L5

Question 1

Cells communicate with each other in three ways:

Answer 1

• By diffusible chemical signals.
• By direct surface contact between adjacent cells.
• By direct cytoplasmic contact between adjacent cells via gap junctions.

Question 2

Cells use chemical signals in three ways:

Answer 2

• For localised signalling – autocrine and paracrine signalling.
• For generalized signalling to sites remote from the site of secretion – endocrine signalling.
• As neurotransmitters in synaptic signalling – provides discrete signalling between nerves and their target tissues.

Question 3

Hormones are suitable for regulating the activity of a variety of cell types. BUT: (2)

Answer 3

• Their effect cannot be restricted to an individual cell • The speed of signalling is relatively slow

Question 4

Signalling molecules can be divided into at least nine different chemical classes (examples e.g.):

Esters –

Amino acids (AA) -

Amines -

Peptides -

Proteins -

Steroids-

Iodinated amino acids (AA) –

Eicosanoids -

Inorganic gas –

Answer 4

Esters – acetylcholine.

Amino acids (AA) - glutamic acid (glutamate).

Amines - adrenaline (epinephrine).

Peptides - Antidiuretic hormone (ADH)

Proteins - insulin, growth hormone.

Steroids - testosterone, oestradiol.

Iodinated AA – thyroid hormones.

Eicosanoids - prostaglandin E2.

Inorganic gas – nitric oxide.

Question 5

Signalling molecules can be divided into at least nine different chemical classes: (wymień 9)

Answer 5

Esters

Amino acids (AA)

Amines

Peptides

Proteins

Steroids

Iodinated amino acids (AA)

Eicosanoids

Inorganic gas

Question 6

agonists -

Answer 6

Substances that activate a receptor

Question 7

antagonists -

Answer 7

Drugs that block the effects of an agonist

Question 8

All receptors are …

Answer 8

proteins.

Question 9

Those receptors that detect water soluble signals are located …

Answer 9

in the plasma membrane e.g. insulin receptors.

Question 10

Hydrophobic signalling molecules ….

Answer 10

cross the plasma membrane and bind to intracellular receptors e.g. oestrogen receptors.

Question 11

Some intracellular organelles possess receptors for molecules generated within the cell e.g. ….

Answer 11

endoplasmic receptors for inositol trisphosphate (IP3).

Question 12

Przypomnienie G protein messengers

Answer 12

Certain G protein subunits activate intracellular enzymes that synthesise intracellular signalling molecules, which then act on specific intracellular targets. • This intracellular signalling molecule is called a second messenger - the original hormone is the first messenger.

Question 13

Examples of second messengers (3):

Answer 13

• Cyclic AMP (cAMP) – activates protein kinase A which regulates the activity of a large number of enzymes e.g. hepatic phosphorylase • Inositol trisphosphate (IP3) – IP3 triggers the release of calcium from intracellular stores • Diacylglycerol (DAG) – regulates the activity of certain enzymes via protein kinase C.

Question 14

Przypomnienie G proteins obrazki

Answer 14

Question 15

Cells respond to specific signals in four basic way. Wymień je:

Answer 15

How a given cell responds depends both on the chemical nature of the signalling molecule and on the type of receptor.

Question 16

Control of adrenaline secretion by acetylcholine (ACh) - obrazek

Answer 16

Question 17

Signal transduction pathway for the action of adrenalin (epinephrine) - obrazek

Answer 17

Question 18

Steroid hormones pass through the plasma membrane and bind to intracellular receptors to regulate gene transcription. - obrazek

Answer 18

Question 19

transduction -

Answer 19

process in which cells respond to chemical signals by initiating an appropriate physiological response.

Question 20

There are four basic ways in which activation of a receptor can alter the activity of a cell (4):

Answer 20

1. First, it may open an ion channel and so modulate the membrane potential.

•2. Second, it may directly activate a membrane-bound enzyme.

•3. Third, it may activate a G-protein linked receptor that may modulate an ion channel or change the intracellular concentration of a specific chemical called a second messenger - the original signalling molecule is the first messenger. Second messengers may be molecules such as cyclic AMP that are synthesized in response to receptor activation or inorganic ions such as Ca2+ that may enter the cytoplasm via the plasma membrane or from intracellular stores.

•4. Finally the signal may act on an intracellular receptor to modulate the transcription of specific genes.

Question 21

Some cells are joined together by a specific type of junction known as …….1

These junctions are formed by specific membrane proteins that associate to form doughnut shaped structures known as …….2

When the ……2 of two adjacent cells are aligned, the cells become joined by a water filled pore. As the ……2 jut out above the surface of the plasma membrane the cell membranes of the two cells forming the junction are separated by a small gap - hence the name ……1

Unlike ion channels, the pores of ……1 are kept open most of the time so that small molecules of less than 1500 D and inorganic ions can readily pass from one cell to another The cells are thus electrically coupled and depolarisation of one cell causes current to pass between it and its immediate neighbours which also become depolarized. Consequently, current from a single point of excitation spreads across a whole population of cells such as the muscle tissue of the heart.

Answer 21

1. a gap junction
2. connexons