Cell Structure Flashcards
(93 cards)
1
Q
What does Cell Theory state?
A
- Basic unit of all living organisms and they are the smallest unit capable of independent life.
- New cells are formed only by the division of pre-existing cells.
- The cell contains information that acts as the instructions for growth. This information can be passed to new cells.
2
Q
What two things are involved in microscopy?
A
Magnification and resolution
3
Q
What is the relationship between magnification and resolution when looking through a microscope?
A
The higher the magnification and lower the resolution, the better the microscope.
4
Q
What is magnification?
A
The number of times greater an image is than the object.
5
Q
How is magnification worked out?
A
Magnification = Image size / actual size
6
Q
What normally happens when you magnify an image?
A
If you magnify an image, the quality will normally decrease.
7
Q
What is resolution?
A
The ability to distinguish two separate points as distinct from each other.
-The smaller the resolution, the closer the points are together while still being seen separate so the better the resolution.
8
Q
What are the two different microscopes?
A
Light Microscope
Electron Microscope
-Scanning (SEM)
-Transmission (TEM)
9
Q
Light Microscope: What happens in a light microscope?
A
- Light microscopes use a number of lenses to produce an image that can be viewed directly at the eyepieces.
- Light passes from a bulb under the stage, through a condenser lens, then through the specimen.
- This beam of light is focused through the objective lens, then through the eyepiece lens.
- To view specimens at different magnifications, light microscopes have a number of objective lenses that can be rotated into position.
- Usually four different lenses are present.
- The eyepiece lens then magnifies the image again. This is usually x10.
10
Q
Light Microscope: What is the job of the mirror?
A
To reflect light from the lamp onto the condenser lens.
11
Q
Light Microscope: What is the job of the eyepiece lens?
A
It magnifies the image, usually x10.
12
Q
Light Microscope: What is the job of the objective lens?
A
Four lenses of different magnification to increase the size of the image.
13
Q
Light Microscope: What four objective lenses are normally present?
A
x4, x10, x40 and x100.
14
Q
Light Microscope: Why is the x100 objective lens different from the others?
A
It is an oil immersion lens.
15
Q
Light Microscope: How do you work out final magnification?
A
Final magnification = objective magnification x eyepiece magnification
16
Q
Light Microscope: Normally what is the maximum magnification?
A
Up to x1500
17
Q
Light Microscope: Normally what is the maximum resolution?
A
200nm
18
Q
Light Microscope: Does it require staining?
A
Not always but staining usually helps as it highlights certain parts of the cell, making it easier to see. The colour usually binds to certain membranes.
19
Q
Light Microscope: Does specimens need preparation?
A
Some specimens can be viewed directly, however, a lot of biological material is not coloured so you can’t see the details. Along with this, some material distorts when you try to cut it into thin sections.
20
Q
Light Microscope: How are specimens prepared by staining?
A
Coloured stains are chemicals that bind to chemicals on or in the specimen. This allows the specimen to be seen. Some stains bind to specific cell structures.
21
Q
Light Microscope: What types of staining are used?
A
- Acetic orcein stains DNA dark red.
- Gentian violet stains bacterial cell walls.
22
Q
Light Microscope: How are specimens prepared by sectioning?
A
Specimens are embedded in wax. Thin sections are then cut without distorting the structure of the specimen. This is particularly useful for making sections of soft tissue, such as brain.
23
Q
Light Microscope: What are the advantages of light microscopes?
A
- Wide range of specimens can be viewed using a light microscope, including living organisms such as Euglena and Daphnia. Thin sections of larger plants and animals can also be viewed, along with smear preparations of blood or cheek cells.
- Preparation is simple, it does not require staining or sectioning, but it often helps.
- They are failing cheap, often only costing hundreds of pounds, meaning they are good for education.
24
Q
Light Microscope: What are the disadvantages of light microscopes?
A
- Most light microscopes are only capable of magnification up to a maximum of x1500.
- The maximum resolution using light is 200nm, so if two objects are closer together than 200nm, they will be seen as one object.
- The limit of resolution is due to the magnitude of the wavelength of light. Two objects can only be distinguished if light waves can pass between them.
25
What are the units of length from largest to smallest?
