Test 2 (Exam) Flashcards
ECM
Extracellular matrix: specialized material outside the cell, found in animal cells
Saccharomyces cervevisiae
Single-celled model organism
- animal cell
- has a cell wall
Lysosome
Deagradation of cell components that are no longer needed (animal cells)
Vacuoles, two types
- Degradation, like animal lysosome
- Storage for small molecules and proteins
Chloroplast
Site of photosynthesis
Cytoplasm
Contents of the cell outside the nucleus, includes organelles, ribosomes, cytoskeleton
Cytosol
Aqueous part of cytoplasm, does not include the membrane-bound organelles, DOES include ribosomes and cytoskeleton
Lumen
Inside of organelles
- for nucleus, space between two membranes of nucleus
- mitochondria includes whole organelle
Phospholipid basic structure
Hydrophilic head group
Two hydrophobic tails
Amphipathic
Two different biochemical properties on different sides
Ex. Polarity of phospholipid
Membranes are composed of three types of lipids
- Phospholipids
- Sterols
- Glycolipid
Phosphoglyceride general composition
A type of phospholipid, many different types of phosphoglyceride
- Different group and phosphate make head group
- GLYCEROL
- Hydrophobic tail
- 12-14 carbon atoms long, can be saturated or unsaturated
- if tail has a kink it is unsaturated, contains cis double bond
- single bonds means it is saturated
In aqueous environment, phospholipids…
Spontaneously associate into bilayer
- hydrophilic heads interact with water, hydrophobic tails face in away from water
Will then form sphere because it is more energetically favourable
Liposomes
Artificial lipid bilayer, used for drug delivery
Phospholipid movements
Phospholipids within each leaflet
- diffuse laterally
- rotation
- flex
They rarely flip flop, or move from one leaflet to another on their own
Factors affecting membrane fluidity
- Temperature
- lower temperatures make it more viscous, less fluid (not good) - Composition changes that can increase mobility if it’s too cold
-cis-double bonds increase fluidity at lower temperatures (give kink to tail)
- shorter hydrocarbon tails increase fluidity at lower temperatures (lipid tails interact less)
- additional of cholesterol in animal cell membranes, stiffens membrane and makes it less permeable to water
Sterols
In animals, mainly cholesterol
- decreases mobility of phospholipid tails (stiffens membrane)
- plasma membrane is less permeable to polar molecules
Lipid movement to the other leaflet
Scramblase catalyzes flip flops in ER membrane randomly
- needed since phospholipids are synthesized in cytosolic leaflet of ER, would become lopsided without flip flop since the only grow on one leaflet (one side of bilayer)
Asymmetry of the lipid bilayer
Noncytosolic face
Cytosolic face (always faces cytosol)
Membranes bulge, form vesicles and fuse, no flip flop, to form membranes of organelles
-maintains two distinct faces throughout this process
Flipases - enzyme in the Golgi membrane
Catalyzes flip flop of specific phospholipids to the cytosolic leaflet
Enzymes in the Golgi membrane
Flip lipids from one leaflet to another
- flipase
Glycolipids and glycoproteins
- formed by addition of sugars to lipids and proteins on luminal face of golgi
- end up on plasma membrane, inside some organelles - GLYCOPROTEIN FACES NONCYTOSOLIC FACE
- protect membrane from harsh environments
4 Types of membrane proteins
Transmembrane
- protein passes through entire lipid bilayer
Monolayer-associated
- associate with one leaflet
Lipid-linked
- attached to lipids which insert into the membrane
Protein-attached
- associated non-covalently to proteins which are inserted
3 types of integral membrane proteins
Proteins that insert in some way directly into the membrane
1. Transmembrane
2. Monolayer-associated
3. Lipid-linked
Peripheral membrane proteins
Associate with membrane or integral membrane proteins non convalently
- protein-attached or lipid-attached
Extraction methods for integral membrane proteins
Use detergents, lipid bilayer will be destroyed but proteins will remain
Extraction methods for peripheral membrane proteins
Gentle extraction methods, lipid bilayer and protein both remain intact
Transmembrane proteins hydrophilic and hydrophobic regions
Hydrophilic domains interact with cytosol and extracellular space
Hydrophobic domains span the membrane
- about 20 hydrophobic amino acids
Two techniques for identifying protein structure
- X-ray crystallography determines 3D structure
- Hydrophobicity plots
- segments of 20-30 hydrophobic amino acids which can span lipid bilayer as an alpha helix
