BMB II test 1

What does this image reflect?

The major pathways of carbohydrate metabolism are connected, especially through glucose, glucose-6-phospate, and pyruvate

Based on the diagram, what molecule acts as the starting point connecting glycolysis, glycogen metabolism, and the pentose phosphate pathway?

Glucose-6-phospate (G6P)

Based on the diagram, what happens to glucose before it goes through glycolysis?

Glucose is converted into glucose-6-phosphate

What pathway is represented by the downward movement from glucose → glucose-6-phosphate → pyruvate?

Glycolysis

What pathway is represented by the movement from pyruvate back to glucose?

gluconeogenesis

What does the dashed arrow extending from glucose-6-phospate represent?

It shows how glucose-6-phosphate can be siphoned into the pentose phospate pathway (PPP)

What storage molecule is shown at the top of the diagram?

glycogen

What process converts glucose into glycogen?

Glycogen synthesis or glycogenesis

what process converts stored glycogen back toward usable glucose

glycogen degradation or glycogenolysis

According to the diagram, what major metabolic process can pyruvate eventually feed into?

The Citric Acid Cycle (TCA) after pyruvate is converted into acetyl-CoA

What energy producing process is shown downstream of the TCA cycle?

Oxidative phosphorylation

What is the general order of the following processes:
glucose, glycolysis, oxidative phosphorylation, TCA cycle, pyruvate

Glucose→glycolysis→pyruvate→acetyl-CoA→TCA cycle→oxidative phosphorylation

What does the two way relationship between glycogen and glucose represent?

glucose can be stored as glycogen and glycogen can be broken down to provide glucose

What is glycolysis?

The conversion of glucose to pyruvate

what molecule does glycolysis begin with?

glucose

What molecule does glycolysis end with

Pyruvate

Does glycolysis require oxygen

No. Glycolysis can occur in the presence or absence of O₂

Why can glycolysis occur in both aerobic and anaerobic conditions?

The glycolytic pathway itself does not require oxygen

What is one major advantage of glycolysis as an energy producing pathway

It provides a rapid way to produce energy

How many total steps does glycolysis have?

10 steps

Which steps of glycolysis are irreversible?

Steps 1, 3, and 10

How many irreversible reactions are present in glycolysis

Three

Which enzyme catalyzes irreversible step 1 of glycolysis?

Hexokinase

What reaction occurs during step 1 of glycolysis?

Glucose → glucose-6-phospate

What energy molecule is consumed during step 1 of glycolysis?

ATP which is converted to ADP

Which enzyme catalyzes irreversible step 3 of glycolysis?

Phosphofructokinase-1 (PFK-1)

What reaction occurs during step 3 of glycolysis?

Fructose-6-phospate → fructose-1,6-bisphosphate

What energy molecule is consumed during step 3?

ATP which is converted to ADP

Which enzyme catalyzes irreversible step 10 of glycolysis?

Pyruvate Kinase

What reaction occurs during Step 10 of glycolysis?

Phosphoenolpyruvate (PEP) → pyruvate

What energy molecule is produced during the pyruvate kinase reaction

ATP

What enzyme catalyzes the rate limiting step of glycolysis?

Phosphofructokinase 1 (PFK/PFK-1)

What enzyme catalyzes the committed step of glycolysis?

PFK 1

Which step of glycolysis is the rate limited and committed step?

Step 3

What does it mean for PFK to catalyze the “rate limiting step” of glycolysis

This step plays a major role in determining the overall rate of glycolysis

What does “committed step” mean in glycolysis?

Once the molecule passes this step it is committed to proceeding through glycolysis

Why is step 3 of glycolysis important compared with many other glycolytic reactions

It’s irreversible, rate-limiting, and the committed step of glycolysis

Is the first irreversible reaction neccesarrily the committed step of glycolysis?

No, step 1 is irreversible but step 3 catalyzed by PFK is the committed step

Based on the diagram what are the three enzymes highlighted at irreversible glycolytic reactions?

Hexokinase, phosphofructokinase-1, and pyruvate kinase

Why does gluconeogenesis use different enzymes around the irreversibel glycolytic steps?

because steps 1, 3, and 10 of glycolysis are irreversible so gluconeogenesis must use different reactions to move in the oppsoite direction

what glycolytic intermediate is produced immediately after glucose?

Glucose-6-phosphate

What molecule is converted into fructose-1,6-bisphosphate?

Fructose-6-phosphate

What 6 carbon molecule is split into smaller molecules during glycolysis?

