Bio Lecture 15
You isolated an RNA molecule from a cell and determined that 35% of the nucleotides are A's. Can you figure out the percentages of U's? G's? C's? If so, what are the percentages? If not, why not? (Hint: remember that RNA is a single stranded molecule)
No because RNA is single stranded Mastering Bio Input: Because an RNA molecule is just one strand (single-stranded), the number of Cs and Gs (or As and Us) are not necessarily equal. A single strand of RNA can fold into different shapes due to the hydrogen bonds that form between complementary nucleotides (G with C and A with T). However, because there isn't a second, complementary strand in RNA (like there is in DNA), it isn't guaranteed that for every C there is a G or that for every A there is a U.
Explain what it means that nucleic acid strands have a specific direction.
Nucleic acid strands have a phosphate end (5') and a hydroxyl end (3'). The order of nitrogenous bases matter which give the strand directionality. Strands are written/ read from phosphate to hydroxy group and this is the direction in which they are formed in cells essentially: Nucleic acid strands begin at the phosphate group on one end and end at the hydroxyl group at the other end. A new strand is created from its phosphate end to its hydroxyl end.
Describe the structure of an RNA molecule
one strand (single stranded) and looped back upon itself (ribbon); has uracil instead of thymine as a base; nucleotides have ribose not deoxyribose as its attached monosaccharide
What correctly describes the chemical bonds in a DNA molecule?
Covalent bonds connect nucleotides within a strand; hydrogen bonds hold the two strands of a DNA molecule together
Describe the structure of a DNA molecule. What type of bond connects nucleotides within a strand? What type of bond forms between the two strands of a DNA molecule to hold it together? what is a base? base pair?
DNA molecule has an antiparallel double helix structure (the two strands go in the opposite directions); hydrogen bonds hold two strands of DNA together; A base is a nucleotide in a strand while a base pair is the nucleotides that interact via hydrogen bonds and hold two strands together.
A DNA helix that is mainly A-T base pairs is easier to separate than a helix with the same number of base pairs, but mostly G-C pairs. Based on what you know about the structure of DNA, why is this true? Why would it be problematic if G and T or C and A were paired together?
G and C form three hydrogen bonds and A and T form two hydrogen bonds. G and C form three hydrogen bonds and A and T form two hydrogen bonds giving a uniform size which determine shape; This pairing allows for maximization of hydrogen bonding and more hydrogen bonds means stronger interaction between strands. Note: if G-T and A-C were bonded, for example, there would be fewer interactions and bases would not line up correctly to form a uniform helix
What nitrogenous bases are present in DNA? RNA?
DNA: Cytosine, Guanine, Adenine, Thymine RNA: Cytosine, Guanine, Uracil, Adenine
List the three components (parts) of nucleotides. What components differ between nucleotides? What makes DNA and RNA nucleotides different?
Nucleotides are comprised of a phosphate group, a 5 carbon monosaccharide that can have 1,2, or 3 phosphates, and a nitrogenous base that makes each nucleotide unique. DNA and RNA have a different monosaccharide (simple sugar); DNA is made of deoxyribose, there is one hydroxyl group and one hydrogen attached to the monosaccharide; RNA is made of ribose, there is two hydroxyl groups deoxy = missing oxygen compared to ribose
Are the bonds that connect DNA nucleotides in a strand the same as the bonds that connect nucleotides in a strand of RNA?
Nucleotides are connected by phosphodiester bonds (covalent) to form nucleic acid strands in both DNA and RNA; there is a phosphodiester covalent bond that connect DNA nucleotides in a strand and a phosphodiester covalent bond that connects RNA nucleotides in a strand " A covalent bond connects one nucleotide to another, when we see one covalent bond connecting one nucleotide to another we call that a phosphodiester bond; the covalent bond that connects nucleotides together to form a nucleic acid to form the bigger molecule is called a phosphodiester bond"
Describe the differences between the DNA present in prokaryotic vs. eukaryotic cells. List ALL the features of DNA common to BOTH prokaryotic and eukaryotic cells.
