what is the structure of dna

ATI TEAS 7

ATI TEAS Science Practice Test

1. What is the structure of DNA?

A. Single-stranded, linear
B. Double-stranded, linear
C. Double-stranded, helix
D. Single-stranded, helix

Correct answer: C

Rationale: The correct answer is C: Double-stranded, helix. DNA is structured as a double helix formed by two strands of nucleotides. The nucleotides are paired with complementary bases (A-T and C-G) in the center, held together by hydrogen bonds. This double-stranded helical structure is a fundamental characteristic of DNA and essential for its function in storing genetic information. Choices A, B, and D are incorrect because DNA is not single-stranded; it consists of two strands that run antiparallel to each other and are connected via hydrogen bonds. Additionally, DNA does not have a linear structure but rather a helical one, providing stability and protection to the genetic information it carries.

2. Where is the thymus gland, crucial for immune system development, located?

A. Chest
B. Abdomen
C. Pelvis
D. Head and neck

Correct answer: A

Rationale: The thymus gland is located in the chest, specifically in the upper part of the chest behind the breastbone (sternum). It plays a crucial role in the development and maturation of T-lymphocytes (T cells), which are important for the immune system's function. Choice B (Abdomen), C (Pelvis), and D (Head and neck) are incorrect locations for the thymus gland. The thymus is not found in the abdomen, pelvis, head, or neck regions; it is uniquely situated in the upper chest area.

3. Which of the following statements is NOT true about DNA?

A. DNA contains the nucleotides A, T, C, G and is read 5' to 3'.
B. DNA contains genetic information and is tightly coiled with proteins to form chromosomes.
C. DNA contains the nucleotides A, T, C, G and is read 3' to 5'.
D. DNA is a double-stranded molecule connected by hydrogen bonds.

Correct answer: C

Rationale: The correct answer is C because DNA is typically read from the 5' end to the 3' end, not from 3' to 5'. Choices A, B, and D are all true statements about DNA. DNA contains the nucleotides A, T, C, G and is read in a 5' to 3' direction. DNA also contains genetic information and is tightly coiled with proteins to form chromosomes. Additionally, DNA is a double-stranded molecule connected by hydrogen bonds.

4. What does 'monophyletic' mean in the context of classification?

A. A group with a single representative organism
B. A group with diverse and unrelated members
C. A group with similar functions but different origins
D. A group descended from a common ancestor

Correct answer: D

Rationale: In the context of classification, 'monophyletic' refers to a group that includes a common ancestor and all of its descendants. This group shares a single evolutionary origin and forms a complete branch on a phylogenetic tree. Monophyletic groups are considered natural and valid taxonomic units because they reflect evolutionary relationships accurately. Option D is the correct choice as it accurately defines the term 'monophyletic' in the context of classification. Choices A, B, and C are incorrect. Choice A is incorrect because 'monophyletic' does not refer to a group with a single representative organism but rather a group descended from a common ancestor. Choice B is incorrect as a monophyletic group consists of related, not diverse and unrelated, members. Choice C is incorrect as a monophyletic group includes descendants from a common ancestor, not just organisms with similar functions but different origins.

5. Iron is a transition metal, which means it often forms a cation with a charge of what?

A. 2- or 3-
B. 1-
C. 2+ or 3+
D. 1+

Correct answer: C

Rationale: The correct answer is C: 2+ or 3+. Transition metals, like iron, are known for their ability to exhibit variable oxidation states. This characteristic allows them to form cations with charges such as 2+ or 3+. Specifically, iron can form cations with these charges due to the varying electron configurations in its d-orbitals. The other choices are incorrect because transition metals typically form positively charged cations, not negatively charged ones. Additionally, while iron can form cations with charges of 2+ or 3+, it does not commonly form cations with charges of 1- or 1+. Transition metal cations play a crucial role in forming coordination complexes with ligands, highlighting their importance in various chemical reactions.