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Thyroid

2015-10-18T07:44:03Z

150015938:

Your thyroid gland is an [[endocrine gland|endocrine gland]] found in the neck. It is responsible for producing the [[hormonesthroxine|hormonesthroxine]] (T4) and [[triiodothyronine|triiodothyronine]] (T3) which are then secreted into the blood. If the thyroid doesn't function correctly it can results in thyroid diseases. [[Hypothyroidism|Hypothyroidism]] occurs as a result of an underactive thyroid, while [[Hyperhyroidism|Hyperhyroidism]] arrises from an overactive thyroid. The thyroid itself is composed of 2 sections: the right lobe and the left lobe. The thyroid is controlled by the [[pituitary gland|pituitary gland]] situated just under the brain. It monitors levels of T4 and T3 in the body, and secretes appropriate hormones to stimulate the thyroid activities<ref>http://www.btf-thyroid.org/index.php/thyroid/your-thyroid-gland</ref>.

=== References ===

<references />

Thyroid

2015-10-18T07:43:08Z

150015938:

Your Thyroid gland is an [[endocrine gland|endocrine gland]] found in the neck. It is resposble for producing the [[hormonesthroxine|hormonesthroxine]] (T4) and [[triiodothyronine|triiodothyronine]] (T3) which are then secreted into the blood. If the thyroid doesn't function correctly it can results in thyroid diseases. [[Hypothyroidism|Hypothyroidism]] occurs as a result of an underactive thyroid, while [[Hyperhyroidism|Hyperhyroidism]] arrises from an overactive thyroid. The thyroid itself is composed of 2 sections: the right lobe and the left lobe. The thyroid is controlled by the [[pituitary gland|pituitary gland]] situated just under the brain. It monitors levels of T4 and T3 in the body, and secretes appropriate hormones to stimulate the thyroid activities<ref>http://www.btf-thyroid.org/index.php/thyroid/your-thyroid-gland</ref>.

=== References ===

<references />

Telophase II

2014-11-18T13:39:39Z

150015938:

Telophase II is marked by a transition to the [[interphase]] condition of the chromosomes and the disassembly of [[mitotic spindle]]. During this process, [[nuclear envelope]] and [[nucleolus]] are reformed and the cells undergo [[cytokinesis]] as in [[mitosis]]. In Telophase II, the final stage of meiosis II, four haploid daughter cells are formed, each with a haploid set of [[chromosomes]]. Each daughter cells are genetically different from one another and their parent cell, as independent assortment of homologous chromosomes and [[crossing over]] in prophase I lead to different genetic composition in these cells.

'''References''':

1.Bruce Alberts...[et al.].(2007:1090)Molecular biology of the cell,5th edition, United States of America: Garland Science.

2.Daniel L. Hartl and Maryellen Ruvolo.(2012:131)Genetics: Analysis of genes and genomes,8th edition, United States of America: Jones & Bartlett Learning Canada.

'''External link''':
[http://www.cliffsnotes.com/sciences/biology/biology/meiosis-and-gamete-formation/meiosis]
[http://cyberbridge.mcb.harvard.edu/mitosis_7.html]

Telophase II

2014-11-18T13:34:47Z

150015938:

Telophase II is marked by a transition to the [[interphase]] condition of the chromosomes and the disassembly of mitotic spindle. During this process, [[nuclear envelope]] and [[nucleolus]] are reformed and the cells undergo [[cytokinesis]] as in [[mitosis]]. In Telophase II, the final stage of meiosis II, four haploid daughter cells are formed, each with a haploid set of [[chromosomes]]. Each daughter cells are genetically different from one another and their parent cell, as independent assortment of homologous chromosomes and [[crossing over]] in prophase I lead to different genetic composition in these cells.

'''References''':

1.Bruce Alberts...[et al.].(2007:1090)Molecular biology of the cell,5th edition, United States of America: Garland Science.

2.Daniel L. Hartl and Maryellen Ruvolo.(2012:131)Genetics: Analysis of genes and genomes,8th edition, United States of America: Jones & Bartlett Learning Canada.

'''External link''':
[http://www.cliffsnotes.com/sciences/biology/biology/meiosis-and-gamete-formation/meiosis]
[http://cyberbridge.mcb.harvard.edu/mitosis_7.html]

Telophase II

2014-11-18T13:18:00Z

150015938:

Telophase II is marked by a transition to the [[interphase]] condition of the chromosomes and the disassembly of mitotic spindle. During this process, nuclear envelope and nucleolus are reformed and the cells undergo cytokinesis as in [[mitosis]]. In Telophase II, the final stage of meiosis II, four haploid daughter cells are formed, each with a haploid set of [[chromosomes]]. Each daughter cells are genetically different from one another and their parent cell, as independent assortment of homologous chromosomes and [[crossing over]] in prophase I lead to different genetic composition in these cells.

