The School of Biomedical Sciences Wiki - User contributions [en]

‘sticky’ ends

2012-10-23T11:06:04Z

110025526:

A [[Restriction enzyme|restriction enzyme]] can cut [[DNA|DNA]] at a specific sequence of [[Nucleotides|nucleotides]] usually 4, 6 or 8 [[Nucleotides|nucleotides]] long. This may result in [[Blunt ends|symmetrical cleavage]] leading to [[Blunt ends|"blunt" ends]] or [[‘sticky’_ends|assymetrical cleavage]] causing [[‘sticky’_ends|"sticky" ends]]. A [[‘sticky’_ends|"sticky" end ]]is produced when the [[Restriction enzyme|restriction enzyme]] cuts at one end of the sequence, between two bases on the same strand, then cuts on the opposite end of the complementary strand. This will produce two ends of [[DNA|DNA]] that will have some [[Nucleotides|nucleotides]] without any complementary bases. A [[Restriction enzyme|restriction enzyme]] will only cut at a specific sequence, and it recognises palindromic sequences that is, sequences that are the same whether they are read forwards or backwards. These "sticky" ends allow the insertion of 'foreign' DNA into the host [[Genome|genome]]. By using the same restriciton [[Enzyme|enzyme]] to cut a [[Plasmid|plasmid]], for example, complementary bases of the plasmid can pair with those of the host DNA. The [[Genes|genes]] carried on the plasmid will now be incorporated into the hosts genome. Also see [[Blunt end|"blunt" ends]].

Amino acids

2011-12-02T16:37:52Z

110025526:

Amino acids are the building blocks of proteins. There are 20 naturally occurring amino acids. Amino acids exist in proteins as L-optical isomers, however they can extist as D-isomers in isolated examples, e.g. some bacterial cell walls contain D-isomers.

Amino acids can also be characterized as [[Polar amino acids|polar]] or [[Non-polar amino acids|non-polar]], these dictate the amino acid function. There are 10 non-polar amino acids, these are found in [[Protein|protein]] core. There are also 10 polar amino acids, these have [[Enzyme|enzymatic]] roles, they can be used to bind [[DNA|DNA]], metals and other naturally occuring ligands. There are essential amino acids and non-essential amino acids. Essential amino acids are the ones that the body cannot synthesise on its own. These amino acids have to be supplied to the body via digested proteins. The digestion of cellular proteins is also an important source for amino acids. Non-essential amino acids can be synthesised from compounds already existing in the body.

Amino acids have been abbreviated into a 3 letter code as well as a 1 letter code. For example, [[Glycine|glycine]] has the 3 letter code 'Gly' and is assigned the letter 'G' (see single letter amino acid codes).

'''List of the 20 Amino acids, single letter code, three letter code, their charges, and side chain [[Polarity|polarity]]:'''

{| style="width: 357px; height: 460px" border="1" cellspacing="1" cellpadding="1" width="357"
|-
| '''Amino acid'''
| '''single letter code'''
| '''three letter code'''
| '''charge'''
| '''polarity'''
|-
| [[Alanine|alanine]]
| A
| ala
| neutral
| nonpolar
|-
| [[Arginine|arginine]]
| R
| arg
| +ve
| polar
|-
| [[Asparagine|asparagine]]
| N
| asn
| neutral
| polar
|-
| [[Aspartate|aspartate]]
| D
| asp
| -ve
| polar
|-
| [[Cysteine|cysteine]]
| C
| cys
| neutral
| polar
|-
| [[Glycine|glycine]]
| G
| gly
| neutral
| nonpolar
|-
| [[Glutamine|glutamine]]
| Q
| gln
| neutral
| polar
|-
| [[Glutamate|glutamate]]
| E
| glu
| -ve
| polar
|-
| [[Histidine|histidine]]
| H
| his
| +ve
| polar
|-
| [[Isoleucine|isoleucine]]
| I
| ile
| neutral
| nonpolar
|-
| [[Leucine|leucine]]
| L
| leu
| neutral
| nonpolar
|-
| [[Lysine|lysine]]
| K
| lys
| +ve
| polar
|-
| [[Methionine|methionine]]
| M
| met
| neutral
| nonpolar
|-
| [[Phenylalanine|phenylalanine]]
| F
| phe
| neutral
| nonpolar
|-
| [[Proline|proline]]
| P
| pro
| neutral
| nonpolar
|-
| [[Serine|serine]]
| S
| ser
| neutral
| polar
|-
| [[Threonine|threonine]]
| T
| thr
| neutral
| polar
|-
| [[Tryptophan|tryptophan]]
| W
| trp
| neutral
| nonpolar
|-
| [[Tyrosine|tyrosine]]
| Y
| tyr
| neutral
| polar
|-
| [[Valine|valine]]
| V
| val
| neutral
| nonpolar
|}

=== '''Amino acid structure''' ===

All amino acids have a carboxyl terminus, and an amino terminus, but they differ in their residual groups. Amino acids are bonded together by a [[Covalent|covalent]] linkage called a [[Peptide bond|peptide bond]] <ref>Alberts, B et al. (2008). Molecular Biology of the Cell. 5th ed. US: Garland Science. 1268. (Page 59)</ref>. Amino acids contain both a [[Carboxyl group|carboxyl group]] (COOH) and an [[Amino group|amino group]] (NH2). The core amino acid structure is: 

              NH2-----C(H)(R)----COOH

where R is the side chain tha differ in all amino acids.

Large amino acids form the rigid region of the polypeptide backbone while the small amino acids form the flexible regions of the polypeptide allowing the protein to fold into it's three dimensional shape. The core of the polypeptide is made up of the hydrophobic amino acids like phenyalanine, tyrosine, and tryptophan.

=== References: ===

<references />J.M.Berg, J.L.Tymoczko, L.Stryer,(2007) ''Biochemistry, ''6th edition, New York: W.H.Freeman and company (page 27)

Amino acids

2011-12-02T16:37:13Z

110025526:

Axon

2011-11-28T05:35:27Z

110025526:

Axons are part of the specialised [[Neuron|neuron]] cell that transmit electrical signals from the cell body to the [[Axon terminal|axon terminal]] leading to the [[Synapse|synapse]], where the electrical signal turns into a chemical signal. The network of axons and [[Dendrites|dendrites]] allows complex [[Signal pathway|signal pathways]] to occur simultaneously, together or independently. [[Microtuble|Microtubles]] fill the interior of the axon with the minus end at the cell body and the plus end at the [[Axon terminal|axon terminals]]. The microtubles allow key [[Protein|protein]] structures, [[Vesicle|vesicles]] and [[MRNA|mRNAs]] to be transported to the [[Synaptic cleft|synaptic cleft]]. Just beneath the [[Plasma membrane|plasma membrane of]] the axon lies [[Actin filaments|actin filaments]] which provide mechanical strength and transport mechanism to the [[Cytoskeleton|cytoskeleton]] <ref>Molecular Biology of the Cell Alberts et al Fifth Edition page 1047-1048</ref><ref>Molecular Biology of the Cell Alberts et al,. 5th Edition. Page 1047-1048</ref>.

The speed at which the axon transmits electrical impulses depends on the diameter of the axon, the membrane resistance of the axon(how permeable the membrane of the axon is to electrical signal, the lesser the permeability, the faster the speed of transmition) and the presence or absence of myelin sheath<ref>Bruce Alberts et al.(2008)Molecular Biology of the Cell,pg 678, 5th edition, New York:Garland Science.</ref>.

=== References ===

<references />