Module 2.1 - Cell Structure Flashcards
1
Q
What kind of magnification do microscopes produce and what does this mean?
A
Linear - if an image is x100 magnification appears to by 100x wider and 100x longer than specimen
2
Q
What are light microscopes also known as?
A
Optical microscopes
3
Q
What are the advantages of light microscopes?
A
- Relatively cheap
- Easy to use
- Portable as can use in field or laboratories
- Can study living specimens
4
Q
What is the maximum magnification of a light microscope?
A
X1500 (x2000 in some)
5
Q
What is the maximum resolution of a light microscope and why?
A
200nm, source is visible light with wavelength of 400-700nm, so structures close than 200nm appear as one
6
Q
What is the equation for magnification?
A
Magnifying power of objective lens x magnifying power of eyepiece lens
7
Q
How do laser scanning microscopes work?
A
- Use laser light to scan an object point by point + assemble pixel info into one image by computer, displayed on a computer screen
- Images are high resolution + show high contrast
- Have depth selectivity + can focus of structures at different depths within a specimen
- Used in the medical profession for a quick diagnosis + earlier/more effective treatment
- Used in many branches of biological research
8
Q
How do electron microscopes work?
A
- Use a beam of fast travelling electrons
- Wavelength of about 0.004nm so have a greater resolution to give a clear, highly magnified image. Higher resolution than light microscopes as shorter wavelength
- Electrons fired from a cathode + focused by electromagnets rather than glass lenses onto a screen or photographic plate making a black + white image (electron micrograph)
9
Q
How do transmission electron microscopes (TEMs) work?
A
- Specimen has to be chemically fixed by being dehydrated + stained
- Beam of electrons passes through specimen stained with metal salts. Some electrons pass through + are focused on a screen or plate
- Form a 2D grey scale image (electron micrograph)
10
Q
What is the maximum resolution of a TEM?
A
0.1nm
11
Q
What is the maximum magnification of a TEM?
A
x500000
12
Q
How does a scanning electron microscope (SEM) work?
A
- Electrons cause secondary electrons to bounce off the specimen’s surface + be focused on a screen
- Gives a 3D image
- Black + white but a computer can add false colour
13
Q
What is the maximum resolution of an SEM?
A
10nm
14
Q
What is the maximum magnification of a scanning electron microscope?
A
x100000
15
Q
What is differential staining?
A
Stains that bind to specific cell structures, staining each structure differently so the structures can be easily identified within a single preparation
16
Q
Give an example of an all purpose stain.
A
Methylene blue
17
Q
Give some examples of stains used in microscopy and what they stain.
A
- Acetic orcein: binds to DNA + stains chromosomes dark red
- Eosin: stains cytoplasm; Sudan red stains lipids
- Iodine in potassium iodide solution: stains cellulose in plant cell walls yellow + starch granules blue/black (look violet under a light microscope)
18
Q
How are specimens prepared for light microscopy?
A
- Specimen is dehydrated
- Embedded in wax to prevent distortion during slicing
- Use a special instrument to make thin slices called sections. These are stained + mounted in a special chemical to preserve them
19
Q
What is the equation that links the image size, magnification and the actual size of the specimen?
A
Magnification = image size / actual size
same units
20
Q
How do you use a stage graticule to calibrate the eyepiece graticule?
A
- Insert eyepiece graticule into x10 eyepiece of microscope. Ruler has 100 divisions (0.01mm/10micrometre divisons, 1mm total).
- Place stage microscope on microscope stage + bring into focus using lower power (x4 objective so x40 magnification).
- Align eyepiece graticule + stage graticule. Check value of 1 eyepiece division at this magnification.
- Divide length of the stage graticule (1000 micrometres) by the number of eyepiece units it takes up, giving the division of each epu in micrometres.
- Now do the same for the x10 magnification and x40 magnification (eyepiece).
21
Q
Give the rough value of each epu in micrometres in most modern microscopes used in schools (rough if asked in exams) when the magnification of the eyepiece lens is x10.
