Molecular Biology. I. History:Ground breaking discoveries T.H. Morgan Griffith, Avery and McCleod...
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Transcript of Molecular Biology. I. History:Ground breaking discoveries T.H. Morgan Griffith, Avery and McCleod...
![Page 1: Molecular Biology. I. History:Ground breaking discoveries T.H. Morgan Griffith, Avery and McCleod Hershey and Chase Watson and Crick (refer to your article.](https://reader031.fdocuments.in/reader031/viewer/2022032707/56649e155503460f94afedc3/html5/thumbnails/1.jpg)
Molecular Biology
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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!)
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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.
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II. What is DNA
Structure: What do we already know about DNA’s
structure? (think back to biochem!)
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II. What is DNAStructure: The backbone of DNA is made of covalent bonds between the phosphate and sugar
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II. What is DNAStructure:
DNA you have a choice of 4 bases:Purines
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II. What is DNAStructure:
DNA you have a choice of 4 bases:Pyrimidines
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II. What is DNAStructure: - 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
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II. What is DNAG and C form 3 hydrogen bonds
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II. What is DNA
A and T form 2 hydrogen bonds
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II. What is DNA
Why can’t the others pair up?
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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
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II. What is DNA
Structure: Heating DNA causes it to denature Which is harder to denature? - GCCGGCGCG or - AATATTATAA
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III. Replication–Semi-conservative:
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III. Replication
• Happens in the nucleus (of course!)• Ingredients:
–Energy – Form??? –Free Nucleotides: single, not attached–Specific Enzymes
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• There are three basic steps. Watch the animation and tell me what is happening.
– Helicase– DNA Polymerase
– Ligase
– Involves many other enzymes, as well asprimers.
III. Replication
http://www.johnkyrk.com/DNAreplication.html
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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.
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III. Replication
Solution: - in a few cells – telomerase
- in other cells – Hayflick limit (max. number of cell divisions before self destructing)
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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….
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Structure of RNA• Think back: what are the structural
differences between RNA and DNA?
–SS–Uracil–Ribose sugar–Location
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Types of RNA• mRNA –
–Has the encoded info to assemble proteins
• rRNA – –Make up part of the ribosome
•tRNA – - brings Amino Acids to ribosome
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• Transcription: transfer of information from DNA to RNA
– only genes that encoded proteins necessary to that cell get transcribed
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IV. Transcription:
Similar to replication in mechanism
- Watch the animation and tell me what is different!
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• Transcription: transfer of information from DNA to RNA in nucleus–Using sequence of DNA to make a
complementary strand of RNA
–The WHOLE strand of DNA doesn’t get turned into RNA at once
–Instead, as needed, small sections of DNA are transcribed into RNA•Sections are called??? GENES
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IV. Transcription:
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
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IV. Transcription:
5’ 3’3’ 5’
5’ 3’
5’ 3’3’ 5’3’ 5’
RNAPol.
5’ RNAPol.
3’5’ RNAPol.
5’ 3’RNAPol.
At the end, DNA goes back to its double stranded helix;
Pre-mRNA “transcript” needs to be edited
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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 as it is transcribed!
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IV. Transcription:
Step 2: Splicing: Editing or Processing of pre-mRNA into mRNA
- remove “introns”: unused sections
- glue together “exons”: important sections
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5’
IV. Transcription: 3’
Exons linked
together
Exon ExonIntron Intron
Introns discarded
Exon
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IV. Transcription:
Step 3: GC Cap added to one end; Poly A tail added to other end of exons to make mature mRNA
Specialized Guanine
Several Adenines in a row
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IV. Transcription:
Step 4: Mature mRNA leaves the nucleus and moves to the ribosomes where the message will be read and translated into a protein sequence.
5’ 3’
Specialized Guanine
Several Adenines in a row
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IV. Transcription:
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
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IV. Transcription:
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.
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V. Genetic Code:
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V. Genetic Code:
How many 3 base combinations are there of ATGC?
How many amino acids are there?
What does this mean?
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V. Genetic Code:
You are responsible for knowing 4:
AUG
UAA, UAG, UGA
You MUST be able to use a codon table
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VI. Translation:
Decoding the information in the mRNA to build a protein.
We need:
1. The mRNA
2. The ribosome
3. tRNA’s
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V. Translation:
Ribosomes: - two subunits made of rRNA and protein - sandwich mRNA between them
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V. Translation:
Ribosomes: - 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)
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V. Translation: tRNA
- Twisted up piece
of RNA
- amino acid gets attached to one end
- opposite end is the anticodon
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V. Translation: So how does it work? Watch the animation and
explain it to me!
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf
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Central Dogma
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What’s strange about the term Central Dogma???
What does dogma mean?
Hmmmmmm good essay question