Cell and Developmental Biology
Term 2
Week 1: Be able to draw lateral connections in the course
Cell biology is the study of processes such as cell growth, division and maintenance. These
processes are controlled by mechanisms. These are regulated systems which can respond to
intracellular and extracellular signals
Year 1 recap:
1. Cytoskeleton: involved in cell growth, division, shape and movement as well as
communication between cells
2. Critical for cellular organisation and polarity
3. Able to do this due to its exible nature and being made of
polymers which are dynamic and are polar
4. Made of actin, microtubules and intermediate laments
5. Flagella and cilia control cell movement. Flagella changes shape to
swim and cilia wafts
6. Microtubules generate these structures. Made from heterodimer
forming polymer. 13 proto laments are arranged in a hollow tube
7. Hollow centre called axenein. this arrangement is important for
movement.
• Dynein is a motor protein which ‘walks’ along the cytoskeleton. Carries the cargo
• Cytoskeletal tracks have a polarity, a positive and minus end
• Kinesin and Dynein motors move along microtubules
• Kinesin generally move toward MT plus end
• Dynein moves toward MT minus end
• Myosin moves along actin
Movement:
1. Axoneme bends
2. Dynein arms connecting microtubule doublets tries to slide
microtubules over one another
3. Dynein tries to walk to minus end but is stopped by linking
proteins
4. Cross linking proteins stop sliding and cause axoneme to
bend
flfi fi
, Intracellular Signalling Part 1
Components of a simple signalling pathway:
1. Extracellular signal molecule
2. Receptor protein which receives the signal
3. Intracellular signalling proteins
4. Intracellular second messenger
5. Response
The cell surface receptor is a single protein made up of three domains being the extracellular
domain, the transmembrane domain and the intracellular domain
Ligand binding - induced conformational changes are important in receptor activation
Intracellular second messengers:
1. Simple molecules that amplify the stimulus
2. The concentration of second messenger increases in the cytosol following cell stimulation and
decrease when the stimulus is removed
3. An increase in the concentration of second messenger activates target proteins so the
stimulus is relayed further in the cell
Intracellular signalling proteins:
1. Rely information from protein to protein to transmit the signal closer to its nal target. They
may also amplify the signal
2. Two examples of mechanisms of information relay between intracellular signalling proteins: 1.
Protein-protein interactions (conformation changes), 2. Protein post-translational
modi cation (protein changes something on another protein, phosphorylation most common)
3. Protein kinases phosphorylate their substrates (add phosphate)
4. Phosphoprotein phosphatases dephosphorylate their substrates
5. Protein kinases and phosphoprotein phosphatases function as molecular switches activating
or deactivating their substrates
6. Phosphorylation can work in both directions where adding a phosphate turns the protein on or
o
To relay the signal into the cell protein kinases can work together working along a phosphorylation
cascade with chains of kinases
An example of signalling pathway is bacterial chemotaxis:
1. Uses an intracellular signalling pathway called the bacterial two component system
2. Allows the bacterium to sense changes in its environment and couple these to changes in its
locomotion
Chemotaxis is the directed motion of an organism toward environmental conditions it deems
attractive and/or away from surroundings it nds repellent
E.coli move using agella:
1. When agella rotate counterclockwise they bundle and E.coli moves forward in a smooth
swimming run
2. In contrast, clockwise rotation disrupts the agellar bundle and the cells tumble
3. Tumbles last only a fraction of a second which is su cient to e ectively randomise the
direction of the next run. By controlling the amount of time in each state
dictates the direction of the bacterium
4. If its not detecting a stimulus it goes into a tumble
5. To move towards an attractant, decrease tumble frequency allowing
more smooth runs
The bacterial agellar motor:
1. The response in this signalling pathway is controlling the direction of
rotation of the agellar motor- so FLiM is the target
2. FLiM is the switch controlling direction of rotation
ff fifl flfl fl fifl ffi ff fi
, At its simplest this system has two components:
1. A histidine protein kinase (HPK) (also called a sensor kinase). In bacterial chemotaxis this is
CheA
2. A response regular (RR). In bacterial chemotaxis this is CHeY
The HPK (sensor kinase) is made up of two domains known as the input domain and the
