3. Cell Structure Flashcards
1
Q
What is the wavelength of light microscopes?
A
0.2 micrometers
2
Q
What does a wavelength of 0.2 mean?
A
It means they can only distinguish between objects if they are 0.2 micrometers or further apart
3
Q
How can you overcome the limitation of the wavelength of the light microscope?
A
By using beams of electrons instead (electron microscope).
4
Q
What is resolution?
A
The minimum distance apart two objects can be in order for them to be seen as separate
5
Q
What can resolution also be known as?
A
Resolving power
6
Q
What does having greater resolution mean?
A
Having greater clarity, this makes it clearer and more precise
7
Q
What is the magnification equation?
A
Magnification = size of image divided by size of real object (I AM)
8
Q
What is cell fractionation?
A
The process where cells are broken up and the different organelles they contain are separated out
9
Q
What has to be done to the tissue before cell fractionation?
A
It has to be placed in a cold, buffered solution with the same water potential as it
10
Q
Why does the tissue the cell gets placed into have to be cold?
A
To reduce enzyme activities
11
Q
Why does the solution the tissue has to be placed in have to be buffered?
A
So the pH does not fluctuate
12
Q
Why does the solution the tissue is placed in have to be of the same water potential as the tissue?
A
To prevent organelles bursting or shrinking (osmotic effect)
13
Q
What are the two stages in cell fractionation?
A
Homogenation and ultracentrifugation
14
Q
What happens in Homogenation?
A
The cells are broken up by a homogeniser (blender) to release the organelles from the cell. Then the resultant fluid is filtered so any complete cells or large debris is removed
15
Q
What happens during ultracentrifugation?
A
The fragments from the filtered homogenate are separated in a machine called a centrifuge
16
Q
What does a centrifuge do?
A
It sprints tubes of the homogenate at a very high speed to create centrifugal force
17
Q
What is step 1 of ultracentrifugation?
A
Tubes of filtrate are spun at a low speed and the heaviest organelles are forced to the bottom where they form a thin sediment/pellet
18
Q
What is step 2 of ultracentrifugation?
A
The fluid at the top (supernatent) of the spun filtrate is removed
19
Q
What is step 3 of ultracentrifugation?
A
The supernatent is removed and spun again but t a faster speed, the heaviest organelles are forced to the bottom
20
Q
How many times do you repeat ultracentrifugation?
A
You repeat until all the organelles are separated out
21
Q
What is the electron microscope?
A
A microscope that used a beam of electrons instead of light
22
Q
What are the two main advantages of an electron microscope?
A
- Electron beams have a very short wavelength, so it has a high resolving power
- The electrons are negatively charged so the beam can be focused using electromagnetics
23
Q
What has to be created for an electron microscope to work?
A
A near vacuum has to be created within the chamber of an electron microscope
24
Q
Why does a near vacuum need to be created?
A
Because electrons can be absorbed or deflected y the molecules in the air
25
What are the two types of electron microscope?
- The transmission electron microscope (TEM)
- The scanning electron microscope (SEM)
26
What does the TEM consist of?
An electron gun that produces a beam of electrons that is focused onto the specimen t by a condenser electromagnet
27
Why do the images of the cells look both dark and light?
- When the beam passes through some of the specimen absorbs electrons so appears dark
- Some of the specimen allow the electrons to pass through so appear bright
28
What are main limitations of the TEM?
- Living specimens cannot be observed as the whole system must be in a vacuum
- A complex staining process is required
- The specimen must be extremely thin
- The image may contain artefacts
- The image produces will only be 2d as the specimen has to be really thin
29
What are artefacts?
Things that result in the way the specimen was prepared and are not part of the natural specimen
30
How can you overcome the image being 2d?
By taking a series of sections through a specimen which can be built up to build a 3d image, BUT this is a slow and complicated process
31
What are the limitations of the SEM?
They have all the same limitations as the TEM, BUT the specimen does not need to be extremely thin
32
Why does the specimen of the SEM not need to be extremely thin?
This is because the electrons do not penetrate rathe are passed through a portion of the specimen at a time
33
What is the resolution of the SEM?
20 nanometers
34
How do we measure the size of actual objects in a microscope
By using an eyepiece graticule
35
What is an eyepiece graticule?