'''References''':

1.Bruce Alberts...[et al.].(2007:1090)Molecular biology of the cell,5th edition, United States of America: Garland Science.

2.Daniel L. Hartl and Maryellen Ruvolo.(2012:131)Genetics: Analysis of genes and genomes,8th edition, United States of America: Jones & Bartlett Learning Canada.

'''External link''':
[http://www.cliffsnotes.com/sciences/biology/biology/meiosis-and-gamete-formation/meiosis]
[http://cyberbridge.mcb.harvard.edu/mitosis_7.html]

Telophase II

2014-11-18T13:16:31Z

150015938:

Telophase II is marked by a transition to the [[interphase]] condition of the chromosomes and the disassembly of mitotic spindle. During this process, nuclear envelope and nucleolus are reformed and the cells undergo cytokinesis as in [[mitosis]]. In Telophase II, the final stage of meiosis II, four haploid daughter cells are formed, each with a haploid set of [[chromosomes]]. Each daughter cells are genetically different from one another and their parent cell, as independent assortment of homologous chromosomes and [[crossing over]] in prophase I lead to different genetic composition in these cells.

References:

1.Bruce Alberts...[et al.].(2007:1090)Molecular biology of the cell,5th edition, United States of America: Garland Science.

2.Daniel L. Hartl and Maryellen Ruvolo.(2012:131)Genetics: Analysis of genes and genomes,8th edition, United States of America: Jones & Bartlett Learning Canada.

External link:
[http://www.cliffsnotes.com/sciences/biology/biology/meiosis-and-gamete-formation/meiosis]
[http://cyberbridge.mcb.harvard.edu/mitosis_7.html]

Telophase II

2014-11-18T13:16:12Z

150015938:

Telophase II is marked by a transition to the [[interphase]] condition of the chromosomes and the disassembly of mitotic spindle. During this process, nuclear envelope and nucleolus are reformed and the cells undergo cytokinesis as in [[mitosis]]. In Telophase II, the final stage of meiosis II, four haploid daughter cells are formed, each with a haploid set of [[chromosomes]]. Each daughter cells are genetically different from one another and their parent cell, as independent assortment of homologous chromosomes and [[crossing over]] in prophase I lead to different genetic composition in these cells.

Reference:

1.Bruce Alberts...[et al.].(2007:1090)Molecular biology of the cell,5th edition, United States of America: Garland Science.

2.Daniel L. Hartl and Maryellen Ruvolo.(2012:131)Genetics: Analysis of genes and genomes,8th edition, United States of America: Jones & Bartlett Learning Canada.

External link:
[http://www.cliffsnotes.com/sciences/biology/biology/meiosis-and-gamete-formation/meiosis]
[http://cyberbridge.mcb.harvard.edu/mitosis_7.html]

Telophase II

2014-11-18T13:14:34Z

150015938:

Telophase II is marked by a transition to the [[interphase]] condition of the chromosomes and the disassembly of mitotic spindle. During this process, nuclear envelope and nucleolus are reformed and the cells undergo cytokinesis as in [[mitosis]]. In Telophase II, the final stage of meiosis II, four haploid daughter cells are formed, each with a haploid set of chromosomes. Each daughter cells are genetically different from one another and their parent cell, as independent assortment of homologous chromosomes and [[crossing over]] in prophase I lead to different genetic composition in these cells.

Reference:

1.Bruce Alberts...[et al.].(2007:1090)Molecular biology of the cell,5th edition, United States of America: Garland Science.
2.Daniel L. Hartl and Maryellen Ruvolo.(2012:131)Genetics: Analysis of genes and genomes,8th edition, United States of America: Jones & Bartlett Learning Canada.

External link:
[http://www.cliffsnotes.com/sciences/biology/biology/meiosis-and-gamete-formation/meiosis]
[http://cyberbridge.mcb.harvard.edu/mitosis_7.html]

Telophase II

2014-11-18T13:13:56Z

150015938:

Telophase II is marked by a transition to the [[interphase]] condition of the chromosomes and the disassembly of mitotic spindle. During this process, nuclear envelope and nucleolus are reformed and the cells undergo cytokinesis as in [[mitosis]]. In Telophase II, the final stage of meiosis II, four haploid daughter cells are formed, each with a haploid set of chromosomes. Each daughter cells are genetically different from one another and their parent cell, as independent assortment of homologous chromosomes and [[crossing over]] in prophase I lead to different genetic composition in these cells.

Reference:
1.Bruce Alberts...[et al.].(2007:1090)Molecular biology of the cell,5th edition, United States of America: Garland Science.
2.Daniel L. Hartl and Maryellen Ruvolo.(2012:131)Genetics: Analysis of genes and genomes,8th edition, United States of America: Jones & Bartlett Learning Canada.