Fructose-1,6-bisphosphate

If PFK activity changes why could this affect glycolysis

Because PFK catalyzes the rate-limiting and committed step of the pathway

What is gluconeogenesis

The resynthesis of glucose from non-sugar sources (amino acids, lactate, glycerol)

what is the overall purpose of gluconeogenesis

to produce glcuose from molecules that are not sugars

what are three non sugar sources of glucose used in gluconeogenesis

amino acids, lactate, glycerol

How does the overall direction of gluconeogenesis compare with glycolysis

They generally proceed in opposite directions

What is the primary organ responsible for gluconeogenesis

the liver

approximately what percentage of gluconeogenesis occurs in the liver

75%

aside from the liver what other organs can perform gluconeogenesis

the kidneys and intestines

Does gluconeogenesis require energy

yes it requires a lot of energy

why can gluconeogenesis be thought of as an energy consuming pathway rather than an energy producing pathway

beacuse the pathway requires substantial energy to resynthesize glucose

How is gluconeogenesis pathway related to glycolysis

it is largely the reverse of glcyolysis

is gluconeogenesis the exact reverse of glycolysis

no it needs to bypass glycolysis’ irreversible steps

What must gluconeogenesis do at the irreversible glyvolytic steps

it must bypass them using alternative reactions

What two enzymes are shown helping gluconeogenesis bypass the pyruvate kinase reaction

pyruvate carboxylase and PEP carboxykinase

What enzyme bypasses the phosphofructokinase-1 reaction during gluconeogenesis

Fructose-1,6-bisphosphatase

What enzyme bypasses the hexokinase reaction during gluconeogenesis

glucose-6-phosphatase

If glycerol is being used to resynthesize glucose, what pathway is occuring

gluconeogenesis

What molecule enters the pentose phosphate pathway (PPP)?

Glucose-6-phosphate

What are the two phases of the pentose phosphate pathway

oxidative and nonoxidative phases

which phase of the pentose phosphate pathway is irreversible

the oxidative phase

which phase of the pentose phosphate pathway is reversible

nonoxidative phase

what are two major purposes/products of the pentose phosphate pathway

Production of NADPH and ribose-5-phosphate

What is the starting molecule of the oxidative phase of the pentose phosphate pathway

Glucose-6-phosphate

what intermediate is formed from glucose-6-phosphate during the oxidative phase

6-phosphogluconate

what molecule is produced from 6-phosphogluconate

ribulose-5-phosphate

what important reducing molecule is produce during the oxidative phase

NADPH

What molecule is converted to NADPH during the oxidative phase?

NADP+

How many NADPH-producing reactions are shown in the oxidative phase

TWo

what molecule is released during the conversion of 6-phosphogluconate to ribulose-5-phosphate

CO₂

Is the oxidative phase of the PPP reversible

No it is irreversible

What are the two major uses of NADPH

glutathione reduction and reductive biosynthesis

What enzyme uses NADPH in the glutathione system

glutathione reductase

What does glutathione reductase convert using NADPH

GSSG → 2 GSH

What types of molecules are listed as products of NADPH-dependent reductive biosynthesis

Fatty acids and sterols

If a cell needs reducing power for fatty acid or sterol synthesis what PPP product is important

NADPH

What is ribulose-5-phosphate converted into in the Pentose Phosphate Pathway

Ribose-5-Phosphate

What is ribose-5-phosphate used to produce

nucleotides, coenzymes, DNA, and RNA

What Pentose Phosphate Pathway product is especially important for nucleotide and nucleic acid production

Ribose-5-phosphate

If a cell needs to make DNA or RNA, which product of the PPP would be useful

Ribose-5-phosphate

Is the nonoxidative phase of the Pentose Phosphate Pathway reversible or irreversible

Reversible

What two enzymes are highlighted in the nonoxidative phase?

Transketolase and transaldolase

What important feature of the transketolase/transaldolase reactions are emphasized in the diagram

the reactions are reversible

What metabolic pathways does this slide show as being coregulated

Glycolysis, gluconeogenesis, glycogen synthesis, and glycogen

What does it mean when pathways are coregulated

their activities are coordinated with one another so glucose can be appropriately used, produced, and stored

Why would glycolysis and glycogen metabolism need to be coordinated

because glucose can either be used for energy through glycolysis or stored as glycogen

why would gluconeogenesis and glycogen metabolism need to be coordinated

both are involved in controlling the availability of glucose

What is glycogen

storage form of glucose

what is glycogen synthesis

process of storing glucose as glycogen

what is glycogen degradation

process of breaking down glycogen to make stored glucose available

what important glucose intermediate is located near the glycogen branch shown in the figure

glucose-6-phosphate

why wouldn’t it make metabolic sense to strongly promote glucose breakdown and glucose production at the same time?

they have opposing metabolic purposes which is why their activity needs to be coordinated

structurally, what is glycogen?

a branched polymer of glucose

what does it mean that glycogen is a polymer of glucose

glycogen consists of many glucose molecules that are linked together

What is the overall purpose of glycogen storage

to store glucose for later use

What are the two main sites of glycogen storage

liver and muscle

what is the primary role of glycogen stored in the liver

it helps maintain blood glucose levels

what is the primary role of glycogen stored in muscle

it provides a source of glucose for the muscles