Isfa: (3) The Nucleus And The Cell Cycle

Front 1

Chromatin

Back 1

Protein-DNA complex responsible for the basophilia of the nucleus in histological sections.

Front 2

Heterochromatin

Back 2

Highly condensed, darkly staining material, typically containing the transcriptionally INACTIVE genes.

Front 3

Euchromatin

Back 3

Loose, lightly stained, typically containing the transcriptionally ACTIVE genes.

Front 4

Gene transcription

Back 4

The process of transcribing DNA to RNA within the nucleus.

Front 5

Nucleosomes

Back 5

The DNA-histone complex, or "beads on the string."

Front 6

Histone

Back 6

DNA-binding protein.

Front 7

Nuclear envelope

Back 7

Separates the nucleoplasm from the cytoplasm, selectively permeable. Composed of two unit membranes.

Front 8

Nucleoplasm

Back 8

The content of the nucleus MINUS the chromatin and the nucleolus. Includes nuclear proteins, ions, and metabolites.

Front 9

Chromosome

Back 9

Formed during mitosis. A chromosome consists of two chromatids joined by the centromere; 46 chromosomes in human = 23 homologous pairs (22 autosomes, 1 sex chromosome)

Front 10

Nuclear pore

Back 10

Openings in the nuclear membrane; serve as gated channels. Active exchange of proteins and RNA and passive diffusion of small molecules and ions.

Front 11

Nuclear (fibrous) lamina

Back 11

Layer of intermediate filaments that exists just inside the inner membrane (i.e. in contact with the chromatin) of the nuclear envelope. When the lamins are phosphorylated (during cell division), the nuclear lamina and the nuclear envelope disassemble.

Front 12

Nuclear pore complex

Back 12

Mediates and regulate bi-directional, nucleocytoplasmic transport.

Front 13

Nucleolus

Back 13

A non-membranous, intranuclear structure; the site for rRNA synthesis and initial ribosomal assembly. Stains intensely with hematoxylin.

Front 14

rRNA synthesis

Back 14

Occurs in the nucleolus.

Front 15

Mitosis

Back 15

Separation of the genome through
chromosome movements, division of the cell into two daughter cells.

Front 16

Interphase

Back 16

The entire period when the cell is not in mitosis. Consists of G1, S, and G2 phase.

Front 17

G1 (gap 1) phase

Back 17

Longest and most variable (from hours to years); it is the control point for of cell division; once a cell leaves G1, it proceeds through the remaining phases in a regular, stereotyped fashion.

Front 18

S (synthesis) phase

Back 18

Period of DNA synthesis; the entire genome is duplicated; histones are synthesized largely or exclusively during S-phase; cells in S-phase can be detected by the incorporation of specially labeled DNA precursors; centrioles are also replicated during S phase.

Front 19

G2 (gap 2) phase

Back 19

The period between DNA synthesis and the beginning of mitosis; "proof-reading" of newly synthesized DNA occur and DNA repair are performed.

Front 20

M phase

Back 20

Separation of the genome through
chromosome movements, division of the cell into two daughter cells.

Front 21

Prophase

Back 21

Chromosomes condense into separate visible bodies; the nuclear membrane breaks down.

Front 22

Metaphase

Back 22

Interzonal and kinetochore spindle
fibers are formed; chromosomes line up between the spindle poles.

Front 23

Anaphase

Back 23

Sister chromatids separate; the
centromere divides; chromatids move to the opposite spindle poles.

Front 24

Telophase

Back 24

Chromosomes decondense; nuclear envelope forms around them; nucleus resumes its interphase appearance; cytokinesis divides the cytoplasm between the two daughter cells, and the cells assume their interphase morphology.

Front 25

Karyokinesis

Back 25

During cell division, the process of partition of a cell's nucleus into the daughter cells.

Front 26

Haploid

Back 26

Half the numbers of chromosomes and DNA content.

Front 27

Chromatid

Back 27

Constituents of a chromosome, two sister chromatids are homologous.

Front 28

Cyclins

Back 28

Fig. 3.11 in Histology; a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (Cdk) enzymes.

Front 29

Mitotic spindle

Back 29

The spindle is a distinct and coherent domain of the
cytoplasm containing filaments and membranous vesicles.
At each pole of the spindle there is an organizing center, the centrosome, appearing as amorphous material surrounding a pair of centrioles.

Front 30

Kinetochore

Back 30

Form on each side of the centromere. Microtubules attach to the kinetochore at one end and the spindle pole at the other to form the kinetochore fibers.

Front 31

Kinetochore fibers

Back 31

Consist of microtubules; connect the kinetochore to the spindle pole at the centrosome.

Front 32

Centrioles

Back 32

Consist of microtubules and found at the poles of mitotic/meiotic spindles. Involved in the organization of the mitotic spindle and in the completion of cytokinesis.

Front 33

Centromere

Back 33

Region typically found near the middle of a chromosome where two identical sister chromatids attach.

Front 34

Meiosis

Back 34

Involves two sequential nuclear and cell divisions that produces the gametes with half the numbers of chromosomes and DNA content (haploid) of the somatic cells (diploid). Fusion of the haploid cells forms new diploid cells during fertilization. Sexual reproduction creates novel recombination of genomes, enabling a species to adapt
efficiently and thrive in a variable environment.

Front 35

Diploid

Back 35

Contains two sets of chromosomes (2 sets of 23 in humans). The pairs are homologous, one from the paternal and one from the maternal line.

Front 36

Homolog

Back 36

A gene related to a second gene by descent from a common ancestral DNA sequence.

Front 37

Apoptosis

Back 37

Programmed cell death; active, “suicidal” process of the cell that requires active nucleic acid and protein biosynthesis. Especially important during embryonic development.
Hallmarks: DNA fragmentation, reduced cell volume, loss of mitochondrial functions, apoptotic cell bodies.
Fig. 3.18 in Histology book.

Front 38

Necrosis

Back 38

Pathologic process caused typically by various types of physical or chemical injuries;
Hallmarks: swelling, membrane breakdown, disintegration of cell.
Fig. 3.18 in Histology book.

Front 39

DNA fragmentation

Back 39

A hallmark of apoptosis.
Fig. 3.18 in Histology book.