topic 1.2- ultrastructure of cells Flashcards
what is the maximum resolution of a light microscope?
0.2 micrometers (μm)
what is the maximum resolution of an electron microscope?
0.001 micrometers (μm)
why does an electron have a much higher resolution than a light microscope?
beams of electrons have a much shorter wavelength.
explain how light microscopes work
light passes through the specimen, which filters out certain wavelengths of light
explain how an electron microscope works
electrons pass through the specimen and get absorbed.
define resolution
making the separate parts of an object distinguishable
state the two main differences between prokaryotes and eukaryotes
- prokaryotes have a simple cell structure that is not compartmentalised; eukaryotes have a compartmentalised cell structure
- eukaryotes have a nucleus bounded by a nuclear envelope consisting of a double membrane; prokaryotes do not have a nucleus
what do prokaryotes always have that eukaryotes only sometimes have?
a cell wall
give the three functions of a cell wall
- protects cell
- maintains cell shape
- prevents cell from bursting
in prokaryotes, the cell wall contains ——–
peptidoglycan
what is the size of prokaryotic ribosomes?
70S
what does the unit ‘S’ stand for?
Svedberg units
why does the DNA (or nucleoid) in prokaryotes appear lighter on electron micrographs?
it is not associated with proteins
list all the features of a prokaryotic cell that should be drawn.
- cell wall
- cytoplasm
- pili
- flagella
- plasma membrane
- 70S ribosomes
- nucleoid (with naked DNA)
what is the function of the flagella and pili?
- flagella are mainly responsible for motility (sensitive to temperature, chemicals and metals)
- pili are mainly responsible for attachment during conjugation and motility
give 4 advantages of a cell being compartmentalised
- enzymes/substrates for a process can be more concentrated than if they were spread throughout cytoplasm
- substances that could cause damage to cell can be kept inside membrane of an organelle (eg digestive enzymes of a lysosome)
- conditions such as pH can be maintained at ideal for a particular process (may be different to optimum levels for cells)
- organelles with their contents can be moved around within the cell.
list the features of eukaryotic cells that should be drawn
- plasma membrane
- cytoplasm
- 80S ribosomes
- nucleus
- mitochondria
(- rough endoplasmic reticulum)
(- Golgi apparatus)
(- lysosomes)
(- chloroplast)
(- vacuoles and vesicles)
(- microtubules and centrioles)
(- cilia and flagella)
describe the nucleus in eukaryotic cells
- nuclear envelope: a double membrane with pores
- contains nucleolus, where ribosomes are made
- contains chromosomes, consisting of DNA associated with histone proteins, and chromatin (uncoiled chromosomes)
- where transcription occurs (DNA-> mRNA)
describe the rough endoplasmic reticulum (rER) in eukaryotic cells
- consists of cisternae (flattened membrane sacs)
- 80S ribosomes attached to outside of cisternae
- rER synthesises proteins for secretion/cell membrane from the cell
describe the ribosomes in eukaryotic cells
- not surrounded by a membrane
- 80S
- synthesise proteins and release it to work in the cytoplasm
describe the Golgi apparatus in a eukaryotic cell
- consists of cisternae (flattened membrane stacks)
- processes proteins brought in vesicles from the rER
- most are then carried in vesicles to plasma membrane for secretion
describe how the cisternae in the Golgi differ from the cisternae in rER
- not as long
- often curved
- do not have attached ribosomes
- many vesicles nearby
describe the lysosomes in eukaryotic cells
- approximately spherical with a single membrane
- formed from Golgi vesicles
- contain high concentrations of protein and digestive enzymes which are used to break down ingested food/organelles/whole cell
describe the mitochondrion in eukaryotic cells
- surrounded by a double membrane
- inner membrane invaginated to form structures called cristae
- contains matrix (fluid)
- produce ATP by aerobic respiration
- fat digested here if it is being used as an energy source
- contains own DNA
