Cell topic 1 questions Flashcards
Which are the smallest and most numerous organelles?
Ribosomes
Which are the most extentions of the inner membrane in mitochondria?
Cristae
What organelle contain hydrolytic enzymes?
Lysosomes
What is the cell wall made of in a prokaryote?
Murein
What is the resolving power (resolution) of a microscope?
The minimum distance apart 2 objects can be seen as separate objects.
What does a centrifuge do?
Spins cell fragments at very high speed.
What is a homogenate?
Fluid containing intact organelles released from a cell
In microschopy, the actual length of an object is calculated as?
Image size/Magnification
What microscope has the highest resolving power?
Transmission Electron Microscope (TEM)
What stage takes up the most time in the cell cycle?
Interphase / S-phase
By what process do prokaryotic cells divide
Binary fission
Phosopholipids form a bilayer in cell membrane structure because they contain…
Hydrophillic heads and hydrophobic tails.
Why can’t most molecules free difuse across a cell membrane?
Not soluble in lipids.
Why is facilitated diffusion a passive process?
It does not require ATP from respiration
What are the four factors that affect rate of diffusion?
- Concentration gradient
- Temperature
- Surface area
- Thickness of exchange surface
When can facilitated diffusion occur?
Can only occur at protein channels and carrier proteins.
What is the function of the SER (Smooth endoplasmic Reticulum?
Synthesises, stores and transports lipids and carbohydrates.
Why do specimens have to be kept in a vacuum to be viewed with an electron microscope?
Because electrons are absorbed by molecules in the air and will not reach the specimen.
Describe the steps you might take to isolate mitochondria from a cell culture in the laboratory.
- Lyse the cells - The cells in the sample are broken open using a blender - this step is known as homogenisation.
The cells must be kept under very specific condtion
Ice cold: reduces the activity of the enzymes. Isotonic solution: there is no water potential for osmosis to occur, which could cause the organelles to shrink or burst. Buffered solution: this keeps the pH at a constant level to prevent damage to protein structure. - Filtration - The homogenised sample is filtered through a gauze. Filtration separates the larger components from the smaller organelles.
- Ultracentrifugation - The filtered samples are spun at a low speed in a centrifuge. It is important that each tube is
balanced with a tube directly opposite. Heavier
components are forced to the bottom of the tube. Lighter components rise to the top. - Repeat - The supernatant from the first round of centrifugation is centrifuged again. The pellet this time will be the nuclei from the cells (this is the first pellet). The process is repeated and the mitochondria will be isolated in the third pellet.
Having isolated the mitochondria, why would TEM be favourable to SEM to image the organelle and identify the double membrane structure?
Higher resolution - Transmission electron microscopy can achieve a higher resolution than scanning electrons microscopy which would be needed to identify the two separate membranes.
Can see internal structures - Electrons pass through the sample in TEM rather than being scattered off the sample in SEM. This means that TEM can visualise structures within the cell.
Greater magnification - Mitochondra are between 0.5 - 10 micrometers in size and so it requires very high magnification to visualise their internal consituents.
What are the steps involved in cell fractionation?
- The tissue sample is homogenised using a blender to break the cells.
- The tissue sample is filtered into tubes through a gauze to separate larger components from the small organelles.
- The organelles are filtered into tubes to be fractionated using ultracentrifugation.
- The samples are spun at a low speed in a centrifuge to separate the sample into fractions.
- The supernatant is poured off and centrifuged at a higher speed to separate the next heaviest organelles. This is repeated at increasingly higher speeds to separate each fraction.
What are the two types of electron microscopes?
There are two main types of electron microscopes:
- Transmission Electron Microscope (TEM)
- Scanning Electron Microscope (SEM)
What’s the differences between the SEM and TEM?
- TEMs use electromagnets to focus the electron beam. Whereas in SEMs, a beam of electrons moves back and forth across a cell’s surface, creating details of cell surface characteristics.
- TEMs are high resolution microscopes whereas in SEMsResolution is lower.
What is the approximate maximum magnification of a optical light microscope?
1,500x
