Cell Structure Flashcards
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 membrane bound organelles
State the relationship between a system and specialised cells.
Specialised cells —> tissues that perform specific function —> organs made of several tissue types —> organ systems
Describe the structure and function of the cell-surface membrane.
Fluid mosaic phospholipid bilayer.
- isolates cytoplasm from extracellular environment
- selectively permeable to regulate transport of substances
- involved in cell signalling / cell recognition
Explain the role of cholesterol, glycoproteins & glycoproteins in the cell-surface membrane.
Cholesterol: steroid molecule connects phospholipids & reduces fluidity.
Glycoproteins: cell signalling, cell recognition & binding cells together
Glycolipids: 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 and semi-conservative replication
Describe the structure of a mitochondrion.
- surrounded by double membrane folded inner membrane form cristae: site of electron transport chain
- fluid matrix: contains mitochondrial DNA, respitory 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 and chloroplasts.
- mitochondria: site of aerobic respiration to produce ATP
- chloroplasts: site of photosynthesis to convert solar energy to chemical energy
Describe the structure and function of the Golgi apparatus.
Planar stach of membrane-bound, flattened sacs 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:
- digests 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 translate:
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 encelope:
- 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 lamella acts as boundary between adjacent cell 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 hydrolyse potentially harmful substances to detoxify cytoplasm
Explain some common cell adaptations.
- folded membrane or microvilli increase surface area
- many mitochondria = large amounts of ATP for active transport
- walls one cell thick to reduce distance of diffusion 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.
Both have:
- cell membrane
- cytoplasm
- ribosome
Contrast eukaryotic and prokaryotic cells.
Prokaryotic:
- small cells & always unicellular
- no membrane-bound organelles
- circular DNA not associated with proteins
- 70s ribosomes
- binary fission
- murein cell walls
- capsule
Eukaryotic:
- larger cells & often multicellular
- always have organelles & nucleus
- linear chromosomes associated with histones
- 80s ribosomes
- mitosis and meiosis
- cellulose cell wall
- no capsule
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
- surrounded by capsid
- 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 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 particles 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.
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 transmission electron microscope 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 (500000)
- 2D image
- requires a vacuum = cannot show living structures
- extensive preparation may introduce artefacts
- no colour image
Describe how a scanning electron microscope (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 photograph plate
Suggest the advantages and limitations of using a SEM.
+ 3D image
+ electrons have shorter wavelength than light = high resolution
- requires a vacuum = cannot show living structures
- no colour image
- only shows outer surface
Define magnification and resolution.
Magnification: factor by which the image is larger than the actual specimen
Resolution: smallest separation distance at which 2 separate structures can be distinguished from one another
Outline what happens during cell fractionation and ultracentrifugation.
- Homogenise tissue to break open cells & release organelles
- Filter homogenate to remove debris
- Perform differential centrifugation
a) spin homogenate in centrifuge
b) the most dense organelles in the mixture form a pellet
c) filter off the supernatant and spin again at a high speed
State the order of sedimentation of organelles during differential centrifugation.
Most dense —> least dense
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
