Chapter 5: Cell Signaling and Chemical Messengers

Question 1

Everything an animal does involves____.

Answer 1

Communication or signals.

Question 2

Animal Signal Forms

Answer 2

1. Sounds
2. Scents
3. Visual Cues

Question 3

Within animal signal forms:

Answer 3

Chemical and Electrical

Question 4

Most familiar types of signals

Answer 4

1. Nervous System

2. Endocrine System

Question 5

Complexity of animal physiology and behavior requires

Answer 5

diversity of signaling mechanisms

Question 6

Cell Signaling

Answer 6

1. Production of a signal in one cell (signaling cell)
2. Transport of that signal (chemical messenger) to a target cell
3. The messenger binds to a receptor to transduce signal into the target

Question 7

Types of Cell Signaling

Answer 7

Direct Signaling

1. Gap Junctions
2. Connexions

Indirect Signaling

1. Autocrine Signaling
2. Paracrine Signaling
3. Endocrine Signaling
4. Neural Signaling

Question 8

Direct Signaling

Answer 8

• Gap junctions or specialized membrane junctions (tunnels) of adjacent cells
• Messengers can travel through the tunnel directly
• Without ever leaving the aqueous envelope of the cell
• Messengers: Ions, small molecules and water
• Not passive: opened and closed to regulate communication of substances between cells.

Question 9

Indirect Signaling

Answer 9

-other strategies must be used to send signals to distant cells or to neighboring cells that are not connected by gap junctions

Question 10

Steps for Indirect Signaling

Answer 10

1. Release of chemical messenger from signaling cell into environment
2. Transport of chemical messenger through environment to target cell
3. Communication of signal to target cell by receptor binding

Question 11

Autocrine/ Paracrine Signaling

Answer 11

• Messenger moves by diffusion
• when the messenger affects the signaling cell-Autocrine
• when the messenger affects near by cells-Paracrine
• distance limits the rate of diffusion
• diffusion is insufficent to carrying signals to distant target cells

Question 12

Endocrine Signaling

Answer 12

• Messenger is secreted (Hormone)
• Secretory cells of the exocrine and endocrine tissues are often grouped together into structures called-glands
• travel from signaling cell to the target cell carried by circulatory system
• long distance to target cell

Question 13

Nervous (Neural) Signaling

Answer 13

-Electrical signal travels across a long distance
-Reaches terminus trigger release of a chemical messenger called a neurotransmitter
-Binds to receptor on target cell (produces a signaling cascade)
-Some neurons can secrete neurotransmitters directly into the circulatory system
(Messenger is termed a neurohormone)
(Secreted by a neuron but acts like a hormone)

Question 14

The most important distinction among the different systems

Answer 14

• Distance messenger must travel

- Speed of communication

Question 15

time of Autocrine and Paracrine Signaling

Answer 15

Milliseconds-Seconds

Question 16

time of Nervous Signaling

Answer 16

milliseconds

Question 17

time of Endocrine Signaling

Answer 17

• seconds to minutes

- longer-lived

Question 18

time of Exocrine Signaling

Answer 18

pheromone

Question 19

There are six main classes of chemicals known to participate in cell signaling in animals. The six classes are:

Answer 19

1. Peptide Messengers
2. Steriod Messengers
3. Biogenic Amine Messengers
4. Lipid Messengers
5. Purine Messengers
6. Gas Messengers

Question 20

Peptide Messengers

Answer 20

• Amino Acid Residues: Hydrophilic or Hydrophobic. Act as Neurotransmitters
• Peptides-50 Amino acid Chains: Hydrophilic

Need a specific receptor to bind

• Synthesized in Ribosomes on the rough ER
• synthesized as large inactive polypeptides called prehormones
• possess a signal sequence that targets the polypeptide for secretion
• prior to being packaged into secretory vesicles, signal sequence is cleaved for preprohormone, forming the prohormone (inactive)

Question 21

Biogenic Amine Messengers

Answer 21

-Small Water Soluble Hormones
requires specific receptor because:
-cannot cross plasma membrane 
-too large
-carry a charge at physiological pH
-released in vascular system when stimulated
-carried freely to needed site

Question 22

Not all hormones are perceived by cell surface receptors, most are recognized by _____.

Answer 22

intracellular receptors

Question 23

Hormones are synthesized from ____.

Answer 23

chloestrols

Question 24

Hormones are synthesized and secreted from____.

Answer 24

endocrine cells to act on distinct target sites in the human body. Commonly referred to as steroid hormones.

Question 25

Examples of Steroid Hormones

Answer 25

Estrogen, Progesterone, Testosterone, Thyroid Hormones-Thyroxin, Retinoids (vitamin A), cortisol, and Vitamin D.

Question 26

What is Cell Signaling?

Answer 26

- Extracellular signaling molecules (1st Messenger) recognized by receptor - Leads to production of small transient signaling inside the cell (2nd messenger) - Leads to alter activity of the next component of transduction pathway. - Formation of chains of molescules (cascades) where each molecule passes the message to the next - Until the final signal causes the desired cell event

Question 27

Ligand Binding will initiate a series of molecular events

Answer 27

1. Binding causes a conformational change in the outer domain of the receptor. 2. Change is transmitted through membrane to induce conformational change in the intracellular domain of the receptor 3. Change will either activate or inhibit receptors intrinsic activity.

