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Biochemistry - Lecture 15 + 16 (19-22/03/18)
Glycolysis Pathway And The Citric Acid Cycle
OXIDATION OF CARBON MOLECULES:
NAD+: Nicotinamide Adenine Dinucleotide.
NADP+: Nicotinamide Adenine Nucleotide Phosphate.
- NADP+ is formed through the addition of a phosphate group to the 2' position of the adenyl nucleotide through an ester linkage.
- NADH is the reduced form of NAD+; NADPH is the reduced form of NADP+.
- Cells synthesize NAD+ from niacin, also known as nicotinic acid or vitamin B3.
NAD+ IS AN…:
- Oxidising agent - it accepts electrons and is reduced
NAD+ + H+ + 2e- NADH
- Reducing agent - it loses electrons and is oxidised
NADPH NADP+ + H+ + 2e-
REDUCED COENZYMES ARE PRODUCED:-The reduced form is NADH, and the oxidized form is NAD+.
In the reduction reaction one electron is transferred to the positively-charged nitrogen and one hydrogen attaches to the carbon atom opposite to the nitrogen
NAD+/NADH is used extensively in glycolysis and the citric acid cycle. The reducing potential stored in the NADH molecule can be converted to synthesis of ATP through the electron transport chain or used for anabolic metabolism.
Energy used to produce ATP from ADP & Pi The electron-receiving unit in NAD+ is the nicotinamide group
NAD+ VS NADP+:NAD+
NADP+ has an extra PO4 group and has different enzyme recognition
(enzymes recognise either NAD+ or NADP+, rarely both) as the enzymes are involved in different metabolic pathways and so they provide different specificities
NAD+ used in catabolic reactions as oxidizing agent - aims at producing free energy. NADPH used in anabolic reactions as reducing agent - uses free energy.
FLAVIN REDOX COFACTORS - PROSTHETIC GROUPS:
FAD (Flavin adenine dinucleotide)
FNM (Flavin mononucleotide)--
Flavin adenine dinucleotide (FAD) is a redox cofactor, more
specifically a prosthetic group of a protein, involved in several important enzymatic reactions in metabolism.
A flavoprotein is a protein that contains a Flavin moiety, this may be in the form of FAD or Flavin mononucleotide (FMN).
FAD has similar structural elements to ATP/ADP etc., with the ribose and phosphate groups
FNM has the Flavin group and the phosphate group but no ribose or adenine
The prosthetic group (3 rings = Flavin group) is strongly attached by a covalent bond to the enzyme (hence is different to a coenzyme)
NAD+ etc is not bound covalently to the enzyme and so are coenzymes which can be released
Their function is to capture electrons from other molecules
FAD becomes reduced by 2 electrons to produce FADH2 STAGES OF CATABOLISM:
CATABOLIC REACTION = a metabolic reaction that degrades a molecule to provide smaller molecular building blocks and energy to an organism. GLYCOLYSIS:
NET REACTION OF GLYCOLYSIS:Two molecules of ATP produced
Two molecules of NAD+ reduced to NADH
Two molecules of pyruvate produced
Glucose + 2 ADP + 2NAD+ + 2Pi 2Pyruvate + 2ATP + 2NADH + 2H+ + 2H2O
First half of glycolysis is the investment phase, as you have to invest 2ATP for the later stages
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