cell structure and methods of studying cells Flashcards
Define magnification
The ability to make the image of the specimen larger
Define resolution
The ability to distinguish between objects that are close together
Explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure
- Place micrometer on stage to calibrate eyepiece graticule
- Line up scales on graticule and micrometer, count how many graticule divisions are in 100um on the micrometer
- Use calibrated values to calculate actual length of structures
State and equation to calculate actual size of a structure from microscopy
Actual size = image size / magnification
Outline what happens during cell fractionation and ultracentrifugation
- The sample is homogenised in a cold isotonic buffer solution to release organelles
- Filter homogenate to remove debris
- Ultracentrifuge sample at low speed so the largest organelles form a pellet and the rest stay suspended in the supernatant
- Filter out the pellet and re-centrifuge at a higher speed
State the order of sedimentation of organelles during centrifugation (least to most dense)
Lysosome → Ribosome → Mitochondria → Chloroplast → Nucleus
Explain why fractioned cells are kept in a cold, buffered isotonic solution
- Cold = slow actions of hydrolase enzymes
- Buffered = maintains constant pH
- Isotonic = prevent osmotic lysis/shrinking of organelles
How do you calculate total magnifications?
Eyepiece lens magnification x objective lens magnification = total magnification
Define the terms eukaryotic and prokaryotic cell
Eukaryotic: DNA is contained in a nucleus, contains membrane-bound specialised organelles
Prokaryotic: DNA is free in cytoplasm, no organelles
What are tissues and how do they form?
Tissues are formed by a group of cells working together to perform a particular function
What are organs and how do they form?
Organs are made from different tissues working together to perform a particular function.
What are organ systems and how do they form?
Organ systems are different organs working together to form organ systems.
Describe the structure and function of the cell surface membrane
- Fluid mosaic phospholipid bilayer with extrinsic and intrincsit proteins embedded
- Isolates cytoplasm from extracellular environment
- Selectively permeable to regulate transport of substances
- Involved in cell signalling/cell recognition
Describe the structure of the nucleus
- Surrounded by a 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: site of mRNA transcription, mitosis
Describe the structure of a mitochondrion
- Surrounded by a double membrane, folded inner membrane forms cristea a which is the site of the electron transport chain
- Fluid matrix contains mitochondrial DNA, respiratory enzymes, lipids and proteins
Describe the structure of a chloroplast
- Double membrane
- Thylakoids: flattened discs stack to form grana, contains chlorophyll
- Stoma: fluid-filled matrix
State the function of mitochondria and chloroplasts
Mitochondria: site of anaerobic respiration to produce ATP
Chloroplasts: site of photosynthesis to convert solar energy to chemical energy
Describe the structure and function of the Golgi apparatus
- The Golgi apparatus is are flattened sacs of fluid-filled membrane
- Golgi apparatus modifies proteins and lipids before packaging them into the Golgi vesicles
Describe the structure and function of the Golgi vesicles
- The vesicle is a membrane-bound sack for transport and storage
- The Golgi vesicles transport the proteins and lipids across the cell
Describe the structure and function of a lysosome
- Round organelle surrounded by a membrane with no clear internal structure
- Contain digestive enzymes (hydrolytic enzymes) which digest waste materials such as worn-out organelles or invading cells.
Describe the structure and function of a ribsosome
- Formed of protein and RNA, free in the cytoplasm or attached to the rough endoplasmic reticulum
- Site of protein synthesis via translation, the large subunit joins amino acids whereas the small subunit contains mRNA binding site
Describe the structure and function of the rough endoplasmic reticulum
- System of fluid-filled membranes with ribosomes covering the surface
- Folds and processes proteins made by the ribosomes
Describe the structure and function of the smooth endoplasmic reticulum
- System of fluid-filled membranes with no ribosomes
- Involved in the production, processing and storage of lipids and carbohydrates.
Describe the structure of the cell wall
- In bacteria, it is made of polysaccharide murein
- In plants and algae its made of cellulose microfibrils
- In fungal cells, its made of chitin
State the functions of the cell wall
- Mechanical strength and support
- Physical barrier against pathogens
- Part of appoplast pathway to enable easy diffusion of water
Describe the structure and function of the cell vacuole in plants
- Surrounded by a single membrane, contains cell sap
- Controls turgor pressure
- Absorbs and hydrolyses potentially harmful substances to detoxify the cytoplasm
Explain cell adaptations for efficient diffusion
- Folded membrane or microvilli to increase surface area for diffusion
- Many mitochondria so large amounts of ATP are synthesised for active transport
- Walls are once cell thick to reduce the diffusion pathway distance
State the role of plasmids in prokaryotes
- Small ring of DNA that carries non-existential genes
- Can be exchanged between bacterial cells
State the role of flagella in prokaryotes
- Rotating tail propels organism
State the role of the capsule in prokaryotes
- Acts as a food reserve
- Provides mechanical protection against phagocytosis
- Sticks cells together
What are the similarities between eukaryotic and prokaryotic cells
Both have:
- Cell membrane
- Cytoplasm
- Ribosomes
What are the dissimilarities between eukaryotic and prokaryotic cells?
- Prokaryotes are unicellular, and eukaryotes are multicellular
- Prokaryotes have no membrane-bound organelles and no nucleus, eukaryotes have organelles and nucleus
- Prokaryotes have circular DNA not associated with histone proteins, eukaryotes have linear chromosomes associated with histones
- Prokaryotes have smaller ribosomes than eukaryotes
- Prokaryotes have a capsule
Why are viruses referred to as particles instead of cells
They are acellular and non living
Describe the structure of a viral particle
- Linear genetic material (DNA or RNA)
- Surrounded by a capsid
- No cytoplasm
- Attachment protein
State the role of attachment proteins on viral particles
Enable viral particles to bind to complementary sites on host cells
Describe how optical microscopes work
- Lenses focus rays of light and magnify the view of a thin slice of a specimen
- Different structures absorb different amounts of wavelengths of light
- Reflected light is transmitted to the observer via the objective lens and eyepiece
Outline a method how a student could prepare a temporary mount of tissue for an optical microscope
- Obtain a thin section of tissue
- Place plant tissue in a drop of water
- Stain tissue on a slide to make structures visible
- Add a coverslip using a mounted needle to avoid trapping air bubbles
State the advantages of using an optical microscope
- Colour image
2. Can show living structures
State the disadvantages of using an optical microscope
- 2D image
2. Lower resolution than electron microscopes, cannot see ultrastructure
Describe how a transmission electron microscope work
- Pass a high energy beam of electrons through thin slice of specimen
- More dense structures appear darker since they absorb more electrons
Suggest advantages of using a transmission electron microscope
- Electrons have a shorter wavelength of light giving a high resolution so ultrastructure can be observed
- High magnification
Suggest disadvantages of using a transmission electron microscope
- 2D image
- Requires a vacuum so cannot show living structures
- Extensive preparation may induce artefacts
- No colour image
Describe how a scanning electron microscope works
- Focus a beam of electrons onto a specimens surface
2. Reflected electrons hit a collecting device and are amplified to produce an image
Suggest the advantages of using a scanning electron microscope
- 3D image
2. Electrons have a shorter wavelength than light so high resolution
Suggest the disadvantages of using a scanning electron microscope
- Requires a vacuum so cannot show living structures
- No colour image
- Only shows outer surface
