Week 3 Flashcards
What makes up the cytoskeleton ?
Actin microfilaments, intermediate filaments , micro tubules
Microfilaments :
What is the structure ?
Diameter ?
Main functions ?
2 intertwined strands of actin, each a polymer of actin subunits
7nm
Maintenance of cell shape, changes in cell shape, muscle contraction , cytoplasmic streaming , cell motility , cell division
What are cellular extensions driven by ?
Actin polymerization
what do myosin molecules use to derive their energy to “walk” along actin filaments ?
ATP hydrolysis
What does the toxin Phalloidin do ?
Binds to F-actin preventing disassembly
What is the network of actin filaments just below the cell surface called ? What is its role ?
The cell cortex
It supports the plasma membrane and facilitates cell movement
What is the structure of micro tubules ?
Diameter ?
Protein subunit ?
main functions ?
Hollow tubes, wall consists of 13 columns of tubulin molecules
25nm with 15nm lumen
Tubulin , dimmer consisting of a-tubulin and b-tubulin
Maintenance of cell shape , cell motility ( cilia and flagella ) , chromosome movement in cell division , organelle movements
What happens when ATP is added to flagella and cilia ?
Bending of the flagella , causes motion
Which microtubule motors pull chromosomes ?
Kinetochores
What does ALS affect ? ( amyotrophic lateral sclerosis )
Affects nerve cells and spinal cord, affects movements and electrical signals due to alterations to nerve filaments
What happens with Epidermolysis Bullosa Simplex?
Defect in keratin 14 gene, skin peels at slight touch
What is the structure of intermediate filaments ?
Diameter ?
Subunits ?
Main function ?
Fibrous proteins supercoiled into thicker cables
8-12 nm
One of several different proteins depending on cell type
Maintenance of cell shape ( tension bearing elements ) , anchorage of nucleus and certain other organelles
Formation of nuclear lamina
What’s the difference between G actin and F actin ?
G actin is monomeric whereas F actin is the polymeric form that is involved in providing ell support and maintaining cell structure
What holds together the 2 lobes of the actin monomer ?
ATP
How is actin polymerization involved in fertilisation ?
The acrosome reaction in echinoderm sperm requires actin polymerization
What are the functions of microtubules ?
Maintenance of cell shape
Cell motility
Chromosome movement
Organelle movements
What does the drug taxol do ?
It is a cancer drug , it is used for ovarian cancer , breast cancer and lung cancer which prevents microtubules disassembly and therefore cell division in cancer cells.
What is the structure within each microtubule?
A core of axonemal microtubules ensheathed in an extension of the plasma membrane
9 doublets arranged in a ring , with 2 central ones connected by radial spokes 9 + 2 arrangement
What are doublets connected with in cilia and flagella ? What is its role ? What is the role of the cross links ?
Dynein protein which contracts at the expense of ATP forcing the doublets to move relative to each other
The cross links prevent the doublets sliding past each other so that the cilia or flagella bend
What are some differences between prokaryotic and eukaryotic flagella ?
Prokaryotic flagella are proton driven but eukaryotic flagella are ATP driven
Prokaryotic - rotary movement eukaryotic - bending movement
What do kinesin and dynein motor proteins transport along microtubules at the expense of ATP ?
They transport membrane bound vesicles , proteins and organelles along microtubules at the expense of ATP
What end do kinesins move the cargo ? What about dyneins ?
+ end
- end
What are the 2 main types of microtubules ?
Cytoplasmic - more dynamic and loosely organised found in the cytoplasm
Axonemal - highly organised and stable found in cilia flagella and basal bodies
What are impermeable junctions ?
Tight junctions
What are adhesive junctions ?
Adherens junction and adhesive desmosome
What are communicating junctions ?
Passage of small molecules between cells. Gap junctions or chemical synapses
What are the functions of tight junctions ?
Fence Function: Separate the apical plasma membrane from the basal plasma membrane, thus allowing them to have different compositions. This also gives rise to cellular polarity.
Barrier/gate Function: Prevent molecules from leaking between adjacent cells.
What is the importance of tight junctions in the stomach ?
