Final Exam Review slides Flashcards
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What are hemidesmisomes?
- Form rivet-like links between cytoskeleton and extracellular matrix components such as the basal laminae that underlie epithelia.
- Like desmosomes, they tie to IF (keratin) in the cytoplasm, but their transmembrane anchors are integrins, not cadherins.
- Focal Adhesion
What are desmosomes?
- Rivets through plasma membrane of adjacent cells.
- Uses cadherin molecules to form actual anchor by attaching to the cytoplasmic plaque and binds to other cadherins of adjacent cells.
- IF (keratin)
What are adherens junctions?
- Share characteristic of anchoring cells through their cytoplasmic ACTIN filaments.
- Transmembrane anchors composed of cadherins (adjacent cells) and integrins (anchor to extracellular matrix).
Describe tight junctions.
- Only in vertebrates
- Act as barrier that regulates the movement of water and solutes between epithelial layers.
- Usually to prevent gut fluids from leaving.
Describe GAP junctions.
- Connexon = 6 connexin subunits. 2 adjacent cell connexons interact to for gap junction channel.
- Allows for direct chemical communication between adjacent cellular cytoplasms through diffusion w/o contact of extracellular fluid.
Describe MT building plan.
- Helical symmetry interrupted by seam because the building block = heterodimer ab-tubulin.
- Polar structure with high dynamic plus end and less dynamic minus end.
- GTP-tubulin hydrolyzes to GDP-tubulin = dynamic instability.
- GDP lost from minus end, GTP ends come in at plus end.
- Concentration of free tubulin + rate of GTP hydrolysis = rate of assembly.
- High conc = GTP cap = High affinity for binding at plus end.
- Low conc = GTP -> GDP = GTP cap falls apart (tubulin affinity goes down.
- Strain at plus end causes protofilaments to curl outward and shrink.
- Rapid growth and shrinkage allow MTs to be dynamic.
Describe Actin filament building plan.
- Treadmilling, actin filaments slowly move towards positive barbed end. (ATP dependent)
- In the presence of ATP, actin monomers polymerize to form a flexible, helical filament.
- Barbed plus end (fast growing)
- Pointed minus end (slow growing)
- ADF/Cf
Describe IF building plan.
- They are composed of mostly alpha-helical coiled coiled dimer => tetramer.
- 10 nm diameter
- No polarity (builds as polar, but not in tetramer)
- Rod-like tetramer formed by two dimers aligned side by side in a staggered fashion with N and C termini pointing in opposite directions (antiparallel).
- Monomer -> dimer -> tetramer
- Unit length of filament ~ 60nm
What is desmin and where?
- Located at the Z-line in sarcomere of cardiac and skeletal muscle, but also found in smooth muscle.
- Gradually replaces vimentin after embryogenesis and higher differentiation of muscle cells.
- Only found in vertebrates, but with homologous proteins in other metazoan cells.
- Also links mitochondria to sarcomere.
- Important for proper filament assembly.
Keratins are a major component of what?
Hair, nails, skin
What are lamins?
Type-V IFs that form a basket underlying the nuclear membrane (NM) giving it strength and organization.
Nuclear lamina are linked to the NM by what?
Lamin-B
Where are lamins reversibly phosphorylated and what is the result?
At their head and tail domains during mitosis, causes disassembly of the nuclear lamina.
Where are Lamin A and B found?
Metazoan cells
Where are Lamin A/C and B found?
Humans
What is the product of the LMNA gene and its function?
Lamin A/C is the product and is a major component of the nuclear lamina.
- Lamina A and C are different splicing products.
- Other lamins in vertebrates are lamina B-type
Where are lamins found?
IF in the nucleus.
Properties of 3 filaments.
Refer to slide 15.
IF groups in Lens
- Phakinin (orphan)
- Filensin (orphan)
(lens eyeball)
IF groups in Epidermal keratins
- Keratin 1, 2, 5, 6 (II)
- Keratin 9, 10, 14-17, 19 (I)
(shoulder skin??)