Question 28

5 Main Classes of Receptors

Answer 28

1. G-protein coupled receptors (GPCRs) 2. Ion channel linked receptors 3. Intrinsic enzyme receptors 4, Tyrosine Kinase-linked recepetors 5. Intracellular receptors

Question 29

G Protein Coupled Receptors (GPCRs)

Answer 29

- G protein-coupled receptors are found only in eukaryotes, yeast and animals - receptors are coupled to trimeric G proteins and function as guanine exchange factors to transduce signal - G protein-coupled receptors are involved in many diseases - Target of 40% of all modern medicinal drugs

Question 30

Ion Channel Linked Receptors

Answer 30

- Membrane bound receptors also called ligand gated channels - Involved in the detection go neurotransmitters and peptide hormones used in synaptic signaling on electrically excitable cells - Undergo a conformational change when a ligand binds forming a "water tunnel" allowing passage of a specific molecules, such as sodium (Na+) or potassium (K+) - Alters the ion permeability and charge across the plasma membrane - Transient event

Question 31

Transient Event

Answer 31

The ion channels open for a short time, after which the ligand dissociates from the receptor and the receptor is available once again for a new ligand to bind.

Question 32

Ion Channel Linked Receptors- Clinical Revelance

Answer 32

- Likely to be the major site at which anesthetic agents and ethanol have their effect, GABA - Drugs such as barbiturates used to treat insomnia, depression and anxiety have been linked to receptors - Diseases include schizophrenia, Parkinson's disease, epilepsy and autism have been linked to receptor defects

Question 33

Ion Channel Linked Receptors- Nicotinic Acetylcholine Receptor (nAChRs)

Answer 33

Function: - When Acetylcholine is bound, alter the receptor's configuration and cause an internal pore to open - pore allows Na+ ions to flow into the cell - inward flow Na+ ions depolarizes the postsynaptic membrane sufficiently to initiate an action potential - Ionotropic receptors, nAChRs are directly linked to ion channels and do not use second messengers - When an agonist binds to the site, all present subunits undergo a conformational change and the channel is opened and a pore with a diameter of about 0.65nm opens. NORMALLY: nAChRs may exist in different interconvertible conformational states AGONIST BINDING: stabilizes the receptor in the open allowing positively charged ions to move across it - It will remain open until the agonist diffuses away - Usually takes about 1 millisecond

Question 34

Ion Channel Liked Receptors-Snake Venom

Answer 34

- snake venom (alpha neurotoxins)-antagonistics - bind tightly and noncovalently to nAChRs of skeletal muscles - block the action of ACh at the postsynaptic membrane, inhibiting ion flow - leading to paralysis and death

Question 35

Intracellular Receptors

Answer 35

RECEPTORS FOR: - steroid hormones - thyroid hormones - retinoids - fatty acids - prostaglandins - leukotrienes COMMONALITIES: small and hydrophobic - allows for dress passage into cell - insoluble in aqueous fluid - free access to the cell - still have to bind to a receptor to initiate the signaling cascade -Several different types-focus on Nuclear Receptor Family -Are all transcription factors -Depending upon the intracellular steroid hormone they bind,they have two modes of action (located in the cytosol and move to the cell nucleus upon activation) (located in the nucleus waiting for the steroid hormone to enter and activate them (covered up by heat shock proteins (HSP) which binds the receptor until the hormone is present.

Question 36

Cytosolic

Answer 36

hormone binding causes receptor conformational change, freeing the receptor for HSP and the receptor hormone complex enter the nucleus to act upon transcription factor

Question 37

Nuclear

Answer 37

hormone binding causes receptor conformational change, freeing the receptor from HSP and the receptor hormone complex can act upon transcription factor.

Question 38

Regulation of Cell Signaling

Answer 38

- Sensor: regulated variable - integrating center - effector - Negative Feedback - Positive Feedback

Question 39

Feedback Regulation

Answer 39

- Local Level (Pacacrine Signals and Autocrine Signals) | - Long Distance (Nervous System and Endocrine System)

Question 40

Direct Feedback Loop

Answer 40

- Endocrine System Only - Endocrine cell itself sense a change in the extra cellular environment and releases a chemical messenger that acts on target cells elsewhere in the body. - The endocrine cell acts as the integrating center that interprets the change in the environments

Question 41

First Order Feedback Loops

Answer 41

- Nervous System becomes involved - A sensory organ perceives a stimulus and sends a signal via the NS to an integrating center (brain) that interprets the signal - Neurons then transmit the signal (Neurotransmitter or Neurohormone) to a specific target organ causing a response - only single step links the integrating center and the response

Question 42

Second Order Feedback Loops

Answer 42

- there are 2 steps that link integrating center and the response - sense organ perceives a stimulus and sends a signal to the integrating center - integrating center will then send a signal by a neuron telling the neuron to secrete either a neurohormone or a neurotransmitter - act on an endocrine gland will secrete a hormone into the bllod

Question 43

Third-Order Feedback Loops

Answer 43

- 3 steps - Every step in a response loop may act as a control point over the pathway - Provide the most sophisticated and tightly regulated feedback - Sense organ perceives a stimulus and sends a signal to the integrating center - sends a signal by a neuron telling the neuron to secrete either a neurohormone or a neurotransmitter - Act on an endocrine gland to secrete a hormone into the blood - Travel to the target cell of 2nd endocrine, which will then induce a response