Topic 2 Cell Structure & Microscopy Flashcards
Explain why it’s not possible to identify the particular structure using an optical microscope.
-Because the wavelength of visible light is too long to distinguish between it.
-Resolution is too low.
Two structures that are found in all prokaryotic and eukaryotic cells.
-ribosomes
-cell surface membrane
Suggest a reason for faster rate of plasmid replication growing in a culture with a high AA conc.
AA used in protein synthesis
So more enzymes for plasmid replication.
Describe how a sample of chloroplasts could be isolated from leaves.
-homogenise/ grind it to break open cells
-ice cold (slow enzyme activity)
-buffered (minimise pH change so no denatured enzymes)
-isotonic solution (same WP no burst/shrinking)
-add to centrifuge spin at slow speed before inc the speed.
-1st pellet - nuclei
-2nd pellet - chloroplasts
Feature of chloroplast that allows protein to be synthesised inside it and a difference between this feature in the chloroplast and similar features in the rest of the cell.
Ribosomes
- smaller than cytoplasmic ribosomes
Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. (Don’t include details of transcription and translation)
- DNA in nucleus - code for proteins
- Ribosomes - synthesise proteins
- Mitochondria - produce ATP used for energy required in protein synthesis
- Golgi - packages and modifies proteins into vesicles.
- Vesicles - fuse with the cell membrane to release proteins from cells
Suggest why a nucleus isn’t visible in the microscope image.
Nucleus not stained
Why would details not be seen in a microscope image from an optical microscope?
-The wavelength of light is too long to distinguish between the different organelles.
- because the resolution is too low.
What is the cell wall component of plants?
Cellulose
What is the cell wall component of algae?
Cellulose
What is the cell wall component of Prokaryotes?
Murein
What is the cell wall component of fungi?
Chitin
Process by which prokaryotes divide?
Binary Fission
Contrast using TEM and optical microscope.
TEM:
- beam of e-
- higher resolution + magnification -> smaller organelles can be seen
- vacuum - no living specimen
- thinner specimen
- B&W only
Optical:
- visible light
- lower resolution + magnification
- living specimen
- colour
Name two structures present in plant cells that aren’t present in animal cells.
-chloroplasts
-vacuoles
Explain why biologists use a blender and filter mixtures in ultracentrifugation?
To break open the cells and remove any large chunks.
Suggest why the centrifuge tube was spun at a higher speed to obtain the sample of organelles named in example?
Because they are less dense than the nucleus.
What are the features of a bacterium?
- cell-surface membrane
- cytoplasm
What are the features of a virus?
- capsid
Two ways in which the nucleotides in DNA are different from nucleotides in RNA?
- deoxyribose vs ribose
- RNA has U instead of T
Why can cell-surface membranes only be seen with a TEM but not with an optical microscope?
The electron microscope has higher resolution than optical microscope.
Why are no organelles are visible in the cytoplasm of this red blood cell?
No organelles to make more space for haemoglobin to carry O2.
Why when under an electron microscope does a stain cause the cell-surface membrane to appear as two dark lines?
- because cell surface membrane made from phospholipid bilayer
- stain is attracted to phosphate groups “head” on phospholipid on inside and outside of molecule
Name two structures in a eukaryotic cell that cannot be identified using an optical microscope.
-ribosome
-mitochondria