Monolayer-associated membrane protein characteristics
Anchored on cytosolic face by an amphipathic, horizontal alpha helix
Lipid-linked membrane protein synthesis and anchoring
Synthesized in ER lumen, end up on cell surface (don’t flip flop)
Have a GPI anchor
T/F Proteins can’t flip flop
TRUE
Extraction of membrane proteins by detergent addition
Integral membrane proteins
- Triton X-100 detergent has hydrophobic head and hydrophilic tail
- hydrophobic tails interact with tails of phospholipid
- hydrophilic heads interact with water
- protein can then be purified, phospholipids can be added to reform lipid bilayer and remove detergent
FRAP (fluorescent recovery after photobleaching) method
Some proteins can’t move laterally
- protein labelled with green fluorescent protein
- photobleach an area white
- measure how quickly protein can recover (become green again) to see how much the protein can diffused laterally
- quicker recovery = more lateral diffusion
A faster FRAP time corresponds to…
Faster lateral movement
Permeable and impermeable molecules across a lipid bilayer
Permeable: small nonpolar molecules, small uncharged polar molecules
Impermeable: large uncharged polar molecules, ions
Permeable
Movement via simple diffusion through the lipid bilayer
- high to low concentration gradient, down the gradient
- more hydrophobic or nonpolar have faster diffusion across lipid bilayer
Impermeable molecules and ions require…
Membrane proteins for transport
- each transport protein is selective as to what it will transport
Two main classes of membrane transport proteins
- Channel
- binds weakly to transported molecule
- does not change much in conformation
- selectivity based on size and charge - Transporter
- binds strongly to transported molecule
- undergoes conformational change during transport
- selectivity based on binding site
Passive transport
Down concentration gradient
- does not directly require energy
Active transport
Against concentration gradient
- does directly require energy
Electrochemical gradient =
Concentration gradient + Membrane potential (difference in charge)
Electrochemical gradient is stronger when voltage and concentration gradients work in the same direction
Channel proteins only do _____ transport
Passive
T/F Transporter proteins can do both passive and active transport
True
Channel proteins
- hydrophilic pore across membrane
- most are selective based on ion size and electrical charge
- faster type of passive transport
- interactions with solute are transient
Two types of ion channels
- Non-gated ion channels, always open
- K leaks out of the cell, generates resting membrane potential - Gated ion channels
- some signal is required for channel opening
Four types of gated ion channels and their signals
- Mechanically-gated
Signal: mechanical stress - Ligand-gated (extracellular signal)
Signal: ligand (ex. neurotransmitters) - Ligand-gated (intercellular ligand)
Signal: ligand (ex. ion, nucleotide) - Voltage-gated
Signal: change in voltage across membrane
Transporter proteins
- binds to a specific solute
- goes through conformational change
Passive transport by transport proteins: Uniport
Uniport means one solute passes, direction of transport is reversible (if concentration becomes reversed, but will always remain down the electrochemical gradient)
Ex. GLUT Uniporter transports glucose passively down the electrochemical gradient
- can work in either direction
Active transport by transporter proteins and examples
Against the electrochemical gradient, so needs energy (but not necessarily in the form of ATP)
Ex. Gradient driven pump: first solute down gradient, makes energy, second solute against gradient, uses energy
Ex. ATP driven pump use ATP hydrolysis to move solute against its gradient
Ex. Light driven pump in bacteria uses light energy to move solute against its gradient
Two types of gradient driven ports
Symport
- both solutes move in the same direction
Antiport
- two solutes move in opposite directions
Both use free energy from first solute moving down electrochemical gradient to move second solute against electrochemical gradient
Symport example
Sodium glucose symporter
- sodium ion moves down its electrochemical gradient to provide energy to move glucose against its concentration gradient
- both are moving into the cell
Antiport example
Na+ H+ exchanger
- use energy from Na going down electrochemical gradient to move H against electrochemical gradient out of the cell
- regulates pH of cytosol
- drop in cytosolic pH makes transporter activity increase
How is Na+ electrochemical gradient maintained?
