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Native states are like a twisted ladder. The rungs of the ladder are made from a base of one strand attached to the base of the other strand. Heat and chemicals can denature these strands. When this happens, the DNA is single stranded – it is a long ribbon with short projections along its length. Renaturation, which requires special conditions, returns the DNA to the double helix state (renatured state).
In the laboratory, the double helix can be denatured to single-stranded DNA through exposure to heat or chemicals, and then renatured through cooling or removal of chemical denaturants to allow the DNA strands to reanneal. (credit: modification of work by Hernández-Lemus E, Nicasio-Collazo LA, Castañeda-Priego R)
  • What are the two complementary base pairs of DNA and how are they bonded together?

Dna function

DNA stores the information needed to build and control the cell. The transmission of this information from mother to daughter cells is called vertical gene transfer and it occurs through the process of DNA replication. DNA is replicated when a cell makes a duplicate copy of its DNA, then the cell divides, resulting in the correct distribution of one DNA copy to each resulting cell. DNA can also be enzymatically degraded and used as a source of nucleosides and nucleotides for the cell. Unlike other macromolecules, DNA does not serve a structural role in cells.

  • How does DNA transmit genetic information to offspring?

Paving the way for women in science and health professions

Historically, women have been underrepresented in the sciences and in medicine, and often their pioneering contributions have gone relatively unnoticed. For example, although Rosalind Franklin performed the X-ray diffraction studies demonstrating the double helical structure of DNA, it is Watson and Crick who became famous for this discovery, building on her data. There still remains great controversy over whether their acquisition of her data was appropriate and whether personality conflicts and gender bias contributed to the delayed recognition of her significant contributions. Similarly, Barbara McClintock did pioneering work in maize (corn) genetics from the 1930s through 1950s, discovering transposons (jumping genes), but she was not recognized until much later, receiving a Nobel Prize in Physiology or Medicine in 1983 ( [link] ).

Today, women still remain underrepresented in many fields of science and medicine. While more than half of the undergraduate degrees in science are awarded to women, only 46% of doctoral degrees in science are awarded to women. In academia, the number of women at each level of career advancement continues to decrease, with women holding less than one-third of the positions of Ph.D.-level scientists in tenure-track positions, and less than one-quarter of the full professorships at 4-year colleges and universities. N.H. Wolfinger “For Female Scientists, There's No Good Time to Have Children.” The Atlantic July 29, 2013. http://www.theatlantic.com/sexes/archive/2013/07/for-female-scientists-theres-no-good-time-to-have-children/278165/. Even in the health professions, like nearly all other fields, women are often underrepresented in many medical careers and earn significantly less than their male counterparts, as shown in a 2013 study published by the Journal of the American Medical Association . S.A. Seabury et al. “Trends in the Earnings of Male and Female Health Care Professionals in the United States, 1987 to 2010.” Journal of the American Medical Association Internal Medicine 173 no. 18 (2013):1748–1750.

Why do such disparities continue to exist and how do we break these cycles? The situation is complex and likely results from the combination of various factors, including how society conditions the behaviors of girls from a young age and supports their interests, both professionally and personally. Some have suggested that women do not belong in the laboratory, including Nobel Prize winner Tim Hunt, whose 2015 public comments suggesting that women are too emotional for science E. Chung. “Tim Hunt, Sexism and Science: The Real 'Trouble With Girls' in Labs.” CBC News Technology and Science , June 12, 2015. http://www.cbc.ca/news/technology/tim-hunt-sexism-and-science-the-real-trouble-with-girls-in-labs-1.3110133. Accessed 8/4/2016. were met with widespread condemnation.

