transcriptionandtranslation-100505182952-phpapp02

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Transcription and Translation


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Transcription and Translation

1. What is transcription? Explain whathappens during transcription.

2. What is translation? Explain what

happens during translation.3. Explain how transcription and translation

are related to DNA replication.

4. If you begin with a parent DNA strand ofA A T G C A G T, what will thecomplementary mRNA strand be? (Thinkabout it before you answer.)


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Compared structures of DNA and

RNA

A. DNA-Deoxyribonucleic acid

1. Bases-cytosine, guanine, adenine and

thymine

2. Double stranded

3. Function-store genetic information


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B. RNA-Ribonucleic acid

1. Base-Cytosine, guanine, adenine and uracil

2. Single stranded

3. Functions-a. rRNA-ribosomal RNA (makes up about 60% of

ribosomal structure

b. mRNA-messenger RNA (record information from

DNA and carry it to ribosomes)c. tRNA-transfer RNA (delivers amino acids to

proteins at the ribosome to extend the chains)

Compared structures of DNA and

RNA


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RNA

nucleotide

DNA

nucleotide
http://upload.wikimedia.org/wikipedia/en/2/2c/RNA_chemical_structure.GIFhttp://upload.wikimedia.org/wikipedia/en/2/2c/RNA_chemical_structure.GIF


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Comparison of RNA and DNA

sugars

Deoxyribose

Ribose
http://en.wikipedia.org/wiki/Image:Ribofuranose-2D-skeletal.pnghttp://upload.wikimedia.org/wikipedia/commons/9/94/Deoxyribose.svg


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Compared

structures ofDNA and RNA
http://upload.wikimedia.org/wikipedia/commons/0/04/NA-comparedto-DNA_thymineAndUracilCorrected.png


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Reading Quiz (Orange book-Chapter 6)

1. Transcription is the process of making:a. RNA b. tRNA c. mRNA d. rRNA

2. An intron is found in:

a. DNA b. RNA c. mRNA d. tRNA

3. The enzyme used in transcription is:

a. RNA primase b. RNA polymerase

c. DNA polymerase d. a and b are both correct

4. How many bases make a codon?a. 1 b. 2 c. 3 d. 4

5. Translation occurs in the:

a. nucleus b. cytoplasm c. both


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Transcription

A. Transcription=the synthesis of mRNA

from a DNA template

B. Occurs in the 53 direction (if you dont

know what this means go back and look

it up!!)

C. Involves RNA polymerase

D. mRNA, tRNA and rRNA must all be

transcribed for protein synthesis to take

place
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.html


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E. mRNA

-the sequence of mRNA nucleotides determinethe primary sequence of the polypeptides

F. tRNA-carries the amino acids to mRNA

-tRNA folds in on itself

-see p. 305 figure 17.12

G. rRNA

-major components of ribosomes

Transcription (three types of

RNA)


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Transcription (Initiation)

A. RNA polymerase binds to the promoter site

B. Promoter=region of DNA where RNApolymerase attaches and initiates transcription

-Determines which strand of DNA will serve as thetemplate

C. RNA polymerase -hooks together RNAnucleotides as they base pair along the DNA

templateD. Transcription unit -area of DNA that will betranscribed


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E. Transcription initiation complex -thearea where transcription factors and RNA

polymerase are bound to the promoter

F. TATA box -promoter DNA sequence-the actual sequence is 5'-TATAAA-3'

-RNA polymerase binding site

G. After polymerase is bound to the promoterDNA, the two DNA strands unwind and the

enzyme starts transcribing the template

strand

Transcription (Initiation)


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Transcription (RNA strand

elongation)

A. RNA polymerase moves along DNA

template

B. It unwinds 10-20 DNA bases at a time

C. RNA polymerase adds nucleotides in the

53 direction

D. As RNA polymerase moves along, theDNA double helix reforms

E. The new section of RNA peels away as

the double helix reforms


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Transcription (termination)

A. Transcription stops when RNApolymerase reaches a section of DNAcalled the terminator

B. Terminator sequence = AAUAAAC. Next, the RNA strand is released and

RNA polymerase dissociates from the

DNAD. The RNA strand will go through more

processing


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Sense vs. Antisense DNA strands

