Chapter 10 - Molecular Structure of Genes and Chromosomes

Barbara McClintock

________ discovered the first mobile elements while doing classical genetic experiments in maize (corn) during the 1940s.

genetic material

During interphase, when cells are not dividing, the ________ exists as a nucleoprotein complex called chromatin, which is dispersed through much of the nucleus.

≈0.15 M

When the DNA from eukaryotic nuclei is isolated in isotonic buffers (i.e., buffers with the same salt concentration found in cells, ________ KCl), it is associated with an equal mass of protein as chromatin.

multicellular animals

Most genes in ________ and plants contain introns, which are removed during RNA processing.

15 kb DNA sequence

The ________ encoding chicken lysozyme constitutes a simple transcription unit containing four exons and three introns.

H1

The five major types of histone proteins- termed ________, H2A, H2B, H3, and H4- are rich in positively charged basic amino acids, which interact with the negatively charged phosphate groups in DNA.

diploid

In the mating by fusion of haploid yeast cells, both parents contribute equally to the cytoplasm of the resulting ________; thus inheritance of mitochondria is biparental.

major cytoskeletal

Invertebrates, the ________ proteins are the actins, tubulins, and intermediate filament proteins like the keratins Tandemly Repeated Genes Encode rRNAs, tRNAs, and Histones.

lineages

In ________ leading to higher eukaryotes, homologous recombination between mobile DNA elements dispersed throughout ancestral genomes may have generated gene duplications and other DNA rearrangements during evolution.

genomes of all eukaryotes

The ________ studied from yeast to humans contain retrotransposons.

repetitive oligomers

Sequencing of telomeres from a dozen or so organisms, including humans, has shown that most are ________ with a high G content in the strand with its 3 end at the end of the chromosome.

germ line

Similar to other mobile elements, most SINEs have accumulated mutations from the time of their insertion in the ________ of an ancient ancestor of modern humans Mobile DNA Elements Probably Had a Significant Influence on Evolution.

organellar DNA

Like mitochondria, chloroplasts contain multiple copies of the ________ and ribosomes.

nucleic acid

In molecular terms, a gene commonly is defined as the entire ________ sequence that is necessary for the synthesis of a functional gene product (polypeptide or RNA)

full complement

The importance of repeated rRNA genes is illustrated by Drosophila mutants called bobbed (because they have stubby wings), which lack a(n) ________ of the tandemly repeated pre- rRNA genes Most Simple- Sequence DNAs Are Concentrated in Specific Chromosomal Locations.

Early microscopic observations

________ on the number and size of chromosomes and their staining patterns led to the discovery of many important general characteristics of chromosome structure.

SARs

Generally, ________ are found between transcription units.

DNA polymerases

Most proteins localized in mitochondria, such as the mitochondrial RNA and ________, are synthesized on cytosolic ribosomes and are imported into the organelle by processes The Size and Coding Capacity of mtDNA Vary Considerably in Different Organisms.

Genes

________ are located primarily within chromatin loops, which are attached at their bases to a chromosome scaffold.

Translation initiation

________ can begin at any of these multiple internal sites, producing multiple proteins.

Invertebrates

________ and ________, the genes encoding rRNAs and some other noncoding RNAs such as some of the snRNAs involved in RNA splicing occur as tandemly repeated arrays.

enzyme

The ________ is a protein and RNA complex called telomere terminal transferase, or telomerase.

YACs

To construct ________, TEL sequences from yeast cells or from the protozoan Tetrahymena are combined with yeast CEN and ARS sequences.

multicellular organisms

In ________, roughly 25- 50 percent of the protein- coding genes are represented only once in the haploid genome and thus are termed solitary genes.

ORF1

________ and ORF2 proteins are from a LINE RNA.

Genetic studies

________ in yeast indicate that specific histone acetylases are required for the full activation of transcription of a number of genes Nonhistone Proteins Provide a Structural Scaffold for Long Chromatin Loops.

DNA transposition

________ by the cut- and- paste mechanism can result in an increase in the copy number of a transposon when it occurs during S phase.

H2A

The amino acid sequences of four histones (________, H2B, H3, and H4) are remarkably similar among distantly related species.

yeast genome

The ________ contains many ≈100- bp sequences, called autonomously replicating sequences (ARSs), that act as replication origins.

salt concentration

When chromatin is extracted from nuclei and examined in the electron microscope, its appearance depends on the ________ to which it is exposed.

telomerase

While ________ prevents telomere shortening in most eukaryotes, some organisms use alternative strategies Yeast Artificial Chromosomes Can Be Used to Clone Megabase DNA Fragments.

telomere repeat

The ________ sequence in humans and other vertebrates is TTAGGG.

Eukaryotic chromosomes

________ are apparent when we consider that all known DNA polymerases elongate DNA chains at the 3 end, and all require an RNA or DNA primer.

DNA sequences

Most genes are transcribed into mRNAs, which encode proteins, clearly, some ________ are transcribed into RNAs that do not encode proteins (e.g., tRNAs and rRNAs)

second group of protein-coding

Duplicated genes constitute the ________ genes.

mtDNA

The ________ is located in the interior of the mitochondrion, the region known as the matrix.

Eukaryotic DNA Transposon

________: McClintocks original discovery of mobile elements came from the observation of certain spontaneous mutations in maize that affect the production of any of the several enzymes required to make anthocyanin, a purple pigment in maize kernels.

Replication of DNA

________ begins from sites that are scattered throughout eukaryotic chromosomes.

DNA

In cells, newly replicated ________ is assembled into nucleosomes shortly after the replication fork passes.

LTR retrotransposons

Since LINEs do not contain LTRs, their mechanism of transposition through an RNA intermediate differs from that of ________.

Interphase chromatin

________ and metaphase chromosomes also contain small amounts of a complex set of other proteins.

LINE sequences

________ are present at ≈900, 000 sites in the human genome, accounting for a staggering 21 percent of total human DNA.

flexible amino

Each of the histone proteins making up the nucleosome core contains a(n) ________ terminus of 11- 37 residues extending from the fixed structure of the nucleosome; these termini are called histone tails.

cluster of genes

The ________ that form a bacterial operon comprises a single transcription unit, which is transcribed from a particular promoter into a single primary transcript.

Individual interphase chromosomes

________, which are less condensed than metaphase chromosomes, can not be resolved by standard microscopy or electron microscopy Chromatin Contains Small Amounts of Other Proteins in Addition to Histones and Scaffold Proteins.

RNA polymerase III

SINEs are transcribed by ________, the same nuclear RNA polymerase that transcribes genes encoding tRNAs.

Structure of Condensed Chromatin

________: When extracted from cells in isotonic buffers, most chromatin appears as fibers ≈30 nm in diameter.

DNA transposons

Integrase, another enzyme encoded by retroviruses that is closely related to the transposase of some ________, uses a similar mechanism to insert the double- stranded retroviral DNA into the host cell genome Retrotransposons That Lack LTRs Move by a Distinct Mechanism.

Human DNA

LINEs: ________ contains three major families of LINE sequences that are similar in their mechanism of transposition, but differ in their sequences: L1, L2, and L3.

H1

In certain tissues, ________ is replaced by special histones Chromatin Exists in Extended and Condensed Forms.