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Flashcards in Nucleus Deck (62):
1

Components of nucleus

nuclear envelope(membrane), nucleoplasm, chromatin, nucleolus

2

Chromatin of nucleus contains

DNA encoding genetic apparatus of chromosomes

3

nuclear pores are formed by the fusion of

the inner and outer nuclear membranes and associated with nuclear pore complex

4

Nuclear pore complex contains how many different proteins

>450 different proteins

5

What is a nuclear pore complex?

proteins arranged around each nuclear pore in an octagonal symmetry (cylindrical aqueous channel opening)

6

What can diffuse across NPC?

Ions, small molecules and proteins

7

Transport of larger molecules in across NPC requires

nuclear pore receptor proteins (fibril associated)

8

All proteins in the nucleus are imported from

cytoplasm

9

Nuclear pore receptor proteins recognize what on the protein?

nuclear localization signals

10

When larger molecules are recognized they are transported via

active transport

11

Protoplasm surrounded by nuclear envelope

nucleoplasm

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two forms of chromatin that reside with the nucleus

heterochromatin and euchromatin

13

Where is heterochromatin located in the nucleus

concentrated at nucleus periphery, around the nucleolus and scattered throughout the nucleoplasm

14

Heterochromatin is transcriptionally

inactive

15

Euchromatin is transcriptionally

active

16

Chromatin

Double stranded DNA in chromatin complexed with histones and non-histone acidic proteins.

17

Histones have

+charged amino acids that bind to DNA

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Nucleosome

fundamental packing unit of chromatin

19

How many copies of each histone does nucleosome contain?

2 copies of each H2A, H2B, H3, and H4, which form the nucleosome core around which the DNA double helix is wrapped two full turns

20

Describe what composes the "beads of a string" analogy for chromatin

beads= nucleosomes; string=linker DNA

21

condensed chromatin contains

an additional histone, H1, which wraps around groups of nucleosomes forming 30nm diameter fibers, the structural unit of the chromosome

22

When do chromosomes become visible?

Chromosomes become visible during mitosis and meiosis when their chromatin is condensed

23

Barr body

corresponds to one of the two X chromosomes; present in nearly all somatic cells of female mammals

24

What phase is the barr body (inactive X chromosome) visible as a dark staining evagination protruding from the nucleus

Interphase

25

Two major periods of cell cycle

Interphase and Mitosis

26

Cells in G0 state

Temporarily suspended in nondividing resting cells. Such cells may reenter cycle and divide again

27

Which is longer? Interphase or Mitosis

Interphase is much longer

28

Period during which cell doubles in size and DNA content

Interphase

29

Three phases of interphase

G1, S, and G2

30

Cells that fail to reach restriction point become

resting cells and enter the G0 state

31

How long does the G1 phase last

lasts from a few hours to several days

32

In the cell cycle, G1 phase(gap phase) occurs when

Just after mitosis-cell growth and protein synthesis occur-restoring daughter cells to normal volume and size

33

The synthesis of regulatory proteins in G1 phase enables the cell to

reach a threshold(restriction point) and proceed to S phase

34

What occurs in the S phase (synthetic phase)

DNA replication and protein synthesis occur. Chromosomes duplicated

35

Centrioles in S phase

self-duplicated

36

Cells in S phase will uptake

tritiated thymidine- counted in scintillation counter or by autoradiography

37

When does G2 phase(gap phase) occur in the cell cycle?

Follows the S phase and extends to mitosis

38

What occurs in G2 phase (the gap phase)

Cell resting and preparing to divide: centrioles grow to maturity; energy for mitosis is stored; RNA and proteins necessary for mitosis are synthesized

39

Cell cycle control factors

cyclins; cyclin-dependent kinases

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CDK

cyclin dependent kinases

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Cyclins and cyclin dependent kinases basic function

regulate the cell cycle and move it in one direction

42

How are cyclins and cyclin dependent kinases controlled

controlled by regulatory proteins – inhibit activity of kinases (cyclin kinase inhibitors) and degrade cyclins (polyubiquinated and degraded by proteosome

43

Start Kinase is used to

initiate S phase

44

M-phase promoting factor

initiate mitosis

45

Two primary ways to control cell cycle

1) Regulation of genes that suppress cell proliferation 2) Regulation of growth factors that stimulate cell growth

46

Tumor suppressor gene-Normal cell has

2 copies of retinoblastoma gene.(Normal Rb protein prevents mitosis (entry into S phase))

47

If one copy of Rb mutated

other copy of gene still suppresses growth

48

Mutation in both tumor suppressor genes

results in abnormal Rb gene product and cancer

49

p53

DNA repair gene which exhibits frequent mutations; p53 acts prior to DNA replication by detecting DNA damage and delaying entry into S phase until damage repaired

50

mutation in how many of four subunits may result in an abnormal p53 protein

mutation in 1 of 4 p53 subunits may result in abnormal p53 protein

51

When does mitosis occur

follows the G2 phase and completes the cell cycle

52

Karyokinesis

Division of the nucleus

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Division of the cytoplasm

cytokinesis

54

Mitosis results in

two identical daughter cells

55

Centrosome

Pericentriolar material plus associated 2 centrioles oriented orthogonally to each other. Centrosomes function as microtubule organizing centers and function as the mitotic spindle pole during mitosis

56

Astral microtubules

radiate from centrosomes; function to separate the spindle poles and position them in the cell

57

Polar microtubules

extend from each pole and overlap in middle of cell- responsible for pushing poles of cells apart

58

Kinetochore microtubules

attach to kinetochore that forms at the centromere of duplicated chromosomes- moves separated daughter chromatids to each pole

59

Centromere

constriction in the middle of the attached sister chromatids where a protein complex (kinetochore) is assembled. Kinetochore microtubules
will attach to the kinetochore and pull the sister chromatids towards opposite poles of the cell

60

Normal process of programmed cell death. May be triggered by multiple pathways and stimuli (cytokines, toxins, hormones, and other cell stressors – radiation, viruses, oxygen or nutrient deprivation)

Apoptosis

61

When are caspases activated

Caspases are activated in apoptosis and drive apoptotic cascade

62

Function of caspases

cleave cell proteins and activate other enzymes like DNAse