions
Protein synthesis is under nuclear direction
 DNA specifies Proteins
?
DNA
mRNA
?
Protein
Redundancy of Genetic Code (p 115)
A combination of three bases forms
a codon
1 start codon
3 stop codon
60 other codons for
19 aa
Transcription
DNA is transcribed into
complementary mRNA
by
RNA Polymerase
+ nucleotides
+ Mg2+
+ ATP
Gene = elementary
unit of inheritance
Compare to Fig. 4-33
Protein synthesis
fig 4-27
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
peptide bond.
Fig 4-34
Primary
Structure
Post – Translational protein modifications:
Folding, cleavage, additions  glyco- , lipo- proteins
Protein Sorting

No signal sequence  protein stays in cell

Signal sequence  protein destined for translocation
into organelles or
for export
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
DNA Replication

Semiconservative

DNA
polymerase