IF groups in Simple epithelial keratins
- Keratin 7, 8 (II)
- Keratin 18-20
Liver, intestines, lungs
IF groups in Nucleus
- Lamin A, C (V)
2. Lamin B1, B2 (V)
IF groups in blood vessel/other mesenchyme
Vimentin (III)
IF groups in Muscle
- Desmin (III)
- Syncoilin (III)
- Synemin (IV)
( Cardiac, skeletal, smooth)
IF groups nervous system
- Neurofilaments: L, M, H (IV)
- alpha-internexin (IV)
- nestin (IV)
- Peripherin (III)
- GFAP (III)
BRAIN
IF groups in Hair shaft and nail
- Keratin Ha1-8 (II)
2. Keratin Hb1-6 (I)
IF connections slide
Slide 18
What does ADF/Cofilin do?
Actin-associated protein: actin filament disassembly (ADF = actin depolymerizing factor)
What does ARP2/3 do?
Actin-associated protein: Actin filament polymerizing/branching
What does Gelsolin/Villin do?
Actin-associated protein: Actin filament severing
What does the spectrin family do?
Actin-associated protein: Actin filament cross-linking
What does the myosin family do?
Actin-associated protein: multiple motor functions in cytoplasm and muscles
What does tropomyosin do?
Actin-associated protein: Regulates myosin-actin interactions in sarcomeres, controlled by troponin.
What does Troponin do?
Actin-associated protein: Regulates myosin-actin interactions in sarcomeres via tropomyosin (Ca2++ dependent)
What are the 3 types of muscle?
- Skeletal
- Cardiac
- Smooth
Which muscle types are striated?
Skeletal and cardiac
Where is Ca++ in skeletal muscle?
Stored in the muscle.
Where is Ca++ in cardiac muscle?
Floating around
In striated muscle, which bands move when contracted vs relax?
Sarcomere, Z-line, H-Band, I-Band
In striated muscle, which bands remain in place when contracted vs relaxed?
A-Band and M-Band
The I band contains only ____.
Thin filaments
The H zone only has ___.
Thick filaments
The A band represents the ___.
Region of overlap and contains both types of filaments.
How does Troponin and Tropomyosin regulate the actin-myosin interaction?
Tropomyosin is a coiled structure around the actin held there by troponin. High Ca++ => bind to troponin => moves tropomyosin out of the way allowing myosin heads to bind to actin (walking up the actin). Low Ca++ => troponin in standard conformation => makes tropomyosin block binding sites.
What is titin and its purpose?
Connects between the Z-line and the M-line of the thick filaments, thereby maintaining myosin filaments in proper position (A-band) between Z-lines (hence, a single titin molecule spans half of the sarcomere length).
- Prevents sarcomere from becoming pulled apart during muscle stretching.
- Highly elastic
What is nebulin for?
Molecular ruler
- Regulates number of actin monomers that are allowed to assemble into a thin filament.
- Controls length of thin filament.
How many ATP binding sites does Kinesin have?
One, Uno, 1
How many ATP binding sites does Dynein have?
6 binding sites (AAA ATPase)
What happens in S phase?
Chromosome replication (DNA replication)
What happens in S/G2 phase?
Centrosome duplicates
What happens in Prophase?
Chromosome condensation
What happens in Prometaphase?
- Nuclear envelope breakdown (NEBD) initiated by MPF.
2. Kinetochore/Centromere maturation
What happens in Metaphase?
- Rearrangement of MT into spindle
- Attachment of MT to Kinetochore
SAC regulated
What happens in Anaphase?
Chromosome separation: APC degrades cohesins
What happens in Telophase?
Formation of contractile ring
What happens after Telophase?
Cytokinesis
What steps are in M-phase?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What happens in the G1 phase?
- Cell grows and carries out normal metabolism.
