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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

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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!”)

Net gain?

The Steps of

Glycolysis

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

NADH

NADH NADH

FADH2

Energy Yield of Krebs Cycle

See Fig. 4-24

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

Protein synthesis fig 4-27

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 ??

Fig 4-34

Primary

Structure

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

DNA Replication

Semi-

conservative

DNA polymerase