A
- Mag. of objective lens: x4, total: x40, each epu = 25
- Mag. of objective lens: x10, total: x100, each epu = 10
- Mag. of objective lens: x40, total: x400, each epu = 2.5
- Mag. of objective lens: x100 (oil-immersion lens), total: x1000, each epu = 1.0
22
Q
Which kingdom’s cells are eukaryotic?
A
- Animals
- Plants
- Fungi
- Protoctists
23
Q
What do all eukaryotic cells have?
A
- Nucleus surrounded by nuclear envelope containing DNA organise + wound into linear chromosomes
- Nucleolus in nucleus containing RNA where chromosomes unwind. Involved in making ribosomes
- Cytoplasm in which organelles are suspended
- Cytoskeleton: network of protein filaments (actin or microtubules) within cytoplasm that move organelles within the cell. Allow some cells (amoebae + lymphocytes) to move. Allow contraction of muscle cells
- Plasma membrane
- Membrane bound organelles e.g. mitochondria, Golgi, ER
- Small vesicles
- Ribosomes where proteins are assembled
24
Q
What is the structure of the nucleolus?
A
- Doesn’t have a membrane around it
- Contains RNA
25
What is the structure of the nucleus?
- Surrounded by a double membrane - nuclear envelope
- Pores in the nuclear envelope
- Contains DNA. Chromatin if the genetic material, consisting of DNA wound around histone proteins. When cell isn't dividing, chromatin is spread out or extended. When cell is about to divide, chromatin condenses + coils tightly into chromosomes. These make up nearly all the organism's genome
26
What is the function of the nuclear envelope?
- Separates contents of nucleus from rest of cell
- In some regions outer + inner membranes fuse together. At these points dissolved substances + ribosomes can pass through
- Pores enable larger substances e.g. messenger RNA (mRNA) to leave nucleus. Substances e.g. steroid hormones, may enter nucleus from cytoplasm via these pores
27
What is the function of the nucleolus?
Where ribosomes are made
28
What is the function of the nucleus?
- Control centre of the cell
- Stores organism's genome (chromosomes contain organism's genes)
- Transmits genetic information
- Provides instructions for protein synthesis
29
What is the structure of the rough endoplasmic reticulum (RER)?
- System of membranes, containing fluid-filled cavities (cisternae) continuous with the nuclear membrane
- Coated with ribosomes
30
What is the function of the rough endoplasmic reticulum?
- Is the intracellular transport system: cisternae form channels for transporting substances from one area of a cell to another
- Provides large SA for ribosomes, which assemble amino acids into proteins. These actively pass through membrane into cisternae + are transported to Golgi apparatus for modification + packaging
31
What is the structure of the smooth endoplasmic reticulum (SER)?
- System of membranes, containing fluid filled cavities (cisternae) continuous (in line with) nuclear membrane
- No ribosomes on its surface
32
What is the function of the smooth endoplasmic reticulum?
- Contains enzymes that catalyse reactions involved with lipid metabolism, e.g. synthesis of cholesterol, lipids/phospholipids needed by the cell, or steroid hormones
- Involved with absorption, synthesis + transport of lipids (from gut)
33
What is the structure of the Golgi apparatus?
- Consists of a stack of membrane-bound flattened sacs
| - Secretory vesicles bring materials to + from Golgi apparatus
34
What is the function of the Golgi apparatus?
- Proteins are modified e.g. adding: sugar molecules to make glycoproteins, lipid molecules to make lipoproteins, + being folded into their 3D shape
- Proteins packages into vesicles that are pinched off then stored in cell or moved into plasma membrane, either to be incorporated into plasma membrane or exported outside the cell
35
What is the structure of the mitochondria?
- May be spherical, rod-shaped or branched. 2-5μm long
- Surrounded by 2 membranes with a fluid-filled space between them. Inner membrane is folded into cristae
- Inner part of mitochondrion is a fluid filled matrix
36
What is the function of the mitochondria?