Prokaryotic Cell: chromosome is circular prokaryotic; DNA/Chromosome not in nuclei but in cytoplasm; cells have one chromosome; not wrapped around proteins (naked); smaller; generally fewer total base pairs Eukaryotic Cell: chromosomes are linear; chromosomes are found in the nucleus of a cell; have multiple chromosomes; wrapped around proteins; larger; generally more total base pairs Both: Helical structure; A,T,C, & G; has direction; phosphodiester bonds DNA molecules in prokaryotic cells are circular while DNA molecules in eukaryotic cells are linear; DNA is found in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells; Prokaryotic cells have one chromosome and eukaryotic cells have multiple chromosomes; DNA is wrapped around proteins in eukaryotic cells but DNA is not wrapped around proteins in prokaryotic cells Mastering Bio Input: Prokaryotic cells lack organelles; this includes nuclei. All cellular DNA exists as a double-stranded helix. Prokaryotic cells have one circular chromosome. Eukaryotic cells have multiple linear chromosomes.
Compare the structures of DNA and RNA. List all the similarities and differences you can remember
Similarities: They share guanine, adenine, and cytosine; their nucleotides are connected by phosphodiester bonds; Nucleotides that are complementary can interact via hydrogen bonds between the nitrogenous bases. This is true for the nucleotides found in both DNA and RNA; present in both prokaryotic and eukaryotic cells; the two ends of a strand are different (strands have a direction) OR::::::Strands have direction; nucleotides in a strand are connected by phosphodiester bonds; have complimentary nucleotides Differences: DNA has thymine; RNA has Uracil; DNA has deoxyribose monosaccharide; RNA has ribose monosaccharide; RNA is single stranded; DNA is more stable; RNA is less stable; DNA is permanent information storage and must be passed to next generation; RNA is temporary message and is only needed when expressing a particular gene...don't need it to exist forever Mastering Bio Input: Both DNA and RNA nucleotides are connected by phosphodiester bonds to form nucleic acid strands. Only DNA molecules consist of two strands; RNA molecules are single-stranded. DNA and RNA function as information carrying molecules in all types of cells, prokaryotic and eukaryotic. The two ends of both DNA strands and RNA strands are different - one end has a phosphate group, the other a hydroxyl group (-OH). Because the two ends of a strand are different, the strands have a direction meaning that a molecule with the sequence ACGCC is different than a molecule with the sequence CCGCA.
You isolated a DNA molecule from a cell and determined that 35% of the nucleotides are A's. Based on that, can you figure out the percentages of T's? G's? C's? If so, what are the percentages? If not, why not?
T-35 G-15 C-15 Mastering Bio Input: In cells, DNA exists as a double helix. The two strands of a double helix are complementary, which means that A interacts with T, and C interacts with G on opposite strands (and the strands are antiparallel). Therefore, the percentage of A in a helix is equal to the percentage of T. The remaining percentage consists of C's and G's, and is equally split between the two nucleotides because they pair up. True for both prokaryotic and eukaryotic cells
The melting temperature of a DNA molecule is the temperature at which the two strands of the helix become separated from each other. If the two strands of a DNA molecule are held together more tightly, the melting temperature is higher because it takes more energy (heat) to separate them. If the two strands are held together less tightly, the melting temperature is lower. Based on what you know about the structure of DNA molecules, it is reasonable to predict that if you compare two DNA molecules with the same total number of base pairs, will A-T base pairs have higher or lower melting point? why?
a DNA helix that has mostly A-T base pairs will have a lower melting temperature than one with mostly G-C base pairs. There are fewer hydrogen bonds between the two strands Mastering Bio Input: The two strands of a DNA double helix are held together by hydrogen bonds between complementary nucleotides. Three hydrogen bonds form between G and C nucleotides, but only two hydrogen bonds form between A and T nucleotides. Therefore, when comparing DNA molecules that have the same number of base pairs, a helix with more A-T base pairs is held together by fewer hydrogen bonds compared to a helix with more G-C base pairs. If two strands are held together by fewer interactions, they can be separated more easily, which corresponds to a lower melting temperature.
