Bk1 Ch3 tour of cell Flashcards
What is the limiting factor that prevents small structures being discriminated using a light microscope?
The wavelength of visible light.
What does a scanning electron microscope (SEM)do?
Studies surface of intact cells and tissues
What does a transmission electron microscope (TEM) study?
Studies internal organisation of cells by passing beam of electrons through a very thin tissue section allowing analysis of organelles and other components
Cell fractionation
Process involving the separation of components of cells by disruption followed by ultracentrifugation.
What is a physiological solution
An artificially prepared solution that has pH and salt concentrations that mimic the internal environment of the cell.
Endospores
Dormant structures formed within some types of bacteria when growth conditions are unfavourable, which can later germinate and give rise to new individual bacteria
Cytoplasmic inclusions
Gas versicles, endospores, glycogen granules
Gas versicle
Surrounded by protein shell and have role in buoyancy of some aquatic bacteria
Glycogen granules
Glycogen is a polymer of glucose, which some bacteria store as an energy reserve
Peptidoglycan
Large polymer consisting of complex arrangement of sugars linked by amino acids including three amino acids are not found naturally in proteins
What are the cell walls of a bacteria composed off?
Peptidoglycan
What is the difference between the cell walls of gram positive and gram negative bacteria?
The peptidoglycan layer is much thicker in gram-positive bacteria
Suggest some Key cellular functions or processes
Synthesis of DNA, lipids, carbohydrates, proteins. Secretion, movement, protection, Cell division.
Suggest two functions of the cell surface
Protection, and absorption of nutrients. Secretion of signalling molecules or enzymes, disposal of selling of wastes, gas exchange, cell to cell recognition.
One major difference between different eukaryotes is the presence or absence of a cell ball in which eukaryotic kingdom to all cells lack a cell wall?
Animalia
Transmembrane proteins
Integral membrane protein which interacts with and spans the hydrophobic core of the lipid bilayer; may be described as single pass or multipass, depending on whether the polypeptide crosses the membrane once or more than once.
Peripheral proteins
Membrane proteins that are not associated with the hydrophobic interior of the lipid membrane; instead they either associate with the membrane indirectly via noncovalent interactions with other membrane proteins, or directly via interactions with the hydrophilic head groups of the lipids. The proteins that mediate attachment of integral membrane proteins to the cell cytoskeleton are examples of peripheral proteins.
Cytoskeleton in eukaryotic cells
System of specialised protein assemblies in cytosol of eukaryotes
Not fixed – highly dynamic – essential role in transport of organelles and some molecules within cell
Cytoskeleton in prokaryotes
Filaments assembled from proteins similar to eukaryotic cells e.g. actin
Prokaryotic cytoskeleton has role in cell division and maintaining cell shape and polarity.
How many types of filament does the cytoskeleton have?
Three
Microfilaments
Actin filaments
In all eukaryotes
Thinnest – diameter 6 nm thread like appearance under EM
actin in long helical chain mostly in networks or bundles
Prominent in cell cortex and in microvilli of absorptive epithelial cells
Microtubules
Tubulin
Alpha and beta form - maintains cell shape. Intracellular movement of organelles. Reorganisation of chromosomes during cell division
Hollow tubes of 13 parallel filament of tubulin assemblies. External diameter 25 nm
Animal cells microtubules radiate from MTOC – centrosome to cortex
Plant cells no centrosome MTOC appears different times to organise
Unstable assembles and disassembles till reaches organelle or capping protein
Determining cell shape.
Intermediate filaments
Diameter 8 to 10 mm
Several types protein e.g. keratin
Eight protofilaments round each other like rope
Main role: mechanical strength to cells and tissues.
What might happen to the shape of a cell if the capping proteins become confined to one part of the cell cortex?
Microtubules would only become stabilised at that region of the cell periphery so the cell could become polarised; that is, it could acquire an asymmetrical shape.
