A2.2 Cell structure Flashcards
( ˘•~•˘ )
Light microscope
- inexpensive to purchase and operate
- simple and easy specimen
- up to 2000x
- living OR dead specimens
Electron microscope
- expensive to purchase and operate
- complex, length specimen preparation
- up to 500,000x
- specimens must be DEAD, fixed in plastic material
- structural features they do not exist (artefacts) are seen in pictures
Steps for microscope calibration and measurement :(
- Calibrate: Use a stage micrometer slide with known measurements to calibrate the microscope
- Magnification: Select desired magnification level using eyepiece and objective lens
- Measure: Focus on the specimen and measure its size using the calibrated ruler on the magnification slide
- Convert: Convert measurements to actual units based on the units increments
- Account for magnification: Adjust measurements to reflect the actual size, considering the magnification factor
- Calculate: Multiply measured units by conversion factor to determine specimens size
- Verify: double check results for consistency and accuracy
2 techniques to prepare for electron microscopy
Freeze fracture EM:
Purpose: to prepare sample for observation
Process: rapid freezing of biological sample followed by physically breaking the sample apart
Makes clear: plane through sample
Enhanced understanding of: cell membrane (surface of the specimen)
Cryogenic EM
Purpose: enables image to be formed using computer enhancement that shows the 3D protein framework for functions of a cell
Process: utilises low temperature to freeze specimens in ice
Makes clear: 3D structure of biomolecules and their assemblies
Enhanced understanding of: structural biology (virus composition/structure, cell membrane components and arrangement, cellular protein synthesis…)
2 preparation techniques for light microscopy
Fluorescent stains:
Principle: substances/dye combine with specific cellular components. When the samples are irradiated with UV/violet-blue substances, the parts that accept dye fluoresce. When fluorescence occurs, assorted colours are produced, allowing for more detailed visibility.
Application: Recently been used to target RNA
Immunofluorescence:
Principle: involves antibodies that already have dyes combined to them. Specific antibodies combined with unique coloured dyes recognise and target certain molecules, allowing the target (usually a protein) to be detected.
Application: detect viral proteins that have infected cells
Structures common in all cells + their functions
DNA - genetic material, regulates chemical reactions by controlling enzyme production in organelles
Cytoplasm - site of all chemical reactions, contains all necessary ingredients (e.g. carbon compounds, ions etc)
Plasma membrane - phospholipid bilayer, protects contents from surrounding environment. Membrane proteins give cells identity, facilitate communication and transport btwn cells
Difference btwn eukaryotic and prokaryotic cells (5)
Prokaryote:
- Dna in ring form w/o protein
- 70s ribosome
- No mitochondria
- DNA free in cytoplasm in nucleoid region
- No internal compartmentalisation
- Divide by binary fission
Eukaryote:
- Dna with proteins as chromosomes
- 80s ribosome
- mitochondria
- DNA enclosed in nuclear membrane
- Internal compartmentalisation
- Divide by Mitosis/meiosis
(In-depth) Features of prokaryote cells
Cell wall - (same function as plant cells) made of peptidoglycan. Some bacteria have a polysaccharide capsule outside to adhere to structures
Plasma membrane - similar in composition to that of eukaryotic cells. Plays a role in binary fission
Pili - hair-like growth on the outside of the bacterial cel wall. Main function is to join with other bacterial cells in preparation of transfer of DNA
Flagella - Longer than pili, anchored to cell wall and plasma membrane. Allows the cell to move
70s ribosomes - protein synthesis, occur in large numbers. Composed of protein and ribosomal RNA
Cytoplasm - all cellular processes take place in cytoplasm as there is no compartmentalisation.
Nucleoid - Region NOT surrounded by membrane. Contains a naked loop of DNA (no coiling around histone proteins)
Plasmids - Small, circular DNA molecules. Replicated independently of chromosomal DNA. Not normally required but can help the cell to adapt under unusual circumstances.
Binary Fission
- DNA is copied, resulting in 2 daughter chromosomes.
- Daughter chromosomes become attached to 2 different parts of the cell membrane and divides into 2 genetically identical daughter cells.
