Cell Signalling and Communication

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Questions and Answers

What type of receptors are responsible for transmitting signals through a second messenger?

Nuclear receptors

G-protein linked receptors (correct)

Serine/threonine kinase receptors

Tyrosine kinase receptors

Which type of receptors are typically found in the cytoplasm and bind to ligands such as steroids or retinoids?

Serine/threonine kinase receptors

Tyrosine kinase receptors

Nuclear receptors (correct)

G-protein linked receptors

What is the role of Hsp chaperones in the activation of nuclear receptors?

To bind to the receptor in its inactive form (correct)

To hydrolyze GTP to GDP

To release the receptor from the nucleus

To phosphorylate the receptor

What is the response of a G-protein linked receptor upon ligand binding?

It releases GDP and takes up GTP Signup and view all the answers

What is the role of Smads in signal transduction through Serine/threonine kinase receptors?

They act as transcription factors in the nucleus Signup and view all the answers

What type of receptors bind to the TGFb family of signals?

Serine/threonine kinase receptors Signup and view all the answers

What is the role of Ga in G-protein linked receptors?

It dissociates from Gbg Signup and view all the answers

What is the ultimate effect of signal transduction through nuclear receptors?

Activation of transcription of target genes Signup and view all the answers

What is the primary function of cell signalling?

To facilitate communication between cells Signup and view all the answers

Which type of signal acts on a local set of cells?

Paracrine signal Signup and view all the answers

What is the result of cell-cell signalling on gene expression?

Change in the repertoire of transcription factors Signup and view all the answers

What determines cell fate in some signalling pathways?

Signal concentration Signup and view all the answers

What is the function of nuclear receptors in cell signalling?

To allow signals to pass through the plasma membrane Signup and view all the answers

What is the term for the process by which a signal is translated into changes in cell physiology or gene expression?

Signal transduction Signup and view all the answers

What is the characteristic of autocrine signals?

They act on the secreting cell Signup and view all the answers

What is the purpose of signal gradients in cell signalling?

To determine cell fate Signup and view all the answers

What is the main difference between simple diffusion and facilitated diffusion?

The size of the molecules being transported Signup and view all the answers

In which type of solution will a cell swell, potentially causing lysis?

Hypotonic solution Signup and view all the answers

What is the primary function of channel proteins?

To form a hydrophilic passage through the membrane Signup and view all the answers

What is the direction of movement in active transport?

Against a concentration gradient Signup and view all the answers

What type of proteins are involved in facilitated diffusion?

Channel proteins and carrier proteins Signup and view all the answers

What is the energy source for direct active transport?

ATP hydrolysis Signup and view all the answers

What is the term for the diffusion of water molecules through a selectively permeable membrane?

Osmosis Signup and view all the answers

What is the state of a solution that has the same concentration of solutes as the cell interior?

Isotonic Signup and view all the answers

What is the primary mechanism by which cells maintain an ionic gradient across the membrane?

Direct ATP-powered pumps Signup and view all the answers

What is the approximate electrical potential maintained across the membrane due to differences in ion concentrations?

70mV Signup and view all the answers

How do cells synthesize new membranes?

By the expansion of existing membranes Signup and view all the answers

What is the characteristic of the cytosolic K+ concentration compared to the extracellular concentration?

Higher in the cytosolic space Signup and view all the answers

What is the purpose of regulating hydrogen ion concentration in the cytosol?

To regulate pH levels Signup and view all the answers

What is the mechanism by which some membranes grow and receive new lipids?

Vesicle-independent mechanism Signup and view all the answers

What determines the fluidity of the membrane?

The ratio of saturated to unsaturated fatty acids and the length of the fatty acid tails Signup and view all the answers

What is the role of cholesterol in the membrane?

To buffer the fluidity of the membrane Signup and view all the answers

What is the term for the movement of lipids from one leaflet to another in the lipid bilayer?

Flip-flop Signup and view all the answers

What is the term for the fluid mosaic model of membrane structure?

Fluid mosaic model Signup and view all the answers

What type of membrane proteins are anchored to the cytoskeleton or extracellular matrix?

