BIOC212FINAL Flashcards
What are the pros and cons of the confocal microscopy?
Pros:
1) 3-dimensional rendering of cells
2) live cell imaging
3) multiple snapshots per second
Cons:
1) Limitation of specificity markers
2) “co-localization” only implies co-function
3) limited by resolution ability, wavelength of light is larger than that of the protein and the wavelengths can be bleached which causes overexposure.
Define resolution
Ability to see if there are two separate objects. In electron microscopy, provides means to evaluate quality of macromolecular structures computed from sets of their two-dimensional line projections.
How does bacteria generated energy vs animals/plants?
- Bacteria uses their 2 membranes (inner and outer), and create a potential that separates and concentrates things to create a gradient. Either PE or KE to generate chemical energy source.
- Animals use specialized organelle mitochondrion and plants use chloroplasts. Need to be multiple membranes.
What is the difference between respiration and photosynthesis?
In respiration, you take energy from food and you derive electrons from it. You pump the protons into separate compartments and create a gradient.
Photosynthesis is the reverse. You take energy from sunlight and create an electrochemical gradient.
What is the process of respiration in the mitochondrion?
At the mitochondrion, there is fat, carbohydrate and protein degradation. Once it is degraded, we can create a substrate and break it down further. This is done in the citric acid cycle, releasing C02. Then Redox reactions take place, and 2 electrons release, then NADH, NAD+ and 2 electrons are in the electron transfer chain. H+ gets pumped and oxygen is the terminal acceptor as well as H20 being a product of respiration.
What is the process of respiration in the chloroplast?
The opposite takes place than what is happening in the mitochondrion. CO2 and H20 is coming in, and glucose (carbohydrate molecules) and 02 is coming out. This is the product of the photosynthesis - the purpose is to fix carbons and make sugars.
Where are two places that respiration happens more?
1) Cardiac muscle - needs energy all of the time therefore it is filled with many mitochondria.
2) Sperm tail (lots of mitochondria there)
What is cristae?
- Inner membrane of mitochondria folds up into little loops called cristae. Important regions with a lot happening. They have a lot of surface area for chemical reactions to take place on.
Why do mitochondria undergo fission and fusion events?
1) If they undergo oxidative stress and are not doing well, they need fission events to throw out all the garbage in one part of the mitochondria, then they can cut it out and bring to lysosome for degradation (autophagy)
2) Sometimes they fuse, during the cell cycle this happens many times, they want to share recourses between mitochondria and there are specific proteins needed in this process.
What is an example of mitochondrion undergoing fission events?
- Protein (Dynamin - GTP-dependent protein) that forms polymer that wraps around the centre of mitochondria, eventually constricts it so it pops apart. This is GTP dependent constriction of microtubules mediated by a dynamin protein.
What is an example of mitochondrion undergoing fusion events?
- Myocytes, fuse to form long muscle fibres of arms and legs. They need to get rid of nuclei, mitochondria also needs to fuse.
Define NADH.
NADH is an electron carrier, it donates electrons to the electron transport chain. Passed through complexes, pump 1 protein each time from matrix to inter-membrane space.
Use protons to derive formation of ATP.
- From NADH, donate electrons to transport chain, passes complex 2 and goes from 1 –> 3 –> 4.
What are ketone bodies?
They are a carbon source used if you are in a starved state, diabetes uses this, it is for energy for your brain, and RBC’s.
What is the process of generating ATP by eating food?
- There are food derived molecules from cytosol: amino acids, fatty acids, pyruvate, ketone bodies.
- They go into the mitochondrial matrix where the main business is happening and derive Acetyl CoA.
- Then they get put into the citric acid cycle.
- There is an enzyme called citrate synthase that combines with acetyl coA (2 carbons) and oxaloacetate (4 carbons). Now we have a 6 carbon compound, citrate.
- Citrate undergoes enzymatic steps, looses 2 carbons (regenerate oxaloacetate - cycle). 2 carbons that came in as acetyl CoA come out as C02.
- Generated 1 GTP, 2 NADH, 1 FADH2,
- For every NADH, we have 3 ATP< every FADH2 we have 2 ATP.
Is Acetyl CoA glucogenic?