Metre > Decimetre > Centimetre > Millimetre > Micrometre (μm) > Nanometre
26
How big are most animal cells?
Between 20 and 40 μm (micrometres)
27
What is the typical size of most ribosomes?
20nm in diameter
28
What is the typical size of most cell membranes?
10nm in diameter
29
What is the equation to work out actual size (after magnification)?
Actual size = Image size / magnification
30
What two things can be fitted to a light microscope in order to measure cells and organelles?
- Graticule
| - Stage micrometer
31
What is a graticule?
A mini ruler which is added to the eyepiece of the microscope.
- As the specimen is viewed, the eyepiece graticule scale is superimposed on it.
- The scale of the eyepiece graticule is arbitrary - it represents different lengths at different magnifications but the actual specimen has not increased in size. The eyepiece scale has to be calibrated for each different objective lens.
32
What is a stage micrometer?
A microscopic ruler on a special slide that's placed onto the stage next to the sample. Its 1mm long and divided into 10μm intervals.
-You need to calibrate the stage micrometer for each magnifications.
33
Electron Microscope: How do electron microscopes work?
They generate a beam of electrons which bounce off the sample and produce an image which is projected onto a screen or photographic paper. A black and white micrograph is produced.
-Electromagnets are on each side of the electron microscope to keep electrons travelling in a straight line.
34
Electron Microscope: What is the resolution of an electron microscope?
0.1 nm (2000x more than in light microscopes)
35
Electron Microscope: What are the two different types of electron microscopes?
- SEM (scanning electron microscopes)
| - TEM (transmission electron microscopes)
36
Electron Microscope: What is an SEM?
Scanning Electron Microscope
- The electron beam is directed onto a sample. The electrons don't pass through the specimen.
- They are 'bounced off' the sample.
- The final image produced is a 3D view of the surface of the sample.
- The magnification possible with an SEM is about x100,000.
37
Electron Microscope: What is a TEM?
Transmission Electron Microscope
- The electron beam passes through a very thin papered sample.
- Electrons pass through the denser parts of the sample less easily, so giving some contrast.
- The final image produced is two-dimensional.
- The magnification possible with a TEM x500,000.
38
Electron Microscope: How are samples prepared before being investigated with an electron microscope?
- Chemical Fixation (stabilise the specimen's structure)
- Cryofixation (freezing specimen rapidly, to preserve specimen in snapshot of its solution state)
- Dehydration (freeze drying/replacement of water with organic solvents, e.g. ethanol)
- Embedding (infiltration of tissue with resin
- Sectioning (sliced on a ultramicrotome with a diamond knife)
- Staining (using heavy metals like lead, uranium and tungstun, to add contrast)
- Freeze-fracture (useful for examining cell membranes)
- Ion Beam Milling (firing ions, e.g. argon at surface from an angle).
- Conductive Coating (ultrathin coating of electrically-conducting material)
39
Electron Microscope: How are electron micrographs coloured?
Electron micrographs are sometimes shown in colour. The final image produced from an electron microscope is always black, white and grey the colours are added afterwards using specialised computer software. Such images will be labelled as 'false-colour' electron micrographs.
40
Electron Microscope: What are the advantages of electron microscopes?
- The resolution is 0.1nm (2000x more than in light microscopes.
- Electron microscopes can be used to produced more detailed images of the organelles inside cells.
- The SEM produces 3D images that can reveal the detail of contours and cellular tissue arrangements - that is not possible using light microscopes.
41
Electron Microscope: What are the disadvantages of electron microscopes?
- Electron beams are deflected by molecules in the air, so samples have to be placed in a vacuum.
- Electron microscopes are extremely expensive (hundreds of thousands of pounds)
- Preparing samples and using an electron microscope both require a high degree of skill and training.
42
What seven characteristics do all living organisms share?
- Movement
- Respiration
- Sensitivity
- Nutrition
- Excretion
- Reproduction
- Growth
43
What is a cell ultrastructure?
The detail of the inside of cells (the organelles), as revealed by the electron microscope, is termed the cell's ultrastructure.
44
Division of Labour: What is division of labour?
Most organelles are found in both plant and animal cells. They have the same functions in each type of cell. Each type of organelle has a specific role within the cell. This is called division of labour. The different organelles work together in a cell, each contributing its part to the survival of the cell.
