Lecture 27

Question 1

describe genomic imprinting and how it can lead to a disease state

Answer 1

genomic imprinting is caused by DNA methylation

basically, the methylated DNA of one parent is “shut down” so the other parent’s genes will be the only gene expressed in the offspring

Prader Willi Syndrome (PWS) is caused by a paternal deletion on chromosome 15 being expressed due to methylated maternal genes (if the maternal genes weren’t methylated, the maternal genes could have been expressed and the PWS avoided)

Question 2

Females are _____ of the paternal and maternal X genes

Answer 2

mosiacs

Question 3

Describe the decision of specialization method of controlling gene expressions

Answer 3

the specialization of cells occurs as the induction of or decisions NOT to induct different regulatory proteins are made

different specializations of cells are created with different combinations of collections of inducted proteins

Question 4

Describe the coordinated gene expression method of controlling gene expressions

Answer 4

gene expression is triggered in response to need

ex. is glucocorticoid cortisol being heavily expressed in the morning and not being expressed at night

Question 5

explain the difference between an unfolded protein that is ubiquitinated once and an unfolded protein that is ubiquitinated 10 times.

Answer 5

the protein that has a 10 ubiquitin chain will most likely be recognized, and therefore degraded by the proteasome before the protein with only one ubiquitin on it

the more ubiquitin, the more likely the protein is to be degraded

Question 6

Describe the symptoms of Prader-Willi Syndrome (PWS)

Answer 6

Stage one: infantile hypotonia (floppy) and poor suck/feeding difficulties

Stage two: hyperphagia (uncontrollable eating) leading to early childhood obesity

hypogonadism

short stature

mental deficiency

Question 7

describe proteasomes function and how that relates to their structure as well

Answer 7

a molecular machine that carries out the degradation of proteins that have been ubiquitinated

it is a hollow cylindrical structure with a cap on each end and a hollow chamber in the center

the cap binds to the ubiquitinated protein and acts as a gate

the chamber has 6 active sites that degrade proteins in an ATP dependent manner

Question 8

An miRNA variant of SLITRK1 gene is associated with _____ _____ . SLITRK1 gene expression is decreased when miR-189 binds more efficiently to the same target sequence.

Answer 8

Tourettes Syndrome

this miRNA variant basically competes with the SLITRK1 gene for the same target sequence

Question 9

Describe the decision of specialization method of controlling gene expressions

Answer 9

the specialization of cells from stem cells to their specific specialization is triggered by the expression of various genes

Question 10

Describe the DNA methylation method of controlling gene expressions. be sure to mention the role of maintenance methyltransferase” and an example of a phenomenon caused by DNA methylations

Answer 10

methylated DNA sequences are silenced

methylation of cytosine occurs at “CG” sequences and is conducted/conserved through DNA replication cycles by maintenance methyltransferase

genomic imprinting is a phenomenon caused by DNA methylation

Question 11

Explain how gene expression is regulated at the post-transcriptional level in terms of RNA.

Answer 11

Alternative splicing: can produce different forms of proteins from the same gene

Spatial localization of mRNA: there are several ways that mRNA’s leave the nucleus

Regulation via RNA stability: the 5’ cap and Poly A tail determine how long an mRNA structure will survive until it is degraded

Question 12

What is IRP? state the name of the IRP involved in iron metabolism

Answer 12

Iron responsive regulatory protein: basically regulates what mRNA is translated and what mRNA isnt translated

cytosolic aconitase

Question 13

What is IRE?

Answer 13

iron responsive elements: are recognition sites on mRNA for binding to a regulatory protein

Question 14

describe the activation of the target protein degradation signal

Answer 14

phosphorylation of the signal via protein kinase

unmasking by protein dissociation

creation of destabilizing N-terminus

Question 15

Describe the symptoms of Prader-Willi Syndrome (PWS)

Answer 15

Stage one: infantile hypotonia (floppy) and poor suck/feeding difficulties

Stage two: hyperphagia (uncontrollable eating) leading to early childhood obesity

hypogonadism

short stature

mental deficiency

Question 16

describe what the serum levels of miR-141 and miR-29 can serve as biomarkers for, and how each of them presents

Answer 16

miR-141 is elevated in prostate cancer

miR-29 is decreased in heart disease

Question 17

Explain how proteins are regulated by post-translational processing. Be sure to list the 3 types of post-translational modification that may occur in order to achieve a functional protein

Answer 17

post-translational processing is required in order for proteins to be functional and includes the following

folding/cofactor binding

covalent modifications such as phosphorylation (via 
kinases) or acetylation

binding to other subunits

Question 18

Describe the steps and enzymes (E1, E2, E3) involved in the ubiquitination of unfolded or abnormal proteins

Answer 18

E1 is the ubiquitin activating enzyme that is involved in the first step by using it’s cysteine side chain to link to ubiquitin

E2 and E3 (or ubiquitin ligase) are complexed, and receive the ubiquitin from E1. E1 leaves

the target protein, which must have a degradation signal, is then bound to the complex by interacting with E3 (ubiquitin ligase)

each successive round of ubiquitination must begin with another E1 enzyme that brings the ubiquitin to the complex and adds it to the chain

Question 19

The following are all examples of what?

