Uncaught TypeError: undefined is not a function, object created in for loop

I'm building a small Quiz application where users can build their own quizzes but have run into a problem with creating objects in a for loop.

Here is the constructor for the Question object:

var question = function(questionNumber, question, choices, correctAnswer) {
    this.questionNumber = questionNumber;
    this.question = question;
    this.choices = choices;
    this.correctAnswer = correctAnswer; //The number stored here must be the location of the answer in the array

    this.populateQuestions = function populateQuestions() {
        var h2 = $('<h2>').append(this.question);
        $('#quizSpace').append(h2);
        for (var i = 0; i < choices.length; i++) {
            //Create the input element
            var radio = $('<input type="radio">').attr({value: choices[i], name: 'answer'});

            //Insert the radio into the DOM
            $('#quizSpace').append(radio);
            radio.after('<br>');
            radio.after(choices[i]);
        }
    };
    allQuestions.push(this);
};

I have a bunch of HTML that is generated dynamically which I then pull the values from and place them in a new object like so:

$('#buildQuiz').click(function() {
    var questionLength = $('.question').length;
    for ( var i = 1; i <= questionLength; i++ ) {
        var questionTitle = $('#question' + i + ' .questionTitle').val();
        var correctAnswer = $('#question' + i + ' .correctAnswer').val() - 1;
        var inputChoices = [];
        $('#question' + i + ' .choice').each(function(){
            inputChoices.push($(this).val()); 
        });

        var question = new question(i, questionTitle, inputChoices, correctAnswer);
        }
    allQuestions[0].populateQuestions();
    $('#questionBuilder').hide();
    $('#quizWrapper').show();
});

However, when I click the #buildQuiz button I receive the error:

Uncaught TypeError: undefined is not a function 

On this line:

var question = new question(i, questionTitle, inputChoices, correctAnswer);