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NESC 3670: Genes, Brain & Behaviour > Lec 5/6: Epigenetic Mechanisms of gene regulation > Flashcards

Lec 5/6: Epigenetic Mechanisms of gene regulation Flashcards

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1
Q

what are the 2 components of the epigenome?

A

1) Histones associated with DNA

2) DNA methylation- covalently bound to genome, stable long-term signal

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2
Q

what is DNA methylation?

A

methyl marks added to certain DNA bases repress gene activity

  • covalently modification of cytosine in C-pyruvate- G sequence
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3
Q

what is histone modification?

A

combo of different molecules can attach to the “tails” of proteins called histones.
- alter activity of DNA wrapped around them

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4
Q

what is the end product of DNA methylation?

A

5-methyl cytosine

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5
Q

_____ first discovered methylated DNA in 1948

A

Rollin Hotchkiss

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6
Q

what did Hotchkiss discover in experiments of DNA methylation?

A

DNA from certain sources had a 5th base group = 5-methyl cytosine

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7
Q

(1970s) Harold Weintraub & colleagues noticed active genes are ___ or _____

A

low in methyl groups

under methylated

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8
Q

conclusion that Weintraud made

A

methylation helped repress genes

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9
Q

genes associated with high levels of chromatin have ____ levels of methylations

A

lower level of methylation

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10
Q

DNA methylation is chemical ____ of DNA

A

modification

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11
Q

DNA methylation can be inherited without ____ ____

A

sequence change

  • able to fit into epigenetic paradigm
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12
Q

which species is DNA methylation common in?

A

30%- plants
10%- vertebrates
- most fungi

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13
Q

which species is DNA methylation absent from?

A

yeast
flies
nematodes

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14
Q

at what positions on the gene does DNA methylation occur?

A

5’- CG- 3’ (CpG) positions

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15
Q

in DNA methylation, high frequency of __ dinucleodites aka ____

A

CG dinucleotides

aka CpG islands

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16
Q

what are CpG islands?

A
  • typically 300-3000 base pairs in length
  • hypomethylated
  • near approx 70% human promoters
  • methylation correlated with tissue-specific gene expression
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17
Q

methylation of cytosine is regulated by…

A

DNA methyltransferase (DMNT)

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18
Q

how does DMNT work?

A

deoxycytidine + SAM

–> (DMNT) —>

5-methyl-cytidine + SAH

[cytosine–> 5-methylcytosine]

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19
Q

measure levels of SAM and SAH to look at ???

A

levels of methylation

levels of DMNT

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20
Q

CG nucleotides predominantly found where?

A

within major grooves

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21
Q

blocking Tc by CG groups

A
  • through major groove
  • can block Tc factors from binding
  • methyl groups need to be removed for Tc to bind
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22
Q

cytosine methylation maintains ____ ____ ____

A

inactive-condensed chromatin site

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23
Q

steps to cytosine methylation

A

Tc + RNA polymerase
–> transcription, acetylation

–> DNA methyltransferase, 5-methyl-C

–> methyl- CpG binding proteins associated with co-repressors, histone deacetylase

–> transcription blocked, deacetylation

–> chromatin compaction
transcriptional silencing

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24
Q

what is the association of DNA methylation with compacted heterochromatin?

A
  • gene expression is silenced
  • active part of chromatin, the acetylation is removed, law down acetylation into histones
  • to shut down, need HDAC and presence of DNA methylation = compaction of chromatin
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25
Q

active genes are associated with histone ___ and DNA _____

A

ACTIVE

histone acetylation

DNA demethylation

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26
Q

repressed genes are associated with histone ____ and DNA ____

A

REPRESSED

histone deacetylation

DNA methylation

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27
Q

describe the distribution of cytosine methylation in mammals, how do we examine this?

