1 - Basics of communication

Question 1

Why are signalling systems needed?

Answer 1

• Coordinate the activities of cells/tissues in a multi-cellular organism
• neurotransmission
• homeostasis

Question 2

Types of signalling between cells

Answer 2

1. free diffusion between cells
2. via cytoplasmic connections
3. direct cell-to-cell contact

Question 3

signalling by free diffusion

Answer 3

autocrine, paracrine, endocrine

Question 4

autocrine signaling

Answer 4

signalling and reception by the same cell

• cells secrete chemicals that modify its own behaviour
• associated with growth regulation

Question 5

paracrine signaling

Answer 5

signalling between nearby cells

• effects are local and short-lived
• coordinates actions of neighbouring cells in embryonic development

Question 6

endocrine signalling

Answer 6

signalling between distant cells (by hormones)

• endocrine glands secrete hormones into extracellular spaces, which then diffuse into the circulatory system

Question 7

synaptic signalling

Answer 7

A highly specific and localized type of paracrine signalling between two nerve cells or between a nerve cell and a muscle cell.

Question 8

signalling via cytoplasmic connections

Answer 8

Transfer of signal from one cell to its neighbour through pores in the membrane

• The fastest mode of cell-cell communication

Question 9

signalling by cell-to-cell contact

Answer 9

Involves specific interactions between surface molecules on one cell and receptors on another cell
• Responsible for cell-cell recognition in animals
• Important in embryonic development and immune response

Question 10

types of signalling molecules

Answer 10

local regulators and hormones

Question 11

what do local regulators do?

Answer 11

act on cells in the vicinity (autocrine + paracrine)

Question 12

what do hormones do? (signalling)

Answer 12

act at a distance (endocrine)

Question 13

what types of local regulators are there?

Answer 13

1. growth factors
2. gases
3. prostaglandins
4. neurotransmitters

Question 14

growth factors

Answer 14

Peptides or proteins that stimulate cell proliferation

May have >1 target cells and hence >1 function

Question 15

gases (nitric oxide)

Answer 15

acts as a paracrine signal molecule - Synthesized from arginine by nitric oxide synthase

-Induces vasodilation in the cardiovascular system

Question 16

who discovered nitric acid as a signalling molecule?

Answer 16

Furchgott, Ignarro and Murad (1998)

Question 17

prostaglandins

Answer 17

modified fatty acids

functions include:

• Excitability of the uterine wall during childbirth (induces labour)
• Induction of fever and inflammation in the immune system

Question 18

Neurotransmitters

Answer 18

• Acetylcholine
• Biogenic amines
• Amino acids
• Neuropeptides
• Some neurotransmitters are inhibitory, some are excitatory, and some can be either
• Some occur in both the central nervous system and the peripheral nervous system

Question 19

hormones

Answer 19

Secreted by endocrine glands and transported in the bloodstream

• Hormone production controlled by neuroendocrine system (hypothalamus is control centre)

Question 20

major glands of the endocrine system

Answer 20

• pineal
• hypothalamus
• pituitary
• thyroid
• parathyroid
• thymus
• adrenal
• pancreas
• ovaries
• testes

Question 21

simple endocrine pathway

Answer 21

endocrine cells respond directly to an internal or environmental stimulus by secreting a particular hormone

Question 22

negative feedback

Answer 22

A primary mechanism of homeostasis, whereby a change in a physiological variable that is being monitored triggers a response that counteracts the initial fluctuation.

Question 23

Homeostasis

Answer 23

maintenance of a relatively stable internal environment in the face of stress from the external and internal environments

Question 24

2 main classes of hormone

Answer 24

1. peptides/proteins

2. steroids

Question 25

peptides/proteins

Answer 25

• Bind to receptors on the cell surface

* Trigger events within cell cytoplasm through second messengers

Question 26

steroids

Answer 26

• Manufactured from cholesterol

* Can pass across lipid bilayer of plasma membrane and bind to receptors within cell

Question 27

signal transduction pathway

Answer 27

The conversion of a signal at the cell surface to a specific cellular response

Question 28

3 main stages of signal transduction

Answer 28

1. reception of signal at cell surface
2. transduction of the signal
3. cellular response -output

Question 29

Reception of the signal at cell surface

Answer 29

Involves binding of a signal molecule to a specific receptor at the cell surface, changing the conformation of the receptor

Question 30

transduction of the signal

Answer 30

Converting the signal into a response is usually multiple steps

Question 31

multistep pathways

Answer 31

• Can amplify a signal: A few molecules can produce a large cellular response
• Provide more opportunities for coordination and regulation

Question 32

The cellular response - output

Answer 32

• The response may occur in the cytoplasm or may involve action in the nucleus
• Some pathways regulate the activity of enzymes
• Other pathways switch on genes by activating transcription factors

Question 33

Signal Specificity

Answer 33

Different cells respond to the same signal in different ways because of differences in signal receptor proteins, relay proteins, and proteins needed to carry out the response
• Pathway branching and ‘cross-talk’ further help the cell coordinate incoming signals