• Eukaryotic Regulation

Regulation of Gene Expression – Part IISpring 2013 - Althoff Reference: Mader & Windelspecht Ch. 13)

Lec19

• With few known exceptions….____________ of a multicellular eukaryote has a complete complement of genes.

• Cell type differences (i.e., muscle vs. nerve vs. liver vs. etc.) result because only a certain set of genes is “___________” in the ___________…thus, a different set of proteins are “active” in the cytoplasm.

• There are 5 primary levels of control: 3 pertain to the __________, 2 of them pertain to the _____________

Eukaryotic Regulation

• Chromatin Structure – in the nucleus

• Transcriptional Control – in the nucleus

• Posttranscriptional Control – in the nucleus

• Translational Control — in the cytoplasma

• Posttranslational Control – in the cytoplasma

Eukaryotic Regulation – 5 types of control

1

2

3

4

5

1

2

3

4

5

Nucleus

Cytoplasma

• Chromatin packing is used as a way to keep genes turned ____. If genes are not accessible to ________________, they cannot be ___________.

•

• Chromatin structure is one method of __________ ___________ = transmission of genetic information “__________” the ______________ of a gene.

• Chromatin is a “stringy” variety of proteins material… most prevalent during interphase of the cell cycle

Type: Chromatin Structure

1

• One class of DNA-associated proteins are ____________. They play an important role in ________________ of DNA.

• Without histones, DNA could not fit inside the nucleus. Each human cell contains about 2 meters of DNA…yet the nucleus is only 5-8 цm in diameter.

• _______________ chromatin = ______________

• _______________ chromatin = ______________

Type: Chromatin Structure

1

Nucleus with staining showing…heterochromatin and euchromatin

nucleolus

DNA Unpacking

1

_____________ promoter

chromatin remodeling

nucleosome

___________ promoter

DNA to be __________3

2

• Heterochromatin is not transcribed…

• Heterochromatin does not permit access by RNA polymerase

• Genes contained by heterochromatin __________ _______ get transcribed…therefore they are not expressed

• Example: Barr body in mammalian females (XX): chromatin adheres to inner edge of the nuclear membrane—resulting in one inactive X chromosome (i.e., produces no products)

Type: Chromatin Structure

1

• __________ Inheritance: sometimes caused by histone modification…changes that result not in sequence of DNA nucleotides.

• Epigenetic inheritance term is not restricted to the genes themselves causing variation.

•

• Epigenetic inheritance may explain unusual patterns of inheritance …and may play a role in growth, aging, and cancer.

Type: Chromatin Structure

1

• This is considered the _____________ of the 5 control levels

• Keep in mind that the first step towards transcript is availability of DNA

• A eukaryote may have many different types of _________________—proteins that help regulate transcription by assisting RNA polymerase to bind to the _______________.

• There may be __________________ transcription factor active at a single promoter…thus, the absence of one can prevent transcription from taking place

Type: Transcriptional Control

2

• Even with all transcription factors present, transcription might not begin without the presence of a DNA-binding protein called a _____________ ______________

• Transcription activators bind to regions of the DNA called _______________.

• Enhancers may not be located near promoters…

• “Distance” reduced with _____________ in the DNA

Type: Transcriptional Control

2

enhancer

transcriptionactivator

_________________________

1

2

3

• Occurs in the nucleus

• Includes alternative mRNA splicing and controlling of the _____ with which mRNA leaves the nucleus

• During pre-mRNA splicing, ________ (non-coding regions) are excised…and ________ (expressed regions) are joined together to form an mRNA.

• Result: if an exon is _________, it may be is excised along with flanking introns…the result…

• ….the ___________ has an altered sequence and the protein it encoded is altered

• Example: in thyroid, a slightly different calcitonin than what the hypothalamus produces.

Type: Posttranscriptional Control

3

Protein product 1 Protein product 2

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at h

app

ens

in t

he

cyto

pla

sma

wh

at h

app

ens

in t

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nu

cleu

s

• Occurs in the cytoplasma

• Happens __________ a protein product is made

• Associated with activity of the mRNA for translation at the ______________

• Affected by the presence…or…absence… of the 5’ cap and the length of the poly-A (i.e., adenine nucleotide) tail at the 3’ end…this can affect the whether a) __________________…or for _____ _____ the mRNA is active.

• Example: persistence 5’ end caps and long 3’ poly-A tails long-life of mRNAs that code for hemoglobin in mammalian red blood cells

Type: Translational Control

4

• Occurs in the cytoplasma

• Begins once the __________________________ and become active.

• It represents the last chance the cell has for influencing gene expression

• This highlights the fact that not all proteins are “active” after synthesis. Value of this: a protein is only activated when it is appropriate to do so. Example: bovine proinsulin is “held” as such before special bonding process that results in “active” insulin.

Type: Posttranslational Control

5

• Length of time a protein remains active in a cell usually regulated by ____________ = enzymes that breakdown proteins.

• Proteases usually confined to ____________ or special structures called _________________.

Type: Posttranslational Control

5

• For a protein to enter a proteasome, it has to be “tagged” with a signaling protein recognized by the proteasome’s cap.

• When the cap recognizes the tag, it opens up and allows the protein to enter the core of the structure where it is ___________________________.

• This is gene expresssion control” because it regulates the amount of protein product in the cytoplasma

Type: Posttranslational Control

5

5 Posttranslational Control: “________”

Which leads to ________ into proteasomewhere…

5 Posttranslational Control: “___________”

…break down to _______________________.

In summary….

DNAtranscription

mRNAtranslation

protein

modification of DNA via

transcriptional

chromatin structure

posttranscriptional

translational

posttranslational