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44 Cards in this Set
- Front
- Back
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Intermediate filaments (3 points) |
-Provide strength and structural support -Self-assembling, apolar filaments -Regulated by phosphorylation |
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Microtubules (3 points) |
-Deliver and recieve signals to/from other parts of the cell -Polar tubes -Regulated by direct ATP binding |
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Actin filaments (3 points) |
-Provide force, movement and directionaity -Polar filaments -Regulated by direct ATP binding and treadmilling |
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Regulation of actin cytoskeleton |
Initial step is energetically unfavourable although once it is initiated, it will continue spontaneously |
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Signalling occurs through... |
...molecular switches By phosphorylation or GTP binding |
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GTP binding proteins (4 points) |
-Have intrinsic GTPase activity -Bind and hydrolyse GTP -Cause a change in 'switch' region which alters protein and activates it -Hydrolysis of GTP resets the switch |
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GAP GEF GDI |
= GTPase activating protein. Inactivates GTP protein = Guanine nucleotide exchange factor. Activates protein = Guanine dissociation inhibitor. Binds and sequestors protein |
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Cellular processes are reguated by GTPase families Ras Rho Rab Ran Arf |
Master regulator of cell growth Maintenance of cell structure Regulation of vesicle trafficking Control of nuclear import and export Membrane trafficking |
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Rho family GTPases - function Cdc42 Rac1 RhoA |
-Co-ordinate actin cytoskeletal organistion - controls cell morphology, movement and polarity -Cdc42 - polymerisation of actin filaments -Rac1 - controls organisation of filaments into ruffling structures -RhoA -stabilises filaments into stress fibres |
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What does a point mutation mimic? |
Mimics GTP-bound state to make the protein 'constitutively active' so it is always on |
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Constitutively active mutant Dominant negative GTPase mutant |
No GTP bound but cannot be turned off by GAP - it is always on Protein is already turned of - binds to GEF in cell. GTPase is unable to be activated |
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Rho mutant |
-affects actin cytoskeleton -leads to membrane ruffling and filopodia formation |
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The failure of cells to migrate and aggregate leads to... |
... cell, tissue and organism dysfunction and death |
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Classical study - Cell aggregation (HV Wilson, 1907) (4 points) |
-Sponges were sieved so made into individual cells -When placed together, they re-attached to form sponge -Different species placed in same culture - sort themselves into their different species -Embryonic cells will re-sort by tissues |
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L-cells (5 points) |
-Cell line expresses no cadherins -transfection induces homophilic sorting -with adhesion, need same cadherin to stick together -transfection induces graded sorting -high levels of E-cadherin will stick together |
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Monoclonal antibodies (7 points) |
-Mouse immunized with antigen X - cells make antibody -Mutant cell line derived from a tumour of B lymphcytes -Both fuse and then gives 3 populations -Only hybridomas will grow on selective medium -500-600 wells per experiment -Allow cells to multiply -Test supernatent for anti-X antibodies |
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Families - Ca2+ dependent - cadherins, selectins and integrins |
-Have integral membrane glycoproteins (750 amino acids) -Low Ca2+ levels - cadherins won't go near membrane -High Ca2+ levels - cadherins bind to hinge region which alters conformation of cadherin molecule |
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E-cadherin N-cadherin P-cadherin |
Found in epithelia Found in neurons, heart and skeletal muscles Placenta and epidermis |
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Proto-cadherin |
-Has hypervariable region - can generate many proteins |
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Selectins (4 points) |
-work on cell surfaces -Induced by inflammation e.g. trauma -Cells express selectin and lectin domain, binds to sugar domain on endothelial cells -Slows the cells down so a stronger attachment can be made |
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Selectin-dependent Integrin-dependent |
Weak adhesion and rolling Strong adhesion and emigration |
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Ca2+ independent CAMS (3 points) |
-Major are neural cell adhesion molecules (N-CAMS) -Binding is homophilic and is in the ECM and cell -Variable in polysialic acid - more in immature cell, less adhesion |
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ECM Integrin composition |
- a mesh of secreted proteins and helps cell attach - 18 alpha and 8 beta subtypes = 24 variants. They pass through the transmembrane region to accessory proteins. They can alter strength of attachment through the cell. |
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FAK - focal adhesion kinase (3 points) |
-Activated on formation of adhesions -Regulated by Ca2+ and can recruit multiple tyrosine kinases -Increased myosin activity - leads to more stress fibres and integrin clustering and focal adhesino formation |
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What does the cortex aid? What is ruffling? Amoeba mutant |
Membrane tension This is the movement downwards and throwing back of the cell body Can still move even with no myosin |
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ARP complex (3 points) |
-Seven subunit protein complex -Plays major role in regulation of actin cytoskeleton -Leads to nucleated actin interaction |
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Focal contacts and mobility |
-Clutch mechanism is present |
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Adhesions |
Low density adhesions are immobile and are Cdc42-dependent while high density adhesions will slide into the membrane and are actin-myosin interaction dependent |
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Cancer |
disease of genetic instability. This results in cells throwing away core machinery or parts that inhibit proliferation to generate architecture |
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What is the main principle of the cell cycle? |
To produce 2 daughter cells which are copies of the parents |
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How do we know how long each phase takes? |
-By functional assays =quantify functioning of an active substance rather than just its quantity -Morphological markers - staining to see a difference |
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How can the cell cycle be analysed biochemically? |
Use animal embryos e.g. Xenopus
Place tightly packed eggs into a tube then centrifuge it, the eggs will get crushes Add sperm nucleaus without membrane and this causes reassembly of the nucleus DNA replication then occurs |
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Cyclically activated proteins (2 points) |
Cyclins are proteins expressed at different levels during the cell cycle. Cyclins bind to CDKs to activate them |
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Positive induction of cell cycle transition Roo and Johnson, 1970 |
-Fused cells in interphase and mitosis to cause interphase cells to enter early mitosis |
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What did Roo and Johnson experiment lead to the discovery of? How did this occur? (4 points) |
Discovery of factors essential for mitotic entry -Egg is mounted onto slide and cytoplasm is taken out -Injected into an oocyte and causes oocyte to enter M-phase - chromosomes condense so sister chromatids are seen -Led to knowledge of MPF - maturation promoting factor |
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What was the experiment done by Hunt et al? (4 points) |
-Purified cells using phosphorylating proteins and histone H1 -Radioactive thymine leads to accumulation of protein -This disappeared just before cells were about to divide -This was synchronous cell division |
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Nurse et al experiment (4 points) |
-took linear yeast through temperature sensitive cell division mutations -cdc25 works upstream of cdc2 -cdc25 is a positive regulator -wee1 was also analysed and worked negatively |
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What are two functions of cyclins? |
Activate catalytic subunit and target catalytic subunits |
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Why does the 'S phase' only occur once? |
The DNA was only "licenced" to undergo one round. During replication the licence is destroyed. This licence is "Pre-RC" |
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What type of cells are tumours created by? |
Those that have lost the ability to assemble |
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Hyperplasia Metaplasia |
Tissue growth with excessive number of cells Tissue growth containing displaced normal cells |
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Dysplasia Neoplasia |
Tissue growth where cells appear abnormal Invasive abnormal tissue growth |
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What can we use histopathology for? |
To provide clues to the trace origins of tumours - can predict common behaviours among diverse tumours |
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Environment and lifestyle - experiment on migration to Hawaii (4 points) |
-Profile of cancer in Hawaii -Looked at caucasian at same time and compared to Japanese that emigrated to Hawaii -Stomach cancer is lower while prostate is high = Hawaiian Japanese acquire caucasian profile whilst there - environmental risk is significant |
