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Cell Bio Semester 1 > Nucleus > Flashcards

Nucleus Flashcards

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1
Q

what is found in the nucleus?

A

DNA, RNA, proteins

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2
Q

what kind of membrane does the nucleus have?

A

double memb- 2x phospholipid membs
inside- contact w/ nuclear lamina
outside- contact w/ ER

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3
Q

function of nucleus?

A
  • separate fragile chromosomes from cytoskeletal cytoplasmic filaments
  • separate RNA transcription from TRANSLATION machinery
  • regulate RNA export
  • regulate import/export of other proteins

ENABLES ADDITIONAL COMPLEXITY OF EUKARYOTIC CELLS

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4
Q

how could the nucleus have evolved to exist?

A
  • DNA and ribosomes were attached to cell memb at many points
  • memb INVAGINATES forming MESOSOMES
  • repeated invagination forms NUCLEUS
  • ER formed from invaginations
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5
Q

what is DNA?

A

double helix of a SUGAR PHOSPHATE BACKBONE with PAIRS OF BASES protruding into the middle

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6
Q

what does T bond with? how many h bonds?

A

with A, 2 H bonds

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7
Q

what does C bond with? how many h bonds?

A

G, 3 H bonds

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8
Q

in the double helix, one turn is how many base pairs?

A

roughly 10

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9
Q

what does the helix structure cause?

A

MAJOR (big) and MINOR (small) groove

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10
Q

function of DNA

A
  • store genetic info

- for replication and expression

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11
Q

what decides where transcription starts?

A

REGULATORY (promotor) sequences

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12
Q

when does RNA processing take place?
what does RNA processing do?
where does it occur?

A

1- takes place after transcription by RNA polymerase II
2- it:
- tops and tails the message (CAPPING and POLYADENYLATION)
- removes introns (SPLICING)
3- in NUCLEUS

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13
Q

what are non sex chromosomes called?

A

AUTOSOMES

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14
Q

where is the telomere on a chromosome?

A

at the ends

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15
Q

what is the function of telomeres?

A

PROTECTION- as ends are most vulnerable to nucleases (degrade DNA)

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16
Q

what happens to telomeres with age?

A

SHORTEN w/ age

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17
Q

function of centromere?

A
  • hold metaphase chromosomes together

- attaches to mitotic spindle

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18
Q

structure of centromere?

A
  • repetitive sequences
  • highly packaged
  • don’t contain genes (like telomeres)
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19
Q

what is the name of the short and long arms of chromosomes?

A 
p = short arm 
q = long arm
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20
Q

in terms of classifying autosomes, what are the three names that you can give autosomes?

A

1- METACENTRIC (centromere in middle)
2- SUBMETACENTRIC (centromere is intermediate)
3- ACROCENTRIC ( centromere is TERMINAL)

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21
Q

what are the levels of packaging of DNA from double helix to chromosome?

A 
1 DNA in double helix
2 beads-on-a-string form of chromatin
3 30nm chromatin fiber of packed nucleosomes
4 chromosome section in extended form
5 condensed  section of chromosome 
6 entire chromosome condensed
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22
Q

what is the structure of NUCLEOSOMES (beads-on-a-string) (packaging factor 3x)?
how is an octamer made?
what kind of bonding is present?

A
  • core nucleosomes made of histone proteins
  • OCTAMER from: 2 of each H2A, H2B, H3 and H4
  • DNA winds 1.65 times around the histone core to form the nucleosome
  • H bonds form between DNA and histone octamer
  • each nucleosome separated from next by up to 80nt of LINKER DNA
23
Q

can DNA in nucleosome structure be used for transcription?

A

yes, as the packaging is loose enough for RNA polymerase etc

24
Q

what is the first structure formed in the packaging of DNA? what is the packaging factor?

A

NUCLEOSOME- (beads on a string)

3x packaging factor

25
Q

what is the second structure formed in the packaging of DNA?

what is the packaging factor?

A

chromatin thread—–> 30nm FIBRE

10x packaging factor

26
Q

what is the structure of the 30nm fibre?

A
  • H1 in centre pulls nucleosome into spiral
  • interactions between the tails of 4 core histones help nucleosomes attach to each other
  • O forms 30nm fibre
27
Q

can DNA in 30nm fibre structure be used for transcription?

A

no, it is too tightly packaged

28
Q

what else is found in the 30nm fibre structure?

