2.5. STEM cells, chemical signaling

Question 1

What is exo/endocytosis? Due to what property of PM is it possible?

Answer 1

• active transport of large particles or entire cells across the membrane by means of vesicles
• due to the fluidity of the membrane – it can change shape, break, and reform during exo/endo

Question 2

Describe endocytosis.

Answer 2

a vesicle containing substances from the outside is engulfed by the cell/plasma membrane - transported into the cytoplasm and then fuse with lysosomes where the enzymes digest the engulfed substances - the undigested components get transported by exocytosis

Question 3

Compare the conditions of freshwater and ocean fish (regarding hypertonic/hypotonic).

Answer 3

Freshwater fish: Hypotonic environment, Water into, Large urine V, Diluted urine, Active transport into, Doesn’t drink water
Ocean fish: Hypertonic environment, Water out, Small urine V, Concentrated urine, Active transport out, Drinks water

Question 4

When does cell specialization start?

Answer 4

when the morula turns into a blastocyst - morphogens released and they impact the gene expression of cells

Question 5

What are morphogens?

Answer 5

chemical signals released by some cells during the blastocyst stage - they diffuse and cells specialize according to what concentration of morphogens they are exposed to – morphogen gradient (indicates to a cell its position in the embryo)

Question 6

What are STEM cells?

Answer 6

cells with the ability to divide endlessly and differentiate along different pathways

Question 7

What are the types of STEM cells? Outline each type (where can they be found, examples).

Answer 7

Totipotent – can become any cell type in the body (+ placenta), all genes switched on, zygote and morula
Pluripotent – can become any type of cell in the body, blastocyst (inner cell mass)
Multipotent (tissue-specific) – liver, skin, and bone marrow – important for the regeneration of adult tissues, hematopoietic SC in bone marrow

Question 8

What is a SC niche? Give examples. Which tissues do not have any SC?

Answer 8

the precise location of SC in the organism - where SC can either remain inactive for a long period or proliferate and rapidly differentiate (determined by the microenvironment of the niche) - bone marrow and hair follicles

Question 9

What does the cell volume determine and what is the surface area?

Answer 9

• the rate of metabolism and therefore the amount of substances transported in and out of the cell
• determines the effectiveness of the exchange of materials

Question 10

Why does cell division happen? SA/V ratio is…

Answer 10

when the SA can no longer meet the requirements of the V, the decreasing SA/V ratio will stimulate cell division, and by division, the cell size will be reduced and kept within limits
…the factor that limits the size of the cell

Question 11

What does a smaller cell size mean for the cell?

Answer 11

molecules have a shorter distance to diffuse within the cell = smaller cell requires fewer nutrients and waste to be transported out = has relatively more membrane for transporting materials in and out

Question 12

How can cells exchange information?

Answer 12

via chemical or electrical signalling (neuron - both)

Question 13

What is a ligand?

Answer 13

a molecule that binds selectively to a specific site on another molecule. They are released by a source and affect target cells

Question 14

Describe ligand action.

Answer 14

approaches the binding site of the target cell – causes changes in the receptor’s conformation – this change is recognized by other processes in the cell, the signal is passed on and the cell changes its behavior (metabolic activity) like, for example, expressing some genes, increasing/decreasing amount of certain proteins – ligand dissociates from the binding site

Question 15

What are receptors? What are two types of ligand receptors?

Answer 15

proteins to which signaling chemicals bind at a specific site - they initiate changes in the target cell in response to the binding of the chemical signal
- transmembrane and intracellular

Question 16

What is the signal transduction pathway? Outline STP for transmembrane and for intracellular receptors.

Answer 16

• the sequence of interactions in cells triggered by ligand binding
  TR STP:
  1| Reception – binding causes a reversible conformational change of the receptor.
  2| Signal transduction - reactions producing second messengers – the newly catalytically active receptor causes the production of a secondary messenger within the cell.
  3| Response - activation of cellular responses – signal is carried over to effectors that carry out the response by the secondary messenger.
  IR STP:
  1| Steroid hormone enters the cell (hydrophobic)
  2| Hormone-receptor complex formed.
  3| Complex travels to the nucleus where it binds to the promotor region on the DNA and directly controls the gene expression process.

Question 17

What are the requirements for a signaling chemical?

Answer 17

1) Distinctive in shape and chemical properties so the receptor can distinguish between it and other chemicals
2) Small and soluble enough to be transported

Question 18

Outline the chemical nature of hormones, neurotransmitters, cytokines, and Ca ions.

Answer 18

Hormones - Amines, peptides, steroids, Neurotransmitters - Amines, gases, amino acids, esters, Cytokines - a group of small proteins

Question 19

Outline the source of hormones, neurotransmitters, cytokines, and Ca ions.

Answer 19

Hormones - Groups of specialized cells in glands, Neurotransmitters - Presynaptic neuron, Cytokines - Wide range of cells, Ca ions - Pumped out by calcium pumps

Question 20

Outline where they go from the source for hormones, neurotransmitters, cytokines, and Ca ions.

Answer 20

Hormones - Into blood capillaries to all parts of the body, Neurotransmitters - Across the synapse, Cytokines - Intercellular space, Ca ions - Diffuse through voltage/ligand-gated channels