Week 7 - Cytoskeleton. Cell division of eukaryotic cells - mitosis and meiosis Flashcards
3 filamentous structures of the cytoskeleton of a cell
Microtubuli
Microfilaments = actin filaments
Intermediate filament
Functions of cytoskeleton
Shape of cell;
Maintains cells shape. Changes shape of cell during movement (e.g. organelle migration or cell division)
Positions organells
Resist deformation
Transports material from cell (e.g. vesicles), helps in transporting communication signals between cells.
Tell me more about the largest type of filament;
- What does it consist of?
- They can do 2 things, what and how?
Microtubules
- Protein tubulin (25 nm)
Tubulin consists of α- and β-tubulins assembled into linear protofilaments
- SPECIAL ATTACKS
Can rapidly grow: Polymerization
Or rapidly shrink : Depolymerization
Depending on how many tubulin molecules they have
A single microtubule contains about how many protofilaments
… that wind together and forms what?
10 - 15
We humans have 13
Forms a hollow cylinder
OBS FRÅGA
om man ska kunna förklara de hon säger i videolecture
- pt1
7.58
What is MTOCs
Centrosomes consists of 2 what?
What role do they play in?
Microtubule organizing centers
Minus ends of microtubule are anchored in MTOC
Primary MTOC = centrosome
2 centrioles build up centrosomes
Centrosomes and both centrioles play important role during cell division. Origin where mytotic spindle is growing.
Duplicated during S phase of the cell cycle.
Centrioles
Paired cylindrical organells
together with periocentriolar material (PCM, 100+ different proteins)
Built up by microtubules
Cylindrical formation + PCM = produce microtubules e.g. miotic spindle fibers
Intermediate filaments
- Size? Composed of?
- What are they associated with?
Intermediate meaning size is between actin and microtubules!
Composed from many different protein subunits (70 in humans)
Associated with specific cell types:
- Neurofilaments in neurons
- Desmin filaments in muscle cells
- Keratins in epithelial cells
Microfilaments
- Size?
- Consists of?
- Prevalent where?
- Similar to microtubules how?
- Smallest of all filaments
- Consists of actin (contracile)
- Prevalent especially in muscle cells, takes part in muscle contraction
- Similar to microtubules in having a (+) and (-) end which allows them to extend.
Motor proteins
What do they do?
3 motor proteins that are involved in cell movement?
They use energy from ATP hydrolysis to generate movement and force
Kinesin ; Moves along microtubules, pulls organells toward the cell membrane
Dynein ; Pulls cellular components inwards towards nucleus. Work to slide microtubules?
Myosin; NPC interaction with actin → muscle contractions
Also involved in cytokinesis, endocytosis and exocytosis
Somatic cell division in eukaryotes (simple)
Result?
Function?
Result: 2 genetically identical daughter cells
Needed for
Tissue growth, regeneration or vegetative reproduction
M-phase in eukaryotic cell cycle
Consists of what 2 parts?
In what order?
Mitosis and Cytokinesis
1st phase in M-phase
Mitosis: All five phases are called karyokinesis – division of the
nucleus
2nd phase in M-phase
Cytokinesis: - the two daughter cells become independent by
division of cytoplasm and the rest of organoids
OBS both parts partly overlapping!!
5 phases of mitosis
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Struggling to remember? Remember following
pro = before
pro meta = before mid
meta = mid
ana = upper
telos = end.
Key cell cycle regulation proteins are …?
- What is their main thing?
- What is Kinase and what does it do?
cyclin-dependent kinases; CDK
Ensures accurate cell cycle progression
CDK does not have kinase activity unless bound with cyclin.
Kinase: an enzyme, adds phosphate groups (PO4 3−) to other
molecules. Kinases can phosphorylate the amino acids serine,
threonine, and tyrosine.
Concentration of cyclins in the cell fluctuate, CDKs
concentration is stable.
What are PLKs and Aurora kinases
Another type of kinases
Plks (Polo-like kinases) and Aurora kinases control phosphorylation
Major regulators of
- centrosome function
- spindle assembly
- chromosome segregation
- cytokinesis
What does this picture show?
OBS ask if we should know what is activated during different phases
Picture shows different kinases being active during different phases. Through changing different kinases activity by phosforylating different proteins → physical seperations of the nucleus takes place
Picture showing before m-phase starts and start of prophase
Vill du höra mer yapping?
