Chapter 17: Protein Synthesis Flashcards by Blen Daniel

“One Gene, One Enzyme”

Archibald Garrod in 1909 suggests that genes dictate phenotypes through enzymes

1940: Beadle & Tatums - grew strains of mold that were unable to grow in a certain medium. They lacked enzymes

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Central Dogma

Flow of genetic information in cell

(replication)DNA-transcription-> RNA-translation->protein–>trait

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What has metabolisms taught us about genes

inheritance of metabolic diseases
- suggested that genes coded for enzymes
- each disease (phenotype) is caused by non-functional gene product

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Transcription

DNA nucleic acid language to RNA nucleic acid language

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RNA

ribose sugar
N-bases
- U:A
- G:C
single stranded
lots of different types of RNA
-tRNA, mRNA, rRNA

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Transcription

Making mRNA, the synthesis of complementary RNA

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Template Strand

transcribed DNA strand

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Coding Strand

untranscribed DNA strand(same squence as RNA except the T is now a U in RNA)

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What is the enzyme that creates the mRNA

RNA polymerase

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How many RNA polymerase enzymes are there?

3, each with their own specific promoter sequence it recognizes

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RNA polymerase I

only transcribes rRNA genes
makes ribosomes

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RNA polymerase II

transcribe genes into mRNA

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RNA polymerase III

only transcribes tRNA genes

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Are eukaryotic genes continuous?

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Exons

the real gene
-expressed/coding DNA

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Introns

the junk
-in between sequence

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mRNA splicing

eukaryotic mRNA needs work after transcription. Edit out introns to make a mature mRNA transcript

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Primary Transcript

pre- mRNA

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What happens if there is a mistake in splicing?

a single base added or lost throws off the reading frame, which can then create a different protein than wanted

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snRNPs

small nuclear RNA, proteins

Spliceosome

several snRNPs, recognize splice site sequence
- cut & paste gene

Alternative Splicing

Alternative mRNAs produced from same gene
-when is an intron not an intron
-different segments treated as exons

What’s the purpose of exons & introns?

One gene van code for different proteins
-depending on which sections of the mRNA template are considered exons during processing.
-explains why humans have a low number of genes for such complex organisms

How is the mRNA protected on its trip from nucleus to cytoplasm?

Enzymes in the cytoplasm attack mRNA
-protect the ends of the molecule by adding the 5’GTP cap and poly-A tail
-the longer the tail, mRNA lasts longer:produce more proteins

Translation

nucleic acid language to amino acid language

How does mRNA codes for proteins?

It codes for proteins in triplets

Codon System

3 letter codon system

Nirenberg & Khorana

determined mRNA-amino acid match added fabricated mRNA to test tube of ribsomes, tRNA & amino acids -created artifical UUUU mRNA -found that UUU coded for phenylalanie

The Chart is filled with the code...

Code for all life - strongest support for a common origin for all life Code is redundant -several condons for each amino acid -3rd base wobble

Start Codon

AUG, methionine

Stop codons

UGA, UAA, UAG

What type of codon does tRNA have?

Anti-codon

Where is the genetic code found?

The genetic code is nearly universal and found in all organisms

Where does the universality of the genetic code split between organisms?

In the translation system

What does the near universality of the genetic code say about the history of life?

That it has been operating very early in the history of life.

"Clover Leaf" structure

-anticodon on "clover leaf" end -amino acid attached on 3' end

Aminoacyl tRNA synthetase

enzyme which bonds amino acid to tRNA -bond requires energy -ATP-->AMP - bond is unstable - so it can release amino acid at ribosome easily

How are ribosomes involved in the DNA replication process?

It facilitate coupling of tRNA anticodon to mRNA codon Structure - ribosomal RNA (rRNA) & proteins - 2 subunits - large - small

How many sites are in a ribosomes ?

3 A site P site E site

A site (aminoacyl-tRNA site)

holds tRNA carrying next amino acid to be added to chain

P site (peptidyl-tRNA site)

holds tRNA carrying growing polypeptide chain

E site (exit site)

empty tRNA leaves from exit site

What are the steps to building a polypeptide?

Initiation - brings together mRNA, ribosome sub-units, initiator tRNA Elongation -adding amino acids based on condon sequence Termination - end codon

Protein Synthesis in Prokaryotes

DNA in cytoplasm circular chromosome naked DNA no introns

Protein Synthesis in Eukaryote Genes

DNA in nucleus linear chromosomes DNA wound on histone proteins introns vs. exons

Translation in Prokaryotes

Transcription & translation are simultaneous in bacteria -DNA is in cytoplasm -no mRNA editing -ribosomes read mRNA as it is being transcribed

Difference b/tw prokaryotes & eukaryotes

time & physical separation b/tw processes - takes eukaryote ~ 1 hour from DNA to protein - no RNA processing in prokaryotes

Mutations

Changes in the genetic material of a cell or virus

Point mutations

chemical changes in just one base pair of a gene the change of a single nucleotide in a DNA temple strand can lead to the production of an abnormal protein