NAME: ERICKA L.

FRIGILLANA COURSE& SECTION: DVM-1B DATE: JULY 15, 2021

ASSIGNMENT IN BIO CHEMISTRY

1. What is the function of metabolic pathway? Give the 2 type of metabolic pathways and describe each.

 Metabolic pathways are a series of intracellular chemical reactions that create and break down
molecules for cellular processes. The Anabolic pathway synthesizes molecules and requires
energy. The catabolic pathway breaks down molecules to produce energy. Metabolic pathways
has 2 types, but it is characterized by the ability to synthesize molecules using energy,
decompose complex molecules (assimilation pathway), and release energy in the process
(woman-flower path or catabolic pathway).

2. What is carbohydrate metabolism and why it is important?

 Carbohydrates are an important source of energy for most living organisms. The continued
activity of every living cell depends on highly coordinated biochemical reactions, which are
fueled by energy generated through carbohydrate metabolism. The most important
carbohydrate is glucose, which can be broken down via glycolysis, enter into the Kreb's cycle
and oxidative phosphorylation to generate ATP.

3. How does the body break down carbohydrates? And how the body controls the sugar level in the
body increase?

 When people eat a food containing carbohydrates, the digestive system breaks down the
digestible ones into sugar, which enters the blood. As blood sugar levels rise, the pancreas
produces insulin, a hormone that prompts cells to absorb blood sugar for energy or storage.

4. What is the key enzyme of carbohydrate metabolism and How it works?

 The excess or unutilized energy is stored as fat or glycogen for later use. Carbohydrate
metabolism begins in the mouth, where the enzyme salivary amylase begins to break down
complex sugars into monosaccharides. These can then be transported across the intestinal
membrane into the bloodstream and then to body tissues.
 Glucose gets taken up into cells and either gets immediately broken down to produce energy or
gets converted into glycogen (storage form of glucose). The main glycogen stores in the body
are in the liver and muscles. These sources can be utilised for energy if required.

5. Where does carbohydrate metabolism occur and how is the process called?
  This process is called cellular respiration. In carbohydrate metabolism, the breakdown starts
from digestion of food in the gastrointestinal tract and is followed by absorption of
carbohydrate components by the enterocytes in the form of monosaccharides.

6. Define/describe the following pathways of carbohydrates metabolism.

a. Glycolysis

Glycolysis ultimately splits glucose into two pyruvate molecules. One can think of glycolysis as having
two phases, occurring in the cytosol of cells. The first phase is the “investment” phase due to its usage of
two ATP molecules, and the second is the “payoff” phase.

b. Citric acid cycle and oxidative phosphorylation

Tricarboxylic acid cycle, (TCA cycle), also called Krebs cycle and citric acid cycle, the second stage of
cellular respiration, the three-stage process by which living cells break down organic fuel molecules in
the presence of oxygen to harvest the energy they need to grow and divide.

Oxidative phosphorylation is the process in which ATP is formed as a result of the transfer of electrons
from NADH or FADH 2 to O 2 by a series of electron carriers. This process, which takes place in
mitochondria, is the major source of ATP in aerobic organisms

c. Pentose phosphate pathway

The pentose phosphate pathway (also called the phosphogluconate pathway and the hexose
monophosphate shunt) is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses
(5-carbon sugars) as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides.

d. Gluconeogenesis

Gluconeogenesis (GNG) is a metabolic pathway that results in the generation of glucose from certain
non-carbohydrate carbon substrates. It is a ubiquitous process, present in plants, animals, fungi,
bacteria, and other microorganisms.

e. Glycogenolysis

Glycogenolysis is the biochemical pathway in which glycogen breaks down into glucose-1-phosphate and
glycogen. The reaction takes place in the hepatocytes and the myocytes. The process is under the
regulation of two key enzymes: phosphorylase kinase and glycogen phosphorylase.
 f. Glycogenesis

Glycogenesis, the formation of glycogen, the primary carbohydrate stored in the liver and muscle cells of
animals, from glucose. Glycogenesis takes place when blood glucose levels are sufficiently high to allow
excess glucose to be stored in liver and muscle cells. Glycogenesis.

7. Know the step in glycolysis and

Step 1- Phosphorylation of glucose

In the first step of glycolysis, the glucose is initiated or primed for the subsequent steps by
phosphorylation at the C6 carbon. The process involves the transfer of phosphate from the ATP to
glucose forming Glucose-6-phosphate in the presence of the enzyme hexokinase and glucokinase (in
animals and microbes). This step is also accompanied by considerable loss of energy as heat.

Step 2- Isomerization of Glucose-6-phosphate

Glucose 6-phosphate is reversibly isomerized to fructose 6-phosphate by the enzyme

phosphohexoisomerase/phosphoglucoisomerase. This reaction involves a shift of the carbonyl oxygen
from C1 to C2, thus converting an aldose into a ketose.

