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Genetics > Lecture 12 > Flashcards

Lecture 12 Flashcards

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1
Q

posttranscriptional factors

A

plays an equal, if not more significant, role compared to transcriptional control

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2
Q

mechanisms of posttranscriptional gene regulation

A
  • control of alternative splicing
  • mRNA stability
  • translation
  • RNA silencing
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3
Q

alternative splicing

A
  • generates different forms of mRNA from identical pre-mRNA
  • expression of one gene gives rise to numerous proteins with similar and different functions
  • increases the number of proteins made from one gene called isoforms
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4
Q

casette exons

A

3 exons with 2 introns between them

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5
Q

alternative 5’ or 3’ splice sites

A

4 exons with 2 introns between them, leaving the second and third exon together

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6
Q

intron retention

A

3 exons with 2 introns between them

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7
Q

mutually exclusive exons

A

4 exons with 3 introns between them

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8
Q

alternative promoters

A

3 exons with 2 introns between them

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9
Q

alternative polyadenylation

A

3 exons with 2 introns between them

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10
Q

steady-state level of mRNA

A
  • amount of mRNA in cell available for translation

- determined by combination of transcription and mRNA degradation rates

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11
Q

half-life

A
  • mRNA s degraded at some point after synthesis
  • lifetime of mRNA varies
  • regulated by cell needs
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12
Q

what are the pathways of degradation?

A
  • exoribonuclease enzymes: shorten length of poly-A called deadenylation dependent decay
  • decapping enzymes: removes 7-methylguanine cap mRNA now unstable
  • endonuclease cleaves mRNA internally
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13
Q

phosphorylation

A

the most common type of posttranslational modification

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14
Q

kinases

A

catalyze the addition of a phosphate group to ser, tyr, and thr amino acid side chains

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15
Q

phosphatases

A

-enzymes that remove phosphate

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16
Q

epigenetic trait

A

-a stable, mitotically and meitocally heritable phenotype that results from changes in gene expression without alterations in the DNA sequence

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17
Q

epigenetics

A

the study of the ways in which these changes alter cell and tissue specific patterns of gene expression

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18
Q

epigenome

A

-refers to the epigenetic state of a cell

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19
Q

what has epigenetic been implicated in?

A
  • progressive restriction of gene expression during development
  • allele-specific expression in gene imprinting
  • environment genome interactions during interactions during prenatal development that affect adult phenotypes
  • human genetic disorders
  • the loss or alteration of other epigenetic states can result in cancer
20
Q

epigenetic process

A
  • stably alter gene expression patter and/or transmits the alteration at cell division
  • includes cytosine methylation
  • post-transcriptional modification of histone proteins and remodeling of chromatin
  • RNA based mechanisms
21
Q

methylation

A
  • reversible, addition of methyl groups

- epigenetic changes

22
Q

histone modification and chromatin remodeling

A
  • alter the accessibility of genes for transcription

- epigenetic changes

23
Q

methylation

A

-occurs on cytosine bases adjacent to guanine called CpG dinucleotides, which are clustered in regions called CpG islands

24
Q

CpG islands

A
  • located in and near promoter sequences adjacent to genes
  • adjacent to essential genes are unmethylated and available for transcription
  • other genes are methylated and transcriptionally silenced
25
Q

heterochromatic methylation

A

-maintains chromosome stability by preventing translocations and other chromosomal abnormalities

26
Q

histone modification

A

-important epigenetic mechanism of gene regulation

27
Q

what is chromatin composed of?

A

-DNA wound around an octamer of histone proteins to form nucleosomes

28
Q

where do histone modification occur?

A

-conserved amino acid sequences in the N-terminal histone tails, which protrude from the nucleosome

29
Q

what do chemical modifications of histones do?

A

-alter the structure of chromatin, making genes accessible or inaccessible for transcription

30
Q

how can amino acids in the N-terminal region of region of histones?

A

-modified by acetylation, methylation, and phosphorylation

31
Q

acetylation by histone

A
  • acetyltransferase opens up the chromatin structure

- makes genes available for transcription

32
Q

removal of acetyl groups

A
  • by histone deacetylase closes the configuration

- silences genes by making them unavailable

33
Q

histone code

A

the sum of the complex patterns and interactions of histone modifications that change chromatin organization and gene expression

34
Q

monoallelic expression (MAE)

A

only one allele is transcribed, while the other allele is transcriptionally silent

35
Q

what are the three major classes of MAE

A
  1. parent of origin monoallelic expression: imprinting
  2. random monoallelic expression: inactivation of the X chromosome
  3. random monoallelic expression of autosomal genes
36
Q

what do imprinted genes show?

A
  • parent of origin
  • the expression of only the maternal allele of the paternal allele
  • occurs during gamete formation
37
Q

what produces allele specific imprinting and subsequent gene splicing?

A

differential methylation of CpG rich regions

38
Q

what happens when a gene is methylated and imprinted?

A

it remains transcriptionally silent during embryogenesis and development

39
Q

what happens in the pattern of imprinting in mammals?

A
  • it is reprogrammed every generation
  • when gamete formation begins in female/male germ cells, both chromosomes sets have their imprints erased and are each reprogrammed by changing the pattern of methylation to carry a female/male imprint that is transmitted to the next generation through the egg/sperm
40
Q

where does reprogramming occur?

A

in the parental germ line and in the developing embryo just before implantation
-after implantation, differential genomic remethylation recalibrates which maternal and paternal alleles will be activated

41
Q

what do most implanted genes encode for?

A

growth factors or other growth-regulating genes

42
Q

where is the origin of most imprinted disorders?

A

during fetal growth and development

43
Q

BWS

A
  • Beckwith-Weidemann Syndrome
  • disorder of imprinting
  • caused by abnormal patterns of DNA methylation resulting in altered patterns of gene expression
44
Q

random inactivation of an X chromosomes

A
  • about half of embryonic cells randomly inactivate the maternal X chromosome and the other half inactivate the paternal X chromosome
  • silencing over 900 or so genes
  • once silenced it remains silent
45
Q

where are the 4 places that MAE genes can be throughout the genome

A
  1. expression of both alleles (biallelic expression)
  2. expression of only the maternal allele
  3. expression of only the paternal allele
  4. expression of neither allele
46
Q

what can alter gene expression?

A
  • environmental agents including nutrition, chemicals, and physical factors such as temperature
  • affects the epigenetic state of the genome

Genetics (11 decks)

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