Cell structure Flashcards
what are microscopes used for
to produce magnified images of objects
describe how light microscopes work
use visible light beam focused by a glass lense ( 400nm - 700nm) to produce a 2D photomicrograph
what’s the resolution in light microscopes and what are the limitations of this?
- 200nm
- ribosomes (20nm) aren’t distinguishable
what are the advantages of using light microscope
- cheap
- easy to use
- portable
- able to view living specimens
equation for total magnification
total magnification = objective lens magnification x eyepiece lens magnification
describe how laser scanning microscopes (confocal microscopes) work
they use lasers to scan images point by point
what are the advantages of using laser scanning microscopes (confocal microscopes)
- high-resolution, high contrast computer image is formed from pixels
- depth selectivity allows the microscope to view specimens at different depths
what can laser scanning microscopes be used for
- can be used to swiftly diagnose conditions
describe how electron microscopes work
- e- fired from cathode and focused by magnets onto a screen or photographic plate
- use a beam of electrons with a wavelength 0.004nm to produce much higher resolution images
what is are some disadvantage of electron microscopes?
- samples must be placed in a vacuum so living organisms can’t be viewed
- large and very expensive
- need a great deal of skill and training to use
- metallic salt stains can be hazardous to user
how are specimens prepared in TEMs (transmission electron microscopes)
specimen dehydrated and stained
what role do electrons play in TEMs
pass through the specimen
what’s the product of TEMs
2D black and white micrograph
what’s the magnification and resolution of TEMs
- 2 million x magnification
- 0.1nm resolution
how are specimens prepared in SEMs ( scanning electron microscopes)
specimen coated with metal film
what role do electrons play in SEMs
bounce off specimen
what’s the product of SEMs
3D image formed, can be enhanced
what’s the magnification and resolution of SEMs
- 15-200,000x magnification
- 20nm resolution
why are specimens stained
make structures in the cell visible and provides contrast
what’s differential staining
when different stains bind to specific structures in the cell
steps in specimen preparation
- dehydration
- embedded in wax, preventing distortion
- slicing into thin sections
name 3 stains
- acetic orcein
- eosin
- iodine in KI
what’s the function of acetic orcein
binds DNA, dark red in colour
what’s the function of eosin
stains the cytoplasm pink
what’s the function KI stain
stains cellulose yellow, starch grains blue-black
what are eyepiece graticules used for
to measure object sizes in eyepiece units (epu)
what are stage graticules used for
used to calibrate the eyepiece graticule
how do you measure specimen size
- fit eyepiece (10x) and stage graticules focus with objective lens for a given magnification
- work out what length each epu represents. Stage graticule measures in microns
- measure object epu and multiply by this value
define magnification
the number of times larger an image appears compared to the real specimen
define resolution
the ability to distinguish two different points clearly and produce fine detail
why do electrons microscopes have better resolution
they use electron beams with smaller wavelengths
equation for image size
Image size = object size x magnification
I
A x M
What’s the difference between organelles in eukaryotic cells and prokaryotic cells
membrane bound organelles in eukaryotic cells
function of nucleus
- stores chromatin made of DNA and histones
- contains nucleolus, which makes ribosomes
structure of nucleus
- has double membrane and nuclear pores
function of ribosomes
- synthesises polypeptides using mRNA
- free floating or attached to rough ER
structure of ribosomes
- are 20nm in diameter
- made up of two subunits ( 60s and 40s), each containing roughly equal ratios of rRNA and protein
function of mitochondria
- site of aerobic respiration
- found in animal and plant cells
- produces ATP from ADP + Pi
structure of mitochondria
- double membrane, inner membrane highly folded into cristae
- spherical/rod/branched (2-5um)
function of chloroplasts
- site of photosynthesis
- produces glucose and oxygen
where are mitochondria found
- found in animal and plant cells
where are chloroplast found
- found in plant and algae cells only
structure of chloroplasts
- double membrane, starch grains and DNA loop
- inner membrane is continuous with stacks of flattened sacks called thylakoid
- fluid filled matrix - stroma
- 4 - 10 um in length
structure of rough ER
- contains membranes containing fluid-filled cavities called cisternae that provide a large SA for ribosomes to attach
- continuous with nuclear membrane
function of rough ER
- site of protein synthesis and helps move substances around the cell
structure of smooth ER
- contains membranes containing fluid filled cavities called cisternae that provide large SA
- continuous with nuclear membrane
- has no ribosomes attached to it
function of smooth ER
- is a site of carbohydrate and lipid synthesis, storage and transport
structure of Golgi apparatus
- has membranes called cisternae
- secretory vesicles bring materials to and from Golgi apparatus
function of Golgi apparatus
- creates lysosomes; vesicles come to and from the Golgi
- modifies proteins by adding sugar ( to make glyporoteins), lipids (to make lipoproteins).
- proteins folded into 3D chape
- packages and transports proteins in vesicles
- transports, modifies and stores lipids
function of lysosomes
- contain hydrolytic enzymes known as lysozymes
- hydrolyse and break down cells in apoptosis, or phagocytosed bodies
structure of lysosomes
- vesicles of membrane
what are lysosomes created by
Golgi apparatus
function of vacuole
- supports the cell when turgid
- acts as a store of fluid, sugars, amino acids and pigments
where are large permanent vacuoles found
plant cells
structure of vacuole
vacuole surrounded by a membrane called the tonoplast, and contains fluid
in which cells are cell walls found in
- plants
- fungi
what are plant cell walls made of
cellulose
what are cell wall in fungi made of
chitin
what are membranes
partially permeable barriers
what’s the cytoskeleton
a complex network of proteins found throughout the cell
what are centrioles
bundles of microtubules arranged into two cylinders that are at right angles to each other
what’s the cytoskeleton made of
- made of microfilaments (actin), microtubules and intermediate filaments
what’s the function of the cytoskeleton
- helps anchor organelles and provide cell shape and provides mechanical strength
- moves organelles around cell
what are centrioles made of
- tubulin subunits, forms spindle fibres
function of centrioles
spindles move chromosomes in nuclear division via motor proteins
what do centrioles form
cilia and undulipodia
what are cilia, undulipodia and flagellum
projections of cell membrane formed from centrioles, and which contain microtubules
features of cilia
- multiple protrusions
- eukaryotic and prokaryotic cells
- example - ciliated epithelium in airways moves mucus upwards
features of undulipodia/ flagellum
- single protrusion
- called undulipodia in eukaryotes and flagellum in prokaryotes
- example - bacterial flagellum for motility & undulipodia in human sperm
how are proteins synthesised, transported and secreted
- Transcribed mRNA leaves nucleus via nuclear pores and attaches to ribosomes at the RER
- Ribosomes translate mRNA into polypeptide, which enters RER
- Vesicles from cisternae take protein to Golgi apparatus
- Golgi apparatus modifies and packages protein and release it into vesicle bound for destination, such as exocytosis
features of prokaryotic cells
- smaller than eukaryotic cells
- no membrane bound organelles
- smaller (70s) ribosomes
process by which prokaryotic cells divide
binary fission
process by which yeast cells divide
budding
what’s the function of capsule in prokaryotic cells
waxy, surrounds cell wall for protection
what’s the function of flagella in prokaryotic cells
long projections for movement
what’s the function of pili in prokaryotic cells
small projections for adhesion