- includes an elongation of the cell and a partitioning of the newly produced DNA by specialised fibres
Bacillus and Staphylococcus shape
Bacillus: rod shaped
Staphylococcus: spherical shaped
structure and function of eukaryotes (14)
Nucleus - Double membrane with pores to allow mRNA to enter the nucleus, allowing for compartmentalisation of eukaryotic DNA. Chromosomes associated with histone proteins found inside.
80s ribosomes - Protein synthesis
Mitochondria - Aerobic respiration, produces ATP. Has its own DNA, double membraned, matrix inside inner membrane, cristae provides large surface area for chemical reactions to occur. 70s ribosomes.
RER - Membrane structure with ribosomes attached. Site of protein synthesis. Involved in transportation of proteins to Golgi apparatus
SER - Membrane structure without ribosomes attached. Involved in lipid synthesis and detoxification. Production of phospholipids and sex hormones e.g. testosterone
Golgi apparatus - Consists of flattened sacs (cisternae) stacked on top of one another. Modifies and packages proteins to be excreted from the cell. Cis side receives vesicles from RER, vesicles leave by the trans side.
Cytoplasm - Site where most metabolism of the cell occurs. Mostly comprised of water, contains cytoskeleton
Plasma membrane - Made of phospholipids. Controls what enters and exits the cell.
Lysosomes - Specialised vesicles containing enzymes, involved in the digestion of large molecules. Involved in phagocytosis, carry modified materials wherever needed.
Cytoskeleton - Comprised of protein microtubules. Actin filaments aid in cell division and movement. Intermediate filaments reinforce cell shape and anchor some organelles. Microtubules provide shape and support and serve as tracks for organelle movement.
Chromosomes - DNA wrapped around histone proteins, genetic material for growth and development of the cell.
Vacuoles - Plants have large vacuoles (aid in water uptake, provide rigidity) involved in storing nutrients. Animal cells have numerous small vacuoles involved in the removal of waste, storage of potential food, toxins, water.
Chloroplasts - double membraned, 70s ribosomes, own DNA, interior has grana, thylakoids, stroma (contains enzymes and chemicals necessary for photosynthesis)
Centrosome - in Animal cells consists of a pair of centrioles. In plant cells consists of centrosome-like regions. Both are involved in the assembly of microtubules, which are important as they provide cell structure and movement.
Difference in eukaryote cell structure btwn plants, animals, fungi cels. (6)
Plants:
- Exterior of cell composes of a cell wall made of cellulose, with a plasma membrane within
- Chloroplasts present in cytoplasm, enabling production of carbohydrates
- Large central vacuole
- stores carbohydrates as starch
- Rigid cell wall = fixed cell shape
- centrosomes with no centrioles
Animals:
- Exterior of cell is plasma membrane
- no chloroplasts present
- small and numerous vacuole
- stores carbohydrates as glycogen
- No cell wall = flexible, round
- centrosomes with centrioles
Fungi:
- Exterior of cell is cell wall made of chitin, with a plasma membrane inside
- no chloroplasts present
- small and numerous vacuole
- stores carbohydrates as glycogen
- cell wall allows for a degree of flexibility
- centrosomes with no centrioles
Examples of atypical eukaryotic cells with more/less than one nucleus (4)
Aseptate fungal hyphae: Fungi have a filamentous structure called hyphae separated by internal cell walls called septa. Some fungal hyphae are not separated by septa and are MULTINUCLEATED
Straited skeletal muscle fibre: Multinucleated
RBC: no nucleus = carry more oxygen
Phloem sieve tube elements: no nucleus to allow transportation by acting as a hollow tube, having minimal cellular components (ribosomes, cytoskeleton, cytoplasm) and sustained by companion cells
Describe endosymbiotic theory
- Larger cell with nucleus and capable of sexual reproduction engulfs smaller prokaryotic cell capable of energy production = mutually beneficial relationship
- Large cell provides protection and carbon compounds, smaller cell provides energy, evolving to become a mitochondria
Evidence to support endosymbiotic theory
- Mitochondria are about the size of bacterial cells
- Divide by binary fission
- have their own circular DNA independent of host cell
- have 70s ribosomes
- double membrane consistent with an engulfing process, with inner membrane having the composition of a prokaryote and outer membrane resembling the eukaryote
- RNA in prokaryotic ribosomes closely resembles that of RNA in mitochondria ribosomes
