Download 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?
• T.H. Morgan showed that differences
in chromosomes determined fly traits
• Think back: What are chromosomes
made of???
DNA and Protein.
II. What is DNA
Structure:
What do we already know about DNA’s
structure? (think back to biochem!)
II. What is DNA
Structure:
The backbone of DNA is made of
covalent bonds between the phosphate
and sugar
II. What is DNA
Structure:
DNA you have a choice of 4 bases:
Purines
II. What is DNA
Structure:
DNA you have a choice of 4 bases:
Pyrimidines
II. What is DNA
Structure:
- 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
II. What is DNA
G and C form 3 hydrogen bonds
II. What is DNA
A and T form 2 hydrogen bonds
II. What is DNA
Why can’t the others pair up?
II. What is DNA
Structure:
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
II. What is DNA
Structure:
Heating DNA causes it to denature
Which is harder to denature?
- GCCGGCGCG
or
- AATATTATAA
III. Replication
–Semi-conservative:
III. Replication
• Happens in the nucleus (of course!)
• Ingredients:
–Energy – Form???
–Free Nucleotides: single, not attached
–Specific Enzymes
III. Replication
• There are three basic steps. Watch the
animation and tell me what is happening.
III. Replication
• Telomere problem:
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.
III. Replication
Solution:
- 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 DNA
Why? When?
DNA is ALSO used as a template to make
an RNA “copy” of a gene
Why? When?
So first a little about RNA….
Structure of RNA
• Think back: what are the structural
differences between RNA and DNA?
Types of RNA
• mRNA –
– Has the encoded info to assemble proteins
• rRNA –
–Make up part of the ribosome
•tRNA –
- brings Amino Acids to ribosome
• Transcription: transfer of information
from DNA to RNA
– only genes that encoded proteins
necessary to that cell get transcribed
IV. Transcription:
Similar to replication in mechanism
- Watch the animation and tell me
what is different!
IV. Transcription:
In eukaryotes, mRNA transcript has to
be modified before leaving the nucleus
to be translated.
In prokaryotes, the mRNA is ready to
go
IV. Transcription:
Remember transcription is the KEY to
getting a protein!!
- this is the On/Off switch
V. Genetic Code:
V. Genetic Code:
How many 3 base combinations are
there of ATGC?
How many amino acids are there?
What does this mean?
V. Genetic Code:
You are responsible for knowing 4:
AUG
UAA, UAG, UGA
VI. Translation:
Decoding the information in the mRNA
to build a protein.
We need:
1. The mRNA
2. The ribosome
3. tRNA’s
V. Translation:
Ribosomes:
- two subunits made of rRNA and protein
- sandwich mRNA between them
V. Translation:
Ribosomes:
- Have three spots that tRNA’s can fit in
A site –
P site –
E site –
V. Translation:
tRNA
- Twisted up piece
of RNA
- amino acid gets
attached to one
end
- opposite end is
the anticodon
V. Translation:
So how does it work? Watch the animation and
explain it to me!
Central Dogma
What’s strange about with the
central Dogma???