Hline too long or midrule too short

Question

Probably due to the specifications I made in tabular, I can't put a line that covers all my columns. If I out hline it's too wide and when I put midrule is too short. Can someone help me to put a line that is the right length?

\begin{table}[h!]
  \centering
  \caption{Response of \glspl{Tas2r} stimulated with bitter compounds}
    \begin{tabular}{p{15.93em}p{13.57em}p{12.57em}}
    \textbf{Taste receptor} & \textbf{Ligand} & \textbf{Article} \\
    \hline
    TAS2R38 & ptc   & \cite{meyerhof2010molecular} \\
    TAS2R1, TAS2R10 & dxm   & \cite{meyerhof2010molecular} \\
    TAS2R4, TAS2R7, TAS2R10, TAS2R14, TAS2R39, TAS2R40, TAS2R43, TAS2R44, TAS2R46 & quinine & \cite{meyerhof2010molecular} \\
    mouse Tas2r5 & cycloheximide & \cite{chandrashekar2000t2rs} \\
    chicken Tas2r1 & 10 (5 natural and 5 synthetic) & \cite{behrens2014tuning} \\
    chicken Tas2r2 & 8 (6 natural and 2 synthetic) & \cite{behrens2014tuning} \\
    chicken Tas2r7 & 17 (14 natural and 3 synthetic) & \cite{behrens2014tuning} \\
    turkey Tas2r3 & 15 (12 natural and 3 synthetic) & \cite{behrens2014tuning} \\
    turkey Tas2r4 & 8 (5 natural and 3 synthetic) & \cite{behrens2014tuning} \\
    zebra finch Tas2r5 & 5 (1 natural and 4 synthetic) & \cite{behrens2014tuning} \\
    zebra finch Tas2r6 & 3 (2 natural and 1 synthetic) & \cite{behrens2014tuning} \\
    zebra finch Tas2r7 & 5 (3 natural and 2 synthetic) & \cite{behrens2014tuning} \\
    \end{tabular}%
  \label{tab:ligand}%
\end{table}%

Answer 1

The big problem is that you're overspecifying the widths, so the table turns out to be wider than the available text width.

I suggest one X column (from tabularx) to cope with the overlong first column entry, but also to use vertical space to separate the groups.

\begin{filecontents*}[overwrite]{\jobname.bib}
@article{meyerhof2010molecular,
 author={X. Meyerhof},
 title={title},
 journal={Journal},
 year={2010},
}
@article{chandrashekar2000t2rs,
 author={Chandrashekar, Y.},
 title={title},
 journal={Journal},
 year={2000},
}
@article{behrens2014tuning,
 author={Behrens, Z.},
 title={title},
 journal={Journal},
 year={2014},
}
\end{filecontents*}

\documentclass{article}
\usepackage{booktabs}
\usepackage{tabularx,array}

\newcommand{\glspl}[1]{#1}% because there is no hint on how glossary is used

\begin{document}

\begin{table}[htp!]
  \centering
  \caption{Response of \glspl{Tas2r} stimulated with bitter compounds}
  \label{tab:ligand}

  \begin{tabularx}{\textwidth}{
    @{}
    >{\raggedright}X
    l
    @{}
    c
    @{}
  }
  \toprule
    \textbf{Taste receptor} & \textbf{Ligand} & \textbf{Article} \\
  \midrule
    TAS2R38 & ptc   & \cite{meyerhof2010molecular} \\
  \addlinespace
    TAS2R1, TAS2R10 & dxm   & \cite{meyerhof2010molecular} \\
  \addlinespace
    TAS2R4, TAS2R7, TAS2R10, TAS2R14, TAS2R39, TAS2R40, TAS2R43, TAS2R44, TAS2R46 & quinine & \cite{meyerhof2010molecular} \\
  \addlinespace
    mouse Tas2r5 & cycloheximide & \cite{chandrashekar2000t2rs} \\
  \addlinespace
    chicken Tas2r1 & 10 (5 natural and 5 synthetic) & \cite{behrens2014tuning} \\
%  \addlinespace
    chicken Tas2r2 & 8 (6 natural and 2 synthetic) & \cite{behrens2014tuning} \\
%  \addlinespace
    chicken Tas2r7 & 17 (14 natural and 3 synthetic) & \cite{behrens2014tuning} \\
  \addlinespace
    turkey Tas2r3 & 15 (12 natural and 3 synthetic) & \cite{behrens2014tuning} \\
%  \addlinespace
    turkey Tas2r4 & 8 (5 natural and 3 synthetic) & \cite{behrens2014tuning} \\
  \addlinespace
    zebra finch Tas2r5 & 5 (1 natural and 4 synthetic) & \cite{behrens2014tuning} \\
%  \addlinespace
    zebra finch Tas2r6 & 3 (2 natural and 1 synthetic) & \cite{behrens2014tuning} \\
%  \addlinespace
    zebra finch Tas2r7 & 5 (3 natural and 2 synthetic) & \cite{behrens2014tuning} \\
  \bottomrule
  \end{tabularx}
\end{table}

\bibliographystyle{plain}
\bibliography{\jobname}

\end{document}

I added mock bibliographic entries to get actual numbers. The third column can have no intercolumn space before it because there's no risk of clash due to the wide “Article” header.

The \label is related to \caption, so it belongs near it.

Answer 2

\begin{tabular}{p{3cm}p{2cm}p{1cm}}
    \textbf{Taste receptor} & \textbf{Ligand} & \textbf{Article} \\
    \hline
    TAS2R38 & ptc   & \cite{meyerhof2010molecular} \\
    TAS2R1, TAS2R10 & dxm   & \cite{meyerhof2010molecular} \\
    TAS2R4, TAS2R7, TAS2R10, TAS2R14, TAS2R39, TAS2R40, TAS2R43, TAS2R44, TAS2R46 & quinine & \cite{meyerhof2010molecular} \\
    mouse Tas2r5 & cycloheximide & \cite{chandrashekar2000t2rs} \\
    chicken Tas2r1 & 10 (5 natural and 5 synthetic) & \cite{behrens2014tuning} \\
    chicken Tas2r2 & 8 (6 natural and 2 synthetic) & \cite{behrens2014tuning} \\
    chicken Tas2r7 & 17 (14 natural and 3 synthetic) & \cite{behrens2014tuning} \\
    turkey Tas2r3 & 15 (12 natural and 3 synthetic) & \cite{behrens2014tuning} \\
    turkey Tas2r4 & 8 (5 natural and 3 synthetic) & \cite{behrens2014tuning} \\
    zebra finch Tas2r5 & 5 (1 natural and 4 synthetic) & \cite{behrens2014tuning} \\
    zebra finch Tas2r6 & 3 (2 natural and 1 synthetic) & \cite{behrens2014tuning} \\
    zebra finch Tas2r7 & 5 (3 natural and 2 synthetic) & \cite{behrens2014tuning} \\
\end{tabular}%][1]][1]