Chapter 2: Basic Components Of Living Systems Flashcards
Microscope
An instrument that allows you to magnify cells and see details of their ultrastructure
Advantages of light microscopes
Can observe living and dead things
Does not use harsh chemicals
Easy to setup and use
Cheap and portable
Disadvantages of light microscopes
Low magnification (x2000) Low resolution (200nm)
What is transmission electron microscopy?
Beam of electrons
Transmitted through a specimen
Focused to produce an image
Advantages of transmission electron microscopy
High magnification (x 5 000 000) High resolution (0.5nm) Can see internal cell structure
What is scanning electron microscopy?
Beam of electrons
Sent across surface of specimen
Electrons reflected and collected to produce image
Advantages of scanning electron microscopy
High magnification (x 500 000) High resolution (3-10nm) Can see the surface of cells
Disadvantages of transmission electron microscopy
Can only see dead material
Harsh chemicals used in prep
Expensive
Disadvantages of scanning electron microscopy
Can only see dead material
Harsh chemicals used (damaging to cell stature)
Expensive
What is laser scanning confocal microscopy?
Single spot of focused light
Moves across thin section of specimen
Light re-emitted is filtered through a pinhole aperture
Advantages of laser scanning confocal microscopy
Can see living cells - non invasive
Can observe cell processes - tracking
Higher resolution than light microscopy
Disadvantages of laser scanning confocal microscopy
Low magnification (x 2000)
More expensive than light microscope
Only a 2D image is produced
… 3D by creating images at different focal planes
Three cell theory statements
Plants and animals are composed of cells
Cells are the basic unit of all life
Cells can only develop from existing cells
What is brightfield microscopy?
Sample is illuminated from below
Observed from above
What is whitefield microscopy?
Whole sample is illuminated at once
Disadvantages of using microscopes
Organelles have low contrast in images
Cells do not absorb much light
How the general disadvantage of using microscopes can be overcome
Use stains
What is the purpose of staining cells?
Increase contrast
Different components absorb different amounts
Easier to differentiate between organelles
What are the four methods of preparation for sample light microscopy?
Dry mount
Wet mount
Squash slides
Smear slides
What is a dry mount?
Solid specimen
Sectioned
Placed between slide and cover slip
What is a wet mount?
Specimens are suspended in liquid
Cover slip is placed on top of slide
What is a squash slide?
Wet mount is prepared
Lens tissue is used to press down cover slip on slide
What is a smear slide?
Edge of a slide
Smears sample thinly and evenly on another slide
Cover slip is placed on top of slide with the smear
What are the two lenses in a compound microscope called?
Objective lens - placed near the object to produce a magnified image
Eyepiece lens - used to view the object and further magnify the object - reducing chromatic aberration
How do you prepare a sample for staining?
Sample placed on slide Allowed to air dry Passed through flame Sample adhered to slide Able to take up stains
What happens when positively charged dyes are used to stain cells?
Attracted to negatively charged materials in the cytoplasm
Name two common dyes
Methylene blue
Crystal violet
What is the charge of cystosol in cells?
Negative
What happens when negative dues are used to stain cells?
Negative charged components in the cytoplasm repel the dye
Cells are left unstained and so stand out against stained background
What is the purpose of differential staining?
Used to differentiate between two types of organisms that are somewhat similar
Used to differentiate between different organelles of a single organism in a tissue sample
Describe the gram stain technique
Separates bacteria into positive and negative groups
Crystal violet used to stain cells -> Iodine fixes the dye -> Sample is washed with alcohol -> Positive bacteria retain the stain (thicker cell walls)
What does a counterstain do?
Safranin dye makes gram-negative bacteria turn red, whereas the crystal violet left them colourless
Due to their thinner cell walls, gram-negative bacteria do not retain due and are not susceptible to penicillin
… inhibits cell wall formation
Describe the acid-fast technique
Used to separate different species of Mycobacterium -> Lipid solvent carries carbolfusion dye into the cells -> Cells are washed with a dilute acid-alcohol solution -> Mycobacterium retain the stain and turn red -> Other bacteria are exposed to the blue methylene stain
What are the four methods of producing slides?
Fixing - chemical, preserve cells, near-natural state
Sectioning - alcohols, dehydrate cells, placed in mould, sliced thinly
Staining - dyes, multiple ones used to show multiple structures
Mounting - sample being secured between a slide and cover slip
What do scientific drawings include?
Title Magnification Smooth continuous line No shading Straight lines parallel to page
What is an artefact?
A visible structural detail caused by processing the specimen but is not a feature of it E.g. Bubbles trapped under a cover slip
What is the purpose of a dichroic mirror in a laser scanning confocal microscope?
It reflects one wavelength but allows other wavelength to pass through - non blurred image
What is the purpose of antibodies with fluorescent tags?
Laser scanning confocal microscopy allows specific features to be targeted and studied with more precision than when using staining and light microscopy
How do fluorescent tags work?
