Genetics Chapter 17

Exam 3

What enzyme is used in histone acetylation, and what is its effect on transcription?

Acetyl transferase; activation

What enzyme is used in histone deacetylation, and what is its effect on transcription?

Deacetylase; repression

What enzyme is used in DNA methylation, and what is its effect on transcription?

DNA methyltransferase; repression

What enzyme is used in DNA demethylation, and what is its effect on transcription?

DNA demethylase; activation

What are the ways that eukaryotic cells differ from bacteria in gene regulation?

• Each structural gene has its own promoter and is transcribed separately (monocistronic)

• DNA must unwind from the histone proteins before transcription; if too condensed, DNA is not accessible, and chromatin cannot be formed

• Transcription and translation are separated in time and space; evolution separated these processes

What are DNase I hypersensitive sites and where are they located?

more open chromatin configuration site; upstream of the transcription start site

What are examples of histone modification?

• Addition of methyl groups to the histone protein tails

• Addition of acetyl groups to histone proteins

What does chromatin remodeling complexes allow for?

It repositions the nucleosomes and allows transcription factors and RNA polymerase to bind to promoters and initiate transcription

What occurs from acetylation of histone proteins?

It alters chromatin structure and permits some transcription factors to bind to DNA

What is an example of acetylation of histones?

• Flowering locus C (FLC) gene

• Flowering locus D (FLD) gene

What controls flowering in Arabidopsis? REVIEW

FLD, a gene that encodes a deacetylase enzyme, which acts on histones and results in no repression of flowering

What are chromatin-remodeling complexes?

Complexes that bind directly to DNA sites and reposition nucleosomes

Where does DNA methylation occur?

DNA methylation occurs in cytosine bases adjacent to guanine nucleotides (CpG), aka CpG islands

What can Chromatin immunoprecipitation (ChIP) be used for?

It can be used to identify DNA-binding sites of a specific protein and the locations of modified histone proteins

What are the jobs of transcription factors?

• Stimulate and stabilize basal transcription apparatus at core promoter

• Mediator

• Regulation of galactose metabolism through GAL4

What do transcription factors bind to and what is their job?

Sites on DNA and regulate transcription

What do the consensus sequences in the promoters of three eukaryotic genes illustrate?

It illustrates the principle that these sequences are mixed and matches in different combinations in different promoters

What does an insulator block and when?

It blocks the action of an enhancer on a promoter when the insulator lies between the enhancer and the promoter

What is an enhancer?

DNA sequence stimulation transcription a distance away from promoter

What is a silencer?

DNA sequence with an inhibitory effect on the transcription of distant genes

What is similar between enhancers and silencers?

Silencers are position and orientation independent, and they contain binding sites for transcription factors that decrease transcription. if moved, it can still enhance/repress transcription

What is an insulator?

DNA sequence that blocks or insulates the effect of enhancers

• May function by causing loops of chromatin that form interacting regions of genes and regulatory elements

What do insulators and their binding proteins do?

May help create “neighborhoods” of regulatory elements and genes that are able to physically interact but are insulated form regulatory elements in other neighborhoods

What can RNA polymerase do at some genes?

At some genes, RNA polymerase may pause or stall downstream of the promoter

What do regulatory factors affect?

They affect stalling and the elongation of transcription

What are response elements?

Common regulatory elements upstream of the start sites of a collective group of genes in response to a common environmental stimulus

Where are multiple response elements (MREs) found?

In the upstream region of the metallothionein gene

How can gene regulation occur through RNA splicing?

Eukaryotic genes can be regulated through the control of mRNA processing. The selection of alternative splice sites leads to the production of different proteins

What is an example of Gene regulation through RNA splicing?

Alternative splicing in Drosophila sex determination

• XX embryos; Sxl gene is activated to produce a protein that causes the embryo to develop into a female

• XY embryos: Sxl gene is not activated and the Sxl protein isn’t produced, which causes the embryo to develop into a male

REVIEW slide 25 what is the purpose of it

How does Dicer and RISC cause RNA-induced silencing complex?

Dicer cleaves and processes double-stranded RNA to produce single-stranded siRNAs or miRNAs 21 to 25 nucleotides long, which combine with proteins to form a RISC

What does the RNA component of RISC pair with?

Complementary base sequences in specific mRNA molecules, often with sequences in the 3’ UTR of the mRNA

What do small interfering RNAs base-pair with?

They base-pair perfectly with mRNAs; microRNAs often form less-than-perfect pairings

What are mechanisms of gene regulation by RNA interference?

• RNA cleavage

• Inhibition of translation

• Transcriptional silencing

• Silencer-independent degradation of mRNA

What is RNA cleavage?

RISC containing an siRNA, pair with mRNA molecules and cleavage to the mRNA

What is transcriptional silencing?

altering chromatin structure

What does RNA silencing lead to?

The degradation of mRNA, or the inhibition of translation or transcription

What is the significance of the control of development by RNA interference?

miRNA molecules are key factors in controlling development in animals, including humans and plants

What is RNA crosstalk?

Different RNA molecules that share binding sites for miRNAs may compete among themselves for available miRNAs

What can impact the rate of translation?

The availability of ribosomes, charged tRNAs, and initiation and elongation factors

What is translation of some mRNAs regulated by?

Some mRNAs are regulated by proteins that bind to the 5’ and 3’ untranslated regions of the mRNA

What regulated the expression of some eukaryotic genes?

They are regulated by the availability of components required for translation

• Example: Exposure to an antigen stimulates an increased availability of initiation factors, and a subsequent increase in protein synthesis, leading to T-cell proliferation