NOTES; DNA

A T G C 2 3 E HYDROGEN PURINES PYRIMIDINES = FIT TOGETHER, LIKE PUZZLE PIECES A T 2 HYDROGEN G C 3 THYMINE CYTOSINE PURINES PYRIMIDINES

D T SUGAR C T T G N G A A G PHOSPHATE C C A

As the bases “stack”, they spiral forming a “helix” and since DNA is made of 2 strands it’s a… DOUBLE HELIX

(the first step in mitosis When the time comes For dna to copy itself (the first step in mitosis And meiosis), the helix Must be “unzipped” You need an… NZYME!!! (HELICASE) Hmmm…you need to “break a BIG molecule into 2 smaller pieces”…

An EXACT copy of the original …for the next generation!! TEMPLATE A A T A C G G T T COMPLEMENTARY An EXACT copy of the original (double) strand… …for the next generation!!

The process of COPYING DNA REPLI The process of COPYING DNA COPY #1 ORIGINAL STRAND COPY #2

DNA is replicating less than 1% of a cell’s “life cycle”…so what is DNA doing the other 99%? FIRST, THE DNA IS UNZIPPED

A A T A C G G T T Most of the time the template DNA is read by a DIFFERENT kind of Nucleic Acid…one that has a backbone made of RIBOSE

A And there are other differences R N A U The sugar is RIBOSE RNA is SINGLE stranded RNA contains URACIL instead of Thymine And being single-stranded, THYMINE won’t “fit”!! So it is replaced by another pyrimidine called… R A “base” that is very similar to Thymine, also forming 2 Hydrogen bonds, making it COMPLEMENTARY to… N A Finally, unlike DNA, there are different kinds of RNA A U

The first kind of RNA “reads” This RNA “copy” must now the DNA…it is called… This RNA “copy” must now leave the nucleus… RNA RNA essenger U U A U G C C A A THIS PROCESS IS CALLED COMPLEMENTARY BASE PAIRING!! CRIPTION A A T A C G G T T RNA LEAVES NUCLEUS THE PROCESS OF MAKING AN RNA COPY OF THE DNA

REMEMBER! REPLI DON’T CONFUSE with CRIPTION

THAT UP THERE HAS ABSOLUTELY NOTHING TO DO WITH THIS REPLI COPYING DNA so new cells have a set of instructions HAS ABSOLUTELY NOTHING TO DO WITH THIS THAT UP THERE CRIPTION CRIPTION The first step in making proteins

THIS involves both DNA AND RNA involves NOTHING but DNA

THIS is what cells do 1% of the time is DNA copying itself DNA can REPLICATE So don’t mess up Major Concept #2 is what cells do 1% of the time is DNA copying itself is the first step needed to build stuff is what cells do 99% of the time In fact, the only thing they have in common is

Once Transcription is complete, the mRNA leaves the nucleus CYA L8r G8r!! DNA

so it is called mRNA rRNA Where it enters a RIBOSOME A structure made entirely out of …RNA… ribosomal RNA, to be exact mRNA rRNA so it is called

Biologists wondered… is the code “read” just ONE base at a time? Or two? Or… They knew they needed a code that was able to have AT LEAST 20 varieties (to account for the 20 different amino acids)

But what about the other 16? A 1-base code wouldn’t A T G C Would code for, say… ALAnine Would code for, oh, I don’t know… LEU cine? Would code for, maybe… ISOleucine and would code for, say… TRYptophan But what about the other 16?

What about a 2-base code? Still…not enough combinations AA CA GA UA AC CC GC UC AG CG GG UG AU CU GU UU These are all the possible combinations of just two bases Still…not enough combinations for all 20-something amino acids.

And the UGC was created; With 3 bases you get 64 combinations…more than enough! And the UGC was created; A 3-base code is enough to include all 20 AAs

And so this 3-base set became known as a CODON

amino acids are “delivered” to the ribosome by a third kind of RNA: Just remember, the Universal Genetic Code (UGC) is based on CODONS (the mRNA) NOT anticodons called transfer RNA or tRNA And the complement to a CODON is an ANTICODON

So exactly what happens inside the ribosome? One language* gets turned into another AMINO A A A U U G U U C *the language of Nucleic Acid is converted into the language of…

U U U LYS The codon AAA is next-in-line. The tRNA that “fits” is… UUU Remember!! The UGC reads CODONS!!!!! UUU LYS As you can see, each tRNA has a “personal payload”, a unique “cargo” that it brings to the ribosome…an amino acid U U U So the codon AAA called for the tRNA anticodon UUU carrying LYSINE Which amino acid?? That’s where the UGC is needed

One more time… DNA codes for RNA which dictates the (1) The DNA sequence TTT is read by the mRNA DNA codes for RNA which dictates the AMINO ACID sequence which is what “stuff” is made of! (2) The mRNA “codon” of AAA then leaves the nucleus (3) The mRNA is grabbed by the first available ribosome (4) As the codon AAA is drawn into position, a tRNA with the anticodon UUU momentarily binds to its complement, bringing with it the amino acid LYSINE (5) The LYSINE then forms a (peptide) bond with the other amino acids already in the chain (6) Eventually the amino acid chain is released by the ribosome, now a fully-functional PROTEIN

Let’s finish the notes… ribosome ALA peptide PHE C G A LYS AMINO A A A ANTICODON Let’s finish the notes… U U U tRNA mRNA CODON rRNA Followed by GCU The next codon in the sequence is UUU Using the UGC, determine the AAs

or what we like to call a… PROTEIN ALA MET TRY or an ENZYME or HORMONE aka STUFF!!!!!!!!!!!!!!!! This final step of converting DNA into Protein, where nucleic acids dictate the order of amino acids, is called… As MET-TRY-VAL-LYS-PHE-ARG emerge from the ribosome, their UNIQUE sequence forces the chain to BEND/FOLD, giving THIS CHAIN its UNIQUE properties or what we like to call a… C A ? G U ? UGG The AA valine (VAL) preceded LYS because of the codon (and anticodon) Now try it “backwards” Let’s do a couple more The ? is due to the fact that there are 64 codons for 20 AAs LATION Converting the language of NAs into the language of AAs

INSIDE THE How are these NUCLEUS related within the cell? MC #2 MC #1 REPLI MC #1 D N A MC #3 PROTEINS R N A TESTOSTERONE AMYLASE KERATIN INSULIN or CHLOROPHYLL! MC #4 CHAINS of AAs