Regulation of Gene Expression Flashcards
Which type of chromatin is transcriptionally active and inactive?
Heterochromatin = inactive Euchromatin = active
What is gene expression?
Production of functional and active gene products
What is constitutive gene expression?
Made by all cells at all times
Often called housekeeping genes
Expression constant
What is regulated gene expression?
Time, place, amount, in response to signals
Under very tight control
What kind of processing does a primary transcript undergo?
Addition of - 5' cap - Poly(A) tail Excision of introns Splicing of exons via spliceosome
What does the 5’ cap do?
Directs mRNA to ribosome
What does the poly(A) tail do?
Stabilises transcript
Are some non-coding RNAs involved in primary transcript splicing?
Yes
Are mutations or variants spliced the same as the normal RNA?
No, they produce alternative splicing
Sometimes this is on purpose, sometimes they have adverse effects
What is a spliceosome?
Large ribonucleoprotein complex > splcies primary transcripts to remove introns
Does transcription only occur at the promoter regions?
No
Where can some RNAs be transcribed from, if not from promoter regions?
Introns
Intergenic regions
What is chromatin?
DNA + RNA + protein
When is chromatin present?
Only during cell division
What must happen to the chromatin for transcription to occur?
Must go from closed to open conformation
What proteins have an important role in altering the conformation of chromatin?
Histone proteins
What is the most typical chemical modification that happens to DNA?
Methylation
What does DNA methylation change?
Conformation of DNA
What is nucleosome occupancy?
Density of nucleosome varies along DNA
True or false: local location of DNA in nucleus influences its conformation
True
What does chromatin remodelling require?
Chemical modification (epigenetic markers) to histones and DNA
What effect does DNA methylation have on transcription?
Generally “locks in” transcriptional inactivity
How does DNA methylation happen to a new DNA strand?
Large proportion of cytosines in CG adjacent methylated
DNA replication > new DNA strands
New DNA strands initially lack methyl groups
Original pattern of DNA methylation transmitted to daughter cells
What are CpG-rich islands associated with?
5’ region of genes
What does gene expression or silencing seem to be more related to in terms of methylation?
Methylation status of other CpGs, not CpG islands
What is hyper-acetylation of histones associated with in terms of transcription?
Transcriptionally active
What is hypo-acetylation of histones associated with in terms of transcription?
Transcriptionally silent
What are writer enzymes?
Add on chemical modifications to chromatin
What are eraser enzymes?
Remove chemical modifications to chromatin
What are reader enzymes?
Read chemical markers on chromatin, and allow other proteins to bind
How can transcription be regulated in the gene itself?
Promoters major on-off switches
Looping of DNA
Direct interactions with other DNA sequences, non-coding RNAs, and trans-acting proteins
Do genes only have one promoter?
No, many genes have 1+ promoter
What can alternative splicing of different exons lead to?
Different protein products, often tissue specific
What are some examples of non-coding RNAs that regulate gene expression?
Long non-coding RNAs (lncRNAs) Short interfering RNAs (siRNAs) Micro RNAs (miRNAs)
What are long non-coding RNAs?
Long enough to fold over and associate with themselves, creating secondary structure
What are short interfering RNAs?
Sub-category of long RNAs
Complementary to mRNA
Degrade mRNA
What are micro RNAs?
Not completely complementary to mRNA
Binding feeds back to ribosome and represses its activation
Reduction of gene expression
