#ch1820

Chapter 18: Regulation of Gene Expression

Describe the structure of an operon. Include a model with your discussion.

[Source: Pearson Education, Inc.]

An operon is the entire stretch of DNA that includes the promoter, operator, and the genes that they control. 

Compare and contrast an inducible operon and a repressible operon. Include an example of each.

An inducible operon is usually “off” since it is, hence its name, able to be induced. An example of an inducible operon is the Lac operon that produces enzymes to break down lactose. In order to turn it “on” and make it active, a corepressor must be removed. (A corepressor is a moleule that cooperates with a repressor protein to switch an operon off). On the other hand, a repressible operon is usually “on”. In order to turn it “off”, a corepressor must be added. An example of a repressible operon is the Trp Operon. 

Explain the role of repressor genes in operons and why they are important.

Repressor genes prevent transcription/expression of the operon gene by binding to operator region on the operon. Additionally they prevent the RNA polymerase from synthesizing the operon gene.

Describe the impact of DNA methylation and histone acetylation on gene expression.

In histone acetylation, acetyl groups are attached to positively charged lysines in histone tails which loosens chromtin structure. This is useful since genes within highly packed heterochromatin are usually not expressed, and histone acetylation allows those to be demonstrated. In DNA methylation, the addition of methyl groups to certain bases in DNA is associated with reduced transcription in some species and causes long-term in activation of genes in cellular differentiation.

Compare and contrast the role of oncogenes, proto-oncogenes, and tumor suppressor genes in cancer.

Oncogenes are cancer causing agents, whereas Proto-oncogenes are the corresponding normal cellular genes that are responsible for normal cell growth and division. Tumor-suppressor genes help prevent uncontrolled cell growth, repair damaged DNA, control cell adhesion, and inhibit the cell cycle in the cell-signalling pathway. 

Chapter 19: Viruses

Develop a model and explain the components of a virus.

[Source: Untraceable]

Viruses are very small infectious particles consisting of nucleic acids enclosed in a protein coat and, in some cases, a membranous envelope. (Viral genomes may consist of either double or single stranded DNA or RNA). The shell built from protein subunits called capsomeres that covers the viral genome is called a capsid.

Compare and contrast the differences between lytic and lysogenic life cycles of a virus.

The lytic cycle is a phage reproductive cycle that results in the death of the host cell. It does this by producing new phages and digesting the host’s cell wall, releasing the progeny viruses. (A phage that only reproduces by the lytic cycle is a Virulent phage). The lysogenic cycle replicates the phage genome without killing the host. By this, the viral DNA molecule is incorporated into the host cell’s chromosome. Every time the host divides, it copies the phage DNA with it and passes the copies to daughter cells. (Phages that use both the lytic and lysogenic cycles are called temperate phages).

Chapter 20: DNA Technology and Genomics

Briefly discuss the following genetic engineering techniques - include a model of each and explain how each can be used to manipulate DNA

Gel Electrophoresis

[Source: Encyclopedia Britannica, Inc.]

An indirect method of rapidly analyzing and comparing genomes is gel electrophoresis. It uses a gel as a molecular sieve to separate nucleic acids or proteins by size. Current is applied across the gel and since DNA is negatively charged, it is attracted to the positive side of the gel. Molecules are sorted into “bands” by their size (shorter molecules move farther).

Plasmid-based Transformation

[Source: Universtiy of Walkato]

Plasmids can be used as vessels to carry foreign DNA into a cell. Once a DNA sequence of interest is cut by restriction enzymes, the two newly paired DNA sequences are joined by DNA ligase and the transformed plasmid is now ready for insertion into a host cell. Once inside the cell, the plasmid is copied by the host cell’s own DNA replication machinery and can be implemented in the cell.

Polymerase Chain Reaction (PCR)

[Source: Pearson Education, Inc.]

The polymerase chain reaction (PCR) can produce many copies of a specific target segment of DNA. A three-step cycle--heating, cooling, and replication--brings about a chain reaction that produces an exponentially growing population of identical DNA molecules.

Restriction Enzyme Analysis of DNA

[Source: Pearson Education, Inc.]

In restriction fragment analysis, DNA fragments produced by restriction enzyme digestion of a DNA molecule are sorted by gel electrophoresis. It is useful for comparing two different DNA molecules, such as two alleles for a gene. (Can also be used to prepare pure samples of individual fragments).

Develop a model involving the steps in gene cloning with special attention to the biotechnology tools that make cloning possible.

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This is a diagram of molecular cloning using bacteria and plasmids. Even though it is not my own model, I feel like this model is so much more intricate than anything I could attempt to make by the due date of this portfolio.Therefore, I offer this as my model, since I really did learn a lot from it.

Explain the key ideas that make PCR possible.

The method relies on a thermal cycle, consisting of cycles of repeated heating and annealing of the reaction for enzymatic replication of the DNA. As the polymerase chain reaction progresses, the DNA generated is used as a template for replication, which begins a chain reaction in which the DNA template is increasingly amplified. 

Develop a model and explain how gel electrophoresis can be used to separate DNA fragments.

[Source: GBS IB Biology]