Na+ K+ pump
- plasma membrane ATP driven pump
- both moved against electrochemical gradient
- 3 Na out for every two K in
- low cytosolic Na+, high cytosolic K+ gradients
Three types of ATP driven pumps
- P type pump
- always phosphorylates itself during pumping cycle
- generate and maintain electrochemical gradients
Ex. Na K pump in animals, H+ pump in plants - ABC transporter
- use 2 ATP to pump small molecules across cell membranes
Ex. Toxins - V type proton pump
- use ATP to pump H+ into organelles to acidify the lumen
- in lysosome, plant vacuole
What is Na+ gradient used for
Transporting nutrients like glucose into the cell (Symport), maintains pH (Antiport)
Pumping cycle of Na+ K+ pump
- 3 Na+ bind
- pump phosphprylates itself, hydrolysing ATP
- phosphorylation triggers conformation change, Na ejected out of cell
- 2 K+ bind
- pump dephosphorylates itself
- goes back to original conformation, K goes into cell
V type pump VS F type ATP synthase
V type proton pump:
uses ATP to pump H+ against electrochemical gradient
F type ATP:
synthase uses the H+ electrochemical gradient to produce ATP (reversible)
Two cellular processes regulated by transport proteins
- Trans cellular transport of glucose by transporters
- Generation of membrane potentials
Generation of membrane potentials is done by
- channel proteins
- transporter proteins: passive and active
- active transport by transporter proteins includes gradient driven pumps (Symport and Antiport) and ATP driven pumps (P type, V type, ABC)
K+ leak channel
Outward flow of K+
Electrogenic
Net charge
Ex. Sodium potassium pump net +1 charge outside cell
- a bit more positive on outside membrane than inside, varies from -20 to -200 mV
- this number is always measured from inside the cell
Ions in extracellular space vs cytosol
Extracellular space: high Na+, low K+, high Cl-
Cytosol: low Na+, high K+, low Cl-, cell’s fixed anions (nucleic acids, proteins, cell metabolites)
Plant cell membrane potential
Plasma membrane P type pump
- H+ pump generates H+ electrochemical gradient
- -120 to -160 mV inside cell
- used to carry out active transport, electrical signalling, regulate pH
How much of the cell volume is the cytosol, role of cytosol
50%
- volumes differ for different cells
Role: protein synthesis and degradation, many metabolic pathways, cytoskeleton
Rough ER
- membrane bound ribosomes
- synthesis of soluble proteins and transmembrane proteins for the endomembrane
Smooth ER role
Phospholipid synthesis, detoxication
Are there more membranes in the cell or around it
More in the cell
Rough ER and Smooth ER make up about ____% of membranes
50%
Organelles that are not membrane bound examples
Nucleolus, centrosome
Protein sorting overview
- mRNA arrives in cytoplasm, translation start on ribosomes in cytosol
- cytosolic protein have no sorting signal
- proteins that are sorted have a signal sequence
Signal sequence
- a couple of amino acids that are part of the protein (not something separate added on)
- directs protein to the correct compartment
- specifies specific destination in cell
- recognized by sorting receptors
Sorting receptors
Recognize signal sequences and take proteins to their destinations
Protein sorting two options
Post-translational sorting
OR
Co-translational sorting
Post-translational sorting
- proteins are fully synthesized in cytosol before sorting (nuclear encoded)
- folded before sorting: nucleus and peroxisomes
- unfolded during sorting: mitochondria, plastids
Co-translational sorting
- nuclear encoded
- proteins have ER signal sequence, associated with ER during protein synthesis
- protein synthesis in the cytosol
Peroxisomes
- contain enzymes for oxidative reactions
- detoxify toxins, break down fatty acid molecules
- enzymes imported into the peroxisome through a transmembrane protein complex
Proteins are unfolded for import to the mitochondria and the chloroplast by _____
hsp70 chaperone proteins
Why do proteins sort to the ER?
