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BIO107- CELL AND MOLECULAR BIOLOGY > Lecture 4: Nucleus > Flashcards

Lecture 4: Nucleus Flashcards

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1
Q

Parts of the Nucleus

A
  • Nuclear Envelope
    -Nuclear Pore
  • Nucleoplasm
    -Nucleolus
  • DNA (Chromatin)
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2
Q

-made of phospholipid bilayer
-separates cytoplasm and nucleoplasm
-Inner and outer membrane separated by perinuclear space
-Outer nuclear membrane continuous with RER and studded with ribosomes

A

Nuclear envelope

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3
Q

a network of protein fibers that support and organize the chromatin and other structures

A

Nuclear Matrix

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4
Q

2 types of Chromatin

A

-Active Chromatin
-Inactive Chromatin

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5
Q

Appear Lighter

A

Active Chromatin

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6
Q

Active Chromatin

A

euchromatin

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7
Q

is darker
and located near periphery
of nucleus

A

Inactive chromatin

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8
Q

Inactive chromatin

A

heterochromatin

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9
Q

*a granular region
*site of ribosome
assembly

A

Nucleolus

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10
Q

two types of heterochromatin

A

-Constitutive heterochromatin
-Facultative heterochromatin

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11
Q
  • Regions that are always heterochromatic
  • Permanent part of the genome and not convertible to euchromatin
  • Permanently inactive with regard to transcription
A

Constitutive heterochromatin

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12
Q
  • Regions that can interconvert between euchromatin and
    heterochromatin
  • Takes on staining and compactness characteristics of heterochromatin
    during some phases of development
  • Example: Barr body
A

Facultative heterochromatin

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13
Q

Heterochromatin lies against the __________ in patches and is broken up at the site of the __________.

A

-Nuclear Envelope
-Nuclear pore

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14
Q
  • Results from packaging of
    chromatin
  • Transcription stops
  • Chromosomes visible in
    microscopy
  • Separation of haploid
    chromosome sets occurs in
    nuclear division
  • Packaging ratio about 10000:
A

CHROMATIN CONDENSATION

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15
Q

basic structural unit of eukaryotic
chromosome

A

Nucleosome

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16
Q

Nucleosome is an octamer composed of two each of __, ___, ___, and ___ histone proteins

A

H2A, H2B, H3 and H4

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16
Q

DNA wrapped around octamer and H1 stabilizes association of nucleosomes to form _________

A

solenoid

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17
Q

A nucleosome is a complex of a _______ and _____________

A

histone and 146 nucleotide pairs

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18
Q

-highly conserved sequences (universality in eukaryotes)
- H3, H4 first to form, tightly bound, most conserved
- H2A, H2B, well conserved with species-specific variation
-H1 divergent, absent in S. cerevesiae

A

Histones

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19
Q

The compaction of linear DNA in eukaryotic chromosomes involves interactions between ______ and ______________

A

DNA and various proteins

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20
Q

Proteins bound to DNA are subject to change during the life of the cell. These changes affect the _______________________

A

degree of chromatin compaction

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21
Q

Proteins are brought into the nucleus from the cytoplasm, and can be sent out too by __________

A

Nuclear Pore

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22
Q

RNAs (messenger RNA, ribosomal RNA and transfer RNAs) are all transported out of the nucleus but only when they are _________

A

completed

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23
Q

– a specific amino acid sequence marks protein for nuclear entry (Laskey, 1982)
– a series of positively charged amino acids in specific sequence: (pro – lys – lys – lys – arg – lys – val –)

A

Nuclear Location Signal (NLS)

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24
Q

family of proteins
associated with the
nuclear pore
complex

A

nuclear transport
receptors

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25
Q

Example of Nuclear transport receptors mentioned in the PPT

A

Importin and Exportin

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26
Q

recognize
the NLS and bring
proteins into the nucleus

A

Importin

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27
Q

Work in the opposite direction with importin. These recognize other signals

A

Exportin

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28
Q

__________ have no nucleus

A

Prokaryotes

29
Q

The nucleus is About _______ of the cell volume

A

10%

29
Q

Eukaryotes generally have 1 nucleus except
for ____, _______and ______________

A

rbcs, osteoclasts and skeletal muscles

29
Q

-nucleus is the first organelle to be discovered
-First described by _______________

A

Franz Bauer in 1804

29
Q

Overall Function of the Nucleus

A

-Storage of genetic material
-Controls cell growth and reproduction
-Home of essential cellular processes (i.e.
replication, transcription )
- Regulates passage of materials in and out of
nucleus (RNA, ions, nucleotides, aa etc)

30
Q

The Nucleus contains __________ nuclear pores,
regulated by a protein structure,
the ____________.

A

-3000
-nuclear pore complex

30
Q

The discovery of nucleus was presented by Scottish botanist, ___________
during the 1831 meeting of the Linnaean
Society of London

A

Robert Brown

31
Q

In the nuclear pore __________ (<mw 20,000) can pass right through, _________ are strongly
regulated.

A

-small molecules
- larger molecules

32
Q

The Interior of nuclear envelope is supported
by _______________ ( on the
nucleoplasm side)

A

nuclear lamina

33
Q

A network of 10nm-diameter
protein fiber

A

Lamins

34
Q

3 Functions of nuclear Lamina

A

(1)reinforces structure of the nucleus,
(2) anchors chromatin
(3) important in replication and transcription

34
Q

*analogous to
cytoplasm
* Includes the soluble protein
nucleoplasmin
* Highly gelatinous, sticky
fluid that supports
chromosomes and nucleolus
* Suspension substance for
organelles inside nucleus
* Also dissolved are
nucleotides and enzyme

A

Nucleoplasm

35
Q

Nucleoplasm includes soluble protein called?