transmitter domain. The RR is also made up of two domains the Receiver domain and the
output domain
Summary of steps:
1. The stimulus is sensed by the input domain
2. This activates the transmitter domain
3. This has protein kinase activity and phosphorylates itself
4. The phosphoryl group is then transferred to the receiver domain on the RR
5. This then activates the output domain
6. Causing the response
In more detail:
1. HPK input domain senses the stimulus and
2. Activates the transmitter domain which
3. Autophosphorylates on histidine residue, next
4. The phosphoryl group from the phosphohistidine residue is transferred to an aspartate residue
on the receiver domain of the RR (the process is known as phosphorelay), which
5. Induces a conformational change in the output domain of the RR and this
6. Allows it to generate the response
Bacterial agellar motor real life example
Structure of signalling pathway is
important
E.coli encounters an increased concentration of repellent. Escape mechanism requires increased
tumbling
When the phosphorylated CheY protein (CheY-P) interacts with the component of the agellar
motor called FliM, this causes the motor to rotate clockwise. Result: tumbling
fl fl
, Variations of the two component signalling system are also found in other bacterial responses and
in plants (ethylene and cytokinin signalling)
Intracellular signalling Part 2
Cholecystokinin (CKK) signalling and G protein coupled receptors (GPCRs)
CKK-stimulates secretion of a-amylase from the acinar cells of the pancreas:
1. CKK is a polypeptide secreted by the mucosal cells of the duodenum into the bloodstream in
response to the presence of the products of the digestion of foods
2. When CKK reaches the pancreas it binds to a GPCR on the surface of pancreatic acinar cells
3. This causes zymogen granules (containing digestive enzymes a-amylase and the trypsin
precursor) to fuse with the plasma membrane
4. This results in alpha amylase being secreted into the bile duct. This empties into the
duodenum
5. The a-amylase breaks down starches during digestion
• CKK binds to its GPCR (present as a dimer)
• The GPCR is a single polypeptide that criss-
crosses the plasma membrane 7 times
• The activated GPCR then activates the associated
heterotrimeric (3 subunits) G protein, which
activates the e ector protein (in this case
phospholipase C (PLC))
ff
Term 2
Week 1: Be able to draw lateral connections in the course
Cell biology is the study of processes such as cell growth, division and maintenance. These
processes are controlled by mechanisms. These are regulated systems which can respond to
intracellular and extracellular signals
Year 1 recap:
1. Cytoskeleton: involved in cell growth, division, shape and movement as well as
communication between cells
2. Critical for cellular organisation and polarity
3. Able to do this due to its exible nature and being made of
polymers which are dynamic and are polar
4. Made of actin, microtubules and intermediate laments
5. Flagella and cilia control cell movement. Flagella changes shape to
swim and cilia wafts
6. Microtubules generate these structures. Made from heterodimer
forming polymer. 13 proto laments are arranged in a hollow tube
7. Hollow centre called axenein. this arrangement is important for
movement.
• Dynein is a motor protein which ‘walks’ along the cytoskeleton. Carries the cargo
• Cytoskeletal tracks have a polarity, a positive and minus end
• Kinesin and Dynein motors move along microtubules
• Kinesin generally move toward MT plus end
• Dynein moves toward MT minus end
• Myosin moves along actin
Movement:
1. Axoneme bends
2. Dynein arms connecting microtubule doublets tries to slide
microtubules over one another
3. Dynein tries to walk to minus end but is stopped by linking
proteins
4. Cross linking proteins stop sliding and cause axoneme to
bend
flfi fi
, Intracellular Signalling Part 1
Components of a simple signalling pathway:
1. Extracellular signal molecule
2. Receptor protein which receives the signal
3. Intracellular signalling proteins
4. Intracellular second messenger
5. Response
The cell surface receptor is a single protein made up of three domains being the extracellular
domain, the transmembrane domain and the intracellular domain
Ligand binding - induced conformational changes are important in receptor activation
Intracellular second messengers:
1. Simple molecules that amplify the stimulus
2. The concentration of second messenger increases in the cytosol following cell stimulation and
decrease when the stimulus is removed
3. An increase in the concentration of second messenger activates target proteins so the
stimulus is relayed further in the cell
Intracellular signalling proteins:
