Cell Structure Flashcards
(36 cards)
1
Q
2.1 Microscopy
A
- m to cm (x100)
- cm to mm (x10)
- mm to μm (x1000)
- μm to nm (x100)
2
Q
Light Microscope
A
- cannot distinguish objects closer than ½ wavelength of light
- max resolution = 200 nm
- max magnification = 1,500 X
- observes eukaryotic/whole cells (nuclei, mitochondria & chloroplasts)
- CANNOT observe ribosomes, lysosomes & endoplasmic ret.
3
Q
Electron Microscopes
A
- beam of electrons used have a smaller wavelength than light
- max resolution = 0.2 nm
- max magnification = 1,500,000 X
- CAN observe ribosomes, lysosomes & endoplasmic ret.
- CANNOT observe live specimens as water must be removed
- requires very thin specimen & careful staining
- stains can create artefacts
- cannot produce coloured images
4
Q
Transmission Electron Microscope (2D)
A
- max mag. = 500,000 X
- electromagnets are used to focus electron beams which are then transmitted through specimen
- denser specimen absorbs more electrons
- dense areas of cell appear darker (contrast)
- allows internal structure to be seen
5
Q
Scanning Electron Microscope (3D)
A
- max mag. = 100,000 X
- scans electron beams across specimen which bounce of surface creating an image
- can be used on thick specimen
- specimen must be coated with a metal
- allows external structure to be seen
- lower resolution than TEMs
6
Q
Laser Scanning Confocal Microscope
A
- cells are stained with fluorescent dyes
- cells are scanned with laser beams that reflect off the dye
- multiple depths of organism is scanned to produce a 3D image
- specific proteins & structure within cell can be observed
- higher res. than light microscopes
- slow process
- possibility of photodamage
7
Q
Magnification & Resolution
A
- image/actual
- total mag = eyepiece mag x objective lens mag
- light is diffracted as it passes through specimen
- light rays overlap as points get closer which can “blur” images
8
Q
Slide Preparation
A
Dry Mount e.g. hair
- solid specimen cut into very thin slices (or whole) aka ‘sectioning’
- specimen placed in centre of slide
- cover slip placed over specimen
Wet Mount e.g. cheek cell
- used for specimen suspended in water or immersion oil
- cover slip is placed at an angle to avoid air bubbles
9
Q
Slide Preparation 2
A
Squash Slide e.g. root tip
- wet mount prepared first
- a lens tissue is used to press down cover slip to prevent finger residue
Smear Slide e.g. blood
- slide used to smear specimen to create a thin layer
- cover slip is placed over the thinnest section of specimen at a 45° angle
10
Q
Staining
A
- ‘Crystal Violet’ & ‘methylene blue’ are positively charged dyes that stain negatively charged material in cytoplasm
- ‘Nigrosin’ & ‘Congo red’ are negatively charged dyes that are repelled by cytosol
- ^ the dye remains outside cell so it stands out from background
11
Q
Differential Staining
A
Gran stain technique:
- separates bacteria into two groups (gram-positive & gram-negative)
- counterstains are used
Acid-fast technique:
- separates species of mycobacterium from other bacteria
- chloroplasts don’t need stains as they show up green (natural colour)
- dyes used in electron microscopes cause tissues to show up black or different shades of grey
12
Q
Calibration
A
- an eyepiece graticule has no fixed units
- a stage micrometer is a stage with a 1mm line on it
- ^ used to find out how many µm each graticule unit represents
- each objective lens needs to be calibrated separately
- micrometer & eyepiece grat. must be aligned
13
Q
2.4 Eukaryotic Cells
A
- DNA is contained in a membrane-bound nucleus and is a linear molecule
- DNA is coiled around histone proteins
- contains membrane-bound organelles
- has larger ribosomes than prokaryotes
14
Q
Cell Wall
A
- freely permeable to most substances (including water molecules)
- offers structural support to cell
- support is provided by cellulose
- microfibril mesh produces strength
- helps resist hydrostatic pressure; making cell wall rigid to maintain structure
- cell wall in fungi is composed of chitin
15
Q
Plasma Membrane
A
- controls exchange of materials between the internal and external cell environment
- partially permeable due to phospholipid bilayer
16
Q
Nucleus
A
- present in all eukaryotic cells except red blood cells
- contains chromatin (a complex of DNA and histone proteins)
- contains nucleoplasm [which contains nucleotides & enzymes]
17
Q
Nucleolus
A
- spherical structured
- the darker stained region of nucleus on an electron micrograph
- produces & transcribes ribosomal RNA (rRNA) and it’s subunits
18
Q
Nuclear Membrane
A
- surrounded by a double membrane aka. ‘nuclear envelope’
- outer mem. is continuous with RER
- DNA is too large to leave nucleus to the site of p. synthesis in the cell cytoplasm
- nuclear pores allow mRNA & ribosomes to be transcribed out of nucleus
19
Q
Mitochondria
A
- double (mitochondrial) membrane
- site of aerobic respiration in all e. cells
- inner membrane is folded to form ‘cristae’, therefore; great S.A.