Entry point to the endomembrane system
Sorting proteins to the ER
- cotranslational sorting
- proteins are nuclear encoded and have an ER signal sequence
- associated with ER during synthesis in the cytosol
- ER signal sequence is hydrophobic
Protein sorting to the ER steps
- mRNA arrives in cytoplasm, translation starts on ribosomes in the cytosol
- ER signal sequence causes half made protein to be inserted into the ER as translation continues (CO-TRANSLATIONAL TRANSLOCATION)
- proteins entering ER are soluble proteins (go into lumen) and transmembrane proteins
Co-translational translocation steps
- Translation starts
- ER signal sequence recognized by SRP, elongation stops
- SRP-ribosome complex gets taken to the SRP receptor and then to the translocon
- Translocation protein opens
- Protein synthesis resumes with protein transfer into ER lumen
- Signal peptidase cleaves ER signal sequence which is hydrophobic so found in lipid bilayer (eventually degraded)
- Protein released into ER lumen
- Translocon closes
SRP
Signal recognition particle, takes ribosome to ER membrane
Co-translational Translocation of TRANSMEMBRANE proteins
Steps 1-5 the same
6. Stop-transfer sequence enters translocon
7. Protein transfer stops and transmembrane domain is released into lipid bilayer
8. Signal peptidase cleaves ER signal sequence and translocon closes
9. Protein synthesis completed and signal sequence is degraded
Constitutive exocytosis pathway
- all eukaryotic cells
- continual delivery of proteins and lipids to plasma membrane
- includes constitutive secretion of soluble proteins (ex. Collagen for ECM)
Two secretory pathways (two types of exocytosis)
- Constitutive exocytosis pathway
- Regulated exocytosis pathway
Regulated exocytosis pathway
- in specialized cells
- stored in specialized secretory vesicles
- extracellular signal (ex. Hormone, neurotransmitter etc.) needed for vesicle to fuse with plasma membrane and release contents
Ex. Insulin released when blood glucose increases in pancreatic beta cells
Golgi apparatus role
Receives proteins and lipids from the ER, modifies them, dispatches them to other destinations in the cell
Protein glycosylation
- starts in the ER: one kind of oligosaccharide is attached to many proteins
- Golgi apparatus: complex oligosaccharide processing occurs, multistage processing unit (different enzymes in each cisterna), glycosylation modifications for proteins and lipids
Endosomes and what they mature into
- membrane-bound organelles
- contain material ingested by endocytosis
- early endosomes fuse with vesicles to eventually mature into late endosomes
- late endosomes mature into lysosomes
Lysosomes
- membrane-bound organelles
- contain hydrolysis enzymes to digest worn-out proteins, organelles, waste
- containing forty hydrolytic enzymes
Main site of intracellular digestion
Lysosomes
Lysosomes are acidified by
H+ pump, acidity needed for hydrolytic enzymes
Lysosomal membrane proteins and their protection
Need to be protected from proteases in the lysosome, this is accomplished by glycosylation
Transport proteins in lysosomal membrane role
Transfer digested products to cytosol (amino acids, sugars, nucleotides)
3 components of cytoskeleton
- Actin filament
- Microtubules
- Intermediate filaments
Components of cytoskeleton important for internal organization
Microtubules
- organelles, vesicle transport
Cytoskeleton components involved in cell division
Actin filament, Microtubules
- chromosome segregation, divide cell in two
Cytoskeleton component involved in large scale movements
Actin filament
- crawling cell, muscle contraction
Microscopy techniques to look at cytoskeleton
Light microscope too small
- can use fluorescence microscopy, labels added to detect specific proteins
- MOST USEFUL: transmission electron microscope, uses beams of electrons
Immunofluorescence microscopy
Used to determine location of proteins
- cells are dead
- primary antibody binds to protein of interest
- fluorescent marker (secondary antibody) attached to primary antibody
- use fluorescence microscope to visualize
How are cytoskeleton filaments held together
Noncovalent interactions
Actin filaments
Smallest filament, made of actin
Intermediate filaments
Medium size, made of intermediate filament proteins