Tight junctions keep the apical membrane components separate from the basal membrane components , in the gut this stops acid being pumped into the bloodstream
What are 4 types of tight junction proteins and an example of an affecting protein?
Claudins - Clostrodium difficile
Occludin - vibrio cholerae
JAM-A - reovirus
ZO-1 - Rotavirus
What is the main junction protein for adherens junction ?
E-Cadherin
What do hemi-desmosomes connect ?
The cell base to the basal lamina
Where are gap junctions very abundant ?
Cardiac tissue and muscle tissue
Why do unicellular organisms need to divide?
To reproduce
Why do multicellular organisms have to divide ?
Growth and cell replacement
What are the phases of the cell cycle ?
G1 (growth phase )
S ( synthesis phase )
G2 ( growth phase )
Mitosis
Cytokinesis
What happens in the G2 phase of interphase ?
-intact nuclear envelope
-chromosomes replicated
-centrosome replicated
-microtubules extend radially forming asters
What are the phases of prophase ?
- Chromatin fibres condense - forming discrete chromosomes
- Nucleoli disappear
- Centrosomes move away from each other
- Mitotic spindle begins to form
What are the stages of prometaphase ?
- Breakdown of nuclear envelope
- Some microtubules attach to chromosomes at their kinetochores
- Other microtubules interact with those from opposite poles
Stages of metaphase ?
Centrosomes at opposite poles
Chromosomes align on the metaphase plate
Sister kinetochores attached to microtubules coming from opposites poles
What are the stages of anaphase ?
Begins with separation of centromeres
Sister chromatids move towards opposite poles of the cell
Each chromatid becomes a new chromosome
Poles move further apart
What are the stages of telophase ?
Elongation of cell by polar microtubules
Daughter nucleoli begin to form at poles of cell
Nuclear envelopes form
Chromatin begins to decondense
During telophase what is also happening ?
Cleavage furrow ( protein complex ) forming
Cytoplasm splits (cytokinesis )
What does the mitotic spindle consist of ?
Tubules
Centrosomes
Chromatid pairs
What are the 3 types of microtubules in the mitotic spindle ?
Astral
Kinetochore
Non-kinetochore/polar
What is the function of the mitotic spindle ?
To organise chromatids along the metaphase plate and then pull sister chromatids apart
How do astral motors work ( dynein ) ?
pull astral microtubules towards poles during prophase
microtubules de-polymerise and shorten
hold astral microtubules in place during metaphase and later
What is the role of the kinetochore motors ?
attach chromosomes to microtubules
pull on microtubules during anaphase - chromosomes move towards centrosomes
microtubules de-polymerise and get shorter
What is the role of non-kinetochore motors ?
motors are attached to a microtubule from either side where the polar microtubules overlap
motors push the microtubules away in opposite directions during metaphase and anaphase
microtubules polymerise and get longer
cell elongates
What is the pulling force in chromosomal pulling?
Dynein
kinetochore motors pull chromosomes towards the centrosome/pole.
astral motors pull centrosomes toward inner face of the plasma membrane
Both shorten depolymerise microtubules
What is the pushing force in separation of chromosomes ?
Kinesin
non-kinetochore/polar motors add subunits (polymerises) microtubules to drive the poles of the spindle apart. This elongates the cell to aid telophase/cytokinesis
Describe the physical separation of chromosome pairs in anaphase ?
- Proteins holding sister chromatids together are inactivated
- Chromatids separate
- Kinetochore microtubules have motor proteins (dynein) which ‘walk’ a chromosome to the nearest pole
- Microtubules shorten by depolymerisation at their kinetochore ends
Non-kinetochore microtubules elongate whole cell during anaphase
Motor proteins (kinesin) attach to microtubules and lengthen them by addition of subunits
Describe cytokinesis in animal cells
Microfilaments form a ring at the furrow
- Ring contracts - owing to interaction between actin and myosin filaments
- furrow deepens until cell is pinched in two
Describe cytokinesis in plant cells
- Cell plate forms at equatorial plane of the cell
- Cell wall forms - from plate contents
