Final Exam Part 4 Flashcards
1
Q
Cell junctions: connections
A
- cells in multicellular organisms need to be stably attached to each other
2
Q
Cell junctions: communication
A
- both multicellular and unicellular organisms need to communicate and coordinate
- theses can be through signalling molecules sent through the environment, or direct cell to cell contact
- Need tissues communicating with other tissues. Cell types communicating with other cell types for activity.
3
Q
Cell junctions in plants
communicating and connecting junctions
A
- One of the roles of the plant cell wall is gluing cells together.
- Communicating junctions – the cell walls are porous – sending vesicles and proteins may never get through the cell wall so the communicating junctions provide passage from one cell to another.
4
Q
Do plants need junctions to join cells together?
A
NO. no connecting junctions in plants.
5
Q
Plasmodesmata
A
- membrane-bound tubes of cytoplasm that penetrate through the plant cell wall.
- cytoplasm of most cells in plants is continuous.
- Tubes of cytoplasm through the plant cell wall. Free movement between the cells.
- channels are about 20-50 micrometres diameter
- each cell has approxiametly 1000 channels
- They has some smooth endoplasmic reticulum running through them call the desmotubule. The er is continuous with each other through the plant so that water soluble molecules can go through and can transport lipid molecules, hydrophobic molecules.
6
Q
Plasmodesmata function
A
- Gene expression tests showed protiens up to 30 kDa and pieces of mRNA move.
- plasmodesmata can close or open under various conditions
- Pieces of mRNA up to 30kDa can move through under certain conditions so open channels can move small molecules through passively. But can also open up to let large molecules through in a very regulated way.
- involved in plant development and cell fate determination
- The neighbouring cells communicate through plasmodesmata to decide what cell type the cells will become,
Misfunction where viruses have worked out how to use plasmodesmata to move from cell to cell. Cell wall – not easy for viruses to move through but can use the channels.
RNA comes out of the cell and copy their RNA and then repackage themselves in the capsids but withint he organism if they want to move between cells the gene codes for a movement protein and this will control the closing and opening of the plasmodesmata and it will make proteins that look like movement proteins and that will let through the mRNA of the plant virus.
7
Q
Do animals need junctions to join cells together?
A
- Yes they do – we have an extracellular matrix – holds cells loosely in place and we have junctions to hold the cells together.
Not all cell types are joined together – red blood cells, white blood cells have no junctions because they move through the bloodstream, don’t want them to be anchored to cells around them
Cells that are important to be junctioned together – skin cells – barrier to the environment – tightly joined together, lining of out digestive tract – making sure we don’t let any bad come into our digestive tract.
8
Q
Communicating and connecting junctions in animals
A
- Connecting junctions – hold the cells together – sealing the cells to their neighbouring cells.
Communicating junctions – allowing certain molecules through to other cells.
9
Q
Tight junctions - animal cells
A
- tight junctions form a continuous seal, to block movement of molecules - lipds and material between cells,
- specific proteins hold cells together forming a water proof layer.
- no movement of molecules
- important in epithelial tissues
- tight junctions demonstrated using tracer molecules in the gut - we don’t want bacteria to go to the blood stream - molecules can only move through, through a cell.
10
Q
Tight junction form the blood brain barrier
A
- the blood brain barrier prevents molecules from passing from the blood into the central nervous system
- tight junctions help to block passage of molecules between the cells.
- One set of nerve cells in the brain – once they die you can’t get them back. Highly regulated
- Hijacks the cell to get rid of tight junctions to get access to the brain binds to receptors on the epithelial cells and communicates to the cell to move the junctions to the top of cell where the pathogens accumulate, once they are gone it leads the pathogens through the blood brain barrier where it can infect.
11
Q
How does the plasmodesmata form?
A
- How does the plasmodesmata form?
- In telophase the cell splits down the new cell wall but wants to leave sections where the plasmodesmata go – the ER is a branching meshwork shape that branches all the way through the cytoplasm.
- Cytokinesis occurs where the new cell wall and plasma membrane are put down – when the cell wall is formed – when it comes to a part of the ER that is where the plasmodesmata will be formed.
- Stops and then continues on the other side – gets built around the ER. These are called primary plasmodesmata – formed during cell division.
- Might decide it wants more junctions and can put a new secondary plasmodesmata in if it wants to.
