3. cell structure Flashcards
formula for magnification
m= image/object
what must be prepared before cell fractionation and why (3)
must be in a cold, isotonic (same water potential), buffer solution
cold;
reduce enzyme activity
isotonic;
no osmotic effect
buffered;
ph stays the same, which might affect cell and enzymes
describe the two steps of cell fractionation
cells are broken up by homogenizer resulting in homogenate, which is filtered
the homogenate is spun at different speeds, resulting in:
- at a slow speed, the heaviest organelles (nucleus) are forced to the bottom forming a pellet
- the (supernatant) is removed and spun at a high speed the next heaviest organelles (mitochondria) are forced to the bottom
process repeats, separating smaller and smaller organelles
explain the main differences between TEM and SEM
TEM transmits beams of electrons through the specimen, denser=darker
SEM scans a beam of electrons that bounce off the specimen and are detected producing 3d image
give advantages and disadvantages of TEM
advantage- high resolution, internal structures can be seen
disadvantages- only very thin specimens can be used, cannot use live specimens, black and white
give advantages and disadvantages of SEM
advantages- 3d, used on 3d specimens
disadvantages- lower resolution (compared to TEM) , connect on live specification, black and white
Describe five features of the nucleus
- nuclear envelope- the double membrane surrounding the nucleus, continuo with SER and RER. controls entry and exit of materials in and out of the nucleus.
- nuclear pores- allows passage of large molecules eg. mRNA
- nucleoplasm- jelly-like material making up most of the nucleus
- chromosomes
- nucleolus, manufacturers rRNA and builds ribosomes
What are the functions of the nucleus? (3)
act as a ‘control center’ producing mRNA and tRNA
retain genetic material in form of DNA and chromosomes
manufacture of rRNA and ribosomes
Describe the structures of the mitochondrion (2)
Double membrane, the inner membrane is folded to form cristae, providing a large SA
Matrix, contains proteins, lipids, DNA, and ribosomes. allowing mitochondria to make their own proteins. eg enzymes
Describe the structure of the chloroplasts
grana
- stacks of thylakoids which are filled with chlorophyll
- absorption of light (first stage)
the stroma
- fluid filled matrix
- production of sugars (second stage)
Describe the overall process of interphase
Cell is enlarged
Organelles are duplicated
DNA is stored in nucleus
Prophase
- chromosomes form, consisting of two identical sister chromatids, joint at centromere
- centrioles move to opposite poles of cell
- nuclear envelope brakes down
- centromere forms spinal fibre
Metaphase
- spinal fibres connect to chromosomes
- chromosomes are lined up on the equator
Anaphase
- spinal fibres contract, chromatids separated from centromere
- chromosomes move to opposite poles of cell
- requires ATP
Telophase
- spinal fibres
- chromosomes decadence
- nuclear membrane reforms around each set of chromosomes
