1. Introduction to Genetics

If thymine makes up 21% of the DNA nucleotides in the genome of a plant species, what are the percentages of the other nucleotides in the genome?

What reactive chemical groups are found at the 5' and 3' carbons of nucleotides? What is the name of the bond formed when nucleotides are joined in a single strand? Is this bond covalent or noncovalent?

Identify two differences in chemical composition that distinguish DNA from RNA.

A portion of a polypeptide contains the amino acids Trp-Lys-Met-Ala-Val. Write the possible mRNA and template-strand DNA sequences. (Hint: Use A/G and T/C to indicate that either adenine/guanine or thymine/cytosine could occur in a particular position, and use N to indicate that any DNA nucleotide could appear.)

The following segment of DNA is the template strand transcribed into mRNA:
      5'-...GACATGGAA...-3'

What is the amino acid sequence produced by translation?

The following segment of DNA is the template strand transcribed into mRNA:
      5'-...GACATGGAA...-3'

What is the sequence of mRNA created from this sequence?

Fill in the missing nucleotides (so there are three per block) and the missing amino acid abbreviations in the graphic shown here. 

Suppose a genotype for a protein-producing gene can have any combination of three alleles, A₁, A₂, and A₃.

Each allele produces a protein with a distinct electrophoretic mobility. Allele A₁ has the highest electrophoretic mobility, A₃ has the lowest electrophoretic mobility, and the electrophoretic mobility of A₂ is intermediate between them. Draw the appearance of gel electrophoresis protein bands for each of the possible genotypes. Be sure to label each lane of the gel with the corresponding genotype.

Suppose a genotype for a protein-producing gene can have any combination of three alleles, A₁, A₂, and A₃.

List all the possible genotypes involving these three alleles.

Shorter fragments of DNA (those with fewer base pairs) have a higher electrophoretic mobility than larger fragments. Thinking about electrophoresis gels as creating a matrix through which fragments must migrate, briefly explain why the size of a DNA fragment affects its electrophoretic mobility.

Four nucleic-acid samples are analyzed to determine the percentages of the nucleotides they contain. Survey the data in the table to determine which samples are DNA and which are RNA, and specify whether each sample is double-stranded or single-stranded. Justify each answer.
[A table of nucleotide percentages appears below the problem]
              

Consider the following segment of DNA:
       5'-...ATGCCAGTCACTGACTTG...-3'
       3'-...TACGGTCAGTGACTGAAC...-5'

How many hydrogen bonds are present in this DNA segment?

Consider the following segment of DNA:
       5'-...ATGCCAGTCACTGACTTG...-3'
       3'-...TACGGTCAGTGACTGAAC...-5'

How many phosphodiester bonds are required to form this segment of double-stranded DNA?

Consider the following segment of DNA:
       5'-...ATGCCAGTCACTGACTTG...-3'
       3'-...TACGGTCAGTGACTGAAC...-5'

If the lower strand of DNA serves as the template transcribed into mRNA, how many peptide bonds are present in the polypeptide fragment into which the mRNA is translated?