Biology 9th Chap 2 : Topic 7 - Maryam Publications

Biology Chapter 2 : Topic 7

Structure of DNA

1 / 15

DNA is best described as a:

A) Double helix made of nucleotides

B) Single chain of amino acids

C) Chain of glucose molecules

D) Lipid molecule with two layers

2 / 15

The basic structural unit of DNA is:

A) Fatty acid

B) Nucleotide

C) Monosaccharide

D) Amino acid

3 / 15

Which set correctly represents the components of a DNA nucleotide?

A) Protein, sugar, phosphate

B) Lipid, phosphate, base

C) Sugar, phosphate group, nitrogenous base

D) Glucose, amino acid, phosphate

4 / 15

Which nitrogenous base pairs with adenine (A) in DNA?

A) Cytosine

B) Uracil

C) Thymine

D) Guanine

5 / 15

If one DNA strand contains the sequence A-G-C-T, the complementary strand will be:

A) T-C-G-A

B) G-A-T-C

C) T-G-C-A

D) A-G-C-T

6 / 15

Which base pairs with guanine (G) in DNA?

A) Cytosine

B) Adenine

C) Thymine

D) Uracil

7 / 15

The two strands of DNA are held together mainly by:

A) Peptide bonds

B) Ionic bonds only

C) Glycosidic bonds

D) Complementary base pairing

8 / 15

Which statement correctly describes the double helix model of DNA?

A) DNA contains only one type of nucleotide.

B) DNA is made entirely of proteins.

C) DNA consists of four separate strands.

D) DNA is made of two twisted strands.

9 / 15

A DNA molecule contains 30% adenine. What percentage of thymine is expected?

A) 40%

B) 30%

C) 20%

D) 60%

10 / 15

If a DNA sample contains 25% guanine, what percentage of cytosine will it contain?

A) 75%

B) 12.5%

C) 50%

D) 25%

11 / 15

Which component forms the “rungs” of the DNA ladder?

A) Amino acids

B) Paired nitrogenous bases

C) Sugars only

D) Phosphate groups only

12 / 15

Which component forms the sides of the DNA ladder?

A) Nitrogenous bases only

B) Lipids

C) Sugar-phosphate backbone

D) Amino acids

13 / 15

A scientist finds equal amounts of adenine and thymine in a molecule. This observation supports the idea of:

A) Lipid formation

B) Enzyme activity

C) Protein synthesis

D) Complementary base pairing

14 / 15

Which statement about DNA nucleotides is correct?

A) All nucleotides contain the same nitrogenous base.

B) Nucleotides differ mainly in their nitrogenous bases.

C) Nucleotides lack phosphate groups.

D) Nucleotides are made of amino acids.

15 / 15

A mutation changes a cytosine (C) on one DNA strand. Which base on the opposite strand is most directly affected?

A) Guanine

B) Adenine

C) Another cytosine

D) Thymine

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