Step 3- Phosphorylation of fructose-6-phosphate

This step is the second priming step of glycolysis, where fructose-6-phosphate is converted into
fructose-1,6-bisphosphate in the presence of the enzyme phosphofructokinase. Like in Step 1, the
phosphate is transferred from ATP while some amount of energy is lost in the form of heat as well.

Step 4- Cleavage of fructose 1, 6-diphosphate

This step involves the unique cleavage of the C-C bond in the fructose 1, 6-bisphosphate. The enzyme
fructose diphosphate aldolase catalyzes the cleavage of fructose 1,6-bisphosphate between C3 and C4
resulting in two different triose phosphates: glyceraldehyde 3-phosphate (an aldose) and
dihydroxyacetone phosphate (a ketose). The remaining steps in glycolysis involve three-carbon units,
rather than six carbon units.

Step 5- Isomerization of dihydroxyacetone phosphate

Glyceraldehyde 3-phosphate can be readily degraded in the subsequent steps of glycolysis, but
dihydroxyacetone phosphate cannot be. Thus, it is isomerized into glyceraldehyde 3-phosphate instead.
In this step, dihydroxyacetone phosphate is isomerized into glyceraldehyde 3-phosphate in the presence
of the enzyme triose phosphate isomerase. This reaction completes the first phase of glycolysis.

Step 6- Oxidative Phosphorylation of Glyceraldehyde 3-phosphate

Step 6 is one of the three energy-conserving or forming steps of glycolysis. The glyceraldehyde 3-
phosphate is converted into 1,3-bisphosphoglycerate by the enzyme glyceraldehyde 3-phosphate
dehydrogenase (phosphoglyceraldehyde dehydrogenase). In this process, NAD+ is reduced to coenzyme
NADH by the H– from glyceraldehydes 3-phosphate. Since two moles of glyceraldehyde 3-phosphate are
formed from one mole of glucose, two NADH are generated in this step.

Step 7- Transfer of phosphate from 1, 3-diphosphoglycerate to ADP

This step is the ATP-generating step of glycolysis. It involves the transfer of phosphate group from the 1,
3-bisphosphoglycerate to ADP by the enzyme phosphoglycerate kinase, thus producing ATP and 3-
phosphoglycerate. Since two moles of 1, 3-bisphosphoglycerate are formed from one mole of glucose,
two ATPs are generated in this step.

Step 8- Isomerization of 3-phosphoglycerate

The 3-phosphoglycerate is converted into 2-phosphoglycerate due to the shift of phosphoryl group from
C3 to C2, by the enzyme phosphoglycerate mutase. This is a reversible isomerization reaction.

Step 9- Dehydration 2-phosphoglycerate

In this step, the 2-phosphoglycerate is dehydrated by the action of enolase (phosphopyruvate

hydratase) to phosphoenolpyruvate. This is also an irreversible reaction where two moles of water are
lost.

Step 10- Transfer of phosphate from phosphoenolpyruvate

This is the second energy-generating step of glycolysis. Phosphoenolpyruvate is converted into an enol
form of pyruvate by the enzyme pyruvate kinase. The enol pyruvate, however, rearranges rapidly and
non-enzymatically to yield the keto form of pyruvate (i.e. ketopyruvate). The keto form predominates at
pH 7.0. The enzyme catalyzes the transfer of a phosphoryl group from phosphoenolpyruvate to ADP,
thus forming ATP.

8. The citric acid cycle

 The Citric acid cycle is a central pathway that provides a unifying point for many metabolites, which
feed in at various points. It takes place over eight different steps:

Step 1: Acetyl CoA (two carbon molecule) joins with oxaloacetate (4 carbon molecule) to form citrate (6
carbon molecule).

Step 2: Citrate is converted to isocitrate (an isomer of citrate)

Step 3: Isocitrate is oxidised to alpha-ketoglutarate (a five carbon molecule) which results in the release
of carbon dioxide. One NADH molecule is formed.

The enzyme responsible for catalysing this step is isocitrate dehydrogenase. This is a rate limiting step as
isocitrate dehydrogenase is an allosterically controlled enzyme.

Step 4: Alpha-ketoglutarate is oxidised to form a 4 carbon molecule. This binds to coenzyme A forming
succinyl CoA. A second molecule of NADH is produced, alongside a second molecule of carbon dioxide.

Step 5: Succinyl CoA is then converted to succinate (4 carbon molecule) and one GTP molecule is
produced.

Step 6: Succinate is converted into fumarate (4 carbon molecule) and a molecule of FADH₂ is produced.

Step 7: Fumarate is converted to malate (another 4 carbon molecule).

Step 8: Malate is then converted into oxaloacetate. The third molecule of NADH is produced.