External link:
[http://www.cliffsnotes.com/sciences/biology/biology/meiosis-and-gamete-formation/meiosis]
[http://cyberbridge.mcb.harvard.edu/mitosis_7.html]

Telophase II

2014-11-18T13:12:06Z

150015938:

Telophase II is marked by a transition to the [[interphase]] condition of the chromosomes and the disassembly of mitotic spindle. During this process, nuclear envelope and nucleolus are reformed and the cells undergo cytokinesis as in [[mitosis]]. In Telophase II, the final stage of meiosis II, four haploid daughter cells are formed, each with a haploid set of chromosomes. Each daughter cells are genetically different from one another and their parent cell, as independent assortment of homologous chromosomes and crossing over in prophase I lead to different genetic composition in these cells.

Reference:
Bruce Alberts...[et al.].(2007:1090)Molecular biology of the cell,5th edition, United States of America: Garland Science.
Daniel L. Hartl and Maryellen Ruvolo.(2012:131)Genetics: Analysis of genes and genomes,8th edition, United States of America: Jones & Bartlett Learning Canada.

External link:
[http://www.cliffsnotes.com/sciences/biology/biology/meiosis-and-gamete-formation/meiosis]
[http://cyberbridge.mcb.harvard.edu/mitosis_7.html]

Telophase II

2014-11-18T12:49:02Z

150015938: Created page with "Telophase II is marked by a transition to the interphase condition of the chromosomes and the disassembly of mitotic spindle. During this process, nuclear envelope and nucleolus..."

Telophase II is marked by a transition to the interphase condition of the chromosomes and the disassembly of mitotic spindle. During this process, nuclear envelope and nucleolus are reformed and the cells undergo cytokinesis as in mitosis. In Telophase II, the final stage of meiosis II, four haploid daughter cells are formed, each with a haploid set of chromosomes. Each daughter cells are genetically different from one another and their parent cell, as independent assortment of homologous chromosomes and crossing over in prophase I lead to different genetic composition in these cells.

Neurotransmitter

2014-11-17T08:56:39Z

150015938:

Neurotransmitters are signalling [[Molecule|molecules]] released by [[Exocytosis|exocytosis]] from vesicles in the pre-synaptic cell causing [[Depolarisation|depolarisation]], they diffuse across the synaptic cleft in response to an [[Action potential|action potential]]. The neurotransmitter causes an electrical change in the post-synaptic cell.

The signals can be excitatory (open [[Cation channels|cation channels]] (e.g. [[Sodium|Na]][[Sodium|+]])) or inhibitory (open Cl- or [[Potassium Channel|K]][[Potassium Channel|+]][[Potassium Channel|channels]]). Excitatory signals bring the cell closer to threshold where as inhibitory signals cause the cell to move away from threshold value. When the cell reaches threshold an [[Action potential|action potential]] is fired <ref>Alberts, B et al. (2008). Molecular Biology of the Cell. 5th ed. US: Garland Science</ref>.

Transmission of a signal between two neurones can be improved if the neurotransmitter is repeatedly released from the presynaptic membrane, this is called [[Long term potentiation|long term potentiation]] (LTP). An example of this is the release of the neurotransmitter [[Glutamate|glutamate]]. The postsynaptic membrane holds two ligand-gated ion channels ([[Iontrophic receptor|iontrophic receptors]]): the [[AMPA receptor|AMPA receptor]] and the [[NMDA receptor|NMDA receptor]]. When [[Glutamate|glutamate]] diffuses across the synaptic cleft and binds to the [[AMPA receptor|AMPA receptor]], the ion channel opens and allows the entry of sodium ions into the postsynaptic cell. This iniates an EPSP ([[Excitatory post-synaptic potential|excitatory post-synaptic potential]]) which in turn can trigger an action potential if the voltage reaches or exceeds the threshold (-55mV).  In contrast, [[Glutamate|glutamate]] initially has no effect on the [[NMDA receptor|NMDA receptor]] as a [[Magnesium|magnesium]] ion attached to the receptor inhibits it from opening. But as [[Glutamate|glutamate]] is repeatedly released, furthur depolarisation of the postsynaptic membrane triggers the release of the [[Magnesium|magnesium]] ion from the receptor. This allows the entry of [[Calcium|calcium]] ions which then activates other [[Molecules|molecules]] in the [[Secondary messenger|secondary messenger]] pathway <ref>Alberts B, Johnson A, Lewis J, Raff M, Walter P (2008) Molecular Biology Of The Cell, Garland Science Taylor and Francis Group, New York pg 691-692</ref>. 

