After describing the structure of DNA, they released a second paper◦ Basically stated that the base pairing model

indicated a method for replication Each strand would serve as a template for a

new companion chain, called the complement

As a result, each daughter strand has a strand from the original molecule

This is referred to as semi-conservative replication

So, from the parent strand, new bases are added to added according to the base pairing model

A strand of ATTCGACT would match up with TAAGCTGA

A wide variety of enzymes are used during the replication process (recall anything ending in –ase is an enzyme)

The enzyme that opens the parent molecule by breaking the hydrogen bonds is helicase

It “unzips” the molecule The other principle enzyme is DNA

polymerase (actually three variations on it!) It moves along the unwound strand, adding

the appropriate bases

Another version of the polymerase “checks” to ensure that no mistakes were made

Now that we know the structure of DNA, we can analyze how proteins are made

Broken down into two processes: transcription and translation

This is where RNA is used in our body Structurally, RNA contains a ribose sugar

◦ The 2’ carbon contains a hydroxyl group as opposed to a hydrogen

Additionally, RNA tends to be single stranded, and contains a uracil in the place of thymine

In protein synthesis, three unique types of RNA are used:

Messenger RNA (mRNA) RNA copy of the DNA strand to be “read”

during translation

Transfer RNA (tRNA) Carries individual amino acids to site of

replication

Ribosomal RNA (rRNA) Attached to ribsome complex, site of

protein synthesis

rRNA tRNA

A complementary strand of mRNA is made, first by unzipping the DNA molecule◦ This time, by RNA polymerase

This only happens on specific regions of DNA known as promoter regions

That way, it isn’t just a random region Similar regions cause the transcription

process to stop

Certain regions of DNA do not code for any proteins that we use, called introns ◦ We mentioned these before as the “junk” regions

The introns must be spliced out, joining all the coding regions known as exons

Finally, a 5’ cap and poly A tail must be tacked on to the ends to finish the editing process

The processed mRNA is now reading to be decoded

The “language” is spoken in three base “words”

Translation begins when the mRNA binds to the rRNA on a ribosome

This moves along the sequence until an AUG codon is found◦ This is the start codon, and the methionine code,

hence all protains begin with Met tRNA then attaches and drops off the

appropriate amino acid◦ It does this by have a matching anticodon

Sequential amino acids are linked by peptide bonds◦ So, it is called a polypeptide

This process continues until a stop codon is found

Polypeptide and mRNA are release Polypeptide goes through up to four stages

of folding to become a mature protein