Gå t lecture 7 pt 2; 10.18
Prophase
chromosomes condense into compact structures, condensins attach to chromosomes that coil chromosomes into highly compact forms
- H1 histone phosphorylation and attachment of condensins are mediated by Cdk1
- H3 phosphorylation is mediated by Aurora B kinase
Cohesin
holy fuck så mkt hon yappa (innan) lecture 7 pt2 13.00
cohesin forms rings that hold the sister chromatids together
Sister chromatides arises during replication where duplication of DNA takes place. Proteins that help with this process are already created before this phase.
Since condensine helps to condense chromosomes → cohesin helps to hold something together
nuclear membrane breaks down to form a number of small vesicles, nucleolus disintegrates (nuclear membrane),
transcription and synthesis stop
- beginning of formation of the mitotic spindle
- centrosomes gradually move to take up positions at the poles
of the cell - process is mediated by Plks and Aurora A kinases
Prometaphase
chromosomes are completely attached to the mitotic spindle, spindle fibers bind to kinetochore
chromosomes, led by their centromeres, start migrate to equatorial plane in the mid-line of the cell, this region of mitotic spindle is known as
the metaphase plate
Metaphase
Chromosomes line up along the metaphase plate
A key cell cycle checkpoint – the mitotic spindle checkpoint can be activated in the case of mistake in the mitotic spindle assembly
Mediated by APC/C complex – anaphase-promoting complex/cyclosome –
and cyclins A and B
Anaphase
Anaphase starts by: initiation of sister chromatid separation. Enzymatic breakdown of cohesin
Spindle fibres attach to the centromeres of the sister chromatids, fibres act as tow cables to
separate sister chromatids
Separated chromatids now called = daughter chromosomes
Vad yappar hon om lect.7 pt.2; 19.30
◼ The role of astral microtubules in mitosis is to ensure
correct positioning and orientation of the mitotic spindle
apparatus based on cell polarity. In anaphase they pull the
poles further apart.
◼ Kinetochore microtubules attach to the kinetochore of
chromosomes. In anaphase they shorten and draw the
chromosomes toward the spindle poles.
◼ Interpolar microtubules extend from the spindle pole
across the equator. In anaphase they slide past each other,
exerting additional pull on the chromosomes.
21.36 i lect 7 pt2???
Final boss yappimir we are not palla to lyssna
Telophase
The chromosomes arrive at the cell
poles.
◼ The mitotic spindle disassembles.
◼ The vesicles that contain fragments of the original nuclear membrane
assemble around the two sets of
chromosomes.
◼ Phosphatases dephosphorylate the
lamins at each end of the cell. This
dephosphorylation results in the
formation of a new nuclear
membrane around each group of
chromosomes.
What is Cytokinesis
(simple explan.)
Signal for start of cytokinesis?
◼ The physical process that finally splits the parent cell into two identical daughter cells.
◼ The signal for the start of cytokinesis is dephosphorylation of proteins, which are targets of Cdks.
Cytokinesis
The cell membrane pinches in at the cell equator, forming a cleft
called the cleavage furrow.
The position of the furrow depends on
the position of the astral and interpolar microtubules during anaphase. The action of a contractile ring of overlapping actin and myosin filaments forms cleavage furrow.
What is she yapping about regarding this picture?
We have cells (e.g. epithelial cells) which are joined together with the cell junctions. In cytokinesis → not complete separation but leave cell junction open between 2 newly divided daughter cells
Biological role of mitosis
◼ Growth of the organism.
◼ Repair.
◼ Replacement.
◼ Asexual reproduction (in plants vegetative multiplication).
Meiosis in eukaryotes
◼ Meiosis (in Greek: «reduction»).
◼ Process where diploid cells give rise to haploid gametes. Accomplished by combining two rounds of division with only one round of DNA replication.
◼ A type of cell division that is unique to germ cells.
◼ Within the gonads, the germ cells proliferate by mitosis until they receive the right signals to enter meiosis.
◼ Meiosis involves two cell divisions - Meiosis I and Meiosis
II.
Meiosis 1 consists of what parts?
◼ Meiosis I consist of four stages:
➢Prophase I;
➢Metaphase I;
➢Anaphase I;
➢Telophase I.
Prophase 1
➢Leptotene (Greek for “thin threads”) - chromosomes begin to
condense.
➢Zygotene (Greek for “paired threads”) - chromosomes become
closely paired. Homologous chromosomes begin to align along
their entire length - pairing or forming synapsis. Chromosomes
are held together by a synaptonemal complex.
➢Pachytene (Greek for “thick threads”) - synapsis
completed, and each pair of homologues appears as a
bivalent. Crossing over occurs.
