Week 7 - Cytoskeleton. Cell division of eukaryotic cells - mitosis and meiosis Flashcards

1
Q

3 filamentous structures of the cytoskeleton of a cell

A

Microtubuli

Microfilaments = actin filaments

Intermediate filament

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2
Q

Functions of cytoskeleton

A

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.

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3
Q

Tell me more about the largest type of filament;

  • What does it consist of?
  • They can do 2 things, what and how?
A

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

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4
Q

A single microtubule contains about how many protofilaments

… that wind together and forms what?

A

10 - 15
We humans have 13

Forms a hollow cylinder

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5
Q

OBS FRÅGA

om man ska kunna förklara de hon säger i videolecture

  1. pt1
    7.58
A
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6
Q

What is MTOCs

Centrosomes consists of 2 what?

What role do they play in?

A

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.

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7
Q

Centrioles

A

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

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8
Q

Intermediate filaments

  • Size? Composed of?
  • What are they associated with?
A

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
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9
Q

Microfilaments
- Size?
- Consists of?
- Prevalent where?
- Similar to microtubules how?

A
  • 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.
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10
Q

Motor proteins

What do they do?

3 motor proteins that are involved in cell movement?

A

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

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11
Q

Somatic cell division in eukaryotes (simple)

Result?

Function?

A

Result: 2 genetically identical daughter cells

Needed for
Tissue growth, regeneration or vegetative reproduction

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12
Q

M-phase in eukaryotic cell cycle

Consists of what 2 parts?
In what order?

A

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!!

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13
Q

5 phases of mitosis

A

Prophase

Prometaphase

Metaphase

Anaphase

Telophase

Struggling to remember? Remember following
pro = before
pro meta = before mid
meta = mid
ana = upper
telos = end.

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14
Q

Key cell cycle regulation proteins are …?
- What is their main thing?

  • What is Kinase and what does it do?
A

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.

Picture shows different CDK depended on different cyclin. + CDK activity increase + different CDK and cyclin in different phases
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15
Q

What are PLKs and Aurora kinases

A

Another type of kinases

Plks (Polo-like kinases) and Aurora kinases control phosphorylation

Major regulators of
- centrosome function
- spindle assembly
- chromosome segregation
- cytokinesis

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16
Q

What does this picture show?

OBS ask if we should know what is activated during different phases

A

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

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17
Q

Picture showing before m-phase starts and start of prophase

Vill du höra mer yapping?
Gå t lecture 7 pt 2; 10.18

A
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18
Q

Prophase

A

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
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19
Q

Cohesin
holy fuck så mkt hon yappa (innan) lecture 7 pt2 13.00

A

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
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20
Q

Prometaphase

A

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

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21
Q

Metaphase

A

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 complexanaphase-promoting complex/cyclosome –
and cyclins A and B

22
Q

Anaphase

A

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

23
Q

Vad yappar hon om lect.7 pt.2; 19.30

A

◼ 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.

24
Q

21.36 i lect 7 pt2???
Final boss yappimir we are not palla to lyssna

25
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.
26
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.
27
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.
28
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
29
Biological role of mitosis
◼ Growth of the organism. ◼ Repair. ◼ Replacement. ◼ Asexual reproduction (in plants vegetative multiplication).
30
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.
31
Meiosis 1 consists of what parts?
◼ Meiosis I consist of four stages: ➢Prophase I; ➢Metaphase I; ➢Anaphase I; ➢Telophase I.
32
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.
33
6:21 lect. 7 pt 3 VAD YAPPAR HON OM??
34
Summarise prophase 1
35
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.
36
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.
37
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
38
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).*
39
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.
40
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.
41
Meiosis overview
42
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.
43
Lect. 7 pt.4; 2:00
44
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?
45
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.
46
What is she yappdoodling about lect 7 pt 4 13:30
47
FRÅGA: Should we know this????????????????? obs fråga case finns mer om i lecture
48
16.48 pt 4
49
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.
50
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
51
23.30 till slutet pt 4 VAD yappar hon om så länge???