What are the main macromolecules and what are their functions?
- nucleic acids: carry genetic information
- proteins: enzymatic and structural
- lipids: structure and energy; delineate inside of cell with outside
Can these macromolecules have other functions?
RNA can do all of the same things as NAs, proteins, and lipids
- RNAs can store information
- RNAs can fold and have enzymatic activity
- Through base pair binding, they can have more ordered structures
For the reason that RNA can have several functions, what is believed?
It is believed that RNA can behave as self-replicating molecules. Before we had modern cells, we had RNA that catalyzed certain cells.
Today, nothing that is alive only has RNA. Everything alive on earth has cells and different macromolecules. But, some RNA viruses don't have any DNA. They have RNA as a genetic material
Central dogma then vs. now.
Then: RNA makes RNA, which continues to make more RNA
- Now: DNA makes RNA, which makes protein
- It is information storage--> information storage/ information transmitter--> function
The first steps in the development of life on earth: __.
-- __ and __ may have originated in the __.
the RNA world
Viroids and RNA viruses
We believe that RNA viruses are hte first group of viruses to evolve. What are the second group of viruses we believe to have evolved?
Transposable elements: it is a gene that is capable of moving itself around within a genome. Some make copies of themselves; some excise themselves, with the use of a transposon enzyme, and end up somewhere else
ex: domesticated grasses
Why are transposons a great way of allowing evolution/
When you move genetic elements around, you change the gene or interrupt it, thus altering the structure and function of proteins. This allows for the devleopment of diversity.
A lot of elements act as transposons. Explain.
A transposon gene gone rogue will turn itself into a virus. If the transposon was on all the time and didn't care about the host genome, it will replicate itself and become viral.
What was the third time we thought viruses evolved?
Evolved in terms of pathogen size.
For a long time, it was known that even the largest virus was simpler than the smallest bacterial cell.
The transition to the DNA-based world
- __ could have arisen as independently replicating genetic elements in cells
Small and medium-sized DNA viruses
Why is the idea that viral genomes were extremely small being refuted?
we are now finding viruses that are turning the information on its head.
Ex: chlamydia is one of the smallest bacteria with a smallgenome. Pandoravirus, on the other hand, is more than twice the sie of a known living bacterium. Its' actually larger than some bacteria and infects single celled organisms
Virus structure-- how similar are they?
All viruses have a capsid. Nucleic acid alone is not a virus. it needs a covering.
There are one or a small number of proteins that fit together to fit and protect the genome to give it a higher order structure
The capsid can have a lipid envelope covering it
Capsid+ nucleic acid= virion
What do capsids do?
package viral genomes and transmit them to a new host cell
rigid, symmetrical container composed of viral protein
capsid with enclosed genome
complete, infectious virus particle possibly including an envelope
What is a common theme in virology? Explain.
Viruses are small and have small genomes with limited genes
They work on borrowed time since speed is of the essence. Many viral capsids are made of one or a small number of proteins and have self-assembly capabilities to eliminate the need for a lot of energy and time
Many viruses come in __. What are the characteristics of capsids?
simple, symmetrical packages
- genomic economy
- identical subunits
composed of many copies of identical subunits
can assemble spontaneously
give the capsid symmetry
- shape= the geometry of its outline
- symmetry= rotational and translational operations that describe it
What are the two types of symmetry?
- icosahedrom= a shape with 20 triangular faces/ a 3D polygon made out of these triangles
- icosahedral capsids have 5-fold, 3-fold, and 2-fold rotational axes
Simpler capsids have ___.
More complex capsids have ___.
- repeating subunits with identical interactions
- repeating subnits interactions in a quasi-equivalent manner
The more subunits, what?
the greater the ability to stretch the capsid structure while keeping it regular and symmetrical
How many subunits can be accommodated on teh capsid surface?
Quasi-equivalent icosahedral structures are composed of subunits present in multiples of 60 (60 x T)
T= triangulation number= total number of subunits that make of the virus
The simples virus has a T of 1. So, 60 subunits make up the capsid
Larger viruses, due to their ability to make them, come in more complex packages. Explain.
Their capsids contain two types of structural subunits: hexons and pentons
Different than t numbers
Other structures, large and small, display __.
The other type of symmetry is __. Explain.
- helical symmetry
- organized as helical tubes composed of identical, repeating subunits that rotate around endlessly, protecting genetic material that is on the inside
- derived from __ and are composed of __.
- They can __.
- cellular membranes
- lipid bilayers (with the same composition as the cell membrane from which they were derived) and viral glycoproteins (from host ER that virus uses to get inside others)
adopt a variety of shapes
How are viral envelopes obtained?
by a process called budding
- - viral glycoproteins are inserted into membrane
- - nucleocapsids associate with glycoprotiens and get wrapped in membrane
Capsid assembly occurs in a variety of ways. What are they?
- Some form and then pull their genes in
- Some form around genes
- Some make scaffold/intermediate proteins, which assist with formation of pro-capsid and are not in the final, mature virion
Multiple modes of capsid assembyl exist depending on:
- size, shape, and complexity of capsid
- genomic composition
Specific packaging signals do what?
__ may accompany the viral genome inside the capsid.
Formation of viral envelopes by __ is driven by __.
direct incorporation of viral genomes into virions/ some viruses don't care which genes are incorporated. Otehrs are very specific
budding/ interactions between viral proteins
- envelope like; wormlike; on the inside, its RNA genome is protected by a nucleocapsid protein
- Other nucleocapsids are used to protect the RNA; it also signals when to step in and out of the life cycle stages
Two human viruses: __ and __
some can give you diseases like polio
They are naked, unenveloped viruses with RNA and a protein shell.
viruses that give you Yellow Fever, etc
They almost look exactly like picornaviruses. They have a capacity to select their genes