12
Q
Connecting junction - Adheren junctions
A
- found in most tissue types
- Gap – not a water tight junctions – have proteins protruding – called cadherins Protein connections connect with the actin microfilaments. Form in a way and frequently used in coordinated movements of cells – oesophagus and the gut to move food.
A key gene that is missing or mutated it cadherins. Why do cancers have mutated cadherins – migration – if the cell can breakaway and move to the bloodstream and spread around the body – losses anchoring junctions so can move around the body.
13
Q
Communicating junctions in animals: gap junctions
A
- Pores that connect cytoplasm of adjacent cells
- similar in function to plasmodesmata
- found in most animal tissues
- Direction connections through neighbouring cells to allow passage of molecules. For segments they are pasted together full of gap junctions that are structures crossing between the two membranes.
14
Q
Structure of gap junctions
A
- formed by the protein connexin
- 6 connexxin proteins form a pore
- pores from adjacent cells align to make the gap junctions
- Made of proteins. They form a ring shape with a channel where the molecules pass through. Forms a pore and then the neighbouring cell will connect the pores together. From the cytoplasm of one to another cell. 1 ½ nanometres wide so only small molecules can go through.
15
Q
Function of gap junctions
A
- To know how big the pores are we can inject a dye molecule into one and see if it’s able to move into the neighbouring cell. They find that molecular weights of 100-1000 they can but large molecules they can pass through. Proteins can’t pass through the gap junctions – they don’t widen but they can close – immune comprimisation etc.
the gap junctions don’t stop the calcium from spreading into all the other cells so that they can contract at the same time – one nerve cell connected to a bunch of muscle cells – communicates to the muscles to contract and release calcium into the cell. Don’t have to individually send a signal to each cell.
16
Q
Communicating junctions in animal cells - tunnelling nanotubes
A
- membrane tubules that contain a thin tube of cytoplasm
- can connect cells over long distances
- tubules are transient, lating minutes to several hours
- implicated in early development of embyronic tissues
- can form between two cells a large distance away from each other, narrow compared to a cell, allow for proteins and RNA and small organelles can pass. Not permanent – transient – formed and then disassembled. Important for development of embryonic tissue.
- Contain actin microfilaments actively moving molecules through the junctions. Vesicles pulled along the microfilaments.
- proteins, membrane lipids, vesicles and whole organelles can move between cells.
17
Q
What can humans sense?
A
- We can sense other things in our environment – temperature, balance, body position, pain, vibration, pressure.
- sight, taste, sound, smell, touch
18
Q
What don’t humans detect?
A
- humans don’t detect electrical or magentic signals
- humans don’t detect ultrasound or UV
- bats can take an echo and generate spatial information
- birds can sense a magnetic signal and navigate accordingly
- plants can sense gravity and grow directionally
19
Q
Signalling at a cellular level - 3 processes
A
- signal reception
- signal transduction
- signal response
20
Q
What can cells sense?
A
- multicellular organisms sense signals - touch, sound, light etc. using specialised signals
- cells also sense signals but using proteins called receptors.
- Cells can sense:
- Temperature – receptors called thermoreceptors that can feel the temperature
- Some cells have photoreceptors detecting photons which can detect light. Also found in the skin cells – to detect how much light to produce more melanin.
- Receptors for mechanical receptors – mechanoreceptors.
- Cells cant detect chemical signals – called chemoreceptors.
21
Q
cellular signalling
A
- signal - a nutrient is detected by a receptor. Receptors In the membrane and there are molecules in the environment that the cell has receptors for – nutrient, amino acid or sugar – something to consume to get energy. The nutrient is detected by a receptor – receiving of the signal,
- the signal is relayed (transduced) protein can’t respond to the signal it will bind to the signal, pass on the signal through the cell through the different molecules, and will finally go to part of the cell that can respond to the signal – for example the flagella – to tell it to continue to go int that direction there’s food that way.
If it’s a toxin – the signal will be passed through the cell in a different way and end up at the flagella, it will tell the motor to turn around and go the opposite way.
- response - keep swimming in that direction
22
Q
Touching a hot stove
A
The ell that detects the signal can be a long way form the one responding to it – touching a hot stove the first step -t thermoreceptors int eh skin receiving the signal and the cells can’t respond directly to the signal so instead the signal is sent to the nervous system in the spine and then to the muscle cells in the arm and then the muscle cells responds to contract to move away from the heat.
