C2.1

Question 1

Signalling Molecules

Ligand?

Answer 1

• Molecules that bind reversibly to specific proteins
• Re-usable signalling molecules released from one cell and recieved by another, initating a type of action potential in the target cell
• E.g., hormones, nuerotransmitters.

Question 2

Signalling Molecules

Receptors

Answer 2

• A protein that has a compatible shape to a ligang and which initiates a response in a target cell.
• They are only found in target cells for that particular ligand, enabling specific responses only in the necessary cells.
• Most receptors are intergral proteins in cell membranes, yet some are intracelllular requiring ligands to enter the cell to initate a response.

Question 3

Signalling Molecules

Signal Transduction Pathways?

Answer 3

• A series of steps that start with activation of the receptor.
• This causes the next step, which causes the next step and so on until the response in initiated.
• Having several steps allows for more regulation and control of the response..

Question 4

Signalling Molecules

Quorum Sensing?

Answer 4

• The mechanism by which bactiera alter group behaviour depending on population density.
• This allows for coordination of individual bacteria allowing them to act as a colony
  Done with signalling molecules released by bacteria

Question 5

Signalling Molecules

Autoinducers?

Answer 5

• The signalling molecule that cause quorum sensing
• They are chemicals released by individual bacteria
• If low bacteria density = concentration of autoinducers is low and the response is NOT inititated
• If there’s many bacteria, the conc. of autoinducers is high and they signal responses in all inidividual bacteria –> group coordinated response.

Question 6

Signalling Molecules

Bioluminescence by Quorum Sensing

Answer 6

• Bioluminscne done by a colony of bacteria by qurorum sensing
• Happens when reproducing individual bacteria release an autoinducer from their cell membranes
• As the no. bacteria increase, the conc. of autoinducers increase –> reaches threshold level, pass into cells and bind to a lux receptor protien
• This activates Lux, causing it to bind to a DNA site
• This causes the transcription of the gene for Luminescent protein

Question 7

Signalling Molecules

Chemical Type and Role of: HORMONES

Answer 7

• Signalling chemicals secreted by specialized endocrine cells and carried through the circulatory system to act on target cells at distant body cells.
• They are a very specific – can only bind with certain a specific recepter on its intended target cell.
• They are chemically diverse (polar /non-polar)

Question 8

Signalling Molecules

Chemical Type and Role of: Neurotransmitters

Answer 8

• Signalling chemicals released from one cell that acts on neighbouring target cells
• They don’t enter the bloodstream, they move through the synapse between two nuerons and bind to a receptor on the nearby nuerons.

Question 9

Signalling Molecules

Chemical Type and Role of: Cytokines

Usually within the immune system

Answer 9

• Glycoproteins that act as messengers between cells.
• They can act locally on nearby cells & can enter the bloodstream to impact distant cells.

Question 10

Signalling Molecules

Chemical Type and Role of: Calcium ions

Answer 10

• A common ligand in animals
• They act as a primary ligand in muscle contraction and hormone secretion
• In muscle fibres, Ca is pumped into the sacroplasmic reticulum (form of ER)
• When muscle fibre recieves this electrical signal, Ca ions diffuse out and bind to proteins (actin!) allowing for muscle conctraction.
• In nuerons, Ca triggers the release of nuerotransmitters

Question 11

Signalling Molecules

Benefit of a Chemically Diverse Range of Ligands

Answer 11

• Key chemical differences include: size, polarity and make-up.
• Distinct shapes allows for specialized action only on compatible receptors
• Diverse structures enables some ligands to enter cells and others not, also ensures different types of cell signalling are possible.

Question 12

Signalling Molecules

Transmembrane vs Intracellular Receptors

Answer 12

• Intracellular receptors sit inside the cytoplasm of the cell/nucleus.
  1. Hydrophillic amino acids allowing them to remain dissolved in the cytoplasm.
  2. Ligands that bind to them are non-polar (must be able to cross plasma membrane to bind to them)
• Transmembrane receptors are embedded in the membrane.
  1. Have a band of hydrophobic amino acids in contact with the phospholipids and polar amino acids on each side. (amphiprotic)
  2. Polar lignads that can’t cross the membrane bind to them.