Integral membrane proteins Signup and view all the answers

What is the term for the layers of the lipid bilayer?

Leaflets Signup and view all the answers

What is the mechanism by which van der Waals forces stabilize the packing of phospholipids?

Van der Waals forces Signup and view all the answers

What is the result of having longer fatty acid tails in the lipid bilayer?

Decreased fluidity Signup and view all the answers

What is the primary function of the cell wall in plant cells?

To support the cell and prevent it from bursting in a hypertonic solution Signup and view all the answers

What is the composition of the cell wall in plant cells?

Cellulose microfibrils embedded in pectin and hemicellulose Signup and view all the answers

What is the relationship between the plasma membrane and the cell wall in plant cells?

The plasma membrane is sandwiched between the cell wall and the cytoskeleton Signup and view all the answers

What is the structure that provides support to the cell and is located beneath the plasma membrane?

Cytoskeleton Signup and view all the answers

What is the environment within a membrane often different from?

The environment outside the membrane Signup and view all the answers

What is the function of the cytoskeleton in relation to the plasma membrane?

To provide support to the plasma membrane Signup and view all the answers

What is the primary function of membranes in the cell?

To regulate the transport of solutes Signup and view all the answers

What is the characteristic of lipids found in cell membranes?

They are amphipathic and have a polar head Signup and view all the answers

What is the result of the hydrophobic and hydrophilic interactions between lipids in a membrane?

The formation of a lipid bilayer with a hydrophobic core Signup and view all the answers

Which type of lipid is a steroid and found in membranes?

Cholesterol Signup and view all the answers

What is the function of membranes in cell signaling?

To detect and transmit both electrical and chemical signals Signup and view all the answers

What is the role of lipid bilayers in membranes?

To create a barrier between the cell and its environment Signup and view all the answers

Why do different membranes have different lipid compositions?

Because they have different functions in the cell Signup and view all the answers

What is the characteristic of the Rough Endoplasmic Reticulum?

It is a type of membrane that provides a surface for reactions Signup and view all the answers

Study Notes

Cell Signalling

Cell signalling is the communication between cells, involving a chemical messenger (signal/ligand) released by the signalling cell.
The signal is detected by the responding cell (receptor), triggering intracellular reactions that influence the behaviour of the responding cell.

Tasks of Cell Communication

Signal release: synthesis and excretion of the signalling molecule by the signalling cell.
Signal detection: interaction of signal and receptor.
Signal transduction: translation of detection to changes in cell physiology or gene expression.

Types of Signals

Paracrine signals: act on a local set of cells.
Autocrine signals: act on the secreting cell itself.
Endocrine signals: long-range signals moving through the bloodstream.

Signalling and Control of Gene Expression

Cell-cell signalling can change the repertoire of transcription factors in the responding cell, resulting in different gene expression.
Some signals can form gradients, and cell fate depends on signal concentration.

Signal Entry into the Cell

Two strategies for signal entry:
- The signal can pass through the plasma membrane (e.g., nuclear receptors).
- The signal can activate a membrane receptor (e.g., G protein linked receptors, Serine/threonine kinase receptors).

Nuclear Receptors

Signals are steroids or retinoids.
These signals can pass through the plasma membrane and encounter nuclear receptors in the cytoplasm.
The receptor-ligand complex then enters the nucleus to activate genes.

Signalling through Nuclear Receptors

Nuclear receptors like the glucocorticoid receptor are cytoplasmic proteins.
In their inactive form, they are bound to Hsp chaperones.
Ligand binding releases the Hsp, and the receptor-ligand complex moves to the nucleus to activate the transcription of target genes.

G-Protein Linked Receptors

Transmembrane receptors are linked to a G-protein.
Upon ligand binding, the G protein releases GDP and takes up GTP.
Ga dissociates from Gbg and activates downstream 'second messengers' (e.g., cAMP).
GTP is hydrolyzed to GDP, and Ga reassociates with Gbg.