Perhaps girls should be supported more from a young age in the areas of science and math ( [link] ). Science, technology, engineering, and mathematics (STEM) programs sponsored by the American Association of University Women (AAUW) American Association of University Women. “Building a STEM Pipeline for Girls and Women.” http://www.aauw.org/what-we-do/stem-education/. Accessed June 10, 2016. and National Aeronautics and Space Administration (NASA) National Aeronautics and Space Administration. “Outreach Programs: Women and Girls Initiative.” http://women.nasa.gov/outreach-programs/. Accessed June 10, 2016. are excellent examples of programs that offer such support. Contributions by women in science should be made known more widely to the public, and marketing targeted to young girls should include more images of historically and professionally successful female scientists and medical professionals, encouraging all bright young minds, including girls and women, to pursue careers in science and medicine.

a) Photograph of Barbara McClintock. B) Photograph of 2 women scientists in lab.
(a) Barbara McClintock’s work on maize genetics in the 1930s through 1950s resulted in the discovery of transposons, but its significance was not recognized at the time. (b) Efforts to appropriately mentor and to provide continued societal support for women in science and medicine may someday help alleviate some of the issues preventing gender equality at all levels in science and medicine. (credit a: modification of work by Smithsonian Institution; credit b: modification of work by Haynie SL, Hinkle AS, Jones NL, Martin CA, Olsiewski PJ, Roberts MF)

Part 2

Based upon his symptoms, Alex’s physician suspects that he is suffering from a foodborne illness that he acquired during his travels. Possibilities include bacterial infection (e.g., enterotoxigenic E. coli , Vibrio cholerae , Campylobacter jejuni , Salmonella ), viral infection (rotavirus or norovirus), or protozoan infection ( Giardia lamblia , Cryptosporidium parvum , or Entamoeba histolytica ).

His physician orders a stool sample to identify possible causative agents (e.g., bacteria, cysts) and to look for the presence of blood because certain types of infectious agents (like C. jejuni , Salmonella , and E. histolytica ) are associated with the production of bloody stools.

Alex’s stool sample showed neither blood nor cysts. Following analysis of his stool sample and based upon his recent travel history, the hospital physician suspected that Alex was suffering from traveler’s diarrhea caused by enterotoxigenic E. coli ( ETEC ), the causative agent of most traveler’s diarrhea. To verify the diagnosis and rule out other possibilities, Alex’s physician ordered a diagnostic lab test of his stool sample to look for DNA sequences encoding specific virulence factors of ETEC. The physician instructed Alex to drink lots of fluids to replace what he was losing and discharged him from the hospital.

ETEC produces several plasmid-encoded virulence factors that make it pathogenic compared with typical E. coli . These include the secreted toxins heat-labile enterotoxin (LT) and heat-stabile enterotoxin (ST) , as well as colonization factor (CF) . Both LT and ST cause the excretion of chloride ions from intestinal cells to the intestinal lumen, causing a consequent loss of water from intestinal cells, resulting in diarrhea. CF encodes a bacterial protein that aids in allowing the bacterium to adhere to the lining of the small intestine.

  • Why did Alex’s physician use genetic analysis instead of either isolation of bacteria from the stool sample or direct Gram stain of the stool sample alone?

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Key concepts and summary

  • Nucleic acids are composed of nucleotides , each of which contains a pentose sugar, a phosphate group, and a nitrogenous base . Deoxyribonucleotides within DNA contain deoxyribose as the pentose sugar.
  • DNA contains the pyrimidines cytosine and thymine , and the purines adenine and guanine .
  • Nucleotides are linked together by phosphodiester bonds between the 5ʹ phosphate group of one nucleotide and the 3ʹ hydroxyl group of another. A nucleic acid strand has a free phosphate group at the 5ʹ end and a free hydroxyl group at the 3ʹ end.
  • Chargaff discovered that the amount of adenine is approximately equal to the amount of thymine in DNA, and that the amount of the guanine is approximately equal to cytosine . These relationships were later determined to be due to complementary base pairing.
  • Watson and Crick, building on the work of Chargaff, Franklin and Gosling, and Wilkins, proposed the double helix model and base pairing for DNA structure.
  • DNA is composed of two complementary strands oriented antiparallel to each other with the phosphodiester backbones on the exterior of the molecule. The nitrogenous bases of each strand face each other and complementary bases hydrogen bond to each other, stabilizing the double helix.
  • Heat or chemicals can break the hydrogen bonds between complementary bases, denaturing DNA. Cooling or removing chemicals can lead to renaturation or reannealing of DNA by allowing hydrogen bonds to reform between complementary bases.
  • DNA stores the instructions needed to build and control the cell. This information is transmitted from parent to offspring through vertical gene transfer .

