Properties of Optical Microscopes
- Image: Colour; 2D, Low resolution
- Specimen: alive or dead
- Prep: cheap, quick, easy (precision not required); uses stain, mobile
- Method: Light
Properties of Transmission Electron Microscopes
TEM
- Image: B&W, 2D, high resolution (e- = low λ), denser areas absorb more e- so darker, detailed organelle structure
- Specimen: Dead (thin)
- Prep: expensive, specialist skills required, metal coating (imprint), large/immobile
- Method: e- beam (fast) through electromagnetic lenses λ=h÷p; beam passes through sample
Properties of Scanning Electron Microscope
SEM
- Image: 3D, B&W, high res, detailed organelle structure
- Specimen: dead (very thin),
- Prep: expensive, specialised skills, metal coating, large/immobile/high power
- Method: e- beam (fast) through electromagnetic lenses λ=h÷p
SEM vs TEM
Microscopes
- image: 3D surface vs 2D internal cross section (atomic)
- electrons e- reflected vs passed through
- specimen: thin vs ultra thin
- magnification & resolution: lower vs higher
- BUT both have similar limitations: B&W, complex prep, sample dead in vacuum, artefacts present
slightly unecessary
Ultracentrifugation steps
- Spin at low speed
sediment = nucleus - Spin supernatant at higher speed
sediment = chloroplast & mitochondria - Spin supernatant at very high speed
sediment = ribosomes (70s/80s)
More dense = faster to separate
4 points
cell fractionation and ultracentrifugation method PREP
- Homogenise - breaks open cells & evenly spreads
- Filter - remove large debris / whole cells
- Buffered & Isotonic solution - stable pH, stops protein denaturing, prevent damage to organelles eg. osmotic shock
- Cold - reduce enzyme action
what makes prokayrotic cells different from eukaryotic?
- cell wall = peptidoglycan
- nucleoid (large circular DNA & not associated w/ histone proteins)
- no membrane bound organelles
- small ~mitochondia size
- smaller ribosomes
- plasmids (small, separate from chromosome carry different useful alleles)
- can have: flagella, capsule, slime layer
- unicellular
structure of virus particles
- nucleic acids (DNA/RNA)
- protein capsid
- lipid envelope (some eg. HIV)
- attachment proteins
- enzymes (eg. reverse transcriptase in retroviruses)
retrovirus = contains RNA
what is virus
non-living, acellular infectious parasite that must enter a host cell’s to replicate
4 main structural elements
Binary Fission Bacteria
- replication of the nucleoid and plasmids
- division of cytoplasm produces 2 daughter cells, each with:
single copy of the circular DNA (nucleoid),
variable number of copies of plasmids.
what organisms undergo mitosis?
all eukayotes
bacteria = binary fission
When does nuclear envelope breakdown?
Prophase
What is centrosome?
organelle containing centrioles (which form spindle fibres)
where does oxidative phosphorylation occur in bacteria
ETC in mesosome
Large SA infolding on cell membrane allows respiration enzymes to bind
Types of bacterial gene transmission
idk if acc need 🤷♀️
- To each other = horizontal
- Down family line = vertical
what is a pathogen
organism that has the ability to cause disease
what is antigen
a molecule (usually protein) that stimulates an immune response
Why are antibodies effective against a specific antigen?
Variable region has specific tertiary structure that is complementary to the antigen.
antibody-antigen complexes form
similar to enzyme-substrate; codon-anticodon
Describe phagocytosis
Non-specific immunity
- Phagocyte detects antigen
- Phagocyte engulfs antigen
- Vesicle forms = phagosome
- Lysosome fuses, forms phagolysosome
- Lysosome releases hydrolytic enzymes
- Pathogen hydrolysed & egested
How do B lymphocytes respond when stimulated by an antigen?
- Undergo clonal selection/expansion to mitotically divide
- Produce B memory cells
- Differentiate into plasma cells
- Plasma cells secrete antibodies
Why would a glycoprotein likely act as an antigen?
eg. virus, RBC
- Different shape to body proteins
- Located on outer surface of cell/virus
Properties of plasma cells
- many mitochondria
- many ribosomes/RER
- more golgi
- produce antibodies
explain function of each relative to producing antibodies
Role of macrophage in stimulating (lymphocytes)
eg Bm or Th cell
Q practice
- antigen on membrane (apc) presented (to lymphocyte)
- produces cytokines
Th also produce to pass onto B
How would antigenic variability lead to infection by same virus twice?
2° response
Q practice
- Memory B cells / T cells don’t recognise antigen
- Antibodies produced for previous antigen ineffective because not complementary tertiary structure
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1 - Biological molecules7
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2 - Cells29
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4 - Genetic information, variation & relationships between organisms24
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7 - Genetics, populations, evolution and ecosystems61
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3 - Organisms exchange substances with their environment8
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5 - Energy transfers in & between organisms19
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6 - Organisms respond to change of internal & external environment25
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8 - Control of gene expression10
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RGS-BIO quizlet deck161