A glass disc that is placed in the eyepiece of a microscope
36
Why can an eyepiece graticule not be used to directly measure the size of objects under a microscopes objective lens
Each objective lens will magnify to a different degree
37
How do you calibrate an eyepiece graticule?
You need to use a special microscope called a stage micrometer
38
How do you calculate the scale for different objective lenses?
By dividing the differences in magnification
39
What is magnification ?
How many times bigger the image is compared to the object
40
What are the two types of lenses of a microscope?
Objective lens + Eye piece lens
41
What do you se to change the resolution of a microscope?
The course focus
42
When preparing a slide why do you use a small piece of the specimen?
You use a small bit as when your using a light microscope, the light needs to be able to penetrate the cell
43
When testing pigmented specimens, why do you still use drops of iodine?
You use the drops of iodine to secure it to the slide
44
When testing a non pigmented specimen, why do you use iodine drops?
You use iodine drops to stain the cell and make it look transparent
45
What safety equipment do you have to use when handling iodine?
Safety google
46
What chemical do you use when magnifying a plant cell
You use iodine
47
What chemical do you use to magnify an animal cell
You use methylene blue
48
What do you have to do with cover slip when preparing a wet mount slide and why?
You need to lower the cover slip slowly and at an angle to avoid getting air bubbles in the solution
49
When using a microscope what lens do you start and why?
You start with the lowest power lens to get a greater field of view
50
What is an ultrastructre?
The internal structure of a cell that suits it for its jobs
51
What does the nucleus contain?
It contains the organism's hereditary material (DNA)
52
What is the function of the nucleus?
It controls the cell's activities
53
What is the shape of a nucleus?
It is usually spherical and between 10 and 20 nanometers in diameter
54
What is a nuclear envelope?
A double membrane that surrounds the nucleus
55
What is the outer membrane of the nuclear envelope continuous with?
The endoplasmic reticulum of the cell and often has ribosomes on its surface
56
What are the two functions of the nuclear envelope?
- Controls the entry and exit of materials in and out of the nucleus
- Contains the reactions taking place within it
57
What do nuclear pores allow?
The passage of large molecules out of the nucleus (such as messenger RNA
58
How many nuclear pores are in each nucleus?
Around 3000
59
How big are the nuclear pores?
40-100 micrometers in diameter
60
What is nucleoplasm and what does it make up?
It is a granular jelly like material and it makes up the bulk of the nucleus
61
What do chromosomes consist of?
They consist of protein bound linear DNA
62
How many nucleolus are in the nucleus?
There may be more than one in a nucleus
63
What are the functions of the nucleus?
- Control centre of the cell through production mRNA and tRNA
- Retains the genetic material (DNA and chromosomes)
64
What shape are the mitochondria?
They are usually rod shaped and 1-10 micrometers in length
65
What is the structure of the mitochondria?
- Double membrane around the organelle, that controls entry and exit of material
- Cristae
- Matrix
66
What is Cristae?
extensions of the inner membrane, that provides a large surface area for the attachment of enzymes and other proteins involved in respiration
67
What is Matrix?
Makes up the remainder of the mitochondrion, contains protein, lipids, ribosomes and the DNA
68
What does the Matrix allow the mitochondrion?
Allows the mitochondrion to control the production of some of their own proteins
69
What is the function of the mitochondrion?
- Site of the aerobic stages of respiration
- Responsible for the production of the energy-carrier molecule (ATP) from respiration
70
What are chloroplast?
They are the organelles that carry out photosynthesis
71
What are the main features of chloroplasts?
Chloroplasts envelope
-Grana
- Stroma
72
What is the chloroplast envelope?
Double plasma membrane that surrounds the organelles, highly selective in what is allowed to enter and leave the chloroplast
73
What is grana?
- Stack of up to 100 disc like structures called thylakoids, which contain photosynthetic pigment called chlorophyll
- Where the first stage of photosynthesis occurs
74
What is Stroma?
- Fluid filled matrix which contains a number of other structures such as starch grains
- where second place of photosynthesis occurs
75
What is the function of chloroplasts?
Harvesting sunlight and carrying out photosynthesis
76
How are chloroplasts adapted to their function?
