Topic 2.1 Eukaryotic and Prokaryotic cell structure and function Flashcards
State the principle of cell theory
Cells are the fundemental units in all living organisms. They determine the function and organisiation of all biological systems. Cell theory is accepted as a unifying concept in biology.
State the relationship between a system and specialised cells
Specialised cells -> tissues that perform a specific function -> organs made of several tissue types -> organ systems
Who are the three “architects” of cell theory, what were the concepts they proposed?
- Mathius Schleiden (1804-1881) - the botanist - proposed plants are made from cells
- Theodore Schwann (1810-1882) - the physiologist - proposed animals are made of cells
- Rudolf Virchow (1821-1902) - the doctor - proposed cells come from pre-existing cells
What is a prokaryote?
Unicellular organisms with no membrane bound organelles - e.g. bacteria
What is the nucleoid?
Irregularly-shaped region of cytoplasm where loop of bacterial DNA is located
What is a plasmid?
One or more rings of DNA found in some bacterial cells.
Contains non-essential genes.
Can be exchanged between cells via conjugation.
Describe the structure of a bacterial cell wall and slime capsule
Peptidoglycan (murin) cell wall provides mechanical strength.
May be coated by slime layer to prevent dessication, adhere cells and provide nutrients.
Outline the process of gram staining
- Stain culture with crystal violet. Remove and rinse with water.
- Add iodine solution and remove after one minute.
- Add alcohol.
- Counterstain with red safranin for one minute.
- Dry and examine sample under microscope.
Describe gram positive cell walls
Thick peptidoglycan layer (insoluble in alcohol).
Purple under microscope when stained
Describe gram negative cell walls
Thin peptidoglycal layer with outer lipopolysaccharide membrane (alcohol-soluble).
Red under microscope when stained (as they hold safranin counterstain).
Why do Gram positive and Gram negative bacteria respond differently to certain antibiotics?
Antibiotics that inhibit peptidoglycan formation e.g. penicillin work on Gram positive bacteria. Since Gram negative bacteria have an outer membrane and a much thinner peptidoglycan layer, they aren’t affected.
Compare ribosome in eukaryotic and prokaryotic cells
Formed of protein and rRNA.
Have a large subunit which joins amino acids and small subunit with mRNA binding site.
Contrast ribosomes in eukaryotic and prokaryotic cells
Large subunit eukaryotic: 80S (bigger)
Large subunit prokaryotic: 70S (smaller)
What is a eukaryote?
Eukaryotic cells have a nucleus and membrane bound organelles - e.g. All plants, animals, fungi, algae and protists
Describe the structure of the nucleus
Surrounded by nuclear envelope, a semi-permeable double membrane.
Nuclear pores allow substances to enter/exit.
Dense nucleolus made of RNA and proteins assembles ribosomes.
Describe the function of the nucleus
Contains DNA coiled around chromatin into chromosomes.
Controls cellular processes: gene expression determines specialisation and site of mRNA transcription, mitosis, semiconservative replication.
Describe the structure and function of the endoplasmic reticulum (ER)
Both smooth and rough
Cisternae: network of tubules and flattened sacs extends from cell membrane and connects to nuclear envelope.
Rough ER: many ribosomes attached for protein synthesis and transport.
Smooth ER: lipid synthesis.
Describe the structure of the mitochondrion
Surrounded by double membrane folded inner membrane forms cristae: site of electron transport chain.
Fluid matrix: contains mitochondrial DNA, respiritory enzymes, lipids, proteins.
Describe the structure of the chloroplast
- Vesicular plastid with double membrane
- Thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll
- Intergranal lamellae: tubes attach thylakoids in adjacent grana
- Stroma: fluid filled matrix
State the function of the mitochondria
Site of aerobic respiration to produce ATP
State the function of the chloroplasts
Site of photosynthesis to covert solar energy to chemical energy
Describe the structure and function of the Golgi apparatus
Planar stack of membrane-bound, flattened sacs cis face aligns with rER:
molecules are processed in cristernae vesicles bud off trans face via exocytosis
- Modifies and packages proteins for transport
- Synthesises gylcoproteins
Describe the structure and function of the lysosome
Sac surrounded by a single membrane embedded H+ pump maintains acidic conditions contains digestive hydrolase enzymes gylcoprotein coat protects cell interior
- Digests contents of phagosome
- Exocytosis of digestive enzymes
Describe the structure and function of a plant cell wall
- Made of cellulose microfibrils for mechanical support
- Plasmodesmata form part of apoplast pathway to allow molecules to pass between cells
- Middle lamella separates adjacent cell walls
Describe the structure and function of the cell vacuole in plants
Surrounded by a single phospholipid membrane called a tonoplast.
Store cell sap, which contains mineral ions, water enzymes, soluble pigments.
Describe the function of the cell vacuole in plants
- Controls turgor pressure
- Absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm
Describe the structure and function of animal vacuoles
More commonly reffered to as vesicles.
Temporary membrane-bound sacs containing water and chemicals.
Numerous and much smaller than in plants.
Describe the structure and function of centioles
Spherical group of 9 tubules arranged in triples.
Located in centrosomes.
Migrate to opposite poles of cell during prophase and spindle fibres form between them.
Why do samples need to be stained for microscopy?
Stains bind to structures.
Heavy metals: electron microscopes
Coloured dye: optical microscopes
Facillitates absorbtion of electrons/ wavelengths of light to produce image. Contrast between heavily and lightly stained areas distinguishes structures.
Define magnification
Factor by which the image is larger than the actual specimen
Define resolution
Smallest separation distance at which two separate structures can be distinguished from one another
State the magnification and resolution of a compound optical microscope
Magnification: x2000
Resolution: 200nm
How does an optical microscope work?
- Lenses focus rays of light and magnify the view of a thin slice of specimin
- Different structures absorb different wavelengths of light
- Reflected light is transmitted to the observer via the objective lens and eyepiece
What limits the resolution of an optical microscope?
Diffraction of light.
Any structure closer than half the wavelength of light cannot be distinguished as separate.
Describe how a transmission electron microscope (TEM) works
- Pass a high energy beam of electrons through thin slice of specimin
- More dense structures appear darker since they absorb more electons
- Focus image onto fluorescent screen or photographic plate using magnetic lenses
State the magnification and resolution of a TEM
Magnification: x500,000
Resolution: 0.5nm
Describe how a scanning electron microscope (SEM) works
- Focus a beam of electrons onto a specimin’s surface using electromagnetic lenses
- Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate
State the magnification and resolution of an SEM
Magnification: x500,000
Resolution: 3-10 nm
Explain how to use the eyepiece graticule and stage micrometer to measure the size of a structure
- Place the micrometer on stage to calibrate eyepiece graticule
- Line up scales on graticule and micrometer. Count how many divisions are in 100μm on the micrometer
- Length of 1 eyepiece division = 100μm / number of divisions
- Use calibrated values to calculate actual length of structures
State an equation to calculate the actual size of a structure from microscopy
Actual size = Image size / Magnification
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