Lecture 6: Biological agents as causes of disease

Question 1

___ are the ultimate pathogen

Answer 1

viruses

Question 2

viruses consist of

Answer 2

a simple genome encapsulated in coat protein - called a capsid. This may be enveloped in a membrane.

Question 3

DNA virus life cycle

Answer 3

• entry
• uncoating
• transcription and translation
• genome replication
• assembly
• exit

Question 4

Most viruses rely entirely on the ____ cellular machinery to make new viruses.

Answer 4

HOST

Viruses often shut down most cellular processes that are unrelated to their replication: inhibitory factors stop host-cell DNA, RNA, and protein synthesis.

Question 5

some viruses integrate as __

Answer 5

DNA into the host genome for a period of quiescence or latency.

Question 6

Viruses edit the cell either when

Answer 6

it lyses (dies) or by budding in the case of enveloped viruses

Question 7

viruses are classed by their

Answer 7

genome type and how their mRNA (+ strand ) is made

Question 8

Virus 1

Answer 8

DNA virus, RNA & DNA strand. (+&-) –> mRNA
Most similar to normal cells
Adenoviruses:respiratory disease, conjunctivitis
SV40 (simian virus 40)
Herpes viruses: chicken pox, herpes sores, carcinomas
Papilloma viruses: genital warts, cervical cancer

Question 9

Virus 2

Answer 9

DNA virus, DNA or RNA –> DNA & RNA –> mRNA.

Question 10

virus 3

Answer 10

RNA virus, DNA & RNA (+&-) –> mRNA

Segmented genomes (several pieces) 
Rotavirus: acute gastroenteritis

Question 11

virus 4:

Answer 11

RNA virus, RNA (+) –> DNA (-) –> mRNA
mRNA makes polyproteins that are cleaved
Polio viruses, Toga viruses: yellow fever,
SARS viruses

Question 12

virus 5:

Answer 12

RNA virus. DNA (-) –> mRNA

V The virion carries RNA transcriptase
“RNA-dependent RNA polymerase”
Ebola viruses, Influenza viruses
Paramyxoviruses: measles

Question 13

virus 6:

Answer 13

RNA virus, RNA (+)
–> DNA (-) –> double stranded (=&-) –> mRNA (+)

VI Retroviruses - enveloped - reverse transcriptase
human T-cell lymphotrophic viruses: leukemia
human immunodeficiency virus: AIDS

Question 14

virus 7

Answer 14

VII Double stranded DNA and Reverse transcriptase
DNA is made into genomic RNA
Hepatitis B Virus

Question 15

Viruses have different entry strategies:

Answer 15

Like bacteria, viruses rely on receptors present on the host’s surface to gain entry into the cell. Check points at each step ensure that the next phase of entry is not entered prematurely
(4 different types)

Question 16

DNA viruses: Papillomaviruses virus causes

Answer 16

6% of al human cancer in the world. Pap smear allows early detection and curative treatment

Question 17

DNA viruses: Papillomaviruses virus results in malignant tumour how?

Answer 17

Proteins produced by the viral genome upregulate DNA replication and proliferation by the host cell to allow more production of viral genome.

Accidental integration of the virus can result in too much proliferation and is the first step in malignant tumour formation.

Question 18

DNA viruses: Papillomaviruses virus genome contains several __

Answer 18

oncogenes

Question 19

human genome is

Answer 19

3 billion bp

Question 20

E6 & E7 in human genome normally act by

Answer 20

turning up the hosts DNA replication machinery - to make more virus, not necessarily more host cells.
Transformation results when the viral genome is integrated into the hosts genome and malfunctions producing too much E6 and E7. This results in unregulated cell proliferation.

Question 21

DNA viruses: E6 and E7 take the brakes off

Answer 21

of host cel proliferation

Question 22

E6 & E7 bind to..

Answer 22

the host proteins Rb and p53 to inactivate them. This release constraints on DNA replication. Mis-regulation of Rb and p53 is often involved with other viral as well as non-viral cancers.

Question 23

retroviruses cause cancer by

Answer 23

incorporating human genes into their genome

Question 24

oncogene:

Answer 24

a gene which in certain circumstances can transform a cell into a tumour cel

Question 25

Retroviruses usually cause cancer by incorporating human..

Answer 25

proto-oncogenes into their genome. This is thought to occur when mistakes are made during integration of the viral genome into the host genome.

The genes are usually altered when incorporated into the viral genome. They referred to by a v- prefix:
v-abl (viral)
c-abl (host gene also called proto-oncogenes)

Question 26

proof of retroviruses incorporating human genes:

Answer 26

Inoculation of 150 mice with MuLV results in one with a tumour. When MuLV is isolated from this mouse it has changed to Ab-MuLV.

Question 27

porto-oncogenes are proteins involved with

Answer 27

cell proliferation

Question 28

Most retroviruses that cause tumours have

Answer 28

oncogenes.

Question 29

Many viral oncogenes are also involved with

Answer 29

non-viral cancers

Question 30

c-src is a kinase that is powerful activator of

Answer 30

cell proliferation. Normally the cell down regulates c-src activity by phosphorylating one end of the protein (puts the brakes on). This causes the protein to fold on itself to become inactive

Question 31

v-src does not have the

Answer 31

c-terminus - this change creates the oncogenic form of src.

Question 32

Many oncogenes encode

Answer 32

host kinases which have lost regulation by fusion to viral genes or deletion of regulator sequences.