1. Cellular & Molecular Structure & Function Flashcards
(230 cards)
1
Q
What is the approximate size of the nucleus?
A
5-10μm
2
Q
What is the approximate size of a cell?
A
20-30μm
3
Q
What is the approximate size of a RBC?
A
7μm
4
Q
What is the smallest separation between two points that the eye can see?
A
0.1mm
5
Q
Define a cell.
A
- A single unit or compartment enclosed by a border or membrane.
- Smallest metabolically functional unit of life.
6
Q
Will extra magnification always help see the object in better detail?
A
No, because resolution depends on the wavelength of magnifying rays, so magnifying beyond a certain point will just “magnify the blur”.
7
Q
Give an example of a biological scale marker.
A
Red blood cells - They are usually exactly 7μm, so they give a good comparison for size in a magnified image.
8
Q
What are the two types of sample section?
A
- Transverse section (TS)
- Longitudinal section (LS)
9
Q
Describe the difference between the two types of tissue section.
A
- Transverse section - Cross section of a long structure
- Longitudinal section - Cut parallel to long axis of structures inthe sample
10
Q
What things give need for section preparation before observing it under a microscope?
A
- Tissue decay
- Loss of structural detail
- Autolysis (break down by own chemicals)
11
Q
What is fixation?
A
The process by which tissue decay and degradation is stopped. It often involves cross-linking proteins to give additional rigidity.
12
Q
What are the main steps of section preparation for observation under a light microscope?
A
Fixation, Sectioning, Staining
13
Q
What are the two ways in which tissues being prepared for observation are stopped from decaying, autolysis and loss of structural detail?
A
- Chemical cross-binding
- Cryo (low temperature)
14
Q
Describe how a sample may be sectioned.
A
- Embed in wax block
- Cut wax block into sections
15
Q
What are the three routine staining techniques you need to know about?
A
- Histochemistry
- Immunohistochemistry (a.k.a. Immunocytochemistry)
- In situ hybridisation
16
Q
What is histochemistry?
A
Staining of cells with specific chemicals (such as with a H&E stain).
17
Q
What is another name for immunohistochemistry?
A
Immunocytochemistry
18
Q
What is immunohistochemistry?
A
Localisation of specific tissue antigens using labelled antibodies.
19
Q
What is in situ hybridisation?
A
Localisation of a specific nucleic acid sequence by adding a complementary strand of RNA or DNA, then adding a labelled molecule similar enough to bind with it.
20
Q
What are the main types of microscope?
A
- Light microscope (LM)
- Electron microscope (EM) -> Transmission and scanning
- Fluorescence microscope (FM)
- (EXTRA) Confocal scanning laser microscope (CF)
21
Q
Describe how a light microscope works.
A
Light from source:
- focussed by condenser lenses
- light passes through section
- section detail magnified by objective lens
- further magnified by eyepieces
- eyes see the contrast in the magnified image
22
Q
Draw a diagram of how a light microscope works.
A
23
Q
What is the resolution of a light microscope?
A
0.2µm
24
Q
What is the significance of the resolution of light microscopy?
A
Can see:
- Bacteria
- Details within nucleated cells such as nuclei, mitochondria, ribosomes and storage ‘granules’.
25
Give an example of an artefact that often arises in light microscopy sample preparation.
Lipids are often dissolved in processing (when the wax is dissolved), leaving behind empty space.
26
Describe the staining process for light microscopy.
* Cut section of wax
* Dewaxed using chemical
* Stained by H&E or trichrome stain
27
What does H&E stain stand for?
Haematoxylin and eosin
28
What are the colours seen in a H&E stain?
Purple and pink
29
Describe the general histological appearance of a H&E stain.
* Purple -\> Nuclei and areas rich in nucleic acids
* Pink -\> Other structures, specially proteins
30
EXTRA: Describe the principle on which H&E stains work.
* Basophilic structures, such as nucleic acids, bind to basic dyes, in this case haematoxylin -\> This turns them purple
* Acidophilic structures, such as proteins, bind to acidic dyes, in this case eosin -\> This turns them pink
31
What is the full name for the trichrome stain?
Masson's trichrome
32
What is the advantage of trichrome staining over H&E staining?
It allows cells to be distinguished from surrounding connective tissue.
33
Describe the colours and their significance in trichrome staining.
* Blue/Green - Collagen
* Pink - Cytoplasm
* Dark red/Brown/Black - Cell nuclei
34
What is fluorescent microscopy a subset of?
Light microscopy
35
Describe how fluorescence microscopy works.
* Lamp produces light for excitation
* Microscope focusses light on to section and collects fluorescence emission light
* Sample is preserved, chemically or by freezing
* Sample is labelled to tag/label specific molecules
* Live fluorescent protein
* Antibodies target specific protein (immunofluorescence)
* Different dyes emit visible light of different colours
36
Can a fluorescence microscope sample be viewed through an eyepiece?