Question 13

Transmembrane Receptor, Transduction Pathways

Multi-pass protiens?

Answer 13

• A transmembrane protien composed of many domains that thread back & forth across the membrane several times.
• More complex intergral protins - ex: acetycholine receptor

Question 14

Transmembrane Receptor, Transduction Pathways

G-protein?

Answer 14

• A protien with a GDP attached to it
• The G protein with GDP attached binds to a receptor (currently inactive)
• IF GDP becomes GTP with the addition of a third phosphate, the G-protien becomes activated and leaves the receptor now with the energy to activate a nearby enzyme.

Question 15

Transmembrane Receptor, Transduction Pathways

Secondary Messenger?

Answer 15

• Helps in continuing the signal transduction pathway but isn’t the initial ligand.
• The receptor (when activated), often initiates a secondary messenger that is intracellular and able to activate enzymes within the cystoplasm.
• EX: Cyclic AMP

Question 16

Transmembrane Receptor, Transduction Pathways

Cyclic AMP?

Answer 16

• A secondary messenger in many signalling pathways - like in those using a G-protien.
• The energy released from the activated G protin activates the membrane enzyme Adenyl cyclase - this activates cyclic AMP
• Cyclic AMP binds to kinase enzymes in the cytoplasm, beginning a series of one enzymes activating (phophorylating) another until the response is initiated.

Question 17

Transmembrane Receptor, Transduction Pathways

Kinase?

Answer 17

• An enzyme that catalyses the transfer of a phosphate group from ATP to another substance.
• Kinase phosphorylates things – activates them, often leading to the production of ADP and a substate.

Question 18

Transmembrane Receptor, Transduction Pathways

Phosphorylated?

Answer 18

• A phosphate is added to a substance.
• ADP is phosphorylated to make ATP
• Also used for when phosphate is removed from ATP and transferred to a protien ( often an enzyme ).
• Often, the phosphorylated enzyme is now active & can carry out a reaction.
• Phosphorylating a series of enzymes makes up signal transduction pathways

Question 19

Transmembrane Receptor, Transduction Pathways

Structure & Function of: Chemically Gated Ion Channels

Answer 19

• Large, multi pass proteins with a central pore.
• When ligand is not bound, the channel is closed (ions cant move through)
• When ligand (usually nuerotransmitter) binds to the receptor, the ion channel opens and ions move through.
• This influx of ions causes the cellular response, which is how nuerotransmitters lead action potentials - they bind to their receptor, initating an influx of sodium, causing the onset of action potentials.

Question 20

Transmembrane Receptor, Transduction Pathways

Structure & Function of: Enzymatic Receptors

Answer 20

• Transmembrane receptors that are smaller, simpler in structure (single pass over multi pass).
• Contain two key regions: an extracellular region that the ligand binds to and an intracellular region that is capable of enzymatic activity when the ligand binds to the extraceccular region.
• Ex: Tyrosine Kinase Receptors

Question 21

Transmembrane Receptor, Transduction Pathways

Structure & Function of: G Protein coupled receptors

Answer 21

• Another type of transmembrane protein, they are large multi pass proteins with a G-protien attached to the receptor (when inactive)
• When ligand binds, the protien phosphorylates the G-protein, casuing it to detach and activate another separate enzyme.
• EX: Epinephrine uses a G-protien coupled receptor

Question 22

Transmembrane Receptor, Transduction Pathways

Acetycholine Signalling Pathway

Answer 22

• A neurotransmitter released from one nueron into a synapse
• Then it binds to AChR (Acetylcholine receptor) leading to a shape change that opens the protein to create a hydrophillic channel, allowing for sodium ions to enter a channel into the cell, causing a depolarization inside the axon that initaties the action potential allowing the nuron to fire an electrical message.

