Cell Structure Flashcards
1
Q
what is the formula for finding the size of a cell
A
magnification=size of image/size of real object
2
Q
what is the comman unit of cell study
A
micrometer
3
Q
micrometer is
A
x10-6
4
Q
how do you convert between units
A
1mm x1000 = 1000 micrometers
1000 micrometers x1000= 1000000 nano
1mm x1000000= 1000000 nm
5
Q
magnification
A
how many times bigger the image is compared to the object
6
Q
resolution
A
the ability to distinguish between two separate points
7
Q
the resolution depends on
A
the wavelength of the radiation source
8
Q
2 examples of radiation
A
-light ray
-electron beam
9
Q
what makes the image clearer
A
being hit by two waves of radiation
10
Q
what makes up a light microscope
A
- condenser lens- focuses light up onto the stage
- the specimen - the thing you want to view
- objective lens - magnifies the specimen
- eyepiece lens - magnifies image further
11
Q
how is total magnification achieved
A
by multiplying mag of both lenses together
12
Q
how are different shades produced
A
different parts of specimen have different densities
therefore parts of the specimen absorbs different amounts of wavelength
13
Q
what is the total magnification of a light microscope
A
x1500
14
Q
what is the total resolution of a light microscope
A
0.2 micrometers
15
Q
advantages of light
A
-cheap and easy to maintain
- easy to prepare specimens, can use a stain
- living specimens can be used
16
Q
disadvantages of light
A
-limited magnification
-low resolution
17
Q
when were electron microscopes invented
A
1930 , not used until 1950
18
Q
when was the light microscope invented
A
1667 - robert hooke
19
Q
types of microscope
A
transmission electron microscope
scanning “”
20
Q
advantages of electron
A
-high resolution
-high magnification
21
Q
what is the magnification of an electron
A
x250000
22
Q
disadvantages of electron
A
-only dead specimens can be viewed
-cannot use harsh stains
- expensive
-have to have special training
23
Q
what is an artefact
A
features that are caused by preparation and do not really exist in the cell
24
Q
how do you combat artefacts
A
ask other scientists to see if they see what you see
25
why do electron microscopes have to be in a vacuum
the electrons are too small and can scatter easily
26
how do you prepare specimens for electron
cut extremely thin using a diamond knife
27
how do TEMs work
-electron beams are emitted by an electron gun
-they are then narrowed by electromagnetic lenses onto the specimen
-electrons penetrate through the specimen
-different areas appear dark and light due to the levels of electrons that they absorb (electron densities)
28
how do SEMs work
-electrons fired out of a gun
-narrowed by electromagnetic lenses
-scan over the top ad under the specimen, instead of going through
29
what is an advantage of scanning
3D images can be produced
30
how do you measure cells
using an eyepiece graticule and stage micrometer
31
what is an eyepiece graticule
-small glass disc that is placed in the eyepiece lens
-usually divided into 100 units
32
how do you chose the correct setting for the eyepiece
calibrate it against a known length
33
how do you calibrate it
using the stage micrometer
34
what is the typical length of stage micrometer
1mm divided into 100 divisions therefore each one is usually 10 micrometers
35
example
each division is 10 micrometers
24 divisions line up with 90 on the eyepiece graticule
24x10= 240 micrometers
240=90
240/90 = each eyepiece division is 2.67 micrometers
36
what do you have to do each time you change the magnification
you have to re-calibrate it
37
what do you have to do before each calculation
line both EPG and SM up to closet lines and count distance between
38
what to do when measuring a picture of a cell
count how many cells and that equal the number of units
39
to find mean when calculating cell size
count up all and get average
OR divide by total number of cells
40
how do you differentiate with the two types of cell
the word 'karyo' means to do with the nucleus
41
what is a prokaryotic cell
bacterial cells- they do not contain a true membrane-bound nucleus or any membrane bound organelles
42
what is a eukaryotic cell
true membrane bound nucleus and contain membrane bound organelles
animal, fungal, plant and protoctist cells
43
what is an organelle
something that performs a specific role inside a cell
44
what is compartmentalisation
when organelles are bound by a membrane and thus a particular job is carried out in a specific area of the cell
45
what is the internal structure of a cell called
the ultra-structure
46
what does the nucleus do