Yes, it is just like light microscopy.
37
What are the two things that can be seen in fluorescence microscopy?
* Live fluorescent proteins -\> Proteins that are fluorescent, either naturally or by DNA modification to include a reporter protein
* Immunofluorescence -\> Labelling proteins using fluorescent antibodies
38
What is immunofluorescence?
* Antibody specific to a protein is labelled with a fluorescent marker (either directly or with another labelled antibody) so it can be traced
* Therefore, the protein can be seen
39
(EXTRA) What does GFP stand for?
Green Fluorescent Protein
40
What does GFP allow for?
Live imaging of cells and the function of their proteins.
41
What is the resolution of TEM?
10nm to 0.5nm
42
What are the main differences of TEM compared to light microscopy?
* In a vacuum
* Electromagnets instead of lenses
* No colour contrasts, just heavy metal salts, which scatter electrons, producing contrast
* More careful fixation, because of need to preserve details that can be seen by electron beam
* Resin used instead of wax -\> Gives more support
* Thinner sections
43
How does staining work in TEM?
Heavy metals salts (e.g. uranium), which are electron dense, act as "stains". They scatter electrons.
44
What is the significance of the resolution of TEM?
Shows structure within organelles, lipid membranes, viruses and macromolecules e.g. DNA and proteins.
45
Draw the structure of a TEM.
46
Describe the sample sections in TEM.
Thin plastic resin sections approx 50-100 nm thick.
47
What is confocal microscopy and how does it work?
It is a technique used to produce 3D images of a sample thicker than in LM, with no need for taking several sections:
* Often uses fluorescence microscopy
* Scanned beam focussed at different levels of section
* Image produced by detector and photomultiplier system
* Cathode ray tube (CRT) screen used for imaging
48
What are 3 examples of methods used to study the surface of samples?
1) Light microscopy
2) Capsule endoscopy
3) SEM
49
What is the resolution of SEM?
2nm to 0.2nm
50
Describe how SEM works.
* Fixation as for LM or TEM
* Sample may be very large; glued on to rivet or unsupported
* Scanned with electrons, the scattering of which is detected
* Conducting coating to minimise build-up of electrons which would produce areas lacking detail
51
What are eukaryotic cells?
Cells that have a true nucleus containing the DNA as well as various other membrane-bound organelles.
52
What are the 4 tissue types?
* Epithelium
* Muscle
* Connective tissue
* Nerve
53
What details of the nucleus does light microscopy let you see?
Just the nuclei, when they are stained by H&E.
54
What details of the nucleus does TEM let you see?
* Nuclear membrane/envelope
* Nuclear matrix
* Chromatin
* Nucleolus
55
What are the two types of chromatin in an interphase nucleus?
* Euchromatin
* Heterochromatin
56
What is the size of the nucleus?
5 - 10μm
57
What are the parts of the nucleus?
* Nuclear membrane/envelope
* Nuclear matrix
* Chromatin
* Nucleolus
58
What are the functions of the nucleus?
* Gene replication and repair
* Genetic transcription
* Ribosome production
59
What are the two types of DNA in the interphase nucleus?
* Euchromatin
* Heterochromatin
60
What is euchromatin?
The finely dispersed, lightly stained form of DNA in the nucleus.
61
What is heterochromatin?
The clumped, coarse form of DNA in the nucleus.
62
What is the function of the nucleolus?
Synthesis of rRNA -\> Ribosome production
63
What is the function of the nuclear envelope?
Transport of substances into and out of the cell.
64
Describe how the structure of nuclear pores was discovered.
* EM imaging showed 8-fold symmetry and petal-shaped structures
* Then studied with sophisticated imaging techniques -\> Showed they were 80nm across and showed more details
* Later, protein analysis showed 30 other components
65
How do cell membranes appear in low and high power TEMs?
* Low power -\> Single line
* High power -\> Dark/Light/Light lines (called a unit membrane
66
What part of the nuclear envelope defines eukaryotes?
Nuclear envelope
67
What goes into and out of the nucleus through the nuclear pores?
* In: Proteins
* Out: RNA
68
Describe the structure of the endoplasmic reticulum.
Network of membrane-limited channels called cisternae.
69
What is the function of the RER?
Synthesis of proteins
70
What is the function of the SER?
Specialised functions, such as production of lipids and hormones (e.g. secretion of steroid hormones).
71
Describe the structure of the Golgi apparatus.
Multi-layered network of membrane-bound cisternae.
72
What are the names and functions of the two faces of the the Golgi apparatus?
* Cis face -\> Receives vesicles from the ER
* Trans face -\> Sends vesicles to cell membrane and endosomal pathway
73
What is the function of the Golgi apparatus?