- signal (heat) is detected by thermoreceptros in the skin
- signal is relayed (transduced) as an electrical signal through the spine
- muscles respond mechanically to the signal by contracting
23
Q
Kinds of intracellular signalling: direct cell to cell signalling
A
Signalling between two cells
- direct cell to cell signalling. Signal only to neighbouring cells. Direct cell to cell signalling – cell junctions, sends signal molecules to the neighbouring cells.
- cell-cell recognition.
- where the signal molecule is displayed don the outside of the cell and its received by the cell which has receptors matching to the signal. This is involved in embryonic tissue. Some cells do antigen presentation where they find bacterium to viruses and break it into small pieces and send a then they send a piece of the virus to the surface of the cells where they display it and then another immune cell will receive/detect the signal and that will lead to a response switching on an inflammatory response for example.
24
Q
Kinds of signalling: local signalling
A
Sometimes cells need to be sent further – by local signalling. Cell signalling to other cells in the environment.
- paracrine signalling. Paracrine signalling – cells signalling to other cells within the same tissue. Might be a liver cell with liver damage and a signal cell might communicate to its neighbouring cells to switch on cell division to make more liver cells to replace the missing part of the liver. May be sent into the plasma membrane by ion channels by transporters or in this case by exocytosis – some vesicles can contain molecules and then fuse with the plasm membrane and spill out their contents.
- synaptic signalling. only found in nerve cells – long distance – on a molecular level the are sent very short distances. Not directly touching – small gap called the synapse and across the nerve cells a signal will be sent and the signal is sent through a nerve pathway. The nerve cell sending the signal will have an electrical signal that’s transmitted along the nerve that electrical signal will signal to the vesicles containing neurotransmitters (small molecules that communicate between nerve cells) the electrical signal will cause the vesicles to go to the plasma membrane at the synapses to spill out the contents and will have a gap to diffuse across to the other cell, communicating to the other cell and open ion channels – calcium or iron causing an electrical signal in that cell.
25
Kinds of signalling: **long distance signalling**
* called endocrine signalling
* mediated by hormones
## Footnote
Longest distance signalling – endocrine signalling from one tissue to another tissue generally by the bloodstream. Mediated by hormone molecules.
Produces adrenaline which will communicate the cells to break down glycogen to glucose so she has energy immediately so she can run away.
The person is growing and other specialised cell in the body will secrete growth hormones which will go through the blood and will signal to specific organs and tissue types to tell them to keep dividing we aren’t big enough yet.
Mediated by hormones – the cells that send out the signal are specialised endocrine cells found in special organs like glands.
* Ethelene – gaseous molecule used for signalling – plant hormone. The signals for fruit to ripen, banana with different amounts of ethylene gas – the gas can be released to the environment and can signal between plants. Plants can send chemical signals between individuals in a species – the longest distance that we have.
26
Signalling molecules can be:
* gaseous, water-soluble, lipid-soluble
* small molecules or proteins
* Can be gaseous, small molecules – chemicals, most cases are water soluble – transported through the blood or watery media, quite hydrophobic and lipid soluble – steroid molecules and sez hormones. Can be proteins – sent out by one cell and travels to a neighbouring cell. Insulin is a signalling molecule – involved in metabolism and is a protein.
27
Signal reception
binding of a signal to a receptor protein
When a signal reaches the target cell, the signal will get received, protein is found in the plasma membrane which receives the signal.
28
Signal transduction
signal transduction = relay of molecules within cell
The protein will send on signal activator pathway inside the cytoplasm of the cell to relays the signal through the cytoplasm
relay moelcules in a signal transduction pathway
29
Signal transduction pathway and response
Which leads to a response – activates a signal to switch on a metabolic pathway or cell division if it's a growth hormone.
Called this the signal transduction pathway – how the message is sent through a cell to lead to a response.
30
Reception of signals
* A signalling molecule binds to a receptor and it changes sjape
* receptors are specigic for certian signals
* so that only the correct cells respond
* so that the cells don't respind to the wrong signals
* a ligand is the specific signalling molecule that binds to a specific receptor.
* How cells can receive signals – reception of signal sis done by proteins, the receptors are always proteins. Receptors are specific for certain signals. The biding of the molecule cause a change in the receptor allowing the signal to be passed on into the cell.