A
  • associated with heterochromatic region s

- use cytogenetics, heterogeneity visible at cytogenetic scale

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28
Q

DNA methylation and histone modifications help to ____ (role in epigenetics)

A

compartmentalize the genome into domains of different transcriptional potentials

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29
Q

(high/low) histone acetylation of

euchromatin vs heterochromatin

A

euchromatin= high histone acetylation

heterochromatin= low histone acetylation

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30
Q

DNA methylation

euchromatin vs heterochromatin

A

eu= low

hetero= dense

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31
Q

what type of methylation in euchromatin vs heterochromatin

A

eu= H3-K4 methylation

hetero= H3-K9 methylation

  • methylation can be associated on the protein level, there is relationship between protein tails and target
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32
Q

DNMT3L is a protein closely (structurally) related to ___ and _____

A

DNMT3A and DNMT3B

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33
Q

what is the known function of DNMT3L

A

support protein for functions of DNMT3A and DNMT3B

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34
Q

what is the function of DNMT1?

A

replication of methylation sequences from mother to daughter during cell division

  • maintenance of methylation
  • inactivity associated with cancer cells
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35
Q

DNMT3A/3B associated with what type of methylation?

A

De Novo methylation

  • occurs after cells divided, adding methylation groups
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36
Q

Name the 2 types of DNA methylation and which DNMT groups associated with each

A

maintenance methylation = DNMT1

De novo methylation= DNMT3A, 3B

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37
Q

what is maintenance methylation/

A

methylation of newly synthesized DNA strand at positions opposite methylated sites on parent strand

  • after DNA replication
  • DNMT1 will sit at point of replication and scan across sequence of newly synthesized DNA, copying methylation group of opposite strand
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38
Q

what is De Novo methylation?

A
  • methylation of new positions

- changes the pattern of methylation in a localized region of the genome during gametogenesis and early development

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39
Q

sodium bisulfite sequencing is a method of …..

A

DNA methylation analysis

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40
Q

what occurs during sodium bisulfite sequencing?

A
  • methylated cytosine is unaffected
  • converts unmethylated cytosine to uracil
  • during PCR(converts U-T) and sequencing, the ration of C and T present at CpG sites is quantified, reflecting methylation level of that site in genomic DNA
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41
Q

sodium bisulfate converts….

PCT converts….

A

C–> U

C–> T

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42
Q

what is the difference between sodium bisulfate and ChIP?

A

??

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43
Q

what happens to methylated DNA if treated with sodium bisulfate?

A

they are protected from conversion (no C–>U)

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44
Q

name 3 biological functions of DNA methylation

A
  • transcriptional regulation of ‘cellular’ genes
  • role in mammalian development (imprinting)
  • heterochromatin formation
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45
Q

why is imprinting important in mammalian development?

A

DNA methylation is important process for inheritance of gene expression

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46
Q

why is heterochromatin formation important in DNA methylation?

A

silencing gene expression

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47
Q

what is the PWWP domain named after?

A

Pro-Trp-Trp-Pro motif

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48
Q

what are PWWP domains?

A
  • domains on the DNMT3A and DNMT3B enzymes
  • target DNA methyltransferase activity to heterochromatin
  • important to recognize binding to methylated DNA
  • have to be recruited by Tc
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49
Q

what 2 types of RNA are important for shutting down regions of chromatin material?

A

RNA-I & non-coding RNA

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50
Q

what is a MBD?

A

methyl-CpG- binding protein

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51
Q

what is the function of MBD?

A

help recruit other larger complexes and HDAC

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52
Q

readers vs writers?

A

readers= DNA methyl binding proteins (MBD)

writer= DNMT

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53
Q

what is MECP2?

A

methyl-CpG-binding protein 2

  • if the gene encoding this protein is mutated= Rett syndrome (mental retardation)
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54
Q

name 6 characteristics of MECP2

A
  • transcription repressor
  • X-linked
  • able to bind single methyl- CpG
  • binds tightly to chromosomes, heterochromatin
  • associates with HDAC complex
  • expression correlates with maturation of neural system
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55
Q

mutations of MECP2 result in (3)

A
  • Rett syndrome (females)
  • Angelmann syndrome
  • autism
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56
Q

what happens if we knock-out MECP2?

A

no embryonic development

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57
Q

why are DNMTs essential? if mutate/KO they result in??

