Question

how does dna in the same helix bond to itself?
the sugars bond to each other
the base bonds to the sugar
the phosphate bonds to the base
none of the above

a strand of dna has 18% adenine. what are the percentage of cytosine?
18%
32%
64%
we cant tell

what is the shape of dna?
single helix
double helix
triple helix
none of the above

in dna adenine always bonds with
guanine
adenine
thymine
none of the above

why is dna polymerase the key enzyme for replication?
dna polymerase seals unjoined strands of a dna helix together
dna polymerase adds new dna bases to the dna chain
dna polymerase unzips the strands of dna
none of the above

why are telomeres important to the long term health of a cell?
telomeres are essential dna bases at the end of the strand that may be lost
telomeres are junk dna bases in the middle of the strand that may be lost
telomeres are essential dna bases in the inside of the strand that may be lost

Explanation:

First Question: How does DNA in the same helix bond to itself?

In DNA, the nitrogenous bases (adenine, thymine, cytosine, guanine) form hydrogen bonds with their complementary bases (A-T, C-G) across the two strands. The sugar - phosphate backbone is linked by phosphodiester bonds (sugar of one nucleotide bonds to phosphate of next). The options: "The sugars bond to each other" is incorrect (sugars bond to phosphates). "The base bonds to the sugar" is part of nucleotide structure (base - sugar - phosphate), not intra - helix bonding of the same helix. "The phosphate bonds to the base" is incorrect. So the correct option is "none of the above".

Step 1: Recall Chargaff's Rule

Chargaff's rule states that in DNA, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). Also, the sum of all bases is 100%, i.e., \(A + T+G + C=100\%\).

Step 2: Calculate the amount of T

Since \(A = T\) and \(A = 18\%\), then \(T=18\%\).

Step 3: Calculate the sum of G and C

First, find the sum of \(A\) and \(T\): \(A + T=18\%+ 18\% = 36\%\). Then, the sum of \(G\) and \(C\) is \(100\%-(A + T)=100\% - 36\%=64\%\).

Step 4: Calculate the amount of C

Since \(G = C\), we can find \(C\) by dividing the sum of \(G\) and \(C\) by 2. So \(C=\frac{64\%}{2}=32\%\).

The structure of DNA is a double - helix. It consists of two strands of nucleotides that wind around each other like a twisted ladder. "Single helix" is incorrect, "triple helix" is not the structure of normal DNA, and "none of the above" is incorrect as DNA is a double helix.

Answer:

none of the above

Second Question: A strand of DNA has 18% adenine. What is the percentage of cytosine?