Ch.5 - Biological MoleculesWorksheetSee all chapters
All Chapters
Ch.1 - Introduction to Biology
Ch.2 - Chemistry
Ch.3 - Water
Ch.4 - Carbon
Ch.5 - Biological Molecules
Ch.6 - Cells
Ch.7 - The Membrane
Ch.8 - Energy and Metabolism
Ch.9 - Respiration
Ch.10 - Photosynthesis
Ch.11 - Cell Signaling
Ch.12 - Cell Division
Ch.13 - Meiosis
Ch.14 - Mendelian Genetics
Ch.15 - Chromosomal Theory of Inheritance
Ch.16 - DNA Synthesis
Ch.17 - Gene Expression
Ch.18 - Regulation of Expression
Ch.19 - Viruses
Ch.20 - Biotechnology
Ch.21 - Genomics
Ch.22 - Development
Ch.23 - Evolution by Natural Selection
Ch.24 - Evolution of Populations
Ch.25 - Speciation
Ch.26 - History of Life on Earth
Ch.27 - Phylogeny
Ch.28 - Prokaryotes
Ch.29 - Protists
Ch.30 - Plants
Ch.31 - Fungi
Ch.32 - Overview of Animals
Ch.33 - Invertebrates
Ch.34 - Vertebrates
Ch.35 - Plant Anatomy
Ch.36 - Vascular Plant Transport
Ch.37 - Soil
Ch.38 - Plant Reproduction
Ch.39 - Plant Sensation and Response
Ch.40 - Animal Form and Function
Ch.41 - Digestive System
Ch.42 - Circulatory System
Ch.43 - Immune System
Ch.44 - Osmoregulation and Excretion
Ch.45 - Endocrine System
Ch.46 - Animal Reproduction
Ch.47 - Nervous System
Ch.48 - Sensory Systems
Ch.49 - Muscle Systems
Ch.50 - Ecology
Ch.51 - Animal Behavior
Ch.52 - Population Ecology
Ch.53 - Community Ecology
Ch.54 - Ecosystems
Ch.55 - Conservation Biology
Nucleic Acids
Additional Practice
Cumulative Macromolecules

Which of the following does not provide evidence to support the conclusion that nitrogenous bases pair in specific combinations?

A. a purine-purine pair is too wide to account for the 2-nm diameter of the double helix.

B. The sugar-phosphate backbone is held together by phosphodiester bonds.

C. The X-ray data suggested that the double helix had a uniform diameter.

D. Whenever one strand of DNA has a C, the partner strand has a G.

E. A pyrimidine-pyrimidine pair is too narrow o account for the 2nm-diameter of the double helix.


Nucleic acids are polynucleotides with building blocks that are made of a nitrogenous base, a pentose, and a phosphate group. RNA makes use of the pentose, ribose, while DNA uses deoxyribose. In addition to this, DNA is also know for its usual double-stranded character, the nucleotide bases pair up based on complementarity. This happens as a purine-pyrimidine base pairing. This can be proven by a number of points.

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