- enzymes for oxidative phosphorylation are found in cristae
20
Q
Mitochondria 2
A
- contains a gel-like material called the ‘matrix’ which contains enzymes needed for the ‘Krebs Cycle’ in aerobic respiration
- ^ this produced ATP (the energy-carrying molecule)
- contains loop of mtDNA & mitochondrial ribosomes
21
Q
Chloroplast
A
- double membraned
- membrane-bound flattened discs called ‘thylakoids’ are where light-dependent reactions take place
- thylakoids contain chlorophyll needed
- stack of thylakoids = ‘grana’
- grana is joined together by lamellae
- ‘lamellae’ = flattened membranes
- ^ allows chemicals to pass between grana
22
Q
Chloroplast 2
A
- fluid material = ‘stroma’
- ^ where light-independent reactions take place
- starch is stored as ‘starch granules’
- contains loop of chloroplast DNA & ribosomes
23
Q
Ribosome
A
- found freely in cytoplasm of all cells
- a complex of rRNA + proteins
- site of translation (protein synthesis)
- some are attached to the RER in e. cells
- not membrane-bound
24
Q
Rough Endoplasmic Reticulum (RER)
A
- sheets of membrane formed in flattened sacs called ‘cisternae’
- ‘cisternae’ contains range of enzymes
- processes cell-secretion proteins that are made by it’s ribosomes
- polyP. chain folds into tertiary structure & becomes modified in RER’s lumen
- polyP. is packed into vesicles and transported to Golgi Apparatus
25
SER & Golgi Apparatus
- SER is involved in production and storage of lipids and carbohydrates
- G.A. also consist of ‘cisternae’
- protein may pass through G.A. for further modification
- polyP. eventually becomes a “functional protein” as it reaches its final structure
- protein is packed into vesicles again, fused w cell mem. & secreted from cell
- some proteins form lysosomes
26
Vesicle & Lysosome
- vesicles are membrane-bound, liquid filled sacs for transport & storage
- lysosomes contain hydrolytic enzymes that digest large biological molecules into smaller ones
- ^ they absorb/destroy toxic substances and waste organelles
- internal fluid is acidic in order to digest bacteria (phagocytosis)
- may transfer enzymes outside cell (exocytosis)
27
Cytoskeleton
- extensive network of microfilaments + microtubules (protein fibres)
- contain intermediate fibres that provide cell w mechanical strength
- aids transport by forming 'tracks' along which organelles can move
- allows cell movement via cilia + flagella
28
Microfilaments & Intermediate fibres
- m. filaments are solid strands; mostly made of the protein ‘actin’
- causes cell movement by moving against each other
- responsible for cell contraction during cytokinesis
- intermediate fibres give mechanical strength to cells
- m. villi increases S.A. of plasma mem. to increase exchange rate of substances
29
Microtubules
- m. tubules are hollow strands; mostly made of the protein polymer ‘tubulin’
- cell contents are moved along fibres using ATP to drive this movement
- forms a ‘scaffold-like’ structure that determines shape of cell
- acts as tracks for the movement of organelles (inc. vesicles)
- spindle fibres are composed of m. tubules
30
Centriole
- made of microtubules
- 2 perpendicular centrioles form a ‘centrosome’
- centrosome organises spindle fibres during cell division (in animal cells)
- absent in flowering plants & fungi
31
Cilia
- ‘hair-like’ organelles made from m. tubules
- allows movement of substances over cell surface by beating in a rhythmic manner; creating a current
- pairs of parallel m. tubules slide over each other causing cilia to move
- stationary cilia senses chemicals around cell e.g. lining of nose
32
Flagella
- ‘whip-like’ organelle found in specialised cells
- made of longer m. tubules compared to cilia
- contracts to provide cell movement e.g. sperm cells
- used as a sensory organelle in some cells
- has a “9+2 structure”
33
Vacuole
- larger, longer life-spanned vesicles
- surrounded by partially permeable mem. called ‘tonoplast’
- ^ this controls which chemicals enter/leave vacuole
- fluid inside vac. = ‘cell sap’
- cell sap contains dissolved sugars, mineral salts, amino acids + waste
- temporary in animal cells
34
Prokaryotic Cells
- 100-1000x smaller than eukaryotic cells
- cytoplasm lacks membrane-bound organelles
- cell wall contains the glycoprotein ‘murein’
- ribosomes are structurally smaller (70 S) than those in eukaryotic cells (80 S)
- has a single circular DNA molecule that is free in the cytoplasm and isn’t associated w histone proteins
35
Prokaryotic Cells 2
- small loops of DNA that are separate from the main circular DNA = ‘plasmids’
- plasmids can contain antibiotic resistant genes that can be passed between prokaryotes
- final outer layer = ‘slime capsule’ which helps protect bacteria from drying out
- ^ also helps attack cells from the immune system of host
- fine proteins strands that help bacteria attach to each other = ‘pilli’
- some prokaryotes have more than one flagellum
36
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Size is not a structural feature so if you are asked for a structural difference between a prokaryotic and eukaryotic cell don't include size in your answer
