Metabolism and Cellular Respiration: Pathways, Enzymes, and Energy Production

Metabolism

All chemical reactions in a cell/body

Metabolic pathway

Series of reactions converting substrates to products

Catabolism

Breakdown → releases energy

Anabolism

Build up → requires energy

3 ways to activate proteins

Allosteric activator, cofactor, proteolytic cleavage

2 ways to inhibit proteins

Competitive, allosteric (noncompetitive)

Allosteric activator

Binds away from active site → stabilizes active form

Cofactor

Non-protein helper (metal/vitamin) → enzyme works

Proteolytic activator

Enzyme activated by cleavage of peptide bond

Allosteric inhibitor

Binds away from active site → enzyme inactive

Competitive inhibitor

Binds active site → blocks substrate

Overcome allosteric inhibitor

Not easily overcome (shape change)

Overcome competitive inhibitor

More substrate outcompetes inhibitor

Catalyst

Speeds up reaction without being used

Catalyst type

Usually a protein (enzyme)

Substrate

Molecule enzyme acts on

Product

Molecule formed after reaction

Substrate specific

Enzyme binds only certain substrate

Feedback inhibition

End product inhibits earlier step

Activation energy

Energy barrier enzymes lower

Induced fit

Enzyme molds around substrate

Optimal conditions

Best temp/pH for enzyme

How enzymes speed reactions

Lower activation energy

Forms of released energy

Heat, light, mechanical, chemical (ATP)

Coenzyme function

Organic carrier of electrons/atoms (often vitamins)

Cellular respiration pathways

Glycolysis, Intermediate step, Krebs cycle, ETC

Glycolysis location

Cytoplasm

Glycolysis start

Glucose

Glycolysis end

2 pyruvate

Glycolysis yield

2 ATP, 2 NADH

Intermediate step location

Mitochondrial matrix

Intermediate step start

Pyruvate

Intermediate step end

Acetyl-CoA + CO2

Intermediate step yield

0 ATP, 2 NADH, 2 CO2

Krebs cycle location

Mitochondrial matrix

Krebs cycle start

Acetyl-CoA

Krebs cycle end

Oxaloacetate regenerated

Krebs cycle yield

2 ATP, 6 NADH, 2 FADH2, 4 CO2

ETC location

Inner mitochondrial membrane

ETC process

Electrons flow → H+ gradient → ATP synthase

Oxygen function

Final electron acceptor → H2O

Complex IV function

Transfers e− to O2 → pumps H+

ATP synthase function

H+ gradient drives ATP production

Electron function

Carry energy to pump H+

ATP per NADH

≈3 ATP

ATP per FADH2

≈2 ATP

Where NADH drops e−

Complex I

Where FADH2 drops e−

Complex II

ATP per glucose

≈30-32 ATP

Lipolysis

Breakdown of fat to glycerol + FA

Lipogenesis

Make fat from nutrients

Gluconeogenesis

Make glucose from non-carbs

Glycogenolysis

Breakdown glycogen → glucose

Glycogenesis

Make glycogen from glucose

Beta oxidation

Fatty acids → Acetyl-CoA

Anaerobic respiration

ATP without O2 (glycolysis + fermentation)

Pyruvate with O2

→ Acetyl-CoA

Pyruvate without O2

→ Lactate

Carbohydrates used

→ Glucose → ATP

Lipids used

FA → β-oxidation; glycerol → glycolysis

Proteins used

AA → deaminated → Krebs

Energy use order

1st carbs, 2nd fats, 3rd proteins, last ketones