Ch 13

Steps in viral replication - FIVE steps

1. Attachment - random collision and attaches to receptor proteins on the host cell. The bacteriophage T4 has tail fibers that it uses for attachment to these receptor proteins. 2. Entry - the T4 virion uses enzymes to weaken the peptidoglycan in the bacterial cell wall and a tail sheath is used to inject the phage genome into the cell. This method allows the genome to be placed inside the cell without causing damage 3. Synthesis - of viral parts, requires enzymes that are either carried in the phage capsid or produced by the bacterial cell using genes from the viral genome. 4. Assembly - spontaneous process that occurs when the different viral parts, capsomeres etc. have been synthesized. If the capsid is assembled around pieces of the host DNA as well as the viral genome then transduction has occurred. 5. Release - accomplished in order for the newly produced virions to go on to other cells. For a bacterial cell this is done by destroying the integrity of the cell wall. The time from attachment to release is called the burst time and the number of viruses released from each cell is called the burst number.

Know the difference between a provirus and a prophage. Example: A virus is called a ________ when its DNA becomes incorporated into an animal host's DNA

A prophage is an integrated virus in a bacterial genome. A provirus is an integrated virus in a eukaryotic genome. Example: A virus would be called a provirus when its DNA becomes incorporated into an animal hosts dna

What is an extracellular virus called?

A virion - composed of a protein coat or capsid around the nucleic acid "core". Together they are sometimes called the nucleocapsid. Many animal viruses also have a phospholipid membrane called an envelope on the outside of the capsid which helps protect it and also helps it gain entry into the animal host cell.

What is an intracellular virus called?

A virus and consists of just the nucleic acid core.

Compare the differences in animal virus and bacteriophage replication.

Animal viruses go through the same stages of infection and replication that bacterial cells do. However, due to differences in bacterial cell structure and animal cell structure there are differences in the replication of animal viruses. The first difference occurs during attachment. Although animal viruses also attach using receptor proteins this is done using the glycoprotein spikes on their capsid or envelope. Enveloped viruses gain entry into the animal cell by fusing with the cell membrane resulting in a phagocytic process that brings the virion into the cell. or simply animal virus fuses with cell wall

Difference between oncogenes and proto-oncogenes.

Cancer is caused by uncontrolled cell growth. Genes control replication and reproduction of cell growth. Proto-oncogenes - cell division, "turned off" when not needed. Tumor repressor genes - inhibit cell division, stay turned on. When proto-oncogenes are not repressed, they are called oncogenes. Viruses can be activators of oncogenes. Viruses may cause cancer by acting as proviruses. Viruses can transport copies of oncogenes, promoting oncogenes or interfering with genetic expression.

Different forms of nucleic acid that a virus may contain (sRNA, etc.)

DNA or RNA but is not both in the same virus. double stranded (dsDNA; dsRNA) single stranded (ssDNA, ssRNA).

Understand the connection between HIV and retroviruses

HIV is closely related to simian immunodeficiency virus (SIV), a retrovirus found in chimpanzees and gorillas. Following retrovirus infection, reverse transcriptase converts viral RNA into proviral DNA, which is then incorporated into the DNA of the host cell in the nucleus. HIV is called a retrovirus because it works in a back-to-front way. Unlike other viruses, retroviruses store their genetic information using RNA instead of DNA, meaning they need to 'make' DNA when they enter a human cell in order to make new copies of themselves.

Explain how a latent virus can stay hidden and what causes a latent virus to be reactivated. Example: A known RNA virus was isolated from a patient with symptoms of an infection that could only be acquired in Asia. Upon further investigation the physician learned that the patient had returned from a trip to Asia 6 months prior to showing symptoms of the infection and within the last two weeks had been working overtime on a new project that he was in charge of. Use this information to answer the following question. The last step in a lysogenic cycle was caused by working overtime. What is this step called?

Induction

Describe how viruses can cause damage to the host cell.

Lysis, busts the cell open to spread more viruses that were created

Be able to describe and compare lytic cycle and lysogeny.

The lytic cycle involves the reproduction of viruses using a host cell to manufacture more viruses; the viruses then burst out of the cell. The lysogenic cycle involves the incorporation of the viral genome into the host cell genome, infecting it from within.

Prions

The term prions come from proteinaceous infectious agents. Prions are misfolded proteins with the ability to transmit their misfolded shape by using the prion PrP amino acid sequence as an enzyme to cause PrP to form Beta pleated sheets instead of the alpha helix. The protein PrP is the cause for prion diseases; there is not a nucleic acid involved. The PrP protein does not replicate, but rather causes a change in the normal amino acid sequence resulting in several prion infections. These diseases cause fatal neurological degeneration. Prion diseases as a group are referred to as spongiform encephalopathies because of the sponge like appearance of infected brain matter. Infections are slow to develop and usually go undiagnosed or misdiagnosed as acute onset dementia.

Explain how viruses cause cancer

There are several factors involved for cancer development. The activation of oncogenes, and the inactivation of oncogene repressors. Carcinogens and viruses play an important role in cancer formation. Viruses cause 20%-25% of human cancers. Viruses, specifically, have been known to carry copies of oncogenes as part of their genome and other viruses promote oncogene activity already present in the host cells. Viruses also interfere with oncogene repressors when they insert themselves into repressor genes causing the repressors to become inactivated causing oncogenes activation.

Terms connected with cancer such as tumor and neoplasm.

Tumor - uncontrolled growth benign tumor - one that stays in place and nor particularly harmful malignant tumor - tumor that has spread Neoplasm - what makes up the tumor. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and it persists growing abnormally, even if the original trigger is removed

How are viruses classified?

Type of genetic material they contain, the size and shape of the virus and the presence or absence of an envelope. Viruses have been grouped by families but not all the orders needed to classify them have been established.

Explain the difference between viroids, prions and viruses.

Viroid- small pieces of RNA that infect plants Prion-proteinaceous agent Virus- Fully formed agent

Viral parts and function

Viruses are acellular, obligate intracellular parasite. Composed of single or double stranded DNA or RNA, have no cytoplasmic membrane, cytosol, or organelles (one exception). Because they are acellular, they "kidnap" the host cells metabolic pathways to be used for their own survival and replication

Be able to recognize when RNA virus has become part of host DNA.

lysogenic conversion (In this way the prophage DNA will be replicated each time the bacterial cell DNA is replicated. If the lysogenic phage changes the phenotype of the bacterial cell the process is called lysogenic conversion. Sometimes lysogenic conversion results in a more virulent bacterial cell.)

Viroids

viroid - plant pathogen that goes by same name inside and outside of host cell. Viroids are tiny circular pieces of infectious RNA that often appear linear because of the hydrogen bonding within the molecule. Viroids do not have a capsid and infect plants. Viroid-like agents are particles or RNA that do not have a capsid but infect fungi instead of plants.