=== Different types of Neurotransmitters: ===

''''''

'''Ligand gated ion channel (Ionotropic neurotransmitters):''' 

 

=== G-protein linked receptors (Metabotropic neurotransmitters): ===

*[[Histamine|Histamines]]
*Epinepherine
*ATP
*Acetylecholine 

=== Other Neurotransmitters (that don't require receptors): ===

*Nitric oxide
*Testosterone 

=== References ===

<references />

Okazaki fragments

2014-11-17T08:50:04Z

150015938:

During [[DNA replication|DNA replication]] the [[DNA|DNA]] duplex is unwound and two daughter strands are formed at the [[Replication fork|replication fork]]. [[DNA polymerase|DNA polymerase]] can only add [[Nucleotide|nucleotides]] in the 5' to 3' direction, hence the synthesis of the one of the daughter strands, the leading strand, can proceed continuously in the same direction as movement of the [[Replication_fork|replication fork]].

However a complication arises with the replication of the other daughter strand, the lagging strand. As growth must occur in the 5' to 3' direction the copying of the template must somehow occur in the opposite direction as the movement of the replication fork. The cell accomplishes this by synthesising a new [[RNA|RNA]] primer every hundred bases or so as more of the strand is exposed. Each of these primers is elongated in the 5' to 3' direction forming segments called Okazaki fragments, named after their discoverer [[Reiji Okazaki|Reiji Okazaki]]. The RNA primer is then removed and the [[Enzyme|enzyme]] [[DNA ligase|DNA ligase]] joins the adjacent fragments together <ref name="null">Molecular Cell Biology, 7th Edtion, Harvey Lodish et al., Page: 146</ref>.

=== References ===

<references />

Clatharin

2014-11-17T08:47:13Z

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Clatharin is a protein which is present on the cystolic (inside) surface of a membrane and very important in intracellular vesicular trafficking. It forms an intracelular vesicle by budding off the membrane via endocytosis. Clathrin also coats COPI & COPII vesicles which bud off rom the Golgi and Endoplasmic Reticulum respectiviely<ref>Molecular Biology of The Cell, 5th Edition, Alberts et al, pg 754-756.</ref>. The structure of [[Clathrin|Clathrin]] itself consists of three large and three small polypeptide chains that form a three-legged structure called a ''triskelion''. Triskelions assemble into a basketlike structure of pentagons and hexagons to form the Clathrin-coated pits on the cystolic surface of membranes.

 

<references />

Cell signalling

2014-11-17T08:44:56Z

150015938:

Cell Signalling is the transfer of information, that controls the [[Cell|cell]] behaviour, whether from cell to cell, or from environment to cell.

There are many different types of cell signalling that vary immensely. About 10-15% of the [[Genome|genome]] codes for the creation of these cell signalling molecules. Most signals involved are chemicals but some can be physical signals such as light. 

Different signalling mechanisms are used depending on how far the signal needs to travel. For short distances, there is a pathway between adjacent cells and takes place via a [[Gap junction|gap junction]]. The pathway sizes increase from gap junction, to contact dependant, where the signal is displayed on the surface and a receptor on another cell surface, for example, an immune response cell. [[Paracrine signals|Paracrine pathways]] secrete a signal into the interstitial fluid within the same tissue. The next longer pathway is [[Autocrine signalling|Autocrine signalling]] and [[Synaptic signalling|Synaptic signalling]]. The longest signalling pathway, which usually has the longest response time to the stimulus is [[Endocrine signalling|Endocrine signalling]], where the signal is secreted into the [[Blood|blood]] stream which flows around the body. 

A signal molecule coming from either a long or short distance functions as a ligand by binding to a receptor. The ligand is the 'primary messenger', and its binding to the receptor often causes additional molecules inside the cell to receive the signal. These are known as 'second messengers' and they relay the signals to different parts of the cell, initiating a cascade of changes (to behaviour or gene expression) within the receiving cell<ref>Hardin, J. et al. (2011). Becker's World of the Cell. 8th ed. San Francisco: Pearson. p392-3.</ref>.

There are 5 stages:

#Signal
#Reception
#[[Transduction|Transduction]]
#Amplification
#Response

=== References ===

<references />

Striated muscle

2014-11-17T08:33:02Z

150015938:

[[myofibrils]]Straited muscle consists of hundreds of [[Myofibrils|myofibrils]] packed into a regular parallel arrangement to form a muscle fibre. Striated muscle is given its name due to dark and light bands that can be seen down a light microscope when viewing [[Myocytes|myocytes]]. Striations are present in skeletal and cardiac muscle but not in [[Smooth muscle|smooth muscle]]. The bands that can be seen are fibers that have repeating [[Sarcomeres|sarcomeres]]. The dark bands (A bands) that can be seen are [[Myosin|myosin]] filaments and are so named as they are anistropic. The light bands (I bands) that are observed are made up of [[Actin|actin]] filaments, and are so named because they are isotopic.

[[Image:Lrg-1348-skeletal muscle.jpg|center|Image of skeletal muscle showing striations]]