Textbook Practice

why might a a normal enzyme be 227 amino acids long, but the mutant form is 312 amino acids long?The extra 85 amino acids occurred as a block in the middle of the normal sequence.

this could have occurred from an intron that wasn’t spliced out or an insertion mutation

what RNAP would encounter first along a gene

promoter

what RNAP would encounter second along a gene

methylated cap site

what RNAP would encounter third along a gene

5’ UTR

what RNAP would encounter fourth along a gene

initation/start codon

what RNAP would encounter fifth along a gene

stop codon 

what RNAP would encounter sixth along a gene

3’ UTR

what RNAP would encounter seventh along a gene

poly-A tail site

what RNAP would encounter eighth along a gene

transcription terminator 

transcribed portion of a gene consists of

all exons and introns, ignoring UTRs

size of primary transcript consists of 

the gene size (exons+introns)

size of mature mRNA consists of 

exons + poly-A tail 

location of start codon

compare the size of the 5' UTR to that of the first exon; if the 5’ UTR is larger than the first exon, then the first exon is included in the UTR plus extra. If the second codon is larger than the extra, the start codon must be in exon 2.

No ____ ____ encode the 5' cap because the cap is added _________.

base pairs, posttransciptionally

The sequence encoding the ______ ______ does not exist in the gene because poly-A is added ________ by poly-A polymerase.

poly-A tail, posttransciptionally

if you transform a piece of DNA encoding insulin into E. coli, why can’t the E. coli cells containing the human insulin gene make any insulin?

• The promoters for the human insulin gene may not work in E. coli

• Bacterial cells do not have introns and thus have not evolved the machinery necessary to remove them from the RNA.

• The human insulin mRNA may not have sequences like the Shine- Dalgarno box or transcription termination signals that operate in bacterial cells.

  • correct folding of the polypeptide and other post translational modifications may not occur in the same ways in prokaryotic cells

how can companies create E. coli cells that make human insulin used to treat patients?

You would replace the protein-coding part of the bacterial gene

with the (properly spliced) protein-coding part of the human insulin gene.

if a protein is a positive regulator,

a LOF mutation in the gene encoding the DNA binding protein would result in little or no expression 

When a gene encoding a DNA binding protein has a loss-of-function mutation and the result is constitutive expression,

The wild-type must be a negative regulator since it blocks transcription

charged tRNA^Trp

RNA + small molecule (the amino acid Trp); negative regulator; transcription elongation; in trans

Trp repressor

protein; negative regulator; transcription initiation; in trans

CRP-binding site

DNA; positive regulator; transcription initiation; in cis

CRP

protein; positive regulator; transcription initiation; in trans

lac operator

DNA; negative regulator; transcription initiation; in cis

Lac repressor

protein; negative regulator; transcription initiation; intrans

a single nucleotide difference in an enhancer of a human gene contributes to hair color. People with an A:T = dark hair, while G:C = blond hair. blond is 80% as frequently transcribed as the dark hair. How can this difference have this effect? 

The blond allele's enhancer has lower affinity for an activator (or higher affinity for a repressor) than the dark allele's enhancer does.

Heterozygous calico female cats have patches of orange and black fur. In some patches of cells, the X chromosome with the _____ allele is inactivated so the coat is black as determined by the recessive allele. In other patches of cells, the X chromosome with the _____ allele is inactivated so the fur is orange because the dominant allele is functional.

dominant, recessive

Male tortoiseshell or calico cats could be ____ males who are heterozygous. One of their X chromosomes would be inactivated in some patches of cells; the other X chromosome would be inactivated in other patches of cells, just as for the tortoiseshell females

XXY