Explore Biochemistry and Molecular Biology (BIOC0001) at University College London through this set of notes tailored for Year 1 students. Focused on the metabolism chapter, the comprehensive resource navigates key topics, including metabolic strategies, energy currency, glycolysis, fatty acid oxid...
Glycolysis
Glycolysis
Glycolysis
o Glycolysis = breakdown of glucose into 2 3 carbon compounds (first step in breakdown of glucose)
Allows cell to use glucose to produce energy + reducing power + carbon compounds
Reducing power and carbon compounds can be metabolised further to produce
more energy
o Oxygen and mitochondrial energy – most cells use mitochondria to produce energy = requires
oxygen for respiration
Red blood cell
Do not have any membrane bound organelles = no mitochondria
Ischemic heart tissue
Area of the heart that has had blood vessels that supply oxygen damaged = no
oxygen supply for respiration
Active white skeletal muscle
White muscle fibres are poor in mitochondria + have poor oxygen supply
Fast-growing tumour
Not enough oxygen supply
o Glycolysis = only way to produce ATP without using mitochondria or oxygen
Glycolysis does not release all of the potential energy from glucose
Products of glycolysis are usually further metabolised by aerobic respiration =
requires oxygen – releases more energy
Occurs in cytosol of cells
Sources of glucose
o Fed state
Glucose from digestion – stomach
o Fasting state
Glucose from glycogen – liver glycogen
o Exercise
Glucose from glycogen – muscle glycogen
o Starvation
Glucose from gluconeogenesis – glucose from non-carbohydrates – lactate / amino acids /
glycerol
Breakdown of glycogen
o Glycogen phosphorylase
Uses phosphorolysis to break bonds between glucose residues
Produces free glucose-1 phosphate molecules
o Phospho-glucomutase
Changes the position of the phosphate in glucose-1 phosphate = forming glucose-6
phosphate
Glycolysis Pathway
Overall pathway
o 1 glucose 2 pyruvates
Divided into 2 stages
1
o 2 ATP used to prepare the glucose molecule = requires energy investment
2
o Intermediate from preparation of glucose split into 2 molecules of
glyceraldehyde 3-phosphate
Each glyceraldehyde 3-phosphate produces 2 ATP
,Glycolysis
Overall
o Net production of 2 ATP
2 ATP used in glycolysis + 4 ATP produced = net 2 ATP
o Production of 2 NADH
o Enzymes
Kinase
Phosphorylates compounds using ATP or dephosphorylates compounds to produce
ATP
Dehydrogenase
Catalyse redox reactions – one compound is reduced + other compound is oxidised
o Produces reduced coenzymes = energy currency
Isomerase
Catalyses structural rearrangement of compound
Stages in glycolysis
o Stage 1
Glucose is free to enter or leave the cell
Hydrophilic molecule – needs transporter to move in and out of
the cell
o Surface of cell – glucose transporter binds to glucose >
changes shape > releases glucose inside or outside
(depending on concentration gradient)
Glucose is phosphorylated by hexokinase enzyme = forming glucose 6- Glucose
phosphate
Hexokinase enzyme – used to phosphorylate glucose
o Forming glucose 6-phosphate
ATP hydrolysis – provides energy needed for unfavourable
reaction (phosphorylation of glucose) to occur
o Couples unfavourable reaction (phosphorylation of
glucose = positive ΔG) with favourable reaction
(hydrolysis of ATP = negative ΔG) Glucose 6-
Resulting in negative ΔG phosphate
Glucose 6-phosphate cannot leave the cell
No transporter to move compound out of the cell
Glucose 6-phosphate isomerase enzyme rearranges glucose 6-
phosphate = forming fructose 6-phosphate
Glucose 6-phosphate isomerase rearranges glucose 6-
phosphate
Fructose 6-phosphate
, Glycolysis
o Makes it easier to phosphorylate carbon-1
Fructose 6-phosphate is phosphorylated at carbon-1 by
phosphofructokinase 1 enzyme = forming fructose 1,6 –
bisphosphate
Phosphofructokinase 1 – used to phosphorylate
fructose 6-phosphate
o Forming fructose 1,6-bisphosphate
Fructose 1,6-
ATP hydrolysis – provides energy needed for bisphosphate
unfavourable reaction (phosphorylation of fructose 6-
phosphate) to occur
o Couples unfavourable reaction (phosphorylation of fructose 6-phosphate =
positive ΔG) with favourable reaction (hydrolysis of ATP = negative ΔG)
Resulting in negative ΔG
o Stage 2
Aldolase splits fructose 6-phosphate into dihydroxyacetone phosphate +
glyceraldehyde 3-phosphate
Triose phosphate isomerase enzyme converts dihydroxyacetone
phosphate into glyceraldehyde 3-phosphate
Triose phosphate isomerase TPI = kinetically perfect enzyme Glyceraldehyde
o So efficient at lowering the activation energy – rate is 3-phosphate
limited by speed at which compounds bind to active
site
Equilibrium favours reverse reaction = formation of
dihydroxyacetone phosphate
Glyceraldehyde 3-phosphate dehydrogenase enzyme oxidises +
phosphorylates glyceraldehyde 3-phosphate = forming NADH + 1,3- Dihydroxyaceton
bisphosphoglycerate e phosphate
Reaction is coupled with reduction of NAD = forming 1 NADH (favourable process)
o Oxidation of glyceraldehyde 3-phosphate dehydrogenase generates enough
energy to reduce NAD + phosphorylate glyceraldehyde 3-phosphate again
1,3- Phosphoglycerate kinase enzyme removes phosphate from 1,3-
bisphosphoglyce bisphosphoglycerate = forming 3-phosphoglycerate + ATP
rate
Phosphorylation of ADP
o Phosphate removed is lost to ADP = forming 1 ATP
Rearrangement of phosphate into less stable position – to produce ATP
Phosphoglycerate mutase enzyme converts 3-phosphoglycerate 3-
into 2-phosphoglycerate phosphoglycera
Enolase enzyme converts 2-phosphoglycerate into te
phosphoenolpyruvate
2- Pyruvate kinase dephosphorylates phosphoenolpyruvate = forming
phosphoglycera pyruvate + ATP
te Phosphorylation of ADP Phosphoenolpyru
o Phosphate removed is lost to ADP = forming 1 ATP vate
Summary
o Stage 1
Glucose molecule is free to enter or leave the cell
To prevent molecule from leaving the cell – structure must be altered = cannot bind
to transporter protein
Hexokinase + ATP used to phosphorylate glucose = forming glucose 6-phosphate
Glucose phosphate isomerase rearranges glucose 6-phosphate = forming fructose 6-
phosphate
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