contains the genetic code which is used to produce genes for protein synthesis
47
what are some features of the nucleus
Present in all eukaryotic cells, the nucleus is relatively large (10-20um) and separated from the cytoplasm by a double membrane (the nuclear envelope) which has many pores
Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes (eg. DNA polymerases) and signalling molecules to travel in- communication
The nucleus contains chromatin (the material from which chromosomes are made)
Chromosomes are made of sections of linear DNA tightly wound around proteins called histones
Usually, at least one or more darkly stained regions(denser electron region) can be observed – these regions are individually termed ‘nucleolus’ and are the sites of ribosome production and RNA
48
what is the role of the mitochondria
the site of aerobic respiration and production of ATP
49
what are some features of the mitochondria
Surrounded by double-membrane with the inner membrane folded to form cristae which provide a large surface area for efficient enzyme reaction
cristae contain the electron transport chain
The matrix formed by the cristae contains enzymes needed for aerobic respiration, producing ATP and produces its own proteins
Small circular pieces of DNA (mitochondrial DNA) and ribosomes are also found in the matrix (needed for replication)
50
what is the role of the ribosomes
site of protein synthesis
51
what are some features of ribosomes
Found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells
Each ribosome is a complex of ribosomal RNA (rRNA) and proteins
80S ribosomes (composed of 60S and 40S subunits) are found in eukaryotic cells
they contain two sub-units made of RNA-l manufactured in nucleolus and leave nucleus through pores
52
what is the endoplasmic reticulum (ER)
series of membranes in the outer cell membrane
series of interconnected tubes and sacs called cisternae
53
what are some features of (ER)
-Rough Endoplasmic Reticulum (RER)
Surface covered in ribosomes
Formed from continuous folds of membrane continuous with the nuclear envelope
Processes proteins made by the ribosomes- and these pass through pores from mebrane into the lumen and are then transported around the cell
-Smooth Endoplasmic Reticulum (ER)
Does not have ribosomes on the surface, its function is distinct to the RER
Involved in the production, processing and storage of lipids, carbohydrates and steroid
54
what is the role of the golgi apparatus(body)
modify and package/process proteins
modify and package/process lipids
55
what are some features of the golgi body
Flattened sacs of membrane similar to the smooth endoplasmic reticulum- cisternae
Modifies proteins and lipids before packaging them into Golgi vesicles
The vesicles then transport the proteins and lipids to their required destination
Proteins that go through the Golgi apparatus are usually exported (e.g. hormones such as insulin), put into lysosomes (such as hydrolytic enzymes) or delivered to membrane-bound organelles
56
what are lysosomes
Sacs / compartments surrounded by a membrane
And contain digestive enzymes
57
what is the role of lysosomes
-fuse with cell surface mem and release enzymes outside of the cell
-fuse with phagocytic vacuoles containing foreign material which has been taken in by the cell
-may destroy old worn out organelles
58
what is the cell surface membrane
-phospholipid bilayer
-folded into microvilli- increases surface area for absorption
-controls what comes in to and out of the cell
59
what is the role cytosol
liquid material containing dissolved material eg nutrients
60
what is the cytoskeleton
a system of protien microtubules and microfilaments which give the cell support
61
what is the cellulose cell wall
only in plant cells and made of polysaccharide cellulose
Cell walls are formed outside of the cell membrane and offer structural support to cell
Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells
permeable to water
62
permanent central vacuole
fluid filled sac surrounded by a single layer of membrane
exerts turgor pressure and helps support cell and plant
can also function as a storage area - contains dissolved nutrients eg amino acids
63
what is the role of the chloroplasts
site of photosynthesis
64
what are some features of the
Chloroplasts
Larger than mitochondria (2-10um), also surrounded by a double-membrane
Membrane-bound compartments called thylakoids containing chlorophyll stack to form structures called grana
Grana are joined together by lamellae (thin and flat thylakoid membranes)- chemical reactions happen here
granum contain chloroplasts
Chloroplasts are the site of photosynthesis:
The light-dependent stage takes place in the thylakoids