When the signal binds to the receptor this is the lock and key way where the signal is the key and has a specific shape and will bind to a specific receptor with a matching shape. Happens so that cells respond to the correct signal.
The signal molecule is the ligand – molecule that is specific for a receptor, fits the receptor perfectly to switch on the receptor.
31
Receptors
Receptors bind to the signal molecule – in a lock and key – specific.
Sit in the plasma membrane – cell-surface receptor protein – soluble hydrophilic molecules trying to get into the cell, can’t get in by themselves..
* cell surface receptors
* Ligand-gated ion channel receptrs
* G protein-coupled receptors
* enzyme coupled receptors
* cytoplasmic receptors
* steroid receptors
Steroid signal molecules can pass into the cell because they are small and hydrophobic, so the receptors don't need to be in the plasma membrane they can just wait in the cytoplasm of the cell.
32
Ligand gated ion channel receptors
* system involves signal molecule, gated ion channel
* when the signalling molecule binds to the channel it opens and allows the flow of specific ions.
* it is critical that the gate returns to the closed position at the end of the signal.
* Ion channels – proteins in the plasma membrane that allow ions like calcium, sodium or magnesium to pass into the cell. In the state when there is no signal the ion channel will be closed.
* When the signalling molecule binds to the protein it changes shape of the protein and allows ions to pass through to the cell. The ions will mediate the next step in the signalling pathway. Has to be a mechanism to switch off the pathway. The ligand is loosely bound – when the signalling molecule isn’t being actively produced anymore it will float away and the receptor will close
33
Ligand-gated ion channel receptors: **nerve cell signalling**
* example chemical synapses
* ligand: nuerotransmitter - dopamine acelty choline
* receptor - transmitter gated ion channel
* effect: activation of the next nerve cell by ions entering the cell.
* Nerve cell signalling – nerve cells signal to each other not directly, an electro signal is sent along the nerve cell and this is ions – sodium or calcium – something with positive charge in the cell. Even when the cell is switched on it will have vesicles containing signal molecules containing the neurotransmitter – when the electrical signal reaches the vesicles it will stimulate them to go fuse with membrane and spill out their content, the contents are neurotransmitter molecules that diffuse a short way across the synaptic cleft and bind to the receptor on the other nerve cell, causing a conformational change in that ion channel causing it open up and allow ions to go through.
34
G protien coupled receptors - GPCRs
* G protein receptors are singla receptors found associated with the plasma membrane
* found in all eukaryotes
* Taste and smell – has a GPCR that's specific for it. They have 7 alpha helices with loops sticking out where the ligand binds. The loops inside the cell pass on the signal inside the cell to a protein called the G protein.
* GPCR sits in the plasma membrane, nearby is a G protein, and the protein that's the next step – usually some kind of enzyme.
* System involves - signal molecule (ligand), G-protein coupled receptor, G protein, enzyme
* G protein – means it binds GTP. When the G protein binds to GTP its in an ‘on’ state. At some point one of the phosphates is hydrolysed off spontaneously and goes into a GDP bound state – in an off state. Protein that can be switched on and off.
35
G protein coupled receptors - how it works
* the signal molecule binds to the receptor
* receptor shape changes to allow G-protein to bind
* G protein is activated by switching GDP for GTP.
* G protein in bound to GDP – off, and then the signalling molecule comes along and binds to the receptor and activates it – the signal molecule causes a change in shape of the receptor and this allows the G protein to bind and lose its GDP and have GTP bound instead – active state. once activated it floats off the receptor and will activate the next protein in the signal transduction pathway – usually an enzyme.
* activated G protein than activates an enzyme that triggers a cellular response
* G protein deactivated by hydrolysis of GTP to GDP
* signalling system turned off and reset.
* We need to be able to switch it off again.
The signal molecule will float off and the GTP will hydrolyse to GDP and the G protein won’t be active anymore and cant switch on anymore – can only do this once. System returns to an off state.
36
G protein coupled receptors - examples
* Adrenaline receptor
* 7 helices. Form a bundle, in the middle the signal molecule binds.
* Rhodopsin - photoreceptor
* Sight – photoreceptor – molecule bound permanently. The signal is a photon of light.
