Cell Cycle Definitions

Question 1

G2/M transition

Answer 1

Point in the eukaryotic cell cycle at which the cell checks for completion of DNA replication before triggering the early mitotic events that lead to chromosome alignment on the spindle.

Question 2

Mitogen

Answer 2

Extracellular signal molecule that stimulates cells to proliferate.

Question 3

Protein phosphatase

Answer 3

Enzyme that catalyzes phosphate removal from amino acids of a target protein.

Question 4

Retinoblastoma protein (Rb protein)

Answer 4

Tumour suppressor protein. Produced by RB1 gene. Acts at restriction point (in G1). Halts cell cycle by binding and inhibiting E2F. For cell cycle progression, it is phosphorylated by Cyclin D-CDK4/6, inactivating it and causing it to release E2F.

Question 5

SCF complex (Skp, Cullin, F-box containing complex)

Answer 5

A multi-protein E3 ubiquitin ligase complex that catalyzes the ubiquitination of proteins destined for degradation.

Question 6

Ubiquitin

Answer 6

Small, highly conserved protein present in all eukaryotic cells that can be covalently attached to lysines of other proteins.

Question 7

Anaphase (Meiosis)

Answer 7

Stages during which chromosome homolog pairs separate (I), and then sister chromatids separate (II).

Question 8

Anaphase (Mitosis)

Answer 8

Stage of mitosis during which sister chromatids separate and move away from each other.

Question 9

Bivalent

Answer 9

A four-chromatid structure formed during meiosis, consisting of a duplicated chromosome tightly paired with its homologous duplicated chromosome.

Question 10

Centrosome

Answer 10

Centrally located organelle of animal cells that is the primary microtubule-organizing center (MTOC) and acts as the spindle pole during mitosis.

Question 11

Chiasma

Answer 11

X-shaped connection visible between paired homologous chromosomes during meiosis. Represents a site of chromosomal crossing-over, a form of genetic recombination.

Question 12

Contractile ring

Answer 12

Ring containing actin and myosin that forms under the surface of animal cells undergoing cell division. It contracts to pinch the two daughter cells apart.

Question 13

Cyclin

Answer 13

Protein that periodically rises and falls in concentration in step with the eukaryotic cell cycle.

Question 14

Kinetochore

Answer 14

Large protein complex that connects the centromere of a chromosome to microtubules of the mitotic spindle.

Question 15

Kinetochore microtubule

Answer 15

In the mitotic or meiotic spindle, a microtubule that connects the spindle pole to the kinetochore of a chromosome.

Question 16

Meiosis I

Answer 16

Separation of homologous chromosomes.

Question 17

Meiosis II

Answer 17

Separation of sister chromatids.

Question 18

Midbody

Answer 18

Structure formed at the end of cleavage that can persist for some time as a tether between the two daughter cells in animals.

Question 19

Mitotic spindle

Answer 19

Bipolar array of microtubules and associated molecules that forms in a eukaryotic cell during mitosis.

Question 20

Non-kinetochore microtubule

Answer 20

In the mitotic or meiotic spindle, a microtubule that forms between the spindle poles and is not attached directly to kinetochores.

Question 21

Spindle assembly checkpoint

Answer 21

Regulatory system that operates during mitosis to ensure that all chromosomes are properly attached to the spindle before sister-chromatid separation starts.

Question 22

Centromere

Answer 22

Region of a mitotic chromosome that holds sister chromatids together. Also the site where the kinetochore forms.

Question 23

Chromatin

Answer 23

Complex of DNA, histones, and non-histone proteins found in the nucleus of a eukaryotic cell. The material of which chromosomes are made.

Question 24

Chromosome

Answer 24

Structure composed of a very long DNA molecule and associated proteins that carries hereditary information of an organism.

Question 25

Euchromatin

Answer 25

Less condensed than heterochromatin, can be transcriptionally active.

Question 26

Exon

Answer 26

Sequence of nucleotides in a gene that will be represented in mRNA or other mature RNA molecule.

Question 27

Flow cytometry

Answer 27

Streaming a suspension of cells past an illuminator and to measure the fluorescence intensity of individual labelled cells.

Question 28

Heterochromatin

Answer 28

Chromatin that is highly condensed even in interphase; generally transcriptionally inactive.

Question 29

Histone

Answer 29

One of a group of small abundant proteins, rich in arginine and lysine, that combine to form the nucleosome cores around which DNA is wrapped in eukaryotic chromosomes.

Question 30

Histone acetyltransferases (HATs)

Answer 30

Enzymes that acetylate conserved lysine amino acids on histone proteins. Only in euchromatin.

Question 31

Histone deacetylases (HDAC)

Answer 31

Enzymes that remove acetyl groups from lysine amino acids on histone proteins.

Question 32

Histone H1

Answer 32

Linker’ histone protein that binds to DNA where it exits from a nucleosome and helps to compact nucleosomes.

Question 33

Hybridization

Answer 33

In molecular biology, the process whereby two complementary nucleic acid strands form a base-paired duplex DNA-DNA, DNA-RNA, or RNA-RNA molecule.

Question 34

Intron

Answer 34

Noncoding region of a eukaryotic gene that is transcribed into an RNA molecule but is then excised by RNA splicing during production of the mRNA or other functional RNA.

Question 35

Mitotic chromosome

Answer 35

Highly condensed duplicated chromosome as seen at mitosis, consisting of two sister chromatids held together at the centromere.

Question 36

Nuclear lamina

Answer 36

Fibrous meshwork of proteins on the inner surface of the inner nuclear membrane.

Question 37

Nuclear pore complex (NPC)

Answer 37

Large multiprotein structure forming an aqueous channel (the nuclear pore) through the nuclear envelope; it allows selected molecules to move between nucleus and cytoplasm.

Question 38

Nucleosome

Answer 38

Beadlike structure in eukaryotic chromatin, composed of a short length of DNA wrapped around an octameric core of histone proteins.

Question 39

Rough ER

Answer 39

Endoplasmic reticulum with ribosomes on its cytosolic surface. Involved in the synthesis of secreted and membrane-bound proteins.

Question 40

Smooth ER

Answer 40

Region of the endoplasmic reticulum not associated with ribosomes.

Question 41

Telomerase

Answer 41

Enzyme that elongates the telomere sequences in DNA, which occur at the ends of eukaryotic chromosomes.

Question 42

Telomere

Answer 42

End of a chromosome, associated with a characteristic DNA sequence that is replicated in a special way.

Question 43

DNA transcription

Answer 43

Copying of one strand of DNA into a complementary RNA sequence by the enzyme RNA polymerase.

Question 44

RNA translation

Answer 44

Process by which the sequence of nucleotides in an mRNA molecule directs the incorporation of amino acids into protein.

Question 45

Zygote

Answer 45

Diploid cell produced by fusion of a male and female gamete. A fertilized egg.