A. The DNA double helix has two strands

B. Only one of them is transcribed

C. The transcribed strand is the antisensestrand

D. The non transcribed strand is the sense

strandE. mRNA is comp lementary to the

anitsense strand


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RNA splicing (in eukaryotes)

A. In eukaryotes RNA transcripts have long non-coding stretches of nucleotides

-these regions will not be translated

B. The non-coding sections are dispersed betweencoding sections

C. Introns-non-coding sections of nucleic acidfound between coding regions

D. Exons-coding regions of nucleic acids(eventually these are expressed as aminoacids)


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E. RNA polymerase transcribes introns and

exons,

-this is pre-mRNA

F. Pre-mRNA never leaves the cells nucleus

G. The introns are excised and exons are

joined together to form mRNAH. pre-mRNA

I. Mature mRNA

RNA splicing (in eukaryotes)


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Translation

A. Translation-forming of a polypeptide

-uses mRNA as a template for a.a.

sequence

-4 steps (initiation, elongation,

translocation and termination)

-begins after mRNA enters cytoplasm-uses tRNA (the interpreter of mRNA)


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B. Ribosomes

-made of proteins and rRNA

-each has a large and small subunit

-each has three binding sites for tRNA onits surface

-each has one binding site for mRNA

-facilitates codon and anticodon bonding

-components of ribosomes are made inthe nucleus and exported to the cytoplasm

where they join to form one functional unit

Translation


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B. Ribosomes (continued)

-the three tRNA binding sites are:

1. A site=holds tRNA that is carryingthe next amino acid to be added

2. P site= holds tRNA that is carrying

the growing polypeptide chain

3. E site= where discharged tRNAs

leave the ribosome

#8. Translation
http://www.cellsalive.com/cells/cell_model.htmhttp://www.cellsalive.com/cells/cell_model.htm


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Ribosomal structure

EP A

Large subunit

Peptidyl-tRNA binding site

Aminoacyl-tRNA binding site

mRNA

5

Exit

site

Small subunit

3


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C. The genetic code

Four RNA nucleotides are arranged 20

different ways to make 20 different amino

acids Nucleotide bases exist in triplets

Triplets of bases are the smallest units that

can code for an a.a. 3 bases = 1 codon = 1 a.a.

There are 64 possible codes (64=43)

Translation


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C. The genetic code

Most of the 20 a.a. have between 2 and 4possible codes

The mRNA base triplets are codons In translation the codons are decoded into

amino acids that make a polypeptide chain

It takes 300 nucleotides to code for a

polypeptide made of 100 amino acids (Why?)

Translation


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C. The genetic code (continued)

61 of 64 codons code for a.a.

Codon AUG has two functions

-codes for amino acid methionine (Met)-functions as a start codon

mRNA codon AUG starts translation

The three unaccounted for codons act asstop codons (end translation)

Translation


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D. How it works

DNA (antisense)

A C C A A A C C GmRNA (transcription)

U G G U U U G G C

polypeptide (translation)Trp - Phe - Gly-

Translation


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E. More on tRNA tRNA is transcribed in the nucleus and must enter the

cytoplasm

tRNA molecules are used repeatedly

Each tRNA molecule links to a particular mRNAcodon with a particular amino acid

When tRNA arrives at the ribosome it has a specific

amino acid on one end and an anticodon on the other

Anticodons (tRNA) bond to codons (mRNA)p. 304 (red book)

Translation


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Where the a.a. attaches

Hydrogen bonds

Anticodon

=

tRNA diagrams

Although we

draw tRNA in

a clovershape its

true 3-D

conformation

is L-shaped.
http://upload.wikimedia.org/wikipedia/commons/f/f1/3d_tRNA.pnghttp://upload.wikimedia.org/wikipedia/commons/f/f1/3d_tRNA.pnghttp://upload.wikimedia.org/wikipedia/commons/f/f1/3d_tRNA.pnghttp://upload.wikimedia.org/wikipedia/commons/f/f1/3d_tRNA.pnghttp://upload.wikimedia.org/wikipedia/commons/f/f1/3d_tRNA.pnghttp://upload.wikimedia.org/wikipedia/commons/f/f1/3d_tRNA.pnghttp://upload.wikimedia.org/wikipedia/commons/f/f1/3d_tRNA.png


