Unit 10: Gene Expression
In this unit, we learn about the universal genetic codes deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). We call DNA and RNA universal because we find them in every known organism. As we learned in Unit 7, the DNA and RNA in every organism are made up of the same few ingredients.
However, extremely slight differences often account for the differences between species. What makes a dog different from a toadstool? What accounts for the differences within species? What makes you different from your neighbor? This unit will give you a greater understanding of the genetic code and its impact on your life.
Completing this unit should take you approximately 5 hours.
Upon successful completion of this unit, you will be able to:
- explain the molecular basis of heritable traits, and how information in DNA is ultimately expressed as a protein;
- define the role of DNA and its means of replication;
- distinguish between the two main phases of gene expression: transcription and translation; and
- discuss some technological advances of molecular biology.
10.1: DNA Replication and Synthesis
Cells make copies of their DNA before they divide into identical daughter cells. This process is called DNA replication or synthesis. Chromosomes for sister chromatids after the copying of DNA. This allows cells to receive genetic information and produce proteins for identical phenotypes.
Watch this lecture to review the structure of DNA. All of the nucleotides in DNA are made of the same basic parts: deoxyribose sugar molecules and nitrogenous bases (the purines: adenine and guanine, and the pyrimidines: thymine and cytosine). Adenine pairs with thymine, and guanine pairs with cytosine. After you finish this section, you should be able to create complementary base pairs on a DNA strand.
Review this 3D model of the double helix structure of a DNA molecule.
Read this text, which explains what occurs during DNA replication. Pay attention to how different enzymes catalyze the production of leading and lagging strands of DNA.
After you have read the text, you should be able to explain how DNA replicates in a semiconservative manner, describe the process of DNA replication, describe the functions for the variety of enzymes that catalyze this process, and define Okazaki fragments.
Watch this video animation of DNA replication. It shows how both strands of the DNA helix are unzipped and copied to produce two identical DNA molecules.
10.2: DNA Transcription
Genes are expressed by the production of proteins through two processes: transcription and translation. Transcription is the process of using the DNA code as a template to make mRNA messages. Translation involves the ribosome interpreting that message to build proteins.
First, let's review these five lectures which discuss protein synthesis. After you have watched these lectures and read the text that follows them, you should be able to describe the steps and catalysts of transcription, and describe the structure and function of mRNA.
Read this text, which discusses this process of transcription. Pay attention to the discussion on alternative splicing and mutations found in organisms in the "Evolution Connection" box.
10.3: Translation and Synthesis
Now that we have learned about transcription, let's review the second process of gene expression with a series of lectures on translation. Translation refers to how the ribosome uses messenger RNA (mRNA) and transfer RNA (tRNA) to attach amino acids together to make proteins.
Watch these videos. After you watch, you should be able to describe the structure and function of mRNA, rRNA, and tRNA, the structures and function of the ribosome, and the steps and catalysts of transcription.
Read this text, which discusses the process of transcription.
10.4: Regulating Gene Expression
Gene expression must be regulated through much of life. During certain times of development, growth, or repair, genes must be turned on and off. This helps cells interact with their environment and maintain homeostasis.
Read this section, which explores the regulation of genes and how gene regulation is used in cells. After you read, you should be able to explain how genes are modified before or after transcription and translation and explain the differences of regulation between prokaryotic and eukaryotic gene regulation.
10.5: Using DNA Technology
DNA technologies have benefited our society in many ways. For example, today's scientists use the concepts you have studied in this course to improve our criminal justice system, enhance our food supply, and treat previously incurable diseases.
Forensic scientists have developed next-generation DNA sequencing techniques using ever-smaller amounts of DNA evidence to identify criminals who have escaped criminal justice for years. These technologies have simultaneously allowed us to exonerate individuals who have been wrongly convicted and imprisoned for crimes they did not commit.
Humans have used selective breeding techniques to artificially alter the genomes of plants and animals for thousands of years. However, today's biochemists use modern genetic manipulation techniques to quickly and efficiently modify the DNA in plants to create genetically modified organisms (GMOs). Farmers plant these genetically modified seeds to grow crops that produce more edible plant material, grow well in drought conditions, resist diseases, and repel destructive insects.
Scientists have also created the gene-editing technique called CRISPR to swap faulty genes with healthy ones to treat human genetic disorders that cause debilitating diseases and cancers.
As you watch this video, pay attention to the ethical concerns that these genetic altering technologies present. There is a grave risk that scientists could inadvertently create damaging genetic mutations that could seriously harm humans, animals, and our very biosphere.
This article discusses the CRISPR technique in more detail.
Watch this video. What disease are the scientists studying? What is the hypothesis that the scientists hope to support? What causes human genetic variation? How do scientists determine ancestry? In terms of asthma, what can scientists determine when they compare ancestral patterns? How might these findings be used in the future?
Unit 10 Assessment
Take this assessment to see how well you understood this unit.
- This assessment does not count towards your grade. It is just for practice!
- You will see the correct answers when you submit your answers. Use this to help you study for the final exam!
- You can take this assessment as many times as you want, whenever you want.