Cells Flashcards
magnification =
image size / real size
what is the resolution of a microscope?
minimum distance apart that two objects can be in order for them to appear as different items
what is cell fractionation
what happens to cells before fractionation
what are the two processes involved in cell fractionatiom
- process where cells are broken out, dividing up the different organelles
- placed in cold, buffered solution of same water potential
1) homogenation: releases organelles from cells, filtered to leave the homogenate
2) ultracentrifugation: separate organelles separated out from homogenate, heavier organelles sink to bottom: nuclei, mitochondria then lysosomes
give a brief explanation of how a Transmission Electron Microscope works
an electron beam is focussed onto the specimen using condenser electromagnets. the beam goes through a thin section of the specimen - parts of the specimen absorb electrons so appear dark, others don;t so appears light. forms an
what are the limitations of a TEM
- live specimens can’t be used (in a vacuum)
- image not in colour + 2D
- specimen must be v thin + multi-tissue
- image may contain artefacts
- image can’t be seen directly
give a brief explanation of how a Scanning Electron Microscope works
limitations?
SEM directs beam of electrons onto specimen from above, beam passed back and forth. electrons are scattered by specimen in pattern depending on contours of specimen
same as TEM (except specimens don’t need to be really thin bcuz not penetrated) and also has lower resolution
what is an eyepiece graticule?
what is a stage micrometre?
- glass disc fitted into the eyepiece of the microscope
- marked with a fine scale from 0 to 100
- scale on the EG can’t be used directly because each objective lens on a microscope will magnify to a different degree but EG stays the same so need to use a stage micrometer
- used to calibrate an EG
- has scale etched on it with sub-divisions of 0.01mm
structure of the nucleus
function of the nucleus
- nuclear envelope: double membrane around nucleus continuous with the ER = controls movement of substances in/out of nucleus
- nuclear pores = allow large molecules out the nucleus
- nucleoplasm
- chromosomes
- nucleolus = makes ribosomal RNA
- controls activities of the cell (protein synthesis)
- makes RNA/ribosomes
structure of mitochondria
function of mitochondria
- double membrane, inside = folded to form cristae
- matrix on inside, contains respiratory enzymes
- site of aerobic respiration, where ATP produced
structure of chloroplasts
function of chloroplasts
- envelope = double membrane
- grana: stacks of thylakoid discs, contain chlorophyll
- stroma: matrix where 2nd stage of photosynthesis takes place
- carry out photosynthesis
structure of the RER + SER
function of the RER + SER
- 3D system of sheet like membranes
- continuous w/ nuclear membrane
- contains flattened sacs = cisternae
- RER = ribosomes on surface
- RER: large s.a. for (glyco)protein synthesis
- RER: pathways for transport of materials
- SER: synthesise, transport + store lipids and carbs
structure of golgi apparatus/vesicles
function of golgi apparatus/vesicles
- flattened sacs which make up cisternae
- small hollow structures = vesicles
- add carbs to proteins = glycoproteins
- make secretory enzymes
- secrete carbs
- transport, modify, store lipids
- form lysosomes
structure of lysosomes
function of lysosomes
- produced by golgi apparatus (enzyme-containing vesicles)
- contain hydrolytic enzymes
- hydrolyse material ingested by phagocytic cells (e.g. pathogens)
- exocytosis: release enzymes outside the cell
- digest worn out organelles
- autolysis - break down cells after they die
structure of ribosomes
function of ribosomes
- contain 2 subunits
- contain ribosomal RNA + protein
- site of protein synthesis
structure of cell wall
function of cell wall
- microfibules of cellulose (+ other polysaccharide) in a matrix
- thin layer (lamellae): marks the boundary between different cell walls
- provide mechanical strength against move of water by osmosis
- water moves along it throughout plant