It is not glucogenic, it cannot be turned back into glucose. There has been a mechanism developed to maximize the energy, and in return it sacrifices the ability to regenerate as a result.
How is pyruvate regulated and what happens if it is degenerate?
- Pyruvate is regulated by many enzymes: mitochondria pyruvate carrier, pyruvate dehydrogenase, and pyruvate carboxylase.
- If it is degenerated, there is a rare disorder that will happen so it is important to keep this regulated.
What are 7 important functions the mitochondria has?
1) Production of ATP
- oxidative phosphorylation in mitochondria, produces most of the ATP used by eukaryotic cells.
2) Regeneration of NAD+
- NAD+ is required for glycolysis and other reactions under aerobic conditions, NAD+ is regulated when NADH donates electrons via oxygen via the respiratory chain.
3) Provision of precursors for biosynthesis of amino acids, nucleotides, fatty acids.
4) Participation of synthesis of heme and iron-sulfer clusters.
- Plays central role in respiration and other cellular processes.
5) Cell signalling
- Buffer [Ca2+], ion that plays important role (i.e. muscle contraction)
6) Generation of reactive oxygen species.
- They could damage macromolecules, but also involved in signalling.
7) Regulation of apoptosis.
- Molecules released from mitochondria trigger a proteolytic cascade that leads to cell death.
- If the telomere is too short.
- In retina, when you wake up there is a layer of apoptosis, thats why you can’t see straight when you wake up, fresh cells are coming in.
- During development, looks like 5 fingers, there is innervation and skin is removed.
What is an example of a specialized phospholipid?
Cardiolipin
- It takes a much broader position, usually cylinder shaped. This is because two phospholipids joined via the second glycerol, bigger tail than head group, so it spreads out.
- Actively binds to one or more complex of the electron transport chain, if cardiolipin is not there, they do not stick together and you will not get proper electron transport chain.
- Essential for efficient mitochondrial electron transport function.
What is the function of ubiquinone and cytochrome C?
They are transport electrons.
Why is glycerol a useful molecule?
It is useful because it has 3 hands.
- 3 hydroxyls that can attach to 3 different things. You can make triglyceride, phospholipids (useful for making membranes)
What is the difference in electron transport chain in terms of utilizing energy vs explosive combustion?
- If we took hydrogen and oxygen and provides a spark, there would be an explosion, all the energy that was contained in them was expended at once. We can use that to generate energy but it is hard to trap, therefore a lot of this energy is not utilized.
- With our carbon sources, instead of letting it all explode and burn instantly, we trap it into ATP, and we do this w/ Redox Pairs. There needs to be an electron donor and acceptor, otherwise the electrons cannot be passes. The main way to do this is to create a proton-motive force. —> When we pass electrons, we move proton from matrix to inter-membrane space, concentrate them to create a gradient, and harness that to form ATP.
What is the function of Iron-Sulphur clusters?
Carry electrons down the electron transport chain, attached to iron at the middle of the cluster.
Describe (diagram) of the electron transport chain:
1) Complex 1
- NADH donates electrons (2), within complex 1, one proton is pumped out to inter-mitochondrial space.
- Bypasses complex 2, and goes through ubiquinone and citric acid cycle.
2) Passed to complex 3. Passes cytochrome C and complex 4.
- each time it goes through complex it pumps out 1 proton.
- Electron finally given up by cytochrome c to where electron terminal acceptor = oxygen and generates water.
Describe the fate of the breakdown of one molecule of glucose
- Glucose broken to pyruvate, to acetyl CoA, into citric acid cycle, then electrons transported, oxygen into water and the carbons make C02.
What is the difference between NADH and NADH2?
- NAD+ is NADH (It accepts two electrons and one proton)
- NAD2 is used to account for the second hydrogen that gets removed from the substrate being oxidized.
When does FADH2 come in?
FADH2 comes in from the citric acid cycle, it does not join/share the electrons at complex I, it bypasses and shares w/ complex 2, then goes to complex 3, pumps proteins, at complex 4, gets 6 protons and can get 2 ATP from this. (bypass makes it less)
What is the net product from oxidation of one molecule of glucose?
