1.2 : Ultrastructure of Cells Flashcards
why does the electron beam in an electron microscope have a higher resolving power?
because an electron beam has a shorter wavelength than that of light (making them for advanced –>higher resolution)
what is freeze etching?
a method that involves the freezing and scrapping off of surfaces of structures with the use of liquid nitrogen.
what is cytosol?
aqueous fluid of metabolites around organelles.
what type of chromosome do prokaryotic cells contain?
a single, circular chromosome in their nucleus = nucleolus
how does binary fission occur in bacteria?
nucleolus divides –> replication starts at a particular sequence of bases = the gene that codes for the enzyme that triggers replication –> cell splits –> daughter cells each have a copy of chromosome (split nucleolus)
explain the main features and function of the nucleus
- only in eukaryotic cells
- surrounded by double-layered membrane, the nuclear envelope (which has many pores )
- contains chromosomes
- contains one or more nucleoli (site of synthesis of ribosomes)
- cell management and behaviour in cell division.
explain the main features and function of the centriole
- tiny organelle consisting of nine paired microtubules (unbranched, straight cylinders ) arranged in a short cylinder.
- animal cells have two that occur at right angles = centrosome
- important role in cell division –> replicate before animal cell division –> grow spindle fibres (responsible for movement of chromosomes during nuclear division)
- network of microtubules –> made of tubulin (globular protein)
explain the main features and function of the mitochondria
- found in all cells
- has a double membrane
- -> outer membrane = barrier
- -> inner membrane = folded to form cristae (dips)
- interior = matrix (aqueous solution of metabolites)
- site of aerobic stages of respiration (thus, ATP is formed here)
explain the main features and function of the chloroplasts
- biconvex shape
- green plants only (mesophyll cells)
- site of photosynthesis
- has a double membrane
- -> outer = barrier
- -> inner = tucked to form thylakoids –> arranged in flattened circular piles = grana = where chlorophyll & photosynthetic pigments are located.
- -> large amount of grana –> loosely arranged branching membranes between them –> aqueous matrix contains small starch grains = stroma.
- containing in group = plastids
explain the main features and function of the ribosomes
- built of two subunits
- do not have membrane
- contain RNA (protein + nucleic acid)
- found free in cytoplasm –> bound to rough endoplasmic reticulum
- site of protein synthesis = proteins with structural roles (collagen, biological catalysts)
explain the main features and function of the endoplasmic reticulum (SER & RER)
- consists of a network of branched membranes folded to form sheets and sacs that are extensively interconnected
- remains attached to nuclear envelope
RER :
- has ribosomes attached
- has vesicles at margin that form from swellings –> used to store and transport substances around cells
- site of synthesis of proteins –> ‘packaged’ when produced in vesicles & discharged.
SER:
- no ribosomes
- important in synthesis of lipids and carbohydrates & necessary substances needed by cells.
explain the main features and function of the golgi apparatus
- stack-like collection of flattened membranous cells
- -> one side of stack is formed by fusion of membranes of vesicles from the SER
- -> other stack is formed by vesicles (from swelling of SER margin) that become pinched off)
- site of synthesis of certain biochemicals (hormones & enzymes –> packaged into vesicles)
- -> animal cells = vesicles form lysosomes
- -> plant cell = vesicles contain polysaccharides for cell wall formation.
explain the main features and function of the lysosomes
- tiny vesicles bound by a single membrane
- contain a concentrated mixture of hydrolytic enzymes (digestive enzymes) = produced by golgi apparatus/RER
- involved in breakdown of food vacuoles –> any foreign / food particles are taken up into vacuoles –> broken down (occurs when lysosome fuse with vacuole) –> products of digestion escape into cytoplasm
- where autolysis occurs –> when an organism dies –> hydrolytic enzymes escape into cytoplasm & cause self - digestion = autolysis
explain the main features and function of the plasma membrane
- consists of lipid bilayer
- roles : to retain cytosol, forms a barrier (all substances entering and leaving cell must pass), where the cell si identified by surrounding cells (begins to conduct the same function as surrounding cells)
explain the main features and function of the cell wall
- external component
- made of cellulose (polysaccharide - strong & arranged in bundles = microfibrils)
- allows plant to develop high internal pressure during water uptake, without danger of cell bursting.
