DMD Gene (Duchenne
Muscular Dystrophy gene)

What is it the 'Central Dogma'?
- Describes the relationship and process of how DNA instructions
are transferred to RNA and made into proteins

What is 'Gene Expression'?
- Is describes how the DNA sequence of a gene
is used to synthesize proteins

What Processes are Included?
Since central dogma describes the process
of how gene expression is achieved, it is broken
into several crucial steps: transcription + translation

Transcription
- 1st part of central dogma
- Describes the process of a gene's DNA sequence being
copied and created into a mRNA molecule
- Broken down into 3 steps: initiation, elongation, termination

Translation
- 2nd part of central dogma
- The mRNA produced in transcription is decoded and
used to build proteins containing a specific set of amino acids
- Broken down into 3 steps: initiation, elongation, termination

Process:
- Includes 3 steps: initiation, elongation, termination
- Initiation: promoter factors bind to the promoter region within the gene and triggers RNA polymerase to bind to DNA
- DNA separated to 2 strands: coding strand, template strand
- Elongation: RNA polymerase builds mRNA molecules
- In RNA, thymine is replaced by uracil
- Termination: a termination sequence is detected and the mRNA detaches from DNA template
- Before leaving cell, mRNA is protected through capping and tailing to ensure no harm comes to it
- Non-coding regions (introns) are removed from exons via spliceosomes (only in eukaryotes)
- Exons are then joined together to form a mature RNA
- After process of capping, tailing, and splicing, the mRNA now becomes a mRNA transcript

Process:
- Purpose: decodes the mRNA codon by codon using the ribosome with tRNA to create a polypeptide chain
- Translation is divided into 3 phases: initiation, elongation,
and termination
- mRNA is removed of its cap and tail
- Initiation: initiation factors assemble the mRNA, ribosomal sub-units, and initiator tRNA for protein synthesis in ribosome
- tRNA carrying anti-codons bond to the codons on the mRNA
- Each ribosome includes 3 binding sites for the tRNA: P site, A site, and E site
- P (peptide) site: contains the tRNA with a growing polypeptide chain behind it
- A (amino acid) site: contains the tRNA with the required amino acids to add to the polypeptide chain
- E (exit) site: tRNA leaves after using up its amino acid
- Elongation: the amino acids bond together via peptide bonds and become longer and longer
- Termination: termination is initiated by stop codons (ie. UAA) and release factors cut off the polypeptide chain from the last tRNA
- Polypeptide chain now formed and released

Location + Vulnerability to Mutations:
- The DMD/dystrophin gene is located on the short p-arm of the X chromosome
- Vulnerable to mutations (mostly frameshift mutations)
- Hereditary problems can create problems associated with this gene, and make it unable to properly synthesize dystrophin (this causes rips in the muscles and early death) this disease can be passed as a X-linked recessive disease,
and affects mostly males

Process:
- Occurs in nucleus of eukaryotes
- Occurs during interphase of the cell cycle
- Helicase: unzips the double stranded DNA and breaks the hydrogen bonds holding the bases together
- DNA Polymerase: replicates DNA molecules to construct a new strand of DNA
- Primase: makes RNA primers to instruct DNA Polymerase where to construct the DNA
- Ligase: secures the newly constructed parts with the DNA strand
- After helicase separates the 2 strands, the DNA is broken into the leading strand + the lagging strand
-DNA polymerase only builds from 5' to 3', thus creating Okazaki fragments along the lagging strand
- Ligase's job is to fill in the fragments
- In the end, 2 identical semi-conservative DNA strands are produced

Function in the Body:
- Gene product is dystrophin
- Dystrophin mainly located in the muscles and the heart, and
located in small quantities in nerve cells of the brain
- Dystrophin works with other proteins to protect muscles from harm as they move, contract, and relax