1. Rely information from protein to protein to transmit the signal closer to its nal target. They
may also amplify the signal
2. Two examples of mechanisms of information relay between intracellular signalling proteins: 1.
Protein-protein interactions (conformation changes), 2. Protein post-translational
modi cation (protein changes something on another protein, phosphorylation most common)
3. Protein kinases phosphorylate their substrates (add phosphate)
4. Phosphoprotein phosphatases dephosphorylate their substrates
5. Protein kinases and phosphoprotein phosphatases function as molecular switches activating
or deactivating their substrates
6. Phosphorylation can work in both directions where adding a phosphate turns the protein on or
o
To relay the signal into the cell protein kinases can work together working along a phosphorylation
cascade with chains of kinases
An example of signalling pathway is bacterial chemotaxis:
1. Uses an intracellular signalling pathway called the bacterial two component system
2. Allows the bacterium to sense changes in its environment and couple these to changes in its
locomotion
Chemotaxis is the directed motion of an organism toward environmental conditions it deems
attractive and/or away from surroundings it nds repellent
E.coli move using agella:
1. When agella rotate counterclockwise they bundle and E.coli moves forward in a smooth
swimming run
2. In contrast, clockwise rotation disrupts the agellar bundle and the cells tumble
3. Tumbles last only a fraction of a second which is su cient to e ectively randomise the
direction of the next run. By controlling the amount of time in each state
dictates the direction of the bacterium
4. If its not detecting a stimulus it goes into a tumble
5. To move towards an attractant, decrease tumble frequency allowing
more smooth runs
The bacterial agellar motor:
1. The response in this signalling pathway is controlling the direction of
rotation of the agellar motor- so FLiM is the target
2. FLiM is the switch controlling direction of rotation
ff fifl flfl fl fifl ffi ff fi
, At its simplest this system has two components:
1. A histidine protein kinase (HPK) (also called a sensor kinase). In bacterial chemotaxis this is
CheA
2. A response regular (RR). In bacterial chemotaxis this is CHeY
The HPK (sensor kinase) is made up of two domains known as the input domain and the
transmitter domain. The RR is also made up of two domains the Receiver domain and the
output domain
Summary of steps:
1. The stimulus is sensed by the input domain
2. This activates the transmitter domain
3. This has protein kinase activity and phosphorylates itself
4. The phosphoryl group is then transferred to the receiver domain on the RR
5. This then activates the output domain
6. Causing the response
In more detail:
1. HPK input domain senses the stimulus and
2. Activates the transmitter domain which
3. Autophosphorylates on histidine residue, next
4. The phosphoryl group from the phosphohistidine residue is transferred to an aspartate residue
on the receiver domain of the RR (the process is known as phosphorelay), which
5. Induces a conformational change in the output domain of the RR and this
6. Allows it to generate the response
Bacterial agellar motor real life example
Structure of signalling pathway is
important
E.coli encounters an increased concentration of repellent. Escape mechanism requires increased
tumbling
When the phosphorylated CheY protein (CheY-P) interacts with the component of the agellar
motor called FliM, this causes the motor to rotate clockwise. Result: tumbling
fl fl
, Variations of the two component signalling system are also found in other bacterial responses and
in plants (ethylene and cytokinin signalling)
Intracellular signalling Part 2
Cholecystokinin (CKK) signalling and G protein coupled receptors (GPCRs)
CKK-stimulates secretion of a-amylase from the acinar cells of the pancreas:
1. CKK is a polypeptide secreted by the mucosal cells of the duodenum into the bloodstream in
response to the presence of the products of the digestion of foods
2. When CKK reaches the pancreas it binds to a GPCR on the surface of pancreatic acinar cells
3. This causes zymogen granules (containing digestive enzymes a-amylase and the trypsin
precursor) to fuse with the plasma membrane
4. This results in alpha amylase being secreted into the bile duct. This empties into the
duodenum
5. The a-amylase breaks down starches during digestion
• CKK binds to its GPCR (present as a dimer)
• The GPCR is a single polypeptide that criss-
crosses the plasma membrane 7 times
• The activated GPCR then activates the associated
heterotrimeric (3 subunits) G protein, which
activates the e ector protein (in this case
phospholipase C (PLC))
ff
