Lecture 10: Glycolosis Flashcards Preview

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Feedback inhibition

- regulated the whole metabolic pathway (production of amino acids)
• Metabolic pathway includes:
1. threonine
2. alpha-ketobutyrate
3. Isoleucine
- each rxn there there is an enzyme
- Isoleucine will bind to the first enzyme in order to inhibit it


Multiple Feedback Control

- allows cells to adjust the ratio of different compounds (e.g amino acids)


Enzyme Regulation

a) Competitive Inhibition
b) Allosteric Regulation


Competitive inhibition

- The substrates cannot
bind when a regulatory
molecule binds to the
enzyme’s active site.


Allosteric Regulation

• Allosteric Activation:
- The active site becomes
available to the substrates
when a regulatory molecule binds to a different site on the enzyme.
• Allosteric Inhibition:
- The active site becomes
unavailable to the substrates when a regulatory molecule
binds to a different site on
the enzyme.
*each time, the shape of the enzyme changes*
*most common type of regulation*


How is Allosteric Inhibition more efficient?

- comes down to number of regulator molecules that you need
- Competitive inhibition you need 10 million molecules and maybe 1 million regulators
- Allosteric regulator you have 1 regulator: 10 molecules (therefore, less energy)


Cooperative Allosteric Transition

- occurs with two or more subunits
- inhibitor can bind to the enzyme in the place of a substrate.
- It is a difficult transition for the inhibitor to be added, when the enzymes already binded
- it is an easy transition when one inhibitor and one substrate are in and the inhibitor can be added.


Cooperative Allostery

• when multiple subunits bind together
- results in different reaction curve
- the more subunits, the steeper the slope meaning that the enzyme activity lowers a lot faster with more subunits
- some delay at the beginning because it takes a while to bind (first is hardest, then gets easier)


Firs step in Metabolic Pathway

- nearly always a multisubunit enzyme negatively regulated by cooperative allostery



- when glucose is broken down, it produces energy - must be done in little steps to minimize the amount of energy lost
- complete oxidation of glucose is exergonic
- about half of the energy from glucose is collected in ATP (endergonic)


Energy for Life

- sun allows photosynthesis which allows for stored chemical energy which allows for glycolysis
- glycolysis can be aerobic or anaerobic


Aerobic Glycolysis: Cellular Respiration

- complete oxidation
- waste products: H2O, CO2
- net energy trapped: 29 ATP


Anaerobic Glycolysis: Fermentation

- incomplete oxidation
- waste products: organic compound
- net energy trapped: 2 ATP


Redox Reactions

• Transfer electrons
• Made up of 2 half reactions/redox pairs . (meaning one side electrons are collected, then transferred)
- A gain of electrons or hydrogen atoms is called reduction.
- The loss of electrons or hydrogen atoms is called oxidation.


How do you recognize oxidations?

- Fe+2 to Fe+3
- adding a hydrogen meaning you are oxidization (removing an electron, thus increasing the hydrogens)


Oxidation of Organic Molecules

- decreases the number of C-H bonds
- due to the attraction the electrons have to oxygen atoms, more than carbon.



• cofactor
• essential electron carrier in cellular redox reactions
• intermediate within the reaction



• gives up electrons (from glucose) to oxygen (electronegative acceptor)
• Has alternating double bonds that are energetically favoured because of the electrons of all 3 electron pairs form a common electron cloud. This makes it very stable
• forms into NAHH by breaking down glucose and accepting electrons (i.e getting reduced)


Oxidation of NADH with O2 as electron accepter

- exergonic
NADH + H+ + 1/2 O2 → NAD+ + H2O
• Two half reactions or redox pairs:
1. NADH NAD+ + H+ + 2e- (oxidation)
2. 1/2 O2 + 2H+ + 2e- H2O (reduction)
- NADH gives up electrons, oxygen takes those and becomes water.


Redox potential

- the tendency to lose or gain electrons
- a positive redox potential means that thy will have a tendency to gain electrons (become reduced)
- a negative redox potential means they will have a tendency to loose electrons (become oxidized)


Stages of Glycolysis

1. Investment of ATP to activate the sugar followed by splitting of C6 into 2x C3
2. Oxidation of C3 giving NADH + H+ and ATP followed by recovery of initial ATP investment (investment is required to rearrange the sugar to be oxidized)


Glycolysis coverts glucose to pyruvate (Part 1)

• First reaction is catalyzed by HEXOKINASE - forms G6P (adds a phosphate bond)
• Second reaction is catalyzed by PHOSPHOHEXOSE ISOMERASE (creates symmetry for breakup into two 3-C molecules- forms F6P)
• Third reaction is catalyzed by PHOSPHOFRUCTOKINASE (catalyses based on energy levels in cells) (adds another phosphate group to the molecules to make it more symmetrical- forms FBP)


Glycolysis coverts glucose to pyruvate (Part 2)

- takes FBP and splits into 2 3-C molecules called G3P


Glycolysis coverts glucose to pyruvate (Part3)

- G3P is oxidized
- NAD+ is reduced to NADH +H+
- this exergonic reaction releases enough energy to phosphorylate the molecules, forming BPG
- 1,3-bisphosphoglycerate donates one of its phosphate groups to ADP making a molecule of ATP and turning into 3-
phosphoglycerate in the process.


Glycolysis coverts glucose to pyruvate (Part 4)

- 3- phosphoglycerate is converted into its isomer, 2-phosphoglycerate.
- 2-phosphoglycerate loses 2 molecules of water, becoming phosphoenolpyruvate (PEP). PEP is an unstable molecule, poised to lose its phosphate group in the final step of glycolysis.
- PEPP, readily donates its phosphate group to ADP, making a second molecule ATP. As it loses its phosphate, PEP is converted pyruvate; the end product of glycolysis. (overall there are 2 pyruvate)


Substrate- level phosphorylation

- results in the formation of ATP or GTP by the direct transfer of a phosphoryl (PO3) group to ADP or GDP


Unfavourable reactions

• Have positive ∆G
• can be directly coupled to favourable ones (hydrolysis of ATP) or indirectly by sequential coupling.


Where does pyruvate Oxidation occur?

• In mitochondria
- carboxyl group is removed (released as CO2)
- NADH is released
- NAD+ is added along with Coenzyme A
- this results in Acetyl Coenzyme A