Biochemistry Chapter: Glycogen Metabolism

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Questions and Answers

What is the main function of liver glycogen?

To provide glucose exclusively for muscle energy

To store glucose exclusively for liver use

To supply glucose for extrahepatic tissues and maintain blood glucose levels (correct)

To synthesize glucose from fat reserves

Which glycosidic bond is present at the branching points of glycogen?

Both α 1-4 and α 1-6 glycosidic bonds (correct)

β 1-4 glycosidic bonds

α 1-6 glycosidic bonds only

α 1-4 glycosidic bonds only

What happens to liver glycogen after 12-18 hours of fasting?

It is mostly depleted (correct)

It doubles in concentration

It converts back to glucose rapidly

It becomes more branched

Which transport protein is responsible for glucose absorption from the lumen into the bloodstream?

SGLT1 Signup and view all the answers

What process involves the synthesis of glycogen from glucose?

Glycogenesis Signup and view all the answers

What is hypoglycaemia characterized by?

Blood sugar level below 60 mg% Signup and view all the answers

Which process refers to the breakdown of glycogen into glucose?

Glycogenolysis Signup and view all the answers

What does hyperglycaemia indicate?

Increase in blood sugar levels above 180 mg% Signup and view all the answers

Which term describes the formation of glucose from non-carbohydrate sources?

Gluconeogenesis Signup and view all the answers

What is the primary outcome of glycolysis?

Production of pyruvic acid or lactic acid Signup and view all the answers

What role do cytokines play in the immune system?

They regulate the growth and differentiation of cells. Signup and view all the answers

Which component is referred to as complex V in the respiratory chain?

ATP synthase Signup and view all the answers

What is the primary function of the electron transport chain?

To transport electrons to molecular oxygen. Signup and view all the answers

Which molecules are electron carriers in the respiratory chain?

Ubiquinone and cytochrome C Signup and view all the answers

What is the result of the redox reactions in the electron transport chain?

Release of free energy Signup and view all the answers

Which complex in the respiratory chain is responsible for oxidizing NADH?

Complex I Signup and view all the answers

What is the main purpose of establishing a proton gradient across the inner mitochondrial membrane?

To synthesize ATP with ATP synthase. Signup and view all the answers

Which of the following statements about components of the respiratory chain is true?

Complex III contains iron-sulfur clusters. Signup and view all the answers

What is the role of lactate dehydrogenase in anaerobic glycolysis?

Catalyzes the reduction of pyruvate to lactate Signup and view all the answers

Which reaction is considered irreversible in glycolysis?

Conversion of phosphoenolpyruvate to pyruvate Signup and view all the answers

What is the effect of ATP on phosphofructokinase-1 (PFK1)?

Inhibits PFK1 Signup and view all the answers

How does the malate shuttle function in cellular respiration?

Transfers electrons from NADH to the electron transport chain Signup and view all the answers

What substance is produced during anaerobic glycolysis when NADH is oxidized?

Lactate Signup and view all the answers

What condition indicates a shift from aerobic to anaerobic metabolism in muscles?

Excess lactate production Signup and view all the answers

Which enzyme is specifically inhibited by fluoride in glycolysis?

Enolase Signup and view all the answers

Why does glycolysis in red blood cells (RBCs) always end with lactate?

They lack mitochondria Signup and view all the answers

What is the effect of insulin on glycogen synthase?

It activates glycogen synthase by changing its form. Signup and view all the answers

Which molecule is formed from ATP by adenyl cyclase in response to glucagon and epinephrine?

Cyclic-AMP Signup and view all the answers

What is the primary role of glycogen phosphorylase in glycogenolysis?

To hydrolyze the 1-4 glycosidic bond. Signup and view all the answers

What happens to cyclic-AMP in the presence of insulin?

It is converted to ordinary AMP. Signup and view all the answers

Which enzyme is responsible for converting glucose-1-P to glucose-6-P?

Phosphoglucomutase Signup and view all the answers

In which tissue is glucose-6-phosphatase present to release free glucose into the blood?

Liver Signup and view all the answers

How does glucagon affect glycogenesis in the liver?