A
  • REGULATORY PROTEINS like transcription factors that can control how DNA is accessed
  • removal of reg. proteins makes DNA more accessible for transcription and vice versa
29
Q

what is the third structure formed from the packaging of DNA?
what is its structure?

A
  • LOOPED DOMAINS

- held in place, “scaffolded” by proteins

30
Q

how can DNA in a tightly packed looped domain be accessed for gene expression?

A
  • histone modifying enzymes and chromatin remodelling complexes
31
Q

what are the visible differences in HETEROCHROMATIN and EUCHROMATIN?
what are the other differences?

A

HETEROCHROMATIN: DARK, highly packaged DNA O silenced genes

EUCHROMATIN: LIGHT, active genes

32
Q

what is the fourth structure formed in the packaging of DNA?
how is this structure formed?
what is the packaging factor?

A

LOOPED DOMAINS—–>COILED MITOTIC CHROMOSOME

  • formed using ENZYMES called CONDENSINS
  • use ATP to wind+ package chromatin
  • packaging factor= 10,000x
33
Q

do nuclear proteins (eg histones, transcription factors) move in or out of the nucleus via nuclear envelope?

A

IN

34
Q

do RNA molecules (eg mRNA, rRNA, tRNA) move in or out of the nucleus via nuclear envelope?

A

OUT

35
Q

do ribosome subunits (assembled in nucleus) move in or out of the nucleus via nuclear envelope?

A

IN AND OUT

36
Q

what can pass through the nuclear pore and HOW?

how do large molecules pass through?

A
  • small molecules can DIFFUSE through
  • med size diffuse slowly
  • large molecules are regulated by ACTIVE TRANSPORT
37
Q

what can pass through the nuclear pore and HOW?

how do large molecules pass through?

A
  • small molecules can DIFFUSE through
  • med size diffuse slowly
  • large molecules are regulated by ACTIVE TRANSPORT
38
Q

what is a nuclear localisation signal?

A

a.a sequence that

tags a protein for import into nucleus by nuclear transport

39
Q

what are nuclear localisation signals made of?

A
  • rich in POSITIVELY CHARGED (basic) amino acids eg ARg, Lys, Pro
40
Q

what happens if one a.a in a nuclear localisation signal is changed?

A
  • mutant will not go into the nucleus (stay in cytoplasm)
41
Q

how is nuclear import of proteins different to the translocation of proteins across ER membranes?

A

in nuclear import, the proteins transported are FOLDED, whereas in translocation across memb (like mitochondria and ER), proteins are UNFOLDED

42
Q

what are the properties of NLS?

A
  • position in protein seq is VARIABLE
  • sequence can be SPLIT WITHIN THE PRIMARY SEQUENCE making it bipartite
  • after they import a protein into nucleus, they are NOT REMOVED
43
Q

what recognises NLS?

A

nuclear import receptors called IMPORTINS

44
Q

how is protein cargo transported across the nuclear membrane?

A
  • IMPORTINS (receptors) bind to NLS on cargo and to FG repeats of nuclear pore complex
  • protein cargo passes from one subunit to the next and it eventually reaches the nucleus
45
Q

once the cargo protein is in the nucleus, what happens?

A
  • importin-cargo complex DISSOCIATES

- importin can be recycled

46
Q

how is nuclear import regulated? ie how can you control what stays in, goes back out etc?

A
  • nuclear receptors binding to a hormone (eg glucocorticoid) ALLOWS the protein to go into the nucleus
47
Q

where is the nuclear envelope?

A
  • enmeshed between two networks of intermediate filaments
48
Q

what does the nuclear envelope consist of?

A

inner and outer memb

49
Q

where is the nuclear lamina found?

A

in between the inner and outer membs

50
Q

what is the structure of nuclear lamina? what is it made of?

what is its function?

A
  • 2D lattice of fibres called INTERMEDIATE FIBRES
  • made of LAMINS proteins
  • function: provides support and important in organisation
51
Q

what is the structure of a lamin?

A
  • globular head ends
  • rod like central domain in a HELIX O forming a DIMER
  • pairs of dimers (tetramers)twist into long filaments
52
Q

what is the structure of a lamin?

A
  • globular head ends
  • has COOH and NH2 terminals on each end
  • rod like central domain in a HELIX O forming a DIMER
  • pairs of dimers (tetramers)twist into long filaments
53
Q

how does the lamina attach to the membrane?

A
  • LIPID like anchor on COOH terminus of each lamin attaches to inner nuclear phospholipid membrane

Cell Bio Semester 1 (5 decks)

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