- Site of ATP (energy currency) production during aerobic respiration
- Self-replicating, so can be made if cell's energy needs increase
- Abundant in cells where much metabolic activity takes place e.g. liver cells + synapses between neurones where neurotransmitter is synthesised + released
37
What is the structure of chloroplasts?
- Large organelles, 4-10μm long
- Only found in plant cells + some protoctists
- Surrounded by a double membrane. Inner membrane is continuous stacks of flattened membrane sacs, thylakoids (resembling pile of plates) which contain chlorophyll. Each pile of thylakoids called granum (pl. grana). Fluid filled matrix called stroma.
- Grana interconnected by tubular extensions: intergranal lamellae
- Contain loops of DNA + starch grains
38
What is the function of the chloroplasts?
- Site of photosynthesis
- 1st stage of photosynthesis, when light energy trapped by chlorophyll + used to make ATP, occurs in grana. Water also split to supply hydrogen ions
- 2nd stage, when hydrogen reduces CO2 using energy from ATP, to make carbohydrates, occurs in the stroma. Abundant in leaf cells, particularly in palisade mesophyll layer
39
What is the structure of vacuoles?
Surrounded by a membrane called tonoplast + contains fluid
40
What is the function vacuoles?
- Only plant cells have a large permanent vacuole
- Filled with water + solutes + maintains cell stability as when full it pushes against cell wall making cell turgid
- If all plant cells are turgid this helps support plant, especially in non-woody plants
41
What is the structure of lysosomes?
- Small bags, formed from Golgi apparatus. Each is surrounded by a single membrane
- Contain powerful hydrolytic (digestive) enzymes
- Abundant in phagocytic cells e.g. neutrophils + macrophages (types of WBC) that can ingest + digest invading pathogens e.g bacteria
42
What is the function of lysosomes?
- Keep powerful hydrolytic enzymes separate from rest of cell
- Can engulf old cell organelles + foreign matter, digest them + return digested components to the cell for reuse
43
What is the structure of cilia and undulipodia?
- Protrusions from cell + surrounded by the cell surface membrane
- Each contains microtubules
- Formed from centrioles
44
What is the function of cilia and undulipodia?
- Epithelial cells lining airways each have many hundreds of cilia that beat + move the band of mucus
- Nearly all cell types have one cilium that acts as an antenna. Contains receptors + allows cells to detect signals about its immediate environment
- Only type of human cell that has an undulipodium (longer cilium) is a spermatozoon. Enables it to move
45
What is the structure of ribosomes?
- Small spherical organelles, about 20nm in diameter
- Made of ribosomal DNA
- Made in nucleolus, as 2 separate subunits, which pass through nuclear envelope into cytoplasm then combine
- Some remain free in cytoplasm + some attach to the ER
46
What is the function of ribosomes?
- Bound to exterior of RER: mainly for synthesising proteins to be exported outside the cell
- Free in cytoplasm (either singly or in clusters): primarily the site of assembly of proteins to be used inside the cell
47
What is the structure of the centrioles?
- Consist of 2 bundles of microtubules at right angles to one another
- Made of tubulin protein subunits + are arranged to form a cylinder
48
What is the function of the centrioles?
- Before cell divides, spindle (made of threads of tubulin) forms from the centrioles. Chromosomes attach to middle part of spindle + motor proteins walk along tubulin threads, pulling chromosomes to opposite ends of cell
- Making cilia/undulipodia: before cilia form, centrioles multiply + line up beneath plasma membrane. Microtubules sprout outwards from each centriole, forming cilium/undulipodium
- Usually absent form cells of (higher) plants but may be presen in some unicellular green algae (e.g. Chlamydomonas)
49
What is the structure of the cytoskeleton?
- Network of proteins fibres within cytoplasm
- Rod-like microfilaments made of subunits of actin (a protein). They're polymers of actin + each microfilament is about 7nm in diameter
- Intermediate filaments about 10nm in diameter
- Straight, cylindrical microtubules, made of tubulin (protein subunits) 18-30nm diameter
- Cytoskeletal motor proteins (myosins, kinesins + dyneins) are molecular motors. They're also enzymes + have site that binds to + allows hydrolysis of ATP as their energy source
50
What is the function of the cytoskeleton?
