2.1 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 organelles e.g. bacteria and archea
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 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, glycoproteins and glycolipds in the cell surface membrane
Cholesterol: steroid molecule connects phospholipids and reduces fluidity
Glycoproteins: cell signalling, cell recognition (antigens) and binding cells together
Glycolipds: cell signalling and 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 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,semi conservative replication
Describe the structure of a mitochondrion
Surrounded by double membrane, folded inner membrane forms Cristae: site of electron transport chain
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 attached to 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 stack of membrane-bound, flattened sacs cis face aligns with rER
Molecules are processed in cisternae vesicles bud off trans face via exocytosis:
Modifies and packages proteins for export
Synthesises glycoproteins
Describe the structure and function of a lysosome
sac surrounded by single membrane
Contains a embedded H+ pump which maintains acidic conditions and digestive hydrolase enzymes.
glycoproteins coat protects cell interior:
Digests contents of phagosome
Exocytosis of digestive enzymes
Describe the structure and function of a ribosome
Made up of protein and rRNA
Can be found 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: a network of tubules and flattened sacs extends from the cell membrane through cytoplasm and connects to nuclear envelope
Rough ER: many ribosome attached for protein synthesis and transport
Smooth ER: lipid synthesis’s
Describe the structure of the cell wall in plants and bacteria
Bacteria: made of polysaccharide murein
Plants: made of cellulose microfibrils
Plasmodesmata allow molecules to pass between cells, middle lamellla acts as boundary between adjacent cell walls
State the function 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 the cytoplasm
Explain some common cell adaptations
Folded membrane or microvilli increase surface area e.g. for diffusion
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 (usually unicellular) organism
State the role of the capsule in prokaryotes
A capsule is a polysaccharide layer that
Prevents desiccation
Acts as food reserve
Provides mechanical protection against phagocytosis and external chemicals
Sticks cells together
Compare eukaryotic and prokaryotic cells
Both have:
Cell membrane
Cytoplasm
Ribosome
Contrast eukaryotic and prokaryotic cells
Eukaryotic
- larger cells and often multicellular
- always have organelles and nucleus
- Linear chromosomes associated with histones
Prokaryotic
- small cells and always unicellular
- no membrane-bound organelles and no nucleus
- circular DNA not associated with proteins
Why are viruses referred to as ‘particles’ instead of cells
Acellular and non living: no cytoplasm, cannot self-reproduce, no metabolism
Describe the structure of a viral particle
Linear genetic material(DNA OR RNA) and 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 envelop 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 and 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 his 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 wavelength 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 e.g. using ultratome or by maceration
- Place plant tissue in a drop of water
- Stain tissue on a slide to make structures visible
- Add coverslip using mounted needle at 45 degree 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 ultra structure
Describe how a transmission electron microscope (TEM) works
Passes 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 wave length than light = high resolution so ultrastructure visible
+high magnification (X5000000)
-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 specimens 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
-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
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 100 micro meters on the micrometer
- length of 1 eyepiece division = 100 micrometer / 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
Image size = actual size X magnification
Outline what happens during cell fractionation and ultracentrifugation
- Mince and homogenize tissue to break open cells and release organelles
- Filter homogenate to remove debris
3.perform differential centrifugation
A)spin homogenate
B)the most dense organelles in the mixture form a pellet
C)filter off the supernatent and spin again at a higher speed
State the order of sedimentation of organelles during differential centrifugation
Most dense —> least dense
Nucleus—>mitochondria —>lysosome —>RER —>plasma membrane —>SER —>ribosomes
Explain why fractionation 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
