genetics week 6

The human genome contains approximately 106106 copies of an Alu sequence, one of the best-studied classes of short interspersed elements (SINEs), per haploid genome. Individual Alus share a 282-nucleotide consensus sequence followed by a 3'-adenine-rich tail region (Schmid, 1998). Given that there are approximately 3×1093×109 base pairs per human haploid genome, about how many base pairs are spaced between each Alu sequence?

3000 base pairs

Sidney Brenner argued that the code was non-overlapping because he considered that coding restrictions would occur if it were overlapping. A second major argument against an overlapping code involved the effect of a single nucleotide change. In an overlapping code, what is the maximum number amino acid(s) that would be affected by a point mutation? In a non-overlapping code, what is the maximum number of amino acid(s) that would be affected by a point mutation?

3;1

Which of the following contains the three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes?

5'-capping, 3'-poly(A) tail addition, splicing

What is the initiator triplet in both prokaryotes and eukaryotes? Which amino acid does this triplet recruit?

AUG; methionine

Which technique uniquely identifies specific areas of a chromosome composed of heterochromatin?

C-banding This technique involves heat denaturation of chromosome preparations followed by treatment with Giemsa stain. Only the centromeric regions that consist of heterochromatin take up the stain.

Where does the process of transcription fit into the central dogma of molecular genetics?

DNA --> Transcription --> RNA --> translation --> protein

Viral chromosomes exist in a variety of conformations and can be made up of ________.

DNA or RNA

Which of the following statements about heterochromatin is FALSE?

Heterochromatin replicates early in the S phase This statement is false; heterochromatin is replicated relatively late during the S phase

While much remains to be learned about the role of nucleosomes and chromatin structure and function, recent research indicates that in vivo chemical modification of histones is associated with changes in gene activity. One study determined that acetylation of H3 and H4 is associated with 21.1 percent and 13.8 percent increases in yeast gene activity, respectively, and that yeast heterochromatin is hypomethylated relative to the genome average (Bernstein et al., 2000). Based on the finding that acetylation of H3 and H4 histones increases gene activity, what is the mechanism behind this effect? Based on the finding that heterochromatin is hypomethylated, what effect does methylation of histone proteins have on transcription in this case?

It alters the association of DNA and nucleosomes so that genes become more accessible to factors that promote transcription It increases gene expression

What is a "puff" in a polytene chromosome?

It is the site of gene transcription The puff represents a section of DNA that has been uncoiled for transcription

An intron is a section of ________.

RNA that is removed during RNA processing

When considering the initiation of transcription, one often finds consensus sequences located in the region of the DNA where RNA polymerase(s) binds. Which of the following is a common consensus sequence?

TATA

It has been recently determined that the gene for Duchenne muscular dystrophy (DMD) is more than 2000 kb (kilobases) in length; however, the mRNA produced by this gene is only about 14 kb long. What is a likely cause of this discrepancy?

The introns have been spliced out during mRNA processing

The mRNA formed from the repeating tetranucleotide UUAC incorporates only three amino acids, but the use of UAUC incorporates four amino acids. Why?

The triplets UUA and CUU, produced from the first sequence, code the same amino acid

Viral genomes and eukaryotic genomes are similar in which of the following ways?

They have the ability to pack a genome into a small volume Both eukaryotic and viral genomes can be characterized by their ability to pack DNA into a small volume

In human chromosomes, satellite DNA sequences of about 170 base pairs in length are present in tandem arrays of up to 1 million base pairs. Found mainly in centromere regions, these DNA sequences are called ________.

alphoid families

The genetic code is said to be triplet, meaning that there ________.

are three bases in mRNA that code for an amino acid

Eukaryotic chromosomes contain two general domains that relate to the degree of condensation. These two regions are ________.

called heterochromatin and euchromatin

In 1964, Nirenberg and Leder used the triplet binding assay to determine specific codon assignments. A complex of which of the following components was trapped in the nitrocellulose filter?

charged tRNA, RNA triplet, and ribosome

In E. coli, the genetic material is composed of ________.

circular, double-stranded DNA

What is the name given to the three bases in a messenger RNA that bind to the anticodon of tRNA to specify an amino acid placement in a protein?

codon

Both the codons UUU and UUC specify the amino acid phenylalanine. What is the term for this phenomenon?

degenerate Degeneracy of the code means that a given amino acid can be specified by more than one triplet codon

Significant in the deciphering of the genetic code was the discovery of the enzyme polynucleotide phosphorylase. What reactions are catalyzed by this enzyme?

degradation of RNA synthesis of RNA in vitro

All EXCEPT which of the following forms of DNA have been observed in the chromosomes of viruses?

double-stranded branched DNA The linear sequence of information contained in DNA cannot be branched. DNA has no free functional group (2'-OH) to begin a branch in the polynucleotide chain

If one compares the base sequences of related genes from different species, one is likely to find that corresponding ________ are usually conserved, but the sequences of ________ are much less well conserved.

exons; introns

A 3' poly-A tail and a 5'-cap are common components of prokaryotic RNAs

false

Each human contains an identical set of VNTRs

false

In contrast with euchromatin, heterochromatin contains more genes and is earlier replicating

false

Messenger RNA is usually polycistronic in eukaryotes

false

RNA processing occurs when amino acids are removed from nascent proteins

false

Transcription factors function to help move ribosomes along the mRNA.