(cytosol - glycolysis)
1 glucose –> 2 pyruvate + 2 NADH + 2 ATP
What is the net product from mitochondrion (pyruvate dehydrogenase and citric acid cycle)
2 pyruvate —> 8 NADH + 2FADH2 + 2ATP
What is the net product from oxidation of one molecule of Palmitoyl CoA (activated form of palmitate, a fatty acid)
1 palmitoyl coA –> 31 NADH + 15 FADH2 + 8 GTP
Describe Glycolysis
- It is the breakdown of glucose to pyruvate.
What is the concentration of glucose inside the cell?
[glucose] is almost zero. It almost immediately gets transferred to glucose 6 phosphate. This is helpful to trap glucose into the cell.
What is an example of substrate level phosphorylation?
- Add two phosphate groups, break fructose up into two carbon free carbons, add NADH, get pyruvate. Results in 3 carbons, and you get 2 NADh and 2 ATP.
- directly take phosphate off can now add phosphate back to ADP to make ATP.
- anaerobic, most steps are reversible, except for hexokinase.
- Now pyruvate is a 3 carbon compound, this only goes one way. Commit carbon that comes from glucose to citric acid cycle, loose C02, 3 carbon becomes 2 carbon compound.
Conversion of PEP to pyruvate in glycolysis. The enzyme, pyruvate kinase catalyses the transfer of a phosphate group from PEP to ADP, producing pyruvate and ATP as products. This reaction involves substrate PEP donating phosphate group directly to ADP to form ATP, without the need for electron transport or protein gradient.
Define allosteric
Product binds to enzyme and causes activity, which is not the binding site.
What is the rate limiting step?
This is when Acetyl CoA is in the citric acid cycle. We need to regulate this step, it is important because sometimes we might want to stop the process.
ex) Do not want to get rid of all the pyruvate so we turn some of it into Acetyl CoA.
ex) do not turn into glucose, we can store as fatty acid and use if we need it, this is importance for the brain and RBC’s.
What is the function of Insulin?
- Strongly controls pyruvate dehydrogenase (PDH), you have tons of glucose but you need to pump it down.
- Can store it as glucagon (happens mostly in muscle and liver)
- when you start to loose weight, glycogen will go first, has water that holds it there, so you will loose water weight first.
- Glucagon –> increased levels of glucose.
What is Rubisco?
Rubisco is very unique and fixes carbon, adds carbon dioxide and puts it into a molecule that we can degenerate ATP from and put it into storage etc. (valuable)
- enzyme present in plant chloroplasts.
What is a ligand?
It is an extracellular signalling molecule which is what binds to the receptor on the plasma membrane outside of the cell.
How do we send signals across the membrane? What are a few exmaples.
- Signal transduction cascade (intra-cellular signalling molecules), then you get different effector proteins and perform specific functions.
ex.) metabolic enzyme - altered metabolism
ex.) transcriptional regulatory protein - altere gene expression
ex.) Cytoskeletal protein - alter shape or movement.
What are four different kinds of signalling?
1) Contact-dependent (one cell physically interacts w/ another cell)
2) Paracrine (cells release a signalling molecule that attack/go to the target cells around it)
3) Synaptic (never cells are unique cells. They are very long, send signals to the axon to the dendrite. Message from previous neuron to other end of the body, where it reaches the neurotransmitter to send message at synapse)
4) Endocrine (signal goes through blood, from kidney to liver, send a hormone to send the message, communicate either locally at paracrine level or far away at endocrine level)
What are two types of receptors?
1) Cell surface receptors (signals)
- Cell surface ligands that bind ligands, most cases they are hydrophilic molecules, they cannot do it themselves
2) Intracellular receptors (carrier protein)
- Small hydrophobic molecules, it can go right through membrane, sometimes with help of a transporter, they can get in and bind to receptor inside, they are soluble.
- Applies to steroid hormones, receptor is also a transcription factor.
Different cells react to different signals, different cells types will react differently to the same signal. What is an example of this happening on the same cell? If these don’t happen, what is the consequence?
1) Ligands bind to respective receptor, promoting survival of the cell.
2) Ligands bind to respective receptor, making the cell grow and divide.
