molecular biology
DESCRIPTION
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?. - PowerPoint PPT PresentationTRANSCRIPT
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Molecular Biology
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I. History:Ground breaking discoveries
T.H. MorganGriffith, Avery and McCleod
Hershey and ChaseWatson 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 DNAStructure: 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 DNAA and T form 2 hydrogen bonds
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II. What is DNAWhy 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. ReplicationSolution: - 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