Lect 10. Energy & Metabolism - Cell Signalling

Question 1

Cell communication focuses on how a cell ____ from its ____ and ____ and how it transmits messages to other cells.

Answer 1

Cell communication focuses on how a cell receives messages (chemical and physical signals) from its environment and surrounding cells and how it transmits messages to other cells.

Question 2

Cell Communication in Prokaryotes

Cell-cell communication in bacteria is called

Answer 2

quorum sensing

Question 3

Responses to signalling in prokaryotes (by quorum sensing)

Answer 3

• sporulation
• conjugation (sex)
• bioluminescence (light emission) in symbiosis
• virulence: secretion of proteins that allow the bacteria to attack multicellular hosts and cause disease
• production of biofilms - hard, polysaccharide-rich substances that encase the cells and attach them to a surface (like plaque)

Question 4

Types of Signalling in Eukaryotes (plants and animals)

Answer 4

1. Direct Signalling
   a) cell junctions
   b) cell-cell recognition
2. Local Signalling (Paracrine signalling) (neurotransmitters)
3. Long Distance Signalling

Question 5

Long Distance Signalling in Eukaryotes

The activities of cells, tissues, and organs in different parts of a multicellular organism are coordinated by

Answer 5

hormones, which are bound by target cells.

Question 6

Steps of Cell Signalling (Eukaryotes)

cell-cell

Answer 6

1. Signal Reception
2. Signal processing
3. Signal response
4. Signal deactivation

Question 7

Hormones only affect cells that have the precise:

Answer 7

receptors

Question 8

Hormones can bind receptors in a variety of target cells; different kinds of cells can respond differently to the ____ hormone.

Answer 8

Hormones can bind receptors in a variety of target cells; different kinds of cells can respond differently to the ** same** hormone.

Question 9

ex of hormones that have a wide range of targets:

Answer 9

sex hormones

Question 10

ex of hormones that have a narrow range of targets:

Answer 10

gastrin in the stomach

Question 11

Hormones can come into contact with virtually all body cells since the cardiovascular system transports hormones throughout the body. But, a hormone was designed to affect only specific cells which often have receptors on the cell surface or inside the cell that are specific to one hormone. These cells are called:

Answer 11

target cells. Some target cells only have receptors for 1 hormone only, others can respond to as many hormones as it has receptors for.

Question 12

Hormone Receptors

2 general reception methods used by hormones (depending on structure):

Answer 12

1. cell surface receptor-mediated signaling: conversion of an extracellular chemical signal into an intracellular response
2. intracellular receptor-mediated signaling: involves transcription factors.

Question 13

Cell surface receptor-mediated signaling

Hormones using this method are ____ & ____, therefore cannot ____.

Answer 13

Hormones using this method are hydrophilic & polar (non-lipid soluble), therefore cannot diffuse into the cell.

Question 14

Cell surface receptor-mediated signaling

Hormones bind to receptor on cell surface, which activates the receptor. This activation of the receptor in turn activates a ____ leading to activation of a ____.

Answer 14

Hormones bind to receptor on cell surface, which activates the receptor. This activation of the receptor in turn activates a signal transduction pathway leading to activation of a target protein (ex: an enzyme).

Question 15

Cell surface receptor-mediated signaling

These hormones are made from ____, they are called:

Answer 15

These hormones are made from amino acids: peptide hormones

Question 16

Cell-surface receptor-mediated signalling

In a ____, molecules relay the signal. This adds complexity.

Answer 16

signal transduction pathway

transduction, step before response

Question 17

Intracellular receptor-mediated signaling

Hormones using this method are ____, ____ or ____, ____, therefore can ____.

Answer 17

Hormones using this method are hydrophobic, lipid-soluble or small, non polar, therefore **can diffuse into the cell.