37
Steroid receptors
* examples of steroids - sex hormones oestrogen, progesterone and testostrone
* glucocorticoids: regulate glucose metabolism
* plants and fungi also have steroids
* lipid soluble molecules
* can diffuse through the plasma membrane, can be detected within the cytoplasm
38
Steroid receptors: how do they work?
* steroids such as testosterone travel thorughout the body
* diffuse through the plasma membrane in all cells.
* specific cells have receptors and in these, testosterone bidns receptors in cytoplasm
* receptors are then moved to the nuclues where they bind to DNA
* mRNA synthesis is initiated and new proteins synthesised.
39
Signal transduction: second messengers or signalling proteins
* signal transduction pathways can involve only proteins - eg. phosphorylation cascades or they might involve second messengers
* why have multiple steps?
* amplification
* control
* multiple responses
40
Second messengers
* Second messengers – molecules that pass on the signal.
* the first messenger - extra cellular signalling molecule.
* The secon messenger is produced or activated within the cell following receptor activation. the second messenger carriers the signal into the cell
* second messengers are small signalling molecules produced within cells. they transduce external signals into internal responses.
* examples of signal transduction molecules - a small molecule - calcium, a protein - kinase.
41
Second messenger: **calcium**
* Calcium concentrations low inside the cell, the cells is using a lot of ATP to pump ions to maintain ion gradients, also calcium is pumped into the ER and the mitochondria.
* calcium needs to be continually pumped from the cytoplasm.
* calcium concentrations are high in the extracellular space.
* calcium concentrations in certain organelles are also high - mitochondria and endoplasmic reticulum
**how does calcium act as a second messenger?**
* by causing direct effects such as muscle contraction and nuerotransmitter release
* by binding to specific proteins such as calmodulin which then activate further proteins
* calcium triggers the release of vesicles.
42
Second messenger: **calcium in the muscle**
* in a relaxed muscle the thick and thing filaments are widely spaced.
* a calcium trigger and ATP results in muscle contraction
* calcium triggers the movement of tropomyosin filament
* Blue circles are actin molecules. The black is the binding site of myosin. In the absence of myosin the sites are covered by tropomyosin – binds across to stop muscle contractions. Another protein that sits on top is called troponin.
When the muscle fibre is activated by a nerve, the nerve causes calcium to food into the cell (by the ion channels), the calcium will bind to the troponin molecule causing a conformational change, and as it swings down it pulls the tropomyosin with it, the sites are blocked so they are free so myosin can start to bind to the actin and pull it along as its binding ATP.
* calcium binds to specific proteins sych as calmodulin which becomes active when it changes shape and binds to other proteins
* Calmodulin – causes a conformational change where they wrap around each other and bind to a certain sequences to activate another step.
To switch off a calcium mediated pathway you pump the ions back into the cell or back into the ER or mitochondria.
43
Transduction - phosphorylation cascades
* phosphorylation - addition of a phosphate group
* kinase - an enzyme that adds a phosphate group
* phosphorylation acts as an on/off switch to a protein.
* Proteins – kinases – signal transduction molecule. Enzyme – add a phosphate group to another protein – phosphorylation. Take the phosphate group from ATP, and covalently put the phosphate onto the side chain of the protein and it will release ADP. The phosphate group is commonly used as an on/off switch. In some cases the addition of a phosphate group can switch off a protein or it can switch a protein on.
* The phosphate has a negative charge so it makes the protein more negatively charged – maybe it will change the conformation of the protein.
* These are phosphatases that take off the phosphate group.
44
Transduction - how phosphorylation cascades work
* Phosphorylation cascade – multiple kinases in a row in a signalling pathway.
The signalling molecule binds to the receptor,
And then it activates a relay molecule, and that will switch on a kinase, each kinase is specific for a protein in the cell, and this kinase is specific for another kinase, it puts a phosphate group onto a another kinase – switched on, that then finds its target which gets switched on – another kinase, the kinase binds to ATP itself and it takes the phosphate of ATP and puts the phosphate onto its target. The last kinase switches on an active protein to drive some cellular response.
There are multi[le steps – is amplification. Kinase is an enzyme – biological catalyst – not used up in a reaction, one kinase molecule can go on and go on and activate lots of other kinases, when we have a large number of steps we can get a huge amplification of the signal, getting thousands of molecules activated which are quickly spread through a cell and amplify the signal – important when we want a strong response. Adrenaline.