Microtubules
Largest of three components, made of tubulin
Intermediate filament function
- structural support, provides mechanical strength
- form nuclear lamina
Four categories of intermediate filaments
Cytoplasmic
1. Keratin in epithelial cells
2. Vimentin is tissue, muscle
3. Neurofilaments in nerve cells
Nuclear
4. Nuclear lamins in all animal cells (just under nuclear membrane)
Two IMF monomers
Coiled coil dimer
Two IMF dimers
Staggered antiparallel tetramer
8 IMF tetramers
Associate side by side to make a filament
Where are keratin filaments in epithelial cells anchored
Cell-cell junctions (desmosomes)
- provides mechanical strength
Microtubules flexibility
Inextensible — non elastic, does not extend
Microtubules structure
Long hollow tubes
- made up of individual tubulin heterodimers (alpha and beta tubulin) bound to GTP
- gives Microtubules polarity at plus end (beta) and minus end (alpha)
- 13 parallel protofilaments make up a hollow tube
Which ends are beta and alpha
Minus end alpha, plus end beta
Growth and disassembly of Microtubules can occur ____ but is more rapid at _____
Can occur at both ends, more rapid at plus end
Dynamic instability and MTOCs
Microtubules Organizing Centres
- minus ends stabilized at MTO
- plus ends grow out and shrink
- needed for remodelling
Ex. Centrosome
Dynamic instability — growing
Free aB tubulin dimers bound to GTP on plus end
B tubulin hydrolyzes GTP to GDP
If addition of dimers is faster than hydrolysis, GTP cap forms which stabilizes plus end and facilitates growth
Dynamic instability — shrinking
Slower addition of aB tubulin dimers
- slower than GTP hydrolysis in newly added dimers
- GTP cap lost
- now GDP is at plus end, causes weaker binding
- ends curl, microtubules disassembles
Nucleating sites
Sites for microtubule growth in MTOC
Ex. Gamma tubulin ring complex
Microtubules and intracellular transport
Done by motor protons of microtubules
ex. Neurotransmitter transport from ER to axon terminal
Kinesins
Move towards plus end
Dyenins
Move towards minus end
Kinesin-1 and cytoplasmic dyenin are
Dimers
- use ATP hydrolysis for movement
- heads move along microtubules, tails transport cargo
Actin filaments aka
Microfilaments
Myosins found in which filament
Actin filaments, move towards plus end of actin filaments
Actin filament structure
Helical filament made of repeated actin monomers
- 2 protofilaments twisted in helix
- has polarity
- growth faster at plus end
- actin monomers have an ATP cap
Treadmilling
Occurs in actin filaments
- needs continuous ATP
- continuous rates of addition and loss of actin monomers, so length stays constant
Cell crawling
Actin filaments, example treadmilling
- rapid assembly and disassembly to push cell forwards
Junctions in epithelial cells in order from apical to basal (TADGH)
Tight
Adherens
Desmosome
Gap junction
Hemidesmosome
Top three hold sheets of cells together
The two Cell-cell anchoring junctions and what they link
Adherens junction and desmosomes
- link cytoskeletons of neighbouring cells
Cell-ECM anchoring junction
Hemidesmosomes
- link cytoskeleton to basal lamina
Adherens junctions form
Adhesion belts
Tight junctions
- create a tight seal between cells
- prevents mixing of extracellular environments
- acts as fence in the membrane to prevent mixing of membrane proteins
Tight junctions are composed of two transmembrane proteins
Claudin and Occludin
- required in both cells
- extracellular domain in one cell interacts with extracellular domain of neighbouring cells
- occludin-occludin and claudin-claudin pairings
What transmembrane adhesion protein do adherins have?
Cadherins
What cytoskeleton filament do Adherens junctions attach to?
Actin filament
What do desmosomes and hemidesmosomes link to?
Intermediate filaments
- these filaments provide structural strength
What do desmosomes link to?
Keratin filaments and connect to a neighbouring cell
What do hemidesmosomes link to?
Anchor keratin filaments to the basal lamina
Is a hemidesmosomes equal to half a desmosomes?
No, they are made of different proteins
Desmosome transmembrane proteins
Cadherin family members
Ex. Desmoglein, desmocollin
Hemidesmosome transmembrane adhesion protein
Integrins
- binds to laminin in the basal lamina
What do gap junctions do?
