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Mol / Cel Biology > Lecture 7 > Flashcards

Lecture 7 Flashcards

1
Q

The cytoskeleton of a cell consists of three filamentous

structures:

A

Microtubules
Microfilaments = actin filaments
Intermediate filaments

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2
Q

Cytoskeleton functions?

A

Maintains cell’s shape
Positions organelles
Resists deformation
Transports intracellular cargo (e.g. vesicles)

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3
Q

Microtubules consists of?

A

Of a protein tubulin.
Tubulin is composed of α – tubulin
and β -tubulin subunits assembled
into linear protofilaments.

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4
Q

What does microtubules polymerization and depolymerization means?

A

That microtubules can rapidly grow or shrink in size, depending on how many tubulin molecules they contain.

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5
Q

A single microtubule contains?

A

10-15 protofilaments that wind together to form a 24 nm wide hollow cylinder.

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6
Q

In cells, the minus ends of microtubules are anchored in structures called?

A

Microtubule organizing centers (MTOCs).

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7
Q

The primary MTOC in a cell is called?

A

The centrosome

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8
Q

The centrosome consists of?

A

Two centrioles

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9
Q

During what cell cycle happens what to centrosome?

A

It’s duplicated during the S-phase of cell cycle

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10
Q

Centrioles organise what?

A

The pericentriolar material (PCM) to produce microtubules including mitotic spindle fibres

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11
Q

Intermediate filaments are composed of?

A

From different protein subunits. Identified only in animal cells.

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12
Q

Microfilaments are?

A

The smallest type of filament, composed of the contractile protein actin, diameter ~8 nm

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13
Q

Microfilaments are prevalent mostly in?

A

Muscle cells

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14
Q

Motor proteins use energy from?

A

from ATP hydrolysis to generate

movement and force.

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15
Q

Motor proteins involved in cell movement?

A

Kinesin - move along microtubules to pull organelles toward the cell membrane.

Dynein - used to pull cellular components inward, toward the nucleus, work to slide microtubules.

Myosin - interact with actin to perform muscle contractions, involved in cytokinesis, endocytosis, and exocytosis.

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16
Q

Somatic cell division, gives rise to?

A

two genetically identical daughter cells.

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17
Q

Somatic cells ensure in cell division?

A

tissue growth, regeneration or asexual (vegetative) reproduction.

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18
Q

What does mitosis refer to?

A

only to the process of nuclear division (karyokinesis). Karyokinesis usually is followed by cytokinesis.

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19
Q

What happens in cytokinesis?

A

the two daughter cells become independent by

division of cytoplasm and the rest of organoids.

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20
Q

Recap:
Mitosis?
Cytokinesis?

A

Mitosis – the first step of M
phase of the cell cycle.

Cytokinesis - the second step
of M phase of the cell cycle.

Both steps partly overlapping.

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21
Q

Mitosis consists of five phases that are?

A

Prophase - the preparative phase.

Prometaphase – the transition
phase to the next phase.

Metaphase - the middle phase.

Anaphase - the separation phase.

Telophase - the final phase.

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22
Q

The key cell cycle (including M phase) regulation proteins are?

A

Cyclin-dependent kinases (CDKs) - ensure accurate cell cycle progression.

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23
Q

What is a kinase?

A

an enzyme, adds phosphate groups to other
molecules.
Kinases can phosphorylate the amino acids serine,
threonine, and tyrosine

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24
Q

Which two controls phosphorylation?

A

Plks (Polo-Like kinases) and Aurora kinases

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25
Q

Plks (Polo-Like kinases) and Aurora kinases regulates?

A

Centrosome function, spindle assembly,vchromosome

segregation and cytokinesis.

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26
Q

What happens in prophase of mitosis?

A

The chromosomes condense into compact structures. Condensins attach to chromosomes that coil the chromosomes into highly compact forms.

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27
Q

What happens to the nuclear membrane in prophase?

A

The nuclear membrane breaks down to form a number of small vesicles and the nucleolus disintegrates. Transcription and synthesis stops.

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28
Q

During the prophase what is starting to form?

A

The mitotic spindle.

The process is mediated by Plks and Aurora A kinases.

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29
Q

What happens in prometaphase of mitosis?

A

The chromosomes are completely attached to the
mitotic spindle. Spindle fibres are binded to kinetochore.
Nuclear envelope has disappeared.
Chromosomes are moving towards the equatorian plane.

30
Q

In prometaphase the chromosomes, led by their

centromeres, start migrate to the?

A

Equatorial plane in themid-line of the cell. This region

of the mitotic spindle is known as the metaphase plate.

31
Q

What happens in metaphase of mitosis?

A

Chromosomes line up along the

metaphase plate.

32
Q

The key cell cycle checkpoint - the mitotic spindle checkpoint can be activated in case of?

A

in the case of mistake in mitotic spindle assembly.

Mediated by APC/C complex
(anaphase-promoting complex/cyclosome) and cyclins A and B

33
Q

What happens in anaphase of mitosis?