They emit bright green light when illuminated by UV light
Genetically engineered to fluoresce different colours so different structures can be studied
Non invasive technique - gene is isolated and attached to the genes coding for proteins
Allows study of production and distribution of proteins in cells and organisms
Define magnification
By how many time the image has been enlarged
Objective lens
Define resolution
How much detail the object can be viewed in - limited by diffraction
Define diffraction
The tendency of light waves to disperse as they pass close to physical structures in the specimen being studied - causing loss of detail
Define resolved
Seen separately
How can resolution be increased?
Using beams of electrons which have wavelengths thousands of times shorter than light
… beams can be closer together before overlapping
Magnification formula
Magnification = image / object
What is the use of an eyepiece graticule?
Used to measure the size of a sample under a microscope
Glass disk marked with a fine scale of 1 to 100 which has no units and remains unchanged
Relative size of division increases with each magnification factor
What is the use of a stage micrometer?
A microscope slide with a very accurate scale in micrometers (um)
100 divisions = 1mm
1 division a 0.01mm
Measurement equation
Measurement = graticule divisions X magnification factor
Define prokaryote
Single-celled organism
Define eukaryote
Multicellular organism
What is metabolism?
The rate at which molecules are synthesised or broken down
What is a membrane?
Controls what substances enter and exit the cell
Selectively permeable to maintain the cell environment
Definition of nucleus
Contains DNA
- > directs synthesis of proteins
- > controls metabolic activities
What is the nuclear envelope?
Double membrane with pores
Protects DNA from damage from the low pH of the cytoplasm in a cell
What is the nucleolus?
In the nucleus
Produces ribosomes
Composed of RNA (which make proteins)
What is a mitochondrion?
Double membrane organelle
Inner membrane is highly folded (cristae)
Cristae contain the matrix (fluid) and enzymes - for the production of ATP
What is a vesicle?
Singular membranous sac with storage and transport roles
What are lysosomes?
Specialised vesicle
Contains hydrologic enzymes
Break down waste materials and pathogens
Apoptosis ‘programmed cell death’
What is the cytoskeleton?
Network of fibres
Provide shape and stability
Microfilaments - contractile fibres, made of protein actin, responsible for cell movement and contraction
Microtubules - compose spindles fibres (segregate chromosomes in cell division), formed by the polymerisation of globular tubular proteins
What are intermediate fibres?
Fibres made of proteins
Provide mechanical strength
Help maintain cell integrity
What are centrioles?
Components of the cytoskeleton that are composed of micro tubules
2 associated centrioles form a centrosome
…involved in the assembly and organisation of spindle fibres
What is a flagella?
Primary function - cell movement
Secondary function - sensory organelle, fetch change in cell environment
What are cilia?
Stationary - present on surface - sensory organelle
Mobile - beat in a rhythmic manner creating a current to move fluids with trapped pathogens
Which four organelles coordinate the production of proteins in cells?
Ribosomes
ER
Golgi apparatus
Cytoskeleton
What is the endoplasmic reticulum?
A network of membranes enclosing cisternae which is connected to the nuclear envelope
What is the smooth ER?
Responsible for lipid and carbohydrate synthesis and storage
What is the rough ER?
Has ribosomes bound to the surface
Responsible for the synthesis and transport of proteins
What is a ribosome?
Organelle where protein synthesis occurs
Contrasted of RNA made in the nucleolus used to make proteins
What is the Golgi apparatus?
Organelle which modifies and packages proteins into vesicles for transport
Define exocytosis
Vesicles fuse with the cell surface membrane for secretion out of the cell
Some form lysosomes
Define endocytosis
Movement of substances into the cell
Define phagocytosis
Movement through solid e.g. Lysosomes engulfing something
Define pinocytosis
Movement through liquid e.g. Vesicle through the cytoplasm
Define transcription
The copying of DNA so mRNA can exit the nucleus and cell and go to the ER ribosomes
Define translation
The assembly of amino acids into proteins in the ribosomes of the ER
What is the cell wall?
Give plants shape and support (turgor from vacuole)
Freely permeable membrane made of cellulose which acts as a barrier
What is a vacuole?
Membrane lined sacs in cytoplasm
Contains cell sap which maintains turgor
What is a chloroplast?
Organelle with a double membrane (containing stroma, DNA and ribosomes)
Responsible for photosynthesis
Thylakoids -> Granum (joined by lamellae)
What is chlorophyll?
A green pigment from which photosynthesis occurs and produces starch
What are extremophiles?
Organisms that can survive in extreme environments
How do flagella move?
Filament is attached to the cell me ante by a basal body and rotates by a molecular motor by the energy supplied by chemiosmosis
What form is DNA in cells?
Supercoiled -> Histones -> Chromatin
How does DNA structure differ in P and E cells?
P - circular (proteins fold and condense)
E - linear (associated proteins, Histones)
What are cell walls made of?
P - peptidoglycon
E - chitin=fungi, cellulose=plants, none in animal
How do the size of ribosomes differ in P and E cells?
70s - P
80s - E
How do cells in P and E cells reproduce?
P - binary fission
E - asexual or sexual