- Grana membranes provide a large surface area for the attachment of chlorophyll
- Fluid of the stroma possesses all the enzymes needed to make the sugars in the second stage of photoynthesis
- Chloroplasts contain both DNA and ribosomes, so can quickly and easily manufacture some of the proteins needed for photosynthesis
77
What is endoplasmic reticulum?
Three dimensial system of sheet-like membranes spreading through the cytoplasm of the cells
78
What does the membrane of endoplasmic reticulum enclose?
A network of tubules and flattened sacs called cisterna
79
What are the two types of endoplasmic reticulum?
- Rough endoplasmic reticulum
- Smooth endoplasmic reticulum
80
What is the difference between rough and smooth Endoplasmic reticulum ?
Rough endoplasmic reticulum has ribosomes present on the outer surfaces of the membrane where smooth lacks ribosomes and is more tubular in appearance
81
What does the rough endoplasmic reticulum provide?
- Provides a large surface area for the synthesis of proteins and glycoproteins
- Provides a pathway for the transport of materials throughout the cell
82
What does the smooth endoplasmic reticulum do?
- Synthesises, stores and transports lipids
- Synthesises, stores and transports carbohydrates
83
What is cell specialisation?
Where cells of multicellular organisms are each specialised in different ways to perform a particular role
84
How are cells produced?
They are produced by mitotic divisions and so they contain exactly the same genes
85
What is it called when genes are switched on?
Expressed
86
How are tissues formed?
They are cells aggregated together that form a specific function
87
What are examples or tissues?
- Epithelial tissues
- Xylem tissues
88
What are epithelial tissues?
- Found in animals and consists of sheets of cells
- They line the surfaces of organs and often have a protective or secretory function
89
Where are Xylem tissues?
- Occur in plants and is made up of a number of similar cell types
- Used to transport water and mineral ions through the plant and also gives mechanical support
90
What are organs?
They are a combination of tissues that are coordinated to perform a variety of functions but normally have one predominant major function
91
What are two organs?
- The stomach
- Leaf
92
What is the stomach?
- An organ involved in the digestion of certain types of food
- Made of, Muscle (churn and mix the stomach contents), Epithelium (protect the stomach wall and produce secretion), Connective tissues (hold together the other tissues)
93
What is the leaf made up of?
- Palisade mesophyll - made up of cells that carry out photosynthesis
- Spongy mesophyll - adapted for gaseous diffusion
- Epidermis - protect the leaf and allow for gaseous diffusion
- Phloem - transport organic materials away from the leaf
- Xylem - transport water and ions into the leaf
94
What are organ systems?
- Organs working together as a single unit that are grouped together performed particular functions
- There are a number of organ systems in humans, Digestive system, Respiratory system, Circulatory system
95
What is the digestive system?
Digests and processes food made of organs that include salivary gland, oesophagus, stomach, duodenum, ileum, pancreas and liver
96
What is the respiratory system?
Used for breathing and gas exchange, made up of trachea, bronchi and lungs
97
What is the circulatory system?
Pumps and circulates blood, made up of heart arteries and veins
98
What is the main difference between eukaryotic and prokaryotic cells?
- Eukaryotic cells are larger and hav a nucleus bounded by a nuclear membrane
- Prokaryotic cells are smaller and have no nucleus or nuclear membrane
99
What are bacteria?
Versatile, adaptable and very successful
100
What size are bacteria cells?
They are small, normally ranging from 0.1-10 micrometers in length.
101
What shape are bacteria cells?
They have a cellular structure
102
What are the cell walls of bacteria cells made up of?
Made of murein, which is a polymer of polysaccharides and peptides
103
How does bacteria cells further protect themselves?
By secreting a capsule of mucilaginous slime around the wall
104
What size are the ribosomes in a prokaryotic cell?
70S, smaller then the ribosomes inside eukaryotic cells (80S)
105
Where is genetic material in bacteria?
It is in the form of a circular strand of DNA, separate from this are smaller circular strands of DNA called plasmids
106
What is special about plasmids?
They can reproduce themselves independently and give the bacterium resistance to harmful chemicals
107
Does a prokaryotic or eukaryotic cell have a nucleus?
