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Histology & Embryology > Cytology I: The nucleus > Flashcards

Cytology I: The nucleus Flashcards

1
Q

What does the nuclear membrane contain?

A

The nuclear membrane contains 2 unit membranes with nuclear pores.

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2
Q

What is the nuclear membrane continuous with?

A

The nuclear membrane is continuous with the rough endoplasmic recticulum.

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3
Q

What is nucleolus?

A

Non-membrane bound structure, containing fibrils and granules rich in RNA.

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4
Q

How does the nucleolus look under Electron microscope and light microscope?

A
  • It is electron dense in EM

- Appears rounded and intensely basophilic (dark blue)

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5
Q

What is the the function of nucleolus?

A

It is the site of ribosomal RNA synthesis and initial ribosomal assembly.

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6
Q

What happens with the nucleoli in an active cell?

A

Active cells in protein synthesis have well developed and up to 4 nucleoli.

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7
Q

What are ribosomes?

A

Ribosomes are small cytoplasmic granules used to assemble amino acid into proteins.

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8
Q

What are chromosomes?

A

Chromosomes are long threads consisting of DNA, some RNA and associated proteins

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9
Q

How many chromosomes are there in a cell?

A

Most cells contain 46 chromosomes

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10
Q

What condition do chromosomes mainly stay in?

A

Chromosomes usually are tangled threads aka chromatin.

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11
Q

What happens to chromatin in mitosis and meiosis?

A

During mitosis and meiosis, chromatin are very visible and separated.

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12
Q

What are euchromatin?

A

Euchromatin are dispersed and extended chromatin.

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13
Q

How does euchromatin stain?

A

It is present in the lightly stained regions of the nucleus.

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14
Q

What stage of stranscription is euchromatin in?

A

Euchromatin contains the portion of the genome “actively” being transcribed.

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15
Q

What are heterochromatin?

A

Heterochromatin are the condensed and tightly coiled regions of chromatin.

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16
Q

What stage of transcription are heterochromatin in?

A

Heterochromatin is the transcriptionally inactive portion of the genome.

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17
Q

How do heterochromatin appear under EM and LM?

A

Heterochromatin appears electron dense under EM and extremely basophilic under LM.

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18
Q

How is nuclear appearance useful?

A
  • Shape, size, and staining of a nucleus is useful for cell identification
  • It can give clues about eh functional activity of the cell.
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19
Q

What does the proportion b/w euchromatin and heterochromatin indicate?

A

That proportion is an indication of how much of the cell’s genome is in active transcription.

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20
Q

What does this mean?
- Light staining nucleus
+ Lots of dispersed chromatin
+ Large well developed nucleolus

A

This means:
Euchromatic nucleus
- transcriptionally active
- metabolically active

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21
Q

What does this mean?
- Dark staining nucleus
+ Lots of condensed, coiled chromatin
+ small, poorly developed nucleolus

A

Heterochromatic nucleus

  • transcriptionally inactive
  • metabolically inactive
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22
Q

How can a dead or dying cell be identified?

A
  • It can be identified by its abnormally shaped nucleus

- The nucleus may shrink and become very heterochromatic aka pyknotic

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23
Q

What is mitosis?

A

It is a cell division that give rise to 2 identical cells.

24
Q

What are the 2 identical cells given rise by mitosis?

A

They are diploid cells (2N)

25
Q

Is mitosis a continuous or discontinuous process?

A

It is a continuous process but it is divided into 4 stages.

26
Q

What are the 4 stages of mitosis?

A
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
27
Q

What are the events that occur before mitosis?

A
  • Chromosomes are dublicated in S phase

- The two centrioles replicate resulting in 4 centrioles.

28
Q

What happened to the DNA content after S phase?

A

The DNA content goes from 2N to 4N

29
Q

Where are the chromatid and its copy attached?

A

Centromere

30
Q

What are centrioles made of?

A

The centrioles are composed of 9 triplets of microtubules.

31
Q

What is the main function of the centrioles?

A

It is a center that assembles the microtubules of the mitotic spindle

32
Q

What is the function of the mitotic spindle?

A

It attaches and moves the chromsomes during mitosis.

33
Q

What happens in interphase?

A
  1. Nucleus appears normal
  2. DNA duplicated in previous S phase (2N-4N)
  3. Chromatids are attached at centromere.
  4. Two pairs of centrioles are present
34
Q

What happens in prophase?

A
  1. Chromosomes condense, coil, and are visible as dark thread
  2. Each pair of centrioles migrate to each pole.
  3. Mitotic spindle continue to form.
  4. Nuclear membrane disappear at the end of prophase.
35
Q

What happens in metaphase?

A
  1. Mitotic spindle attaches to the chromosomes at the kinetochore.
  2. Chromosomes line up at the equator.
  3. Chromosomes are most condensed.
  4. Chromosomea are karyotyped.
36
Q

What happens in anaphase?

A
  1. Sister chromatids split apart at the centromere forming two separate chromosomes.
  2. Chromosomes are pulled toward the opposite poles.
37
Q

What happens in telophase?

A
  1. Chromosomes begin to uncoil and become invisible.

2. Nuclear membrane and nucleolus reform.

38
Q

What happens in cytokinesis?

A

Cleavage of the cytoplasm into 2 separate cells by constriction of the cell at the equator by the contractile ring composed of actin/myosin filaments.

39
Q

What is karyotyping?

A

It is the visualization of the # and morphology of chromosomes of an individual.

40
Q

Explain the process of Karyotyping

A
  1. Replicating cells are obtained from mouth, blood of amniotic cells from the placenta.
  2. These cells are grown in tissue culture.
  3. Colchicine is added to the medium and attaches to the spindle and blocks the cells in metaphase.
  4. Chromosomes are isolated, counted and examined for abnormalities.
41
Q

What is Barr body?

A

It is an inactivated X chromosome.

42
Q

How many X chromosome is active in each diploid cell?

A

Only one X chromosome is active in each diploid cell.

43
Q

What happens to the inactive X chromosome in female?

A

It is condensed and transcriptionally inactive -> Barr body.

44
Q

What is the appearance of Barr body?

A

It usually appear as a small, dark mass of heterochromatin on the edge of the nucleus.

45
Q

What is Barr body used for?

A

It can be used as a method of sex typing.

46
Q

How is the cell cycle divided?

A

It is divided into cell division (mitosis) and interphase (G1, S, G2)

47
Q

What happens in G1?

A

Protein and RNA synthesis.

Cell grows and perform specialized functions

48
Q

What is G0?

A

G0 is outside the cell cycle where cell is not actively replicating.

49
Q

What happens in S?

A

DNA replication

Synthesis of proteins associated with chromatin.

50
Q

What lays b/w G1 and S?

A

Between G1 and S is a stop point where cell determines if mitosis is possible.

51
Q

What happens in G2?

A

Synthesis of the mitotic apparatus.

52
Q

Which phase are most cells in?

A

Most cells are in G1 or G0

53
Q

What is a labile cell?

A

Labile cells move through this cycle very quickly and can develop into cancer.

54
Q

What are permanent cells?

A

Permanent cells are highly differentiated cells which have exited the cycle and cannot re-enter such as neuron cells.

55
Q

What are Quiescent stable cells?

A

Quiescent stable cells are cells that are in G0 but can re-enter the cell cycle by an appropriate stimulus. e.g. hepatocyte.

Histology & Embryology (5 decks)

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