2. Organelles duplicate
What happens in G2 phase?
Cell grows and prepares for mitosis
Describe type I (skeletal muscles).
Slow twitching type: eg muscles stabilizing the spine
- Red fibers in large muscles.
- Slow twitch fibers keep us upright and help walking or running long distance and bicycle for hours
Describe type II (skeletal muscle).
Fast twitching type: eg muscles in eyelids
- White fibers in fast muscles.
- Fast twitch fibers use anaerobic metabolism for ATP synthesis. They generate shorter bursts of strength or speed than slow muscles, but they fatigue quickly.
Describe type IIA (skeletal muscle).
Semi-fast twitchers: may use aerobic or anaerobic ATP synthesis.
Describe type IIB (skeletal muscle).
Fast twitchers: always anaerobic metabolism
What does cyclin E-Cdk2 do?
Drives the cell into S phase.
What does cyclin B1-Cdk1 do?
aka MPF:
- Drives cell into mitosis
- Prevents a cell from rereplicating DNA that has already been replicated earlier in the cell cycle (During G2 phase)
What does cyclin D do?
Present through entire cell cycle.
1. Provides proper levels of cell division throughout body. (Mice lacking gene are smaller than control animals)
What’s unique about Cdk1?
- Only Cdk required to drive a mammalian cell through all of the stages of the cell cycle.
- Can “cover” for others and ensures required substrates are phosphorylated at each stage of the cell cycle.
- Case of “redundancy”
- Doesn’t prevent abnormalities however.
What does cyclin A-Cdk2 do?
- Helps with G1 to S transition (which includes initiation of replication). (Works along with cyclin E)
- Helps transition G2 to M and passage through early M (works with cyclin B1-Cdk1)
What happens to when there is a lack of Cdk2?
Mice lacking Cdk2 appear to develop normally but exhibit specific defects during meiosis.
What is MPF and what is it composed of?
MPF = Maturation Promoting Factor: Heterodimeric protein made of cyclin B and Cdk1 (aka. Cdc2 or p34 kinase).
What does MPF trigger?
Triggers formation of mitotic spindle.
What does MPF promote?
Promotes mitosis ie chromatin condensation.
MPF causes what breakdown?
Nuclear envelope breakdown by phosphorylating the nuclear lamins.
What interaction does Wee1 have with MPF?
- During G1 and S phase, MPF subunit cdk1 is inactive due to phosphorylation by Wee1.
- In G2, Wee1 inhibited by MPF => positive feedback loop
What activates MPF?
Cyclin Activating Kinase (CAK) triggers onset of Mitosis.
What happens to MPF during Anaphase?
Anaphase-promoting complex (APC) poly-ubiquitinates cyclin B => destruction of MPF.
Describe the “destruction box” in cyclins.
Cyclins contain a N-terminal region called “destruction box”, which can be recognized by the ubiquitin ligase enzyme.
What are the steps in Prophase?
- Chromosomal material condenses to form compact mitotic chromosomes.
- Chromosomes are seen to be composed of two chromatids attached together at the centromere.
- Cytoskeleton is disabled, and mitotic spindle is assembled.
- Golgi complex and ER fragment into little pieces.
- Cdk1 in active phosphorylation and CyclinB retained in nucleus.
- The nuclear envelope starts to disperse.
What are the steps in Prometaphase?
- Complete nuclear envelope breakdown (NEBD).
- Centrosomes and Centromeres mature.
- MT dynamics change.
- Chromosomal MTs attach to kinetochores of chromosomes.
- Chromosomes are moved to spindle equator.
What are the steps in Metaphase?
Chromosomes are aligned along the metaphase plates, attached by chromosomal MTs to both poles.
What are the steps in Anaphase?
- Centromeres split, and chromatids separate.
- Chromosomes move to opposite spindle poles (Anaphase A).
- Spindle poles move farther apart (Anaphase B).
- Formation of the contractile ring initiates transition to telophase.