Packaging of material for transport out of the cell.
74
Practise drawing out the protein secretory pathway.
75
What is the function of lysosomes?
Intracellular digestion by acid hydrolases.
76
What are the two stages of lysosome development?
* Primary -\> Smaller, Produced by budding from the Golgi
* Secondary -\> Larger, Produced when primary lysosomes fuse with endosomes
77
What happens to lysosomes after digestion is complete?
They become residual bodies.
78
What are the two types of lysosomes and what are their functions?
* Autophagosomes -\> Recycling bits of cell no longer needed
* Heterophagosomes -\> Dealing with material brought into the cell
79
What are proteosomes?
Cytoplasmic organelles that degrade unwanted misfolded cytoplasmic proteins.
80
How do proteosomes know which proteins to break down?
They are tagged by ubiquitin.
81
Are proteosomes visible by LM or TEM?
No
82
Describe the structure of proteosomes.
* 4 stacked rings around a core
* Proteases in central pore
83
What is the function of mitochondria?
Generation of ATP.
84
What is the shape of mitochondria?
Spherical or long.
85
Describe the structure of mitochondria.
* Outer membrane
* Inner membrane -\> Folds in to form cristae
86
Are mitochondria acidophilic or basophilic (relevant in LM)?
Acidophilic
87
What is the length and width of mitochondria?
Length: 2 to 7μm
Width: 0.2 to 2μm
88
How can you easily tell apart a LM image from a EM image?
Although both have similar magnification, the EM has a much higher resolution so it appears sharper.
89
What is an easy way of working out the scale of a microscope image?
Use reference markers, such as the size of RBCs.
90
What is the significance of the nucleus in microscope images?
* Helps work out scale of image
* Helps work out type of microscope (EM usually shows far more detail)
* Shows type of cell
* Shows cell activity (lots of heterochromatin = very transcriptionally active cell)
91
Label the following:
* Mitochondrion
* Nucleus
* RER
* Vesicles
* Endocytic invaginations
* Basal lamina
92
Describe the structure of ribosomes.
Eukaryotic cells have 80S ribosomes which consist of:
* Small 40S subunit
* Large 60S subunits
93
What are endosomes?
Vesicles that are formed by endocytosis. Essentially, the process is the reverse of exocytosis.
94
What are peroxisomes?
Small organelles that have an oxidative role in, for example, lipid metabolism.
95
What is the cytoskeleton?
A complex system of inter-linking protein filamnets that extends from the nucleus to the membrane.
96
Why do cells require a cytoskeleton?
* Cell motility
* Cellular organisation -\> Moving organelles and vesicles around
* Mechanical strength
97
What are the types of protein filament that form the cytoskeleton? (from thinnest to thickest)
Include their functions.
From thinnest to thickest:
* Microfilaments (actin) -\> Cell shape and motility
* Intermediate filaments -\> Strength and structure
* Microtubules (tubulin) -\> Position organelles and direct intracellular transport
98
What is the diameter of microfilaments (actin)?
5-7nm
99
Describe the structure of cytoskeleton microfilaments (actin filaments) and how they are arranged in the cell.
* Two-stranded helical polymers of actin monomers with plus and minus end
* 2D and 3D network throughout cell, concentrated just beneath cell membrane
100
What are the functions of cytoskeleton microfilaments (actin filaments)?
* Cell movement
* Determine cell shape (e.g. in muscle contraction)
101
Describe the polarity of actin filaments.
* Plus end -\> Growth and shrinkage are fast
* Minus end -\> Growth and shrinkage are slow
102
Describe how actin filaments allow cell movement.
* Rapid interchange of small soluble units and the large filament polymer allow for changes in shape and movement
* The rapid polymerisation happens at the plus end of the filaments
* This allows a directional response to a signal (e.g. a nutrient source)
103
Give an example of cells using actin for cell motility.
Neutrophils (a type of WBC) can use the actin cytoskeleton to chase and engulf bacteria in response to chemical trails.
104
Describe the importance of actin filaments in brain development.
* Growth cone extensions (filopodia) carry bundles of actin filaments
* These are used to assist with supporting dynamic directional growth in response to stimuli
105
Actin combines with myosin to form...
Myofibrils
106
What is the diameter of microtubules?
25nm
107
Describe the structure of microtubules in the cytoskeleton and how they are arranged in the cell.
* Long, hollow cylinders made of alpha and beta tubulin
* Rigid and straight (unlike actin)
* Often radiate out from a fixed point (MTOC)
108
What are the functions of microtubules in the cytoskeleton?
Direct movement of organelles, vesicles and chromosomes intracellularly.
109
Describe the polarity of microtubules.
They have a plus end and minus end (just like with actin) and growth is faster at the plus end.