45
Division of Labour: What is an example of how a cell uses division of labour?
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Protein synthesis (hormone production)
-Some cells within some organisms produce hormones. Hormones are chemical messenger molecules that help to coordinate the activities of the whole organism, including auxins in plants, and insulin and growth hormones in animals. Plant 'hormones' are usually referred to as plant growth regulators or substances.
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46
Division of Labour: What is the process of protein synthesis using division of labour?
- The instructions to make the hormone are in the DNA in the nucleus.
- The specific instructions to make the hormone is known as the gene for that hormone. The gene is on a chromosome.
- The nucleus copies the instructions in the DNA into a molecule called mRNA.
- The mRNA molecule leaves the nucleus through a nuclear pore and attaches to a ribosome. In this case, the ribosome is attached to rough endoplasmic reticulum (ER).
- The reads the instructions and uses the codes to assemble the hormone (protein).
- The assembled protein inside the rough ER is pinched off in a vesicle and transported to the Golgi apparatus.
- The Golgi apparatus packages the protein and may also notify it so that it is ready for release. The protein is now packaged into a vesicle and moved to the cell surface membrane, where it fuses with it and then opens so the protein is secreted outside.
47
Cytoskeleton: What is the cytoskeleton?
Cells contain a network of fibres made of protein. These fibres keep the cell's shape stable by providing an internal framework called the cytoskeleton.
48
Cytoskeleton: What are the two types of fibres that make up the cytoskeleton?
- Actin Filaments
| - Microtubules
49
Cytoskeleton: What are actin filaments?
Actin filaments are string anchored one end in the plasma membrane. They generate contractile forces which helps the cell move and change shape.
- They are like the fibres found in muscle cells. They are able to move against each other.
- These fibres cause the movement seen in some white blood cells. They also move some organelles around inside cells.
- They are also called microfilaments because they are the thinnest in cytoskeleton family.
50
Cytoskeleton: What are microtubules?
Microtubules are cylinders about 25nm in diameter. They are made of a protein called tubulin.
-Microtubules may be used to move a microorganism through a liquid, or to waft a liquid past the cell.
51
Cytoskeleton: What are the other proteins present on microtubules called?
Other proteins present on the microtubules move organelles and other cell contents along the fibres. These proteins are known as microtubule motors. They use ATP to drive these movements.
- This is how chromosomes are moved during mitosis.
- This is how vesicles move from the endoplasmic reticulum to the Golgi apparatus.
52
What is the structure of undulipodia (flagella) and cilia in eukaryotes?
In eukaryotes, undulipodia and cilia are structurally similar. They are hair-like extensions that stick out from the surface of cells. Each one is made up of a cylinder that contains nine microtubules arranged in a circle. There are also two microtubules in the central bundle.
-The microtubules use energy from ATP allowing undulipodia and cilia to move.
53
How are undulipodia and cilia able to move?
- The motor protein, dynein, has 'arms' that can push one doublet ahead of the other.
- When microtubule pairs, try to slide past each other, the axoneme bends because the microtubules are anchored at the base.
54
What are the differenced between undulipodia and cilia?
Cilia are shorter (less than 10μm long) than undulipodia.
- Undulipodia usually occurs in ones or twos on a cell.
- Cilia often occur in large numbers on a cell.
55
What is the function of undulipodia?
- The undulipodia that forms the tail of a sperm cell can move the whole cell.
- The long, whip-like undulipodium on the protoctist Trichomonus (which causes urinary tract infections) enables it to move.
56
What is the function of cilia?
In ciliated epithelial tissue, the sweeping movements of the cilia move substances such as mucus across the surface of cells.
57
How is prokaryotic flagella different from eukaryotic undulipodia?
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Prokaryotic flagella (bacteria flagella) look like eukaryotic undulipodia, but their internal structure is very different.
-These are true 'motors' - they are made of a spiral of protein called (flagellin) attached by a hook to a protein disc at the base. Using energy from ATP, the disc rotates, spinning the flagellum.
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58
What are vesicles?
Vesicles are membrane-bound sacs found in cell. They are used to carry many different substances around cells.
