Biology True/False Questions

A good, biological definition for a gene is "it is something that makes you who you are."

False A gene is a segment of DNA that encodes a RNA or protein product. The instructions for the synthesis of a RNA or protein

A poly-A tail is part of early developmental genes.

False. A poly-A tail is found on mRNAs exported from the nucleus. The tail acts to slow the degradation of the message by the nucleases that attack from the 3' end of the message. The longer the poly-A tail the longer the message will persist before the coding region is degraded.

DNA contains a hexose sugar.

False. DNA contains a ribose sugar (5 carbon) with one hydroxyl group missing (deoxyribose).

Low melt DNA (the two strands of the double helix come apart at a low temp)would have a high CG content.

False. G and C form three hydrogen bonds while an A-T pair is held together by only two hydrogen bonds. DNA that is rich in G-C pairs is more difficult to "melt" or break apart by disruption of the hydrogen bonds with heat. A-T rich sequences are considered "low melt".

Eukaryotic genomes consist mainly of coding DNA

False. Less than 2% of the human genome, for example, encodes protein

"Antiparallel" means that DNA has a helical twist.

False. See #8. The two strands of the double helix run parallel to one another but one runs 5'to 3' while its complement runs 3' to 5'.

Moving downstream from a promoter, the strand of DNA that will serve as a template for transcription runs in the 5' to 3' direction

False. The RNA polymerase is only able to add to a free 3' end of the growing RNA chain. The growing chain must be antiparallel to the template strand of DNA so that free nucleotides may hydrogen bond with the template to be held in position as they are joined to their neighbors. Therefore the template must run 3' to 5' so the growing strand of newly synthesized nucleic acid can run 5' to 3'

The first AUG in a mRNA signifies the amino acid threonine and ends translation

False. The first AUG codon in a mRNA is the start codon and signifies the amino acid methionine.

DNA carries an overall negative charge due to its sulfur groups.

False. The negative charge on DNA is imparted by its phosphate groups. There is no sulfur in DNA but there is sulfur in protein. No phosphate present in proteins

If the promoter of a gene is deleted from the genome one would expect no change in the expression of that gene.

False. The promoter is the control region for expression. Its binding to transcription factors and its methylation state determines whether or not the gene will be transcribed. One would predict that there would be no gene expression if the promoter is deleted.

The job of the aminoacyl tRNA synthase is accomplished in the nucleus.

False. This enzyme is in the cytosol and loads up tRNAs with the correct amino acids.

Ubiquitination allows a protein to persist without being degraded.

False. Ubiquitination is the kiss of death for a protein. It targets the protein for destruction by a protoesome.

Watson and Crick published a 10 page article on the structure of DNA in Nature in 1953

Right date and journal, but the article was only one page long and was very well written. Read the copy you were given.

A chromosome holds many genes, but not all the DNA in chromosomes is part of a gene.

True Chromosomes are lengths of DNA double helix that may contain hundreds or thousands of genes as well as lots of DNA that is noncoding and is sometimes called "junk" DNA

Condensed chromatin on a region of a chromosome means genes in that region are not being expressed

True Condensed chromatin means that the DNA is tightly coiled around the histones and histones are clustered together. This packing makes the DNA inaccessible to enzymes and proteins that need to interact with it in order to carry out the first step in gene expression - transcription

Chromatin is DNA plus its associated proteins

True The histone proteins help to organize the DNA into nucleosomes. The complex of DNA and organizational proteins is called chromatin.

si RNAs act to attenuate gene expression by triggering the destruction of mRNAs.

True. A recently discovered and amazing level of control over gene expression is waged by tiny, single stranded RNAs that trigger the Argonaut and dicer system of mRNA destruction.

Skin and muscle cell nuclei contain the same DNA.

True. All nucleated body cells in an organism contain the same genome but may express very different arrays of genes

Hydrogen bonding is important at two structural levels of DNA.

True. Both to hold together the Watson-Crick base pairs and then to form the secondary structure of the helix.

According to Chargaff's rule, if the A content in a DNA sample is 16% then the G content would be 34%.

True. Chargaff's data demonstrating that in organisms the A content always seemed to equal the T content and the G content equaled the C content was explained by Watson and Crick when they proposed that A bonds with T and G with C to form the base pairs that hold the two strands of the double helix together. If you know the % content of one of the nucleotides you can calculate the content of all the others.

There is more than one codon per amino acid

True. Check the dictionary of the genetic code. The code is redundant such that there are multiple codons per amino acid, usually having the same first two nucleotides and differing in the third nucleotide of the codon.

The product of gene expression can be a RNA or a protein.

True. Hemoglobin is the product of expression of the hemoglobin gene. Ribosomal RNA is the product of expression of a rRNA gene

If there is a phosphate sticking out at the end of one strand of DNA then it can be assumed that there is a hydroxyl sticking out at the same end of the complementary DNA strand.

True. Nucleotides that hydrogen bond stably are upside down from one another. Two nucleotides in the same orientation (for example, both with the phosphate group to the left) don't hydrogen bond

At the P site of the ribosome the formation of a N to C covalent bond is catalyzed.

True. P stands for "peptidyl" and this is the site where formation of a peptide bond is catalyzed between the amino acids in the P site and the A site of the ribosome.

Covalent bonds between sugar and phosphate connect the individual nucleotides in a single strand of DNA

True. Repeated sugar-phosphate linkages join neighboring nucleotides in a single strand of DNA.

The nitrogenous base T is a single ringed structure, smaller than the double ringed G.

True. T and C are single ringed pyrimidines. A and G are double ringed purines. In Watson-Crick base pairing a pyrimidine pairs with a purine, giving the double helix a uniform width

Enhancers are distal control elements for gene expression.

True. The enhancer region may be 1000s of nucleotides upstream from the promoter.

mRNA found in the nucleus will be longer than mRNA transcribed from the same gene but found in the cytosol

True. The mature mRNA in the cytosol has been edited - its introns have been cut out and exons spliced together.

A protein destined for the extracellular matrix will be translated on a ribosome docked at the rough ER

True. The signal peptide at the leading end of the new protein will target the ribosome to the rough ER where it will dock and continue to translate, extruding the protein into the ER. The protein will be processed through the ER, shipped to the golgi, further processes and sorted, and shipped to the ECM in a golgi vesicle

mRNA is the only type of RNA that is translated

True. tRNA, rRNA, snRNA, siRNA, etc. all function as RNA without ever being translated to protein