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 s through s, discovering transposons jumping genes , but she was not recognized until much later, receiving a Nobel Prize in Physiology or Medicine in Figure 9.
Today, women still remain underrepresented in many fields of science and medicine. 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. 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 public comments suggesting that women are too emotional for science [9] were met with widespread condemnation.
Perhaps girls should be supported more from a young age in the areas of science and math Figure 9. 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.
Figure 9. Possibilities include bacterial infection e. His physician orders a stool sample to identify possible causative agents e. The physician instructed Aamir 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. 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. The work of Rosalind Franklin and R. Gosling was important in demonstrating the helical nature of DNA. Skip to main content. Biochemistry of the Genome.
Search for:. Structure and Function of DNA Learning Objectives Describe the biochemical structure of deoxyribonucleotides Identify the base pairs used in the synthesis of deoxyribonucleotides Explain why the double helix of DNA is described as antiparallel.
Think about It Which scientists are given most of the credit for describing the molecular structure of DNA? 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.
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.
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. Deoxyribonucleic Acid. Ribonucleic Acid. DNA replicates and stores genetic information. It is a blueprint for all genetic information contained within an organism. RNA converts the genetic information contained within DNA to a format used to build proteins, and then moves it to ribosomal protein factories.
DNA consists of two strands, arranged in a double helix. These strands are made up of subunits called nucleotides. Each nucleotide contains a phosphate, a 5-carbon sugar molecule and a nitrogenous base. RNA sometimes forms a secondary double helix structure, but only intermittently.
A chromosome, for example, is a single, long DNA molecule, which would be several centimetres in length when unravelled. A large RNA molecule might only be a few thousand base pairs long. RNA contains ribose sugar molecules, without the hydroxyl modifications of deoxyribose.
Base Pairs. RNA forms in the nucleolus, and then moves to specialised regions of the cytoplasm depending on the type of RNA formed. In molecular biology shorthand, the nitrogenous bases are simply known by their symbols A, T, G, C, and U.
The difference between the sugars is the presence of the hydroxyl group on the second carbon of the ribose and hydrogen on the second carbon of the deoxyribose. The phosphodiester linkage is not formed by simple dehydration reaction like the other linkages connecting monomers in macromolecules: its formation involves the removal of two phosphate groups.
A polynucleotide may have thousands of such phosphodiester linkages. The DNA double helix looks like a twisted staircase, with the sugar and phosphate backbone surrounding complementary nitrogen bases. DNA has a double-helix structure, with sugar and phosphate on the outside of the helix, forming the sugar-phosphate backbone of the DNA. The nitrogenous bases are stacked in the interior in pairs, like the steps of a staircase; the pairs are bound to each other by hydrogen bonds.
The two strands of the helix run in opposite directions. This antiparallel orientation is important to DNA replication and in many nucleic acid interactions. The phosphate backbone indicated by the curvy lines is on the outside, and the bases are on the inside. Each base from one strand interacts via hydrogen bonding with a base from the opposing strand. Only certain types of base pairing are allowed.
This means Adenine pairs with Thymine, and Guanine pairs with Cytosine. This is known as the base complementary rule because the DNA strands are complementary to each other. Antiparallel Strands : In a double stranded DNA molecule, the two strands run antiparallel to one another so one is upside down compared to the other.
The phosphate backbone is located on the outside, and the bases are in the middle. Adenine forms hydrogen bonds or base pairs with thymine, and guanine base pairs with cytosine. At this time it is possible a mutation may occur. A mutation is a change in the sequence of the nitrogen bases. Most of the time when this happens the DNA is able to fix itself and return the original base to the sequence. However, sometimes the repair is unsuccessful, resulting in different proteins being created.
DNA packaging is an important process in living cells. Without it, a cell is not able to accommodate the large amount of DNA that is stored inside. A eukaryote contains a well-defined nucleus, whereas in prokaryotes the chromosome lies in the cytoplasm in an area called the nucleoid.
In prokaryotic cells, both processes occur together. What advantages might there be to separating the processes? What advantages might there be to having them occur together? Eukaryotic and prokaryotic cells : A eukaryote contains a well-defined nucleus, whereas in prokaryotes, the chromosome lies in the cytoplasm in an area called the nucleoid. The size of the genome in one of the most well-studied prokaryotes, E. So how does this fit inside a small bacterial cell?
The DNA is twisted by what is known as supercoiling. Supercoiling means that DNA is either under-wound less than one turn of the helix per 10 base pairs or over-wound more than 1 turn per 10 base pairs from its normal relaxed state.
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