-Protein microfilaments: give support + mechanical strength, keep cell's shape stable + allows movement
-Mircotubules: provide shape + support. Help substances + organelles move through cytoplasm by:
> Forming a track along which motor proteins (dynein + kinesin) walk + drag organelles from one part of cell to another
> Form spindle before cell divides, which enables chromosomes to be moved within the cell
>Make up cilia, undulipodia + centrioles
-Intermediate filaments are made of a variety of proteins:
> Anchor nucleus within cytoplasm
> Extend between cells in some tissues, enabling cell-cell signalling + allowing cells to adhere to a basement membrane, thus stabilising tissue
51
What is the structure of the cellulose cell wall?
- Cell wall of plants on outside of plasma membrane
| - Made from bundles of cellulose fibres
52
What is the function of the cellulose cell wall?
-Not in animal cells. Strong + prevent cell bursting when turgid
-In plants:
> Provides strength + support
> Maintains cell's shape
> Contribute to strength + support of whole plant
> Permeable + allow solutions (solute + solvent) to pass through
53
How is the cell wall of fungi different from that of plants?
Plants: made of cellulose
Fungi: made of chitin
54
How are proteins made in a cell and then secreted from the cell?
- Gene (housed in chromatin) coding from a certain protein transcribed into messenger RNA (mRNA) in nucleus
- Many copies of mRNA made + leaves nucleus through nuclear pores
- Attaches to ribosome (likely RER for proteins for outside the cell) where mRNA translated into a protein
- Protein molecules pass into cisternae of RER + along these hollow sacs
- Vesicle (with protein inside) pinched off + travels towards Golgi apparatus, via microtubules + motor proteins
- Vesicle fuses with Golgi, where protein is modified + packaged ready for release
- Vesicle (with protein inside) pinched off + travels towards plasma membrane
- Vesicle fuses with plasma membrane + protein is released outside the cell
55
How are eukaryotic cells similar to prokaryotic cells?
- Both have a plasma membrane
- Cytoplasm
- Ribosomes for assembling amino acids into proteins
- DNA + RNA
56
How are prokaryotic cells different to eukaryotic cells?
- Prokaryotic are smaller
- Have less well developed cytoskeleton with no centrioles
- Don't have a nucleus
- Don't have membrane bound organelles e.g. mitochondria, ER
- Cell wall made of peptidoglycan not cellulose
- Smaller ribosomes
- Have naked DNA not wound around histone proteins. Floats free in cytoplasm as a loop
57
What do some prokaryotic cells also have?
- Protective waxy capsule surrounding cell wall
- Small loops of DNA (plasmids) as well as main large loops of DNA
- Flagella: long whip like projections enabling them to move. Structure differs from that of the eukaryotic undulipodia
- Pili: smaller hair like projections enabling bacteria to adhere to host cells/to each other + low passage of plasmid DNA from one cell to another
58
How do prokaryotic cells divide? Why can't they divide by mitosis?
- Binary fission
| - Don't have linear chromosomes
59
What is similar about binary fission and mitosis?
DNA divides so each new cell gets the same DNA (genetically identical) as both large loop of DNA + plasmids replicate in prokaryotes
60
How do light microscopes work?
- Light passes through a condenser lens then through a specimen
- Light focused by objective lens then eyepiece lens
- Several objective lenses that can be rotated to different magnifications
- Eyepiece usually x10 + magnifies image more
61
What is sectioning?
Has to be cut thin enough for light to pass through. Useful for making sections of soft tissue like brain/lungs. Specimens embedded in wax + thin sections cut without distorting the structure
62
What is 1μm in metres?
1x10^-6
63
What is 1μm in nm?
1000
64
What is 1nm in m?
1x10^-9
65
What is the length of the average animal cell?
20-40μm long
66
How do you measure specimens under a light microscope?