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Translation (Initiation)

A. Initiation

1. Brings together mRNA, tRNA (w/ 1sta.a.) and ribosomal subunits

2. Small ribosomal subunit binds to mRNAand an initiator tRNA

-start codon= AUG

-start anticodon-UAC-small ribosomal subunit attaches to 5end of mRNA


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B. Initiation2. (continued)

-downstream from the 5 end is thestart codon AUG (mRNA)

-the anticodon UAC carries the a.a.Methionine

3.After the union of mRNA, tRNA and

small subunit, the large ribosomal subunitattaches

4. Initiation is complete

#9. Translation (Initiation)


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B. Initiation

5. The intitiator tRNA and a.a. will sit in the

P site of the large ribosomal subunit

6. The A site will remain vacant and ready

for the aminoacyl-tRNA



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Translation (Elongation)A. Amino acids are added one by one to the first

amino acid (remember, the goal is to make apolypeptide)

B. Step 1- Codon recognition

a. mRNA codon in the A site forms hydrogenbonds with the tRNA anitcodon

C. Step 2- Peptide bond formation

a. The ribosome catalyzes the formation of the

peptide bonds between the amino acids (theone already in place and the one beingadded)

b. The polypeptide extending from the P site

moves to the A site to attach to the new a.a.


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A. The tRNA w/ the polypeptide chain in the

A site is translocated to the P site

B. tRNA at the P site moves to the E site

and leaves the ribosome

C. The ribosome moves down the mRNA in

the 53 direction

Translation (Translocation)


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A. Happens at the stop codon

B. Stop codons are UAA, UAG and UGA

-they do not code for a.a.

C. The polypeptide is freed from the ribosome andthe rest of the translation assembly comes

apart

D.Animation (you move it)E.Animation (you watch it)

F.Animation (McGraw-Hill)

Translation (Termination)
http://repository.uwlax.edu/~Bob/lo_biology/stc_01_translation/conceptual/c_02_trna.htmhttp://student.ccbcmd.edu/biotutorials/protsyn/translat.htmlhttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120077/micro06.swf::Protein%20Synthesishttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120077/micro06.swf::Protein%20Synthesishttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120077/micro06.swf::Protein%20Synthesishttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120077/micro06.swf::Protein%20Synthesishttp://student.ccbcmd.edu/biotutorials/protsyn/translat.htmlhttp://repository.uwlax.edu/~Bob/lo_biology/stc_01_translation/conceptual/c_02_trna.htm


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Gene expression

A. Jacob and Monad (1961)

-studied control of protein synthesis in E.coliand lactose digesting enzymes

-found that E. colido not produce lactosedigesting enzymes when grown in amedium without lactose

-when bacteria were placed in a lactoseenvironment, enzymes were found withinminutes


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B. Genes can be switched on or off as

necessary

-a gene that is on will be transcribed

-in E.coli, the enzyme lactase will be

produced if the gene is on

-if the gene is off mRNA will not be

created and translation can not occur

Gene expression


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C. The operon model

-proposed by Jacob and Monad

-explains how genes switch on and off-operon=promoter, operator and structural

genes

-lac operon is found inE.coli

Gene expression


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D. The lac operon

Gene expression


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D. The lac operon (no lactose)

-lactose is absent, repressor is active,

operon is off, no mRNA is produced, RNA

polyermase cannot bind because it is

blocked by the repressor that has bound to

the operator

Gene expression


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D. The lac operon (lactose is present)

-lactose is present, repressor is inactive, operon

is on, mRNA is transcribed, RNA polymerase

binds to operator-an isomer of lactose binds to the repressor and

changes its shape

-this prevents it from binding to the operator

-lactase is produced

Gene expression

#11 C


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#11. Compare Transcription in

Eukaryotes and Prokaryotes

Link
http://www.phschool.com/science/biology_place/biocoach/transcription/tctlpreu.htmlhttp://www.phschool.com/science/biology_place/biocoach/transcription/tctlpreu.html

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