110
Describe the turnover of microtubules.
* GTP -\> Favours growth
* GDP -\> Favours shrinking
* Subunits are recruited at plus end and lost from minus end, leading to a treadmill effect -\> This is very active
111
What are microtubules often centred around and how do these work?
* Microtubule organising centres (MTOCs)
* The stable minus end is embedded at the MTOC, while the plus end is free for growth and shrinkage
112
Describe how different organelles can move along microtubules.
* They associate with either kinesin motors or dynein motors
* Kinesin motors -\> Move towards plus end
* Dynein motors -\> Move towards minus end
113
Describe the different arrangement of microtubules in different cell types.
* Fibroblasts -\> All microtubules head out from MTOC
* Neuron axon -\> Microtubule plus end at synapse, minus end in cell body
114
What can affect the stability of microtubules?
MAP (microtubule associate proteins) -\> Bind to and stabilise microtubules, resulting in longer tubules
115
What is the clinical relevance of microtubules?
* Tubulin mutations -\> Lead to brain development abnormalities, such as cortical malformations
* Different forms of the MAP protein MAPT allow for higher neuronal plasticity in the embryo and more stability in adults
116
What is an example of an MTOC in human cells and how is it important?
* Centrosome
* It replicates at cell division, allowing the mitotic spindle to form
117
What is the diameter of intermediate filaments?
10-12nm
118
All all intermediate filaments the same? List the different types.
No, there are specific intermediate filament proteins in different cells:
* Keratin
* Desmin
* Neurofilament
* Nuclear lamin proteins
119
What are the functions of intermediate filaments?
Mechanical strength and structure
120
Describe the structure of intermediate filaments.
Multimers twisted into rope-like filaments.
121
Where is keratin found and what is its function?
* It is a group of intermediate filament proteins found in epithelial cells, as well as hair and nails
* It provides mechanical support
122
Where are neurofilaments found and what are their function?
* They are intermediate filament proteins found in axons
* They provide structure -\> Level of NF gene expression determines axon diameter and therefore rate of conduction
123
Where are lamins found and what are their function?
* They are intermediate filament proteins that form the nuclear lamina (lining inner nuclear membrane)
* They provide structure and provide anchoring point for chromosomes and proteins of nuclear pore complex
124
What is the clinical importance of tubulin filament formation?
Tubulin microfilament formation can be targeted by anti-cancer drugs, since microtubules are required for cell division.
125
What are all of the different types of abnormality of cell growth you need to know about?
Decreased growth:
* Developmental
* Agenesis
* Hypoplasia
* Progressive
* Physiological
* Pathological
* General
* Tissue-specific
* Local atrophy
* Disuse
* Ischaemic
* Neuropathic
* Idiopathic
Increased growth:
* Hypertrophy
* Hyperplasia
* Neoplasia
126
What are the two types of decreased growth?
* Developmental -\> Occuring before the organ has reached maturity
* Progressive -\> Occuring after the organ has reached maturity
127
What are the different types of decreased developmental growth?
* Agenesis -\> Complete failure to develop
* Hypoplasia -\> Partial failure to develop
128
Define agenesis and give an example.
* Agenesis is the complete failure of an organ to develop
* Renal agenesis in the fetus can lead to decreased urine production
* Since urine is a contributor to aminiotic fluid, there is decreased amniotic fluid
* This can also lead to problems with pulmonary development (e.g. pulmonary agenesis)
* This is known as Potter's syndrome
129
Define hypoplasia and give some examples.
* Hypoplasia is the partial failure of an organ to develop
Example 1: Klinefelter's syndrome
* Partial failure of testes to develop
* Caused by two or more X chromosomes in males
Example 2: Turner's syndrome
* Partial failure of ovaries to develop
* Caused by a missing or partially X chromasome
130
What are the different types of decreased progressive growth?
* Physiological atrophy (involution) -\> Natural shrinking of an organ, leading to a reduction in function
* Pathological -\> Diseased wastage of organs
* General
* Tissue-specific
* Local atrophy
131
Define physiological atrophy (involution) and give an example.
* Physiological atrophy is the natural shrinking of an organ (after it has matured) due to a reduction in cell number, leading to a reduction in function -\> It is NOT linked to disease
* An example is the shrinking of the thymus at puberty
* The thymus is where T-lymphocytes are trained, but strong immunity is required most when you are young, so the structure is replaced with fat over time
132
What is the difference between agenesis, hypoplasia and atrophy?
They are all types of decreased growth, but:
* Agenesis is the complete failure of an organ to form
* Hypoplasia is the partial failure of an organ to form
* Atrophy is the reduction is size and function of an organ after it had fully developed
133
Define pathological atrophy and state the different types.