3) ligands bind to respective receptor, making the cell differentiate.
- If this does not happen, and they are lacking specific signals, then the cell will go through apoptosis.
Acetylcholine is a signalling molecule. What are some examples of its function?
- It has an acetyl group at the bottom, top part is a choline, and it has a positive charge quaternary amine.
- heart pacemaker cell (binds to the receptor and helps stimulate heartbeat)
- Salivary gland cell (helps secrete saliva)
- Skeletal muscle cell (causes contraction)
- same molecule in different cells/locations causing different results.
What is the function of ion-channel coupled receptors?
- pore that can help bring ions into the cell
- to concentrate them, it depends on which ion you are talking about, often done in combination of other molecules or with help of ATP.
What are G-Protein Coupled Receptors?
- 7 transmembrane domain G protein
- When it is activated by a binding signalling molecule, it recruits three subunits, alpha, beta, gamma.
- They bind and get activated, the signalling event depends on which G-protein you are talking about.
What are enzyme-coupled receptors?
- Two receptors that are separate and when they bind ligand, they homodimerize.
- In the intracellular area, they have enzymatic activity, when they come in contact with its buddy, it transphosphorylates, both activated, and another signalling event can occur downstream.
- Binding of ligand promotes this and binds them together.
- They tend to be in solitary/inactive, by binding the ligand it brings together the two monomers and once together, two active enzymatic catalytic domains that can act on eachother.
- Kinase can phosphorylate together and promote signalling.
What are GTP binding proteins?
- Small molecule GTP binding proteins or small molecule GTPase.
- Turn off by GEF and turn on by GAP.
What are two types of signalling?
1) Signalling by phosphorylation
- turned on by protein kinase, turned off by protein phosphotase
- phosphorylation can either activate or inactive a protein
2) Signalling by GTP protein
a) monomeric GTPase determines turning GTP binding proteins on or off by GAP/GEF.
What happens if you do not have he GDP/GTP GAP/GEF cycle?
Yo can have mutations, this cycle needs to be regulated and you need to have control.
What are some effects that the signalling can have?
- Signal coming down from membrane, activation of protein kinase, inactivation which also effects cascade of proteins, which then affects gene expression,
- Can also directly phosphorylate an inhibitor protein which regulates transcription factors, that go promote transcription.
What is a Scaffold Protein?
-Proteins are not able to create actions themselves, bring lots of proteins together in one place by recruiting them.
- This is done by activating a receptor with a ligand, then many proteins bind.
This is a signalling complex.
What are adaptor proteins?
They are an intermediate - between receptors and what is downstream of it, so they have to connect.
Different domains bind different things, each has its own pH domain to recruit its own protein, to create a critical mass and to bring proteins together to promote signalling events.
What are two types of domains?
1) PTB domains - bind tyrosines that are phosphorylated but in specific motifs. PTB domain containing proteins can bind to phosphotyrosine on the signalling receptor. (NPX motif, asparagine proline, tyrosine, tyrosine gets phosphorylated)
2) pH domain - domain binds all different kinds of lipids that have diff pH domains.
ex. SH2 domain –> bind to proline rich regions. (happens when we need to recruit them)
What is Protein MCAK?
It is an example of clustering receptors together to get important signalling happening.
Two downstream signals are coming together to either inactive or activate.
Wha is cyclic AMP?
It is important to control it.
It is an important signalling molecule.
- You can destroy it with phosphodiesterase
- temporarily make it/destroy it, once you get the desired number of signalling events, you kill it and it is important that we turn it off.
Describing an example of signalling.
1) Binding of G protein coupled receptor, activates the G protein, alpha beta gamma, formation of PI(4,5)P2, recruit phospholipase C-beta, which cuts leaving diacyglycerol, activates protein kinase C, phosphorylates and regulates, inositol trisphosphate released, opens up calcium channel, and protein kinase C is calcium dependent kinase, double activated protein kinase C, to phosphorylate downstream targets and mediates the whole event.
What is GPCR?
G protein coupled receptors
There is major signalling happening for G proteins, it keeps going until it is deactivated. What is a way to deactivate them? and what would this process look like?
