DNA Transcription Amp Trasnlation

7/29/2019 DNA Transcription Amp Trasnlation

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DNA Transcription and

Translation

DNA

mRNA

Transcription

Cell

Polypeptide(protein)

TranslationRibosome


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Gene

Segment of DNA that codes for a protein

DNA codes for RNA and RNA makesprotein


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One Gene One Enzyme

One gene codes for one polypeptide.

polypeptide - a chain of covalentlybonded amino acids.

(proteins are made of one or morepolypeptide)


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DNA, RNA, and Protein

Flow of Information:DNA RNA Proteins

Transcription Translation

Transcription is the process by which a molecule ofDNA is copied into a complementary strand of

RNA.This is called messenger RNA (mRNA) because itacts as a messenger between DNA and the ribosomeswhere protein synthesis is carried out.


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RNAs Structure


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RNA

RNA stands for:

Ribonucleic acid

RNA is found: Nucleus and Cytoplasm


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RNAs Nitrogen Bases

Adenine (A)

Cytosine (C)

Guanine (G) Uracil (U)


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There are 3 types of RNA:

Messenger RNA (mRNA)

Ribosomal RNA (rRNA)

Transfer RNA (tRNA)


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All RNA is

Single stranded

Many different shapes

Cheap copy

of DNA


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Transcription

First step in making proteins

Process of taking one gene (DNA) andconverting into a mRNA strand

DNA -> RNA

Location:

Nucleus of the cell


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Steps to Transcription

1. An enzyme attaches to the promoter

(start signal region) of a gene andunwinds the DNA


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Steps to Transcription (Cont.)

2. One strand acts as a template.


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Steps to Transcription (Cont.)

3. A mRNA copy is made from the DNAtemplate strand by RNA polymerase

4. A mRNA copy is made until it reachesthe termination (stop signal) sequence

5. The two strands of DNA rejoin.


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Template vs. Non TemplateStrand


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DNA

Cytoplasm

Nucleus

Eukaryotic Transcription

Export

G AAAAAA

RNA

Transcription

G AAAAAA

RNAProcessing

mRNA


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Transcription animations

http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html
http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html


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Think- Pair- Share

1. Where in the cell does transcription occur?

2. What is the importance of transcription?

3. In transcription, how come the whole DNA moleculeis not copied into mRNA?

4. How does one gene differ structurally from

another?


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mRNA Processing

Pre-mRNA the original sequence ofRNA created during transcription

mRNA reaches the ribosomes

RNA P i


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RNA Processing


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What is RNA Processing?

After transcription the pre-mRNA molecule

undergoes processing 5 cap is added

Poly A tail is added to the 3 end

Introns are removed.


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RNA Processing

In Eukaryotes only Introns- non-coded sections

Exons- codes for a protein Before RNA leaves the nucleus, introns are

removed and exons are spliced together Acap and poly A tail are added to ends of the

sequence mRNA leaves the nucleus through the nuclear

pores


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Why is it necessary to add the poly A tail

and 5 cap?


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Pg. 339


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Lets an example

Original DNA Sequence (DNA):

5 GTACTACATGCTATGCAT 3

Translate it (RNA): 3 CAUGAUGUACGAUACGUA 5

Add the 5 cap:

3 CAUGAUGUACGAUACGUA 5cap


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Finish the job!

Remove the introns UGUA and AUAC:

3 CAUGAUGUACGAUACGUA 5cap

3 CAUGACGGUA 5cap

Add a poly A tail onto the 3 end

3 CAUGACGGUA 5capPoly A tail


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Try it!

DNA Strand of non-template strand:

5 ATCGGTAGAGTATTTACAGATA 3

Remove introns:

CGGUA UUACAG


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Think, Pair, Share

Take a minute think on your own, then pairwith your partner, and share your ideas!

Evolutionary, why do you think there areintrons?

Where did they come from?

Why do we have them?

Remember there is NO wrong answer!


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PROTEINS!


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Proteins are made up ofamino acids!!!

Proteins arepolymersof amino acids

Only 20 different amino acids

BUT there are hundreds of thousands ofdifferent proteins

How can this be?


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How do amino acids form thesepeptide chains?

