Introduction

Module 8 – DNA Replication and Gene Expression

Introduction

In the last few modules, we learned that DNA is our genetic information and that segments of DNA, called genes , contain the information to produce specific proteins. We know that DNA is stored in the nucleus of eukaryotes, such as plants and animals. We even explored how these genes are passed from parent to offspring. In this module, we will examine how your genetic information, DNA, is used to produce specific proteins. For our work in this module, think first about the molecules that are involved in the process of using the information in DNA to produce a protein. You will want to review DNA, RNA, and proteins (first described in Module 2). Be familiar with their general structure, the monomers which make up the polymers, compare DNA and RNA in terms of structure. Become familiar with the three types of RNA that are mentioned as involved in the process of gene expression.

In the second half of the module, we will take a closer look at the “process” of gene expression. You know that DNA is found in the nucleus of eukaryotes and that proteins are synthesized at the ribosome. For this portion, you will break down the overall process of nuclear gene expression into three main step – transcription, mRNA processing/ editing, and translation.

In short, transcription is the process of using the information in DNA to make a piece of mRNA, the intermediate in the process of using a piece of DNA to produce a protein. RNA, and specifically messenger RNA (mRNA) acts by taking the information found in the DNA (the code) to the ribosomes where protein synthesis will take place. Ask yourself:

  • Why doesn’t DNA just leave the nucleus and go to the ribosomes when a new protein is needed in the cell?
  • Why have the intermediate?

You will work through RNA editing (which only takes place in eukaryotes) and alternative splicing. After transcription and RNA editing, your mature mRNA moves to the ribosomes in the cytoplasm which you know are little protein factories within the cell.

While most of your focus in this module will be in understanding the process of gene expression in eukaryotes, it is also important to consider that this process also takes place in prokaryotes. You know that prokaryotes, like bacteria, have genetic material found in the cell and have the need to make proteins. Ribosomes are found within prokaryotes and are the site of protein synthesis (translation). Once you have reached a good understanding of gene expression in eukaryotes, compare the process to prokaryotes 1 .

Learning Outcomes

This module addresses the following Course Learning Outcomes listed in the Syllabus for this course:

  • Demonstrate knowledge of biological principles.
  • Demonstrate knowledge of scientific method.
  • Communicate scientific ideas through oral or written assignments.
  • Interpret scientific models such as formulas, graphs and tables.
  • Demonstrate problem solving methods in situations that are encountered outside of the classroom 1 .

Module Objectives

Upon completion of this module, the student will be able to:

  • Define gene expression.
  • Define gene.
  • Answer the questions:
    • Where are genes found in eukaryotes vs. prokaryotes?
    • How are genes organized in eukaryotes vs. prokaryotes?
  • Name the cellular structure in eukaryotes and prokaryotes where protein synthesis takes place.
  • Describe the general structure of the DNA and RNA molecule.
  • Name the three types of RNA discussed in this module. For each type (mRNA, tRNA, and rRNA), know where they are involved in gene expression, and what the small letter prior to the “RNA” represents.
  • Describe the general differences between gene expression in eukaryotes and prokaryotes.
  • Focusing on gene expression in eukaryotes, be able to answer the following questions as they relate to transcription in eukaryotes:
    • Name the enzyme that initiates transcription.
    • Identify where this process take place in the cell.
    • Name the general steps of the process.
    • Describe what allows the enzyme that initiates this process to begin in the correct location processes of transcription and translation.
    • Identify what signals the end of transcription.
  • Describe the process of transcription and tranlation. State what signals the end of each process.
  • Describe RNA editing/ processing in eukaryotes.
  • Define alternative splicing.
  • Be able to describe:
    • Translation.
    • Where in the cell this process takes place.
    • How the ribosome is able to “read” your transcript.
    • How rRNA and tRNA are involved in this process.
    • State what type of RNA allows for the change in message from nucleotides to amino acids (DNA and the mRNA intermediate are both composed of nucleotide subunits while protein is composed of amino acids) 1 .