2.1 Cell Structure Flashcards
1
Q
What is the resolution and uses of light microscopes?
A
- Light microscopes use light to create an image
- The maximum resolution of a light microscope is 0.2 uM so the max magnification is 1500x
- they can only be used to look at larger structures like cells and nuclei
2
Q
What is resolution?
A
the smallest distance between 2 distinct points on an image
3
Q
What are some advantages of light microscopes?
A
- They are relatively cheap and small
- the specimen preparation is straight forward
- they can produce colour images
- they can be used with living specimens
4
Q
What are the resolutions and uses of electron microscopes?
A
- They use electrons to form an image
- They have a max resolution of 0.2nm/ 0.0002 um
- They have a max magnification of 1,000,000 - several million
- They can be used to observe smaller structures in cells such as cell membranes and ribososmes
5
Q
What are the limitations of electron microscopes?
A
- they are large and expensive
- specimens must be prepared in a complex way
- images are always black and white.
- the specimens are viewed in a vacumn so no live specimens can be viewed
6
Q
What are the 2 types of electron microscope?
A
- Transmission Electron Microscope
- Scanning Electron Microscope
7
Q
How do TEM Microscopes work?
A
- TEM’s use electromagnets to transmit a beam of electrons through a specimen
- denser parts of the organism absorb more electrons so appear darker on the image
8
Q
What are the properties of images TEM microscopes produce?
A
- they are high resolution
- they allow internal structures in cells and organelles to be seen
- they are two dimensional
9
Q
How do SEM microscopes work?
A
- SEM’s pass a beam of electrons ACROSS a specimen and detect the rate at which they bounce back
10
Q
What are the properties of SEM microscope images?
A
- 3-dimension images
- show the surface of specimens
- have a lower max resolution than TEM’s
11
Q
How do optical microscopes work?
A
- Light is directed through the thin layer of biological material on the slide
- this light is directed through several lenses so an image can be seen from the eyepiece
12
Q
How do you increase the magnification power of an optical microscope?
A
the mag power of the microscope can be increased by using a higher power objective lense
13
Q
What is the eyepiece lens in an optical microscope for?
A
- where the image is viewed from
14
Q
What is the turret in an optical microscope for?
A
rotates to bring each objective lens into place
15
Q
What types of objective lens are there generally on an optical microscope?
A
- 4X (Low), 10 X (medium), 40 x (high power)
16
Q
What is the stage in an optical microscope for?
A
- This is where the microscope slide is placed
- has a whole for the light generally
17
Q
What is the condenser in an optical microscope for?
A
- the condenser is used to vary the intensity of the light hitting the object
18
Q
What is the difference between coarse and fine focus in an optical microscope?
A
- the coarse focus is used for the low and medium power objective lenses
- the fine focus is used for the high power objective lesn
19
Q
What is the method used for preparing a liquid specimen on a microscope slide?
A
- Add a few drops of sample to slide (using pipette)
- Cover liquid with cover slip and press down to remove air bubbles
- wear gloves to ensure no cross contamination
20
Q
What is the method used for preparing a solid specimen on a microscope slide? (general)
A
- Use scissors to cut away small sample of the tissue
- Peel away a thin layer of cells using the forceps (this will be used on the slide and needs to be thin to allow light through)
- Apply a stain
- Place coverslip on top and press to remove air bubbles
- be careful while using a scalpel or forceps and use gloves so the stain does not dye your hands
21
Q
What is the method for preparing a solid specimen on a microscope slide (formaldehyde)
A
- Some cells need to be treated with chemical in order to make them rigid
1. Fixing the specimen using formaldehyde which is a preservative
2. Dehydrating it using ethanol solutions
3. Impregnating with paraffin or resin for support and slicing thin using a microtome
4. The parrafin is removed and a stain is applied
5. Then the specimen is mounted on the stage using a resin and the coverslip is applied (air bubbles)
22
Q
How to prepare a solid specimen on a microscope slide (freezing)
A
- Freeze the specimen in liquid nitrogen or carbon dioxide
- Cut into thin slices using a cryostat
- Place the specimen on the slide and add a stain
- Add a coverslip and press to remove any bubbles
23
Q
Why do we start with a low power objective lens on an optical microscope?
A
- It is easier to find what we are looking for
- Will prevent lense from being scratched if stage is too high
24
Q
How can you prevent dehydration of tissue in specimens on cover slides?
