Ch 15: Metabolism- Basic Concepts and Themes

Phototrophs

Obtain energy from sunlight

Chemotrophs

Obtain energy from oxidation of chemicals

Catabolism

Breaks down complex molecules into smaller molecules

Anabolism

Constructs complex molecules from simple molecules

Which type of reaction generates energy?

Catabolic reactions

What type of reaction consumes energy?

Anabolic reactions

Amphipathic pathways

Either catabolic or anabolic depending my on the energy conditions of the cell

Why can positive deltaG reactions occur in metabolic pathways?

Concentration of reactants and products are not under standard conditions

How are endergonic reactions made energetically favorable?

Coupled with an exergonic reaction

Higher phosphoryl transfer potential than ATP

1,3-BPG

PEP

Creatine Phosphate

Lower Phosphoryl Transfer potential than ATP

G-3P

G-6P

The hydrolysis of what drives metabolism?

ATP

ATP hydrolysis is what type of reaction?

Exergonic

Why is ATP an energy rich molecule?

2 phosphoanhydride linkages in the triphosphide unit

P_i

Orthophosphate

PP_i

Pyrophosphate

Precise DeltaG of ATP hydrolysis depends on what?

Ionic strength of medium and concentrations of metal ions

What metal ions are common for ATP complexes?

Mn²⁺ and Mg²⁺

Why does ATP have a high phosphoryl-transfer potential

Electrostatic repulsion

Resonance stabilization

Increase in entropy

Stabilization due to hydration

The addition of phosphate groups change what?

Molecular geometry and polarity

Why is citrate not suitable to meet the needs of living systems in the place of phosphate?

Not sufficiently charged to prevent hydrolysis

Why is arsenate not suitable to meet the needs of living systems in the place of phosphate?

Unstable and susceptible to spontaneous hydrolysis, which is poisonous to cells

Why are silicate salts not suitable to meet the needs of living systems in the place of phosphate?

Virtually insoluble

NAD+ and FAD

Carrier in the oxidation of fuel molecules, electron acceptors

How many reactive sites does NAD+ have?

One reactive site

How many reactive sites does FAD have?

2 reactive sites

Reductive biosynthesis

Heavily oxidized precursors are reduced

NAD+ is derived from what vitamin?

Niacin

FAD is derived from what vitamin?

Riboflavin

Acetyl CoA

Carrier of acyl groups

Where is the reactive group in CoA?

The terminal sulfhydryl site

What vitamin is the key constituent of coenzyme A

Pantothenate

Acyl groups are important constituents in catabolism for what?

Oxidation of fatty acids

Acyl groups are important constituents in anabolism for what?

Synthesis of membrane lipids

What does acetyl CoA have a high acetyl-group-transfer potential?

The transfer of the acetyl group is exergonic

Activated carriers that act as coenzymes are derived from what?

Vitamins

Why is it more efficient to digest vitamins than synthesize them?

Takes more resources and energy to synthesize the enzymes required to construct them from simple molecules

Typical reaction type of FAD and NAD+

Redox

Typical reaction type of CoA

Acyl-group transfer

Noncoenzyme vitamins

A,C,D,E,K

How is metabolism regulated?

1. Amounts of enzymes

2. Catalytic activity

3. Accessibility of substrates

How are acyl groups linked?

Thioester bonds

Why is the hydrolysis of Acetyl CoA thermodynamically favorable?

The electron of the C=O forms lower stability resonance bonds with C-S than C-O