It inhibits glycogenesis through cyclic-AMP. Signup and view all the answers

What is a major consequence of the absence of glucose-6-phosphatase in muscle tissue?

Lack of energy production from glucose-6-phosphate. Signup and view all the answers

What is the primary role of NADPH in red blood cells?

To reduce oxidized glutathione Signup and view all the answers

Which of the following symptoms is associated with a genetic deficiency of glucose-6-phosphate dehydrogenase (G6PD)?

Hemolytic anemia Signup and view all the answers

What happens to erythrocytes when oxidative stressors, such as fava beans and certain medications, are introduced in individuals with G6PD deficiency?

They cause cell membrane damage Signup and view all the answers

What is a precursor of proteoglycans in the uronic acid pathway?

Glucose Signup and view all the answers

What enzyme is responsible for the synthesis of lactose in the mammary gland?

Lactose synthase Signup and view all the answers

Which type of sugar is primarily involved in the production of glycoproteins and glycosaminoglycans?

Amino sugars Signup and view all the answers

The enzymatic deficiency of gulonolactone oxidase is linked to which dietary requirement in humans?

Ascorbic acid (Vitamin C) Signup and view all the answers

Sialic acid found in human tissues is specifically identified as which compound?

N-acetylneuraminic acid (NeuAc) Signup and view all the answers

Study Notes

Mechanisms of Action of Hydrophilic Hormones

Hydrophilic hormones signal to the interior of the cell via membrane receptors on the plasma membrane.
These receptors bind the hormone outside the cell, triggering a secondary signal inside the cell.
This secondary signal affects enzyme or ion channel activity.

Receptor Types

1-Helix Receptors:
- Proteins span the membrane with a single α-helix.
- Have cytoplasmic domains with allosterically activated enzyme activity (typically tyrosine kinases).
7-Helix Receptors (Serpentine Receptors):
- A large group of integral membrane proteins.
- Transmit signals via G proteins to effector proteins.
- G proteins are heterotrimeric, consisting of α, β, and γ subunits.
- Different G protein types have varying effects (e.g., activating or inhibiting adenylate cyclase).

Signal Transduction by G Proteins

G proteins act as molecular switches, binding GDP or GTP.
Binding of a signaling substance to the receptor causes a conformational change, enabling G protein binding and subsequent GDP to GTP exchange in the α subunit.
The α subunit dissociates from the βγ dimer, influencing effector proteins.
This initiates a downstream cascade of events.

Second Messengers

Second messengers are intracellular chemical messengers, typically with short half-lives.
Important examples include cAMP, cGMP, Ca2+, InsP3, DAG, and NO.
These messengers amplify signals and regulate various cellular processes.

Cyclic AMP (cAMP)

A cyclic nucleotide synthesized by adenylate cyclases.
cAMP acts as an allosteric activator of protein kinase A (PKA).
Adenylate cyclase activity can regulate through G proteins.
Phosphodiesterases degrade cAMP.

Cyclic GMP (cGMP)

Related to cAMP, involved in signal transduction.
cGMP is a second messenger in some pathways.

Inositol 1,4,5-trisphosphate (InsP3) and Diacylglycerol (DAG)

Produced from membrane phospholipids by phospholipase C.
InsP3 releases Ca2+ from intracellular stores.
DAG activates protein kinase C (PKC) within the membrane.

Calcium Ions

Ca2+ regulates enzyme activity and ion channel function via Ca2+-binding proteins (e.g., calmodulin).
These proteins participate in a wide range of cellular processes.

Signal Cascades

Hydrophilic hormone signaling often involves a cascade of protein activation, amplifying the initial signal.
Enzyme activation in one step may trigger further enzymatic reactions or influence other cell signaling pathways.

Eicosanoids

Signaling molecules derived from arachidonic acid.

Cytokines

Peptide hormones.
Released by cells of the immune system and other cell types.
Regulate immune system development and homeostasis.
Influence inflammatory processes, blood coagulation, and cell growth/differentiation.

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Test your knowledge on glycogen metabolism with this quiz. Covering liver glycogen functions, glycosidic bonds, and processes like glycolysis, it's essential for understanding carbohydrate metabolism. Perfect for students studying biochemistry!