Allow for communication between cells
Gap junction structure (numbers of each sublevel)
1 subunit = connexin
6 connexins = connexOn (hemichannel)
2 connexons = intracellular channel (hollow)
12 subunits in one intracellular channel
What can/cant pass through gap junctions
Can: Ions and metabolites, nucleotides, glucose, amino acids (anything less than 1000 daltons)
Can’t: macromolecules, proteins, nucleic acids
Which junction is gated
Gap junctions
- open and closed state dictated by extracellular signals (if one cell leaks, gates will close)
Intracellular junctions in plant cells
Not needed due to cell wall serving function
- plasmodesmata instead
Plasmodesmata
Intercellular junction in plant cells
- allows for communication between cells
- cytoplasmic channels with continuous plasma membrane and ER across plasmodesmata
- allow sugars, ions, nutrients pass (less than 1000 daltons)
- gated by protein and regulatory RNA (ex. Can control callose passage)
Animal tissue composition
EPITHELIAL TISSUE
BASAL LAMINA
CONNECTIVE TISSUE
Cell association in epithelial tissue vs connective tissue
Epithelial tissue: closely associated cells
- cells attached to each other
- limited ECM (thin basal lamina)
- cytoskeletal filaments resist mechanical stress
Connective tissue: cells are rarely connected
- cells are attached to the matrix
- plentiful ECM
- ECM resists mechanical stress
3 major classes of macromolecules in ECM
- Glycosaminoglycans (GAGs) and proteoglycans
- Fibrous proteins (collagens, elastin)
- Glycoproteins (laminin, fibronectin)
Different composition can give tissues different properties
GAGs (glycosaminoglycans) structure charge and role
Disaccharide
- highly negatively charges
- synthesized inside the cell, released by exocytosis
- form hydrated gels which are space filling and resist compression
Ex. Hyaluronan
Hyaluronan
Simple GAG
- long chain of repeating disaccharide units up to 25k
- spun directly from cell surface by a plasma membrane complex
Proteoglycans
Subclass of glycoproteins
- protein with at least one sugar side chain that is a GAG
- 95% sugar
Collagen (makes up connective tissue ECM)
Fibrous protein
- provides tensile strength, resist stretching
- three chains form triple helix, assemble into polymers to form fibrils, fibrils pack into fibers
Collagen is secreted as
Procollagen
- once secreted outside the cell it is assembled into collagen
Connective tissue cells that secrete collagen bind to it in the ECM through
Integrin and fibronectin
Fibronectin
Binds collagen and integrin in different domains
Integrin collagen interaction
Binds fibronectin with extracellular domain and adaptor proteins (actin filaments) with intracellular domain
Elastin
Fibrous protein, gives tissues elasticity
- provides strength and prevents from excessive stretching
Basal lamina (epithelial tissue ECM)
- underlies all epithelial, thin
- secreted by epithelial cells
- influences cell polarity
- separates epithelia from underlying tissue, allows immune cells to pass
Basal lamina anchored by
Hemidesmosomes, organized by laminin
- links Integrin to type IV collagen
Plant cell wall components
More rigid than ECM
- cellulose and pectin
Cellulose microfibrils provide…
Provide tensile strength in cell wall
Pectin
Space filling, provides resistance to compression
Where are cellulose chains synthesized?
Plasma membrane at the cellulose synthetase complex
(Other cell wall components synthesized at Golgi and exported by exocytosis)
Which type of molecule moves faster across the lipid bilayer (diffusion)
Nonpolar, more hydrophobic molecules
Symport
Gradient driven pump where both solutes move in the same direction
Antiport
Gradient driven pump where solutes move in opposite directions
Xray crystallography
Determines 3D protein structure
Where are phospholipids synthesized?
Smooth ER
Three main steps of cell cycle
- Cell growth and chromosome duplication
- Chromosome segregation
- Cell division
Phases of cell cycle
M (mitosis)
G1
S
G2
M phase
- nucleus and cytoplasm divide
- mitosis and cytokinesis
Mitosis definition
Nuclear division
Cytokinesis definition
Cytoplasmic division
Interphase
The period between cell divisions
- G1, D, G2
Cells that divide on an ongoing basis
Epithelial stem cells and hematopoietic
Cells that do not divide are in _____
G0
Metabolically active, just not dividing (nothing wrong with them)
Start transition signal
Is environment favourable
G2/M transition signal
Is all DNA replicated and undamaged
Metaphase to anaphase signal
Are all chromosomes attached to mitotic spindle
What triggers entry to the next phase of the cell cycle?