59
What is the function of the plant cells vacuole?
In plant cells, the large cell vacuole, maintains cell stability. It is filled with water and solutes so that it pushes the cytoplasm against the cell wall, making the cell turgid. If all plant cells are turgid, this helps to support the plant. This is especially important in non-woody plants.
-Animals do not need a vacuole because their cytoskeleton allows them to keep their shape, because plants do not have this, they need a vacuole.
60
How do plant cell walls help support the whole plant?
- They are on the outside of the plant cell plasma membranes (cell surface membranes) and are made of cellulose, a carbohydrate polymer made up of glucose subunits.
- The cellulose forms a sieve-like network of strands that makes the wall strong.
- Because it is held rigid by the pressure inside of the fluid inside the cell (turgor pressure), it supports the cell and so helps to support the whole plant.
61
Which organelles are membrane-bound?
- Nucleus
- Endoplasmic reticulum
- Golgi apparatus
- Mitochondria
- Chloroplasts
- Lysosomes
62
Which organelles are not membrane-bound?
- Ribosomes
| - Centrioles
63
What is the structure of the nucleus?
Membrane-bound
The nucleus is the largest organelles. When stained, it shows darkened patches known as chromatin. It is surrounded by a nuclear envelope. A lot of holes, called nuclear pores, go right through the envelope. These holes are large enough for relatively large molecules to pass through.
64
What is a nuclear envelope?
This is a structure made of two membranes with fluid between them.
65
What is the function of the nucleus?
The nucleus houses nearly all of the cell's genetic material. The chromatin consists of DNA and proteins. It has the instructions for making proteins and some of these proteins regulate the cell's activities. When cells divide, chromatin condenses into visible chromosomes.
66
What is the structure of the nucleolus?
Inside the nucleus, there is a dense spherical structure which is the nucleolus.
67
What is the function of the nucleolus?
The nucleolus makes RNA and ribosomes. These pass into the cytoplasm and proteins assembled at them.
68
What is the structure of the endoplasmic reticulum (ER)?
Membrane-bound
ER consists of a series of flattened membrane-bound sacs called cisternae. They are continuous with the outer nuclear membrane.
-Rough endoplasmic reticulum is studded with ribosomes.
-Smooth endoplasmic reticulum does not have ribosomes.
69
What is the function of the endoplasmic reticulum (ER)?
- Rough ER transports proteins that were made on the attached ribosomes. Some of these proteins may be secreted from the cell. Some will be placed on the cell surface membrane.
- Smooth ER is involved in making the lipids that the cell needs.
70
What is the structure of the Golgi apparatus?
Membrane-bound
| A stack of membrane-bound, flattened sacs.
71
What is the function of the Golgi apparatus?
Golgi apparatus receives proteins from the ER and modifies them. It may add sugar molecules to them. The Golgi apparatus then packages the modified proteins into vesicles that can be transported. Some modified proteins may go to the surface of the cell so that they may be secreted.
72
What is the structure of mitochondria?
Membrane-bound
These may be spherical or sausage-shaped. They have two membranes separated by a fluid-filled space.
-The inner membrane is highly folder the form cristae (it has a large surface area).
-The central part of the mitochondrion is called the matrix.
73
What is the function of mitochondria?
Mitochondria are the site where ATP is produced during respiration. ATP is sometimes called the universal energy carrier because almost all activities that need energy in the cell are driven by the energy released from ATP.
74
What does ATP stand for?
Adenosine Triphosphate
75
What is the structure of chloroplasts?
Membrane-bound
These are found only in plants and the cells of some protoctists. Chloroplasts also have two membranes separated by a fluid-filled space.
-The inner membrane is continuous, with an elaborate network of flattened membrane sacs called thylakoids. A stack of thylakoids are called a granum.
-Chlorophyll molecules are present on the thylakoid membranes and in the intergranal membranes.
76
What is the function of chloroplasts?
Chloroplasts are the site of photosynthesis in plant cells. Light energy is used to drive the reactions of photosynthesis. In which carbohydrate molecules are made from carbon dioxide and water.
77
What is the structures of lysosomes?
Membrane-bound
| These are spherical sacs surrounded by a single membrane.
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What is the function of lysosomes?
