Epigenetics

Question 1

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

Answer 1

epigenetics

Question 2

What is responsible for genomic imprinting?

Answer 2

Epigenetics

Question 3

What controls epigenetics and genomic imprinting

Answer 3

DNA methylation -inactivates genes (heterochromatin)

Question 4

What happens when Histones are acetylated

Answer 4

genes activated (euchromatin)

Question 5

Where on DNA are methyl groups

Answer 5

on the soutside and stick outward to prevent gene activation

Question 6

What transfers a methyl group in DNA methylation

Answer 6

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

Question 7

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

Answer 7

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

Question 8

Is Hypomethylated DNA usually expressed?

Answer 8

d (non-methylated) DNA sequences ARE usually expressed

Question 9

Are hypermethylated DNA sequences usually expressed?

Answer 9

usually NOT expressed

Question 10

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

Answer 10

silence expression of tumor suppressor genes

DNA Hypomethylation causes increased gene transcription of oncogenes

Question 11

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

Answer 11

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

Question 12

What is a Gynogenote?

Answer 12

female pronuclei + female pronuclei

• Bad extraembryonic tissue, placenta
• Ok embryo proper

Question 13

Parthenogenesis

Answer 13

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

Question 14

androgenote

Answer 14

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

Question 15

Histones have what charge

Answer 15

positive

Question 16

DNA has a ___Charge

Answer 16

Negative

Question 17

What is an OVARIAN DERMOID CYSTS

Answer 17

All female derived genetic material.

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

Question 18

What is a HYDATIDIFORM MOLE

Answer 18

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

Question 19

Histones make a major contribution to neutralizing the

Answer 19

negative charge of the DNA backbone and facilitating compaction.

Question 20

Histone acetylation is catalyzed by?,

Answer 20

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

Question 21

How does Hyperacetylation affect transcription

Answer 21

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

Question 22

Histone deacetylation is catalyzed by? how does it affect transcription

Answer 22

Histone deacetylases

hypoacetylation represses transcription.

Question 23

Trichostatin A is example of?

Answer 23

HDAC Inhibitor - reactivate gene

Question 24

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

Answer 24

• to the Zn-containing catalytic domain of HDACs.

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

Question 25

What is the single X or Lyon Hypothesis

Answer 25

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.

Question 26

What regulates x inactivation, what gene?

Answer 26

X inactivation center (XIC), a gene, Xist

Question 27

How does the Xist gene regulate x inactivation

Answer 27

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

Question 28

What are characteristics of an Inactivated X chromosome (4)

Answer 28

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

Question 29

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

Answer 29

Barr Bodies

Question 30

What are the defining characteristics of a patient with Turner Syndrome

Answer 30

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

Question 31

What are characteristics of 47,XXY; Klinefelter Syndrome

Answer 31

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

Question 32

What is an exception to X inactivation?

Answer 32

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

Question 33

Prader-Willi syndrome –PWS

Answer 33

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.

Question 34

Angelman syndrome

Answer 34

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]

Question 35

What is the normal presentation of chromosome 15

Answer 35

(P15)- AS OFF & PWS ON - expresses SNRPN (PWS) | M15)-PWS OFF & AS ON - Expresses UBE3A (AS

Question 36

What causes PWS?

Answer 36

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

Question 37

What causes AS?

Answer 37

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)

Question 38

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

Answer 38

Increase in DNMT (DNA methyltransferase) activity

Question 39

Prader-Willi Syndrome is mostly caused by:

Answer 39

Deletion

Question 40

What is the N-1 rule?

Answer 40

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

Question 41

How many copies of pseudoautosomal genes do males and females have

Answer 41

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