Question 7: Pentose sugar is a component of nucleotide molecule, show how pentose sugar is structured
by drawing the pentose phosphate pathway?
2. The pentose sugar contains five carbon atoms. Each carbon atom of the sugar
molecule are numbered as 1′, 2′, 3′, 4′, and 5′ (1′ is read as “one prime”). The
two main functional groups that are attached to the sugar are often named in
reference to the carbon to whch they are bound. For example, the phosphate
residue is attached to the 5′ carbon of the sugar and the hydroxyl group is
attached to the 3′ carbon of the sugar. We will often use the carbon number to
refer to functional groups on nucleotides so be very familiar with the structure of
the pentose sugar.
The pentose sugar in DNA is called deoxyribose, and in RNA, the sugar is ribose.
The difference between the sugars is the presence of the hydroxyl group on the
2' carbon of the ribose and its absence on the 2' carbon of the deoxyribose. You
can, therefore, determine if you are looking at a DNA or RNA nucleotide by the
presence or absence of the hydroxyl group on the 2' carbon atom—you will likely
be asked to do so on numerous occasions, including exams.
1.Two major phases of the pentose phosphate shunt: oxidative and non-oxidative
phases
The pentose phosphate pathway (PPP; also called the phosphogluconate pathway and
the hexose monophosphate shunt) is a process that breaks down glucose-6-phosphate
into NADPH and pentoses (5-carbon sugars) for use in downstream biological processes.
There are two distinct phases in the pathway: the oxidative phase and the non-oxidative
phase. The first is the oxidative phase in which glucose-6-phosphate is converted to
ribulose-5-phosphate. During this process two molecules of NADP+are reduced to NADPH.
The overall reaction for this process is:
lucose 6-phosphate + 2 NADP++ H2O → ribulose-5-phosphate + 2 NADPH + 2 H+ + CO2
The second phase of this pathway is the non-oxidative synthesis of 5-carbon sugars.
Depending on the body’s state, ribulose-5-phosphate can reversibly isomerize to ribose5-phosphate. Ribulose-5-phosphate can alternatively undergo a series of isomerizations
as well as transaldolations and transketolations that result in the production of other
pentose phosphates including fructose-6-phosphate, erythrose-4-phosphate, and
glyceraldehyde-3-phosphate (both intermediates in glycolysis). These compounds are
used in a variety of different biological processes including production of nucleotides and
nucleic acids (ribose-5-phosphate), as well as synthesis of aromatic amino acids
(erythrose-4-phosphate).
Glucose-6-phosphate dehydrogenase is the rate-controlling enzyme in this pathway. It is
allosterically stimulated by NADP+. NADPH-utilizing pathways, such as fatty acid
synthesis, generate NADP+, which stimulates glucose-6-phosphate dehydrogenase to
produce more NADPH. In mammals, the PPP occurs exclusively in the cytoplasm; it is
found to be most active in the liver, mammary gland, and adrenal cortex. The ratio of
NADPH:NADP+ is normally about 100:1 in liver cytosol, making the cytosol a highlyreducing environment.
The PPP is one of the three main ways the body creates molecules with reducing power,
accounting for approximately 60% of NADPH production in humans. While the PPP does
involve oxidation of glucose, its primary role is anabolic rather than catabolic, using the
energy stored in NADPH to synthesize large, complex molecules from small precursors.
Additionally, NADPH can be used by cells to prevent oxidative stress. NADPH reduces
glutathione via glutathione reductase, which converts reactive H2O2 into H2O by
glutathione peroxidase. For example, erythrocytes generate a large amount of NADPH
through the pentose phosphate pathway to use in the reduction of glutathione.
Question 8: What do you know about glycolysis, focus on structure of intermediates, enzymes, NADHs
and ATPs?
Glycolysis is a series of reactions that extract energy from glucose by
splitting it into two three-carbon molecules called pyruvates, lycolysis is an
ancient metabolic pathway In organisms that perform cellular respiration,
glycolysis is the first stage of this process. However, glycolysis doesn’t
require oxygen, and many anaerobic organisms—organisms that do not use
oxygen—also have this pathway.
Glycolysis takes place in the cytosol of a cell, and it can be broken down into
two main phases: the energy-requiring phase, the energy-releasing phase
Energy-requiring phase. In this phase, the starting molecule of glucose gets
rearranged, and two phosphate groups are attached to it. The phosphate
groups make the modified sugar—now called fructose-1,6-bisphosphate—
unstable, allowing it to split in half and form two phosphate-bearing threecarbon sugars. Because the phosphates used in these steps come from ATP,
TWO ATP molecules get used up

Energy-releasing phase. In this phase, each three-carbon sugar is converted
into another three-carbon molecule, pyruvate, through a series of reactions.
In these reactions, two ATP, molecule are made. Because this phase takes
place twice, once for each of the two three-carbon sugars, it makes
four ATP and two NADH overall.