A

Anaphase starts by the initiation of sister chromatid separation. Enzymatic breakdown of
cohesins.

34
Q

The spindle fibres act as tow cables to?

A

separate the sister chromatids.
The separated sister chromatids
are now referred to as daughter
chromosomes.

35
Q

The role of astral microtubules in mitosis is to?

A

ensure correct positioning and orientation of the mitotic spindle apparatus based on cell polarity.

36
Q

Kinetochore microtubules attach to the kinetochore of

chromosomes. In anaphase they?

A

shorten and draw the chromosomes toward the spindle poles.

37
Q

Interpolar microtubules extend from the spindle pole

across the equator. In anaphase they?

A

slide past each other, exerting additional pull on the chromosomes.

38
Q

What happens in telophase of mitosis?

A

The chromosomes arrive at the cell poles.

The mitotic spindle disassembles.

39
Q

The vesicles that contain fragments of
the original nuclear membrane
assemble around?

A

the two sets of chromosomes.

40
Q

What forms a new nuclear membrane around each group of chromosomes?

A

Phosphatases dephosphorylate the lamins at each end of the cell. This dephosphorylation results in the
formation of a new nuclear membrane

41
Q

What is cytokinesis?

A

The physical process that finally splits the parent cell into two identical daughter cells.

42
Q

The signal for the start of cytokinesis is?

A

Dephosphorylation of proteins, which are targets of Cdks.

43
Q

Biological roles of mitosis?

A

Growth of the organism.
Repair.
Replaicment.
Asexual reproduction (in plants vegetative multiplication).

44
Q

What process is meiosis?

A

The process by which diploid cells give rise to haploid

gametes.

45
Q

Meiosis is accomplished by combining?

A

combining two rounds of division with only one round of DNA replication.

46
Q

Meiosis is unique to?

A

Germ cells

47
Q

Meiosis I consists of how many phases?

A 
Four phases, which are:
Prophase I;
Metaphase I;
Anaphase I;
Telophase I.
48
Q

What happens in prophase I of meiosis I?

A 
Complicated process with several stages:
Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis
49
Q

What is leptotene? (meiosis I)

A

Chromosomes begin to condense

50
Q

What is zygotene? (meiosis I)

A

Chromosomes become closely paired.
Homologous chromosomes begin to align along
their entire length - pairing or forming synapsis.

51
Q

What is pachytene? (meiosis I)

A

synapsis is completed, and each pair of homologues appears as a bivalent. Crossing over occurs.

52
Q

What is diplotene? (meiosis I)

A

after recombination, the synaptonemal complex begins to break down, homologous chromosomes begin to separate but remain attached by the chiasmata.

53
Q

What is diakinesis? (meiosis I)

A

Chromosomes condense and separate until terminal chiasmata only connect the two chromosomes.

54
Q

What is crossing over? (meiosis I)

A

Crossing over is the exchange of genetic material
between non-sister chromatids of homologous
chromosomes during meiosis.

55
Q

Crossing over results in?

A

new allelic combinations in the

daughter cells.

56
Q

Crossing over (Genetic recombination) generates?

A

Genetic variability of the chromosomes.

57
Q

Crossing over is ensured by homologous recombination. What is Homologous recombination?

A

A process in which DNA molecules are broken and the fragments are re-joined in new combinations.

58
Q

Homologous recombination involves?

A 
DSB (double strand breakes) followed by
homologous reparation (re-joining the strands based on sequence of homologous chromosome).
59
Q

In the absence of homologous recombination, chromosomes often fail to?

A

Align properly for the first meiotic division – as the result there is high incidence of chromosomal loss, called nondisjunction.

60
Q

A failure in homologous recombination is often reflected in?

A

Poor fertility

61
Q

What happens in metaphase I of meiosis I?

A

Nuclear membrane disappears.
A spindle forms.
The paired chromosomes align on the equatorial plane
with their centromeres oriented toward different poles.

62
Q

What happens in anaphase I of meiosis I?

A

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

63
Q

What happens in telophase I and cytokinesis of meiosis I?

A

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.

64
Q

What happens in meiosis II?

A

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.

65
Q

Name a form of polyploidy:

A

Triploidy, tetraploidy etc.

66
Q

A possible consequence of chromosome nondisjunction:

A

aneuploidy

67
Q

A consequence of post-zygotic mitotic error:

A

Mosaicism

68
Q

Karyotype that is missing one chromosome:

A

monosomy

69
Q

Movement of chromosomes within the cell division depends on which cellular structures?

A

Microtubules and motor proteins.

70
Q

Homologous chromosomes move toward opposite poles of a dividing cell during?

A

Meiosis I. Obviously! HOMOLOGOUS, which means there are x2

71
Q

Microtubules are smaller in diameter than intermediate filaments?

A

False, mictofilaments are the smallest.

Mol / Cel Biology (17 decks)

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