Molecular Biology. I. History:Ground breaking discoveries. T.H. Morgan Griffith, Avery and McCleod Hershey and Chase Watson and Crick (refer to your article for most of this!). How do we know that DNA is the molecule that transfers info?.
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Griffith, Avery and McCleod
Hershey and Chase
Watson and Crick
(refer to your article for most of this!)
DNA and Protein.
What do we already know about DNA’s structure? (think back to biochem!)
The backbone of DNA is made of covalent bonds between the phosphate and sugar
DNA you have a choice of 4 bases:
DNA you have a choice of 4 bases:
- Two strands of DNA are connected through weaker Hydrogen bonds that form between bases
- Only certain bases can form these hydrogen bonds with each other
- They are called complementary
G and C form 3 hydrogen bonds
A and T form 2 hydrogen bonds
Why can’t the others pair up?
Therefore all A’s are bound to T’s
all G’s are bound to C’s
Chargaff’s Rule: in a given piece of DNA –
A’s = T’s; G’s = C’s
Heating DNA causes it to denature
Which is harder to denature?
- GCCGGCGCG or
Ends of chromosomes difficult to copy
- lose a little DNA each time
The good news: telomeres do not code for anything
The bad news: telomeres are only so long.
- in a few cells – telomerase
- in other cells – Hayflick limit (max. number of cell divisions before self destructing)
Replication uses existing DNA as a template to make more DNAWhy? When?DNA is ALSO used as a template to make an RNA “copy” of a gene Why? When?
So first a little about RNA….
Similar to replication in mechanism
- Watch the animation and tell me what is different!
Step 1: DNA strands are separated and then “copied”
- New RNA will have a Complementary sequence except A’s in DNA bind to U’s in RNA
- RNA Polymerase is the enzyme that links the RNA nucleotides
In eukaryotes, mRNA transcript has to be modified before leaving the nucleus to be translated.
In prokaryotes, the mRNA is ready to go as it is transcribed!
Step 2: Splicing: Editing or Processing of pre-mRNA into mRNA
- remove “introns”: unused sections
- glue together “exons”: important sections
Step 3: GC Cap added to one end; Poly A tail added to other end of exons to make mature mRNA
Several Adenines in a row
If a gene is transcribed into mRNA it is being “expressed”
Having the gene in your DNA is not enough
It MUST be turned into RNA to do anything
Remember transcription is the KEY to getting a protein!!
- some genes within a cell are NEVER transcribed due to a permanently “OFF” On/Off switch that precedes the start codon.
How many 3 base combinations are there of ATGC?
How many amino acids are there?
What does this mean?
You are responsible for knowing 4:
UAA, UAG, UGA
You MUST be able to use a codon table
Decoding the information in the mRNA to build a protein.
- two subunits made of rRNA and protein
- sandwich mRNA between them
- Have three spots that tRNA’s can fit in
A site – acceptor site
P site – peptidyl site (carries the growing chain of aa
E site – has the exiting tRNA (with no aa attached)
Twisted up piece
- amino acid gets attached to one end
- opposite end is the anticodon
So how does it work? Watch the animation and explain it to me!
What does dogma mean?
Hmmmmmm good essay question