Microscopy and cells Flashcards
What is the equation for magnification?
Maginfcation=size of image/actual size of object
Define magnification
The magnification of a microscope refers to how many times larger the image is compared to the object
Define resolution
The resolution of a microscope is the minimum distant between two objects which they can still be viewed as seperate.
Light microscope resolution
Limited to 0.2um and 200nm
Light microscope advantages
Can see living specimens.
Easier specimen preparation.
Variety of coloured stains.
Light microscope disadvantages
Low resolution so organelle detail / smaller components not visible.
TEM electron microscope resolution
0.1 nm but not always achieved as difficult specimen prep. / high energy beam can destroy specimen.
TEM electron microscope advantages
Very high resolution at high magnification.
Detailed organelle / sub-organelle structure.
TEM electron microscope disadvantages
Specimens are not alive i.e. in a vacuum.
Difficult prep. e.g. very thin specimens / complex staining.
Black and white image.
Artefacts can spoil image.
SES microscope resolution
20nm
SES microscope advantages
3D images show structural formation.
Totally sic pics.
SES microscopes disadvantages
Specimens are not alive.
Difficult prep.
Vacuum.
Black and white image.
Describe the structure of a nucleus
Surrounded by a nuclear envelope, a semi-permeable double membrane
nuclear pores allow substance to exit/entry
Dense nucelous made of RNA and proteins assemble ribosomones
Functions of the nucleus
Acts as the control centre of the cell - controls the cell’s activities
Controls synthesis of proteins
Contains the organism’s genetic material (in the form of DNA)
Manufactures ribosomes from ribosomal RNA
Structure of a mitochondria
Double membrane - controls the entry and exit of material
Inner membrane is highly folded to form cristae - this is where respiration (oxidative phosphorylation) takes place and the folds provide a large surface area for increased respirations
Fluid matrix contains mitochondrial DNA, enzymes, lipid and proteins
Usually rod-shaped and around 1-10 micrometers long
Function of mitochondria
Site of aerobic respiration
Produce the energy-carrier molecule ATP during respiration
Therefore, cells with a high level of metabolic activity that require a lot of ATP (muscle cells) have lots of large mitochondria with many cristae
Structure of chloroplasts
Vesicular plastids with double membrane
Thylakoids flattered discs stack to form grana; contains photosytems with chlorophyll
Intergranal lamellae, tubes attach thlyakoids in adjacent grana
stroma- fulid-filled matrix
Functions of chloroplast
Functions:
Carries out photosynthesis (converts light energy to chemical energy)
Structure of Endoplasmic Reticulum (ER)
A 3D system of membranes that spreads throughout the cytoplasm of a cell
The membranes form a network of tubules and flattened sacs called cisternae
It is continuous (attached to) the outer nuclear membrane
There are two types of ER:
Rough ER (RER)
SmoothER (SER)
Functions of ER
Rough ER - has ribosomes on its surface
Provides a large surface area for the synthesis of proteins
Provides a pathway for the transport of proteins throughout the cell
Smooth ER- lipid synthesis
Structure of Gogi apparatus
A stack of membranes that form flattened sacs, called cisternae
Cis face - where vesicles from the ER fuse
Trans face - where golgi vesicles pinch off regularly from the cisternae
Function of Gogi apparatus
Collects, modifies and transports molecules around or out of the cell
Proteins, lipids and carbohydrates produced in the ER enter and are passed through the golgi apparatus
Proteins are modified
The proteins are also ‘labelled’, allowing them to be sorted and then sent to their correct destination
Once sorted, the modified proteins and lipids are transported in golgi vesicles to their destination
Lysosomes structure
Form when vesicles that bud off the golgi apparatus contain hydrolytic enzymes for breaking things down (eg. proteases, lipases or lysozymes)
Lysosomes function
Hydrolyse material taken up by cells (phagocytic cells)
Release enzymes to the outside of the cell (exocytosis) in order to destroy external material