- one way to do this is phosphorylating
1) Activated GPCR stimulates GRK to phosphorylate the GPCR on multiple sites
2) Leads to binding of other proteins –> arrestin (arrestin binds and then inactivates receptor = desensitized GPCR)
3) Blocked which prevents further activation of trimeric G proteins.
This is an important mechanism:
receptor by itself, when it binds to ligand, it dimerizes and transphosphorylate, creates binding site and has other signalling events that occur downstream of this.
Describe an 2 examples of this:
1) EGF binds to EGF receptor, dimerize, transphosphorylates, Now there are multiple signalling events.
- Two monomers, homodimerization, two domain that contain the kinase domains are now in close proximity, they each contain a substrate for tyrosine kinase, each time it phosphorylates, becomes a binding site for another protein.
- Protein 1,2,3 via SH2 or PTB domain.
2) PDGF receptor, 5 different tyrosines can be phosphorylated, and they can create binding sites for different enzymes. Proteins = PI-3 kinase, GAP, PIL-4, have specific activaiton of PDGF, homodimerization, phosphorylation, we can create different signalling complexes.
What four main things do monomeric GTPases bind to?
1) GTP
2) GEFs
3) GAPs
4) Effectors: downstream proteins interact with monomeric GTPase to mediate their cellular function.
Members of the family: Ras, Rho, Rab, Ran, ARF
Describe an example of the Ras signalling pathway:
1) Ras protein is downstream of RTK (receptor tyrosine kinase)
2) binds to receptor, transphosphorylaton occurs.
3) Protein –> Grb2 binds to phosphotyrosine via SH2 domain.
4) binds to proline-rich domain via SH3.
5) recruits second protein: sos
- sos has a GEF binding domain, promotes the binding of GTP, and removal of GDP, ras has now been activated, it goes and does many important functions.
How can PI (phosphoinositol) species act as an important signalling molecule?
- left chain is diaclyglycerol, then phosphate, then inositol. It has 6 positions.
- One position is bound to glycerol
- 2-6 positions are available to be phosphorylated, we continue to phosphorylate them.
- if we have PI-3 kinase, we can generate 3 options, and get all kinds of PI-species, each one is specific for a certain area of the cell.
- Proteins bind specifically to the species, when we don’t want them anymore, we cut them off, fall off, job done.
- if we want them back again, we need to make PI 4 phosphate again.
- true for all PI species, we control them.
Describe the stimulation of growth by the mTOR complex 1:
- mTOR is a major metabolic regulator in the cell, and this is one way that we know it is regulated.
- breaks in the car, stops a lot of metabolic processes from happening based on different cues.
- on surface of lysosome.
- it allows the cell to undergo cell division of mTor, controlled by growth factors, which is what activates mTor.
First thing that it responds to is the amount of amino acids. Reaches into lumen of cytosol and says how many amino acids, if enough build protein, if not enough, stop building new protein. - Also controlling sugar and lipid metabolism.
1) Growth factor. “lets grow” a lot of protein.
2) Receptor binds growth factor, homodimerizes, transphosphorylates, activates two seperate signalling cascades, one via Ras (Erk MAPK) and one via PI 3 Kinase (AkT)
3) Those are major kinase involved. Interact with protein: TSC. A Rheb GAP. ERK and AKT inhibit GAP to turn into GEF. Small molecule GTP binding proteins on surface of lysosome. Need this to activate mTOR. First needs to
4) Rheb activates mTOR and stimulates growth controlled by mtor complex.
5) mTOR attacks Rag. (Ragulator - regulates RAG GEF activates). Lysosomal amino acids tell Rag to grow and activates it if it has enough which activates mtor and you get growth.
6) Cytosolic amino acids, bind to amino acid receptor, inhibitor Gator2, inhibits Rag GAP, which inhibits Rag. Promoting the activator, and inhibitor the inhibitor, which activates Rag that activates mTOR.
Steroids are important major signalling pathways. How do they signal?
1) There is a sterioid hormone
2) There is a hormone receptor complex formed with a receptor in the cytolpasm
3) The complex moves into the nucleus, and binds to sites on the chromatin, activating mRNA transcription and having different cellular responses.
