4: Biochemistry - Glycogen metabolism

Question 1

What is glycogenesis?

Answer 1

Synthesis of glycogen from glucose

Question 2

What is glycogenolysis?

Answer 2

Breakdown of glycogen to form glucose

Question 3

What is glycogen?

Answer 3

A storage unit of glucose

Question 4

Where is glycogen found?

Answer 4

Liver cells

Muscle cells

Question 5

The glycogen stored in the liver is stored and then released to maintain an appropriate [X]_blood.

Name X.

Answer 5

Glucose

Question 6

Muscle glycogen can:

a) only be consumed within a muscle cell
b) be consumed by the blood to maintain [glucose]

Answer 6

a - not available for maintenance of blood glucose

Question 7

By which process do muscle cells use glycogen?

Answer 7

Glycolysis

Question 8

When would muscle cells use glycogen?

Answer 8

During physical activity

Question 9

Glycolysis allows muscle cells to generate ___.

Answer 9

ATP

Question 10

Dietary carbohydrate contributes to blood sugar levels immediately following ___.

Answer 10

meals

Question 11

Which process maintains blood sugar levels between meals?

Answer 11

Glycogenolysis

Question 12

Which process maintains blood sugar levels when dietary carbohydrate isn’t available and liver glycogen stores have been depleted?

Answer 12

Gluconeogenesis

Question 13

Glycogen is a polymer of which monosaccharide?

Answer 13

Glucose

Question 14

Which bonds form long, straight chains of glucose molecules?

Answer 14

α 1-4 glycosidic bonds

Question 15

Which carbons are bonded to form long, straight glycosidic bonds between glucose in a molecule of glycogen?

Answer 15

1 and 4

Question 16

Which bonds form branches in a glycogen molecule?

Answer 16

α​ 1-6 glycosidic bonds

Question 17

The more ___ a glycogen molecule has, the greater the rate at which glucose can be added or cleaved off it.

Answer 17

branches

Question 18

Which protein, found on glucose chains, acts as a catalyst for glycogen synthesis by forming precursor glycogen molecules?

Answer 18

Glycogenin

Question 19

Which protein is added to a glucose primer before glycogen synthesis?

Answer 19

Glycogenin

Question 20

Before glucose can be used by a cell, it must be (phosphorylated / dephosphorylated) by an enzyme.

What is this enzyme called?

What is the end product of this reaction?

Answer 20

phosphorylated

Hexokinase

Glucose-6-phosphate

Question 21

Which product is formed by the phosphorylation of glucose by hexokinase?

Answer 21

Glucose-6-phosphate

Question 22

If immediate energy is required, glucose-6-phosphate can be used in which process?

Answer 22

Glycolysis

Question 23

Name two possible fates of glucose-6-phosphate.

Answer 23

Used in glycolysis for immediate energy

or

Stored as glycogen

Question 24

refer to glycogen synthesis diagram

Question 25

For each glucose which is added to glycogen, **1 ATP is consumed**. Why?

Answer 25

**ATP** is used to regenerate **UDP ⇒ UTP**.

Question 26

Which molecule **activates** glucose-1-phosphate before it is added to glycogen? What is the name of the activated glucose molecule? (Which enzyme carries out this process?)

Answer 26

**UTP** **UDP-glucose** (UDP-glucose pyrophosphorylase)

Question 27

Which enzyme adds UDP-glucose to glycogen? What is a byproduct of this reaction?

Answer 27

**Glycogen synthase** UDP

Question 28

Before precursor molecules can be used in biochemical processes, they need to be \_\_\_.

Answer 28

**activated**

Question 29

Why can UTP be used to transfer glucose to a glycogen molecule?

Answer 29

The bond contains a lot of **free energy** (same concept with ATP)

Question 30

How many glucose molecules are added by each reaction catalysed by **glycogen synthase**?

Answer 30

**1**

Question 31

Can **glycogen synthase** introduce **branches** to a glucose chain?

Answer 31

**No**

Question 32

What is the **rate limiting enzyme** of **glycogenesis**? Why?

Answer 32

**Glycogen synthase** It can only add on **one glucose molecule** at a time

Question 33

Which enzyme introduces **branches** to a glycogen molecule?

Answer 33

**Transglycosylase**

Question 34

Which type of bond introduces **branches** to a glycogen molecule? Which enzyme is responsible?

Answer 34

**α 1-6 glycosidic bonds** **Transglycosylase**

Question 35

Which process involves the removal of glucose molecules from **glycogen**?

Answer 35

**Glycogenolysis**

Question 36

Which enzyme removes a glucose molecule from glycogen by adding a **phosphate molecule** to it?

Answer 36

**Glycogen phosphorylase**

Question 37

Write a word equation for **glycogenolysis**.

Answer 37

**[glucose]_n + Pi ⇒ [glucose]_n-1 + glucose-1-phosphate**

Question 38

What is the **rate limiting enzyme** of **glycogenolysis**? Why?

Answer 38

**Glycogen phosphorylase** It can only remove one glucose molecule at a time

Question 39

How is **glucose-1-phosphate** prepared for glycolysis following **glycogenolysis**?

Answer 39

It's converted back into **glucose-6-phosphate**

Question 40

Which enzyme is responsible for **both:** **glucose-6-phosphate ⇒ glucose-1-phosphate** in glycogenesis and **glucose-1-phosphate ⇒ glucose-6-phosphate** following glycogenolysis?

Answer 40

**Phosphoglucomutase**

Question 41

The **liver** can **dephosphorylate** glucose-6-phosphate and release it into the bloodstream as glucose. Is this **glycolysis**?

Answer 41

No, different shortened process

Question 42

Can **skeletal muscle** dephosphorylate glucose-6-phosphate as the liver does?

Answer 42

**No** - must go through **glycolysis** and Kreb's instead

Question 43

In the liver, which enzyme **dephosphorylates** glucose-6-phosphate into **glucose** for the bloodstream?

Answer 43

**Glucose-6-phosphatase**

Question 44

Which transporter, found in liver cells, transports **glucose** into the blood?

Answer 44

**GLUT2**

Question 45

If glycogenesis and ___ occured at the same rate, the whole process would be pointless.

Answer 45

**glycogenolysis**

Question 46

Which **hormone** regulates the activity of: **glycogen synthase** (glycogenesis) and **glycogen phosphorylase** (glycogenolysis)?

Answer 46

**Insulin**

Question 47

The presence of **insulin** **(stimulates / inhibits)** glycogenesis and **(stimulates / inhibits)** glycogenolysis.

Answer 47

**stimulates** **inhibits**

Question 48

Which **process** and **enzyme** are stimulated by **high insulin levels**?

Answer 48

**Glycogenesis**, catalysed by **glycogen synthase**

Question 49

Which **process** and **enzyme** are stimulated by **low insulin levels**?

Answer 49

**Glycogenolysis**, catalysed by **glycogen phosphorylase**

Question 50

Which hormone, other than insulin, also affects the rates of glycogenesis and glycogenolysis?

Answer 50

**Glucagon**

Question 51

match levels of insulin and glucagon to inhibition / stimulation of the two processes because they work as a pair

Question 52

Which **hormones**, released in **emergencies**, stimulate **glycogen phosphorylase** and therefore **glycogenolysis**?

Answer 52

**Adrenaline** **Cortisol**

Question 53

Glycogen storage disease are associated with **(hormone / enzyme)** defects.

Answer 53

**enzyme**