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
State the relationship between a system and specialised cells
Specialised cells - tissues that perform specific functions - 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 substances
Involved in cell signalling/ cell recognition
Explain the role of cholesterol in the cell surface membrane
A steroid molecule connects phospholipids and reduces fluidity
Explain the role of glycoproteins in the cell surface membrane
Involved in cell signalling, cell recognition and binding of cells together
Explain the role of glycolipids in the cell surface membrane
Involved in cell signalling and cell recognition
Describe the structure of the nucleus
Surrounded by the 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 of mitochondria
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 chloroplast
Vesicular plastid with double membrane
Thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll
Intergranal lamellae: tubes atach 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
Stack of membrane bound, flattened sacs aligned with the rough endoplasmic reticulum
Molecules are processed in cisternae vesicles
Modifies and packages proteins for export
Synthesises glycoproteins
Describe the structure and function of a lysosome
Sac surrounded by a single membrane embedded H+ pump maintains acidic conditions, contains digestive hydrolase enzymes
Digests contents of phagosome
Exocytosis of digestive enzymes
Describe the structure and function of a ribosome
Formed of protein and rRNA free in the cytoplasm or attached to endoplasmic reticulum
Site of protein synthesis via translation:
Large subunit: joins amino acids
Small subunits: contains mRNA binding site
Describe the structure and function of the endoplasmic reticulum
Cristernae: network of tubules and flattened sacs extends from cell membrane through cytoplasm and connects to nuclear envelope
Rough ER: many ribosomes attached for protein synthesis and transport
Smooth ER: lipid synthesis
Describe the structure of the cell wall
Bacteria: made of the polysaccharide murein
Plants: made of cellulose microfibrils, plasmodesmata allow molecules to pass between cells
State the functions of the cell wall
Provide strength and support
Physical barrier against pathogens
Part of the apoplast pathway to enable easy diffusion of water
Describe the structure and function of the cell vacuole in plants
Surrounded by a single membrane: tonoplast
Contains cell sap: mineral ions, water, enzymes, soluble pigments
Controls turgor pressure
Absorbs and hydrolyses potentially harmful substances
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 conjunction
State the role of flagella in prokaryotes
Rotating tail propels organism
State the role of the capsule in prokaryotes
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
Ribosomes
Contrast eukaryotic and prokaryotic cells
Prokaryotic:
Small cells
No membrane bound organelle and no nucleus
Circular DNA
Small ribosomes
Eukaryotic:
Larger cells
Have organelles and a nucleus
Linear DNA
Large ribosomes
How do 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 eye piece
Give 2 advantages and disadvantages of using an optical microscope
+ Colour image
+ Affordable apparatus
- 2D image
- Lower resolution than electron microscopes
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
Give 2 advantages and disadvantages of transmission electron microscopes
+ High resolution as electrons have a shorter wavelength than light
+ High magnification
- 2D image
- No colour image
Describe how a scanning electron microscope 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 disadvantages of scanning electron microscopes
+ 3D image
+ High resolution as electrons have a shorter wavelength than light
- No colour change
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
- Mince and homogenize tissue to break open cells and 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 higher 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