* It is the wastage of an organ (after it has matured) due to a reduction in cell number, leading to a reduction in function -\> It is caused by DISEASE
Types:
* General -\> Affecting many different tissues or organs
* Tissue-specific -\> Affecting many areas of the safe tissue type
* Local atrophy -\> Localised due to various reasons
134
Define general pathological atrophy and give examples.
* It is atrophy affecting many different tissues or organs throughout the body
Examples include:
* Wasting during starvation
* Malignant disease (cachexia)
135
What is cachexia?
Weight loss due to muscle loss in patients with diseases such as cancer. It is an example of general pathological atrophy.
136
Define tissue-specific pathological atrophy and give examples.
* It is atrophy affecting a particular type of tissue throughout the body
* An example is osteoporosis
137
What is local atrophy and what are the different causes?
* Atrophy that affects only part of the body
Causes include:
* Disuse
* Pressure from cysts/tumours/aneurysms
* Ischaemia
* Neuropathy (nerve problems)
* Idiopathic (unknown cause)
138
Give an example of local atrophy due to disuse.
Bone and muscle wastage in an immbolised limb (due to fracture).
139
Give an example of local atrophy due to ischaemia.
* Vascular disease
* Cerebral atrophy
140
Give an example of local atrophy due to neuropathy.
Muscle wasting after nerve injury or poliomyelitis
141
Give an example of local atrophy due to idiopathy.
Neuropathies such as Parkinson's
142
What are the different types of increased growth?
* Hypertrophy -\> Growth of organ/tissue due to increase in cell SIZE
* Hyperplasia -\> Growth of organ/tissue due to increase in cell NUMBER
* Neoplasia -\> Tumour growth
143
What are some of the characteristics of hypertrophy/hyperplasia?
* Occurs in response to stimulus external to affected organ
* Normal histology
* Often provides extra function
* Usually self-limiting and often reversible
Hypertrophy:
* Characteristic of 'permanent' tissues (notably muscle)
* Increase in size WITHOUT increase in number
Hyperplasia:
* Characteristic of 'renewing' tissues
* Increase in number WITHOUT increase in size (cell growth must occur but the cells are the same size as before hyperplasia - 'balanced growth')
144
Compare the tissues in which hypertrophy and hyperplasia occur.
* Hypertrophy -\> Permanent
* Hyperplasia -\> Renewing (+ some 'resting' tissues like endocrine glands)
145
Give an example of healthy and pathological hypertrophy.
* Healthy -\> Skeletal muscle hypertrophy in response to exercise
* Pathological -\> Cardiac hypertrophy
146
Describe when cardiac hypertrophy may occur.
* May be an adaptive response to pressure or volume stress
* Therefore it is a common consequence of many forms of heart disease
147
Give some examples of healthy and pathological hyperplasia.
* Healthy -\> Skin (in response to abrasion), Bone marrow (increased in erythropoiesis at high altitude), Endocrine glands
* Pathological -\> Hyperplasia of the thyroid in Graves' disease
148
What is erythropoiesis and what process does it involve?
* RBC production in the red bone marrow
* At high altitudes, hyperplasia is increased to accomodate for a need for higher rate of RBC production
149
What are the characteristics of neoplasia?
* Excessive proliferation of one cell type
* Results from cumulative genetic and epigenetic changes (usually clonal)
* Abnormal, unbalanced histology
* No useful function
* Progressive; Spontaneous regression is rare
150
What is neoplasia essentailly synonymous with?
Tumour growth
151
Describe the nomenclature of tumour types.
* **Epithelial**
* Surface
* Benign -\> Papilloma
* Malignant -\> Carcinoma
* Glandular
* Benign -\> Adenoma
* Malignant -\> Adenocarcinoma
* **Mesenchymal**
* Benign -\> e.g. Fibroma, Lipoma, Haemangioma (reflect tissue of origin)
* Malignant -\> -sarcoma
* **Haematological (benign/maligant doesn't really apply)**
* Lymphoid -\> Lymphoma, Lymphoproliferative disorders
* Bone marrow -\> Myelodysplasia, Leukaemia
152
What are the two main types of tumour resulting from neoplasia? What is their main difference?
* Benign -\> Grow by expansion
* Malignant -\> Grow by invasion, metastasis and progression
153
Describe the characteristics of benign tumours.
* Grow by local expansion
* Do not invade adjacent tissue, cross basement membrane or spread to distant sites
* Similar differentiation to normal tissue
* May cause harm through pressure, obstruction or secretion of hormones
* May progress to malignancy
154
Are benign tumours always harmless?
No, they may cause harm through pressure, obstruction or secretion of hormones.
155
Do benign tumours remain harmless?
No, they may become malignant due to additional mutations.
156
Describe the main characteristics of malignant tumours.
