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a GENETICS > Epigenetics > Flashcards

Epigenetics Flashcards

1
Q

What are heritable changes in gene function that occur without a change in DNA sequence

A

epigenetics

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2
Q

What is responsible for genomic imprinting?

A

Epigenetics

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3
Q

What controls epigenetics and genomic imprinting

A

DNA methylation -inactivates genes (heterochromatin)

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4
Q

What happens when Histones are acetylated

A

genes activated (euchromatin)

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5
Q

Where on DNA are methyl groups

A

on the soutside and stick outward to prevent gene activation

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6
Q

What transfers a methyl group in DNA methylation

A

by SAM (need Folic Acid) to methylate a DNA base

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7
Q

In humans, DNA methylation is limited to what position? on which base? catalazed by which enzyme? product?

A

C-5 position of cytosine 1; catalyzed by DNA methyltransferase (DNMT) with SAM as methyl donorresidues; resulting in 5-methylcytosine

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8
Q

Is Hypomethylated DNA usually expressed?

A

d (non-methylated) DNA sequences ARE usually expressed

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9
Q

Are hypermethylated DNA sequences usually expressed?

A

usually NOT expressed

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10
Q

Abnormal DNA Hypermethylation is a mechanism used by cancer cells to? Abnormal DNA Hypomethylation causes what in oncogenes?

A

silence expression of tumor suppressor genes

DNA Hypomethylation causes increased gene transcription of oncogenes

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11
Q

What is genomic imprinting? Is expression the same if it is maternal or paternal?

A

causes Imprinted genes - when a copy maternal or paternal is epigenetically silenced - differential gene expression
gene expression is different if it is maternally or paternally derived even though DNA sequence is exactly the same

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12
Q

What is a Gynogenote?

A

female pronuclei + female pronuclei

  • Bad extraembryonic tissue, placenta
  • Ok embryo proper
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13
Q

Parthenogenesis

A

production of offspring by a female, without genetic contribution from the male.

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14
Q

androgenote

A

Double-paternal embryos
Bad embryo
Ok extraembryonic structures, placenta.

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15
Q

Histones have what charge

A

positive

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16
Q

DNA has a ___Charge

A

Negative

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17
Q

What is an OVARIAN DERMOID CYSTS

A

All female derived genetic material.

-Can result from spontaneous ovarian oocyte activation with duplication of the maternal genome

18
Q

What is a HYDATIDIFORM MOLE

A

All male derived genetic material.

  • enucleate egg fertilized by haploid sperm
  • egg fertilized by 2 sperm and loss of maternal pronucleus. - mole contains little or no fetal tissue and hyperplastic extra embryonic growth
19
Q

Histones make a major contribution to neutralizing the

A

negative charge of the DNA backbone and facilitating compaction.

20
Q

Histone acetylation is catalyzed by?,

A 
histone acetyltransferases (HATs).
-addition of a COCH3 to LYS residues at the amino (N terminus) of histone proteins removes positive charges, --reducing the affinity between histones and DNA
21
Q

How does Hyperacetylation affect transcription

A

enhances it; makes it easier for RNA polymerase and transcription factors to access the promoter region of DNA

22
Q

Histone deacetylation is catalyzed by? how does it affect transcription

A

Histone deacetylases

hypoacetylation represses transcription.

23
Q

Trichostatin A is example of?

A

HDAC Inhibitor - reactivate gene

24
Q

HDAC inhibitors bind to which domain? what are they used for?

A
  • to the Zn-containing catalytic domain of HDACs.

- use in psychiatry and neurology as mood stabilizers and anti-epileptics

25
Q

What is the single X or Lyon Hypothesis

A

one of the X chromosomes in a female gets turned off at random, and female is a mosaic in the expression of the X chromosomal genes.

26
Q

What regulates x inactivation, what gene?

A

X inactivation center (XIC), a gene, Xist

27
Q

How does the Xist gene regulate x inactivation

A

makes RNA product and spreads inactivation throughout the X chromosomes
- coats X chromosome with its RNA

28
Q

What are characteristics of an Inactivated X chromosome (4)

A

Heterochromatic, DNA is hypermethylated, Histones are hypoacetylated, Dark-staining.

29
Q

What are the condensed, inactived X’s called in females

A

Barr Bodies

30
Q

What are the defining characteristics of a patient with Turner Syndrome

A

45,X, Female short stature, sterile, broad chest, lymphadema, webbed neck, normal intellect, no barr bodies

31
Q

What are characteristics of 47,XXY; Klinefelter Syndrome

A

have barr body, Infertile Males, Small genitals, big breasts, sparse hair, tall, long limbs, mental problems

32
Q

What is an exception to X inactivation?

A

Genes in pseudoautosomal region escape X inactivation - not all regions of the X in a female are turned off

33
Q

Prader-Willi syndrome –PWS

A

First human disorder attributed to genomic imprinting.
2. Small in utero, diminished fetal activity, neonatal hypotonia, obesity, mental retardation, short stature, hypogonadism, and small hands and feet
- Patients exhibit uncontrollable eating habits. Examples mentioned: chalk, paper, garbage, etc.
floppy, babies
Chromosome 15 region 15q11.2-q13.1.

34
Q

Angelman syndrome

A
  1. “Happy Puppet” syndrome.
  2. Profound motor and mental retardation, ataxia, hypotonia, epilepsy, absence of speech, and unusual faces characterized by a large mandible and open-mouthed expression revealing the tongue.
  3. They can burst into random bouts of laughter.
  4. Cannot fully extend arms or legs. Many are wheelchair bound
    same chromosome 15 region q11.2-q13.1 [40]
35
Q

What is the normal presentation of chromosome 15

A

(P15)- AS OFF & PWS ON - expresses SNRPN (PWS)

M15)-PWS OFF & AS ON - Expresses UBE3A (AS

36
Q

What causes PWS?

A

75% by deletion in P15 15q11.2-q13.1 lack of SNRPN expression.
20% due to uniparental disomy (two maternal chromosomes, no paternal).

37
Q

What causes AS?

A

75% due to deletion in M15, resulting in under-expression of UBE3A protein.
5% imprinting error (wrong gene inactivated on M15)
3% due to uniparental disomy (two paternal)

38
Q

A decrease in the availability of SAM (S-adenosyl-L-methionine) in the cell would cause

A

Increase in DNMT (DNA methyltransferase) activity

39
Q

Prader-Willi Syndrome is mostly caused by:

A

Deletion

40
Q

What is the N-1 rule?

A

the number of Barr bodies is one less than the number of X chromosomes in an individual

41
Q

How many copies of pseudoautosomal genes do males and females have

A

Normal male and females have two copies of these genes no x inactivation

a GENETICS (4 decks)

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