Archaeal origins of the cell Flashcards
What is archaea?
It is one of the three domains of life, along with bacteria and eukarya. Initially, it was grouped together with bacteria but was later separated due to differences in genetic make up and biochemistry
Which features of archaea are bacteria-like
- phenotypically they are a lot like bacteria. They both are small (0/-.5-5 microns) and exist in various shapes such as rod, spherical, filamentous and cocci.
- cell structure: single-celled and lack membrane-bound nucleus and other organelles.
- Genome: the size of most archaea is 2.4 Mbp, similar to bacteria.
- they are both ubiquitous, found in diverse environments
- have a cell wall
- asexual reproduction such as binary fission
- grow rapidly
Which features of archaea are eukaryotic-like?
- Histones
- RNA polymerase (evolutionary link)
- RNA processing (addition to 5’ cap and poly A tail to mRNA)
- Introns
- Initiation of DNA replication (proteins)
- Ribosomal proteins
Name the four archaeal superphyla
- Euryarchaeota
- Proteoarchaeota (TACK)
- Asgard
- DPANN (diapherotrites, parvarchaeota, aenigmarchaeota, nanohaloarchaeota and nanoarchaeota)
Why are Asgard archaea thought to be the ancestors of the eukaryotic cell?
- Asgard genomes have been found to be have ESPs (eukaryotic signature proteins)
- These asgard ESPs are involved in important eukaryotic functions such as:
- membrane trafficking
- vesicle formation and transport
- ubiquitin network
- cytoskeleton formation - This suggests that asgard archaea have eukaryotic intracellular membrane network as well as cytoskeleton system
Which is the family of Asgard archaea that is closely associated to eukaryotes?
The family of asgard archaea that is genetically similar to eukaryotes is called “lokiarchaeota” and it has been speculated to be the ancestors of eukaryotes.
How is the family of proteins found in asgard archaea called?
The asgard archaeal proteins are called Eukaryotic signature proteins (ESPs)
Which functions of these proteins are important for a eukaryotic cell?
These are involved in:
- Membrane trafficking
- Ubiquitin network
- Cytoskeleton formation
- Vesicle formation and transport
Explain hydrogen hypothesis
- A hypothesis that is based on endosymbiont theory, given by muller and martin in 1998.
- proposed explanation for the origin of the first eukaryotic cell, suggesting a symbiotic relationship between two different kinds of cells that led to the formation of a eukaryotic cell
- which cell was the host cell
- which cell was the symbiont
- why did the host cell take up another cell
- a primitive archaeon, asgard archaeal cell, whose energy source was hydrogen and anaerobic
- anaerobic bacterium, alphaprotobacterium, which was respiration-competent, it could use hydrogen for photosynthesis
- the host cell took up this symbiont so that it could produce food using hydrogen which later evolved into the mitochondria
What methods are used to investigate into which cell compartment proteins are transported?
There are two main approaches:
1. In-silico-approaches:
Bioinformatic programmes are used for determining the sub-cellular locations of the protein:
a. ChloroP
b. Target P
c. Predotar
d. Psort
- Experimental:
a. In-vitro import assays:
b. GFP fusion proteins
Why are plant mitochondrial genomes so big?
- large introns and intergenic regions
- large non-coding sequences
- repetitive elements such as tandem repeats and dispersed repeats
- genes are derived from plastids, viral and nuclear DNA and from other unknown sources, which are transcribed but they do not function.
How does the cell know to which cell compartment proteins have to be routed?
- Signalling sequences: cellular compartments recognise specific signalling sequences, NLS, MTS and ER sequences.
- Protein sorting machinery: nuclear pores and translocons of ER
- Gated transport: nuclear pores and receptors on mitochondria (MTS)
- chaperone proetins
- vesicular transport:
- Protein-protein interactions