* Grow by invasion of adjacent tissue, traverse basement membrane and spread to distant sites
* Differentiation is incomplete to some extent (pleomorphism, anaplasia)
* Nuclei are often large, aneuploid; mitotic abnormalities
* Cause harm through destruction of normal tissue function (+ may also induce cachexia)
157
What is the difference between cell growth and proliferation?
* Cell growth is the process by which cells increase in mass and size
* Proliferation is the process of cell division
These processes are frequently co-ordinated and are therefore often used interchangeably.
158
What is morphogenesis?
The process by which an organism develops a shape.
159
Describe the different possible fates of undifferentiated cells.
* Differentiate
* Apoptosis
* Proliferation
* Growth
Note that proliferation and growth usually lead to the same point since they are usually co-ordinated. In other words, the cell may grow and then divide, or divide and then grow.
160
What processes balance the process of cell growth and division?
* Cell loss
* Cell death
161
What does cell growth require in order to occur?
* Increase in cell mass and volume -\> Macromolecule synthesis
* Relative movement at cell surface
162
Name some important times when growth occurs in humans.
* Development (Egg -\> Embryo -\> Fetus -\> Adult)
* Adult
* Hypertrophy -\> Permanent tissues
* Hyperplasia -\> Renewing tissues + Resting tissues
* Disease -\> Neoplasia
163
Describe the different adult tissue types depending on how they grow.
* Renewing tissues -\> Continually dividing stem cells (e.g. skin, gut epithelium, RBCs) -\> Hyperplasia
* Resting tissues -\> Cells multiply only to repair damage (e.g. liver, thyroid) -\> Hyperplasia
* Non-dividing tissues (e.g. neurons)
164
Name some important times when cell/tissue loss or hypoplasia occurs.
* Development
* Tissue patterning (e.g. digit formation)
* Neural patterning
* 'Physiological' atrophy
* Thymus at puberty
* Epithelial cells
* Developmental/physiological disorders
* Hypoplasia e.g. Klinefelter's syndrome
* Atrophy from disuse or disease
165
Describe the coupling of cell growth and proliferation in the cell cycle.
* Cyclin-dependent kinases are responsible for the progression of the cell cycle (e.g. they control the transition from G1 to S phase.
* These kinases are controlled by growth regulators, suggesting that growth causes the cell cycle, not vice versa
* So: Growth -\> Proliferation
166
Give some examples of when cell growth and proliferation are not coupled.
* Proliferation but no growth -\> Cleavage in development
* Growth but no proliferation -\> Skeletal muscle hypertrophy
* Growth and DNA replication but no cytokinesis, so cells are big -\> Many myocardial cells are 4N (tertraploid)
167
What molecules control cell growth?
* Growth inhibitors (not very well characterised though)
* Growth factors
168
Give some experimental evidence for growth inhibitors.
Myostatin deficiency in mice is linked to up to a 3-fold increase in mass. This shows that myostatin is a growth inhibitor.
169
Describe how growth factors work.
* Bind to cell-surface receptor
* This triggers an intracellular signalling cascade, with intracellular signalling molecules becoming active
* These change the properties of transcription factors, often by phosphorylation
* So macromolecular synthesis is increased, triggering growth and therefore the cell cell
170
What are the different types of growth factor?
* Global with global effects -\> Endocrine
* Global with specific effects -\> Endocrine
* Local with local effects -\> Paracrine or autocrine
Local tend to control growth of specific organs, while global tend to control organism-wide growth of multiple organs (e.g. nutrition-dependent).
171
How is organ size regulated?
* It is usually autonomous, which is demonstrated by transplanted organs usually growing to adult size
* Certain organs may be controlled non-autonomously (e.g. spleen)
172
What is generally important in patterning?
Growth factors
173
How do terminally differentiated cells compare to undifferentiated cells?
Similarities:
* Contain the same set of organelles
* Express some common proteins ('housekeeping genes/proteins')
Differences:
* Express cell type-specific proteins not expressed in non-differentiated cells -\> Lead to specilised functions and structures (e.g. sarcomeres)
174
Give an example of a protein that is specific to apoptotic cells and describe some experimental evidence for this.
* Caspases
* When caspase 9 is knocked out in mouse embryos, the brain appears very large. This is because caspase is required for modelling the nervous system and without it neurons do not die.
175
When is a cell terminally differentiated?
It differentiates terminlly after it has exited the cell cycle and entered a quiescent phase (G0).
176
Can a cell exit G0?
Yes, this process may be triggered by growth factors.
177
At what point in the cell cycle do cells enter G0?
After mitosis has finished and the cell is entering G1.
178
Can cells ever de-differentiate?
Mostly no, except for certain cells, such as hepatocytes which can re-enter the cell cycle for liver regeneration.
179
Do cells only differentiate after the have exited the cell cycle?
No, they start to differentiate before they exit the cell cycle.
180
Define differentiation.
