DNA--Translation--> RNA--Transcription--> Protein

^ an easy way of summarizing how the genes in DNA code for proteins

messenger RNA - mRNA

transfer RNA - tRNA

ribosomal RNA - rRNA

structure: single stranded

has a poly A tail (many adenines) 

GTP cap (guanosine triphosphate) which stabilizes the molecule 

function: carries the code for a gene from the nucleus to the cytoplasm 

structure: clover leaf shaped with 3 loops

2 ends - amino acid attatchment site and anticodon end with a specific sequence of 3 nitrogen bases

function: translates the code (sequence of N bases) on mRNA into a specific sequence of amino acids in a polypeptide. each tRNA carries one type of amino acid

structure: has one small subunit and one large subunit

has 3 tRNA binding sites (E,P,A) and 1 mRNA binding site

has a tunnel where the polypeptide exits

function: binds to ribosomal proteins to make ribosomes - the site of protein synthesis 

RNA is single stranded, RNA is never helical, RNA and DNA have different nitrogen bases

RNA - A to U and C to G

DNA - A to T and C to G

In RNA U replaces T

3 tRNA binding sites and 1 mRNA binding sites

3 tRNA binding sites - A (enter), P (translocation), E (exit) 

1. for every gene the template, or, sense strand serves as a pattern
2. RNA base pairing binding to the sense strand produces mRNA
3. mRNA is translated by tRNA into a specific sequence of amino acids 

it is a triplet code - codons consist of 3 nitrogen bases ex. ACA

it is definite - ACA codes for theonine and only theonine (exclusive)

it is redundent - most amino acids are coded for by more than one codon ex. ACA, ACG, ACU all code for theonine - also known as the "wobble effect"

it is universal - all living things use the same code to translate their DNA into proteins 

amino acids are coded for by more than 1 codon...

for example: ACA, ACG, ACC and ACU are all theonine 

the wobble effect makes it less likely for there to be errors or mutations 

1. Initiation - an RNA polymerase molecule binds to the promotor region of a transcription unit and the DNA "unzips" in that area - RNA polymerase begins to form an RNA transcript  
2. Elongation - RNA polymerase  moves down stream unzipping the DNA and elongating the RNA by adding free RNA nucleotides with completementary base pairing 
3. Termination - at the end of the transcription unit the RNA transcript is released from the DNA and polymerase enzyme detatches 

RNA polymerase binds to the promotor region to initiate the RNA sythesis

promotor regions have a "TATA" box or, an "on switch"

transcription factors must bind to the DNA "TATA" box for RNA polymerase to bind 

this is how transcription is regulated 

GTP cap and poly A tail are added 

cap and tail protect mRNA from degradation and allow it to bind to a ribosome for translation

poly A tail makes it more stable

during RNA splicing introns are cut out with spliceosome complex and exons are sealed together yielding a shorter mature RNA

(like a sentence without spaces)

exons are expressed portions of the transcription unit 

introns are not expressed  and are inbetween the exons

1. Initation - mRNA binds to the small ribosomal subunit. intiatior tRNA with anticodon (ex. UAC) binds to the start codon with complementary base pair (AUG). then the large ribosomal subunit binds to the small ribsomal subunit forming an initiation complex 
2. Elongation of polypeptide chain - a tRNA with complementary anticodon binds to mRNA at the empty A (enter) site of the ribosome. a peptide bond forms between amino acid at site A and site P. (the growing polypeptide is now at site) then the mRNA shifts over. now the tRNA that was at A moves to P and P moves to E and is released. A is now empty and holds the next codon to be translated by the correct tRNA
3. Termination - when a stop codon is reached a release factor binds to A site instead of tRNA. the release factor breaks bond between the P site and the last amino acid of the polypeptide. the polypeptide and the last tRNA leave the ribosome

it breaks the bond between the tRNA at the P site and the last amino acid of the polypeptide 

allows for the termination of translation and the release of the polypeptide from the ribosome 

when mRNA is translated by many ribosomes simultaneously 

many copies of the same polypeptide are polysomes

this way a cell can produce many polypeptides only having to use one strand of mRNA 

less effort for more production

• it can be enzymatically cut into 2 parts
• it may have sugars, lipids, or phosphate groups added
• some amino acids at the end of the polypeptide may be removed 

insertions

deletions

substitutions

where one N base is subsituted for another

leads to 

missense - where one amino acid is different

or

nonsense - if there is the formation of an early stop codon

both result in frame shift mutation 

insertions - where N base (s) are added

deletions - where N base (s) are deleted 

frameshift mutations because they can lead to: immediate nonsense if a stop forms

or

extensive nonsense where all of the following amino acids are incorrect

chemical or physical agents in the environment that change DNA

ex. UV radiation, X rays, Viruses, Carcinogens 

through feedback inhibition 

when the product accumulates it binds to the first enzyme in a feedback inhibition pathway and shuts it down

ex. abundence of tryptophan 

a region of DNA whose final product is either a polypeptide or an RNA molecule

they can contain: non-coding and promoter regions that do not code for a polypeptide but are still functional parts of the gene

some genes code for mRNA, tRNA, and rRNA

some genes code for more than 1 polypeptide