Differential Gene Expression- Unit 3

Genetic Equivalence

all the cells of an organism have the same genetic information

Differential Gene Expression

the expression of different genes by cells with the same genomes

Heterochromatin

genes within highly condensed chromatin; usually not expressed

Euchromatin

genes within less condensed regions; can be expressed

What is the function of structural organization of chromatin?

packs DNA into compact form to help regulate gene expression

What determines chromatin status?

chemical modifications of histones and /or DNA 

Whats the purpose of changing heterochromatin to euchromatin?

reveals all the genes that were hidden before

DNA Methylation

addition of methyl (-CH3) group to certain bases in DNA, usually cytosine

What does the addition of methyl groups do?

1) can condense chromatin and lead to reduced transcription

2) create new binding sites for enzymes that further modify chromatin

Where are genes more heavily methylated?

when the genes are not expressed (“hidden”)

Do methylated genes stay that way?

Yes, through successive cell divisions; chemical modifications can be inherited just like other mutations 

How is methylation pattern inherited?

After replication, enzymes methylate the correct daughter strand

Histone acetylation

attachment of acetyl (CH3CO-) group to amino acids in histone tails 

What does histone acetylation do?

Loosens chromatin structure and promotes the initiation of transcription; allows the chromatin structure to be expressed

In DNA methylation where is the methyl group added to?

the nucleotide bases

In Histone Acetylation where is the acetyl group added to?

histones

Transcriptional Control

multiple control elements found associated with eukaryotic genes

Control Elements

noncoding DNA; serves as binding sites for transcription factors

What can transcription factors bind to?

promoter and control elements (noncoding DNA)

Proximal Control Elements

located near the promoter

Distal Control Elements

also called enhancers; may be far away from the promoter (can even be within introns)

General Transcription Factors

act at the promoter of all genes for the start of transcription

Cell-Specific Transcription Factors

those that bind to control elements outside the promoter and are only present in particular cell/cell types; can activate or repress transcription

What do cell-specific transcription factors allow?

allow two different cells to have the same genomes, but express different genes

Activator Transcription Factor

bind to enhancer elements and stimulate transcription of a gene

Repressor Transcription Factor

inhibits transcription of a gene

What does RNA polymerase do once recruited by the complex of trans-factors?

binds to the TATA box and initiates transcription

How do enhancers affect transcription at promoters many base pairs away?

proteins bound to enhancers interact with proteins bound to the promoter that have DNA looping out

Alternative RNA Splicing

different mature mRNA molecules are produced from the same pre-mRNA; if exons are incorrectly removed like an intron then the exons are joined together differently and becomes a slightly different protein

What does the life span of mRNA molecules in the cytoplasm help determine?

pattern of protein synthesis in a cell

Where do the nucleotide sequences that influence the life span of mRNA in eukaryotic cells reside?

in the untranslated region of the 3’ end of mRNA

What is the purpose of non-coding DNA?

it can help code for other RNAs (ribosomal and transfer)

MicroRNAs and Small Interfering RNAs

small, single-stranded RNA molecules that can bind to complementary mRNA sequences; can’t be translated and are often targeted for degradation

How do eukaryotes regulate expression at the post-translational level?

by controlling the activity and/or abundance of expressed proteins

Ubiquitination

modifcation that targets the protein for proteolysis (degradation)