Unit 3 & 7- Genetics & Nucleic Acids Flashcards
What are nucleic acids? What is their role in living organisms? What are they composed of?
Nucleic acids are the primary information-carrying molecules of the cell. They carry genetic information and direct protein synthesis using this information. Nucleic acids are composed of recurring molecules called nucleotides.
What are nucleotides? What are the principal components of nucleotides?
Nucleotides are the monomers of nucleic acids. They are composed of a nitrogenous base (making up the rungs of the DNA ladder), a phosphate group and a pentose sugar. Both the phosphate group and the nitrogenous base are attached to the central pentose sugar. The nitrogenous base is attached to the 1’ carbon atom. The phosphate base is attached to the 5’ carbon atom (fifth carbon atom does not appear in drawings).
What is a pentose sugar? How does this differ from DNA (deoxyribonucleic acid) to RNA (ribonucleic acid)?
A pentose sugar is a monosaccharide with 5 carbon atoms. The pentose sugars found in DNA and RNA are deoxyribose and ribose, respectively. The difference between these two molecules is the removal of the oxygen (from OH) on the carbon atom in the 2 prime position from ribose.
Why are nitrogenous bases considered bases?
Nitrogenous bases are considered bases because they contain an amino group (NH2) which is capable of binding to a third hydrogen ion, hence functioning as bases in chemical reactions. Nitrogenous bases also always include Nitrogen.
What are the two groups of nitrogenous bases? What are the nitrogenous bases in each group?
The two groups of nitrogenous bases are pyrimidines and purines. The main difference between purines and pyrimidines is that purines contain a six membered ring of carbon atoms and nitrogen fused to an imidazole five membered ring whereas pyrimidines contain only a single six membered ring of carbons and nitrogen. Consequently, pyrimidines are smaller in size than purines. Therefore, a purine must always be paired with a pyrimidine so that each rung of the DNA ladder is the same width.
The purines in DNA include Adenine and Guanine and the pyrimidines in DNA include Thymine and Cytosine. In RNA, the thymine is replaced by Uracil.
How are nucleic acids formed? What type of bond joins nucleotides?
Nucleic acids are formed when the phosphate of one nucleotide is linked to the sugar of the next nucleotide by phosphodiester linkages (condensation reaction producing water). The phosphate group (located on the fifth carbon) always attaches to the third carbon atom of the next nucleotide.
What joins nitrogenous bases together? What type of bond holds these bases together?
Nitrogenous bases are joined together by hydrogen bonds. Adenine and thymine form two hydrogen bonds, while cytosine and guanine form three hydrogen bonds. This creates a difference in strength between the two bonds (the bond between cytosine and guanine being the strongest).
What are the primary differences between DNA and RNA?
1) DNA contains the sugar deoxyribose while RNA contains the sugar ribose. The oxygen atom is removed from the OH in the 2 prime position of ribose to get deoxyribose.
2) DNA is a double-stranded molecule, while RNA is a single-stranded molecule.
3) RNA contains Uracil in the place of Thymine.
Describe the structure of DNA? What three components make up the DNA molecule?
The DNA molecule consists of two strands that wind around one another to form a double helix that is similar to a twisted ladder. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four nitrogenous bases (A, T, C, G). The nitrogenous bases make up the rungs of the ladder and they are all made up of two bases (Adenine with Thymine and Cytosine with Guanine). The strands are always anti-parallel.
What joins nitrogenous bases together? How many bonds are formed between Adenine and Thymine. How many bonds are formed between Cytosine and Guanine?
Nitrogenous bases are joined together by hydrogen bonds. Adenine and thymine form two hydrogen bonds, while cytosine and guanine form three hydrogen bonds. This creates a difference in strength between the two bonds (the bond between cytosine and guanine being the strongest).
Which is the significance of the three prime carbon and the five prime carbon of the sugar in nucleotides?
The three prime
