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Biochemistry and Cell Biology Semester 1 > Nucelus > Flashcards

Nucelus Flashcards

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1
Q

how is mRNA modified

A

adding a 5’ cap (guanine) and 3’ polyadenylation (adenosine monophosphate) allowing stability

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2
Q

chromosome

A

defined region of chromatin

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3
Q

nuclear envelope structure

A

double phospholipid bilayer
reticulum continues with envelope
cytoskeleton criss cross

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4
Q

nuclear pore complex (NPC)

A

large quaternary structure
aqueous channel connecting nucleoplasm to cytosol
8 fold symmetry
cytosolic fibrils reach into cytosol
30 types of nucleoporin
dynamic - constantly passing through

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5
Q

sizes of substances passing through NPC

A

<500 da freely move
up to 60KDa longer diffusion
>60 require mechanisms

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6
Q

nuclear localisation signal (NLS)

A

tell protein to go into nucleus
proteins synthesised on cytosolic ribosome containing NLS

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7
Q

nuclear import receptors (NIR)

A

NLS recognised by NIR
NIR bind to FG repeats on nucleoporins
protein moves through by binding sequentially to FG repeats

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8
Q

Ran cycle components

A

GTP
GTP binding protein
GAP
GEF

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9
Q

Ran cycle: GTP binding protein

A

binds to GTP and hydrolyses to GDP

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10
Q

Ran cycle: GAP

A

GTPase activaron protein binds to GTP binding protein and induces hydrolysis

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11
Q

Ran cycle: GEF

A

guanine exchange factor (binds to GTP binding protein to release GDP)

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12
Q

protein import

A

NLS recognised by NIR and binds to it
protein complex binds to cytosolic fibrils
moves through by binding to FG repeats
arrives in nucleoplasm
Ran GTP binds to NIR
NIR releases cargo
empty NIR bound to RanGTP moves through NPC to cytoplasm
Ran GTP bound by ran binding protein and release NIR
Ran GAP hydrolyses Ran GTP to Ran GDP
Ran GDP goes through NPC
Ran Gef converts to Ran GTP

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13
Q

protein export

A

protein binds to nuclear export receptor NER
NER and cargo binds to nucleoporins on basket
moves through NPC arriving in cytoplasm
Ran GTP bound by Ran binding protein
Ran GAP hydrolyses GTP to GDP
NER releases cargo and Ran GDP
Ran GDP travels back to nucleus
Ran GDP become Ran GTP by GEF and binds to NER

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14
Q

mRNA export

A

mature mRNA complex with proteins (messenger ribonucleoprotein mRNP)
mRNP exports using NER
NER binds to adaptor proteins
adaptor proteins bind to 5’ end of mRNA interacting with cap binding complex (CBC)
adaptor proteins only bind if mRNA has processed

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15
Q

nucleolus 2 forms

A

heterochromatin - transcriptionally inactive and densely packed
euchromatin - active and loosely packed

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16
Q

where are ribosomes synthesised

A

nucleolus

17
Q

full make up of a ribosome

A

80S total
1x60S 1x40S
60 = 5S rRNA, 5.8S rRNA, 28S rRNA, 49 proteins
40 = 18S rRNA, 33 proteins

18
Q

where are rRNA found

A

clustered on DNA tandem repeats

19
Q

where are 18, 5.8 and 28S rRNA transcribed

A

nucleolus by RNA polymerase I

20
Q

where are 5S rRNA transcribed

A

nucleoplasm by RNA polymerase II

21
Q

benefit of tandem repeats

A

generate lots in one go

22
Q

how is discrete rRNA formed

A

add ribosomal proteins via ran cycle
45S pre rRNA forms 90S pre ribosome and modified into 3xrRNA’s

23
Q

snoRNP

A

small nucleolar ribonucleoproteins

24
Q

snoRNA

A

small nucleolar RNA’s

25
Q

what is a snoRNP

A

snoRNA and protein

26
Q

what are snoRNA

A

complexed with structural proteins and enzymes which modify 90S

27
Q

how do snoRNA modify

A

recognise specific areas of rRNA that require modification

28
Q

3 methods of RNA modification

A

methylation
conversion of uridine to pseudouridine
cleavage of 45S pre rRNA

29
Q

methylation

A

of hydroxyl groups stabilises ribose sugar acting as a tag to tell its mature

30
Q

conversion of uridine to pseudouridine

A

isomerisation catalysed by psi synthases improves affinity of RNA to tRNA

31
Q

cleavage of 45S pre rRNA

A

snoRNP contain enzymes - exoribonucleaes removing ETS
endoribonucleases remove ITS

32
Q

ETS

A

externally transcribed spacers

33
Q

ITS

A

internally transcribed spacers

34
Q

export of ribosomes

A

5S rRNA binds to 5.8 and 28S forming 60S. 40 and 60S transported separately and recombine

Biochemistry and Cell Biology Semester 1 (12 decks)

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