- Microscope eyepiece can be fitted with a graticule
- Transparent with a ruler etched on
- When looking at specimen the eyepiece graticule is superimposed + specimen can be measured in epu
- Arbitrary units - represent different lengths at different magnifications
- Eyepiece scale has to be calibrated
67
How do you calibrate an eyepiece graticule?
- Stage micrometer placed on a microscope stage
- Each division on the ruler usually 0.01 mm (10μm)
- Stage micrometer compared with eyepiece graticule scale to see how many epu are a length of the stage micrometer
- Then the size of each epu is calculated
68
What is the typical size of plant cells?
10-100μm
69
Which is bigger: plant cells or animal cells?
Animal
70
How many μm are there in a mm?
1000
71
What's the maximum magnification that can be achieved with a light microscope?
X1500
72
Which type of microscope can be done with 3D specimens?
SEM
73
What is the radiation source in light microscopes?
Light source
74
What is the radiation source in electron microscopes?
Electron gun to fire a beam of electrons
75
What is the lens used in a light microscope?
Glass (objective + eyepiece lens)
76
What is the lens used in electron microscopes?
Electromagnets
77
How must the specimen be in light microscopes?
Living or dead, on a glass slide
78
How must specimens be in an electron microscope and why?
Dead as in a vacuum
79
What's the maximum magnification of SEMs?
X100000
80
What's the maximum magnification of TEMs?
X500000
81
What's the maximum resolution of light microscopes?
200nm
82
What's the maximum resolution of TEMs?
0.1nm
83
What's the maximum resolution of SEMs?
10nm
84
What stains are used for electron microscopy?
Stained by metals or non metals
85
Does the light micrograph have colour?
Yes (from dye added)
86
Do electron micrographs from TEMs have colour?
No
87
Do electron micrographs from SEMs have colour?
No but false colour can be added from a computer
88
What is the size of the nucleus?
7.5-10μm
89
What is the size of the nucleolus?
2.5μm
90
What is the width of the nuclear envelope?
0.02-0.04μm
91
What is the width of the cisternae of the ER?
0.5μm
92
What is the width of the cisternae of the Golgi apparatus?
1μm
93
What is the size of the ribosomes?
0.02μm (around 18nm)
94
What is the length of mitochondria?
3μm
95
What is the size of lysosomes?
0.2μm
96
What is the size of chloroplasts?
4-10μm
97
What is the size of the centrioles?
0.2μm
98
What is the length of cilia?
5-10μm
99
What is the length of the flagella?
150μm (??)
100
What is the cytoskeleton?
- Network of protein fibres within a cell
- Gives structure + shape to cell
- Moves organelles around inside the cell
101
What are microtubules?
- Main part of the cytoskeleton
- Hollow cylinders of tubulin (a protein) around 25nm in diameter
- Maintain cell shape
- Connect organelles to each other to keep them in place
- May be used to move microbes through liquid/waft liquid past a cell (when in the form cilia or flagella)
- Microtubules motors (proteins found on microtubules) use ATP (to release energy) to move organelles/cell content along the fibres
- This is how chromosomes are moved in mitosis (spindle fibres are microtubules made by centrioles)
- How vesicles move from ER to Golgi apparatus
102
What are cilia and flagella and what's their structure?
- In eukaryotes they're structurally the same but flagella are longer
- Stick out from the surface of cells
- Each is a cylinder with 9 microtubules in a circle + 2 more in a central bundle (9+2)
- Can move using energy from ATP
103
Where are cilia likely to be found and what's their function?
- Occurs in large numbers on ciliated epithelial cells
- <10μm
- Waft to + fro to move substances across cell surfaces
- Move mucus across airway linings e.g. trachea, bronchi
- Move egg down Fallopian tubes
- Rare in plants
104
What are intermediate filaments?
- Thick cables made of keratin
- 10nm diameter
- Maintain cell shape
- Anchor nucleus + organelles
105
What are actin microfilaments and what do they do?
- 2 intertwined strands of actin
- 7nm diameter
- Maintain cell shape
- Cause muscle contractions
- Involved in cytokinesis (cell division)
- Cause certain type of movement (pseudopia) seen by Amoeba + some WBCs
106
What are vesicles?