The light-independent stage (Calvin Cycle) takes place in the stroma
Also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis
also can contain starch granules- insoluble so not affected by osmotic water potential
65
how can you investigate cell components
by using cell fractionation
66
what does the 1st stage do
breaks up the cell to release the various components
67
what are the cells first suspended in
an
-ice cold- reduce enzyme activity
-isotonic-prevent osmotic damage to the cell-shrinking/bursting
-buffer-same pH concentration as proteins sensitive to change in pH
68
what is homogenisation
Homogenisation is the biological term used to describe the breaking up of cell
69
why do you filter the homogenate
to remove debris and unbroken organelles
This is a blender-like machine that grinds the cells up
70
what is the next stage of fractionation
Ultracentrifugation
71
what is the process of ultracentrifugation
-The filtrate is placed into a tube and the tube is placed in a centrifuge
-A centrifuge is a machine that separates materials by spinning
-The filtrate is first spun at a low speed
-This causes the largest, heaviest organelles (such as the nuclei) to settle at the bottom of the tube, where they form a thick sediment known as a pellet-pick the pellet that you want
-The rest of the organelles stay suspended in the solution above the pellet
-This solution is known as the supernatant
-The supernatant is drained off and placed into another tube, which is spun at a higher speed
-Once again, this causes the heavier organelles (such as the mitochondria) to settle at the bottom of the tube, forming a new pellet and leaving a new supernatant
-The new supernatant is drained off and placed into another tube, which is spun at an even higher speed
-This process is repeated at increasing speeds until all the different types of organelle present are separated out (or just until the desired organelle is separated out)
72
what is the order in which the organelles are collected
Nuclei
Chloroplasts (if carrying out cell fractionation of plant tissue)
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes
73
what are the levels of organisation
-tissue- group of similar cells aggregated and working together to perform a specific function
-organ- a group of organs working together to provide one overall function
-organ system- organs working together to perform an overall function
74
how does cell specialisation occur
differentiation
75
why is specialisation advantageous
wide range of functions can be carried out at the same time making cells very diverse and adaptable
76
what is a prokaryot cell
cells that do not have a true membrane bound nucleus
77
what is a comman example of a prokaryot cell
bacteria
78
what is the size of a bacteria cell
0.1-10 micrometers
79
where is the genetic material stored in a bacterium
in strands in the centre that forms a structure called a nucleoid
80
what is another store of DNA in a bacterium
a ring of DNA known as a plasmid
81
what is the bacterium surrounded by
a cell wall made of murein- only found in bacteria
and is the target for antibiotics eg penicillin
these prevent cell wall from forming and thus bacteria burst due to high pressure
82
what do some cells also contain- bacteria
a slime capsule - makes them smooth
83
what do bacterial cells not have
membrane bound organelles
-ER
-glogi
lysosomes
84
how do the bacterium increase their surface area
by creating folds in the membrane that are known as meosomes
85
what are the ribosomes like in bacteria
smaller than in eukaryotic cells
86
what is the role of the flagellum
Flagellum-e long, tail-like structure that rotate, enabling the prokaryote to move (a bit like a propeller)
some have more than one
87
what is a virus
non-cellular infectious particles
88
what is their size- bacteria
200-300nm
89
what are some common features of a virus
A nucleic acid core (their genomes are either DNA or RNA, and can be single or double-stranded)
A protein coat called a ‘capsid’
Some viruses have an outer layer called an envelope formed usually from the membrane-phospholipids of a cell they were made in
All viruses are parasitic in that they can only reproduce by infecting living cells and using their protein-building machinery (ribosomes) to produce new viral particles
90
what is a bacteriophage
viruses that infect bacteria
91
what does HIV stand for
human immunodeficiency virus
92
what enzyme is in HIV
reverse transcriptase enzyme
this turns the RNA back to DNA for transcription and translation
93
how many micrometers is in a cm
10000
94
resolution of electron microscope
0.12 nanometres
