Ch. 11 Flashcards
Epigenetic Modifications
Heritable chemical modifications to DNA and its associated proteins that alter gene expression, without changing the nucleotide sequence
is reversible
includes DNA methylation, histone modifications, miRNA-mediated gene silencing
What does gene structure include?
5’ enhancer- promoter (regulatory region)- TSS - gene body (contains exons, introns, and regulatory sequences) - TTS 3’
TSS: transcription start site
TTS: transcription termination site
Gene regulatory region
segment of DNA capable of increasing or decreasing expression of specific genes (enhancers & promoters)
Promoter
region of DNA that initiates transcription of particular gene
TATA Box
signature sequence at promoters
consensus sequence: 5’-TATA(A/T)A(A/T)-3’
Enhancer
short region of DNA that can be bound by proteins (transcription factors) to increase transcription likelihood of gene
Histone modification
expose DNA when and where it is to be transcribed and shield it when it is to be silenced
How does acetylated histones allow transcription to begin?
acetyl binding can subtly shift histone interactions to ease transcription
on lysine residues (ONLY gene transcription activation)
MicroRNA
prevents translation when microRNA binds to target mRNA
ex. cancer treatment & concussion markers
Maximizing Genetic Info
proteins > genes
- chromatin remodeling b4 transcription
- alternative splicing (circular RNA) after transcription
- use of introns
- protein modification
- cutting of a precursor protein into 2 proteins
Maximizing Genetic Info
Alternative splicing
alternative splicing of exons and introns may encode several isoforms (possible protein products) of protein
create different transcripts
Maximizing Genetic Info
An intron encoding one isoform
is an exon in another
Maximizing Genetic Info
An intron on one DNA strand
is an exon on the other
Maximizing Genetic Info
Post-Translational Modifications
addition of sugars + lipids to create glycoproteins and lipoproteins
All genes are expressed continuously at the same levels.
False; Different genes vary in the timing and the level of gene expression.
Epigenetic changes alter the base sequence of a DNA molecule.
False
Epigenetic changes affect molecules that associate with DNA
True; such as proteins and RNA molecules.
When a cell divides, epigenetic changes are transmitted to its daughter cells.
True; Epigenetic modifications are passed to daughter cells, but are generally not passed on to offspring.
Epigenetic changes result in modification of gene expression.
True
MicroRNAs are typically about ___ bases long.
21
MicroRNAs regulate gene expression at the level of
translation
MicroRNAs are an example of ___ RNAs.
noncoding
The human genome contains approximately ___ distinct sequences of microRNAs.
2500
MicroRNAs regulate approximately ___ of the protein-encoding genes in the human genome.
1/3
___ explains how one gene can specify multiple mRNAs.
alternative splicing
You are studying two proteins that play a role in cell wall formation in plants. You are interested in determining the genomic location of the genes that encode these proteins. You are surprised to find that the two proteins appear to be encoded by the same gene, and that the sequence encoding one appears immediately before the other one, in frame, although they do not have overlapping sequence.
Which mechanism for maximizing genetic information do you suspect is at play here?
Precursor protein is cut to yield two proteins; Because these proteins appear to be encoded by the same gene, we can rule out that the proteins are encoded on opposite strands. Because there is no overlap in the sequence of the proteins, it seems unlikely that alternative splicing is at play here. In alternative splicing at least the first exon of the gene would be in common. Given that the two proteins are encoded by one gene and are in frame with one another, the most likely explanation is that a precursor protein is cut to yield two proteins.
The collection of all mRNAs in a cell is called a(n)
transcriptome
