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Cells my dear friends, are the simplest collection of matter that is living, and are the smallest unit of function in a larger system (applies to all kinds of ‘cells’). They are units of structure AND function, and they are all bound by a plasma membrane. They enclose a semi-fluid, jelly-like substance called cytoplasm. All cells also contain chromosomes. Prokaryotes, which were the first cells in existence, contain no membrane bound organelles, and they have circular DNA. Eukaryotes however, have most of their DNA in linear form, inside the nucleus. Eukaryotes are much bigger than prokaryotes, and are more specialised. Prokaryotes can only be unicellular, whilst eukaryotes can be organisms made of many cells. 

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This baby, pictured in yellow, is a nucleus. They contain genetic information for every single eukaryotic cell (apart from mitochondrial DNA, and the DNA of chloroplasts).  They are the most conspicuous organelle under the microscope, appearing as a darker, denser area. The nuclear envelope separates the nuclear contents from the cytoplasm. The double membrane (nuclear envelope) is periforated by pores 100nm in diameter. At the lip of each pore, the inner and outer membranes are continous, leaving a space between them of 20-40nm. The inside of the envelope is lined with the nuclear lamina, a netlike array of protein filaments which serve to maintain shape. There is also much evidence for a nuclear matrix within. DNA is present as chromatin or chromosomes in the nucleus, with each species having a characteristic number of chromosomes and genes. A nucleolus is present within the nucleus and is identified as densely stained granules and fibres. The nucleolus synthesises rRBA and studies suggest it also plays a part in is regulation of cellular processes (such as division).

False-colour SEM of a group of human chromosomes

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Transgenesis - plasmids

1. Plasmids (accesory loop of DNA) are extracted from bacteria. 
2. They are cut with restriction enzymes to expose sticky ends.
3. The desired gene (cut with the same restriction enzyme to form complementary sticky ends) is inserted and joined with DNA ligase.
4. The plasmid is returned to the bacteria.
5. The bacteria is used to introduce the DNA into plant cells and integrate the new gene into the genetic material.
6. The tissue can be cultured and a new plant developed.

1. After the plasmid is returned to the bacteria, The bacteria can replicate and pass the DNA on via binary fission, or can replicate the DNA and share it with other bacterial cells via a pilus.

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DNA-DNA HYbridisation

1. Samples of DNA from two species are mixed and heated.
2. The DNA is separated.
3. Strands from each species join in an attempt to form a double helix. 
4. Poorly matched strands indicate a larger difference in DNA.
5. The mixture is reheated to analyse the strength of the bonds within the strands.
6. More heat needed = more energy needed = more bonds = better match

Translocation:

-part of one chromosome moved to another (crossing over)

Inversion:

-segment of chromosome flipped

-if polypeptide still folds correctly it is unharmful`.

-if polypeptide folds differently (from other end first), changes shape and function.

Duplication:

-repeated genes

-can be unharmful

-could cause excess production, e.g. too much of a hormone.

See these two wonderful men here?

Their names are James Watson and Francis Crick, and they are credited as discovering the structure of DNA. They basically explained the nucleotide structure, complementary base pairing mechanism, and hence replication processes. 

“Some day a child is going to sue it’s parents for being born. They will say, my life is so awful with these terrible genetic defects and you just callously didn’t find out.” -James Watson on the question of genetic screening of foetuses (1997)

“Almost all aspects of life are engineered at the molecular level, and without understanding molecules we can only have a very sketchy idea about life itself.” -Francis Crick (1998)

Whorl
(Open me up, 2009, various authors)

Fingerprint loop
(Open me up, 2009, various authors)

Fingerprint arch. (Open me up, 2009, various authors)