Chap 16- Glycolysis Flashcards
Properties of glucose that make it such a prominent fuel
- Glucose is one of several monosaccharides formed from formaldehyde under prebiotic conditions so it may have been available as a fuel source for primitive biochemical systems.
- Glucose is the most stable heroes because the hydroxyl groups and the hydroxymethyl group are all in the equatorial position, less stric clashes
- Glucose has a low tendency, relative to other monosaccharides,to nonenzynatically glycosykate proteins.
Where does glycolysis take place in eukaryotic cells?
In the cytoplasm.
What is the process of substrate channeling?
Increases enzyme efficiency by facilitating movement of substrates and products between enzymes. Prevents the release of any toxic intermediates.
What are the two stages of glycolysis?
Stage 1- the trapping and preparation phase. No ATO is generated k;this stage.
Stage 2- ATP is harvested when the three carbon fragments are oxidized to pyruvate.
Stage 1 in glycolysis
Begins with the conversion of glucose into fructose 1,6-biophosphate, which consists of three steps: a phosphorylation, an isomerization, and a second phosphorylation reaction. The strategy of these initial steps in glycolysis is to trap the glucose into the cell and form a compound that can be readily cleaved into phosphorylated three carbon units.
Step one is completed with the cleavage of the fructose into two phosphorylated three carbon fragments, which are readily intercinvertibke.
How does glucose enter the cell and what is its principal fate?
Glucose enters the cell through specific transport proteins and its fate is to be phosphorylated by ATP to form glucose 6-phosphate.
Why must glucose be phosphorylated into glucose 6-phosphate?
Glusoce 6-phosphate cannot pass through the membrane to the extra cellular side, because it is not a substrate for the glucose transporters.
The addition of the phosphorylated group facilitates the metabolism of glucose to phosphorylated three carbon compounds with high phosphoryl-transfer potential.
What does hexokinase catalyze?
The transfer of the phosphoryl group from ATP to the hydroxyl group on carbon 6 of glucose.
Hexokinase consists of two lobes which move toward each other when glucose is bound. Cleft between the lobes closes and the bound glucose is surrounded by protein. The closing of the cleft in hexokinase is a striking example of the role of induced wth.
What are kinases?
Enzymes that catalyze the transfer of a ohosphoryl group from ATP to an acceptor
Hexokinase catalyzes the transfer of a ohosphoryl group from ATP to a variety of six carbon sugars. Hexokinase requires Mg+2 for activity.
Why are the structural changes in hexokinase a biochemical consequence?
The environment around glucose becomes more nonpolar as water is extruded and the hydrophobic R groups of the protein surround the glucose molecules, which favours the donation of the terminal phosphoryl group of ATP. The removal of water from the active site enhances the specificity of the enzyme.
What reaction is catalyzes by phosphoglucose isomerase
The isomerization of glucose 6-phosphate to fructose 6-phosphate. The open chain form of glucose has an aldehyde group at carbon 1, whereas the open chain form of fructose has a ketone group at carbon 2. Thus, the isomerization of glucose 6-phosphate to fructose 6-phosphate is a conversion of an aldose into a ketose.
What does phosphofructokinase (pfk) catalyze?
It is an Allosteric enzyme that is the hey regulatory enzyme for glycolysis.Catalyzes a second phosphorylation reaction which follows the isomerization step, trapping the sugar s the fructose isomer. Fructose 6-phosphate is phosphorylated by ATP to fructose 1,6-biphosphate.
What do we have after the first two phosphorylation steps?
Transformed one molecule of glucose into two molecules of glyceraldehyde 3-phosphate, but no energy has yet been extracted. But, two molecules of ATP have been used.
What is the initial reaction in the second stage?
The conversion of glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate (1,3-BPG), and oxidation-reduction reaction catalyzes by glyceraldehyde 3-phosphate dehydrogenase.
What are dehydrogenases?
Enzymes that catalyze oxidation-reduction reactions, often transferring a hydride ion from a donor molecule to NAD+ or transferring a hydride ion from NADH to and acceptor molecule.
What does the thioester intermediate do?
Couples the favourable oxidation and unfavourable phosphorylation reactions.
The intermediate also preserves much of the free energy released in the oxidation state.
Substrate-level phosphorylation
Formation of ATP where the phosphate donor 1,3-BPG, a kinase substrate with high phosphoryl-transfer potential. Phosphoglycerate kinase catalyzes the transfer of the phosphoryl group from the amylose phosphate of 1,3-BOG to ADP.
What does the phosphoinositide cascade do?
Converts extracellular signals into intracellular ones. The intracellukar messengers formed by activation of this pathway arise from the cleavage of a membrane phospholipid
.
How is phospholipase C activated?
The binding of a hormone, vasopressin,- which regulates water retention, to its 7TM receptor. The Ga protein that activates phospholipase C is called Gaq.
What does the activated phospholipase C do?
The activated enzyme then hydrolyzes the phosphodiester linkage joining the phosphorylated inositol unit to the acylated glycerol moiety.
What does the cleavage of PIP2 produce and what do the products do?
The cleavage produces two messengers: inositol 1,4,5-triphosphate (IP3) which is a soluble molecule that can diffuse from the membrane and diacylglycerol (DAG), which stays in the membrane
What are the biochemical effects of the second messenger IP3?
IP3 doesn’t does not cause a cascade of phosphorylation to elicit a response from the cell. Instead, IP3 directly causes the rapid release of Ca2+ from intracellular stored- the endoplasmic reticulum and, in muscle cells, the sarcoplasmic reticulum. IP3 associates with a membrane protein called the IP3 receptor to allow the flow of Ca2+ from the ER to the cytoplasm
What does the elevated level of Ca2+ in the cytoplasm trigger?
Elevated levels of Ca2+ triggers a variety of biochemical processes such as smooth-muscle contraction, glycogen breakdown, and vesicle release.
