Genes, Molecules, And Cells > Development > Flashcards

Development Flashcards

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1
Q

What is Growth?

A

Increase in size.

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2
Q

What is development?

A

Change with time.

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3
Q

What is morphogenesis?

A

Development of shape or form.

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4
Q

What is differentiation?

A

Specialisation of function.

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5
Q

What are some key processes in embryogenesis?

A
  • Development of cell polarity: acquisition of asymmetry. Determines subsequent fate.
  • Becoming multicellular.
  • Pattern formation, cell commitment, cell fate.
  • Organogenesis- complex organs produced with the right number and spacial distribution of parts.
  • Differentiation.
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6
Q

What are some aspects of regulation at the cellular level?

A
  • Acquisition of polarity
  • Control of cell division
  • Control of cell size and shape
  • Cell movement and adhesion
  • Responses to external stimuli
  • Communication between cells
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7
Q

What is the Genetic basis of development?

A

Some genes control development e.g. some transcription factors determine cell commitment and organogenesis.

Some genes are expressed as a consequence of a developmental change.

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8
Q

What is needed to understand how development is controlled?

A
  • Establish how processes involved in development are regulated within cells.
  • Identify genes controlling development and determine the functions of the proteins they encode.
  • Determine how expression of genes controlling development is regulated.
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9
Q

What is the ‘forward’ genetic approach to determining gene function?

A
  1. Isolate mutant in selected process.
  2. Identify genes controlling development that has become mutated.
  3. Draw conclusions on gene function.
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10
Q

What are examples of model organisms?

A

Yeast, Caenorhabditis, Drosophilia, Zebrafish, Arabidopsis, and Mice.

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11
Q

What are advantages of model organisms for genetics?

A
  1. Small and easy to grow.
  2. Rapid generation time.
  3. Lots of progeny from each individual.
  4. Preferably self fertile and able to be crossed.
  5. Easy to produce mutants.
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12
Q

What are advantages of model organisms for molecular biology?

A
  1. Small genome- enables full genome sequence to be obtained and helps gene function.
  2. Easy to genetically transform.
  3. Methods for isolating genes corresponding to mutants.
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13
Q

What is polarity?

A

The acquisition of asymmetry. a key step in early development as it leads to the production of cells with different properties and hence different developmental fates.

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14
Q

What determines polarity in the Fucus zygote? (Rhizoid or Thallus)

A

rhizoid develops on shaded side. Takes 12hrs to appear. Polarity not fixed until >10hrs.

In addition, polarity is determined by:
- fertilization (Rhizoid at entry point)
- heat (Rhizoid to warm side)
- pH and salt (Rhizoid to alkaline pH and salt)
- Electrical gradient (Rhizoid at -ve pole)

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15
Q

How is Calcium involved in polarity?

A

Calcium influx at Rhizoid end, calcium effluent at thallus end.
Disruption of calcium gradient prevents development of polarity.
Localisation of Ca2+ channels is observed after 5-6hrs of illumination.

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16
Q

Where does the asymmetry of plant and animal zygotes originate?

A

The asymmetry of the zygote reflects a polar distribution of molecules and organelles in the egg cell gamete.

The zygote is not initially a polar but already has an asymmetric distribution of components.

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17
Q

What is the concept of localised cytoplasmic determinants?

A

The polar distribution of components in the egg cell and hence zygote will give rise to differences in daughter cell composition and developmental fate following the first division.

The polar distribution of components is sometimes visible, but to show a component has an effect on development need to demonstrate its action e.g. by removal or translocation.

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18
Q

Why has the polar distribution of components and their role in determining cell fate been extensively studied in ascidians?

A

The ascidian egg has regions of cytoplasm with different coloured inclusions. These show reproducible patterns of distribution during embryogenesis and are linked to the fate of cells.
The regions of the fertilised egg give rise to different tissues during embryogenesis i.e. have localised cytoplasmic determinants.
Transplantation of different regions into different parts of the egg give rise to altered cell fate.

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19
Q

How does asymmetry of components in egg cells originate?

A

Nurse cells in the ovary synthesise macromolecules that are transported to the oocyte (precursor to egg cell) as it develops via cytoplasmic bridges. Some of these macromolecules (e.g. particular mRNAs) are asymmetrically distributed.

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20
Q

What is the Drosophila bicoid mutant?

A

It has altered embryo development. Wild type drosophila has anterior and posterior polar ends (develop into heads and tails respectively).
The mutant embryos lacks the head and thorax at the anterior end and instead has a second set of posterior structures. Therefore, the wild type Bicoid gene product is required for normal anterior development of the embryo. Bicoid mRNA and protein are localised at the anterior end of the embryo in wild-type.