Fill in the blank

The end of a nucleic acid strand with a free phosphate group is called the ________.

5ʹ end

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True/false

The work of Rosalind Franklin and R.G. Gosling was important in demonstrating the helical nature of DNA.

True

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The A-T base pair has more hydrogen bonding than the C-G base pair.

False

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Short answer

What is the role of phosphodiester bonds within the sugar-phosphate backbone of DNA?

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What is meant by the term “antiparallel?”

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Why is DNA with a high GC content more difficult to denature than that with a low GC content?

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Questions & Answers

what is microbiology
Ayeniyi Reply
microbiology is the study of all living organisms that are too small to be visible to the naked eyes, examples bacteria and fungi etc
Iheme
study of microorganism such as becteria etc
Muhammad
study of microorganisms and their effect on organisms life
Aqsa
characteristic of Gram negative bacteria
jane Reply
Characteristics of Gram Negative Bacteria As with Gram positive bacteria, Gram negative bacteria also contain the peptidoglycan polymer in their cell wall. While this polymer is thin (2 to 4 nanometers in thickness with just about 3 layers of peptidoglycan) in Gram negative bacteria, it's also com
Kaviya
it's also composed of long glycan strands that are cross-linked by peptide molecules. This composition serves a number of functions including protecting the bacterial cell from lysis
Kaviya
Good shot
Enoch
Thanks 😊
Kaviya
what was Hans Christian Gram's supported in the modern Microbiology?
Wilson Reply
what is microbial growth
Chisa Reply
The organism responsible for vulva ulcers
nyiter Reply
Why are vascular pathogen poorly communicable from person to person?
Aj Reply
Most vascular pathogens are poorly communicable from person to person because they need a medium to be communicated i,e a vector that would carry them from one person to other
Kaviya
what's the habit of protista
Afieahngwi Reply
They show both autotrophic and heterotrophic mechanisms...
Swetha
thanks
Afieahngwi
welcome...
Swetha
let me mention some water. Air .Food and so on
Gattiek Reply
causes of infectious diseases
Afieahngwi Reply
water.Air
Gattiek
infectious disease are caused by pathogenic micro organisms like bacteria ,fungi..
Swetha
What is pasteurization?
Wilson
are fungi prokaryote or eukaryotes?
Afieahngwi Reply
fungi are eukaryotes.
Swetha
All fungi are eukaryotes. Even micro fungi.
Lad
have..complex cellular organization and membrane bound nucleus ...and..also... having loops of DNA( like plasmids) as.bacteria
Swetha
what enzyme replaces rna nucleotides with dna nucleotides during replication?
Remi Reply
an enzyme called DNA ligase.
Jael
describe the acid fast staining procedure used in the diagnosis of tuberculosis
Salma Reply
bacterial morphology
lf_ Reply
what is the difference between biogenesis & abiogenesis
Mayuri Reply
biogenesis is when living comes out from other living things as a result of reproduction while a biogenesis is the process where living things comes out from non living things
Usman
living things come form other form living things is biogenesis. ....right?
Mayuri
what is mean by pasturation method?
Mayuri Reply
Pasteurization is a process that kills harmful bacteria and creates an extended shelf life for your milk. ... It's pretty simple—we take the milk from the cows, we rapidly heat it to a high enough temperature to kill the bacteria, and then we cool it back down before packaging and shipping it to you
Kaviya
tell me about abiogenessis &biogenesis
Mayuri

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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