dna replication and protein synthesis
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DNA Replication and Protein Synthesis. Watson and Crick…again. After describing the structure of DNA, they released a second paper Basically stated that the base pairing model indicated a method for replication - PowerPoint PPT PresentationTRANSCRIPT
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