Question 23

Transmembrane Receptor, Transduction Pathways

Epiniephrine Signalling Pathway

Answer 23

• Epinephrine is a hormone released by the adrenal glands that travels by the bloodstream to target muslce cells & the liver.
• It binds to a G-protien couple receptor
• When it binds, the G-protien becomes activated and detaches, transfering energy to the enzyme adenyl cyclase, creating cAMP that activates the first in a series of phosphorylase kinases.
• A possible end result: breakdown of glycogen into glucose

Question 24

Transmembrane Receptor, Transduction Pathways

Insulin Signalling Pathway

Answer 24

• Insulin is a hormone that binds to an enzymatic transmembrane receptor (tyrosine kinase receptor)
• Insulin binds to the extracellular domain of both ends of the receptor, pulling the two intracellular ends of the receptor close and the phosphate groups attached to it.
• This enzyme is now active & transfer the phosphates to other protiens beginning the signal transduction pathway.

Question 25

# Intracellular Receptor Signalling Pathways Receptor-Signal Complex?

Answer 25

* When steroid hormones enter cells they **bind to receptors** that are usually in the **cytoplasm**. * The hormone tends to **stay bound to the receptor** and they move into the nucleus **together**, often to act as a **transcription factor**. * This is called the **receptor-signal complex**

Question 26

# Intracellular Receptor Signalling Pathways Chemical Characteristic to Cross a Membrane

Answer 26

* In order for a **ligand to bind to an intracellular receptor** it must pass through the membrane. * To do this, the ligand must be **hydrophobic/non polar** (lipid soluable) in order to **move through the fatty acid tails** of the bilayer. * Ligands are usually steriod hormones (sex hormones estrogen, progesterone and testerone.)

Question 27

# Intracellular Receptor Signalling Pathways Steroid Hormone Impacts: Oestradiol | Involved in the menstrual cycle

Answer 27

* Released by the ovaries in response to gonadotropin hormones (FSH and LH), released by the anterior pituitary. * As ovaries release more estrogen, its **effect is to travel by the bloodstream to the hypothalamus**. * It **signals the hypothalamus** to **increase the release of GnRH** to the **pituitary** that increases the release of **FSH and LH** that stimulate the **maturation and eventual release of an egg**.

Question 28

# Intracellular Receptor Signalling Pathways Steroid Hormone Impacts: Progesterone

Answer 28

* Function is to **thicken the lining of the uterus** to faciliate implantation. * Hence, one of the key target cells are that of the uterine wall. (target uterine cells) * Progesterone **enters these cells and lead to the response of thickening** (cell proliferation) and **vacularization** (increased blood vessels to the area

Question 29

# Intracellular Receptor Signalling Pathways Chemically Diverse Ligands

Answer 29

* The only way that **intracellular receptors** can be accessed is by ligands that can cross the membrane. * This isn't possilbe with **large hormones** (insulin) or **small polar hormones** (ADH). * Such hormones nessecitate **transmembrane receptors**. * Small hormones made of steroid lipids can cross through **fatty acid tails** to access intracellular receptors. * Hence, having chemically unique ligands enables **distinctive intracellular receptor pathways to exist**

Question 30

# Intracellular Receptor Signalling Pathways Negative Feedback Signalling Loops

Answer 30

* The release of ligands is carefully regulated, often by negative feedback loops. * The example: the regulation of the release of the hormones **insulin and glucagon** (which are ligands that bind to **transmembrane receptors**) * Ligand release is **halted when the body returns to a set point** so the signalling molecules are only binding to receptors when needed.

Question 31

# Intracellular Receptor Signalling Pathways Fever as a Positive Feedback Loop | Non-hormonal example of a positive feedback loop

Answer 31

* Non-hormonal example of a positive feedback loop in response to **infection**. * The presence of a **pathogen** causes the release of specific cytokines, **pyrogens**, that increase the **body temperature**. * This increase **in body temp** reinforces the immune system **casuing the release of more pyrogens,** raising the fever **until the pathogens are disabled** from the **high temperature**.