➢Diplotene (Greek for “two threads”) - after recombination,
the synaptonemal complex begins to break down, homologous chromosomes begin to separate but remain attached by the chiasmata.
➢Diakinesis (Greek for “moving through”) - chromosomes
condense and separate until terminal chiasmata only connect the two chromosomes.
6:21 lect. 7 pt 3
VAD YAPPAR HON OM??
Summarise prophase 1
What does crossing over mean?
+ Homologous recombination
◼ Crossing over is the
exchange of genetic material
between non-sister chromatids of homologous chromosomes during
meiosis.
◼ Result: new allelic combinations in the daughter cells.
Crossing over (Genetic recombination) generates genetic
variability of the chromosomes
Crossing over is ensured by homologous recombination:
process in which DNA
molecules are broken and the fragments are re-joined in
new combinations.
Homologous recombination
◼ Involves DSB (double strand breakes) followed by
homologous reparation (re-joining the strands based on
sequence of homologous chromosome). Many proteins are
involved - recombination complex.
◼ The formation of DSBs is catalysed by highly conserved
proteins with topoisomerase activity.
◼ In the absence of recombination, chromosomes often fail to
align properly for the first meiotic division – as the result
there is high incidence of chromosomal loss, called nondisjunction.
◼ A failure in homologous recombination is often reflected in
poor fertility.
What happens in metaphase 1
◼ Nuclear membrane disappears.
◼ A spindle forms.
◼ The paired chromosomes align on the equatorial plane
with their centromeres oriented toward different poles
What happens in anaphase I
◼ The two members of each bivalent move apart, and their respective centromeres with the attached sister chromatids are drawn to opposite poles of the cell.
◼ A process termed disjunction.
◼ Each maternal and paternal chromosome in a homologous
pair segregates randomly into a daughter cell in meiosis I.
◼ The original paternal and maternal chromosome sets are
sorted into random combinations. The possible number of
combinations of the 23 chromosome pairs that can be
present in the gametes is 2²³ (more than 8 million).
Telophase and cytokinesis
◼ Telophase I - the two haploid sets of chromosomes have normally grouped at opposite poles of the cell.
◼ Cytokinesis - the cell divides into two haploid daughter cells and enters meiotic interphase.
◼ In contrast to mitosis, interphase is brief - interkinesis, and
meiosis II begins.
Meiosis II
◼ The second meiotic division is similar to an ordinary mitosis except that the chromosome number of the cell
entering meiosis II is haploid (n).
There is no DNA replication before the next division.
Meiosis overview
Aneuploidy and polyploidy
◼ The most common form of polyploidy in human is triploidy (3n), caused by the fertilization of an egg by two sperm (dispermy).
◼ Meiotic failure - a diploid sperm or egg cell is produced, can also produce a triploid zygote.
◼ The most common cause of aneuploidy (2n +1/-1) is
nondisjunction, the failure of chromosomes to disjoin
normally during meiosis.
Lect. 7 pt.4;
2:00
The most common aneuploidy?
Down syndrome
➢A particular combination of phenotypic features that includes
mental retardation and characteristic face features.
Trisomy 21
Most cases are caused by
nondisjunction, and most of the remainder are caused by
chromosome translocations.
Extra chromosome often given by mother
Mosaicism?
Somatic and germ line mosaicism
◼ Somatic mosaicism - refers to the occurrence of two genetically distinct populations of cells within an individual, derived from a postzygotic mutation.
◼ Germ line mosaicism - refer to the presence of genetically distinct groups of cells within germ line tissues.
What is she yappdoodling about
lect 7 pt 4
13:30
FRÅGA:
Should we know this?????????????????
obs fråga case finns mer om i lecture
16.48
pt 4
Mitochondrial mosaicism
◼ Mitochondrial populations: often heterogeneous: higher mutation rate for the mt genome.
◼ When a cell divides, its mitochondria are distributed to the
two daughter cells.
However, mitochondrial segregation
occurs randomly and is not nearly as organized as the highly regulated process of mitotic chromosome
segregation.
◼ Cells will receive similar, but not identical, mitochondrial
DNA populations.
Tumorigenesis
◼ Tumour cells typically are characterized by widespread
alteration in DNA, chromosome breaks, and aneuploidy.
This condition is termed genomic instability.
◼ Aneuploidy can contribute to tumorigenesis by
- creating extra copies of oncogenes
or by
- deleting tumour
suppressor genes
23.30 till slutet
pt 4
VAD yappar hon om så länge???