Serine/Threonine Kinase Receptors

Transmembrane receptors that bind the TGFb family of signals.
Ligand brings together type I and type II receptors.
Type II phosphorylates type I.
Smads become phosphorylated and move into the nucleus to act as transcription factors.

Membrane Selective Permeability

Membranes define a barrier between the inside and outside of a cell, and the inside must interact with the outside.
Examples of selective permeability include:
- Bulk transfer by endo and exocytosis
- Secreting and importing proteins
- Solute molecules, such as ions (e.g. Na+, K+, Cl-) and metabolites (e.g. sugars, amino acids)

Transport Across the Membrane

Simple diffusion:
- Occurs down a concentration gradient towards equilibrium
- Small, uncharged polar molecules can diffuse across the membrane best
Osmosis:
- A special case of simple diffusion where water is diffused
- The plasma membrane is highly permeable to water
Facilitated diffusion:
- Larger and/or polar molecules are helped across the membrane
- Two types of integral membrane proteins involved: carrier proteins and channel proteins
Active transport:
- Moves molecules against a concentration gradient
- Divided into direct active transport (uses ATP hydrolysis) and indirect transport (uses co-transport of a solute favorably down its gradient)

Bulk Transfer

Endo and exocytosis are forms of bulk transfer

Ion Concentrations

The cytosolic pH is maintained at around 7.2 by regulating hydrogen ion concentration
K+ is generally higher intracellular than extracellular
Na+ is generally lower intracellular than extracellular
Direct ATP-powered pumps maintain an ionic gradient across the membrane

Synthesis of the Membrane

Cells synthesise new membranes by expanding existing membranes
Lipid precursors are synthesised in the cytosol and ER
Membrane lipids are distributed to target membranes by vesicles and vesicle-independent mechanisms

Membrane Structure and Composition

Varying lipid composition alters membrane physical properties
Fluidity depends on the ratio of saturated to unsaturated fatty acids and fatty acid tail length
Cholesterol affects fluidity by preventing it from becoming too fluid or too crystalline

Lipid Bilayer

The lipid bilayer is fluid, with lipids able to move laterally but not flip into the opposing layer
Long-chain fatty acids pack against each other, stabilized by van der Waals forces
The longer the chain, the less fluidity the lipid has in the membrane

Leaflets and Flippases

The two layers of the lipid bilayer are referred to as leaflets, which often have different lipid compositions
Moving from one leaflet to another is a slower process than lateral movement within a leaflet, facilitated by integral membrane proteins called flippases

Proteins in the Lipid Bilayer

Proteins float in the lipid bilayer, representing the mosaic part of the fluid mosaic model of membrane structure
There are three main groups of proteins associated with the lipid bilayer: lipid-anchored, peripheral, and integral membrane proteins

Asymmetry of the Lipid Bilayer

The layers of the lipid bilayer can be asymmetric in lipid and protein composition
Some proteins are mobile in their layer, while others are anchored to the cytoskeleton or extracellular matrix

Cell Wall and Cytoskeleton

The cell wall is a rigid structure surrounding plant and some fungal cells, composed of cellulose microfibrils embedded in pectin and hemicellulose
The plasma membrane is associated with the cell wall
The cytoskeleton is an array of filaments beneath the plasma membrane, providing support to the cell

Membrane Functions

Membranes define cells and organelles within cells
Membranes regulate the transport of solutes, detect and transmit electrical and chemical signals, and provide surfaces for reactions

Biomembranes

Biomembranes are composed of lipid bilayers
Lipids found in cell membranes are amphipathic, with a polar head and non-polar tail
Amphipathic lipids spontaneously form lipid bilayers with hydrophilic heads facing the aqueous solution and hydrophobic tails stacking upon themselves

Lipid Classes

Examples of amphipathic membrane lipids include phosphoglycerides, sphingolipids, and cholesterol
Lipids are important for membranes, energy storage, and cell signaling
Phospholipids, glycolipids, and cholesterol are the main classes of membrane lipids

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Description

Learn about the process of cell signalling, including the role of chemical messengers, signal detection, and how it influences cell behaviour.