Cellular Signals

Question 1

Autocrine

Answer 1

target cell is the same cell as the one that releases the signalling molecule

Question 2

Paracrine

Answer 2

target cell is a nearby cell to the one that releases the signalling molecule

Question 3

Endocrine

Answer 3

target cell is a distant cell compared to the one that releases the signalling molecule, and must travel in the bloodstream

Question 4

Exocrine

Answer 4

target cell is outside the organism

Question 5

Animal Hormones

Answer 5

Source: endocrine glands in the body, e.g. cells, organs and glands

Three types of animal hormones:

1. Peptide and protein (hydrophilic – only have receptors on the cell membrane)
2. Amino acid derived (hydrophilic – receptors on the cell membrane)
3. Steroid/lipid derived – lipophilic (hydrophobic – receptors found inside the cell)

Question 6

Plant Hormones

Answer 6

Source: plant cells that are undergoing growth, ripening, abscission etc.

1. Act as signalling molecules that target various cells (those undergoing growth, ripening, abscission etc.) and produce specific effects
2. Produced by individual cells in growing regions of the plant (e.g. roots, leaves)
3. Usually transported in the phloem

Question 7

Cytokines

Answer 7

Small protein molecules that act as messengers between cells of the immune system.

Acts on the cells in the immune system with specific receptors.

Source: Immune system
Mode of transmission: autocrine, paracrine, endocrine

Question 8

Pheromones

Answer 8

Chemical signalling molecule released by one animal that carries a signal to the cells of a second member of the same species.

Secreted by an animal into external environments and externally regulates others’ behaviour.

Source: exocrine glands of animals of the same species
Mode of transmission: Exocrine

Question 9

Neurotransmitters

Answer 9

Carries signals from one neuron to the next, and transmits nerve impulses from neurons to muscle cells stimulating their contraction.

Question 10

Function of Neurotransmitters

Answer 10

To either continue or stop a signal from happening (excitatory or inhibitory)

Question 11

Signal Reception

Answer 11

• Reception of a signalling molecule from a cell’s external environment
• When signalling molecules reach their target cells, they bind to a specific receptor
• Each type of receptor protein binds to one signalling molecule with a specific shape
• Cell receptors are located on the plasma membrane of the specific target cell (due to polar and hydrophilic signalling molecules being unable to cross the lipid bilayer), in some cases the receptors are in the cytosol or the nucleus of the target cell
• hydrophobic/hydrophilic nature of signalling molecules determines the location of specific receptor where signal is received

Question 12

Ligand

Answer 12

chemical signalling molecule that binds to the receptor on a target cell

Question 13

Signal cascade

Answer 13

: Multiple cell signals that amplify initial signal by activation of secondary messengers by G-proteins

Question 14

Hydrophobic signalling molecules

Answer 14

the signalling molecule will pass through the plasma membrane and bind to a receptor either in the cytosol or in the nucleus

Question 15

Hydrophilic Signalling molecules

Answer 15

cannot diffuse across the plasma membrane, so they bind to a membrane-bound receptor. This causes a shape change in the receptor, which activates a second messenger. The second messenger causes a chain reaction within the cell

Question 16

Signal Transduction

Answer 16

converts a signal from outside a cell into a response within the cell.
Signal is received in one form and changed to another and is relayed to the target within the cell that responds through an effector protein. The process of signal transduction starts after a signalling molecule binds to its specific receptor, changing its 3D shape and activating it

Question 17

Signal Response

Answer 17

the outcome of the signalling molecule.

Example: apoptosis, increased transcription/translation,

Question 18

Apoptosis

Answer 18

Programmed cell death. Can be triggered by the death receptor pathway or mitochondrial pathway. Used to remove cells that are: at the end of their natural life, dysfunctional, damaged or diseased or found in excessive amounts.

Question 19

Signs of Apoptosis

Answer 19

nucleus condenses, cytoskeleton cut, DNA fragmented, cell shrinks. Apoptotic bodies form

Question 20

Extrinsic Pathway (death receptor pathway)

Answer 20

• Initiated by factors external to the cell. Activated when a signalling molecule from outside a cell binds to a death receptor on the plasma membrane of a cell. Then initiates the activation of a series of enzymes called caspases.
  Caspases release into the cytosol.

Question 21

Summary of Neurotransmitter process

Answer 21

1. Ligand binds to receptor on target cell, changing its shape.
2. Receptor activates a protein at the membrane
3. Original signal is amplified during signal transduction
4. Increased gene expression by target cell

Question 22

Intrinsic Pathway (mitochondrial pathway)

Answer 22

Initiated within a cell. Depends on factors released from the mitochondria. ATP production is reduced, initiating apoptosis by damaged membranes becoming more permeable to releasing caspases.
Mitochondria releases caspases into the cytosol.

Question 23

Necrosis

Answer 23

Unplanned cell death. The dying cells swell, their plasma membranes rupture and their cell contents pour into the surrounding tissues causing local inflammation.

Question 24

Malfunctions in Apoptosis

Answer 24

Apoptosis is involved in foetus development. webbing between our fingers and toes, and the slit that allows our eyelids to open are removed.

Cancer is caused by a damaged cell not undergoing apoptosis. These cells divide rapidly, creating large lumps called tumours.

Overactive apoptosis: leads to diseases like type 1 diabetes
Under-active apoptosis: leads to diseases like cancer