Peptide Bonds Link each amino acidstogether to form proteins


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Translation

Production of proteins from mRNA

mRNA goes to the ribosomes in thecytoplasm or the RER and producesproteins


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Protein Synthesis: Translation

Translationis the process of decoding a mRNAmolecule into a polypeptide chain orprotein.

Each combination of 3 nucleotides on mRNA iscalled a codon or three-letter code word.

Each codon specifies a particular amino acidthat is to be placed in the polypeptide chain(protein).


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Ribosome

Two subunits to the ribosome

3 grooves on the ribosome (A, P, E)

A: tRNA binding site P: polypeptite bonding site

E: exit site


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Ribosome:

Are made up of 2 subunits, a large one and a

smaller one, each subunit contains ribosomalRNA (rRNA) & proteins.

Protein synthesis starts when the two

subunitsbind to mRNA.The initiator codon AUG binds to the firstanticodon of tRNA, signaling the start of a

protein.


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Ribosome:

The anticodon of another tRNA binds to thenext mRNA codon, bringing the 2nd aminoacid to be placed in the protein.

As each anticodon & codon bind together apeptide bond forms between the twoaminoacids.


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Ribosome:

The protein chain continues to grow until astop codon reaches the ribosome, whichresults in the release of the new protein and

mRNA, completing the process oftranslation.


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Steps to Translation

1. mRNA leaves the nucleus and binds toa ribosome

2. the 5 end of mRNA binds to ribosome


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Steps to Translation (Cont.)

3. Ribosome looks for the start Codon(AUG)

Codon: group of 3 nucleotides on themessenger RNA that specifies one aminoacid (64 different codons)

d


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H

PO

O

HO

O

O

CH2NH2N

NH

N

N

HOH

P

O

O

HO

O

O

CH2

NH2

N

N

N

N

H

P

O

OH

HO

O

O

CH2

NH2

N

NN

N

O

A Codon

Guanine

Adenine

Adenine

Arginine


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tRNA



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A three-letter code is used because there are20 different amino acids that are used to

make proteins.If a two-letter code were used there wouldnot be enough codons to select all 20 amino

acids.That is, there are 4 bases in RNA, so 42 (4x4)=16; where as 43 (4x4x4)=64.


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Therefore, there is a total of 64 codons with mRNA,61specify a particular amino acid.

This means there are more than one codon for eachof the 20 amino acids.

The remaining three codons (UAA, UAG, & UGA) arestop codons, which signify the end of a polypeptide

chain (protein).

Besides selecting the amino acid methionine, the codonAUG also serves as the initiatorcodon, which

starts the synthesis of a protein


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4. Amino acids attached to a tRNAmolecule and are brought over to themRNA.

5. This tRNA has an anticodon thatmatches the codon on the mRNA strand

Anticodon:

Group of 3 unpairednucleotides on a tRNAstrand. (binds to mRNA

codon)


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6. tRNA binds to the mRNA sequence and

adds an amino acid 7. Each amino acid matches up with 1-6

tRNA molecules

8. tRNA leaves and amino acids bondtogether through a polypeptide bond


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Translation Animations

http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html

http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf
http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.htmlhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swfhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swfhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swfhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swfhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.htmlhttp://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html


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9. The mRNA sequence continues until astop codon is reached.

10. The amino acids disconnect from the

mRNA sequence and a protein is formed.


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1. Initiation

The two ribosomal subunits cometogether with the mRNA and the first tRNAmolecule which attaches to the start

codon (AUG). This is the only tRNA that will attach to

the P site.

The first amino acid is always methionine.


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2. Codon Recognition

The tRNA anticodon will hydrogen bind tothe mRNA codon in the A site.


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3. Bond Formation

The amino acid in the P site will form apeptide bond with the amino acid in the Asite.


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4. Translocation

The tRNA's and the mRNA move downone site. The empty tRNA is releasedfrom the exit site.


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5. Repeat

This process will repeat hundreds of times.


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6. Termination

Translation is terminated with the stopcodon is reached. There are threedifferent stop codons UGA, UAA, UAG.

The release factor recognizes the stopcodon and releases the polypeptidestrand. All the factors break apart and are

reused.


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DNA Transcription Amp Trasnlation

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