A

DNMT1= embryonic lethal

DNMT3A= perinatal death

DNMT3B= embryonic lethal

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58
Q

the DNA binding proteins will recruit….. which is called??

A

histone deacetylases

called NuRD complex (nucleosome remodeling deacetylase) complex

  • important for deacteylation of chromatin
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59
Q

DNA methylation is facilitated by …..

A

DNMT

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60
Q

methyl binding protein facilitate the recruitment of ….

A

HDAC

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61
Q

what is a mediator in methylation induced gene silencing?

A

methyl-CpG- binding proteins (e.g. MECP2)

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62
Q

how is MECP2 involved in induced gene silencing?

A
  • MBD= repressive
  • MECP2 (KO mouse= embryonic lethal)
  • has methyl CpG binding domain, and transcriptional repression domain
  • interacts with mSin3 co-repressor complex which associates with HDAC to repress transcription
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63
Q

what is a proposed mechanism (to avoid passive methylation during cell cycle)

A

stable repression of gene expression through development

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64
Q

what is the stable repression of gene expression through development

A
  • Tc= transient (DNA methylation is not)
  • Tc pull in specific enzymes involved in epigenetic process
  • MECP2 is removed from DNA to facilitate DNA methylation through phosphorylation
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65
Q

what occurs when MECP2 is removed from DNA to facilitate DNA methylation through phosphorylation?

A
  • change in orientation & structure= no longer able to bind DNA and get removed
  • kinases that phosphorylate MECP2 are important in process of demethylation to get gene expression
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66
Q

name the 3 ways to regulate genes with DNA methylation

A

1) none present- unmethylated promoter allows gene transcription

2) direct mechanism
- methylated CpGs block binding of Tc
- block transcription

3) indirect mechanism
- Me-CpG binding proteins block Tc binding to promoter

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67
Q

role of HDAC in indirect mechanism of gene regulation

A
  • methylation of CpG islands upstream of a gene provides recognition signals for MeCP components of HDAC
  • HDAC modifies chromatin in region of CpG island= inactivates the gene

** shut down gene expression via recruitment

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68
Q

how does drug TSA (trichostatin A) activate gene expression?

A
  • block HDAC activity
  • prevent DNA methylation dependent repression

= HDAC inhibitor

  • facilitates histone acetylation
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69
Q

how does drug sodium butyrate activate gene expression?

A
  • mimic histone acetylation

- ‘loosen up the chromatin’

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70
Q

*** compare:

within transcriptionally inactive chromatin/heterochromatin:

1) chromatin conformation
2) DNA CpG methylation
3) histone modification

A

1) closed chromatin, highly condensed
2) methylated CpG (incl. at promoter regions)

3) histone deacetylated
- methylated H3-K9me

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71
Q

*** compare:

within transcriptionally active chromatin/heterochromatin:

1) chromatin conformation
2) DNA CpG methylation
3) histone modification

A

1) open chromatin, extended conformation
2) unmethylated CpG (especially at promoter region)

3) histone acetylated
- methylated H3-J4me3,

72
Q

name the 7 essential roles of cytosine methylation in mammals

A

1) gene expression
2) chromosomal stability
3) cell differentiation
4) imprinting
5) X-inactivation
6) carcinogenesis
7) aging

73
Q

what are the 4 differentiating points in epigenetic programming during development?

A

totipotent (zygote)

pluripotent (blastocyst, embryonic stem cells)

multipotent (neural stem cells etc. ready to be differentiated into particular cells)

unipotent

  • inc differentiation
  • facilitated through inc in DNA methylation at specific CpG-dinucleotides
74
Q

stages of nuclear transfer (how differentiated cels become totipotent)

A
  • nucleus removed from egg

- replaced by nucleus from donor cell

75
Q

what is nuclear equivalence?

