Week 12 Cell junctions and signalling Flashcards
What are gap junctions?
A type of communicating junction in animal cells that connect the cytoplasm of adjacent cells via pores. It is similar in the function of plasmodesmata. Gap junctions are made out of proteins called connexin.
What is connexin?
A protein that makes up gap junctions
6 connexin proteins form what?
A pore of the gap junction
What can pass through gap junctions?
There is a set limit of solutes below 1.2 kDa, therefore, ions, sugars, amino-acids, and other small molecules ca pass but proteins and viruses cannot.
What are the opening of gap junctions regulated by?
Ca2+ ions and hormones
What do gap junctions function in?
Coordinating activities of cells within a tissue such as muscle contraction
What are tunneling nanotubes? (TNTS)
Membrane tubules that contain a thin tube of cytoplas. It can connect cells over long distances but are not well understood
True or Fasle? Tunneling nanotubes are small.
False, they are really big and allow the movement of membrane lipids, vesciles, and whole organelles between cells.
Where are gap junctions usually found?
In most animal tissues
Are gap junctions involved in connecting or communicating?
Communicating
What can cells sense?
Signals using proteins calling receptors
Signalling enables what in multicellular organisms?
Co-ordination
What are the 3 processes of signalling at a cellular level?
- Signal reception 2. Signal transduction and 3. Signal response
What are mechanoreceptors?
A sense organ or cell that responds to mechanical stimuli such as touch or sound.
What are chemoreceptors?
A sensory cell or organ responsive to chemical stimuli.
What are thermoreceptors?
Thermoreceptors are specialized nerve cells that are able to detect differences in temperature
True or False? Sometimes the cell that detects a signal is the same one that responds
True
True or False? The cell that detects signals is always close to the cells that respond
False, sometimes they can be a long way away
What are the two types of direct cell to cell signalling?
Cell Junctions and Cell-Cell recognition
What are the two types of local signalling?
Paracrine signalling and Synaptic signalling (nerve cells).
What is long-distance signalling?
Also called endocrine signalling. It is a type of communication whereby a signaling molecule acts on a target cell far from the signaling cell. Mediated my hormones
How diverse can signalling molecules be?
Very diverse, they can be gas molecules, lipid soluble, water soluble, small molecules, and even proteins.
What is a signal transduction pathway?
Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellular response. AKA Signal reception - Signal transduction - Signal response (Change in protein activity or expression).
What happens once a signalling molecule binds to a receptor?
It changes shape.
Why are receptors specific for certain signals?
So that only the correct cells respond, and so that the cells don’t respond to the wrong signals.
What is a ligand?
The specific signalling molecule that binds to a specific receptor.
What percentage of human proteins are cell surface receptors?
30%
What are cell-surface receptors?
Cell surface receptors are receptors that are embedded in the plasma membrane of cells. They act in cell signaling by receiving extracellular molecules.
What are cytoplasmic receptors?
Found in the cytoplasm of the cell and respond to hydrophobic ligand molecules that are able to travel across the plasma membrane. Once inside the cell, many of these molecules bind to proteins that act as regulators of mRNA synthesis
What are Ligand-Gated Ion Channel Receptors?
A group of transmembrane ion-channel proteins which open to allow ions such as Na⁺, K⁺, Ca²⁺, and/or Cl⁻ to pass through the membrane in response to the binding of a chemical messenger, such as a neurotransmitter.
What does the system of a ligand-gated ion channel receptor involve?
A signal molecule and a gated ion channel
When the signalling molecule binds to the ligand-gated ion channel its opens and allows the flow of what?
Specific ions
What is critical concerning the opening of the ligand-gated ion channel?
That the gate returns to the closed position at the end of the signal.
What are G Protein-Coupled Receptors (GPCRS)?
Signal receptors found associated with the plasma membrane. They are in all eukaryotes and 60% of drugs target these pathways. These cell surface receptors act like an inbox for messages in the form of light energy, peptides, lipids, sugars, and proteins.
What is the structure of G Protein-Coupled Receptors (GPCRS)?
