topic iii: base pair rules and directionality
within dna, there are four types of nitrogenous bases: adenine (a), thymine (t), guanine (g), and cytosine (c). these bases pair up in a complementary fashion: a always pairs with t, and g always pairs with c. this pairing is facilitated by hydrogen bonds between the bases, holding the two strands of the double helix together. a and t are held together with two hydrogen bonds, while g and c are held together with three. the antiparallel arrangement of the strands, with one running in the 5’ to 3’ direction and the other in the 3’ to 5’ direction, allows for precise replication and encoding of genetic information.
12. what type of bonds hold the nitrogenous bases together?
13. adenine always pairs with which nitrogenous base? how many hydrogen bonds hold them together?
14. cytosine always pairs with which nitrogenous base? how many hydrogen bonds hold them together?
15. how do we label (numbers) each end of a nucleic acid strand?
16. why do we say that dna strands are antiparallel?
17. write the complementary strand of dna to the template strand below. include proper directionality.
3’ — a c t g a t t c g a c t — 5’
—’ — — — — — — — — — — — — —’
topic iv: rna vs dna
images of deoxyribose and ribose structures, dna vs rna diagram, venn diagram labeled rna and dna
17. fill in the venn diagram below with the following terms:
- a nucleic acid
- contains adenine
- contains thymine
- contains guanine
- contains cytosine
- contains uracil
- contains a phosphate functional group
- contains ribose
- contains deoxyribose
- single stranded
- double stranded
- made of nucleotides
- found exclusively in the nucleus
- found all throughout cell

Question

Accepted Answer

### Question 12
# Brief Explanations:
The text states that the pairing of nitrogenous bases in DNA is facilitated by hydrogen bonds. So the bonds holding the nitrogenous bases together are hydrogen bonds.
# Answer:
Hydrogen bonds

### Question 13
# Brief Explanations:
From the text, we know that in DNA base pairing, adenine (A) always pairs with thymine (T), and they are held together with two hydrogen bonds.
# Answer:
Adenine always pairs with thymine (T). Two hydrogen bonds hold them together.

### Question 14
# Brief Explanations:
According to the text, cytosine (C) always pairs with guanine (G), and they are held together with three hydrogen bonds.
# Answer:
Cytosine always pairs with guanine (G). Three hydrogen bonds hold them together.

### Question 15
# Brief Explanations:
The text shows and states that each end of a nucleic acid strand is labeled based on the carbon of the sugar (deoxyribose in DNA) in the backbone. One end is the 5' (5 - prime) end (associated with the phosphate group attachment) and the other is the 3' (3 - prime) end (associated with the -OH group on the sugar).
# Answer:
One end of a nucleic acid strand is labeled 5' (5 - prime) and the other is labeled 3' (3 - prime), based on the carbon atoms of the sugar (deoxyribose in DNA) in the backbone (the 5' end has a phosphate group attached to the 5th carbon of the sugar, and the 3' end has a -OH group on the 3rd carbon of the sugar).

### Question 16
# Brief Explanations:
The text says that the two strands of the double helix are arranged with one running in the 5' to 3' direction and the other in the 3' to 5' direction. Since they run in opposite directions, we say the DNA strands are antiparallel.
# Answer:
DNA strands are antiparallel because one strand runs in the 5' to 3' direction and the other strand runs in the 3' to 5' direction (they run in opposite directions).

### Question 17 (DNA Complementary Strand)
# Explanation:
## Step 1: Recall Base Pairing Rules
In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). Also, the complementary strand runs in the opposite direction (if the template is 3' - 5', the complementary is 5' - 3').
The template strand is $ 3' - A\ C\ T\ G\ A\ T\ T\ C\ G\ A\ C\ T - 5' $
## Step 2: Pair Each Base and Determine Direction
- A pairs with T, C pairs with G, T pairs with A, G pairs with C, A pairs with T, T pairs with A, T pairs with A, C pairs with G, G pairs with C, A pairs with T, C pairs with G, T pairs with A.
- The direction of the complementary strand should be 5' to 3' (opposite of the template's 3' to 5').
So the complementary strand is $ 5' - T\ G\ A\ C\ T\ A\ A\ G\ C\ T\ G\ A - 3' $
# Answer:
$ 5' - T\ G\ A\ C\ T\ A\ A\ G\ C\ T\ G\ A - 3' $

### Question 17 (Venn Diagram - RNA, DNA, and Overlap)
#### RNA (Only in RNA circle):
- Contains uracil (RNA has uracil instead of thymine)
- Single - stranded (RNA is usually single - stranded)
- Contains ribose (RNA has ribose sugar)
- Found all throughout cell (RNA is found in nucleus, cytoplasm, etc.)

#### DNA (Only in DNA circle):
- Contains thymine (DNA has thymine instead of uracil)
- Double - stranded (DNA is double - stranded)
- Contains deoxyribose (DNA has deoxyribose sugar)
- Found exclusively in the nucleus (mostly, for eukaryotic cells, DNA is in the nucleus)

#### Overlap (Both RNA and DNA):
- A nucleic acid (both are nucleic acids)
- Contains adenine (both have adenine)
- Contains guanine (both have guanine)
- Contains cytosine (both have cytosine)
- Contains a phosphate functional group (both have a phosphate group in their nucleotide structure)
- Made of nucleotides (both are polymers of nucleotides)

# Brief Explanations:
We use the properties of RNA and DNA. RNA has uracil, ribose, is single - stranded, and is found throughout the cell. DNA has thymine, deoxyribose, is double - stranded, and is mostly in the nucleus. Both are nucleic acids, have adenine, guanine, cytosine, a phosphate group, and are made of nucleotides.
# Answer:
- **RNA (only)**: Contains uracil, Single stranded, Contains ribose, Found all throughout cell
- **Overlap (both)**: A nucleic acid, Contains adenine, Contains guanine, Contains cytosine, Contains a phosphate functional group, Made of nucleotides
- **DNA (only)**: Contains thymine, Double stranded, Contains deoxyribose, Found exclusively in the nucleus

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Question 12

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