cell structure Flashcards
Chap 2
What is sample preparation?
When samples and specimens are prepared for examination through light microscopy
What are the 4 methods that can be used for sample preparation?
Dry mount
Wet mount
Squash slides
Smear slides
Dry mount dis/ad?
Quick & easy
Specimen is dried out so dies
Wet mount ad?
Prevents dehydration and distortion
Can view live specimen
Squash slides ad?
Can view all cell content at once
Dry mount method?
Solid specimen is cut into slices through ‘sectioning’
Once prepared, it is placed on a slide and covered with a cover slip
Wet mount method?
Specimens are suspended in liquid (water or immersion oil)
Then, the cover slip is placed at an angle
Squash slides method?
A wet mount is prepared
Then, a lens tissue is used to press down cover slip to slide
Smear slides method?
The edge of the slide is used to smear sample into a thin coat
Then the cover slip is placed on top
What are 4 steps to producing a slide? (Elaborate on first and last?)
Fixing (chemical preserves specimen)
Sectioning
Staining
Mounting (put on slide w/ coverslip)
How to stain a slide?
Air dry slide’s stain
Heat-fix by passing thru a flame
Specimen will adhere & absorb stain
What do stains do?
Increase contrast (of cell components)
How do gram negative stains work? Examples?
Repel neg material in cells and sit around cell, making components stand out
Nigrosin & Congo red
How do gram positive stains work? Examples?
Pos stain attracted to neg material in cytoplasm
Crystal violet & methylene blue
What is differential staining? 2 types?
Can identify 2 separate organisms and 2 separate organelles in 1 organism
Gram staining
Acid-fast staining
How do acid-fast stains work? (5 points)
- red dye is added to all bacteria
- bacteria washed w/ acid but bacteria w/ waxy cell walls like mycobacteria hold onto red dye
- blue counterstain applied to all
- other bacteria pick up blue
- fast way of identifying diff bacteria
What is the diff between acid-fast and gram stain USES?
Gram stains separate bacteria into pos & neg groups whereas acid-fast separates mycobacteria from other bacteria
Light microscope’s vs electron microscope’s resolution
Light: 200nm
Electron: 0.1nm
Why do electron microscopes have a higher resolution?
Electrons have shorter wavelengths than light so there’s less diffraction (overlapping)
2 scales on the light microscope and where are they?
Stage micrometer (slide)
Eyepiece graticule (lens)
1 division on the stage micrometer=…
10 micrometres
Contrast
the difference in colour between 2 objects
Max mag of light microscope
x1500
What is the function of the eyepiece graticule?
To find calibration factor of specimen
Why is light mag capped?
At higher mags, res is too low and detail not seen
Artefacts? eg?
artificial structures introduced during prep eg air bubbles
Fluorescent tagging
Tagging a fluorescent dye to a molecule to increase its contrast and make it viewable
Why electron microscopy black and white?
Electron beams only have 1 wavelength so not all wavelengths of visible light
2 advantages of the 4 types of microscope
Light: coloured, live
Laser scanning confocal: coloured, live
TEM: highest res, inner cell
SEM: 3D
Which microscopy requires fluorescent tagging?
Laser scanning confocal
Limitation of TEM
Only works on thin and dead specimens
Limitations of SEM (2)
Lower res than TEM
Only scans surface
Limitation of Light
Low mag and res
Limitation of laser scanning confocal (2)
Time consuming due to stacking layers
The laser can photo bleach and damage specimens
Which microscope has the highest res?
TEM
Principles of laser scanning confocal microscope (2)
- laser scans dyed specimen (and so images may be COLOURED)
- layers can be stacked to form 3D image
Principles of TEM (2)
- electrons transmitted thru specimen
- denser parts absorb more e-
- denser parts appear darker
- electrons have a short wavelength so high res
Principles of SEM (3)
- electrons knock off electrons from specimen
- electrons gathered in cathode ray tube
- 3D image is only the surface
3 functions/advantages of an organelle
- creates distinct environment in cell
- easier for structures to function
- helps metabolism as metabolism requires enzymes that have different optimum conditions
Nucleus function (2)
- contains DNA which will direct protein synthesis
- controls metabolism
Nuclear envelope structure (2)
- double membrane
- nuclear pores
Nuclear envelope function (2)
- protects nucleus
- exports RNA molecules
Nucleolus function
produces ribosomes (by combining rRNA and proteins)
Mitochondria structure (2)
- inner membrane folds to make cristae
- inner fluid called matrix
Mitochondria function (2)
- produces ATP molecules (energy)
- produces own enzymes (eg for respiration) and reproduces using mitochondrial (mt)DNA
Vesicle structure
Membranous sacs of fluid
Vesicle function
store and transport cell material
What are lysosomes and what does its structure allow?