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21
Q

What Maternal Effect Genes are involved in determining anterior-posterior polarity in Drosophilia?

A
  • Bicoid and Hunchback regulate production of anterior structures.
  • Nanos and Caudal regulate production of posterior structures.
    Bicoid, Hunchback and Caudal are transcription factor proteins that regulate other genes controlling later steps in development.
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22
Q

How do Bicoid, Hunchback, Nanos, and Caudal establish polarity in Drosophilia?

A

The polar distribution of Bicoid and Nanos mRNAs is establishes in the ovary.
The Bicoid protein inhibits the translation of Caudal mRNA at the anterior pole, resulting in the accumulation of Caudal protein towards the posterior.
Similarly, Nanos inhibits translation of Hunchback mRNA at the posterior.
The spatial distribution of these proteins regulates subsequent steps in development.

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23
Q

What is the cytoskeleton?

A

Intracellular networks of protein filaments of several types:
- Microtubules
- Actin microfilaments
- Intermediate filaments

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24
Q

What cellular aspects of development involve the cytoskeleton?

A
  • Acquisition of polarity
  • Control of cell size and shape
  • Control of cell division
  • Intracellular movement of components
  • Call movement and adhesion
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25
What are microtubules?
Microtubules are composed of the protein tubulin, which exists as a dimer of two closely related subunits, α and β tubulin. Both tubulin subunits bind guanosine triphosphate (GTP) and this is important in regulating microtubule formation. GTP bound to β tubulin (but not α tubulin) can be hydrolysed to GDP. Microtubules consist of 13 protofilaments, each of which is as polymer of many tubulin dimers.
26
Explain the dynamic structure of microtubules, which undergo continual assembly and disassembly.
The growth and shrinkage of microtubules is regulated by guanoside triphosphate (GTP) Both α and β-tubulin bind GTP. Tubulin dimers bound to GTP are added at the ‘plus’ end of the microtubule. GTP bound to the β-tubulin hydrolyses to GDP shortly after addition to the microtubule.
27
Explain the dynamic structure of microtubules, which undergo continual assembly and disassembly.
The growth and shrinkage of microtubules is regulated by guanoside triphosphate (GTP) Both α and β-tubulin bind GTP. Tubulin dimers bound to GTP are added at the ‘plus’ end of the microtubule. GTP bound to the β-tubulin hydrolyses to GDP shortly after addition to the microtubule. Tubulin dimers containing bound GDP are lost from the minus end of the microtubule.
28
How does [tubulin-GTP] affect microtubules continuous assembly and disassembly?
If [tubulin-GTP] is low, the rate of additional at the + end is slow and GTP hydrolysis will remove the GTP cap. Under these conditions tubulin is rapidly lost from the + end, resulting in complete depolymerisation. Whether a microtubule grows or shrinks will depend on the local concentrations of tubulin bound to GTP.
29
Where do microtubules assemble?
In many cells, microtubules assemble from Microtubule Organising Centres (MTOCs). In animal cells the major MTOC is the centrosome, which often contains 2 centrioles. The microtubules radiate outwards from the centrosome. Plant cells do not have centrosome MTOCs.
30
What affects microtubules stability?
A variety of factors e.g. low temperature causes depolymerisation. The drugs coaching ans colcemid bind tubulin and prevent polymerisation. Stability is also regulated by microtubule-associated proteins (MAPs). In some cells, the microtubules half-life is only a few minutes, allowing the cytoskeleton to be continually remodelled.
31
How are microtubules involved in Intracellular movement (e.g. of chromosomes in mitosis, of vesicles and organelles)?
Movement along microtubules involves motor proteins called kinesins and dyneins, which use the energy of ATP hydrolysis to move components. Kinesin moves ‘cargo’ towards the +ve end of microtubules. Dyenin moves ‘cargo’ towards the -ve end of microtubules.
32
What are actin microfilaments?
The globular actin monomer is called G-actin and it polymerises into F-actin filaments. The filaments consist of a tightly wound helix ~7nm in diameter.
33
How are Actin microfilaments assembled and disassembled?
Actin binds ATP or ADP. Hydrolysis of ATP to ADP follows polymerisation. The filaments have a +/- orientation and monomers are added mainly at the +ve end. The drug cytochalasin B binds at the +ve end preventing elongation.
34
What proteins regulate the dynamic process of actin filament assembly and disassembly?