false

Viral genomes are always linear, double-stranded DNA

false

The size of chloroplast DNA (cpDNA) varies greatly between organisms, while mitochondrial DNA (mtDNA) is fairly uniform in size

false Mitochondrial DNA can vary greatly, from ~16 kb in humans to 367 kb in the mustard plant Arabidopsis. Chloroplast DNA varies between 100 and 225 kb

The second order of chromatin packing occurs when nucleosomes coil together to form a fiber that is 300 nm in diameter

false The second order of chromatin packing occurs when nucleosomes coil together to form a solenoid fiber that is 30 nm in diameter

A class of mutations that results in multiple contiguous (side-by-side) amino acid changes in proteins is probably caused by which one of the following types of mutations?

frameshift

Which type of mutation helped lead to the understanding that the genetic code is based on triplets?

frameshift Insertions or deletions of one or two nucleotides resulted in frameshift mutations. Insertions or deletions of three nucleotides resulted in insertions or deletions of a single amino acid and did not shift the reading frame

Chromatin of eukaryotes is organized into repeating interactions with protein octomers called nucleosomes. Nucleosomes are composed of which class of molecules?

histones

Which of the following are characteristics of LINE sequences? Select all that apply.

interspersed sequence of approximately 6,000 base pairs encodes reverse transcriptase middle repetitive DNA capable of moving around the genome

Introns are known to contain termination codons (UAA, UGA, or UAG), yet these codons do not interrupt the coding of a particular protein. Why?

introns are removed from mRNA before translation

Which of the following two terms relate most closely to split genes?

introns, exons

The relationship between a gene and a messenger RNA is that ________.

mRNAs are made from genes

During what genetic process are lampbrush chromosomes present in vertebrates?

meiosis

In addition to highly repetitive and unique DNA sequences, a third category of DNA sequences exists. What is it called, and which types of elements are involved in it?

moderately repetitive DNA; SINEs, LINEs, and VNTRs

In which cellular organelle do the three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes occur?

nucleus

The chromosome of phage φX174 encodes 11 proteins consisting of a total of more than 2300 amino acids, even though the size of its genome predicts that it should be able to code for only 1795 amino acids. The reason for this discrepancy is __________.

overlapping reading frames Multiple translation initiation points allow a single mRNA to code for more than one protein

In studies of frameshift mutations, Crick, Barnett, Brenner, and Watts-Tobin found that either three nucleotide insertions or deletions restored the correct reading frame. Assuming the code is a triplet, what effect would the addition or loss of six nucleotides have on the reading frame? If the code were a sextuplet (consisting of six nucleotides), would the reading frame be restored by the addition or loss of three nucleotides? six nucleotides? nine nucleotides?

reestablishing of the subsequent reading frame no yes no

Of the following three types of nucleic acids—DNA, mRNA, tRNA—which is most likely to contain modified bases?

tRNA

Most eukaryotic mRNAs are shorter than the genes that encode them. The reason for this is __________.

that eukaryotic genes contain both introns and exons After transcription, the introns are spliced out of hnRNA to form mRNA

All EXCEPT which of the following are examples of repetitive DNA?

the DNA that encodes the telomerase gene The DNA sequence constituting the gene for telomerase is euchromatin and is relatively unique

When scientists were attempting to determine the structure of the genetic code, Crick and coworkers found that when three base additions or three base deletions occurred in a single gene, the wild-type phenotype was sometimes restored. These data supported the hypothesis that ________.

the code is triplet

When examining the genetic code, it is apparent that ________.

there can be more than one codon for a particular amino acid

A base at the first position of an anticodon on the tRNA would pair with a base at the ________ position of the mRNA

third

What genetic process is occurring in a puff of a polytene chromosome?

transcription

RNA synthesis from a DNA template is called __________.

transcription Transcription is initiated when the cell signals for the expression of a particular gene and involves the synthesis of RNA from a DNA template

Heterogeneous nuclear RNA is a primary transcript in eukaryotes that is processed prior to involvement in translation

true

Telomerase is an enzyme involved in the replication of the ends of eukaryotic chromosomes

true

The E. coli chromosome is circular and double-stranded DNA.

true

The code is nonoverlapping, meaning that, assuming "standard translation," a given base participates in the specification of one and only one amino acid

true

The enzyme polynucleotide phosphorylase is capable of generating a random assembly of ribonucleotides

true

The triplet AUG is commonly used as a start codon during translation

true

What makes up the protein component of a nucleosome?

two tetramers of histone proteins The protein component of a nucleosome is composed of two tetramers of histone proteins. One tetramer is composed of two units each of histones H2A and H2B, and the other is composed of two units each of histones H3 and H4

The genetic code is fairly consistent among all organisms. The term often used to describe such consistency in the code is ________.

universal

All EXCEPT which of the following experiments or discoveries helped to identify the "triplet nature" of the DNA code?

universality of the genetic code The universality of the code refers to the fact that, for the most part, all the DNA code of life's genomes can be read in the same way. In other words, a codon that represents leucine in bacteria will also represent leucine in humans. This concept does not include information about the triplet nature of the code.

Which subunit of RNA polymerase establishes its binding to a promoter in prokaryotes?

σ The β subunit recognizes the promoter sequence. Different sigma subunits can be employed to regulate the expression of genes at the transcriptional level.

Which subunit of RNA polymerase establishes template binding to a promoter in prokaryotes?

σ The σ subunit recognizes the promoter sequence. Different sigma subunits can be employed to regulate the expression of genes at the transcriptional level