Introduction molecular exercise physiology - L2

Question 1

What happens to muscle mass as a result of high levels of inflammation?

Answer 1

It promotes breakdown of muscle mass

Question 2

What is the difference between catabolism and anabolism?

Answer 2

Catabolism is the breakdown aspect of metabolism, whereas anabolism is the building-up aspect.

Question 3

Which pathway is important for protein synthesis?

Answer 3

mTOR pathway

Question 4

Describe the ATP-phosphocreatine system.

Answer 4

• The system produces energy for muscle contraction via the release/production of ATP.
• When ATP loses a phosphate (out of 3) energy is released and ATP is converted to ADP.
• Vice versa, when ADP gains a phosphate, it is converted back into ATP to store energy.
• Phosphocreatine is also stored in muscles and is able to add its phosphate to ADP.
• Creatine kinase is responsible for releasing the phosphate molecule from phosphocreatine so that the phosphate can be added to ADP and stored as ATP.

Question 5

How can ATP concentration stay constant while AMP and ADP increase during aerobic exercise?

Answer 5

• As explained in card 4, ATP is converted to ADP when there is an energy demand for muscle contraction.
• Sometimes, ADP is further broken down into AMP as it donates its second phosphate molecule to give (extra) energy for cellular activitities.
• During aerobic exercise, ATP is converted into ADP and/or AMP. When ATP levels decrease and AMP levels increase, AMP binds to AMPK (AMP-activated kinase), which leads to the activation of AMPK (through phosphorylation) in order to activate processes such as activation of catabolic pathways and inhibition of anabolic pathways to regenerate ATP.

Question 6

Besides AMP, another kinase can also activate AMPK for regeneration of ATP. What kinase is this?

Answer 6

Ca2+/calmodulin - dependent protein kinase kinase-beta (CaMKKβ). This kinase activates AMPK by phosphorylation of their activation-loop Thr residues in response to increasing intracellular Ca2+ concentration

Question 7

What processes are associated with AMPK activation?

Answer 7

• Mitochondrial biogenesis
• Angiogenesis

Question 8

Calcium and AMPK activation stimulate the expression of Peroxisome proliferator-activated receptor-γ (PPAR-γ). Describe this pathway and what the result is of the activation of this pathway.

Answer 8

PPAR-γ is a nuclear receptor that is activated when PGC-1a (PPAR-y coactivator-1alpha) interacts with PPAR-γ. This complex activates the transcription of various genes, most importantly:

• the complex activates the transcription factor Nrf1 resulting in the translation of genes related to mitochondrial biogenesis and oxidative metabolism.
• the complex interacts with Mef2 and Nfat, two transcription factors involved in the gene expression of type I myofibers.

Question 9

Mef2 and Nfat can also be activated independently of PPAR-γ-PGC-1a complex activation. How?

Answer 9

With the use of Ca2+ calcineurin or CaM kinases

Question 10

How does endurance training stimulate the biosynthesis of mitochondria?

Answer 10

During (endurance) exercise, your muscles contract repeatedly. Muscles contract as a result of the activation of the sarcoplasmic reticulum (SR) by ATP. Activation of the SR results in the release of Ca2+, which serves as an intracellular messenger molecule for the activation of calcineurin, CaMKII and p-AMPK. These molecules activate other molecules like PGC-1a, COX and citrate synthase (also Mef2 and Nfat), resulting in the biosynthesis of mitochondria.

Question 11

What relationship exists between the number of nuclei per mm muscle fiber length and the total fiber cross-sectional area (FCSA)?

Answer 11

The amount of nuclei/mm fiber length is associated with the amount of FCSA. So a high number of nuclei/mm fiber length = a high total of FCSA.

Question 12

What are satellite cells?

Answer 12

Multipotent cells found in mature muscles. They are precursors of skeletal muscle cells. Normally, they are in their native, quiescent state (i.e. not dividing/differentiating). But when muscle tissue is damaged due to injury or exercise, satellite cells become activated, which leads to proliferation and differentiation into myoblasts (muscle precursor cells capable of fusing to form new muscle fibers or repairing damaged ones).

Question 13

The following molecules are involved in mechanosensation. Explain in short their primary function in mechanosensation.