Membrane bounds sacs used to carry substances around
107
What is the movement of the cytoplasm called?
Cytoplasmic streaming
108
What is there in cytoplasm?
- Organelles
- Simple ions e.g. Na+ and Cl-
- Organic molecules e.g. amino acids, sugars, ATP
- Storage molecules e.g. fat droplets
109
What are the starch granules used for in chloroplasts?
Act as temporary stores of carbohydrates formed during photosynthesis (appear as dark circles on pictures)
110
What is the main difference between prokaryotic cells and eukaryotic cells?
- Eukaryotes has a true nucleus but prokaryotes don't
| - Prokaryotes are smaller (1-5μm)
111
What are the features of animal cells?
- Centrioles
- Ribosomes
- Rough ER
- Nuclear envelope
- Golgi apparatus
- Plasma membrane
- Smooth ER
- Nucleus + nucleolus
- Mitochondria
- Lysosomes
- Cytoskeleton
- Cytoplasm
112
What are the features of plant cells?
- Ribosomes
- Rough ER
- Nuclear envelope
- Golgi apparatus
- Plasma membrane
- Smooth ER
- Nucleus + nucleolus
- Mitochondria
- Lysosomes
- Cytoskeleton
- Cytoplasm
- Chloroplast
- Vacuole
- Cell wall
- Starch granules
- Plasmodesmata
113
What 2 processes inside cells rely on the cytoskeleton for movement?
- Movement of chromosomes (mitosis)
- Protein synthesis
- Move organelles
114
Why might the same organelle look different on a micrograph?
- Cut at different angles
- Longer than wide
- Vary in shape
115
Which organelle controls the movement of cilia?
Cytoskeleton
116
Why might liver cells need lots of mitochondria?
Constantly converting glucose of glycogen and vice versa which requires energy in the from ATP, produced at the mitochondria
117
What is the average diameter of prokaryotic cells?
0.5-5μm
118
What is the average diameter of eukaryotic cells?
20-40μm
119
How do the ribosomes of prokaryotes and eukaryotes differ?
-Prokaryotes smaller (18nm) than eukaryotes (22μm)
120
(MA) Describe the stages of making extra cellular proteins.
- Nucleus contains gene which codes for proteins
- Transcription produces mRNA
- Ribosomes/RER are the site of translation
- Protein transported to Golgi
- Golgi processes and packages proteins into vesicles
- Vesicles move towards the plasma membrane
- Protein released out of the cell by exocytosis
121
(MA) Describe the stages of exocytosis.
- Vesicle moves towards cell surface membrane
- Along microtubules
- Vesicles fuse with plasma membrane
- Protein released out of cell by exocytosis
- The movement of vesicles on microtubules + fusion of vesicles with membrane requires ATP
122
(MA) Describe the stages of endocytosis.
- A molecule binds to a receptor
- Causes cell surface membrane to invaginate
- Requires ATP
- Membrane fuses with itself
- Forms a vesicle
- Vesicle moves through cytoplasm to its destination organelle
123
(MA) What are the roles of the cytoskeleton?
- Provides support + stability to cell to maintain shape
- Movement of cilia
- Movement of flagella to move cell
- Changing shape of the cell e.g. endocytosis/exocytosis
- Move organelles inside cell
- To anchor organelles
- Move chromosomes and mRNA
124
(MA) What are the parts of the cytoskeleton and describe their structure and role?
-Microtubules: hollow cylinders of tubulin, 2-5nm
> Maintain cell shape + anchor organism
> Make up 9+2 flagellum (+ cilia) structure in eukaryotes
> Move vesicles using microtubule proteins (require ATP)
> Spindle fibres move chromosomes
-Intermediate filaments: keratin cables, 10nm
> Maintain cell shape + anchor organelles
-Actin microfilaments: 2 twisted actin strands, 7nm
> Maintain cell shape
> Cause muscle contractions
> Involved in cytokinesis
> Allow pseudopodia