A

differentiated cells maintain the potential to generate an entire organism

  • methylation profile acts as molecular biomarker from the cells we take the DNA from
76
Q

2 examples involving reprogramming of genome

A

1) cloning by nuclear transfer (regenerate entire organism from transfer of single nucleus)
2) induced pluripotent stem cells– expression of 4 genes are sufficient to transform differentiated cells to “Stem cells”

77
Q

describe quantity of nucleosomes in promoter region

A

diminished amount

  • facilitating RNA polymerase must be more accessible for the machinery
  • opening and closing is better facilitated with fewer nucleosomes
78
Q

3 main roles DNA methylation plays in mammalian development

A
  • maintenance and inheritance of tissue-specific gene expression **
  • inhibition of transposone gene expression
  • genomic imprinting
79
Q

what is inhibition of transposone in DNA methylation?

A
  • prevent transposition
  • inhibit DNA recombination between repetitive sequences
  • lower probability of genome rearrangements
80
Q

role of genomic imprinting in mammalian development

A
  • inactivation by methylation of a gene on one of a pair of homologous chromosomes
81
Q

in which species does parent-to-origin gene expression occur?

A

genomic imprinting

  • marsupials, eutherian mammals
  • involved in placenta and nutrient transfer from mother to embryo (not egg)
82
Q

imprints are epigenetic instructions laid down in the ____ ____ cells

A

parental germ cells

83
Q

____ expressed imprinted genes tend to promote growth

____ expressed imprinted genes tend to suppress growth

A

paternal= promote
- genes enhance extraction of nutrients from mother during pregnancy

maternal= suppress
- limits nutrient extraction in pregnancy

84
Q

imprinting anomalies manifested as _____ in early development and _____ when altered later in life

A

early= developmental/neurological disorders

later= cancer

85
Q

what maternal diet during pregnancy alters expression of imprinted genes in offspring

A

maternal methyl deficient diet

86
Q

describe epigenetic imprinting of autosomal genes with a sex

A
  • unequal expression of maternal and paternal alleles of a gene
  • imprinted/marked with their gametic origin
  • imprinting results in parent of origin dependent monoallelic expression
  • maternal and paternal genomes are not functionally
  • have different outcomes depending on which allele is imprinted on the parental genome
87
Q

example of autosomal gene imprinting

A

insulator model for control of gene expression at h19 and Igf2 imprinted locus

88
Q

describe the example: insulator model for control of gene expression at h19 and Igf2 imprinted locus

A

maternal= H19 expressed, Igf2 silenced

paternal= H19 suppressed, Igf2 expressed

89
Q

3 phenotypic effects of imprinting

A

1) in utero effects (insulin & insulin-like growth factors, placental growht)
2) postnatal effects (movement disorders, lactation, brain development/function)
3) genetic disorders (epimutations, Prader-Willi syndrome, Angelmann syndrome)

90
Q

what is Prader-Willi syndrome?

A
  • deletion/inactivation of genes on paternally inherited chromosome 15
  • maternal copy is imprinted and silenced
91
Q

what is Angelmann syndrome?

A
  • deletion/inactivation on the maternally inherited chromosome 15
  • paternal copy is imprinted and silenced
92
Q

what is a methylome?

A

all the CpG sites that could be methylated

93
Q

inc or dec in methylation during fertilization?

A

decreased

  • bc reprogramming is occurring
94
Q

cancer results from loss of methylation in which parental genome?

A

maternal genome

95
Q

changes in DNA methylation during aging in humans occurs when??

A
  • replication errors at cell division

- also at post-mitotic tissues

96
Q

inc gene expression= more loosely _____ histones

A

deacetylated histones

97
Q

2 stages in the history of Barr Body

A

1949: Murray, Barr, Bertram
- dark, drumstick-shaped masses in nuclei in nerve cells
- pattern only seen in cats

1961: Lyon
- Lyon Hypothesis
- condensation of X chromosome mechanism for inactivating the genes on the chromosome
- named inactive X chromosome= Barr body

(when females are inheriting 2X, one has to be inactivated through process of DNA methylation)

98
Q

describe X-inactivation and somatic mosiacism in dosage compensation

A

genomic imprinting that leads to almost total inactivation of one X in female mammalian cell

    • Xist gene is one of the X chromosomes expressed, leads to inactivation of chromosome

– Xist gene in 2nd chromosome is inactive (DNA methylation) – this remains active

mosiac= periods of CpG islands

99
Q

what is the XIC region?

