Cell Structure Flashcards
Define the term eukaryotic cell
DNA is contained in a nucleus, contains membrane-bound specialised organelles
Define the term prokaryotic cell
DNA is ‘free’ in cytoplasm, no membrane-bound organelles
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
Describe the structure and function of the csm
‘Fluid mosaic’ phospholipid bilayer with extrinsic and intrinsic proteins embedded
- isolates cytoplasm from extracellular environment
- selectively permeable to regulate transport of substances
- involved in cell signalling / cell recognition
Explain the role of cholesterol in the csm
Steroid molecule connects phospholipids & reduces fluidity
Explain the role of glycoproteins in the csm
Cell signalling, cell recognition & binding cells together
Explain the role of glycolipids in the csm
Cell signalling & cell recognition
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 & proteins assembles ribosomes
Describe the function of the nucleus
Contains DNA coiled around chromatin into chromosomes
Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis, semiconservative replication
Describe the structure of a mitochondrion
- surrounded by double membrane
- folded inner membrane forms cristae: site of ETC
- fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins
Describe the structure of a 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 mitochondria
Site of aerobic respiration to produce ATP
State the function of chloroplasts
Site of photosynthesis to convert solar energy to chemical energy
Describe the structure and function of the Golgi apparatus
Planar stack of membrane-bound, flattened sacks
Cis face aligns with rER
Molecules are processed in cisternae
Vesicles bud off trans face via exocytosis
- modifies & packages proteins for export
- synthesises glycoproteins
Describe the structure and function of a lysosome
Sac surrounded by single membrane Embedded H+ pump maintains acidic conditions Contains digestive hydrolase enzymes Glycoprotein coat protects cell interior - digest contents of phagosome - exocytosis of digestive enzymes
Describe the structure and function of a ribosome
Formed of protein & rRNA
Free in cytoplasm or attached to ER
- site of protein synthesis via translation
Large subunit: joins amino acids
Small subunit: contains mRNA binding site
Describe the structure and function of the endoplasmic reticulum (ER)
Cisternae: network of tubules & flattened sacs extends from cell membrane through cytoplasm & connects to nuclear envelope
- rough ER: many ribosomes attached for protein synthesis & transport
- smooth ER: lipid synthesis
Describe the structure of the cell wall
- bacteria: made of polysaccharide murein
- plants: made of cellulose microfibrils
plasmodesmata allow molecules to pass between cells, middle lamellae acts as boundary between adjacent walls
State the functions of the cell wall
- mechanical strength and support
- physical barrier against pathogens
- part of apoplast pathway (plants) to enable easy diffusion of water
Describe the structure and function of the cell vacuole in plants
Surrounded by single membrane: tonoplast contains cell sap: mineral ions, water, enzymes, soluble pigments
- controls turgor pressure
- absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm
Explain some common cell adaptations
- folded membrane or microvilli increase SA e.g for diffusion
- many mitochondria = large amounts of ATP for AT
- walls one cell thick to reduce diffusion distance pathway
State the role of plasmids in prokaryotes
- small ring of DNA that carries non-essential genes
- can be exchanged between bacterial cells via conjugation
State the role of flagella in prokaryotes
Rotating tail propels organism
State the role of the capsule in prokaryotes
Polysaccharide layer:
- prevents desiccation
- acts as food reserve
- provides mechanical protection against phagocytosis & external chemicals
- sticks cells together
Compare eukaryotic and prokaryotic cells
- cell membrane
- cytoplasm
- ribosomes (not membrane-bound)
Why are viruses referred to as particles instead of cells?
Acellular & non-living: no cytoplasm, cannot self-reproduce, no metabolism
Describe the structure of a viral particle
- linear genetic material & viral enzymes e.g reverse transcriptase
- surrounded by capsid (protein coat made of capsomeres)
- no cytoplasm
Describe the structure of an enveloped virus
- simple virus surrounded by matrix protein
- matrix protein surrounded by envelope derived from cell membrane of host cell
- attachment proteins on surface
State the role of the capsid on viral particles
- protect nucleic acid from degradation by restriction endonucleases
- surface sites enable viral particle to bind to & enter host cells or inject their genetic material
State the role of attachment proteins on viral particles
Enable viral particle to bind to complementary sites on host cell: entry via endosymbiosis
Describe how optical microscopes work
- Lenses focus rays of light and magnify the view of a thin slice of specimen
- Different structures absorb different amounts and wavelengths of light
- Reflected light is transmitted to the observer via the objective lens and eyepiece
Outline how a student could prepare a temporary mount of tissue for an optical microscope
- Obtain thin section of tissue
- Place plant tissue on a drop of water
- Stain tissue on a slide to make structures visible
- Add coverslip using mounted needle at 45 degrees to avoid trapping air bubbles
Suggest the advantages and limitations of using an optical microscope
\+ colour image \+ can show living structures \+ affordable apparatus - 2D image - lower resolution than electron microscopes = cannot see ultrastructure
Describe how a TEM works
- Pass a high energy beam of electrons through thin slice of specimen
- More dense structures appear darker since they absorb more electrons
- Focus image onto fluorescent screen or photographic plate using magnetic lenses
Suggest the advantages and limitations of using a TEM
+ electrons have shorter wavelength than light = high resolution so ultrastructure visible
+ high magnification (x500000)
- 2D image
- requires a vacuum = cannot show living structures
- long preparation time
- no colour image
Describe how a SEM works
- Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses
- Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate
Suggest the advantages and limitations of using an SEM
+ 3D image
+ electrons have shorter wavelength than light = high resolution
- require a vacuum = cannot show living structures
- no colour image
- only shows outer surface
Define magnification
Factor by which the image is larger than the actual specimen
Define resolution
Smallest separation distance at which 2 points can be distinguished from one another
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 100μm on the micrometer
- Length of 1 eyepiece division = 100μm / number of divisions
- Use calibrated values to calculate actual length of structures
How would you calculate actual size of a structure from microscopy?
actual size = image size / magnification
Outline what happens during cell fractionation and ultracentrifugation
- Mince and homogenize tissue to break open cells & release organelles
- Filter homogenate to remove debris
- Perform differential centrifugation
a) spin homogenate in centrifuge
b) most dense organelles in mixture form a pellet at the bottom
c) filter off the supernatant and spin again at a higher speed
What is the order of sedimentation of organelles during differential centrifugation?
nucleus -> mitochondria -> lysosomes -> RER -> plasma membrane -> SER -> ribosomes
Explain why fractionated cells are kept in a cold, buffered, isotonic solution
cold: slow action of hydrolase enzymes
buffered: maintain constant pH
isotonic: prevent osmotic lysis/shrinking of organelles
