Daily Newsletter March 26, 2012
This week, we move into the Central Dogma of biology (molecular biology to be specific). This is the concept of how genetic information is used to produce the functionality of the cell. We also describe this as Gene Expression. It can ultimately be summed up into one statement: DNA makes RNA which makes Proteins.
The two core genetic processes are Transcription (synthesis of RNA) and Translation (the synthesis of proteins).
Today's Topic: Ground rules for the Central Dogma.
Before digging into each process, let's talk a little about what is at stake here. DNA holds our genetic history. It holds codes on how to build an organism, but what does that really mean?
As we saw at the start of the semester, phospholipids can naturally form bilayers. They can even form spherical structures that create two fluid compartments, outside vs. inside.
Membranes though are passive. As a selectively permeable barrier, only certain materials can cross. Proteins add functionality to the membrane. By embedding proteins, you can chance the permeability of the membrane. This is how cells balance what is on the inside, and what is on the outside. Membrane proteins can also have enzymatic or signal functions. Proteins add functionality to the membrane.
A common expression is that DNA holds the code to make an organism. The meaning of this phrase lies in the concept that by making proteins, we make phospholipid membranes functional. From here we can produce metabolic pathways, produce various chemical compounds, anchor with other cells, and in multicellular complex life, we even have the development of special cellular roles that work together to form a composit whole.
The concept of how we go from DNA to RNA and then Proteins is one of the most critical concepts in biology.
As these are genetic processes, there are a few key phrases and terms you need to start remembering:
- All genetic processes work because of base complimentarity. (why?)
- Gene:
- Sometimes referred to as a unit of heredity.
- It is a segment of DNA that holds the code for how to make a protein.
- In modern biology, we some times refer to a gene product.
- A gene product could be either a protein or a functional RNA.
- Functional RNAs don't code for proteins; instead, they have some function in cellular metabolism.
- Examples of Functional RNA are tRNA, rRNA and snRNA.
- A gene holds the code for a gene product (RNA or Protein), but it is more than just the code.
- All genes have non-coding sites that are critical for correct transcription (Genes will be copied into a molecule of RNA).
- The promoter of a gene is a sequence of DNA nucloetides that indicate the "start" point of a coding region.
- In Eukaryotic cells, a common promoter is a DNA sequence that reads TATAAA.
- This is known as the TATA-Box.
- This sequence is found in the major grove.
- The Initiation Complex of Transcription recognizes this sequence in a major groove, and builds the replication complex at this site.
- The replication complex will transcribe the gene.
- Many genes are regulated, meaning they can be turned on or off.
- A regulated gene will have an Operator region between the promoter and the coding region.
- This is referred to as being down stream from the promoter.
- Regulatory proteins can bind to the operator, preventing transcription.
- House keeping genes produce products that are needed for the general function of the cell.
- House keeping genes in Eukaryotes would include genes for Glycolysis and the Citric Acid Cycle, but also the genes for Ribosomes and tRNA.
- These genes are always ON.
- Genes that are always on are referred to as constituative genes.
- Messenger RNA (mRNA) is a molecule of RNA that carries a gene code to a Ribosome in order to produce a protein.
- The code on mRNA is in Nucleotide Language, being made up of sequences of Ribonucleotides (A, U, G, C).
- In order to make a protein, there needs to be an agent of translation.
- An agent of translation must be a molecule that contains both ribonucleotides and an amino acid.
- A specific ribonucleotide sequence must directly correspond to an amino acid.
- This is the basis of the Genetic Code.
- The agent of translation is Transfer RNA (tRNA).
- In tRNA, there is a direct correspondance between a ribonucleotide sequence (anti-codon) and an amino acid.
- We will discuss more about the codon-anticodon later in the week.
- Amino acids are added to the 3' end of the molecule. (why there?)
- The ribonucleic language is divided into 64 3-letter words known as codons.
- The anticodon of the tRNA matches to codons on mRNA.
- In this way, we have a direct relation of a codon in mRNA to a protein on tRNA.
- There is redundancy in the genetic code (some amino acids can be identified by multiple different codons).
Daily Challenge: Central Dogma
Your challenge today is just to discuss the concept of the Central Dogma. Don't worry about mechanisms yet. Consider the implication of the central dogma. In your own words, express why it is important. What are the important features? You can use questions above in "Today's Topic" as a way of focusing your thoughts.
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