Gene Expression Flashcards
What helps regulate gene expression?
Structural organization of chromatin
What are usually not expressed?
Genes with highly packed heterochromatin
What is heterochromatin?
- Chromosome material of different density from normal
- Heavier
What influences chromatin structure and gene expression?
Chemical modifications to histones and DNA of chromatin
What are histone tails?
- Protruding ends of histone proteins that extend from the nucleosome
What is acetylation?
The addition of acetyl groups to histone tails
Acetylation benefits
Promotes loose chromatin structure that permits transcription
What is DNA methylation?
The addition of methyl groups to DNA
DNA methylation effects
- Can reduce transcription in some species
- Can cause long-term inactivation of genes
- Regulates expression of either maternal or paternal alleles of certain genes at the start of development
Methylation in histone effects
Affects how tightly DNA is packed
How does phosphorylation affect chromatin?
Addition of phosphate groups next to a methylated amino acid can loosen chromatin
What is epigenetic inheritance
Chromatin modifications do not alter the DNA sequence, they may be passed to future generations of cells
What is regulation of transcription initiation?
- Chromatin modifying enzymes provide initial control of gene expression
- Make region of DNA more or less able to bind to transcription machinery
What are control elements?
DNA sequences that regulate gene expression by binding transcription factors
Where are control elements located?
Near (proximal) or far (distal) from the promoter
What is an activator?
A protein that binds to an enhancer and stimulates transcription
Distal elements
- located far from the gene they regulate
- can be grouped as “enhancers”
- Can be located in the intron
What are the two domains of activators?
- DNA-Binding Domain
- Activation Domain
DNA-Binding Domain
Binds to specific DNA sequences like enhancers
Activation Domain
Activates transcription
What is the poly-A signal?
A sequence in the last exon transcribed into RNA that signals where the transcript is cleaved
What happens after the poly-A signal is transcribed?
Transcription continues for hundreds of nucleotides beyond the poly-A signal before terminating
Transcription Factors - Functions
- Initiates transcription
- Some factors function as repressors, inhibiting expression of gene
- Act indirectly by influencing chromatin structure
What is combinatorial control of gene activation?
Transcription is activated only when a specific combination of control elements and appropriate activator proteins are present
How are co-expressed eukaryotic genes organized?
Not in operons; each has its own promoter and control elements
Where are co-expressed eukaryotic genes located?
They are scattered across different chromosomes but share the same combination of control elements
How are co-expressed genes transcribed simultaneously?
Activators recognize shared control elements and promote simultaneous transcription of these genes
How can the initiation of translation be blocked?
Regulatory proteins can bind to mRNA sequences or structures, preventing translation
Why is mRNA lifespan important?
- It determines how much protein is synthesized
- The longer it lasts, the more protein is made
How does eukaryotic mRNA lifespan compare to prokaryotic mRNA?
Eukaryotic mRNA is longer-lived than prokaryotic mRNA
Where is the lifespan of eukaryotic mRNA determined?
It resides in the 3’ UTR of the mRNA
What happens to proteins after translation?
Proteins undergo processing such as cleavage or the addition of chemical groups
How is the length of time a protein functions regulated?
By selective degradation
What does ubiquitin do in protein degradation?
Ubiquitin is a small protein that tags proteins for degradation by proteasomes
What do proteasomes do?
They are large protein complexes that recognize ubiquitin-tagged proteins and degrade them
Noncoding RNAs (ncRNAs)
- They do not code for proteins but regulate gene expression at mRNA translation and chromatin configuration
- Significant amounts of the genome can be transcribed into ncRNAs
What are microRNAs (miRNAs)?
- Small single-stranded RNA molecules that bind to mRNA to degrade it or block its translation
- Expression of at least half of all human genes can be regulated by miRNAs
How do miRNAs interact with mRNA?
- miRNA binds to mRNA with at least 7 complementary bases
- If bases are complementary along the whole thing, mRNA is degraded
- If the match is less complete, translation is blocked
What is RNA interference (RNAi)?
- The inhibition of gene expression by RNA molecules
- Also used in labs to disable genes and study their functions
What controls RNAi?
Small interfering RNAs (siRNAs)
What is cell differentiation?
When cells become specialized
What is morphogenesis?
Physical process giving an organism its shape
Process to transform from zygote to adult
- Cell division
- Cell differentiation
- Morphogenesis
