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Human Molecular Genetics > Chapter 11 > Flashcards

Chapter 11 Flashcards

1
Q

how do differences in anatomy, physiology and behavior between cells appear?

A

those cells are all derived from the same genetic material

> those differences are due to different patterns of gene expression

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2
Q

which RNA polymerase transcribes all protein coding genes?

A

RNA polymerase 2

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3
Q

which RNA polymerase is responsible for mtDNA?

A

mitochondria have entirely different RNA polymerase, encoded by the nuclear “POLRMT” gene

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4
Q

which elements have to be present in the genetic code to start transcription?

but?

A
  1. BRE - TF2B recognitin element
  2. TATA-box - recognized by TBP subunit
  3. Inr - initiator elements, 25-30 bp further than TATA box

> contains transcription start site

  1. DPE - downstream core promotor element

BUT none of these elements is either necessary or sufficient

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5
Q

what is a major difference between RNA and DNA polymerase?

A

RNA polymerase does not need a primer to get started

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6
Q

how is RNA transcription terminated?

A

RNA transcription terminated

> no specific signal in sequence

> protein complex cuts transccript and exonuclease moves along RNA until it reaches polymerase > transcript ends

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7
Q

which transcription factor binds first?

how does it recognize the TATA box?

A

transcriptionfactor TFIID binds first

> one subunit of this factor is called TBP, which recognizes the TATA box

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8
Q

how is transcription regulated by enhancers and activators?

A

transcription regulation

> activators bind to enhancers (or repressors bind to silencers)

> activators bind to transcription factors

> binding of activators stimulates transcription initiation

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9
Q

what are locus of control regions?

A

LCR’s

> stimulate the expression on genes

> contain DNase1 hypersensitivity sites, positions where nucleosomes are modified or absent: proteins can bind

> these binding proteins control the chromatin structure

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10
Q

where are enhancers or silencers located?

how are direct interactions with the promoter possible?

A

enhancers or silencers can be located hundreds of kilobases up or downstream from the gene they control

> DNA looping enables physical interaction between proteins bound to enhancers/silencers and RNA polymerase attached to promoter

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11
Q

what is the definition of epigenetics?

A

epigenetics

heritable changes in gene expression that do not involve changes to the underlying DNA sequence

> a change in phenotype without a change in genotype

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12
Q

by what factors can epigenetics be influenced?

A

epigenetic chance is a regular and natural occurrence but can also be influenced by several factors including age, environment,lifestyle and disease state

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13
Q

what are the two main components of epigenetic code?

A

epigenetic code mainly consists of

  1. DNA methylation

> methyl marks added to certain DNA bases repress gene activity

  1. histone modification

> different molecules can attach to the histone tails and alter the activity of the DNA wrapped around them

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14
Q

where can DNA methylation occur?

> how are those sites called?

> by which enzyme?

A

the 5’ position of a cytosine base can be methylated

> but only cytosines whose downstream neighbor is guanine are subject to methylation

> those sites are called CpG sequences

> the enzyme is called DNA methyltransferase (DNMT)

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15
Q

how much of the cytosine bases are methylated?

A

about 10% in vertebrates

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16
Q

one nucleosome

> how many bp of DNA?

how many histone molecules? which?

>> what happens between nucleosomes?

A

one nucleosome

> 147 bp of DNA

> wrapped around 8 histone molecules, typicall two of each: H2A,H2B,H3,H4

>> between nucleosomes: variable length stretch of free DNA, stabilized by one molecule of linker histone H1

17
Q

what changes at histone

> H2B

> H3

> H4

?

A

H2B: phosphorylation

H3: methylation

H4: acetylation

> acetylation stimulates gene expression

18
Q

what is the difference between

maintenance methylation

and

de novo methylation

A

maintenance methylation:

> when DNA is replicated, the newly synthesized strands are methylated based on the methylation of the original strand

de novo methylation:

> newly occuring methylation

19
Q

is there a relationship between DNA methylation and histone modification?

A

yes, DNA methylation and histone modification interact

> they may reinforce themselves

20
Q

what are the 2 best known heritable epigenetic changes?

A

heritable epigenetic changes?

  1. x- inactivation
  2. imprinting
21
Q

what is genomic imprinting?

A

genomic imprinting:

only one of a pair of genes, present on homologous chromosomes is expressed, the second being silenced by methylation

>>> always the same member of pair of genes that is imprinted, some genes maternal, some genes paternal gene

> 20-30 human genes known

22
Q

when does genomic imprinting happen?

how?

A

silencing usually happens through addition of methyl groups during egg of sperm formation

23
Q

what are consequences of failed genomic imprinting?

> which known disease?

A

genomic imprinting is required for normal development

> improper imprinting can result in an individual having two active copies or two inactive copies of a gene

> prader-willi /angelman syndrome both linked to the same imprinted region on chr. 15

> paternal chr silenced: prader-willi syndrome

> maternal chr silenced: angelman syndrome

24
Q

what are characteristics of prader-willi syndrome?

A

prader willi syndrome

> facial characteristics

> obesity (relentless appetite)

> hypogonadism (delayed puberty, infertility)

25
Q

what are characteristics of angelman syndrome?

A

angelman syndrome

> severe cognitive impairment

> epilepsy

> tremors

> perpetually smiling facial expression, not able to speak

26
Q

20.000 protein coding genes >>> 150.000 proteins

what 3 mechanisms are responsible for creating ultiple transcripts per locus?

A
  1. multiple promoters
  2. alternative splicing
  3. RNA editing
27
Q

how can an additional promotor change the protein a gene is coding for?

> does this change the primary transcript?

A

the promotor will drive transcription of the gene from an alternative first exon

> yes, the primary transcript is changed

28
Q

how can alternative splicing change the protein a gene codes for?

A

alternative splicing can skip one or more exons, include additional internal exons or vary the length of an exon

29
Q

how does RNA editing change the protein outcome a gene codes for?

A

RNA editing:

> involves insertion, deletion or modification of specific nucleotides in the primary transcript

30
Q

what is the relationship between miRNA and cancer?

A

cancer cells show changes expression of many miRNA’s

> general depression of miRNA levels

31
Q

the major changes in gene expression are more often due to … than to …?

A

the major changes in gene expression are more often due to transcription than to translation

32
Q

how can gene expression be altered at the level of translation?

A

protein and miRNA complexes can bind to the 3’ UTR region of the mRNA to influence translation

33
Q

when x-inactivation and imprinting heritable?

when not?

A

x-inactivation/imprinting

> heritable from cell to cell

> not heritable from parent to offspring

>>> mutations that are heritable from parent to offspring are called “paramutations”

34
Q

what is the difference between

DNMT1

and

DNMT3A/DNMT3B

?

A

DNMT1: specifically targets hemimethylated DNA strings

> responsible for maintenance methylation

DNMT3A/DNMT3B: responsible for de novo methylation

35
Q

what happens with x chrom. when inactivated?

A

inactivated x chrom remain condensed during the cell cycle

Human Molecular Genetics (10 decks)

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