A

region where Xist is expressed

100
Q

Xist is transcribed from what ???

A

ONLY from inactive X

101
Q

the XIC gene is responsible for Cis ____

A

Cis inactivation

  • cis= acting on same chromatin material
102
Q

3 steps in how Xist silences the future inactive X

A
  • expressed from the future Xi
  • coats the chromosome
  • establishes the inactive state
  • recruits methyl binding proteins, HDAC, and other machinery to inhibit acetylation to establish inactive state
103
Q

H4 acetylation shows what??

A

levels of activation with Xist expression and X chromosome inactivation

inc acetylation H4= associated with inactive chromosome

104
Q

what are the sequential epigenetic modifications that occur during inactivation to silence the chromosome?

A
  • expression of Xist RNA to coat the chromatin

- results in hypo-acetylation & inc methylation of histones

105
Q

do not get stable inactivation of gene expression until????

A

demethylation occurs

106
Q

evidence of histone code example

A
  • transcriptional silencing of X chromosome correlates with distinct histone modification patterns
    e. g. inactive X chromosome shows reduced H3K4-methylation, then inc H3K27-methylation, then dec H4 acetylation
107
Q

histone modification and gene expression are associated with ????

A

inactivation of chromosome

108
Q

tortoiseshell cat coat colour

A
  • cannot be cloned
  • dosage compensation in cats by X-inactivation
  • all cells have the same genotype, different copy of X chromosome is expressed in different cells
  • random X-inactivation during embryonic development causes patchwork coloured coat in some females

(does not occur in males)

109
Q

name the 3 genetic/epigenetic mechanisms underlying chromatin-related disorders

A

epigenetic
1) genomic imprinting defects= altered DNA methylation

genetic
2) trans effects (indirect)= chromatin effector mutation

3) cis effects (Direct)= regulatory sequence mutation (e.g promoter)

110
Q

name 3 examples of gene imprinting defects

A
  • beckwith-wiedemann syndrome
  • prader-willi syndrome
  • transient neonatal diabetes mellitus
111
Q

name 2 trans effects and examples for each

A

1) defects in methylation machinery
- systemic lupus erythemtosus
- immunodeficiency, facial anomalies syndrome
- RETT syndrom

2) defects in histone modification enzymes
- Rubinstein-Taybi syndrome
- Coffin-Lowry syndrome

112
Q

name 2 examples of cis-effects that result in disorder/disease

A
  • Fragile X syndrome
  • facioscapulohumeral muscular dystrophy
  • mutation causing loss in methylation, which is important in stability of genome, lead to inc in inappropriate genes
113
Q

direction of the DNA methylation reaction is modulated by ….

A

chromatin structure

114
Q

passive DNA demethylation is replication dependent/independent?

A

replication dependent

115
Q

passive DNA demethylation occurs due to….

occurs where??

A

lack of maintenance methylation during several cycles of DNA replication

  • result in ineffective machinery
  • zygotic maternal genome, after fertilization, diving cells (E.g. glial cells)
116
Q

active DNA demethylation is replication dependent/independent?

A

replication independent

117
Q

active DNA demethylation occurs ….

occurs where?

A

in the absence of DNA replication

  • zygotic paternal genome, after fertilization, non-dividing cells (e.g. neurons)
118
Q

list the 4 pathways for active DNA demethylation in animal cells

A

1) hydrolytic demethylation
- removes C

2) dinucleotide excision
- cut out CG

3) 5-meC excision
- replaced by DNA repair machinery

4) deamination and thymine excision
- deamination makes C analogous to T
- recognized by DNA repair machinery, substituted for C

119
Q

what is excision?

A

DNA repair

- how demethylation occurs

120
Q

what is the deamination reaction?

A

C–> T –> C

121
Q

what is the DNA demethylation mechanism that involves base excision repair?

A
  • oxidation of 5-methyl-C to create 5-hydroxy-C
  • provides target facilitating replace of hydroxy methylation to non-methylated cytosine
  • facilated by Tet
122
Q

what is Tet?

