Intro to Metabolism Flashcards
Catabolic pathways
– Break down larger molecules into smaller ones
– General strategy to extract H/e- to be delivered to the electron transport
chain
– Sometimes to make ATP directly (substrate level phosphorylation) –> ATP generating
Anabolic pathways
– Build larger molecules from smaller substrates
– Generally requires input of energy (ATP) or reducing power (NADPH, NADH). –> ATP utilising
ATP
why we use atp
energy currency
VERY STABLE
adenosine triphosphate
energy is required to do work:
chemical : building big molecules e.g. proteins/fats
transport : require ATP for active transport
mechanical : requires movement
–> Reactions that require free energy can be
coupled to ATP hydrolysis to make them
thermodynamically favourable
(breaks 1 or 2 phosphate groups of ATP to ADP/AMP)
kinases
catalyse a phosphorylation reaction
–> phosphorylates proteins, add protein groups
phosphatases
catalyse dephosphorylation reactions
–> dephosphorylates someting, removes phosphate groups
phosphorylases
– catalyse a phosphorolysis reaction
uses phosphate groups to split molecules apart
Synthases vs Synthetases
synthases
– catalyse condensation reactions in which no nucleotide triphosphate is required (no ATP)
synthetases
– catalyse condensation reactions that require a nucleotide triphosphate (needs ATP)
Dehydrogenases
Catalyse oxidation-reduction reactions
– Usually involve NAD+ /FAD as cofactors
– Named for the substrate that is oxidised by NAD+ /FAD
– For example:
pyruvate + NADH –> lactate + NAD+
NADH –> NAD+ is an oxidation reaction and pyruvate –> lactate is a reduction reaction so the substrate is lactate and the enzyme is lactate dehydrogenase.
FAD
Flavin adenine dinucleotide
picks up 2H+/2e-
CH2CH2 –> C=C
NAD+
Nicotinamide adenine
dinucleotide
the reduction of NAD+ because it gains electrons (the “e-“ term in the equation) and a hydrogen ion, leading to a change in charge. The overall result is the conversion of NAD+ to NADH
Coenzyme A
can’t diffuse across plasma membrane, can bind to molecules so won’t escape from cell.
–> tagging/ “recognition flag”
Strategy of Fuel Oxidation: Stage 1
fats –> fatty acid (beta oxidation)
carbs – glucose (glycolysis)
protein –> aa (20 aa so several pathways)
Rip hydrogens/electrons (H/e -)
fatty acid –> acetate
glucose –> pyruvate –> acetate
aa –> acetate
acetate is 2 carbon (2 C)
CoA binds to form acetyl CoA
Strategy of Fuel Oxidation: Phase 2
Rip hydrogens/electrons (H/e -) out of acetate [Acetyl- CoA] (during krebs cycle)
Complete oxidation of carbon atoms to CO2
Making ATP with the H+ gradient
The protons flow (under pressure!) through a channel in the inner mitochondrial
membrane
As they come in, they cause another protein to rotate…
… which, in turn, interacts with the subunits of the ATP synthase
… to generate ATP from ADP and phosphate
SEVEN BIG Concepts!
- The H/e- carriers are in short supply
- ADP is in short supply
- ATP is really stable
- The inner mitochondrial membrane is impermeable to protons
- Protons only flow into the matrix if the ATP is being made
- The proton pumps don’t work if the proton gradient is very high
- No proton pumping, no H/e- movement down the ET chain
Fuels: Fatty Acids
- Nearly all the carbon atoms are fully reduced
- Stored as triglyceride (1 glyercol molecule + 3 fatty acids with ester bonds)
- Totally hydrophobic
- Very energy dense (37 kJ/g)
- Huge stores (many kg)
- Can’t be used by brain
Beta-oxidation
Beta-oxidation
* Fatty acids trapped in cytoplasm as
Fatty Acyl-CoA
* Carnitine acts as carrier and helps transport into mitochondria
* H/e- ripped out by FAD and NAD+ from the fatty acid and it leaves an acetate chunk
* Cycle repeats….
Fuels: Glucose
- Reasonably reduced
- Stored as glycogen
- Hydrophilic, lots of water associated
- Inefficient; 16 kJ/g (but only 6 kJ/g wet)
- Low stores (300 g)
- Can be used by all tissues
- Brain has an obligatory requirement!
Glucose Oxidation
- Glycolysis
- Every cell in your body, from muscle cells to skin cells, can do glycolysis*
- Takes place in cytoplasm
- No requirement for oxygen
- Very, very fast
- Very, very inefficient
- ATP generation almost irrelevant (with
some BIG exceptions) compared to
oxidative phosphorylation - Pyruvate must be transported into
mitochondria for full oxidation
Fuels - Protein
- Many pathways for amino acid catabolism
- Channel into pyruvate, acetyl-CoA or Krebs
- Energy release about 17kJ/g
- Need to dispose of amine groups
- ‘store’ is about 5-10 kg
- We don’t ‘store’ protein – it all has a function
- Making protein has cost us a LOT of energy so breaking down protein is last resort fuel source
