Please excuse me if the material is slightly long or beyond the scope of MCAT. But, I think, this should summarize most of eukaryotic transcription. For the purposes of this post, I’m only going to summarize RNA pol II (mRNA synthesis) mediated transcription. RNA pol I regulates rRNA synthesis and Pol III regulates 5s RNA and tRNA synthesis.

The mechanism of gene transcription by RNA pol II follows 3 general steps, initiation, elongation and termination. These 3 steps are followed by RNA processing.
Initiation
In eukaryotes initiation is regulated by the presence of regulatory regions, promoters and enhancers. Common promoter elements are the TATA and CCAAT boxes, found upstream of the transcription start site. Enhancers can be found upstream, downstream, or within the coding region
Promoters are recognized by basal transcription factors and are necessary for initiating transcription, while enhancers, as the name suggests are necessary for enhancing transcription and also for regulating and mediating cell and tissue specific transcription.
The basal transcription factors (TFs) such as TFIID, along with other TFs, recruit RNA pol II to the promoter element and initiate basal transcription.
Other enhancer elements and TFs mediate higher levels of transcription.
Elongation
During elongation, RNA pol II moves along the DNA, close to the bubble that represents separation of the two strands of DNA. As the enzyme moves forward along the bubble, RNA is synthesized in the 5’ to 3’ direction. DNA ahead of the bubble is unwound and behind it is rewound. Elontation continues until the enzyme reaches a termination point.
Termination
If I may, termination in eukaryotic genes is not very specific. Pol II continues to transcribe RNA for a few thousand (1000-2000) bases past the end of the mature mRNA. The exact end is determined during RNA processing.
Processing
RNA processing is characterized by capping at the 5’ end, polyadenylation at the 3’ end and intron splicing.
5′ Capping
A methylated guanine nucleotide is added to the 5’ end of the mRNA in a 5’ to 5’ phosphodiester linkage. This capping is essential for mRNA recognition by ribosomes during translation.
3′ Polyadenylation
A polyadenylation signal (AUAAA) is present in most of the mRNA transcripts and this signal is reconized by an enzyme that cleaves the transcript about 20 nucleotides downstream and adds a series of As (~200) to the 3’ end. These As are added without the need for a template and prevent the mRNA from degradation.
Splicing
Removal of the introns from the pre-mRNA to yield mature mRNA is called splicing. Splicing is carried out by spliceosomes that contain at least 5 known small nucleotide ribonucleoproteins (snRNPs). These snRNPs contain small nuclear RNAs (snRNAs) and together they detect intron/exon boundaries and cleave the RNA at those specific junctions. The spliced RNA is then joined together to form the mature mRNA transcript.

Salient points of eukaryotic mRNA transcription:
1) occurs in 5’ to 3’ direction
2) mRNA synthesis regulated by RNA pol II
3) mRNA synthesis involves initiation, elongation and termination followed by processing to make the mature transcript.
4) Initiation is mediated by promoters and enhancers, and elongation by the RNA pol II. Termination in eukaryotes occurs way downstream and is not very specific, unlike in prokaryotes.
5) mRNA processing to produce the mature trancript involves 5’ capping, 3’ polyadenylation and intron splicing.

Operons in prokaryotes consist of groups of genes that typically work together and are all controlled by one promoter, which is in turn controlled by an operator region. This means that all of the genes in the operon are turned on and off together.

As far as inducible operons go, the first example that comes to mind is the lac operon. The genes in the operon, lac Z, Y, and A, code for proteins that DEGRADE/utilize lactose. These genes are preceeded by an operator region. the operator region is the "control region" of the operon. With the lac operon, in the absence of lactose, an inhibitor (protein) binds to the operator region DNA, and the operon is effectively turned off because the inhibitor interferes with RNA polymerase binding. When lactose is around, it binds the inhibitor and releases it from the operator DNA. Once the repressing inhibitor is removed, RNA polymerase can bind and transcribe the operon (the Z,Y and A genes), and the operator is considered "induced" or turned on. If you look at this from the standpoint of the cell, it makes sense. The cell only needs the proteins that utilize lactose when lactose is around, right? So it’s set up that the genes that utilize lactose are only "turned on" when there is sufficient lactose in the cell (ie. the cell doesn’t waste energy making proteins it doesn’t need).

For repressible operons, the tryptophan operon comes to mind. In this operon, the genes for tryptophan (Trp) SYNTHESIS are grouped together. These genes are also preceeded by an operator region that controls expression of the operon. However, in this operon, there is a repressor that is only active (i.e., it will only bind the operator) when it is also bound to Trp. This means that there has to be a relatively high level of Trp in the cell to bind the repressor which will then turn off the genes for Trp production. This also makes sense from the standpoint of the cell….if you need more Trp, the genes will be turned on until there is enough Trp in the cell. When there is enough Trp in the cell, the genes will be turned off.

Flash cards can work for memorization, but I consider them a waste of time. The amount of time you spend making them could be better used working to understand the big picture of what’s going on with metabolism.

The MCAT is not about memorization. The MCAT is about critical thinking. You must UNDERSTAND the equations and concepts, not merely memorize them.

All the concepts that are tested on the MCAT are fairly simple, but the MCAT will ask you questions in such a way that if you don’t have a rock solid understanding of the concepts, and have merely memorized them, you will not be able to answer them.

You have to know very little about metabolism for the MCAT anyway, so there would be hardly anything to memorize. Just know the big picture, and the details you need to know will be easy to remember! They’re crucial to the big picture!

So how to do this? Review books by Kaplan and TPR will give you tons more info than you really need, but they can help you to understand what’s really going on with metabolism, or whatever you’re studying. You just have to be able to let go of all the minutiae, which can be hard for those of us who tend to get bogged down in details. EK can give you a solid, bare-bones review. You DO have to know pretty much everything they tell you. It’s up to you!

I will post further details about them at a later time, but for MCAT, DAT, OAT, and PCAT biology, you should know the structure and function of the following organelles:

• nucleus
• cell membrane
• cytosol (cytoplasm)
• cytoskeleton (microtubules, microfilaments, and intermediate filaments)
• endoplasmic reticulum
• Golgi apparatus
• vesicles
• vacuoles
• ribosomes
• lysosomes
• microbodies
• mitochondria
• chloroplasts
• cell wall
• centrioles

You should also know that prokaryotes do NOT have any membrane-bound organelles, such as a nucleus, mitochondria, or Golgi apparatus.