Prokaryotic - no true nucleus only an area where DNA is found
Eukaryotic - distinct nucleus, with a nuclear envelope
108
How is DNA associated in prokaryotic and eukaryotic?
Prokaryotic - DNA is associated with proteins
Eukaryotic - DNA is associated with proteins called histones
109
What is the shape of DNA in eukaryotic and prokaryotic?
Prokaryotic - DNA may be in the form of a circular strand called plasmids
Eukaryotic - No plasmids and DNA is linear
110
Are the organelles bound in eukaryotic or prokaryotic?
Prokaryotic - no membrane-bounded organelles
Eukaryotic - membrane-bounded organelles
111
Do prokaryotic and eukaryotic contain chloroplasts?
Prokaryotic - no chloroplasts, only bacterial chlorophyll associated with the cell-surface membrane
Eukaryotic - chloroplasts present in plants and algae
112
What are the size of ribosomes in eukaryotic and prokaryotic?
Prokaryotic - 70S
Eukaryotic - 80S
113
What are the cell walls made up of in prokaryotic and eukaryotic?
Prokaryotic - cell wall made up of murein
Eukaryotic - cell wall made up of mostly cellulose
114
Are there any capsules in prokaryotic or eukaryotic?
Prokaryotic - outer mucilaginous layer called a capsule
Eukaryotic - no capsule
115
What is the role of the cell wall?
Physical barrier, protects against mechanical damage and osmotic lysis
116
What is the role of the capsule?
Protects bacterium, helps groups of bacteria to stick together for further protection
117
What is the role of cell-surface membrane?
Permeable layer, controls the entry and exit of chemicals
118
What is the role of circular DNA?
Possesses the genetic information for the replication of bacterial cells
119
What is the role of plasmid?
Possesses genes, aids the survival of bacteria
120
What are viruses?
They are acellular, non living particles
121
What is the size of viruses?
220-300 nanometers
122
What do viruses contain?
Nucleus acids such as DNA or RNA as genetic material but can only multiple inside living host cells
123
Where is the DNA or RNA in viruses?
Enclosed within a protein coat called capsid
124
What are viruses surrounded by?
Surrounded by a lipid envelope?
125
What is a lipid envelope?
The capsid have attachment proteins which are essential to allow the virus to identify and attach to a host cell
126
Can all cells divide?
Where cells undergo a regular cycle of division separated by periods of cell growth
127
What are the stages of the cell cycle?
- Interphase
- Nuclear division
- Cytokinesis
128
What is interphase?
Occupies most of the cell cycle, known as the resting phase as no division takes place
129
What is nuclear division?
Where the nuclear divides either into two (mitosis) or four (meiosis)
130
What is cytokinesis?
Follows nuclear division where the cytoplasm divides to produce two (mitosis) or four (meiosis) new cells
131
How long does the typical cell cycle in a mammalian take?
About 24 hours
132
What is cancer?
A group of diseases caused by a growth disorder of cells
133
What is cancer a result of?
Damage to the genes that regulated mitosis and the cell cycle, leads to uncontrolled growth and division of cells
134
Where can tumours develop?
They can develop in any organ but most commonly in, lungs, prostate gland, breast, ovaries, large intestine, stomach, oesophagus and pancreas
135
When do tumours become cancerous?
Only if the tumour turns from benign to malignant
136
Why do most cells divide by mitosis?
Either to increase the size of the tissue during development (growth) or to replace dead and worn out cells (repair)
137
What is mitosis controlled by?
Controlled by the environment of the cell and two types of genes
138
What happens if there is a mutation to the genes that control mitosis?
Results in uncontrolled mitosis
139
What is a malignant tumour?
Grow rapidly, less compact and more likely to be life threatening
140
What is a benign tumour?
Grow slowly, more compact and less likely to be life threatening
141
How do you cease the growth of cancer cells?
By killing dividing cells by blocking a part of the cell cycle
142
How do drugs used to treat cancer disrupt the cell cycle?
- Preventing DNA from replicating
- Inhibiting the metaphase stage of mitosis by interfering with spindle formation
143
Do drugs disrupt the cell cycle of normal cells?
Yes, but they are more affective against rapidly dividing cells