A
  • family of dioxygenases (ten elevent translocation)

- TET family proteins catalyze conversion of 5mC to 5hmC

123
Q

2 mechanisms involved in DNA demethylation?

A
  • DNA methylation

- hydroxymethylation (conversion 5mC to 5hmC in DNA by TET1)

124
Q

in mammalian genome, where does methylation mostly occur?

A

carbon-5 position of cytosine reside of CpG dinucleotides

converting C to 5mC

125
Q

compare the promoter region in the C, 5mC, 5hmC

A

C= promoter is demethylated

5mC= promoter is being silenced

5hmC= promoter on way to gene activation

126
Q

what are the biological functions of 5hmC?

A
  • 5hmC levels are reduced in cancer tissues
  • 5hmC containing DNA= enrichment within exons and near transcriptional start sites
  • role in transcriptional regulation, contribute to ‘poised’ chromatin state
  • undifferentiated cells: reduction 5hmC associated with inc methylation and cellular differentiation
127
Q

in poised state

inc in 5mC= ___ in 5hmC

A

inc 5mC= dec 5hmC

128
Q

what DNA demethylation intermediates can Tet proteins generate?

A

5fC & 5caC

  • derived from 5mc
129
Q

describe the new model for DNA demethylation (including 4caC)

A
  • 5mC and 5hmC are oxidized to 5caC by Tet
  • 5caC recognized and excised by thymine-DNA glycosylase
  • resulting abasic site, induce base excision repair pathway, leading to incorporation of unmethylated cytosines
130
Q

list the 5 steps from 5mC–> C

A

5mC–> 5hmC–> 5fC–> 5caC—> C

131
Q

what % of mammalian genome encodes mRNA?

A

2%

132
Q

majority of genome encodes what type of RNA?

A
  • functional long and short non-protein encoding RNA (ncRNA)
133
Q

ncRNA contribute to ???? which all involved epigenetic processes

A
  • transcriptional and post-transcriptional gene silencing
  • chromosome dosage compensation
  • allelic exclusion
  • germ cell reprogramming
  • para-mutation
134
Q

ncRNA can initiate _____ through???

A

initiate gene silencing through covalent modifications of the DNA or its associated histone proteins, interfering with transcription

135
Q

non-coding RNA is also know as?

A

junk DNA

136
Q

small ncRNA are called???

A

interference RNA

137
Q

small RNAs control what?

A

RNAs that code protein

138
Q

small RNAs are a poll of ____ and generally function in ____ ____

A

pool of 21-24 nt ncRNAs

generally function in gene SILENCING

139
Q

small RNAs contribute to ____ ____ ____ through epigenetic modifications to chromatin

A

transcriptional gene silencing

140
Q

small RNAs contribute to post-transcriptional gene silencing by _____

A

affecting mRNA translation or stability

141
Q

important classes of RNA in humans include: (3)

A

1) endogenous small inferfering RNAs (siRNA, ~700)
2) microRNA (miRNA, ~100)
3) PIWI-interactng RNA (piRNA, possible millions)

142
Q

are are the 2 core components of RNA silencing?

A

dicers and argonautes

143
Q

explain the process and components of RNA silencing

A
  • double stranded RNA (dsRNA) is processed by Dicer or Dicer-like proteins into short RNA duploexes
  • small RNAs associate with ARGONAUTE proteins to confer silencing
144
Q

what are argonaute proteins?

A

catalytic components of the RNA-induced silencing complex (RISC)

145
Q

what does RISC target for?

A

gene silencing

146
Q

what are dicer and dicer-like proteins (DCL)?

A
  • in siRNA and miRNA biogenesis, DCL cleave long dsRNA or foldback RNA into 21-25 nt fragments

** first protein we have interaction with

147
Q

benefit of Dicers structure

A
  • allows to measure RNA it is cleaving

- chops RNA into uniformly-sized pieces

148
Q

what is the second protein we encounter/interact with?