A
- Because the tissue drys out extremely fast, adding a drop of water to the specimen beneath the cover slip can help prevent dehydration
25
What is a cell surface membrane and what cells have them
- All cell have a cell surface membrane which controls the exchange of materials between the internal cell environment and the external environment
- they are partially permeable
26
What is the cell membrane formed of?
- the cell membrane is formed of a phospholipid bilayer of phospholipids
- It has a diamter of around 10nm
- The phospholipids and proteins that form the bilayer are constantly in motion
27
What is the cell wall and where is it found?
- The cell wall is found in plant (cellulose) and prokaryotic(peptidoglycan) not animal cells
- It provides structural support to the cell outside the cell membrane
28
Where is the structural support from the cell wall coming from?
- The structural support from a cell wall is provided by polysaccharides ( cellulose) in plants and peptidoglycan in bacterial cells
29
How permeable is the cell wall?
- the cell wall is freely permeable to most substances
30
How do the cytoplasms of neigbouring plant cells connect?
- threads of cytoplasm called plasmodesmata connect to the cytoplasm of neighbouring plant cells
- the plasmodesmata are surrounded by cell membrane
31
What is the middle lamela made of and what does it do?
- consists of polysaccharides and calcium and magnesium ions
- It acts as a glue between plant cells
32
What are the different layers of the cell wall? (outer to inner)
1. Middle Lamella (outside of cell wall)
2. Pectin
3. Hemicellulose on Cellulose Microfibril
4. Cellulose Microfibril
5. Plasma Membrane (inside of cell wall)
33
How is the nucleus separated from the cytoplasm?
- via a double membrane called a nuclear envelope (which has many pores)
34
What material does the nucleus contain and what are chromosomes made of?
- chromatin
- chromosomes are made of sections of linear DNA tightly wound around proteins called histones (chromatin)
35
Why are the pores in the nuclear envelopes important?
- important channels for mRNA and ribosomes to travel out of the nucleus
- allows enzymes (such as DNA polymerase) to travel in and signals molecules to travel in
36
What cell types are the nucleus present in
- all eukaryotic cells (except red blood cells)
37
What are the darkly stained regions in the nucleus called and what do they do?
- They are called nucleoulus (nucleoli) and are the site of ribosome productions
38
What is the function of the endoplasmic reticulum(s)
- its function is to synthesise and process proteins (RER)
- Its function is also for lipid synthesis, storage of calcium ions, detoxification of drugs and processing and storing carbohydrates (SER)
- it is merged (continous) with the outer nucleus membrane (SER can also not be)
39
What does the mitochondria do in all eukaryotic cells?
- Its is the site of aerobic respiration in ALL eukaryotic cells
- visible with a light microscope
40
What is the structure of membranes in a mitochondrion?
- the mitochondrion has an inner and outer membrane
- the inner membrane is folded in the shape of a cristae
41
why is the matrix formed by the cristae in mitochondrion useful?
- contains enzymes needed for aerobic respiration
- used to produce ATP
42
What is found in the matrix except enzymes? (of mitochondrion)
- small circular pieces of DNA (mitochondrial DNA) and ribosomes are found in the matrix (they are needed for replication)
43
What is a cristae?
- Cristae are the partitions formed by infolding of membranes (in mitochondrion)
44
What is embedded within the inner membrane of a mitochondrion?
- the inner membrane has protein complexes embedded in it which are vital for the later stages of aerobic respiration
45
What are flagella and what is their structure and purpose?
- Flagella are found in specialised cells
- they are made of long microtubules
- they contract to provide cell movement (e.g sperm cells)
- they are cell membrane projections (extenstions of the plasma membrane)
46
What is the structure and use of the Cilia?
- It has hair like projections made from microtubules
- allows movement of substances over the cell surface
- they are cell membrane projections (extenstions of the plasma membrane)
47
Where are microvilli found and what are they used for?
- found in specialised animal cells
- they are cell membrane projections (extenstions of the plasma membrane)
- Used to increase surface area of cell surface membrane/plasma membrane to increase rate of exchange of substances
48
what must the outer cell membrane always be called
cell surface membrane/ plasma membrane
49
What are microtubules and what is their function?
- makes up the cytoskeleton of the cell (25nm in diameter)
- made of alpha and beta tublin which form dimers
- these dimers then join into protofilaments (there are 13 protofilaments in a microtubule around a hollow core)
- found in all eukaryotic cells
50
What are centrioles and what are they made from
- they are hollow fibres made of microtubules
- 2 centrioles at right angles form a **centrosome** which organises the spindle fibres during cell division
51
Where are centrioles not found?
in flowering plants and fungi and prokaryotes
52
What are vesicles?
