Download Biology: Cells and Organisms Notes

Biology: Cells and Organisms Notes
Lecture 1
The cell theory says that:
Evolution – the great unifying theory of biology:
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That the earth has a long history.
All living organisms arose in the course of this history from earlier, more primitive forms.
As a consequence of this theory, all organisms are related or share a common ancestor.
As such – all life shares biochemical processes – also, all organisms have cells
Oldest life known – fossilised cyanobacteria in Grand canyon parallel to Stromatolites in WA
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Living matter is composed of cells;
The chemical reactions of living
organisms take place in cells;
Cells only arise from other cells;
Cells contain the hereditary
information of the organism of which
they are a part, and this information
is passed from parent cell to
daughter cells.
Lecture 2
Prokaryotes
– First inhabitants of earth, primitive compared to highly complex eukaryotes.
Eg/ Cyanobacteria – contain chlorophyll a – first to photosynthesise and produce oxygen.
This caused an increased level of oxygen in the atmosphere, decreasing UV due to O2 to O3 conversion which protected and
facilitated life.
Prokaryotes – contain no organelles or nucleus, have circular DNA as a single molecule, and have specifically prokaryotic
ribosomes. Cell is surrounded by selectively permeable plasma membrane and peptidoglycan wall. Size ranges from 1 to 10
micrometres.
Bacteria – produce resting spores that can be dormant for long periods –
spores can then wake and become functioning bacteria. Divide extremely
fast – only have 0.1% the amount of DNA as eukaryotes – divide every 20
minutes.
Prokaryotes can survive in almost every niche on earth as they have a high
diversity of biochemical processes and tolerances.
The flagella of a prokaryote are a single protein – flagellin, a sheath and a
rotary motor.
Prokaryotic cellular division is Binary fission STEPS:
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3.
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Replicates genome that is always attached at plasma membrane
The two loops of DNA are attached at different points
Cell wall and membrane grows in between, pulling apart DNA loops
Cell wall splits – results in two equally sized prokaryotes. – FtsZ protein
Two super kingdoms – Prokaryote (Archaea, Bacteria) and Eukaryote.
Differences between Archaea and Bacteria:
Morphologically similar
Over half of Archaean genes were new to science when discovered
Biochemically very different
Transcription and translation more similar to EU than BA – Eg/ use Methionine as staring amino acid
Lack peptidoglycan wall, they have different features of lipids
Don’t produce resting spores
Found everywhere (thought they were only extremophiles)
There are NO KNOWN Archaean pathogens
Archaeans have histones linked to their DNA
Not affected by antibiotics
Phylogeny of superkingdoms:
Root
Bacteria
Archaea
Eukarya
Bacteria:
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Ubiquitous and metabolically diverse
Cause of many diseases
Decomposers, recyclers – critical roles in removal and waste decontamination
Nitrogen fixation in root nodules
Have many biotech applications
Lecture 3
Eukaryotes - Organelles
Nucleus
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Contains DNA
Covered in pores (~75nm in diameter) for communication
Contains nucleoli (packets of jumbled protein and RNA – contain ribosome genes – transcription occurs here)
More nuclear pores if highly active and connect outer and inner membranes of nuclear envelope (continuous). Pores are
selective – RNA passes through. Long strands of DNA are covered in globular proteins – histones. DNA double wraps
around histone to form a nucleosome. Histones are +ve, DNA –ve. A core of histones = several nucleosomes.
Euchromatin – loosely packed DNA so it can be accessed / Heterochromatin – tightly packed chromosome.
Mitochondria –cell powerhouse
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Cells may have several hundred, or a single large one
Contains its own circular DNA and ribosomes(prokaryotic)
Surrounded by two membranes, outer and highly convoluted inner (cristae – SA)
Carry out aerobic respiration of all eukaryotes
Inner membrane – matrix- many enzyme complexes
Intermembrane space has very different environment
Mitochondria are highly dynamic, always moving around a cell.
Chloroplasts
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In plant cells – one or many
Outer and highly folded inner membrane – forms complex internal thylakoid network, stack to form grana
Responsible for photosynthesis – produces sugars.
Only chlorophyll a can be used for PHS, accessory pigments transfer energy to CPA
Has own circular DNA and prokaryotic ribosomes.
Origin of Plasmids – mitochondria and chloroplasts
Plasmids are believed to be derived from relic endosymbionts. M – Purple bacteria, C- cyanobacteria. Basic process of
endosymbiosis – primitive eukaryote absorbed prokaryote was not digested, survived in eukaryote – formed into organelle.
Mitochondria from primary endosymbiosis, Chloroplasts from secondary – Primary: A absorbs B, does not digest, mutual
benefit – some DNA lost to host nucleus – therefore not completely autonomous. Secondary: Eu A absorbs Eu B, steals and
uses its organelles.
Evidence for primary endosymbiosis is that some chloroplasts have been found to still have a bacterial peptidoglycan wall
between the inner and outer membranes (in cyanophora).
For secondary endosymbiosis – some chloroplasts found to have 3, or even 4 outer membranes (membrane from original
engulfed cell). Organisms that carry this out are protistan pirates.
Other evidence includes degenerated peptidoglycan wall around chloroplasts of cyanophora, and in cryptomonads there is
a second, degenerated nucleus (nucleomorph).