- can promote or inhibit transcription
- might be a cotransporter to help
What is the function of the cell cycle?
Decision making at the molecular level.
What is the function of the Cdk enzyme?
-Cdk enzyme is needed and it is a protein.
- When it is done its job , it is destroyed and thrown away, there are many different kinds.
- at points where we have to make decisions cyclin increases, and then the choice is made, the amount goes down and it is destroyed, this is regulating the cell.
- There are some that you need input from that are regulating major transition events in the cell cycle.
What is the function of M-Cdk? What is it composes of? What happens if it is not regulated?
It regulates the cell cycle during mitosis, and it regulates transition from metaphase to anaphase. It is a critical step in ensuring the accurate segregation of chromosomes during cell division,
- if M-Cdk is not regulated, then it leads to various diseases, cancer etc.
- Composed of 2 subunits: cyclin B and CdkI, during G2 phase of the cell, levels of cyclin B and CdkI increase, and they peak during mitosis.
What is CAK?
Cdk-activating kinase
- CAK activates cdk and we need cdk for cell regulation.
Describe the first phosphorylation cycle: (Cdk) and the second phosphorylation cycle.
First:
(A) Inactive - Cdk is just there with some ATP.
(B) Partly Active - Cyclin comes along and binds to cdk, changes conformation to a T-loop.
(C) Fully Active - cdk - activating kinase comes and phosphorylates cdk on a certain location and makes it active.
Second:
1) At this point, the Cdk + cyclin is fully active with the activating phosphate.
2) Second kinase comes along –> Wee 1 kinase
3) Phosphorylates Cdk at a second site, inhibits it and inactivates it.
4) Cdc25 phosphotase dephosphorylares this specific phosphate and makes it activates again.
- Cdc25 and Wee1 kinase are in competition.
What is the function of protein p27?
it Inactivates cdk-cyclin.
Describe the pathway to regulate mitosis.
1) M-Cdk (Active) activates the Greatwall Kinase. Which activates ENSA. Which inactivates PP2A-B55.
- ENSA is an inhibitory protein
- PP2A comes and dephosphorylates and prevents mitosis from happening, to stop this from happening, activate Cdk, which activates greatwall kinase, which activates ENSA< which makes PP2A inactive and it cannot prevent mitosis anymore.
2) M-Cdk (active) phosphorylates Cdk substrates which results in mitosis!
3) PP2A-B55 (active) would inhibit mitosis but this gets stopped by activating the greatwall kinase.
Describe the pathway involving CAK, Wee1, Mcdk, Cdc25 etc.
1) You have inactive M-Cdk. CAK ativates it and Wee1 inactives it. You still have an inactive M-Cdk, it has an activating phosphate but it also has an inhibitory phosphate.
2) Cdc25 coimes in and activates the M-Cdk. Two positive feedback looops come from this.
3) Active M-cdk activates PP2A-B55 which activates Wee1 which inactivates M-Cdk.
4) Active M-cdk inactives PP2A-B55 which actives Cdc25 which then activates M-cdk.
Describe the “tug of war” pathway:
- M-Cdk phosphorylates substrates, activates them, and promotes mitosis.
- PP2A-B55, dephosphorylates substrates, prevents mitosis.
- phosphorylation of greatwall kinase activates PP22A which dephosphorylises Cdc25 and Wee1, which activates positive feedback at the top.
After regulating mitosis, with M-Cdk, what is the next pathway/step that happens? Describe it:
- The next step is the Fuse, at some point we want to turn the process off.
1) The M-Cdk is active. Then there is the APC/C inactive, and then the Cdc20 comes in and activates the APC/C to then form APC/C-Cdc20 active complex. This is anaphase onset. And it inactivates M-Cdk.
2) When the M-Cdk is active, there is Cdh1 inactive, but when the M-cdk is inactivated, the Cdh1 is dephosphorylated and it becomes active.
3) After there is the anaphase onset, there APC/C is dephosphorylates and the Cdc20 is released - this is done by the M-Cdk inactivation. And then the APC/C and Cdh1 active join together to form a complex, which is active, and goes to perform other functions in the cell.
