QUESTION 1: DNA is a double-stranded molecule, meaning that each DNA molecule contains two strands of DNA running in opposite directions. Why do you think it is advantageous for the cell to maintain DNA as a double stranded molecule rather than a single-stranded molecule like RNA?

From Adrienne: Q1 = I'm not sure, but perhaps it is advantageous to maintain DNA as a double stranded molecule because it holds extremely important information about genetic make-up, and having two strands by which copies can be made ensures that the copying process will function correctly...kind of like a back-up system for in case something goes wrong.

From SweetPea: Q1 = The double strand is important because as the cells divide, the double strand can separate with each new cell getting identical DNA. Just before the cells divide, the DNA in each cell replicates a second strand. This process goes on for all cells.

From Missy: Q1 = DNA is much more stable and able to repair its self since it is a double strand molecule. Also DNA is used for information storage becuase of it double strand structure. Where as RNA is less stable and unable to repair its self, but has many more functions.

From Dr. Marrs: Good answers! Scientists hypothesize that DNA is double stranded as a 'safeguard' against damage - if something happens to one strand (damage, mutation), the complementary strand could provide the information to restore the sequence of the DNA.

QUESTION 2: In your own words, what is a gene? Do you think there is a gene for everything about 'you' - not only your hair color and eye color, but also for aspects of your personality or behavior? What is a genome? (No, it is not a small ceramic statue in your garden, that would be a a gnome!!! ; )

From mal-function: Q2 = A gene is an active piece of DNA that produces 1 protein. A Genome is complete instructions for making Malinda.

From Jbuck: Q2 = A gene is a piece of DNA that gives us our characteristics, body make-up, hair color, eyes, and are passed through parents. I think that there are genes that make-up some of your behavior or personality. Traits such as patient or impatient, outgoing or shy. There are things you learn throughout life that you use to alter these traits but I think they are orginally inherited. A genome is the contains the complete DNA make up of an organism.

From Steve: Q2 = A gene is an area within a strand of DNA, that gives the commands on how to make 2 or 3 very similiar proteins. There is a gene that controls or influences every aspect of the body. A genome is a set genes, that all correspond to give the body all of the commands for a specified task.

From Dr. Marrs: A gene is a small piece of DNA (~500 bases) that provides the information for the synthesis of 1 protein (or a small set of related proteins). Genes code for our physical traits like eye color, hair color, skin color, and many diseases like sickle cell disease or cystic fibrosis. Some traits, like susceptibility to alcohol addiction, breast cancer, and Alzheimers are genetically determined. Some - but certainly not all - of our behavior is controlled by genes, but an individual's environment, and subtle features of their development, determine their personality and behavior just as much - or even more- than genes. A genome is all of the DNA an individual has in each of its cells. It contains all the instructions to make a new individual or a new cell. We have 1 genome's worth of DNA in every cell in our body! Click here for a listing of some Disease Genes discovered through work on the Human Genome Project.

QUESTION 3: Three different RNAs are involved in turning the information contained in DNA into a 3-dimensional, functional protein. What is mRNA and what does it do? What is rRNA and what does it do? What is tRNA, and what does it do? Please study the figure on translation in your notes carefully!

From mal-function: Q3 = mRNA- carries protein building instructions
rRNA- help build polypeptide chains, the major component of ribosomes
tRNA- the delivery boy for the mRNA it delivers amino acids one by one to a ribosome

From hc: Q3 = Well, this is really tricky, and I read it several times...so here is what I came up with. I think I understand that the RNA is like a copy of the DNA that is sent out for translation. The mRNA is the messenger RNA. As the mRNA enters the cytoplasm it meets with a ribosome that is made of rRNA. Now I'm lost. I think this must meet with or translate into the tRNA, in which the tRNA and mRNA pair up with ribosomes and begin the base pairing (A=T and C=G).I do know that somehow the T in the pairing can become U when it comes the RNA base pairing. I think I may have a little bit of an idea of this, but hopefully it will become more clear in class on Wednesday.

From Ellen: Q3 = mRNA is the RNA that holds the instructions for making proteins. tRNA takes amino acids to a ribosome (rRNA) in the order indicated on the mRNA.

From PS: Q3 = mRNA, messenger RNA, is a single strand of ribonucleotides transcribed from DNA, then translated into a polypeptide chain. mRNA has instructions to make one protein. rRNA is a type of RNA that joins with proteins to form ribosomes. tRNA is another type of RNA that carries amino acids one at a time to a ribosome in an order indicated by mRNA.

Excellent answers! Here is a good figure to hopefully help you out with this complicated process! [Image]

QUESTION 4: (Optional) Rosalind Franklin collected X-ray data crucial to the discovery of DNA's structure. However, she is hardly mentioned in some accounts of the discovery of DNA. Your textbook presents a short essay about the discovery of the structure of DNA (p. 196); read it and speculate why she might be less well known than Watson and Crick. Why was she not awarded a Nobel Prize in 1962 with Watson and Crick?

From Jay Q4 = Because of her lipstick? I have no clue ... : )

From Jess: Q4 = I think that she may be less known than Watson and Crick because number one she was a woman and also because she never said exclusively that DNA was a double helix even though she did take the pictures that would have proved it if she would have had Watson's knowledge. Also, by the time the Nobel Prize was going to be presented to the men, she was already dead.

From Bryn: Q4 = There was a miscommunication where Franklin was working, and Maurice Wilkins took her data and showed it to Watson, who then became famous, along with Crick. He only acknowledged her findings 10 years after her death. So it was too late to do anything about it.

Note from Dr. Marrs. On April 16, 1958, Rosalind Franklin died at age 37 in London of ovarian cancer. The Nobel Prize cannot be given post-humously. Also, the Nobel Prize can only be given to three scientists at a time...had Rosalind Franklin been alive in 1962, would she, rather than Maurice Wilkins, have been given the Nobel Prize and joined the ranks of the 11 Women Nobel Laureates in Science and Medicine? Read more about the race for the double helix in The Double Helix, by James Watson, (contains lots of nasty remarks about Rosalind Franklin and her lipstick) OR, for a more balanced view, Rosalind Fraklin and DNA, by Anne Sayre.

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