Lect 10. Energy & Metabolism - Cell Signalling Flashcards
Cell communication focuses on how a cell ____ from its ____ and ____ and how it transmits messages to other cells.
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.
Cell Communication in Prokaryotes
Cell-cell communication in bacteria is called
quorum sensing
Responses to signalling in prokaryotes (by quorum sensing)
- 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)
Types of Signalling in Eukaryotes (plants and animals)
- Direct Signalling
a) cell junctions
b) cell-cell recognition - Local Signalling (Paracrine signalling) (neurotransmitters)
- Long Distance Signalling
Long Distance Signalling in Eukaryotes
The activities of cells, tissues, and organs in different parts of a multicellular organism are coordinated by
hormones, which are bound by target cells.
Steps of Cell Signalling (Eukaryotes)
cell-cell
- Signal Reception
- Signal processing
- Signal response
- Signal deactivation
Hormones only affect cells that have the precise:
receptors
Hormones can bind receptors in a variety of target cells; different kinds of cells can respond differently to the ____ hormone.
Hormones can bind receptors in a variety of target cells; different kinds of cells can respond differently to the ** same** hormone.
ex of hormones that have a wide range of targets:
sex hormones
ex of hormones that have a narrow range of targets:
gastrin in the stomach
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:
target cells. Some target cells only have receptors for 1 hormone only, others can respond to as many hormones as it has receptors for.
Hormone Receptors
2 general reception methods used by hormones (depending on structure):
- cell surface receptor-mediated signaling: conversion of an extracellular chemical signal into an intracellular response
- intracellular receptor-mediated signaling: involves transcription factors.
Cell surface receptor-mediated signaling
Hormones using this method are ____ & ____, therefore cannot ____.
Hormones using this method are hydrophilic & polar (non-lipid soluble), therefore cannot diffuse into the cell.
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 ____.
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).
Cell surface receptor-mediated signaling
These hormones are made from ____, they are called:
These hormones are made from amino acids: peptide hormones
Cell-surface receptor-mediated signalling
In a ____, molecules relay the signal. This adds complexity.
signal transduction pathway
transduction, step before response
Intracellular receptor-mediated signaling
Hormones using this method are ____, ____ or ____, ____, therefore can ____.
Hormones using this method are hydrophobic, lipid-soluble or small, non polar, therefore **can diffuse into the cell.
Intracellular receptor-mediated signalling
Hormones bind to receptors inside the cell; receptor-hormone complex acts as a:
transcription factor
ex: steroid and thyroid hormones, hormonal form of vitamin D
Steps of intracellular receptor-mediated signaling
- Hormone passes through PM
- Hormone binds to a receptor protein in the cytoplasm, activating it
- Hormone-receptor complex enters the nucleus and binds to specific genes (target gene DNA)
- The bound protein stimulates the transcirption of the gene into mRNA
- The mRNA is translated into a specific protein
step 2 of cell signaling in eukaryotes
Signal processing (signal transduction pathways) involve 2 key elements:
- Second messengers
- Phosphorylation cascades
Second Messengers
The hormone that binds to the receptor is a pathway’s ____. Second messengers are:
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.
ex: What is one of the most widely used second messengers in signal transduction pathways?
Cyclic AMP (cAMP)
Adenylyl cyclase converts ATP to cAMP in response to an extracellular signal.
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:
second messengers.
In many pathways, the signal is transmitted by a series of:
protein phosphorylations (phosphorylation cascade)
What transfers phosphates from ATP to a protein? And in what process?
Protein kinases, phosphorylation
Phosphorylation is a system that acts as a ____, turning activities on and off or up or down, as required.
Phosphorylation is a system that acts as a molecular switch, turning activities on and off or up or down, as required.
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:
- Nuclear
- Cytoplasmic
What happens in a nuclear signal response?
A change in which genes are expressed (SLOW)
DNA transcription involved
What happens in a cytoplasmic signal response?
Activation/deactivation of target protein already in cell (FAST)
step 4 Signal Deactivation
Cells have automatic and rapid mechanisms for signal deactivation. These mechanisms allow the cell to remain sensitive to changes in:
stimulus
Mechanisms that allow cell to remain sensitive to changes in stimulus: (3)
- signal is no longer produced
- removal from receptors
- protein deactivation
Pathway Interactions and Diversity
Interactions leads to a communication web that integrate information to amplify or fine tune responses to stimuli. Diversity leads to:
different responses in different cells.
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:
different proteins
some examples of cell signaling:
- apoptosis
- cell division
- maintenance of homeostasis
What’s apoptosis?
- 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
Abnormal cell signalling in cell division can lead to ____. 2 possible pathways:
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
result: increased cell division
Homeostasis
What are the 2 communication systems in the body?
nervous and endocrine systems
What are the roles of the nervous and endocrine systems?
- respond to stimuli
- act as control centers to maintain homeostasis
- integrate info
- coordinate a response
By what are effector cells stimulated?
neurotransmitters or hormones
Abnormal cell signalling can lead to disorders and diseases. In other words:
homeostatic imbalance
