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Amino acids and protein folding
DNA damage and repair
Mitosis and meiosis
Protein structure and synthesis
Transcription of DNA
Translation of mRNA
Adenosine deaminase deficiency
Acute radiation syndrome
Purine and pyrimidine synthesis and metabolism disorders: Pathology review
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Deep within the cell’s nucleus, there’s our DNA. DNA is made up of genes, and each gene is basically a specific part of the DNA that codes for a protein.
And genes become proteins in two steps: transcription and translation.
Transcription is the first step in creating a protein, during which a specific gene is “read” and copied on an individual mRNA, or messenger RNA molecule - which is like a blueprint with instructions on what protein to build.
Now, DNA has two strands, which wrap one around the other to form the characteristic “double helix”.
Each single strand of DNA is composed of four types of nucleotides - which are the individual “letters” or “building blocks” of DNA.
Nucleotides of DNA are made out of a sugar - deoxyribose, a phosphate, and one of the four nucleobases - adenine, cytosine, guanine, and thymine - or, commonly, A, C, G, T for short.
The nucleotides on one strand pair up through hydrogen bonds with nucleotides on the opposing strand, to create the double-stranded DNA : specifically, A bonds with T, and C bonds with G, so they’re called complementary bases.
Now, with these two strands - one strand is called the coding, or the sense strand, and the other strand is called the template, or the anti-sense strand.
The coding strand has a coding sequence of nucleotides that serves as a master blueprint for our protein.
It’s a what-you-see-is-what-you-get kind of thing.
The template strand, on the other hand, has a sequence of nucleotides that is complementary to the sequence on the coding strand.
In addition, the two DNA strands also have a “direction” - the coding strand runs from the 5’ end towards the 3’ end, while the template strand runs from the 3’ to the 5’ end.
A bit like two snakes coiled up together but facing different directions.
So, if the coding strand looks like this:
The template strand will look like this:
*Disclaimer: no cats were harmed in the making of this strand.
Now, transcription starts with the unpacking of DNA from chromatin and de-helicization - meaning that the double helix unwinds a bit so that individual genes are exposed.
The starting point of a gene is determined by a promoter region, which is a repetitive non-coding sequence of nucleotides - for example, T A T A T A T A sequence is one very famous promoter, called the TATA box - that marks where to begin transcribing.
A few dozen proteins and enzymes come together to form what’s called a pre-initiation complex around the promoter, also featuring an enzyme called RNA polymerase.
Transcription is the process by which genetic information in DNA is copied into RNA. The process occurs in the nucleus and is critical for gene expression. The three main steps involved in transcription are initiation, elongation, and termination. During initiation, RNA polymerase binds to a specific region of DNA called the promoter. During elongation, RNA polymerase adds complementary RNA nucleotides to the growing RNA chain. Termination occurs when the RNA polymerase reaches a sequence of DNA called the terminator, and the RNA molecule is released. Finally, RNA molecules undergo post-transcriptional processing to prepare them for translation, the process by which proteins are synthesized from RNA. The resulting RNA molecule is called messenger RNA (mRNA) and is transported out of the nucleus and into the cytoplasm, where it serves as a template for protein synthesis.
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