A complex multistep process involving gradual specialisation of a cell.
181
What happens to potency as a cell differentiates?
It becomes more restricted.
182
Describe the basis of how cell differentiation occurs.
Cell-type specific gene expression is induced.
183
What are stem cells?
Cells that are:
* Undifferentiated
* Capable of renewal
* Able to divide without limit
184
Describe all of the combinations of the types of the 2 cells that stem cell division produces.
185
What are transit amplifying cells?
Transit-amplifying cells (TACs) are an undifferentiated population in transition between stem cells and differentiated cells.
186
What is the difference between unipotent stem cells, progenitor cells and transit amplifying cells?
All 3 types can only produce a single type of cell:
* Unipotent stem cells -\> Have the potential to divide an unlimited number of times, but tend to divide rarely
* Progenitor cells -\> Have the potential to divide only a limited number of times, but tend to divide rapidly
* Transit amplifying cells -\> Check the difference between this and progenitor cells, because they seem the same
187
What are the different types of natural stem cell and where are they found?
* Totipotent -\> Can become any embryonic cell, plus placental cells -\> Found in fertilised egg
* Pluripotent -\> Can become any embryonic cell, but cannot become placental cells -\> Found in inner cell mass of blastocyst
* Multipotent -\> Can become any of a given type of cell (e.g. any blood cell) -\> Found in adults
* Unipotent -\> Fully "committed" to terminal differentiation -\> Found in adults
188
What are haematopoietic stem cells and what type of stem cell are they?
* Stem cells in red bone marrow that give rise to all of the different mature blood cell types and tissues
* They are multipotent
189
Describe the stages of differentiation.
* The cell undergoes multiple changes from totipotent to pluripotent, then multipotent(?), then unipotent
* Each of these changes involves specification (where the cell differentiates autonomously, but can still be induced to change this) and then determination (where the cell differentiates autonomously in all ways and cannot be induced to change this)
* Finally, the cell terminally differentiates
Remember to check how transit amplifying cells fit into this - it seems that they are the stage between unipotent stem cells and differentiated cells.
190
Describe simply the difference between the processes of specification and determination in differentiation.
* Specification -\> Autonomous differentiation, where the cell is planning on differentiating into something but can still be made to change its mind
* Determination -\> Too late for the cell to change its mind
191
Give an example of the difference between specification and determination.
Taking ectoderm-planning cells and placing them in the right environment causes them to form mesoderm by induction instead.
192
According to the syllabus, what is the principle of the establishment of tissues?
Progressive restriction of developmental potential
193
What are adult stem cells important for?
Maintaining cell populations that last long periods of time and must be renewed:
* Epithelium
* Blood
* Muscle
* Liver
* Brain
194
Is the genome affected by differentiation? Give some experimental evidence for this.
* No
* Animals can be cloned by activating an egg, then inserting a fully differentiated nucleus. Since all of the different cell types of that organism can be formed from this nucleus, it shows that all of the DNA is present in the differentiated nucleus.
195
How is the differentiated state of cells produced and maintained?
Transcription factors:
* Show positive autoregulation (where the product of the gene activates the gene itself - see diagram)
* Block the cell cycle
Epigenetic control:
* Inactive genes -\> Promoter regions are often methylated, while histones are deactylated
* Active genes -\> Vice versa to above
196
Describe how induced pluripotent stem cells may be produced.
* Specific combination of transcription factors is expressed in cell
* These are normally specifically expressed in stem cells
197
Describe some experimental evidence for transcription factors maintaining the terminal differentiated state in some cells.
Conditional genetic removal of the Pax5 transcription factor in mature B cells of the immune system produces uncommitted progenitor cells that can differentiate into other immune cell types. This shows the role of Pax5 in maintaining the cells in the differentiated state.
198
Aside from regulation of the transcription, describe how differential gene expression may occur in differentiated cells.
* Alternative splicing
* RNA editing (post-transcriptional modification)
* Genomic rearrangements (placing different parts of the genome next to each other - NOTE: This is an exception to the rule about not changing the genome in differentiation)
199
What is induction?
When one cell instructs another to become committed and differentiate.
200
What are some mechanisms involved in induction?
* Diffusible ligand binds to a cell surface or intracellular receptor -\> Paracrine or juxtacrine
* Cell surface ligand binds to a receptor -\> Juxtacrine
* Gap junctions -\> Juxtacrine
Juxtacrine is when the cells are right next to each other.
201
Does all development require cell-cell interactions (i.e. induction)?
No, sometimes mosaic development can occur in mammals, where a certain part of the embryo will produce a given part of the organism, regardless of the different cells next to them.
202
Describe the assymetric division of stem cells.
A stem cell will produce two cells: Another stem cell and a cell that can go on to differentiate.
203
Describe the process of skin renewal.
