Download Code Questions Answers 1. Write the reactions of glycolysis

 Code
1.
Questions
Write
the
reactions of
glycolysis.
Answers
Aerobic glycolysis occurs in Cytosol.
Reactions of aerobic glycolysis:
1. First glucose is irreversibly activated to glucose-6-phosphate in the cell. In liver one
more specific enzyme also catalyses this reraction but at higher concentration of
glucose. It is known as glucokinase
(1 Mark)
2.
3.
4.
5.
Glucose-6-phosphate is then isomerised to fructose -6-phosphate :
(1 Mark)
Fructose -6-phosphate
is then irrerversibly phosphorylated to fructose 1,6
bisphosphate. Fructose 1,6 bisphosphate contains two phosphoric acid groups at C1
and C6 of fructose via phosphate ester bond.
(01 Mark)
Later fructose 1-6biphosphate molecule (six carbon sugar) is cleaved by aldolase
enzyme to yield glyceraldyhyde -3-phosphate and dihydroxy acetone phosphate ( two 3
carbon sugars trioses)
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Dihydroxy acetone phosphate formed in the above step is converted back to
Glyceralehyde-3 phosphate .
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6.
Now we have two molecules Glyceralehyde-3 phosphate molecules which get oxidized
to 1,3 bisphosphoglycerate. This step utilizes inorganic phosphate (Pi). In 1,3 bisphosphoglycerate the phosphate group at carbon atom number 1 is high energy
group.
During the oxidation of glyceralhyde-3-phophate the reducing equivalents are transferred to
the acceptor NAD+ (nicotinamide adenine dinucleotide). The reduced NADH under
aerobic conditions enter into mitochondria and produces 3 molecules of ATP through its
passage into electron transport chain or respiratoiry chain. This type of formation of
energy currency ATP through respiratory chain is called oxidative phosphorylation.
(01 Mark)
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7.
8.
In the next step the high energy compound 1,3 bisphosphoglycerate transfers its high
energy to ADP to form ATP resulting in the formation of 3-Phosphoglycerate. This
reaction is catalysed by phosphoglyceratekinase enzyme. This type of formation of
energy currency ATP by high energy substrate is called as substrate level
phosphorylation.
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3 phospoglycerate is then isomerised to 2 phosphoglycerate.
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9.
2 phosphoglycerate is then converted into one more high energy compound called as
phosphoenolpyruvate. This reaction is catalysed by enolase enzyme . The activity of
theis enzyme is completely inhibited by fluoride. Hence fluoride is used in the
vacutainers during blood collection for glucose estimation. This prevents the utilization
of glucose by RBCs.
(01 Mark)
10. Later phosphoenolpyruvate is converted into pyruvate .
2.
Explain
formation
and
utilization of
ketone
bodies.
Under aerobic conditions pyruvate is the end product of glycolysis. Hence pyruvate is
converted into acetyl CoA or oxaloacetate in the mitochondria.
(01 Mark)
Formation of ketone bodies.
Inside the mitochondria HMG CoA is formed using 3 acetyl CoA as …………………………..
acetoacetate and free acetyl CoA.
Acetoacetate is the parent ketone body. It is subsequently reduced by NADH dependent --------------------------------------------- This is known as ketoacidisis.
Utilization of ketone bodies
Acetoacetate and hydroybutyrate can be used as a source of energy in kidney and mucle.
…………………………………………… oxidized in Kreb’s TCA cyle
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3.
4.
Give
detailed
account on
the sources,
daily
requirement,
functions
and
deficiency
symptoms
of vitamin D.
Explain
in
detail
the
regulation of
serum
calcium
levels.
Source – 2 marks
Daily requirements – 2 marks
Functions – 4 marks
Deficiency symptoms – 2 marks
Regulation of serum calcium level (Calcium homeostasis):
Calcium homeostasis is a finely balanced process. The ionic calcium level is maintained by
Vitamin D and hormones like Para thyroid hormone (PTH) and Calcitonin.
(1 mark)
Action of Vitamin D
Increases the absorption of Ca (and phosphate) from the small intestine and causes removal
of Ca from bone (bone resorption).
Mechanism of calcium absorption from intestine through 1-25-dihydroxy Vitamin. D3: The
mechanism of action of 1-25-dihydroxy Vit. D3 is typical of steroid hormone. It enters to the
intestinal cell and binds to a cytoplasmic receptor. The Vitamin D3 receptor complex then
moves to the nucleus where it interacts with DNA. This results in the synthesis of mRNA
and this in turn forms a calcium binding protein. The calcium binding protein increases the
absorption of Ca from intestine.
(4 marks)
Action of PTH on kidney and bone:
1) PTH increases the activity of 1-hydroxylase in kidney which increases the synthesis of 125-dihydroxy Vit. D3 and this in turn enhances the absorption of Ca from intestine.
2) It increases the reabsorption of calcium from glomerular filtrate in kidneys.
3) It causes the resorption of Calcium from bone. These 3 actions correct the
hypocalcemia and bring it back to normal level.
4) PTH also causes excretion of phosphate in urine by inhibiting phosphate reabsorption in
kidney.
(3 marks)
Action of calcitonin: This is a hormone from C cells of thyroid glands. Hypercalcemia
stimulates its secretion. Calcitonin inhibits Calcium++ reabsorption from kidneys and
resorption from bone. Thus it corrects hypercalcemia. (2 marks)
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