• Dystrophin-associated glycoprotein complex
• Costameres
• Focal Adhesion Kinase (FAK)
• Calcium
• Phospholipid cleaving enzyme phospholipase D (PLD)

Answer 13

• Dystrophin-associated glycoprotein complex (DAGC): complex found in muscle cells that connects cytoskeleton to extracellular matrix -> role in maintaining structural integrity of muscle fibers.
• Costameres: located at Z-lines of muscle cells, play a role in transmitting mechanical forces between cytoskeleton and ECM.
• Focal Adhesion Kinase (FAK): activated in response to mechanical forces and plays a role in signal transduction of pathways for cell adhesion and mechanotransduction.
• Calcium: mechanical forces can lead to intracellular calcium level changes, which can trigger various cellular responses, such as muscle contraction.
• Phospholipid cleaving enzyme phospholipase D (PLD): enzyme that cleaves phospholipids to generate lipid second messengers.

Question 14

Explain why there is time-dependent activation of mTOR (in the context of exercise).

Answer 14

• Pre-exercise: basal level of mTOR activity
• During-exercise: muscle cells experience mechanical stress/load and damage, which triggers growth factors such as insulin-like growth factor 1 (IGF-1) and the activation of mTOR.
• Post-exercise: mTOR activation may increase in the hours following exercise, because mTOR is essential for muscle repair, growth and adaptation.

Question 15

What are reactive oxygen and nitrogen species (RONS)?

Answer 15

RONS are molecules containing oxygen or nitrogren atoms that are produced during various processes (metabolism, UV light, radiation, smoking, air pollution, inflammation) capable of causing DNA or protein damage.

Question 16

What are caspases?

Answer 16

Cytoplasmic proteases involved in protein breakdown and apoptosis (programmed cell death induced by intracellular or extracellular signals)

Question 17

Name two ways apoptosis is induced.

Answer 17

• Mitochondrial dysfunction
• Directly by signal proteines binding to a receptor

Question 18

Describe the process of lysosomal proteolysis.

Answer 18

Dysfunctional proteins (or pathogens) are endocytosed into lysosomes. Lysosomes contain enzymes that break down other proteins (e.g. cathepsins, nucleases, proteases).

Question 19

Describe the ubiquitin-proteasome pathway.

Answer 19

• Ubiquitin can attach itself to other (damaged) proteins and acts like a tag. When breakdown of this protein occurs, the protein will be tagged by many other ubiquitin molecules as well (ubiquitination).
• A proteasome regonizes the ubiquitinated protein and breaks down the protein.

Question 20

To initiate the ubiquitin-proteasome pathway, certain enzymes are needed. Describe this.

Answer 20

• Ubiquitin (Ub) is first transferred to E1 in an ATP-dependent way, which activates Ub.
• Active Ub is transferred to E2.
• Active Ub is transferred by an E3 ubiquitin ligase to the target protein, leading to the formation of a polyubiquitin chain.

Question 21

Which E3 ligases of the ubiquitin-proteasome pathway are most important?

Answer 21

MaFbx and Murf1

Question 22

Explain in short how a knock-out mouce is generated.

Answer 22

• Isolation of embryonic stem cells (ECSs)
• Gene of interest inactivated
• Isolation of knocked out ESCs
• Insertion of knocked out ESCs into blastocyst
• Implantation of blastocyst into surrogate mother
• Chimeric mice
• Chimeric mice crossbred with wild-type mice
• Interbreeding of heterozygous mice
• Selection of knock-out mouse

Question 23

What are cultured cells?

Answer 23

The removal of cells from an animal or plant and their subsequent growth in a favorable artificial environment.

Question 24

What is immunohistochemistry?

Answer 24

Selectively identifying antigens in cells of a tissue by seeing what kind of antibodies bind to these antigens.

Question 25

What is western blotting?

Answer 25

A technique where certain tissue broken down into its proteins. The proteins are then segregated based on mass and charge with **gel electrophoresis SDS page**. The proteins are then transfered from the gel to a membrane, where the proteins are detected with the use of antibodies.

Question 26

What is ELISA?

Answer 26

In an ELISA, the antigen of interest is immobilized on a solid surface (microplate) and then complexed with an antibody that is linked to a reported enzyme. Detection is accomplished by measuring the activity of the reporter enzyme via incubation with the appropriate substrate to produce a measurable product.

Question 27

What is the difference between single-omics and trans-omics?

Answer 27

The key difference is that single-omics focuses on one type of molecular data at a time, while trans-omics integrates data from multiple omics disciplines to provide a more comprehensive and interconnected view of biological systems.

Question 28

What is fluorescence-activated cell sorting (FACS)?

Answer 28

Specialized type of flow cytometry. It provides a method for sorting a heterogeneous mixture of biological cells into two or more containers, one cell at a time, based upon the specific light scattering and fluorescent characteristics of each cell.