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Protein Synthesis

by: MaKenna McGough

growth and repairsignaling from one cell to anotherregulation of hormonesenzymatic activity

movement What is a protein?Proteins are complex, unbranched macromolecules that carry out many functions in the body such as…

Thanks to Archibald

Garrod, scientists know that genes are what determine an organism's phenotype (physical characteristics). George Beadle and Edward Tatum, discovered that genes are responsible for changing enzymes (proteins). They were able to discover this by observing mutations in bread mold. They came up with the ”one gene, one enzyme” hypothesis. What codes for proteins?

“You too can win Nobel Prizes. Study diligently. Respect DNA. Don't smoke. Don't drink. Avoid women and politics. That's my formula.”George Beadle

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DNA converts to RNA which travels to the cytoplasm and this is where proteins are synthesized!

DNA holds the “blueprints” for making proteins

but DNA is inside the nucleus where is can’t leave so...

The intermediate between DNA and proteins

Proteins are made up of amino acids and have four different levels - primary, secondary, tertiary, and quaternary

Structure Primary is simply the linkage of amino acids held together by peptide bondsSecondary is a single polypeptide chain held together by hydrogen bonds

Tertiary is 3-D folded protein Quaternary is multiple chains that have folded

The unique thing about the genetic code is that it is shared by all organisms!

It also has..redundancy each codon (3 bases) is specified for an amino acid

How it worksHeinrich Matthaei and Marshall Nirenberg “broke the genetic code” and discovered how it is used in the process of protein synthesis. Nirenberg, Holly, and Khorana shared a Nobel Prize in 1968. Discovery The Genetic Code

Transcription uses a “promoter region” to initiate copying. The “TATA box”

identifies where RNA polymerase should start. How?Transcription takes place inside the nucleus where the DNA is held.

Where?Transcription is the making of a mRNA strand from a DNA template.Four steps:InitiationElongationTermination

RNA processingWhat?

It starts with Transcription

Elongation

After RNA polymerase unwinds the DNA and connects at the TATA box, it pairs RNA nucleotides to the DNA bases. RNA polymerase works in a 5’ to 3’ direction so the DNA gene is in a 3’ to 5’ direction while being copied.

Termination

RNA polymerase will keep transcribing until it reaches a signal or codon to stop (the terminator). In bacteria there are two types…Rho-dependent (extrinsic)The RNA contains a binding site for the protein called Rho factor. Once Rho factor binds, it climbs up towards the RNA polymerase and pulls the transcript and DNA template apart, releasing the RNA molecule.

Rho-independent (intrinsic)This depends on specific sequences in the DNAWhen it is time to stop transcription, RNA polymerase will hit a region of the template that is full of C and G nucleotides, causing the RNA to fold on itself and thus making the C and G bases pair. This results in a “hairpin” structure and causes RNA polymerase to stop.

Poly-A-tail is added 5’ cap is added RNA splicing (introns are removed using a spliceosome)

A guanine nucleotide is added to the 5’ end. This ensures safe transportation to the ribosome where proteins will be synthesized This is how different proteins are made from the same copy of DNA. Different exons are put together.

Many adenine nucleotides are added to the 3’ end to control the length of protein synthesisRNA Processing for Eukaryotes

For Prokaryotes...

they do NOT have introns so there is no processing (splicing)both transcription and translation take place at the site of the DNA because they do not have a nucleus!

turning the mRNA made in the nucleus to a protein made in the cytoplasm

Protein synthesis takes place at a ribosomeTranslation

Elongation TerminationInitiation

tRNA carries the correct amino acid: 3 Steps

Almost always the initiator tRNA is carrying Met, this attaches to the small subunit at the A site. The anticodon binds to the mRNA. Then the large subunit connects.This is the building of the polypeptide chain. There are a total of 20 amino acids that we need to survive! The R side-chain is what makes them different.

A stop codon (release factor) codes for the translation to stop, ending the chain. The ribosome disassembles itself!

The protein is then sent to different parts of the cell where they are needed but most are first fed into the ER.

if they have a SRP (signal recognition particle) the ribosome is taken the ER and the amino acid chain entere the lumen (interior) of the ER. This is where the protein folds and may have other things such as glucose groups attached to them. Most are shipped from there, but some stay to do their “jobs” in the ER. If so, they are tagged.

Type of Mutation

What?

detaileffect

SubstitutionsA single base pair is replaced

3 types: silentnonsensemissense

silent: no effect on amino acidsnonsense: results in a stop codon, unfinished proteinmissense: changes amino acid

Insertions or Deletions

1 or more bases are added or removed

often called frameshift mutationcausing the reading frame to change (reads 3 at a time) unless THREE bases are added or deleted

Any questions?Thanks!playfactile.com/proteinsynthesismcgough

QUIZ TIME!

Please describe the process of transcription in detail using the words: DNA, Nucleus, RNA polymerasePlease describe the process of translation in detail using the words: mRNA, tRNA, cytoplasm, ribosome

If the sequence AGC was added into the DNA, what effect would this have? Would there be a frameshift?Does intrinsic or extrinsic termination use the Rho factor?What is added to the 3’ end of the mRNA?

What about the 5’ end?What happens during RNA processing? Does this happen in prokaryotes?