The idea behind it:
- Cdk lights the fuse and it knows when the job is done. as soon as the job is done, APC/C-Cdc20 dephosphorylates and turns into APC/C-Cdh1 which mediates next step of the cell cycle and promotes regulation.
- Protein complex APC/C is E3 ubiquitin ligase of Cdk cyclin, once activated it acts on E3 ligase of cdk cyclin, with E1/E2 and it leads to degradation of M-cyclin in proteasome, and inactivation of complex.
- Cdk phosphorylares APC/C, why would it want to promote activity of its executioner? Because it is a timer.
What happens in Prophase?
-Replicated chromosomes, each consisting of two closely associated sister chromatids, condense.
- Outside the nucleus, the mitotic spindle assembles between the two centrosomes, which have replicated and moved apart.
What happens in Prometaphase?
- Starts abruptly with the breakdown of the nuclear envelope
- Chromosomes can now attach to spindle microtubules via the kinetochores and undergo active movement.
What happens in Metaphase?
- Chromosomes aligned at the equator of the spindle, midway between the spindle poles
- The kinetochore microtubules attach sister chromatids to opposite poles at the spindle.
What happens in anaphase?
- Sister chromatids synchronously separate to form two daughter chromosomes, each pulled slowly toward spindle pole it faces.
- Kinetochore microtubules get shorter, spindle poles move apart, both processes contribute to chromosome segregation.
What happens in Telophase?
- Two sets of daughter chromosomes arrive at the poles of the spindle and decondense
- Nuclear envelope reassembles around each set, completing formation of two nuclei and marking the end of mitosis.
What happens in cytokinesis?
Cytoplasm divides into two by contractile ring of actin and myosin filaments, pinches the cell in two to create two daughters, each w/ one nucleus.
What is cohesin?
- It is a protein
- Composed of a number of proteins that wrap around DNA to keep sister chromatids in place
- Process of cohesin wrapping around is essential for proper alignment and seperation of chromosomes during mitosis and meiosis, any defects in cohesin function can lead to chromosomal abnormalities and genetic disorders
What is the function of Securin?
Body guard/inhibitor that prevents enzyme seperase.
Describe the process with APC/C, Cohesin, Securin etc.
1) You have inactive APC/C and then Cdc20 activates it.
2) Securin and inactive seperase have formed a complex. Active APC/C comes in and there is ubiquitylation and degradation of securin and the seperase has disattached and is now active.
3) M-Cdk lights the fuse on APC/C to find transition from metaphase to anaphase.
4) Cohesin G2 interacts with M-Cdk and goes to mitotic spindle (metaphase) and then the active seperase comes and it cleaves and dissociates cohesins to anaphase.
- seperase seperates things, protease that cleaves cohesin. Inactive when bound to securin, when APC/C comes and degrades securin, you have active seperase comes and clicks away all the cohesin, that once kepts the 2 sister chromatids together and now can actively do final seperation in anaphase.
Describe the signalling pathway that includes RhoA.
1) You have inactive RhoA that gets turned on by GEF, and turned off by GAP.
- GEF is activated by Aurora-B centralspindin.
2) Now you have Active RhoA that forms two things; Formin, and Rho-associated kinases (including ROCK)
3) Formin forms actin filaments. Which form the assembly and contraction of myosin ring.
4) Rho-associated kinases, inhibite myosin phosphptase, and regulates myosin light-chain phosphorylation, which activates myosin II. This forms the assembly and contraction of myosin ring.
MTORC1 is an important protein complex. How does its pathway work/how does it accomplish the outcomes that it does.
1) There is a growth factor (promotes cell division), attached to a tyrosine receptor kinase, that activates another growth factor receptor. And there are also amino acids that is what regulates the MTORC1 complex.
2) Now that the complex is formed and regulated it can go perform different tasks.
- 4EBP inhibits binding with EIF4E so then protein synthesis can occur.
- S6 Kinase 1 activates EIF4B which leads to protein synthesis. And also S6 Kinase 1 leads to lipid synthesis.
- Lipin inhibits SREBP which leads to Lipid Synthesis.
- Inhibits UIK1 which leads to Protein turnover.
All of these are mediated and regulated by the mTORC1 complex.