- Vesciles are small membrane bound sacs found within cells which are used in transport and storage of substances
- They enclose materials in a lipid bilayer which isolates the contents from the rest of the cytoplasm
53
What are lysosomes?
- specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break down biological molecules)
- they break down waste materials such as worn out organelles
- used extensively by the cells in the immune system and in apopotosis (cell death which is programmed)
54
What are large permanent vaccuoles?
- a sac (pouch like cavity filled with liquid or gas) found in PLANT CELLS which is surrounded by the tonoplast
- generally filled with cell sap
- vaccuoles in animal cells are not permanent and are small
55
What is the tonoplast?
- a partially permeable membrane around vaccuoles
56
What is the function of the golgi apparatus/golgi complex?
- Modifies proteins and lipids then packages them into golgi vesicles
- the vesicles then transport the proteins and lipids to their required destination
57
Proteins that go through the golgi apparatus are usually...
...exported (e.g hormones like insulin), put into lysosomes (hydrolytic enzymes) or delivered to membrane bound organelles
58
Where are golgi found and what do they looks like?
- found in plant and animal cells
- flattened sacs of membrane similar to SER
- also have cisternae (and lumen)
59
What is the rough endoplasmic reticulum (RER), what is its main function and where is it found?
- found in plant and animal cells
- its surface is covered in ribosomes (thats why its rough)
- continous with the nuclear membrane
- processes proteins made by ribosome
60
What is the smooth endoplasmic reticulum?
- found in plant and animal cells
- does not have any ribosomes
- involved in production, processing and storage of lipids, carbohydrates and steroids (type of lipid)
- has detoxifiying enzymes
- storage site for calcium in skeletal muscle cells
- can be but is not always connected to the nuclear envelope
61
Where are ribosomes formed and found?
- found in all cells (cytoplasm in all cells and/or as part of RER in eukaryotic cells)
- formed in the nucleolus
62
What is a ribosome composed of and what is its function?
- each ribosome is a complex of ribosomal RNA (rRNA) and proteins in almost equal amounts
- **it is the site of translation in protein synthesis**
63
What is the structure of a chloroplast?
- only found in plant cells
- larger than mitochondria surrounded by a double membrane
- made of membrane bound compartments called thylakoids which contain chloroplasts (membrane is called thykaloid membrane)
- stacks of thykaloids form structures called grana which are joined by lamellae/lamella (thin and flat thylakoid membranes)
64
What is the function of chloroplasts?
- site of photosynthesis
- light dependent stage takes place in thykaloids
- light independent stage takes place in the stroma
- also has small circular pieces of DNA and ribsomes used to synthesise proteins for chloroplast replication and photosynthesis
65
How are ribosomes involved in protein production?
- mRNA leaves the nucleus and attaches to ribosomes
- translation occurs here, during which a chain of amino acids called a polypeptide is produced
66
How is the RER involved in protein production?
- many ribosomes are attached to the RER surface
- after translation the polypeptides are folded and processed to become proteins in the RER
67
How is the golgi apparatus involved in protein production?
- proteins are modified and prepared for secretion in the golgi
68
How are vesicles involved in protein production?
- vesicles transport the protein from the RER to the golgi
- they then transport the protein from the golgi to cell surface/plasma membrane (the protein inside the vesicle)
- vesicles will fuse with the plasma membrane to secrete proteins via exocytosis (form of active transport)
69
What is the cytoskeleton?
- the extensive network of protein fibres within the cytoplasm of cells
70
What 2 protein fibres is the cytoskeleton mainly made up of?
- microfilaments
- microtubules
71
What are the properties and functions of microfilaments in the cytoskeleton?
- solid strands mostly made of the protein actin
- They can cause some cell movement and organelle movement (within cells) by moving against each other
72
What are the properties and functions of microtubules in the cytoskeleton?
- tubular/hollow strands made of the protein tubulin
- organalles and other cell contents are moved along these fibres using ATP to drive movement
73
What is the third type of fibre found in the cytoskeleton?
- intermediate filaments
74
What are the 3 main functions of the cytoskeleton (that make it important)?
1. Stregnthening and Support
2. Intracellular (within the cell) Transport
3. Cellular Movement
75
How does the cytoskeleton help strengthen and support the cell?
- provides the cell with mechanical stregnth (scaffolding) which helps maintain its shape
- supports the organelles by keeping them in position
76
How does the cytoskeleton help intracellular movement?
