Nucleic Acids and DNA Structure Quiz

Nucleic acids are the building blocks of DNA and RNA.

DNA is formed from a single polynucleotide chain.

The bases in DNA are on the outside of the helix and the phosphate groups are on the inside.

RNA forms a double helix structure similar to DNA.

The sugar in RNA nucleotides is deoxyribose, the same as in DNA.

RNA can form helical loops by folding back on itself due to hydrogen bonding between base pairs.

The base thymine is replaced by the base uracil in RNA.

What is the general formula of alkene?

What is the term used to describe alkenes?

What is the difference between terminal and internal alkenes?

How is the parent structure selected in the nomenclature of alkenes?

What is the purpose of indicating the position of the double bond in the parent chain?

What is the difference between geometric isomers cis and trans?

What is a characteristic of the physical properties of alkenes?

How does branching affect the boiling point of alkenes?

What is the trend in boiling point of alkenes with increasing carbon number?

What is the significance of the double bond in alkenes?

Alkenes

Alkenes are unsaturated hydrocarbons containing a carbon-carbon double bond (C=C) in their molecule.
General formula of alkene is CnH2n.

Types of Alkenes

Terminal alkenes have the double bond at the end of the carbon chain.
Internal alkenes have at least one carbon atom bonded to each end of the double bond.
Cycloalkenes contain a double bond in a ring.

Nomenclature of Alkenes

The parent structure is the longest continuous chain that contains the carbon-carbon double bond.
The name is derived by changing the ending -ane of the corresponding alkane name to -ene.
The position of the double bond in the parent chain is indicated by a number, designating its position by the number of the first doubly-bonded carbon.
The positions of the alkyl groups attached to the parent chain are indicated by numbers.

Examples of Alkene Nomenclature

4-bromo-2-methyl-2-pentene
2-propyl-1-hexene

Geometric Isomerism

Geometric isomers are two or more chemical compounds with the same molecular formula but a different geometric arrangement.
If the two groups are identical, the two isomers are distinguished by adding the prefix cis (same side) or trans (opposite sides).

Examples of Geometric Isomers

trans-2-butene
cis-1,2-dicholroethene
cis-2-butene
trans-1,2-dicholroethene

Physical Properties of Alkenes

Alkenes are insoluble in water but quite soluble in nonpolar solvents like benzene, ether, or chloroform.
They are less dense than water.
The boiling point rises with increasing carbon number; as with the alkanes, the boiling point rise is 20-30 °C for each added carbon.
Branching lowers the boiling point.

Test your knowledge on nucleic acids and the structure of DNA, including the formation of double helix, arrangement of bases, and hydrogen bonding. Learn more about the building blocks of DNA and RNA.