Biology Class 4

Question 1

Virus

Answer 1

Obligate intracellular parasite

Question 2

Components of a virus

Answer 2

Head, Tail fibers, genome (nucleic acid)

Capsid (protein shell containing genetic information)

Question 3

Basic steps of Virus

Answer 3

1. Attachment (adsorption)
   - specific
   - host not yet infected
2. Injection (Penetration)
   - host is infected

Following this, one of 3 life cycles take place

Question 4

3 different life cycles

Answer 4

Lytic, lysogenic & productive life cycle

Question 5

Lytic Cycle

Answer 5

1. Transcribe & translate the viral genome
   Early genes: hydrolase, capsid proteins
2. Replicate the viral genome
3. Lysis of host & release of new viral particles
   Late genes: lysozyme

Question 6

Lysogenic Cycle

Answer 6

1. Integrate viral genome with hos genome
2. Normal host activity, including reproduction
3. Excision & lytic cycle

Question 7

Advantages to productive cycle

Answer 7

1. Protection from immune system
2. Easy infection (envelope can fuse with another membrane)
3. Get more virus (long life)

Question 8

Why does virus want to kill the hose genome in lytic cycle?

Answer 8

1. All cellular energy used to work with the viral genome

2. Create a pool of free dNTPs to use in viral genome replication

Question 9

Why does virus want to kill the hose genome in lytic cycle?

Answer 9

1. All cellular energy used to work with the viral genome

2. Create a pool of free dNTPs to use in viral genome replication

Question 10

While transcribing & translating host genome, how does the virus make sure its genome is not expressed in the lysogenic cycle?

Answer 10

Viral genome codes for repressors to make sure it’s not expressed

Question 11

Lysogen

Answer 11

When virus incorporated in the host genome, host is referred to as lysogen

Question 12

Provirus/Prophage

Answer 12

Host genome and viral genome are incorporated together

Question 13

Animal virus

Answer 13

Virus with an envelope (productive cycle)

Question 14

Subviral particles: Prions

Answer 14

Proteins (both good ones and mutant ones)
Characteristics:
- no DNA or RNA
- non membranes
- no organelles
- very small
- extremely stable

Question 15

How do mutant (bad) prions come?

Answer 15

1. Spontaneous mutation
   - mutation in gene coding for mutant prion and then prions accumulate & lead to cell death
2. Be genetically transmitted
   - can have bad prion & pass off to offspring
3. Ingested through diseased tissue
   - Healthy cell transcribing & translating normal “good” prion
   - Consumption of mutant “bad” prion from diseased tissue
   - Mutant “bad” prion changed normal “good” prions to bad ones
   - Cell death

Question 16

Subviral particles: Viroids

Answer 16

- virus-like
Characteristics:
- circular RNA
- no capsid
- must be coinfected
- don't code for proteins
- act as miRNAs or siRNAs to block translation

Question 17

Mechanism of viroid

Answer 17

Mechanism 1

1. +RNA circular form as template to make -RNA
2. -RNA linear form
3. Ligase to make a circular -RNA
4. Use -RNA as template to make +RNA
5. • RNA makes more circular +RNA viroids

Mechanism 2

1. +RNA circular form as template to make -RNA
2. -RNA is template to make +RNA linear form
3. Multiple +RNA linear form
4. Circularized to form more viroids

Both mechanisms equally preferred

Question 18

How viral genome (+RNA or -RNA) is made

Answer 18

Mechanism 1

1. +RNA (same as mRNA) can either be translated using host ribosomes to form viral proteins OR complementary form using RNA dependent RNA polymerase to make -RNA
2. Use RNA dependent RNA polymerase to make more +RNA
   * In this situation, the virus will code for the enzyme on its +RNA genome

Mechanism 2

1. -RNA available and you use RNA dependent RNA polymerase to make +RNA
2. +RNA is now available to translate using host ribosomes to make viral proteins OR to make complementary -RNA using RNA dependent RNA polymerase
   * In this situation, the virus will have to carry then code for the enzyme

