BIO101 Study Guide

Unit 10: Gene Expression

10a. Explain the molecular basis of heritable traits, and how information in DNA is ultimately expressed as a protein

  • What is the Central Dogma?

DNA indirectly controls traits, because the trait is a direct result of the version of protein the individual can produce. The individual's gene (which is made of DNA) determines the type of protein they can produce. The term gene expression refers to the molecular process of building a particular protein using the code that is stored (in DNA form) as a gene. The central dogma is the teaching of the flow of genetic information to the level of the protein. DNA is used as a template to transcribe RNA, and RNA is used to translate proteins.

Simply diagram how information flows from a gene to a protein and pay particular attention to figure 9.14 in More on Transcription.


10b. Define the role of DNA and its means of replication

  • What is the structure and function of DNA?
  • Why and how does DNA self-replicate?
  • What are the enzymes involved in DNA replication?

Deoxyribonucleic Acid (DNA) is one of the most celebrated molecules in history. It is a double-helical nucleic acid made up of nucleotides. DNA has two functions:

  1. It offers semiconservative replication

  2. It provides a template for RNA transcription

DNA nucleotides consist of phosphate, deoxyribose sugar, and four nitrogenous bases (adenine, guanine, cytosine, thymine). You should understand how the structure of DNA represents a code template for gene expression.

DNA replication is a complex process that has different mechanisms and employs a great variety of enzymes. Two new strands are copied, the leading strand is synthesized continuously, while the lagging strand is synthesized as Okazaki fragments. This is because DNA synthesis can only take place in the 5'-3' direction and the DNA polymerases create the two strands simultaneously.

The main enzymes involved are helicase, primase, DNA Polymerase I and III, and DNA ligase:

  • Helicase: unwinds the DNA

  • Primase: creates an RNA primer

  • DNA Polymerase III: elongates the two strands separately by adding complementary bases.

  • DNA Polymerase I: removes the RNA primer and replaces it with DNA, but leaves a gap between fragments.

  • DNA Ligase: fills in the gap and joins DNA fragments to create fully joined identical copies of DNA.

Review DNA, which demonstrates the role of complementary nucleotide bases in DNA. Review DNA structure in The Chemical Structure of DNA. Review the semiconservative process of DNA replication in DNA Replication. Review Visualizing DNA Replication and pay attention to the steps that involve enzyme catalysis.


10c. Distinguish between the two main phases of gene expression: transcription and translation

  • What are the processes involved in gene expression?
  • In what order do these processes occur?
  • What specifically occurs in these processes?
  • How are these processes regulated?

Gene expression consists of two serial processes, occurring in the following order:

Transcription is the only part of gene expression that directly involves the gene. The cell "reads" the DNA nucleotide sequence of a gene, and uses the sequence as a code to construct a complementary sequence of RNA nucleotides.

That RNA sequence is known as messenger RNA (mRNA), because the mRNA carries the original code, as a message, to a ribosome. DNA's job is done until the gene is read again in a later round of gene expression.

Translation refers to the part of gene expression where the polypeptide (protein) is constructed. A polypeptide is a sequence of amino acids. The code in mRNA (produced earlier by transcription) instructs the cell's ribosomes how to build the polypeptide by conveying how many amino acids to string together, which amino acids to use, and how to order the amino acids in the sequence.

As a ribosome reads each codon (a sequence of three nucleotides) in the mRNA, a type of RNA called transfer RNA (tRNA) delivers the correct type of amino acid to the ribosome. Amino acids are added in this way, one by one, until the polypeptide is complete.

A completed polypeptide (produced by translation) assumes a particular shape, depending on its particular sequence of amino acids. Because of that particular shape, that polypeptide will have a particular function, and it will therefore give the individual a particular trait.

Gene expression occurs differently in organisms. Transcription and Translation occur simultaneously in prokaryotes. However, in eukaryotes, there are several modifications post-transcriptionally and post-translationally. This allows for more regulation.

Review transcription in More on Transcription and the lectures DNA Transcription. Read translation in More on Translation and the lectures Translation and Synthesis. Review How Genes Are Regulated to observe the different ways organisms regulate gene expression.


10d. Discuss some technological advances of molecular biology

  • What is a gene and how is it edited?
  • Why are DNA technologies important?

Biotechnology is the field that uses practical knowledge to solve problems in living organisms. DNA biotechnology incorporates gene modification and other tools to advance certain goals. For example, DNA technology has helped solve problems in the criminal justice system, agriculture, and the medical field.

We know genes reflect specific DNA sequences that help the body produce specific proteins, which in turn express a certain genotype or phenotype. Scientists are learning how to modify problematic genes to alleviate and eradicate disease. For example, they are using gene-editing tools to remove and replace harmful genes that cause certain dysfunctions. CRISPR is a specific type of gene editing method.

Review Biotechnology, What is Gene Editing and How Does it Work? and CRISPR: A Game-Changing Genetic Engineering Technique to understand how scientists use CRISPR in living organisms. Scientists use technology to learn about all of the genes and the phenotypes they represent. Review some genetic advances in Genes, Health, and Moving Beyond Race.


Unit 10 Vocabulary

You should be familiar with these terms as you prepare for the final exam.

  • adenine
  • amino acid
  • biotechnology
  • central dogma
  • codon
  • cytosine
  • DNA
  • gene
  • gene editing
  • gene expression
  • guanine
  • lagging strand
  • leading strand
  • mRNA
  • nucleotide
  • Okazaki fragments
  • phenotype
  • plypeptide
  • protein
  • regulation
  • ribosome
  • RNA
  • semiconservative
  • thymine
  • trait
  • transcription
  • translation
  • tRNA