They always have 7 helices and loops at the end which link and interact with G proteins
What does the system of the G Protein-Coupled Receptors involve?
A signal molecule, A G Protein-Coupled Receptor, A G protein, and an enzyme
What is GDP?
A nucleoside diphosphate. … GDP is the product of GTP dephosphorylation by GTPases, e.g., the G-proteins that are involved in signal transduction. GDP is converted into GTP with the help of pyruvate kinase and phosphoenolpyruvate.
What is the difference between GDP and ATP?
ATP is used to carry energy for almost all energy-requiring chemical reactions in almost all cells. GTP can occasionally be used to carry energy, but it is more often used as a signaling molecule, as in G-linked proteins
How is the G Protein activated?
By switching GDP to GTP
How does the G Protein-Couples Receptor system go back to its resting state?
The G Protein is deactivated by hydrolysis of GTP to GDP
What sort of signal do G Protein-Coupled Receptors receive?
Water soluble
What sort of signal do Steroid Receptors receive?
Lipid soluble
What are steroid receptors?
Steroid hormone receptors are found in the nucleus, cytosol, and also on the plasma membrane of target cells. They initiate signal transduction for steroid hormones which lead to changes in gene expression over a time period of hours to days
What are some examples of steroid receptors?
The sex hormones, and glucocorticoids
Lipid soluble molecules can what?
Diffuse through the plasma membrane and be detected within the cytoplasm
Overall what do steroid receptors do?
They travel throughout the body diffusing through the plasma membrane of all cells. Binds to specific cell receptors in the cytoplasm. The receptors then go to the nucleus where they bind with DNA. Then finally, mRNA synthesis is initiated and new proteins are synthesised.
Signal transduction pathways can involve only what?
Proteins such as phosphorylation cascades or small molecules (Second messengers)
Why may signal transduction pathways have multiple steps?
For amplification, control, and multiple responses
What is the definition of a signal transduction pathway?
The pathway is actually a cascade of biochemical reactions inside the cell that eventually reach the target molecule or reaction.
What is the “First Messenger”?
Extracellular signalling molecule that binds to a cell-surface receptor and initiates intracellular activity
What are some examples of signal transduction molecules?
A small molecules such as calcium or A protein such as Kinases
True or False? Calcium needs to be continually pumped from the cytoplasm.
True!
Where are calcium concentrations high in the cell?
In the extracellular space and certain organelles such as the mitochondria and endoplasmic reticulum
How does calcium act as a secondary messenger?
By causing direct effects such as muscle contraction and neurotransmitter release by binding to specific proteins such as calmodulin which then activate further proteins
In a relaxed muscle how are the thick and thin filaments spaced?
Widely spaced
Calcium triggers the movement of which filament?
The tropomyosin filament
What is phosphorylation?
The addition of a phosphate group
What is a kinase?
An enzyme that adds a phosphate group
Phosphorylation does what?
Acts as an on/off switch to a protein
What are phosphorylation cascades?
A phosphorylation cascade is a sequence of signaling pathway events where one enzyme phosphorylates another, causing a chain reaction leading to the phosphorylation of thousands of proteins.
What do cascade pathways allow for?
Amplification
Amplification allows for what?
A small initial signal to be massively increased.
What is ligand binding?
When receptors are turned on
What is ligand release?
When receptors are turned off
True or False? Second messengers can be turned on and off
True
True or False? Kinases cannot be turned on and off
False, they can be through the addition of phosphate groups
How can enzymes be turned on and off?
By kinases and phosphates
What are a few examples of the various outcomes of signal transduction pathways?
Altered metabolism, Altered gene expression, and Altered cell movement/shape
Do extracellular signals act slowly or fast?
Both
What are extracellular signals?
Extracellular signalling molecules are cues, such as growth factors, hormones, cytokines, extracellular matrix components and neurotransmitters, designed to transmit specific information to target cells.
Does altered metabolism occur fast or slow?
fast
Does altered gene expression occur fast or slow?
slow
Does altered cell movement/shape occur fast or slow?
fast