What is the SAC and how is it produced?
The SAC (spindle assembly checkpoint) is an active signal produced by improperly attached kinetochores which is conserved in all eukaryotes.
What does the SAC make sure of?
Transition to anaphase occurs only once all chromosomes are neatly arranged at the metaphase plate.
The SAC stops what?
Stops cell cycle by negatively regulating CDC20 (preventing activation of the poly-ubiquitylation activities of the APC.
What is the MCC?
Mitotic checkpoint complex: set of proteins responsible for the SAC signal.
How is SAC deactivated?
Upon MT-kinetochore attachment => dynein transports spindle checkpoint proteins away from the kinetochores.
What is APC what is it made of?
APC (anaphase promoting complex) is a large complex of 11-13 subunit proteins.
APC is activated by what?
By either CDC20 or Cadherin-1 (CDH1) (for targeting different substrates).
What triggers the transition from metaphase to anaphase?
E3 ubiquitin ligase triggers transition from metaphase to anaphase by tagging specific proteins for degradation (securin/cyclins).
APC degrades what and what is the result?
APC-triggered degradation of Securin by ubiquitination releases Separase, a protease that in turn degrades Cohesins (linkers between sister chromatids).
How does APC deactivate MPF?
APC-triggered degradation of CyclinB deactivates the MPF.
What do Cohesins do?
Regulate attachment and separation of sister chromatids during mitosis and meiosis.
Cohesins consist of what two proteins?
SMC: Structural Maintenance of Chromosomes.
SCC: Sister Chromatid Cohesin
What are the steps in Telophase?
- Chromosomes cluster at opposite spindle poles.
- Chromosomes become dispersed.
- Nuclear envelope assembles around chromosome clusters.
- Golgi complex and ER reforms.
- Daughter cells formed by cytokinesis.
What is cytokinesis?
A process by which a dividing cell splits into two, partitioning the cytoplasm into two cellular packages.
What are carcinomas?
Characterized by cells that cover internal and external parts of the body such as skin, lung, breast, and colon cancer.
What are sarcomas?
Characterized by cells that are located in bone, cartilage, fat, connective tissue, muscle, and other supportive tissues.
What are lymphomas?
Cancers that being in the lymph nodes and immune system tissues.
What are leukemias?
Cancers that being in the bone marrow and often accumulate in the bloodstream.
What are adenomas?
Cancers that arise in the thyroid, pituitary gland, adrenal gland, liver, and other glandular tissues (usually benign).
Cancers are classified by their ____.
Tissue of origin
What are tumor suppressor genes?
aka anti-oncogene: produces a protein that protects cells from one specific step on the path to cancer.
What happens when a tumor suppressor gene is mutated?
Mutations (loss or reduction of function) in the cell can progress to cancer (usually in combination with other genetic changes).
What is p53?
A tumor suppressor protein:
- Activated by DNA damage
- aka “Guardian of the Genome”
- Role in conserving stability by preventing genome mutation
What is pTEN?
Tumor suppressor: Opposes the action of PI3K, which is essential for anti-apoptotic, pro-tumorogenic Akt activation.
Is Rbp working in cancers?
No, Retinoblastoma protein is dysfunctional in several major cancers. (Tumor suppressor)
What is an oncogene?
A gene that has the potential to cause cancer.
What are oncogenes like in tumor cells?
Often mutated or expressed at abnormally high levels.
What is a proto-oncogene?
A normal gene that can become an oncogene due to mutations or increased expression.
What’s one way a proto-oncogene can become an oncogene?
Through relatively small modifications of its original function.
The expression of oncogenes can be regulated by what?
microRNAs (miRNAs: ~ 21-25 nucleotides) that control gene expression by down-regulating them.
Mutations in microRNAs can lead to what?
Activation of oncogenes.
What is plectin?
A cross bridge that links IFs to other cytoskeletal filaments (one binding site end for IF, the other for microfilament, IF, or MT).