Mechanism 3 (+RNA lysogenic)

1. +RNA that will create ssDNA using RNA dependent DNA polymerase
2. ssDNA will replicate using host DNA polymerase to make dsDNA
3. dsDNA can be inserted into host cell genome which can then be transcribed and translated using host enzymes to make viral proteins OR transcribed using only hosr RNA polyermases to make +RNA

Question 19

Problems with +RNA lysogenic

Answer 19

1. Very rapid mutation
2. Will permanently be in host genome

Ex. HIV

Question 20

Bacteria: Structure

Shape

Answer 20

1. Round - coccus
2. Elongated - bacillus
3. Spiral - spirochetes

Question 21

Bacterial: Structure

Flagella

Answer 21

____“trichous”

• mono (1 flagella)
• amphi (2 flagella)
• peri (multiple flagella)

Have basal unit connected to cell membrane
- hook is connected to basal unit
- flagella is connected to hook
As hook rotates, the cell moves

Question 22

Chemotaxis

Answer 22

Moving towards favourable chemicals & away from unfavourable chemicals

Question 23

Bacteria: Structure

Cell wall/ cell membrane

Answer 23

Gram positive - stains purple
- has cell membrane surrounded by thick cell wall
Gram negative - stains pink
- has thin inner cell membrane, then cell wall, then outer cell membrane

Question 24

Is gram + or gram - harder to kill with antibiotics?

Answer 24

Gram - because it has antibody degrading enzymes in periplasmic space (inbetween OM and IM)

Question 25

Mesophiles

Answer 25

Bacteria that live in medium temperature

Question 26

Psychrophiles

Answer 26

Bacteria that live in cold temperature

Question 27

Thermophiles

Answer 27

Bacteria that live in hot temperatures

Question 28

Faculative Anaerobe

Answer 28

Oxygen Present - use it to survive | Oxygen Absent - ferment & survive

Question 29

Obligate Aerobe

Answer 29

Oxygen Present - use it to survive | Oxygen Absent - Die

Question 30

Obligate Anaerobe

Answer 30

Oxygen Present - Die | Oxygen Absent - ferment & survive

Question 31

Tolerant Anaerobe

Answer 31

Oxygen Present: doesn't use it, but tolerates it to survive | Oxygen Absent: Ferment & survive

Question 32

Energy Sources | Photo vs Chemo

Answer 32

Photo - energy from Sun | Chemo - energy from ATP

Question 33

Where Carbon chains come from | Auto vs Hetero

Answer 33

Auto - CO2 (will build own sugar but needs carbon source) | Hetero - eats other critics

Question 34

Example of photoautotroph

Answer 34

Plants

Question 35

Example of chemoautotroph

Answer 35

Deep sea vent bacteria

Question 36

Example of photoheterotroph

Answer 36

Carnivorous plants

Question 37

Example of chemoheterotroph

Answer 37

Humans

Question 38

Carrying capacity

Answer 38

Maximum amount of bacteria an environment can sustain

Question 39

Phases of Reproduction

Answer 39

1. Lag Phase - little population growth, nothing happening except bacteria getting ready to split 2. Exponential/log phase - bacteria are happily dividing and growing 3. Stationary phase - reach carrying capacity, bacteria is unable to divide because nutrients are depleted and will be over crowded 4. Death - Cells die

Question 40

Binary Fission vs Conjugation

Answer 40

Will grow in population size, but no genetic diversity (phases of reproduction) Produce sexually - will have genetic diversity but no growth in population size

Question 41

Conjugation Process

Answer 41

F+ bacterium (male) that has genome & F plasm - F plasmid is for fertility - F plasmid has everything needed to create conjugation bridge /sex pilus to copy F plasmid into F- (female) - F- now becomes F+

Question 42

Transduction

Answer 42

Transfer genomic DNA from one cell to another by viral infection

Question 43

HFr Cell

Answer 43

- When F plasmid is incorporated into host genome - now called High Frequency of recombinant cell - will be copied over throughout genome and cross over resulting in recombination (increase in genetic diversity)