- cytoskeleton helps transport within cells by forming 'tracks' on which the organalles can move
- e.g movement of chromosomes during cell division
77
DELETE
ME
78
How do prokaryotic and eukaryotic cells differ in terms of cell structure?
- prokaryotes have cytoplasms which lack membrane bound organelles (unlike eukaryotes)
- they have structurally smaller 70S ribosomes compared to eukaryotic 80S ribosomes (NOTE: eukaryotes may also have 70S ribosomes)
- they have no nuclues and instead have a free-floating circular DNA molecule (not associated to a protein)
- they have a cell wall containing murein/peptidoglycan (a glycoprotein) instead of cellulose
79
What structures do prokaryotes have which can provide them with a selective advantage? (unique to them)
- plasmids - small loops of DNA that are separate from the main DNA molecule and can be passed between prokaryotes (can give a gene for antibiotic resistance)
- (slime) capsules - helps protect bacteria from drying out and from attack of immune system cells from host organism
- Flagellum - tail like structures that rotate allowing the prokaryote to move
- THEY ARE NOT PRESENT IN ALL PROKARYOTES
80
What are the 5 cell structures are always present in prokaryotes?
- cell wall (peptidoglycan)
- cell surface membrane
- cytoplasm
- circular DNA
- ribosomes
81
How large can prokaryotes be in diameter (compared to eukaryotes)?
- 0.5 - 5 um in diameter
- compared to up to 100um in diamater for eukaryotes
82
What are the differences between cell division in eukaryotes and prokaryotes?
- prokaryotes cell division occurs by binary fission with no spindle
- eukaryotic cell division is by mitosis or meiosis with spindle fibres to separate chromosomes
83
What is the difference between DNA in prokaryotes and eukaryotes?
- DNA in eukaryotes is associated with histones (proteins) which are formed into chromosomes
- DNA in prokaryotes has no histones/proteins and is just in the cytoplasm
84
What is a graticule used for in microscopy and how is it used?
- a graticule is a disc which has an engraved ruler which can be put on the eyepiece of a microscope to act as a scale
- it is used first by CALIBRATING to the objective lens in use by using the stage micrometer scale
- after this the graticule can be used as a ruler as the number of graticule units per stage micrometer unit is known
85
What are the limitations of using the graticule/ measuring cells on an optical microscope?
1. The size of cells and tissues may be inconsistent with other slides as cells are 3D and may have been cut in different planes
2. the treatment of speciments when preparing slides can affect the structure of cells
86
Why do we need to stain cells in microscopy?
- many tissues in microscopy are naturally transparent so they will let both light and electrons through
- so we use stains to make tissues visible
87
What is differential staining?
- differential staining is when specimens are stained with mutiple dyes to ensure different tissues within specimens show up
88
What are the most common stains used in light microscopy?
- Toluidine Blue turns cells blue
- Phloroglucinol turns cells red/pink
89
Why must specimens be stained before use in electron microscopy?
- when usings TEM's the specimen must be stained to absorb the electrons
- unlike light electrons have no colour so the staining causes tisses to show up different shades of grey and black
90
What are common stains used in electron microscopy?
- heavy-metal compounds are commonly used as they absorb electrons well
- e.g osmium tetroxide and ruthenium tetroxide
91
Formula for Magnification?
magnficiation = size of image/ actual size
92
Conversion between mm, nm, um and m?
nm x 1000 = um
um x1000 = mm
mm x1000 = m
93
Defintion of magnification?
- the number of times larger an image is compared to the actual object
94
Magnification in a light microscope =
eyepiece x objective lens
95
What is resolution?
- the shortest distance between two distinct points on an image
96
What is the limiting factor for resolution in light microscopy?
- light microscopes are affected by the wavelegnth of light (light waves overlap due to their diffraction so points closer than half the wavelegnth of visible light are hard to distinguish)
97
What is the limiting factor for resolution in electron microscopy?
- much higher resolution than light microscopes due to smaller wavelegnth of electrons
- wavelegnth of electrons is still the limiting factor
98
What are the 2 types of ribosomes?
- 80S ribosomes ( 60S and 40S subunits) are found in eukaryotic cells (more complex)
- 70S ribosomes (50S and 30S) are found in prokaryotes, mitochondria and chloroplasts and therefore also eukaryotes (less complex)
99
Are centrioles found in plant, animal and prokaryotic cells
NO ONLY ANIMAL CELLS
100
Do bacterial flagella have microtubules?
NO
101
Do bacterial flagella have microtubules?
NO
102
Are cilia and flagella present in prokaryotes?
Flaglla are, Cilia are NOT
