Genetics › Regulation of Gene Expression in Prokaryotes and Eukaryotes
Which is a function of DNA polymerase III that occurs in the 3' to 5' direction of the template DNA strand?
Exonuclease proofreading
Polymerization of the leading strand
Polymerization of the lagging strand
Removal of primers
DNA polymerase III has these two functions:
1. 5'-3' polymerase requiring a 3' hydroxide primer and a DNA template
2. 3'-5' exonuclease proofreading
Both DNA polymerase I and DNA polymerase III are prokaryotic only. DNA polymerase I excises RNA primers with a 5' to 3' exonuclease.
An autosome is __________.
any chromosome that is not a sex chromosome
a sex chromosome
a series of mutated genes
a gene pattern found only in vertebrates
By definition, an autosome is any chromosome that is not a sex chromosome. Humans have a diploid genome that consists of 22 pairs of autosomal chromosomes, and one special pair of chromosomes (which is nonautosomal) that determines gender (two X chromosomes = female, one X and one Y chromosome = male).
What does the processing of mRNA ensure?
Protection from degradation in cytosol
Translation of introns into a functional protein
Conversion from double stranded strand to single stranded strand
Simultaneous transcription and translation
Removal of all uracil from mRNA transcript
The purpose of mRNA processing is to protect it from degradation during its transport to cytosol. It does not involve introns or uracil. In addition, this concept has nothing to do with being double-stranded or single-stranded. Also, since the question states mRNA is being processed, it would imply that this takes place in a eukaryotic organism and hence, simultaneous transcription and translation is not possible.
Commonly, __________ of histones leads to the silencing of genes.
methylation
acetylation
phosphorylation
All of these would silence the gene
Out of the choices, only methylation of histones is commonly associated with the silencing of genes. Proteins known as histone methyltransferases bind a methyl group to amino acids in the histone, most commonly lysine or arginine. The result is a change in chromatin structure, most commonly blocking transcription sites and preventing expression.
Acetylation of histones is often found in activated genes. Phosphorylation of histones has been seen in DNA regulation, but it is unclear whether or not this modification affects the expression of genes.
Which DNA repair mechanism removes DNA damage caused by ultraviolet light?
Nucleotide excision repair
Base excision repair
Direct repair
Mismatch repair
Nucleotide excision repair (NER) is used to repair thymine dimers, which are caused by ultraviolet damage. It also repairs bulky DNA adducts caused by carcinogens.
Which of the following is a step performed by RNA polymerase during the elongation process of DNA transcription?
Advancement in the 3'-5' direction down the template strand
Catalysis of phosphodiester bond linkage at the initial 2 rNTPs (ribonucleotide triphosphates)
Melting DNA into an open conformation near the transcription site
Binding to the promoter region on the closed DNA complex
During elongation, RNA polymerase advances in the 3'-5' direction down the template, melting and adding rNTPs to growing RNA
The genetic code of an organism is determined by __________.
DNA sequence
RNA sequence
Ribosomal shapes
Number of amino acids per protein
An important concept of genetics is that DNA contains the blueprint of all genetic information. It is the sequence of DNA that determines an organism's genetic code.
RNA primers are removed by which of the following exonucleases?
5'-3' DNA polymerase I
5'-3' DNA polymerase III
3'-5' DNA polymerase I
3'-5' DNA polymerase III
5'-3' exonuclease removal of primers by DNA polymerase I.
DNA polymerase I is prokaryotic only, it degrades RNA primer and fills in the gap with DNA.
Which of the following is a DNA control element?
TATA box
Transcriptional repressors
Transcriptional activators
General transcription factors
DNA control elements are contained within the DNA helix.
DNA control elements:
1. TATA box: 25-35 basepairs (bps) upstream from start site, determines site of transcription and directs RNA polymerase II binding
2. Proximal promoter elements: 200 bps upstream of start and are roughly 20bps long
3. Enhancers are short regions of DNA that can be 50-1500bp long. They can be bound by activators to increase transcription. Can be far from the site of transcription and still be functional
NOT DNA control elements:
Transcription factors: bind to DNA control elements to influence transcription but are not considered control elements themselves.
Transcriptional repressors and activators: proteins coded by one gene that act to regulate transcription
Alternative splicing can result in which of the following?
Removal of an exon
Reversal of an exon
Duplication of an intron
Duplication of an exon
Alternative splicing can:
1. Retain/remove exons.
2. Retain/remove introns.
3. Truncate/extend at 5' or 3' ends.
4. Have mutually exclusive exons (one or the other, but never both).