Cell Diversity, Viruses, Membranes (Lecture 14)

Question 1

What is the cell?

What is the genome?

What do cells arise from?

Cells are _______ & _________

Answer 1

• The cell is the structural unit of all living organisms
• The genome is a dynamic information system
• Cells arise from the division of pre-existing cells (NO spontaneous generation!)
• Cells are complex and organized

Question 2

How can amino acids be synthesized?

Where do chemical reactions occur?

Answer 2

• Amino acids can be synthesized in the lab under conditions mimicking early Earth (anaerobic)
• Chemical reactions occur in selectively permeable compartments to provide homeostasis

Question 3

What are the two classes of cells on Earth?

Answer 3

• Eukaryotic
  
  • Protists, fungi, plants, animals
  • Structurally more complex
• Prokaryotic
  
  • Bacteria, archaea
  • Structurally simpler

Question 4

The cell and its parts

Label the diagram

Answer 4

Question 5

• Cells are _______ _______ & ________
  
  • Cellular organization is very ________
  • _________ throughout evolution

Answer 5

• Cells are highly complex and organized
  
  • Cellular organization is very consistent
  • Conserved throughout evolution

Question 6

Viruses

What are viruses?

What is a virion and what is it made of?

Answer 6

• Viruses are NOT cells
• Viruses are macromolecular packages that can function and reproduce only within living cells
• Outside of cells, a virus exists as an inanimate particle (= virion)
• A virion is made of
  
  • A small amount of DNA or RNA (encoding a few to hundreds of genes)
  • Protein capsule (= capsid)

Question 7

Viruses

What is TMV?

Answer 7

Tobacco Mosaic Virus (TMV)

• one of the first viruses to be characterized

Question 8

What are two characteristics of viruses?

Answer 8

1. Viruses are very small
2. Viruses are very diverse

Question 9

What are 6 examples of viruses?

Answer 9

1. SARS CoV-2
2. Hepatitis B
3. Ebola Virus
4. Adenovirus
5. Influenza
6. Bacteriophage

Question 10

The basic structure of viruses

Label the diagram

What can viruses affect?

Answer 10

Viruses can affect animals, plants, and bacteria

Question 11

Bacteriophage attacking bacteria

Answer 11

Transmission electron micrograph of multiple bacteriophages attached

to a bacterial cell wall.Magnification ~ 200,000x.

Question 12

Virus Host Range

Where do viruses bind to?

What does this define?

Name and give an example of the two host ranges

Answer 12

• Viruses bind to cell surfaces via specific proteins and then enter into the cell
• This defines the cell types the virus can infect and the host range:
• Narrow host range
  
  • e.g., human cold and influenza viruses infect epithelial cells of

human respiratory system

• Wide host range - like rabies
  
  • can infect cells in dogs, foxes, bats, raccoons, and humans.

Question 13

What happens to the virus once it’s inside the cell?

What does it assemble?

Answer 13

• Once inside a cell, the virus hijacks cellular machinery to synthesize nucleic acids and proteins
• Assembles new virus particles

Question 14

What are the two main types of viral infection?

Answer 14

1) Lyctic: production of virus particles ruptures (and kills) cell (e.g. influenza)
2) Non-lyctic or Integrative or Lysogenic:

• viral DNA is inserted in a host genome = Provirus
• a cell can survive, often with impaired function (e.g HIV)

Question 16

What are the 7 stages of a virus life cycle?

Answer 16

1. Virion attaches to host cell
2. Virion penetrates the cell and its DNA is uncoated
3. Early transcription and translation; enzymes are synthesized
4. Late transcription; DNA is replicated
5. Late translation; capsid proteins are synthesized
6. Virions mature
7. Virions are released

Question 17

What is papovavirus?

Answer 17

Papovavirus: large family of viruses, includes human papillomavirus (HPV)

Question 18

Virus Life Cycle

Explain the process of the virus life cycle

Answer 18

The virus is enveloped which means it has a membrane around it. It still contains a genome represented by the red squiggle. They have proteins that stick out and interact with other proteins on the host cell. This interaction causes the plasma membrane to fold and engulf the virus. The virus is now in the membrane, this structure is called an endosome. This helps the virus separate from its envelope and now we have this protein and nucleic acid, this uncoats and the genome goes to make more capsid protein. Now it goes to make this envelope protein and make more copies of its genome. As it leaves the cell it gets its envelope, it pushes its way through the cell, and in the process, it takes a piece of the cell, the host cell with it.

Question 19

What do viruses steal from the host that they do not make themselves?

Answer 19

The envelope comes from the host, viruses do not make plasma membrane.

Question 20

Rabies virus

What are the main points?

Answer 20

• This virus as it leaves the cell goes through a part of the membrane where there are viral proteins embedded, and it used the apparatus of the host to put those proteins there

Question 21

Biological membranes

What do these membranes look like?

• Micelle
• Liposome
• Bilayer sheet
• Fluid membrane model

Answer 21

Question 22

What are the 6 functions of biological membranes?

Answer 22

* cell boundary *

• define /enclose compartments
• control movement of material into/out of cell *
• allow response to external stimuli *
• enable interactions between cells *
• provide scaffold for biochemical activities **

* plasma membrane only
** including energy transduction

Question 23

Electron micrograph of a muscle cell

The plasma membrane

Answer 23

Question 24

What is the structure of the plasma membrane?

What can this be related to?

Answer 24

Trilaminar and it is ≈ 6nm thick

This can be related to an oreo cookie.