Lysosomes contain powerful digestive enzymes. Their role is to break down materials.
- White blood cell lysosomes help to break down invading microorganisms.
- The specialised lysosome (acrosome) in the head of a sperm cell helps it penetrate the egg by breaking down the material surrounding the egg.
79
What is the structure of ribosomes?
Not membrane-bound
| These are tiny organelles. Some are in cytoplasm and some are bound to ER. Each ribosome consists of two subunits.
80
What is the function of ribosomes?
Ribosomes are the site of protein synthesis in the cell. They act as an assembly line where coded information (mRNA) from the nucleus is used to assemble proteins from amino acids.
81
What is the structure of centrioles?
Non membrane-bound
These are small tubes of protein fibres (microtubules). There is a pair of them next to the nucleus in animal cells and in cells of some protoctists.
82
What is the function of centrioles?
Centrioles take part in cell division. They form fibres, known as the spindle, which move chromosomes during nuclear division.
83
What is a eukaryote?
- Cells that have membrane-bound organelles and so a true nucleus (inside a nuclear envelope).
- Animal cells, plant cells, fungi.
84
What is a prokaryote?
Cells that do not have a true nucleus and do not have membrane-bound organelles. They are bacteria and are much smaller than eukaryotic cells, (1-5μm).
-Prokaryotic cells show all the characteristics of living organisms.
85
Prokaryotes: What features do prokaryotic cells have?
- They only have one membrane, the cell surface membrane around the outside (they do not contain any membrane-bound organelles such as mitochondria and chloroplasts),
- They are surrounded by a cell wall, but this is usually made of peptidoglycan, not cellulose.
- They contain ribosomes that are smaller than eukaryotic ribosomes.
- The DNA is in the cytoplasm in the form of a single loop , sometimes called a 'circular chromosome' or 'bacterial chromosome', unlike the linear chromosomes (separate strands) of eukaryotes.
- Many prokaryotic cells also contain very small loops of DNA called plasmids.
- The DNA is not surrounded by a membrane, as in the nuclear envelope of eukaryotic cells. The general are in which DNA lies is called the nucleoid.
- ATP production takes place in specialised infolded regions of the cell surface membrane called mesosomes.
- Some prokaryotic cells have flagella. The function like eukaryotic undulipodia, but they have a different internal structure.
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Prokaryotes: What are prokaryotic cell wall made of?
Peptidogylcan
87
Prokaryotes: Where is prokaryotic DNA held?
In the nucleoid, in the cytoplasm
- Single loop, 'circular chromosomes'.
- Smaller loops, plasmids
88
Prokaryotes: Where does ATP production take place?
In mesosomes
| -Specialised infolded regions of the cell surface membrane.
89
Prokaryotes: What are pathogens?
Most prokaryotes are harmless.
| Pathogens cause infectious diseases
90
Prokaryotes: What is used to kill pathogens?
Antibodies are targeted to kill pathogens by breaking down the cell wall or stopping protein synthesis.
-It is advantageous that prokaryotes don't have membranes because we don't need to destroy those membranes only the cell walls. As our cells do not have cell walls but do have membranes, our cells are not damaged by antibodies.
Antibodies also target enzymes that build the cell wall, so resistance of bacteria isn't a problem for these types of antibodies.
91
Prokaryotes: Why is bacterial resistance a problem?
Some strains of pathogens become resistant to antibodies, MRSA is one such strain.
These resistant strains can cause problems because the resistance is coded on plasmid DNA.
92
Prokaryotes: How is resistance passed on between pathogens?
As resistance comes from DNA codes in their plasmids, resistance can be passed on by;
- Passing to daughter cells during binary fission.
- Bacteria are able to share plasmids with each other, so resistance isn't just inherited, unlike normal DNA.
93
Prokaryotes: What prokaryotic species are important and helpful to humans?
- The food industry uses particular bacterial species, for example for cheese and yoghurt.
- In mammalian intestines, bacterial cells help with vitamin K production and help digest some foods.
- Skin is covered with a 'normal flora' of bacteria. These help to prevent harmful microorganisms getting into the body.
- Sewage treatment and natural recycling rely on bacterial cells digesting and respiring dead and waste material.
