Cell signalling

Question 1

Why do we need cell signalling?

Answer 1

1. to process info
2. for self-preservation
3. for voluntary movement
4. for homeostasis

Question 2

What are the 2 main systems in the body that provide lines of communication?

Answer 2

• Nerve fibres of the central and peripheral nervous system.

- The blood vessels of the cardiovascular system.

Question 3

he nervous system provides a rapid almost instantaneous response

Answer 3

whilst the blood vessels provide a slower more versatile regulation.

Question 4

Neurotransmission steps

bioelectrical signal- chemical signal- bioelectrical signal

Answer 4

1. propagation of the action potential
   2, neurotransmitter release from vesicles
2. Activation of postsynaptic receptors
3. Activation of postsynaptic receptors

Question 5

How is an AP propagated?

Answer 5

• by VGSC’s opening
• Na + influx –> membrane depolarisation –> AP ‘moves along’ neurone
• VGKC opening –> K+ efflux –> repolarisation

Question 6

What is then released from vesicles?

Answer 6

neurotransmitter

• AP opens voltage-gated Ca2+ channels at presynaptic terminal
• Ca2+ influx –> vesicle exocytosis

Question 7

What happens when the postsynaptic receptors are activated?

Answer 7

• NT binds to receptors on the post synaptic membrane

- receptors modulate post-synaptic activity

Question 8

What chemicals utilise the circulatory system for transportation?

Answer 8

hormones

Question 9

Where are hormones produced?

Answer 9

by most of the major organs of the body however there are a few organs that play a more prominent role than others, such as the hypothalamus and the pituitary gland

Question 10

What are 4 main modes of communication?

Answer 10

1. Endocrine communication
2. Paracrine communication
3. Communication between membrane receptors
4. Autocrine communication

Question 11

What is endocrine signalling?

Answer 11

hormone travels within blood vessels to act on a distinct target cell

Question 12

What are some examples of endocrine signalling?

Answer 12

glucagon
insulin (produced in liver acts on liver, muscles + adipose tissue)
adrenalin (produced in adrenal glands acting on the trachea)

Question 13

What is paracrine signalling?

Answer 13

when the hormone acts on an adjacent cell

Question 14

examples of paracrine signalling?

Answer 14

• insulin
• nitric oxide (produced by endothelial cells in blood vessels)
• osteoclast activating factors produced by adjacent osteoblasts

Question 15

What is signalling between membrane-attached proteins?

Answer 15

plasma membrane proteins on adjacent cells interacting

Question 16

examples of signalling between membrane-attached proteins?

Answer 16

• HIV GP120 glycoprotein –> CD4 receptors on T-lymphocytes

- bacterial cell wall components –> toll-like receptors on haematopoietic cells

Question 17

What is autocrine signalling?

Answer 17

signalling molecule acts on the same cell

Question 18

examples of autocrine signalling?

Answer 18

acetylcholine –> presynaptic M2 - muscarinic receptors

- growth factors from tumour cells —> mitogenesis

Question 19

What are ligands?

Answer 19

chemical messages or molecules ->they exert their effects through binding to receptors

Question 20

What are receptors usually?

Answer 20

proteins that bind the chemical mediators known as ligands and upon activation they elicit an effect within a cell

Question 21

What are second messengers?

Answer 21

The intracellular effect evoked by an occupied receptor usually arises due to any chemical messenger that is a separate entity from the receptor or the ligand

Question 22

What are the 4 categories of receptors?

Answer 22

1. Ligand-gated ion channel receptors
2. G protein coupled receptors
3. Enzyme-linked receptors
4. Intracellular receptors

Question 23

What are Ligand-gated ion channel receptors (ionotropic receptors)?

Answer 23

transmembrane receptors which have a central pore incorporated within their quaternary structure

Question 24

What happens when the appropriate ligand attaches to the ‘ligand-binding domain’ on the external surface of the protein?

Answer 24

the pore will open

Question 25

What is the process of ligand-gated ion channel activation?

Answer 25

1. The ligand binds to the receptor protein 2. A change in conformation of the channel protein results in the opening of a pore, which spans the cell membrane. 3. The pore allows ions to move in or out of the cell according to their respective concentration gradients

Question 26

What are G protein-coupled receptors?

Answer 26

7-transmembrane receptors because the channel protein crosses the cell membrane 7 times

Question 27

What are G protein-coupled receptors linked to?

Answer 27

an intracellular G protein complex, which consists of an alpha (α) subunit, a beta-gamma (βγ) subunit and an associated GDP molecule

Question 28

What are the 3 Ga subunits?

Answer 28

Ga q/11 Ga s Ga i/o

Question 29

G protein activation process?

Answer 29

1. In the resting state the G protein complex consists of a Gα subunit, a Gβγ subunit and an associated GDP molecule, which are in close proximity to the receptor 2. Ligand binding causes the G protein complex to associate with the receptor resulting in the GDP molecule being phosphorylated to a GTP molecule 3. The Gα subunit dissociates from the Gβγ subunit 4. Both Gα and Gβγ can act as second messengers 5. When the ligand dissociates from the receptor, internal GTPase on the Gα subunit hydrolyses GTP to GDP 6. The Gα and Gβγ subunits re-associate and are once again available to the receptor

Question 30

What is phosphorylation?

Answer 30

The addition of a PO4 group. This simple chemical reaction activates a number of protein enzymes and is carried out by kinases

Question 31

What is Phosphatase?

Answer 31

An enzyme that remove a phosphate group from its substrate.

Question 32

What is Dephosphorylation?

Answer 32

The removal of a PO4 group. This hydrolysis reaction inactivates a number of protein enzymes and is carried out by phosphatases

Question 33

What are enzyme-linked receptors?

Answer 33

transmembrane receptors ordinarily only consist of one transmembrane domain, which has the ligand-binding domain on the outside and specialised enzymes on the inside

Question 34

Do enzyme-linked receptors work alone?

Answer 34

no, they require clustering of more than one receptor protein to activate the intracellular enzyme. Once activated the intracellular enzymes trigger a signalling cascade within the cell.

Question 35

Enzyme-linked receptor activation process?

Answer 35

1. Ligand binding results in receptors clustering. 2. Receptor clustering activates enzyme activity within the cytoplasmic domain. 3. The enzymes phosphorylate the receptor. 4. This phosphorylation leads to the binding of signalling proteins to the cytoplasmic domain. 5. These signalling proteins recruit other signalling proteins and a signal is generated within the cell. 6. The signal is terminated when a phosphatase dephosphorylates the receptor

Question 36

What are steroid hormones?

Answer 36

membrane permeable + exert their actions on intracellular receptors

Question 37

What are intracellular receptors?

Answer 37

transcription factors + regulate mRNA and protein synthesis

Question 38

What are the 2 classes of steroid hormones?

Answer 38

Type I receptors | Type II receptors

Question 39

Type I steroid receptors

Answer 39

located within the cytosolic compartment and are associated with chaperone molecules (normally heat shock proteins, hsp). Once the hormone binds to the receptor, the hsp molecule dissociates allowing the hormone-receptor complex to form a homodimer with another identical hormone-receptor complex. The homodimer subsequently translocates to the nucleus where it binds to DNA and acts as a transcription factor

Question 40

Type II steroid receptors

Answer 40

located within the nucleus of a cell and are often already bound to DNA. Binding of the hormone ligand to the receptor usually results in direct transcriptional regulation by the activated hormone-receptor complex