Topic 5: cell structure + function Flashcards
What are the 2 types of microscopes?
1) Light microscope =
- Visible light passes through specimen
- Magnification through lenses
2) Electron microscope =
- Focus beam of e- through specimen / onto surface
Factors affecting microscopy image quality
- Magnification = ratio of image size to real size
- Resolution = clarity = minimum distance 2 points distinguishable
- Contrast = visible differences in parts of a sample
Describe light microscopes
- 1000x size of specimen
- Resolution = 0.2 µm = 200 nm
- Subcellular structures = organelles too small
Give light microscopy methods
ALL 2D
1) Brightfield = unstained
- Light passes directly through
- Image has little contrast unless specimen has natural contrast
2) Brightfield = stained
- Dye enhances contrast
- Methyl blue
- Require cell to be fixed
3) Phase contrast = unstained
- Enhances contrast by amplifying densities within specimens
- Useful for examining living unpigmented cells
4) Differential interference contrast = unstained
- Like phase contrast = optical modifications to differences in density = almost appear 3D
5) Fluorescence = stained
- Show location of specific molecules by tagging with fluorescent dye/antibodies
- Tags absorb UV and emit light
ONE 3D
6) Confocal = stained
- Uses lasers + optics on fluorescently stained specimens
- Single plane focus illuminated + out of focus subtracted by computer
- Reconstruction of 3D from obtained images
Describe electron microscopes
- Magnification 250,000x
- Can detect structure small as 0.1nm
- Resolution = 2nm = 100x improvement from light microscope
- Can detect macromolecules
- 2 types = TEM + SEM
Describe TEM
- Focus beam through specimen
- To study internal structure = 2D image
Describe SEM
- Focus beam onto surface
- Study surface of specimen = 3D images
Describe cell fractionation
- Allows isolation of subcellular components = determine organelle function
- Based on size + density
- Centrifugation = used to fractionate cells
- 2 types = differential + density gradient
Describe differential centrifugation
- Solvent concentration = stabilizing solvent gradient
- Multiple centrifugation steps = increase acceleration + time
- Separation basis = size
Describe density gradient centrifugation
- Solvent concentration = steep solvent gradient
- Single centrifugation step
- Separation basis = density
Compare prokaryotic/eukaryotic cells
ALL HAVE:
- Plasma membrane
- Semifluid cytosol
- Have chromosomes
- Have ribosomes
Contrast prokaryotic/eukaryotic cells
PROKARYOTES:
- No nucleus
- DNA unbound in nucleoid
- No membrane-bound organelles
EUKARYOTES:
- Nucleus bound by nuclear envelope
- Bigger than prokaryote
- Membrane-bound organelles
Define cytoplasm
- Region between plasma membrane + nucleus
- Has all subcellular structure except nucleus
Define cytosol
- Intracellular fluid
- Excludes organelles
- Contains ribosomes + cytoskeletal filaments + soluble molecules + water
Describe plasma membrane
- Selective barrier = allows passage of oxygen + nutrients + waste in/out of cell
- Phospholipid bilayer
- Semi-permeable
Describe nucleus
- Contains DNA of cell
- Genes in chromosomes = contain directions for protein synthesis
- Chromosome = complex proteins + DNA = chromatin
- DNA replication + transcription takes place
- Replication = before every cell division
- Transcription = DNA>mRNA
Define nucleolus
- Denser area in nucleus
- rRNA synthesized here
- After synthesis = assembled with proteins = exit nucleus = form ribosomes
Define nuclear envelope
- Encloses nucleus + separating it’s contents from cytoplasm
- Has nuclear pores
Define nuclear pores
- Regulate entry + exit of molecules from nucleus
Describe the ribosome
- Made of rRNA + protein
- Consist of small + large subunit
- Function = protein synthesis
- Location =
1) Free ribosome in cytosol = synthesize cytosolic proteins
2) Bound to RER = synthesize secreted + membrane-bound proteins
Describe the endoplasmic reticulum
- Membranous tubules and sacs
- Inside space = lumen
- ER membrane continuous with nuclear envelope
- 2 types:
1) SER = lacks ribosomes
2) RER = has bound ribosomes
What is the function of SER?
- Synthesize lipids
- Metabolizes carbs
- Detoxifies poison
- Stores calcium
What is the function of the RER?
- Protein synthesis
- Post- translation modifications = functional
- Protein sorting = transport + distribute ny producing membrane-bound transport vesicles
What are some modifications occurring in RER?
- Polypeptide cleavage = polypeptides activated by enzymes that cleave them = functional = insulin
- Protein folding = into tertiary structure
- Subunit assembly = into quaternary structure = functional = haemoglobin
- Chemical modifications = addition of chemical groups
