basic 2 Flashcards
life is
Self assembly of parts
Growth
Replication
Catalysis
Emerging properties
Fidelity of process - Robustness
How did the first living cells appear?
Abiotic (nonliving synthesis of small organic molecules such as amino acids and nucleotides.
The joining of small molecules into macromolecules such as simple proteins and nucleic acids.
The packaging of these molecules into “protobionts”, droplets with membranes that maintaining internal chemistry different to environment.
The origin of self replicating molecules that made inheritance possible.
Cell evalution
A primitive cell developed internal membranes to become the ancestral eukaryote – able to engulf other organisms
It incorporated a respiratory prokaryote – which evolved into the mitochondrion (Ancestral heterotrophic eukaryote> animal)
Some of the mitochondria-containing eukaryotes took up another prokaryote – a photosynthetic organism resembling present-day cyanobacteria.
(This prokaryote evolved into the chloroplast) (Ancestral photosynthetic eukaryote > plant)
the endosymbiotic theory is correct ?
Chloroplasts and mitochondria have their own DNA (circular, no histones), distinct from that of the cell nucleus, and are inherited maternally
Ribosomes are present in chloroplasts and mitochondria. These are smaller than those in the cytoplasm of the cell, but the same size as those in bacteria
Mitochondria are sensitive to the same antibiotics as bacteria eg chloramphenicol.
Both are enclosed by a double membrane. The outer one from the host cell, the inner from the invader.
Both reproduce by division, independently of nuclear division, like bacteria
Cyanobacteria
the prokaryotes that resemble chloroplasts in evolving oxygen, and in their photosynthetic pigments. The cyanobacterium Prochloron resembles chloroplasts more closely than do other cyanobacteria. It lives inside ascidians (sea squirts)
Evolving chloroplasts lost genes
Free-living cyanobacteria possess 3,000 genes, a chloroplast has only 100–200 genes
When the prokaryote took up residence in the host, many genes, such as those coding for cell wall synthesis, were lost; many indispensable genes relocated to the plant cell nucleus: several thousand nuclear genes encode chloroplast proteins .
Sex among the hosts allowed them to share transferred genes; but the chloroplast genes now nuclear needed to express proteins in the chloroplast. To do this the gene was modified by adding a chloroplast-targeting sequence.
Hatena
unicellular organism with a symbiotic unicellular alga inside
The photosynthetic symbiont cell retains its nucleus, mitochondria(on), plastid, and occasionally a vestigial Golgi body, but the flagella, cytoskeleton, and endomembrane system are lost.
When the host cell divides one daughter cell retains,
the other loses the photosynthetic symbiont
Hatena – the life cycle
the host one daughter cell loses its endosymbiont - it has to capture a new one when it is in the heterotrophic phase.
Thus Hatena alternates between a host phase that harbours a green symbiont and a predator phase that acquires the symbiont
In the autotrophic phase the host is guided to the light by an eyespot on the engulfed alga; in the autotrophic phase it has a feeding organ.
Variations on the chloroplast theme: different kinds of plastids
Leucoplasts
Chloroplasts
Chromoplasts
Proplastids
Have DNA, but few structures
In meristematic tissues
Leucoplasts
Colourless, storage plastids Starch (amyloplasts) protein, or oil droplets contain DNA, ribosomes In storage organs seeds, tubers.
Chloroplasts
Chlorophyll, photosynthetic system, well developed membranes, may contain starch.
In leaves and other green parts of plant
contain DNA, ribosomes
Chromoplasts
lipid soluble yellow, red or orange pigments (carotenoids)
In fruits and flowers
contain DNA, ribosomes
Development of plastids from a proplastid:
Proplastid with double membrane
> Formation of vesicles from ingrowths of the inner membrane
> Vesicles lining up in rows
> Coalescence of vesicles to form granal stacks
Mature chloroplast
> Chromoplast formed directly from a proplastid or by reversible redifferentiation of an amyloplast or chloroplast
.> Amyloplast formed directly from a proplastid
As cells grow, vacuoles size
As cells become very large,
increase and it coalesce (join)
the vacuole occupies most of the interior. Most activity is confined to a thin layer of cytoplasm below the cell wall.