Coordinated gene expression
Decision of specialization
DNA methylation
X chromosome inactivation

Answer 19

methods of controlling gene expression

Question 20

Describe the RNA control of ferritin mRNA and transferrin receptor mRNA under condition of iron starvation

Answer 20

IRP binds to IRE of ferritin mRNA at the 5’ end which causes a decrease in ferritin mRNA, as cells do not need to store iron at this time

IRP binds to IRE of transferrin receptor mRNA at the 3’ end which causes an increase in TfR(transferrin receptor) mRNA so that more iron can be transported into the cell

Question 21

True or False: Micro RNA’s bind to mRNA’s to activate the mRNA’s to produce large amounts of protein. explain why

Answer 21

False

microRNAs are regulatory RNAs that silence the expression of specific mRNA targets by binding to the 3’ UT end of the mRNA

this leads to either the degradation of the mRNA or just blocks the translation of that mRNA

Question 22

describe the process by which microRNAs are synthesized and their path to silence mRNAs (probably not a huge deal)

Answer 22

made in the nucleus as precursor miRNA (with a hairpin loop) and are then “cropped” into maturity

this enters the cytoplasm where “dicing” occurs via a dicer enzyme

the microRNA joins with argonaute and other proteins to form “RISC” (RNA-induced silencing complex)

this RISC complex base pairs with mRNA, cleaves the RNA, and is then released as the mRNA fully degrades

Question 23

Describe the X chromosome inactivation method of controlling gene expressions

Answer 23

occurs in females in order to prevent complications caused by an extra chromosome

one of the X chromosomes, randomly chosen, is inactivated by becoming highly condensed

Question 24

list and describe variations in the regulation of gene expression

Answer 24

Genomic imprinting: differential expression of genetic material depending on the parent of origin

Epigenetics: regulation of expression of gene activity without altering the gene structure

X chromosome inactivation: one of the X chromosomes in a female will randomly be inactivated (turned to heterochromatin)

Question 25

describe the function of molecular chaperones. Be sure to include the type of chaperones in environments with elevated temperatures AND the 2 major families of these.

Answer 25

molecular chaperones help fold proteins properly into their mature forms or refold incorrectly folded proteins into the correct form

heat shock proteins are molecular chaperones that are created in high temp. environments to help refold proteins into their proper shape.

Hsp60 and Hsp70 are the 2 major families of heat shock proteins

Question 26

Explain the activation of ubiquitin ligase

Answer 26

protein kinase phosphorylates ubiquitin ligase

ligand binding to ubiquitin ligase causes an allosteric transition

another allosteric transition is caused by protein subunit addition

Question 27

An miRNA variant of SLITRK1 gene is associated with _____ _____ . SLITRK1 gene expression is decreased when miR-189 binds more efficiently to the same target sequence.

Answer 27

Tourettes Syndrome

this miRNA variant of SLITRK1 basically competes with the normal SLITRK1 gene for the same target sequence

Question 28

Are the changes in miRNA expression causative or responsive to disease?

Answer 28

both

Causative if their mutations initiate the disease

responsive when miRNA expression is increased in order to attempt to down regulate the genes that are causing the disease (this just limits severity for the most part)

Question 29

describe the process by which microRNAs are synthesized and their path to silence mRNAs (probably not a huge deal)

Answer 29

made in the nucleus as precursor miRNA (with a hairpin loop) and are then “cropped” into maturity

this enters the cytoplasm where “dicing” occurs via a dicer enzyme

the microRNA joins with argonaute and other proteins to form “RISC” (RNA-induced silencing complex)

this RISC complex the base pairs with mRNA, cleaves the RNA, and is then released as the mRNA fully degrades

Question 30

Describe the RNA control of ferritin mRNA and transferrin receptor mRNA under condition of iron excess

Answer 30

IRP binds to Iron to inactivate it and allows increased ferritin mRNA to be created so that iron may be stored

without the IRP binding to the IRE of TfR, there is no production of TfRn (transferrin receptor) mRNA so that less iron is transported into the cell

Question 31

Describe what Hemosiderin is

Answer 31

Hemosiderin: granules of ferritin

Question 32

State the specificty of E1, E2, and E3 ubiquitin activating enzymes (quantities)

Answer 32

two E1

(one proteasome)

30-40 of E2

hundreds of E3