A

nucleoplasmin

36
Q

Functions of Chromatin

A
  • Determines chromosome structure
  • Changes chromosome structures associated with cell division
  • Regulates chromosome function
37
Q

In all cells of female
individuals, one of the two X
chromosomes is
permanently _________ and
________________________ in
transcription.

A

-inactivated
-does not participate

38
Q

The inactive X chromosome is recognizable in epithelial cells from the oral cavity as a single granule called ___________________ that is attached to the nuclear lamina

A

sex chromatin (Barr body)

39
Q

In _____________, the sex chromatin takes the form of a drum stick-like appendage to
the nucleus. These structures have been used
for gender testing

A

neutrophils

40
Q

-25% of volume of nucleus
-Site of ribosome biogenesis
-Form around specific chromosome regions
known as NOR

A

Nucleolus

41
Q

Main function of the Nucleolus

A

combine rRNA + protein to form
incomplete ribosome

42
Q

Uninterrupted chain from nucleoplasm to
interior of nucleolus (nucleolar passages) allow
macromolecules up to ___________ to circulate
through organelle

A

2000 kd

43
Q

Importance of Folded DNA Structures

A

a. for storage in the limited size of the nucleus
b. during mitosis and meiosis, it allows for neat
segregation into newly formed cells
c. manner of folding determines activity of
genes in a cell

44
Q

All histone proteins have a large positive charge; between 20 and 30% of their sequences consist of the____________,
_____________and _____________

A

-basic amino acids,
-lysine
-arginine

45
Q

Histones are large positive charge, meaning histones will bind very strongly to the _______________ in forming
chromatin.

A

negatively charged DNA

46
Q
  • At the pore, the inner and outer membranes come
    together forming an opening.
  • It is lined with protein
A

Nuclear Pore

47
Q

Nuclear Pores contains at least ________ proteins, including _____________, extending to the cytoplasm.

A

-100 Nucleoporins
-Cytoplasmic Filaments

48
Q

Nuclear Pores regulate traffic into and
out of the nucleus by means of the
_________________

A

Nuclear Location Signal (NLS)

49
Q

How do we know the function of NLS ?(Experiment 1)

A

modify the amino acid sequence (by site-directed-mutagenesis)

50
Q

Modifying the amino acid sequence (by site-directed-mutagenesis). Process and conditions:

A
  • “SV40 virus t-antigen” a protein molecule, M.W. 90,000
  • normally enters the nucleus if injected into cytoplasm.
  • normally accumulates in the nucleus (one-way)
  • experimentally visualize the location of the protein
    – using a fluorescent tag which glows
    under UV light
    – Set up a microscope with ultraviolet light
    source
  • An experimental alteration of the sequence (pro-lys-thr-lys-arg-lys-val-) completely prevents accumulation in the nucleus
51
Q

What happens when we use recombinant DNA techniques to add the NLS to a dummy protein?

A

Adding an NLS to a dummy protein using recombinant DNA techniques allows the protein to be transported into the nucleus of a cell, where it can perform its intended function.

Example of this is Normal or modified Bovine Serum Albumin (NLS added) and injected to the cytoplasm

52
Q

Protein binds to a two-protein complex. Which are?

A

importin a (Alpha) and importin b (beta)

53
Q

___________ is a receptor for the NLS portion of the protein (i.e. it recognizes and sticks to this region.)

A

Importin a (alpha)

53
Q

Complex and protein stick to cytoplasmic filament is mediated by _____________

A

importin b (beta)

54
Q
  • Not an energy consuming step, it can go back at this point unless captured by the RanGTP in next step
A

Complex moves into nucleoplasm

55
Q

importin b stays on the ____________ after binding and complex dissociation.

A

Ran-GTP

56
Q

Ran-GTP - importin b complex moves back to the cytoplasm, ________________

A

down a concentration gradient

56
Q

the Ran-GTP is converted to____________ by the enzyme ______. This causes it to loosen from importin b

A
  • Ran-GDP + Pi
    -RANGAP
57
Q

an exportin molecule binds to ___________, setting it up for transport out of the nucleus

A

importin a

58
Q

Enzyme _______ re-forms Ran-GDP to Ran-GTP

A

RCC1

59
Q

Mechanism of Protein complex through nuclear pore complex

A
  1. Protein binds to a two-protein complex (importin a and importin b)
  2. Complex and protein stick to cytoplasmic filament
  3. Complex moves into nucleoplasm
  4. Complex binds to another protein (Ran-GTP)
  5. Importin b complex moves back to the cytoplasm, down a concentration gradient
  6. the Ran-GTP is converted to Ran-GDP + Pi by the enzyme RANGAP. This causes it to loosen from importin b
  7. an exportin molecule binds to importin a, setting it up for transport out of the nucleus
  8. Ran-GDP diffuses back to the nucleus
  9. Restoration to initial state
60
Q

___________ is an energy source and controls
the process

A

GDP to GTP conversion

61
Q

Molecules always diffuse from high to low concentration, so if the gradient is maintained, it can be used to __________________________

A

bring importin b back to the cytoplasm

62
Q

RCC1 occurs only in the _________, RANGAP occurs in ___________

A

-nucleoplasm
-cytoplasm

63
Q

By breaking down ________ and thereby removing it, RANGAP maintains the concentration gradient. It can take the
other molecule out with it.

A

Ran-GTP

64
Q

By changing _________ back to Ran-GTP, RCC1 maintains the gradient helping _______ to diffuse back into the
nucleus

A

Ran-GDP

BIO107- CELL AND MOLECULAR BIOLOGY (13 decks)

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