M-Cdk : cyclin dependant protein kinases
Interphase is compromised of two phases
G1 phase
S phase
What happens during prophase
- replicated chromosomes condense
- mitotic spindle assembly starts and requires duplicated centrosomes
Cohesin
Hold sister chromatids together
Condensins role
Condense DNA in each sister chromatid
Centrosome structure
- pair of centrioles organized at right angles
Centriole composition
Nine fibrils of three microtubules each
When is centrosome duplication initiated and completed
Initiated G1, completed by G2
What do the duplicated chromosomes form
Poles of mitotic spindle
What phase does mitotic assembly start
Prophase (M phase)
Why does the nuclear envelope break down?
So DNA is available to mitotic spindle
When does nuclear envelope breakdown occur
Between prophase and prometaphase
What breaks down nuclear enevelope
Phosphorylation of lamins and nuclear pore proteins
- triggers disassembly into small membrane vesicles
Prometaphase
- nuclear envelope now disassembled
- mitotic spindle assembly can be completed
- kinetichore microtubules in mitotic spindle attach to duplicated chromosomes
- chromosome movement begins
What does the mitotic spindle require for assembly and function
- microtubule dynamics
- microtubule motor protein activity
Astral microtubules
Position mitotic spindle, has cytoplasmic dyenin
What direction does cytoplasmic dyenin walk
Towards the minus end
Non-kinetochore microtubules
Cross linked microtubules throughout the mitotic spindle
- kinesin-5 and other microtubule associated proteins
What direction does kinesin-5 walk along the non-kinetochore microtubules
Towards the plus end
Kinetochore microtubules role
Attach duplicated chromosomes to the spindle poles
Where are kinetochores located
Centromeres of chromosomes
When does the cell move to metaphase
When all chromosomes are aligned in the middle
Tubulin flux is an example of
Treadmilling
What maintains the metaphase spindle
Tubulin flux
When does anaphase start
Chromosomes aligned on metaphase plate
Anaphase (what is activated, what does it cleave)
- seperase activated, cohesin complex cleaved
- anaphase A and B
Anaphase A
Chromosomes pulled polewards
- kinetochore microtubules shorten to drag chromosomes towards poles
Anaphase B
Poles are pushed and pulled apart
- sliding force kinesin
- pulling force cytoplasmic dyenin
What starts to assemble during telophase
Contractile ring starts to assemble
Nuclear envelope reassembly
Desphosphorylation of nuclear pore proteins and lamins
Cytokinesis marks
The end of M phase
Cleavage furrow
Where cytoplasm divides
Contractile ring of actin and myosin filaments role
Divides cytoplasm in two
Cytokinesis requires
Dymanic actin and myosin filaments
Mitosis in a plant cell has no ____
Centrosome
Cytokinesis in plant cells
Telophase
- phragmoplast forms
Cytokinesis
- cell plate forms
G1
- cell wall turns into plasma membranes and cell wall between daughter cells
Meiosis produces
4 haploid cells
How many rounds of DNA replication in meiosis and mitosis
1
How many rounds of cell division in meiosis
2
Claudin and occludin make up
Tight junctions
Separase
Cleaves cohesin complex during anaphase
Proteins that are folded before sorting head for
Nucleus and peroxisome
Proteins that are unfolded before sorting head for
Mitochondria and plastids
How many subunits in a gap junction connexin
1
How many connexins in a gap junction connexon/hemichannel
6
How many connexons and connexins in an intercellular channel/gap junction
2 connexons, which means 12 connexins
What motor protein provides the sliding force in anaphase B
Kinesin
What motor protein provides the pulling force in anaphase B
Cytoplasmic dyenin
What forms the nuclear lamina
Intermediate filament
Are internal ER signal sequences removed
No
Are N terminal signal sequences removed
Yes, by signal peptidase
What type of proteins sort to the ER
Soluble proteins, transmembrane proteins
Transport of vesicles, organelles, or molecules to the plus end of a microtubule is done by
Kinesin
Flippase
Flips phospholipids from the extracellular leaflet to the cytosolic leaflet
Cell-cell junctions (TADG)
Tight, Adherens, desmosomes, gap
