DNA Review

What are three tasks that DNA performs?

• DNA stores genetic information.

• 1. DNA discards foreign genes.

• 1. DNA copies itself.

• DNA instructs cells to produce needed molecules.

Answer explanation

DNA performs essential tasks: it stores genetic information, copies itself for cell division, and instructs cells to produce proteins and other molecules needed for various functions. Discarding foreign genes is not a task of DNA.

Tags

NGSS.HS-LS1-1

DNA is a polymer made of which monomers?

• Nucleotides

• Monosaccharides

• Amino Acids

• Fatty Acids

Answer explanation

DNA is a polymer made of nucleotides, which are the monomers that link together to form the DNA strand. Monosaccharides, amino acids, and fatty acids are the building blocks of carbohydrates, proteins, and lipids, respectively.

The shape of DNA.

• double helix

• nucleotide

• DNA polymerase

• single-stranded

Answer explanation

The correct answer is 'double helix' because DNA is structured as a double helix, consisting of two strands that twist around each other, unlike the other options which refer to components or forms of DNA.

Tags

NGSS.HS-LS1-1

3. The model shows a nucleotide, a building block of the DNA molecule. Moving from left to right in the model, what are the names of the three components?

• 1. 5-carbon sugar; nitrogenous base; phosphate group

• 1. nucleic acid; 5-carbon sugar; amino group

• 1. 5-carbon sugar; nitrogenous base; carboxyl group

• nitrogenous base; 5-carbon sugar; phosphate group

Answer explanation

The correct answer is 'nitrogenous base; 5-carbon sugar; phosphate group' as these are the three essential components of a nucleotide, which forms the building blocks of DNA.

Tags

NGSS.HS-LS1-1

Using the labels, identify the parts of a DNA molecule.

c

d

e

f

b

a

Base pair

Hydrogen bond

Phosphate

Nitrogen Base

Nucleotide

Deoxyribose sugar

When Chagraff was studying the composition of DNA, he found that there was always a ​ (a)   ratio between the percentage of ​ (b)   and cytosine present and that the same was true for the percentage of ​ (c)   and thymine. This meant that ​ (d)   always had to form a bond with adenine and that cytosine had to form a bond with guanine. For the bonds to always form this way, DNA strands have to run ​ (e)   to each other, creating the double helix.

• 1:1

• guanine

• adenine

• thymine

• 1:2

• parallel

• antiparallel

• cytosine

Answer explanation

Chagraff discovered a 1:1 ratio between adenine and thymine, and between guanine and cytosine, indicating specific base pairing. This complementary bonding requires DNA strands to run antiparallel, forming the double helix structure.

3. Which of these nitrogenous base compositions in DNA describe Chargaff’s rules? Select all that apply.

• 1. The DNA of all members of a species has the same nitrogenous base composition.

• 1. The percentage of A is always almost equal to the percentage of T, and the percentage of G is always almost equal to the percentage of C.

• 1. The percentage of A is always almost equal to the percentage of G, and the percentage of T is always almost equal to the percentage of C.

• 1. For every one adenine in a double-stranded DNA molecule, there has to be exactly one thymine.

Answer explanation

Chargaff's rules state that A pairs with T and G pairs with C, making their percentages equal. Thus, the correct choices reflect these relationships and the uniformity of base composition within a species.

1. The diagram represents a portion of one strand of a DNA molecule in a eukaryotic cell. Which of the four DNA strands matches the strand in the diagram by base pairing during DNA replication?

   
   

• 1. GGTGACT

• 1. CCATATG

• 1. GGTCGAT

• 1. TCCTAGTG

Answer explanation

The DNA strand in the diagram pairs with its complementary strand during replication. The correct match is GGTGACT, as G pairs with C and A pairs with T, maintaining the base pairing rules.

Tags

NGSS.HS-LS3-2

3. Rosalind Franklin’s photographs of the X-ray diffraction pattern of DNA provided important clues about the structure of the DNA molecule.

What was revealed by the photograph that enabled Watson and Crick to build their model of the DNA molecule? Select all that apply.

• 1. The DNA strands are twisted around each other.

• 1. There are two strands in the DNA molecule.

• 1. The nitrogenous bases are near the center of the DNA molecule.

• 1. The nitrogenous bases form the backbone on the outside of each DNA strand.

Answer explanation

Franklin's X-ray diffraction images showed that DNA is a double helix, confirming it has two twisted strands. The images also indicated that the nitrogenous bases are located in the center, not on the outside.

Place the steps of DNA replication in the correct order.

• The parent (original) DNA molecule is unwound and “unzipped” by helicase enzymes, causing the two DNA strands to separate.

• DNA polymerase joins free complementary nucleotides to the original template strands of DNA.

• Two new copies of DNA are created, each containing one strand from the original DNA molecule and one new strand of DNA.

• The parent (original) strands of DNA are separated, and each parent strand acts as a template that determines the order of free nucleotides along a new complementary strand of DNA.

• The parent (original) DNA molecule has two complementary strands of DNA bound together and arranged like a twisted ladder.