10 Points of beginner neurobiology

1. negative and positive feedback systems maintain homeostasis
2. Central Nervous System includes the brain and spinal cord
3. Peripheral Nervous System is made up of systemic and autonomic system
4. the nervous system consists of neurons and glial cells
5. gial cells are like nurses-they support, clean and protect the nerve
6. a nerve is made up of a cell body, dendrites, axons, and myelin sheath
7. dendrites receive and send nerve impulses
8. axons conduct impulses away from cell body
9. myelin sheath insulates axons to speed rate of nerve impulse transmission
10. schwann cells are glial cells that form myelin sheath

How is mRNA translated to an amino acid code?

Key Terms:

• tRNA
• translation factor
• anticodon loop
• ribosome
• rRNA
• polyribosome
• start codon
• missense mutation 
• nonsense mutation

Act 1: Initiation

• initiation factors assemble small unit ribsome, mRNA, initiator tRNA, and large unit ribosome to start synthesis of protein.
• small ribsome attaches to mRNA (5' AUG 3') 
• threee binding sites: P(peptide), A(amino acid), & E(exit) site
• P contains tRNA with peptide attached to it

Act 2: Elongation

• A contains tRNA with another amino acid which is added to polypeptide
• tRNA that no longer has amino acid is translocated to E site
• Amino acid continually added to growing polypeptide chain to make a protein
• The amino acids are attached by peptide bonds (covalent)

Act 3: Termination

• stop codons "UAA", "UAG", or "UGA" stop synthesis of protein
• everything dissociates 

How Does Transcription occur?

RNA Molecules:

• mRNA (Messenger) : template for translation
• tRNA (Transfer) : translation of mRNA
• rRNA (Ribosomal) : translation of mRNA
• snRNA (Small unit) : modify mRNA molecule

Key terms:

• "TATA" Box / Promoter region / Upstream
• Initiation complex
• Coding/Sense strand
• Template / Antisense strand 
• RNA Polymerase II
• Uracil
• RNA Transcript / pre-mRNA
• Primary RNA
• Splicing 
• Spliceosome
• Intron
• Extron
• poly-A-tail
• G-cap
• Transcription factor (protein)
• Ribozyme
• Terminator / "AAA UAA" / Downstream  

Act 1: Initiation

• Transcription factors find TATA Box and bind to it. 
• RNA Polymerase II locates and binds to the transcription factors which create an initiation complex. 
• RNA Polymerase II begins transcription.

Act 2: Elongation

• mRNA transcribed in a 5' to 3' direction
• only one strand is synthesized
• antiparallel to template strand
• Copies coding strand but replaces Thymine with Uracil
• Upstream to Downstream    

Act 3: Termination

• Terminator sequence signals end point of synthesis of mRNA 
• stop codon or "AAA UAA"

How Does DNA Replicate?

DNA replicates in a semi-conservative manner. What does that mean? Well, it means that the new daughter DNA molecule conserves one strand from the parent DNA molecule. Watson & Crick were the first to suggest this model. Although many other models have also been suggested, the semi-conservative model is the only one that scientists have been able to prove.

There are many enzymes that take part in Replication:

• Helicase
• Gyrase
• SSB or Single Stranded Binding Protein 
• Primase
• Polymerase I
• Polymerase III 
• Ligase (like a glue that attaches fragments)

The replication of DNA can be divided into three acts: Initiation, Elongation and Termination. 

Act 1: Initiation

Helicase breaks the hydrogen bonds between the complimentary base pairs and untwists the DNA helix, opening a bubble. 

Since DNA is unstable when not in a twisted form, SSB protein is released so it does not twist back together.  

When a section of the molecule is unwound, it causes tension in the structure. Gyrase is present to cut the ends of the molecule to release the added tension. 

Primase produces Primer (RNA) which signals Polymerase III to add the complimentary base. 

Act 2: Elongation

A new strand grows in a 5' to 3' direction, which is the case for the new daughter strand. 

Since DNA is antiparallel, the new strands will grow in the opposite direction of each other. 

There are two types of growing strands: Leading and Lagging.

Leading (Continuous strand):

The leading strand has Polymerase III continuously adding nucleotides to the Primer. 

Lagging (Fragmented strand):

This strand grows in sections away from the tip of the fork. These discontinuous sections are called Okazaki fragments. 

Act 3: Termination

Upon meeting a Primer of a second Okazaki fragment before it, Polymerase I is released to replace the RNA with DNA. Polymerase I is like a corrector. 
Ligase is released to attach these fragments together.