45
Transduction amplification
* amplification allows a small initial signal to be massively increased.
* example: one molecule of epinephrine binds to a G protein coupled receptor
* Epinephrine – adrenaline. 10 fold amplification each time. The singla molecule binding is amplified to 100 million molecules of glucose-1-phosphate.
46
Turning on and off the signal
* receptors are turned on (ligand binding) and off (ligand release).
* second messengers can be turned on and off
* kinases can be turned on adn off (addition of phosphate group)
* We don't the processes running forever so the switches need to have an on and off switch.
* Second messengers – calcium
* Phosphatases – removes a phosphate group.
47
Themes in the signal response
* receptor changes shaped when ligand binds - casuing the signal to get passed on into the cell.
* receptor is switched off by ligand dissociation
* protein switches - GTP/GDP and phosphorylation/dephosphorylation
* small molecules (second messengers) activate other proteins
48
Response: **altered metabolism**
* Altered metabolism – altering the activity of enzymes in the cell. Adrenalin – does multiple things in different organs – one thing it does is switch on enzymes to break down glycogen to produce glucose. Signal stimulating a metabolic pathway.
* Insulin – will lead to multiple responses. Glucose uptake, glycogen synthesis, block production of glucose, anti-lipolysis.
49
Response: **altered gene expression**
* altered gene expression
* growth factors
* remember steroid receptors
* Altered gene expression
* The protein we want to activate is not switched on – go into the nucleus and switch on the gene that will do the response.
* Example: growth factors – signal to a cell to tell it to go into the cell cycle to tell it to divide. To divide – it has to do a lot of things get bigger etc. needs lots of genes to be switched on, lots of processes switched on.
* The signalling leads to a protein that will go into he nucleus – transcription factors (proteins that switch genes on and off) – bind to DNA and they will make the gene be transcribed and translated into protein.
* Steroid receptors – also often transcription factors. Steroids are hydrophobic small molecules – can pass through the plasma membrane without binding to a receptor – the receptor is in the cytoplasm and when they bind they move into the nucleus and bind DNA and switch on certain genes.
50
Response: **altered cell movement or shape**
* for example activation of actin binding proteins and changes to the cytoskeleton
* involved in muscle contraction, phagocytosis, wound healing, embryo development
* The cytoskeleton – actin microfilaments and microtubules.
Leads to altered cell movement – tell the cell to move somewhere in the body, change the shape of the cell.
Examples – muscle contraction, wound healing – cut open a blood vessels cells will detect them cut and signal to other cells to move into that region to close off the wound – called fibroblasts – cells that are specialised in producing extracellular matrix. Ideal for quickly healing a wound. Physically move through the blood vessels to the damage and then produce collagen and extracellular matrix.
Movement of the cell – embryo development – movement of cells in to the right place where they need to be, flat layer of cells forming the digestive tracts etc. don by the cytoskeleton to form a certain shape. Done through signalling processes outside the cells.
Phagocytosis – process of taking up material outside the cell, specialised kind of endocytosis – cell
51
Response: **altered cell movement or shape - macrophage**
* Macrophage – the signal is a pathogen. This is coated in antibodies recognising it as a dangerous pathogen. On the macrophage are receptors recognising the antibodies bound to a pathogen, which passes a signal into the cell to the actin microfilaments to gather around the site and to branch out and wrap around the particle and swallow it into the cell. The effector molecule is a cytoskeleton element.
52
slowest and fastest: altered metabolis, altered gene expression, altered cell movement or shape
* Some responses are quick and some are slow.
The slowest – altered gene expression. Turing on gene expression is slow.
Fast – altered metabolism, altered cell movement or shape – the target molecules/the effectors are already present in the cytoplasm waiting to be switched on.
53
Response: **timing**
* If we have a signal molecule binding to a receptor on a cell may lead to altered proteins function of protein already within the cytoplasm of the cell – if they are already there it will be a quick process.
* If the protein isn’t expressed or present the signal has to pass the nuclear envelope into the nucleus and activate RNA polymerase to transcribe the gene, the mRNA has to be processed 0 out of the nucleus and find a ribosome to be translates – these steps take quite some time – takes 20 minutes before you have a signal binding to the cell before you have a gene expressed.
* Example fast – adrenaline
Example slow – growth factors. Stimulate cell division and growth – want to be careful about this so it goes slowly.