Digest old, worn out organelles for recycling
Break down of cells that have died
Structure of ribosomes
Small granules found in all cells
Occur in large numbers (can be almost 25% of the dry mass of the cell)
They may either be found in the cytoplasm or be attached to the rough ER
2 types:
80S (found in Eukaryotic cells) - larger
70S (found in Prokaryotic cells, mitochondria and chloroplasts) - smaller
Function of a ribosomes
the site of protein synthesis
Structure of vacuole
A fluid-filled sac with a single membrane
Usually a single large vacuole in plant cells
Contains a solution of minerals, sugars, amino acids, wastes and sometimes pigments
Function of vacuole
They support herbaceous plants (non-woody/soft) or herbaceous parts of woody plants by making cells turgid/rigid
Storage of substances
Sugars & amino acids - temporary food stores
Pigments - give colour in petals to attract pollinating insects
Structure of centroiles
Small hollow cylinders
A centrosome = 2 centrioles (oriented at right-angles to each other)
Form a network of fine fibres in the cytoplasm called the cytoskeleton made out of microtubules and filaments
Function of centrolie
Supports the cell’s shape
Organises and moves organelles
During cell division the pair separate to opposite ends of the cell and form the spindle
Structure of cell wall
Found in plant cells
Made of cellulose micro-fibrils - very strong so supports the functions
Fungi also have
Cell walls (chitin)
Algae also have cell walls (cellulose or Glycoproteins or both)
Functions of cell wall
Providing the cell with strength to prevent it bursting due to osmosis
Providing strength and support to the whole plant
Cytoplasm
Contains enzymes, site of many reactions and dissolve solutes and adds supports to the cell
plamaisa membrane
bi-layer of lipids and proteins channel
it allows certain molecules and charged molecules to enter and exist the cell as it is semi-permeable.
Role of plasimds
small ring of DNA that carries non-essential DNA
can be exchanged between bacterial cells via conjunction
Role of the flagellum
Roating tail propels organism
Role of collapse
Prevent desiccation and chemical attack
Pilus
Transfer of material between bacteria
Describe the first stage of cell fractionation and ultracentrifugation.
Homogenisation: This breaks open the cells to release the organelles. Vibrating the cells, or grinding them up in a blender.
Why use a ice-cold solution
cold to slow down and stop organelle activity, particularly the hydrolytic enzymes in lysosomes
Why is it buffered
to prevent changes in pH levels so organelle proteins are not damaged.
Why use the same water potential or isotonic
isotonic to prevent the movement of water in and out of organelles by osmosis.
Describe stage two of cell fractionation and ultracentrifugation.
Filter the solution through a gauze to remove debris e.g. large cell debris or tissue debris.
Describe stage three of cell fractionation and ultracentrifugation.
Ultracentrifugation:
Spin the solution in a centrifuge at a low speed.
The heaviest organelles (nuclei, chloroplasts) fall the to the bottom. The rest of the organelles stay suspended in the fluid above this sediment. This is the supernatant.
The supernatant is drained off, poured into another tube, and spun again at a very high speed. This time, organelles like mitochondria and lysosomes fall to the bottom. Again, the supernatant is drained off, poured into another tube and spun at a higher speed. Finally, the lightest organelles remain.
Material is separated on the basis of mass / density.
Detail viral replication
Requires a host cell
Complementary attachment proteins bind to cell surface receptors
Viral genetic material injected / enters host cell
Viral genes transcribed and viral proteins produced e.g. capsid
Viral genome replicated many times
New viruses assembled
Exit cell via cell surface membrane e.g. budding
What are the key features of viruses?
Acellular, non-living (NOT cells!)
20-300 nm
Contain DNA or RNA nucleic acids (genome)
Enclosed within a protein coat - capsid
Surface attachment proteins
Require a specific host cell to enter and replicate
no metabolism
no membrane
