Question

1. which two molecules make up the sides (the backbone) of the dna ladder?

a) base pairs and proteins
b) adenine and thymine
c) sugar and phosphate
d) cytosine and guanine

1. which of the following base pairings is correct in dna?

a) adenine - guanine
b) thymine - cytosine
c) adenine - thymine
d) guanine - thymine

1. what happens first when dna replication begins?

a) new bases randomly join the strands
b) the cell divides
c) the dna strands twist tighter
d) the two dna strands separate

1. what is the main goal of dna replication?

a) to produce energy for the cell
b) to create new proteins
c) to only repair damaged dna
d) to make sure new cells have the exact same genetic instructions

1. open - ended questions

answer the following questions in complete sentences.

1. explain the rule of complementary base pairing in dna. if a dna strand has the sequence a - c - g - t, what is the sequence of the new complementary strand that will form?
2. why is it so important for dna to be copied exactly (accurately) during replication?
3. draw and label a simple diagram of a dna structure (a short section). be sure to include and label:

• the sugar - phosphate backbones (the sides of the ladder).
• at least two different nitrogen base pairs (a - t and c - g).

(use the space below for your drawing)

Explanation:

• Question 2: DNA's backbone is made of sugar (deoxyribose) and phosphate. Base pairs (like adenine - thymine, cytosine - guanine) are the "rungs" of the ladder, not the sides. Proteins are not part of the DNA backbone structure.
• Question 3: In DNA, adenine pairs with thymine (A - T) and cytosine pairs with guanine (C - G). These are the complementary base - pairing rules in DNA.
• Question 4: DNA replication starts with the separation of the two DNA strands. This allows new bases to pair with the existing strands (not randomly). The cell divides after DNA replication is complete, and the DNA strands do not twist tighter at the start of replication.
• Question 5: The main goal of DNA replication is to ensure new cells have the exact same genetic instructions. DNA replication is not about producing energy for the cell (that's more related to processes like cellular respiration). It's not just about creating new proteins (translation is involved in protein synthesis from mRNA) and not only about repairing damaged DNA (though repair can occur during replication, the main goal is for new cells to get the correct genetic info).
• Open - Ended Question 1:
• Complementary base - pairing rule: In DNA, adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G).
• For the sequence A - C - G - T, the complementary strand is T - G - C - A.
• Open - Ended Question 2: DNA contains the genetic instructions for the cell's functions (such as protein synthesis, cell division, etc.). If it is not copied exactly, the new cells may have incorrect instructions. This can lead to non - functional proteins (if the gene expression is affected) or improper cell functions, which can cause diseases or developmental issues.
• Open - Ended Question 3:
• Draw two parallel lines (representing the sugar - phosphate backbones).
• Between them, draw pairs of shapes (e.g., for A - T, one shape for A and a complementary shape for T; same for C - G) to represent the base pairs. Label the backbones as "Sugar - Phosphate Backbones" and the base pairs as "Nitrogen Base Pairs (A - T and C - G)".

Answer:

• Question 2: C. Sugar and Phosphate
• Question 3: C. Adenine - Thymine
• Question 4: D. The two DNA strands separate
• Question 5: D. To make sure new cells have the exact same genetic instructions
• Open - Ended Question 1:
• The rule of complementary base - pairing in DNA is that adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G). The sequence of the new complementary strand for A - C - G - T is T - G - C - A.
• Open - Ended Question 2: DNA must be copied exactly during replication because it contains the genetic information that determines the cell's structure and function. Incorrect copying can lead to mutations, which may result in non - functional proteins or improper cell behavior, potentially causing diseases or developmental abnormalities.
• Open - Ended Question 3: (Since this is a drawing task, a textual description of the drawing is provided as above. In an actual setting, a hand - drawn or digital diagram would be made following the described labeling.)