Ch. 7 - Microbial Genetics

Bauman - Microbiology with Diseases by Taxonomy 6th Edition

Bauman6th EditionMicrobiology with Diseases by TaxonomyISBN: 9780134832302Not the one you use?Change textbook

Bauman 6th Edition

Ch. 7 - Microbial Genetics

Problem 2

Chapter 7, Problem 2

This bacteriophage DNA molecule has been warmed. Label the portions that likely have a higher ratio of GC base pairs and the portions that have a higher ratio of AT base pairs.

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Understand that DNA regions rich in GC base pairs have three hydrogen bonds, making them more thermally stable and less likely to denature (separate) when warmed, compared to AT-rich regions which have only two hydrogen bonds.

Examine the image for areas where the DNA appears double-stranded (thicker, more condensed regions) versus single-stranded (thinner, more extended or looped regions). The double-stranded regions likely correspond to GC-rich areas because they resist denaturation.

Identify the thinner, more extended or looped portions of the DNA molecule as regions that have likely denatured due to warming, indicating a higher ratio of AT base pairs.

Label the thicker, more intact double-stranded portions as GC-rich regions, since these areas remain stable and do not separate easily upon warming.

Summarize by marking the DNA molecule with labels indicating 'GC-rich' on the stable, double-stranded segments and 'AT-rich' on the denatured, single-stranded loops or thinner segments.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Base Pairing in DNA

DNA consists of two strands held together by base pairs: adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). The A-T pairs form two hydrogen bonds, while G-C pairs form three, making G-C pairs more thermally stable.

Thermal Stability and Melting Temperature of DNA

Regions of DNA with higher G-C content have higher melting temperatures because the triple hydrogen bonds require more heat to break. Conversely, A-T rich regions melt at lower temperatures due to fewer hydrogen bonds, which affects DNA denaturation patterns.

Transmission Electron Microscopy (TEM) Imaging of DNA

TEM allows visualization of DNA molecules at the nanoscale, showing structural features like loops and bends. In this image, the DNA appears as a single strand, and understanding the scale (20 nm) helps relate physical structure to molecular composition.

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Transmission Electron Microscope (TEM)

Related Practice

Textbook Question

Which of the following is a true statement concerning prokaryotic chromosomes?

a. They typically have two or three origins of replication

b. They contain single-stranded DNA

c. They are located in the cytosol

d. They are associated in linear pairs

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Textbook Question

On the accompanying figure, label:

DNA polymerase I, DNA polymerase III, helicase, lagging strand, leading strand, ligase, nucleotide (triphosphate), Okazaki fragment, primase, replication fork, RNA primer, and stabilizing proteins.

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Textbook Question

A triplet of mRNA nucleotides that specifies a particular amino acid is called a ____________ .

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Textbook Question

List several ways in which eukaryotic messenger RNA differs from prokaryotic mRNA.

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Textbook Question

The three steps in RNA transcription are __________ , ___________ , and __________ .

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Textbook Question

How does the genotype of a bacterium determine its phenotype? Use the terms gene, mRNA, ribosome, and polypeptide in your answer.

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