- specialised vesicles with hydrolytic enzymes THAT BREAK DOWN WASTE
- spherical sacs surrounded by a single membrane, which prevents other structures being damaged from enzyme activity
Lysosome function (2)
- breaks down waste
- breaks down engulfed pathogens
Cytoskeleton structure (3 components)
- microfilaments
- microtubules
- intermediate fibres
Cytoskeleton function
controls organelle movement/holds them in place
Microfilaments structure and what does it allow it do?
contractile fibres made from actin protein (which allow it to change length and move in the cell)
Microtubules structure
tubules polymerised from globular tubulin proteins (which allow it to change length and move in the cell)
Microfilaments function (2)
- controls cell movement
- controls cell contraction (in which the cell splits) in cytokinesis
Microtubules function (2)
forms scaffold like structures which:
- controls cell movement
- form spindle fibres that segregate chromosomes in cell division
Intermediate fibres function
gives cell mechanical strength
Centriole structure
- made from microtubules
- centriole + centriole= centrosome
Centriole/centrosome function
gathers and organises spindle fibres
Flagella structure
whip like long extensions
Flagella function (2)
- enables cell motility
- sensory organelle that detects chemical changes
Cilia structure
hair like short extensions
Mobile cilia function and eg?
beat in rhythmic manner to create a current that moves fluids/objects (eg in trachea w mucus)
Stationary cilia function and eg?
sensory organelle (eg nose)
Endoplasmic reticulum structure and what is it connected to?
Network of membranes enclosing flattened sacs of cisternae which are covered with ribosomes
Outer membrane of nucleus
Smooth ER function
lipid and carb synthesis and storage
Describe how DNA is
packaged in eukaryotes
(3)
- DNA is coiled around proteins called histones
- which form chromatins
- which are supercoiled/condensed into chromosomes
What are the 6 steps in protein synthesis?
(HINT transcription + translation are 3 points, movement is 3 points)
- Gene for protein transcribed onto mRNA molecule in nucleus
- mRNA molecule leaves thru pores
- attaches to ribosomes in rough ER which read the instructions on mRNA to assemble the protein (translation)
- rough ER process proteins into vesicles which will fuse with golgi apparatus
- golgi apparatus modify and package proteins into (different) vesicles
- vesicles fuse with cell surface membrane and release protein via exocytosis
TEM res vs SEM range
TEM: 0.05-2nm
SEM: 5-50nm
Compare the structures of prokaryotes and eukaryotes (6)
SIM
- Both have ribosomes
- Both have a cytoskeleton
- Both have a cell-surface membrane
DIFF
- Pro have 70S ribosomes whereas Euk have 80S ribosomes
- Pro lack membrane bound organelles whereas Euk do eg mitochondria
- Pro have 1 circular free chromosome whereas Euk have many linear chromosomes
Compare DNA organisation in prokaryotes vs eukaryotes (6)
PRO
- 1 circular free chromosome
- plasmids (DNA circles)
- no nucleus
EUK
- many linear chromosomes
- associated with proteins called histones (to form chromatins)
- nucleus bound
Which cells have a cell wall? What is each one made of? (3)
Bacteria- peptidoglycan
Fungi- chitin
Plants- cellulose
What is the role of the plasmid? (2)
Plasmids are small
loops of DNA (1)
sometimes present in
prokaryotes. They often
contain antibiotic
resistance genes (1)
and are used in genetic
engineering.
What is the role of:
pili
capsules
mesosomes
- attachment to other cells (eg for sexual reproduction)
- extra protection
- helps form new cell walls
Mag vs res definition
the number of times larger an image is compared to the object vs the ability to identify 2 separate objects
Diameter of pro vs euk
pro: 0.1-10 micrometres
euk: 10-100 micrometres
4 things that a plant cell has that an animal cell doesn’t? explain the new one?
- amyloplast: small membrane bound organelle producing & storing starch
- cell wall
- chloroplast
- vacuole
4 structures of a chloroplast and explain? how does this contribute to overall function?
- double membrane
- stroma: fluid
- grana: stacks of thylakoid membrane connected to lamellae membranes
- thylakoid membrane: flattened sacs
Overall function: network of internal membranes have a large SA to contain more chlorophyll to increase rate of photosynthesis
What are the 3 structures of the plant cell wall and how do they help its function?
- cellulose= strength
- cell contents push against wall= turgid/support
- plasmodesmata (pores)= permeability + pathogen defence
What is the evidence for the endosymbiotic theory?
Mitochondria and chloroplasts:
- have own DNA
- have ribosomes (like pro’s)
- double membrane (inner one like pro’s)
- same size as bacteria and susceptible to an antibiotic
How did endosymbiosis occur? (3)
Ancestral prokaryote gains infolding of cell membrane
which aerobic bacterium enter via endocytosis
to form ancestral eukaryotes
