The Cell Organelles Part 4

Question 1

Nucleus

Answer 1

Every cell in the body has a nucleus with the exception of mature erythrocytes(red blood cells).
Main components: The nuclear envelope, chromatin, nucleolus, nuclear matrix or nucleoplasm.

Question 2

Nuclear Envelope

Answer 2

The nuclear envelope is formed by two membranes with a perinuclear cisternal space and it separates nucleoplasm from the cytoplasm.

Question 3

Laminopathies

Answer 3

Lamins and their associated proteins have roles in chromatin organization, spacing of nuclear pore complexes, and reassembly of the nucleus after cell division.

Question 4

What are the two hypotheses concerning the pathogenic mechanism of laminopathies have been considered:

Answer 4

1) The gene expression hypothesis- regards lamin A and lamin C as essential for the correct tissue-specific expression of certain genes.
2) The mechanical stress hypothesis- proposes that a defect in lamin A and lamin C weakens the structural integrity of the nuclear envelope

Question 5

Chromatin

Answer 5

Chromatin, a complex of DNA and proteins is responsible for the basophilia of the nucleus.
There are two types of chromatin: Heterochromatin and Euchromatin

Question 6

Heterochromatin

Answer 6

1) Constitutive heterochromatin- is always condensed and consists of repetitive DNA found near the centromere and other regions
2) Facultative heterochromatin cna be either condensed or dispersed

Question 7

Sex chromatin

Answer 7

Sex chromatin helps the study of other anomalies involving the sex chromosomes

Question 8

Chromosomes

Answer 8

Each chromosome iis formed by 2 chromatids that are joined together at a point called centromere.

Question 9

Nucleolus

Answer 9

Spherical structure that is rich in rRNA and protein. In EM, the nucleolus consists of three components: 1) fibrillar centers; 2) a dense fibrillar component surrounding the fibrillar centers; and 3) a granular component

Question 10

Components of the nucleus and nucleolus

Answer 10

1) Nucleolar proteins nucleolin and fibrillarin are found in the dense fibrillar component
2) Nucleostemin is present in the granular component
3) RNA polymerase 1 occupies the fibrillar center

Question 11

Nucleoskeleton

Answer 11

Continuous fibrillar structure that seen where the nucleic acid and soluble compound were removed

Question 12

Cell Cycle

Answer 12

The cell cycle incorporates two principal phases: the interphase, representing continuous growth of the cell, and the M phase (mitosis) characterized by partitioning of the genome.

Question 13

Interphase is itself divided into three phases:

Answer 13

1) G1 (Presynthesis) intense synthesis of RNA and proteins, including proteins that control the cell cycle, and the cell volume restored.
2) S (DNA Synthesis and beginning of the duplications of the centrosomes with their centrioles).
3) G2 (cell growth and reorganization of cytoplasmic organelles, synthesis of RNA & proteins)

Question 14

Mitosis

Answer 14

Mitosis is a process of chromosome segregration and nuclear division followed by cell division that produces two daughter cells with the same chromosome number and DNA content as the parent cell

Question 15

Mitotic cell division consists of the following phases:

Answer 15

Prophase, Metaphase, Anaphae, Telophase, Cytokinesis

Question 16

Prophase

Answer 16

1) Opposite centrosomes initiate the assembly of the mitotic spindle
2) The nuclear envelope breaks down when lamins phosphorylate
3) Replicated chromosomes condense. Each chromosome consists of two identical chromatids held together at the centromere or primary constriction of the chromosome.

Question 17

Metaphase

Answer 17

The kinetochore develops at the centromeric region.

2) Chromosomes align at the equatorial plate
3) Microtubules extending from one cell pole to the other are polar microtubules.
4) Two opposing but balanced forces maintain the chromosomes at the equatorial plate
5) Anaphase-promoting complex disassembles and if the kinetochore is not attatched to the microtubules the APC arrests the mitotic cycle at the metaphase by delaying cyclin activity.

Question 18

Anaphase

Answer 18

1) Sister chromatids separate by the synchronous detachment of the centromeres.
2) Topoisomerase, an enzyme present in the kinetochore region, frees entangled chromatin fibers to facilitate the separation of the sister chromatids
3) Chromatids are pulled to opposite poles by two independent but coincedental processes

Question 19

Telophase

Answer 19

1) The nuclear envelop gradually reforms
2) Chromosomes decondense
3) Transient contractile ring, composed of actin and myosin develops during cytokinesis around the equatorial region and contracts to separate the two daughter cells by abscission
4) Residual microtubules can be found in the core of the contractile ring
5) Radiating, kinetochore, and polar microtubules disappear

Question 20

p53

Answer 20

The tumor suppressor protein protects the integrity of DNA in response to harmful stress called genotoxic stress