A

Argonaute

149
Q

what is the function of Argonaute

A

-after dicer cut up the double stranded RNA, there is association of 21-25 nt RNA with argonaute

  • binds small RNAs and their targets
  • forms RISC complex (RNA-induced silencing complex)
150
Q

Argonaute proteins named after???

A

argonaute1 mutatant of Arabidopsis

  • argo1 has thin radial leaves, named after octopus it resembles
151
Q

how is siRNA produced?

A

made by exogenous infection

152
Q

role of siRNA in RNA interference?

A
  • mediated silencing via post-transcriptional an transcriptional gene silencing
  • siRNA will be cut into short 21-25 nt length and associated with ARGO protein
  • in its single stranded form it will form RISC complex which will bind to complimentary sequences expressed in endogenous cell (to silence the cell)
153
Q

how is miRNA produced?

A

endogenously

154
Q

role of miRNA in RNA interference?

A
  • mediated slicing of mRNA and translational repression
  • able to “knock-down” the gene,
  • inhibiting mRNA accumulation
  • forms RISC complex, which can target the specific regions of RNA
155
Q

why is RNA interference important?

A

used in many different organisms to regulate gene expression

  • involving small interfering
    RNA (siRNA), and microNRAs (miRNA) to silence specific mRNAs in the cytoplasm
156
Q

what % of genome encode RNA sequences that will be used as a template?

A

only 2% of genome

157
Q

control of gene expression involves the control of ____ ____

A

transcription initiation

158
Q

gene expression can be controlled after transcription by which 5 mechanisms?

A
  • RNA interference
  • alternative splicing
  • RNA editing
  • mRNA degradation
  • protein degradation
159
Q

post transcriptional regulation (6)

A

1) initiation of transcription
2) RNA splicing (altering the rate of splicing, alternative splicing can produce multiple mRNA from one gene)
3) passage through nuclear membrane
4) destruction of the transcript
5) protein synthesis
6) post-translational modification

160
Q

RNA interference involves the use of ______

A

small RNA molecules

161
Q

the enzyme ____ chops double stranded RNA into small pieces fo RNA

A

Dicer

162
Q

2 types of RNA that result from Dicer chopping RNA

A

1) micro-RNA

2) small interfering RNA

163
Q

what is function of micro-RNA (in posttranscriptional regulation)

A

bind to complimentary RNA to prevent translation

164
Q

what is the function of small-interfering RNA (in posttranscriptional regulation)

A

degrade particular mRNAs before translation

165
Q

role of introns in posttranscriptional regulation

A

spliced out of pre-mRNAs to produce the mature mRNA that is translated

166
Q

alternative splicing recognizes….

A

different splice sites in different tissue types

167
Q

function of mature mRNAS in posttranscriptional regulation

A

mature mRNAs in each tissue possess different exons, resulting in different polypeptide products from the same gene

168
Q

describe RNA editing in posttranscriptional regulation

A
  • creates mature mRNA that are not truly encoded by the gemone
169
Q

describe the mature mRNA produced from RNA editing

A
  • apolipoprotein B exists in 2 isoforms
  • one isoform is produced by editing the mRNA to create a stop codon (prevent further synthesis
  • 2 sizes of protein: apoB-100 in liver, B48 in intestine
170
Q

apolipoprotein have a role in ____ ____ in the body

A

chaperoning cholesterol

171
Q

describe the half-life of mature mRNAs

A

various half-lifes depending on the gene and location (tissue) of expression

  • amount of polypeptide produced from a particular gene can be influenced by the half life of the mRNA molecules
172
Q

how often are proteins produced and degraded in the cell?

A

continually

173
Q

proteins are labelled with what when degraded?

A

tagged with ubiquitin

  • the protein undergoes conformational change of structure and is targeted towards proteosome for degradation
174
Q

degradation of proteins marked with ubiquitin occurs where????

A

proteosome

  • free enzymes complexes in the cytoplasm
175
Q

what are lysosomes?

A

membrane-bound vesices sacs (bound by single membrane)

  • degradeprotein by endocytosis, phagocytosis and autophagy

NESC 3670: Genes, Brain & Behaviour (12 decks)

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