Question 18

Intracellular receptor-mediated signalling

Hormones bind to receptors inside the cell; receptor-hormone complex acts as a:

Answer 18

transcription factor

ex: steroid and thyroid hormones, hormonal form of vitamin D

Question 19

Steps of intracellular receptor-mediated signaling

Answer 19

1. Hormone passes through PM
2. Hormone binds to a receptor protein in the cytoplasm, activating it
3. Hormone-receptor complex enters the nucleus and binds to specific genes (target gene DNA)
4. The bound protein stimulates the transcirption of the gene into mRNA
5. The mRNA is translated into a specific protein

Question 20

step 2 of cell signaling in eukaryotes

Signal processing (signal transduction pathways) involve 2 key elements:

Answer 20

1. Second messengers
2. Phosphorylation cascades

Question 21

Second Messengers

The hormone that binds to the receptor is a pathway’s ____. Second messengers are:

Answer 21

The hormone that binds to the receptor is a pathway’s first messenger. Second messengers are small, non-protein, water-soluble molecules or ions that spread throughout a cell by diffusion.

Question 22

ex: What is one of the most widely used second messengers in signal transduction pathways?

Answer 22

Cyclic AMP (cAMP)

Adenylyl cyclase converts ATP to cAMP in response to an extracellular signal.

Question 23

ex: a signal molecule binds to a ligand-gated ion channel, the gate allows specific ions, such as Na+ or Ca2+, through a channel in the receptor. These ions act as:

Answer 23

second messengers.

Question 24

In many pathways, the signal is transmitted by a series of:

Answer 24

protein phosphorylations (phosphorylation cascade)

Question 25

What transfers phosphates from ATP to a protein? And in what process?

Answer 25

Protein kinases, phosphorylation

Question 26

Phosphorylation is a system that acts as a ____, turning activities on and off or up or down, as required.

Answer 26

Phosphorylation is a system that acts as a **molecular switch**, turning activities on and off or up or down, as required.

Question 27

# step 3 Signal Response The ultimate response to a cell-cell signal varies from signal to signal and from cell to cell, by fall into 2 general categories:

Answer 27

1. Nuclear 2. Cytoplasmic

Question 28

What happens in a nuclear signal response?

Answer 28

A change in which genes are expressed (SLOW) | DNA transcription involved

Question 29

What happens in a cytoplasmic signal response?

Answer 29

Activation/deactivation of target protein already in cell (FAST)

Question 30

# step 4 Signal Deactivation Cells have automatic and rapid mechanisms for signal deactivation. These mechanisms allow the cell to remain sensitive to changes in:

Answer 30

stimulus

Question 31

Mechanisms that allow cell to remain sensitive to changes in stimulus: (3)

Answer 31

- signal is no longer produced - removal from receptors - protein deactivation

Question 32

# Pathway Interactions and Diversity Interactions leads to a communication web that integrate information to amplify or fine tune responses to stimuli. Diversity leads to:

Answer 32

different responses in different cells.

Question 33

# Cell Signalling in Animals Abnormal cell signaling implicated in various human disorders and diseases. Drugs can be developed to target different regions of signalling pathway by targeting:

Answer 33

different proteins ## Footnote some examples of cell signaling: - apoptosis - cell division - maintenance of homeostasis

Question 34

What's apoptosis?

Answer 34

- programmed/controlled cell suicide - essential in animal development and protection from abnormal/infected cells - abnormal cell signalling in apoptosis resulting in other activity or under activity implicated in human disorders and diseases

Question 35

Abnormal cell signalling in cell division can lead to ____. 2 possible pathways:

Answer 35

cancer 1. normal genes that encode cell cycle "go" (over expressed protein, overstimulated cell cycle) 2. normal genes that encode cell cycle "stop" (absent protein, cell cycle not inhibited) | effects of mutation ## Footnote result: increased cell division

Question 36

# Homeostasis What are the 2 communication systems in the body?

Answer 36

nervous and endocrine systems

Question 37

What are the roles of the nervous and endocrine systems?

Answer 37

- respond to stimuli - act as control centers to maintain homeostasis - integrate info - coordinate a response

Question 38

By what are effector cells stimulated?

Answer 38

neurotransmitters or hormones

Question 39

Abnormal cell signalling can lead to disorders and diseases. In other words:

Answer 39

homeostatic imbalance