* Skin: stratified squamous keratinised epithelium layer
* Basal cell layer contains proliferating stem cells
* Cells move through layers of skin to replace cells sloughed off at surface
* Cells move through states of gene expression towards terminal differentiation
* Cells express a series of different keratin proteins during differentiation
* 30 days from stem cell division to cell sloughed off at surface of the skin
204
Does the basal layer of skin contain many stem cells?
No, it only contains a few which produce transit amplifying cells that divide far more rapidly.
205
Why do stem cells not divide very often?
* Limit the potential for mutations during DNA replication
* Potential for very rapid repopulation when required e.g. wound repair
206
Name the different cells that can be derived from haemapoietic stem cells (HSC).
* RBCs
* WBCs
* Platelets
207
Describe an experiment to show that bone marrow contains stem cells.
208
What is the full name for a bone marrow transplant and what is it used to treat?
Haematopoietic stem cell transplantation (HSCT) used to treat:
* Severe aplastic anaemia (bone marrow failure)
* Leukaemia (cancer of WBCs)
* Non-Hodgkin's lymphoma (cancer of lymphatic system)
* Genetic blood and immune system disorders
209
Describe cardiac and skeletal muscle tissue regeneration.
210
Describe the action of stem cells in the brain.
211
Describe liver regeneration.
212
When do embryonic stem cells become pluripotent rather than totipotent?
At the 8 cell stage.
213
Describe the process of reprogramming cells to be induced pluripotent stem cells (iPS).
* 4 reprogramming factors originally used to convert primary cells into iPS cells: Oct4, Sox2, Klf4, c-Myc
* Delivered by viral vectors
214
Aside from treating diseases, what can iPS cells be used for?
Studying human diseases in vitro - "disease in a dish" models.
215
Give some examples of stem cells being used to treat diseases.
Parkinson's disease:
* Dopamingeric neurons transplanted at site of cell loss or site of dopamine loss
* Experiments in rats and monkeys very successful
* In humans: anecdotal success at best
Muscular dystrophy:
* Using muscle stem cells or muscle precursor cells to regenerate diseased muscle
* Experiments in rats very successful
* In humans: Unsuccessful (due to death of injected cells, immune response, etc.)
216
What are two main types of cell death?
* Apoptosis -\> Programmed cell death
* Necrosis -\> Accidental cell death
217
Describe briefly the mechanism of apoptosis.
Molecular pathway involves activation of proteases and caspases:
* Nucleus condensation and fragmentation
* Membrane blebbing (buldging) seen
* Apoptotic cell fragments (called apoptotic bodies) engulfed by phagocytic cells before bioactive contents can spill out
218
Name two situations where apoptosis is necessary.
* Digit formation
* Epiphyseal plate (apoptosis of hypertrophic chondrocytes)
219
What type of cell is it very important to target in cancer therapy and why?
Stem cells, since they drive the formation of tumours (despite their small number).
220
When a cell detects DNA damage, what are the different possible outcomes?
* Cell cycle checkpoint arrest
* DNA repair
* Apoptosis
221
Which parts of the EM spectrum may cause damage to DNA?
* Ultraviolet
* X-ray
* Gamma
222
Describe how ionising radiation can damage DNA.
* It ionises and excites water so that free radicals are produced
* These can then cause damage to biological molecules, including proteins, RNA and DNA
223
Give an example of highly-targeted radiotherapy.
Iodine-131 therapy:
* Radioactive iodine is ingested
* After ingestion, the iodine tends to affect the thyroid
* The iodine emits ionising radiation, which is used to treat thyroid cancer and hyper-thyroidism (Graves' disease)
224
How common is radiotherapy treatment?
60% of cancer patients in the UK receive radiation therapy.
225
Describe the radiation and technology involved in most radiotherapy.
* X-rays
* Delivered by a linear accelerator -\> Uses synchronised microwaves to accelerate electrons before they are stopped by a metal target
226
What are 'organs at risk'?
Organs surrounding a tumour with normal function. The radiation dose to these areas must be reduced as much as possible.
227
How can the radiation dose in radiotherapy be conformed to the shape of the tumour?
Multi-leaf collimation
228
How can the radiation distribution in radiotherapy be changed?
Using wedges.
229
Describe the different body volumes involved in planning radiotherapy.
* Gross tumour volume (GTV) -\> Extent of disease detectable by imaging or other clinical methods
* Clinical target volume (CTV) -\> Contains GTV and surroudning areas considered likely to contain subclinical disease (e.g. lymph nodes)
* Planning target volume (PTV) -\> Contains CTV and a margin to allow for physiological and technical variations
230
What is 3D conformal radiotherapy?
A method that uses up to 3 different intersecting beams to provide a highly shape-matched treatment that does not affect normal tissue very much.
