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Molecular Biology

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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 Presentation

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Page 1: Molecular Biology

Molecular Biology

Page 2: Molecular Biology

I. History:Ground breaking discoveries

T.H. MorganGriffith, Avery and McCleod

Hershey and ChaseWatson and Crick

(refer to your article for most of this!)

Page 3: Molecular Biology

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.

Page 4: Molecular Biology

II. What is DNAStructure: What do we already know about DNA’s

structure? (think back to biochem!)

Page 5: Molecular Biology

II. What is DNAStructure: The backbone of DNA is made of covalent bonds between the phosphate and sugar

Page 6: Molecular Biology

II. What is DNAStructure:

DNA you have a choice of 4 bases:Purines

Page 7: Molecular Biology

II. What is DNAStructure:

DNA you have a choice of 4 bases:Pyrimidines

Page 8: Molecular Biology

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

Page 9: Molecular Biology

II. What is DNAG and C form 3 hydrogen bonds

Page 10: Molecular Biology

II. What is DNAA and T form 2 hydrogen bonds

Page 11: Molecular Biology

II. What is DNAWhy can’t the others pair up?

Page 12: Molecular Biology

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

Page 13: Molecular Biology

II. What is DNA

Structure: Heating DNA causes it to denature Which is harder to denature? - GCCGGCGCG or - AATATTATAA

Page 14: Molecular Biology

III. Replication–Semi-conservative:

Page 15: Molecular Biology

III. Replication• Happens in the nucleus (of course!)• Ingredients:

–Energy – Form??? –Free Nucleotides: single, not attached–Specific Enzymes

Page 16: Molecular Biology

• 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

Page 17: Molecular Biology

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.

Page 18: Molecular Biology

III. ReplicationSolution: - in a few cells – telomerase

- in other cells – Hayflick limit (max. number of cell divisions before self destructing)

Page 19: Molecular Biology

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….

Page 20: Molecular Biology

Structure of RNA• Think back: what are the structural

differences between RNA and DNA?

–SS–Uracil–Ribose sugar–Location

Page 21: Molecular Biology

Types of RNA• mRNA –

–Has the encoded info to assemble proteins

• rRNA – –Make up part of the ribosome

•tRNA – - brings Amino Acids to ribosome

Page 22: Molecular Biology

• Transcription: transfer of information from DNA to RNA

– only genes that encoded proteins necessary to that cell get transcribed

Page 23: Molecular Biology

IV. Transcription:

Similar to replication in mechanism

- Watch the animation and tell me what is different!

Page 24: Molecular Biology

• 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

Page 25: Molecular Biology

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

Page 26: Molecular Biology

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

Page 27: Molecular Biology

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!

Page 28: Molecular Biology

IV. Transcription:

Step 2: Splicing: Editing or Processing of pre-mRNA into mRNA

- remove “introns”: unused sections

- glue together “exons”: important sections

Page 29: Molecular Biology

5’

IV. Transcription: 3’

Exons linked

together

Exon ExonIntron Intron

Introns discarded

Exon

Page 30: Molecular Biology

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

Page 31: Molecular Biology

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

Page 32: Molecular Biology

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

Page 33: Molecular Biology

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.

Page 34: Molecular Biology

V. Genetic Code:

Page 35: Molecular Biology

V. Genetic Code:

How many 3 base combinations are there of ATGC?

How many amino acids are there?

What does this mean?

Page 36: Molecular Biology

V. Genetic Code:

You are responsible for knowing 4:

AUG

UAA, UAG, UGA

You MUST be able to use a codon table

Page 37: Molecular Biology

VI. Translation:

Decoding the information in the mRNA to build a protein.

We need:

1. The mRNA

2. The ribosome

3. tRNA’s

Page 38: Molecular Biology

V. Translation: Ribosomes: - two subunits made of rRNA and protein - sandwich mRNA between them

Page 39: Molecular Biology

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)

Page 40: Molecular Biology

V. Translation: tRNA

- Twisted up piece

of RNA

- amino acid gets attached to one end

- opposite end is the anticodon

Page 41: Molecular Biology

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

Page 42: Molecular Biology

Central Dogma

Page 43: Molecular Biology

What’s strange about the term Central Dogma???

What does dogma mean?

Hmmmmmm good essay question