Cofilin binds to filaments and promotes disassociation from the minus end. Profilin promotes ATP binding to actin and promotes polymerisation. Arp2/3 proteins act as nucleation sites to stimulate assembly of new filaments.
35
What do actin filaments assemble into?
Bundles (parallel mesh, strong) and networks (branching) held together by different types of cross-linking proteins.
36
What are intermediate filaments?
They are composed of various types of proteins (~50 expressed in different types of cells). They have a diameter of ~10nm. The different filaments have a similar basic structure: N-head-rod-tail-C
37
What does intermediate filaments assembly entail?
Involves multimerisation. No +/- ends. More stable than microtubules and microfilaments.
38
What is the function of intermediate filaments?
They associate with other cytoskeleton elements, the plasma membrane, and organelles. They help to increase mechanical strength and anchor components.
39
How can cytoskeletal components be visualised?
Cytoskeletal proteins can be visualised when they bind a fluorescently labelled ‘tag’ or specific antibody introduced into cells. The cells are examined by fluorescence microscopy.
40
How does the cytoskeleton control the cell shape?
Both microtubules and actin filaments are very important in controlling cell shape. Actin bundles and networks underlie and support the plasma membrane.
41
How and why are human erythrocytes shape controlled by the actin network?
Human erythrocytes lack microtubules and intermediate filaments, so their shape is controlled by the actin network. the actin network is connected by spectrin cross-linking protein and anchored to the plasma membrane by ankyrin.
42
What cytoskeletal component supports protrusion in cells?
Bundles of actin filaments support protrusions such as microvilli of intestinal epithelial cells.
43
What supports the structure of the trichome leaf hairs of Arabidopsis?
The trichome leaf hairs of Arabidopsis are branched single cells. Plants treated with drugs that disrupt microtubule and actin polymerisation produce abnormally shaped trichomes. Several mutants with abnormal trichomes lack normal Arp2/3 proteins.
44
How do microtubules localise mRNAs for polar distribution (e.g. Bicoid mRNA)
Localisation requires mRNAs binding to microtubules via linker proteins. The mRNA protein complexes move along the microtubules bound to kinesin motor protein.
45
What is the (Mitotic) Cell Cycle?
The process that cells undergo to duplicate their contents to pass on to two identical daughter cells. This involves both DNA replication and duplication of cellular constituents such as endoplasmic reticulum, mitochondria etc. and their separation into two daughter cells.
46
What are the two main stages of the cell cycle?
1. Cell replication 2. Cell division (aka cytokinesis)
47
What is the duration of the prokaryotic cell cycle?
Divides every 20-40 minutes- very fast. Continuous cell growth and duplication.
48
What is the process of DNA synthesis in Prokaryotes?
1. Cleavage of DNA to produce three prime end. 2. Synthesis of RNA primer for DNA polymerase. 3. Proteins required- e.g. type II topoisomerase (gives circular structure).
49
What is the size and structure of the Prokaryotic genome?
Small (5-100kb) and circular.
50
How do Prokaryotic cells divide following DNA replication?
“Random” segregation of DNA between cells- 99.9% accurate.
51
What is the duration of the Eukaryotic cells cycle?
It varies. Yeast take 2 hours, humans 24.
52
What are the two main phases of the Eukaryotic cell cycle, conserved in all eukaryotes?
Mitosis and Interphase, both of which are further sectioned.
53
What are the three phases of Interphase?
G1- Gap 1 S- DNA Synthesis G2- Gap 2
54
What are the control points of the Eukaryotic cell cycle?
The Gap 1 and Gap 2 phases.
55
How many genes are in the Eukaryotic genome?
1,000-10,000s of genes.
56
What are ORCs?
Origin Replication Complexes. They are complexes of proteins that drive DNA replication. They are located across all chromosomes. They are activated in S phase only.
57
What are the phases of M phase?
1. Prophase 2. Metaphase 3. Anaphase 4. Telophase
58
What occurs in Prophase?
- Centrioles duplicate - Centrioles move to poles - Chromosomes condense - Mitiotic spindle forms
59
What occurs in Metaphase?
- Chromosomes move to equator of cell
60
What occurs in Anaphase?
- Daughter (sister) chromatids separate and move to poles
61
What occurs in Telophase?
- Membranes form around new nuclei. - Cell divides (cytokinesis)
62
What are the three levels of control in the Eukaryotic cell cycle?
1. Transcription- gene expression 2. Protein levels and stability 3. Protein activity- post-translational modifications e.g. phosphorylation
63
What are the two types of transcription?
1. General gene expression- where gene is transcribed all the time. 2. Specific gene expression- where gene is transcribed only at certain time/place.
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