Protein Synthesis by: MaKenna McGough

What is a protein? growth and repair Proteins are complex, unbranched macromolecules that carry out many functions in the body such as… growth and repair signaling from one cell to another regulation of hormones enzymatic activity movement

What codes for proteins? 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. Later it was discovered that one gene actually produces one protein and then revised again to one gene produces one polypeptide chain which are the monomers of a protein.

“ “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

The intermediate between DNA and proteins DNA holds the “blueprints” for making proteins but DNA is inside the nucleus where is can’t leave so... DNA converts to RNA which travels to the cytoplasm and this is where proteins are synthesized!

Structure Primary is simply the linkage of amino acids held together by peptide bonds Secondary is a single polypeptide chain held together by hydrogen bonds Tertiary is 3-D folded protein Quaternary is multiple chains that have folded Proteins are made up of amino acids and have four different levels - primary, secondary, tertiary, and quaternary

The Genetic Code Discovery How it works Heinrich 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. 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 UUU and UUC can both code for Phe and even GGU, GGC, GGA, and GGG ALL code for glycine

It starts with Transcription Where? What? How? Transcription takes place inside the nucleus where the DNA is held. Transcription is the making of a mRNA strand from a DNA template. Four steps: Initiation Elongation Termination RNA processing Transcription uses a “promoter region” to initiate copying. The “TATA box” identifies where RNA polymerase should start.

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 DNA When 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.

RNA Processing for Eukaryotes 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 synthesis Spliceosomes are made up of smaller snRNP’s

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!

After exon shuffling and the added caps, it is now ready to enter the cytoplasm for translation

Protein synthesis takes place at a ribosome Translation turning the mRNA made in the nucleus to a protein made in the cytoplasm Protein synthesis takes place at a ribosome Ribosomes are made of rRNA and contains two subunits. There are three sites where the tRNA (containing the correct amino acid) attaches. A site is where the tRNA first arrives and the P site is where a second tRNA that attaches to the tRNA in the A site. The E site can stand for EXIT because it is where the tRNA leaves.

tRNA carries the correct amino acid: 3 Steps Initiation Elongation Termination 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. 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. A stop codon (release factor) codes for the translation to stop, ending the chain. The ribosome disassembles itself! ELONGATION : The tRNA has moved to the P site and another anticodon arrives in the A site carying another amino acid which joins to the other one by a PEPTIDE bond.

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.

What? detail effect Type of Mutation A single base pair is replaced Substitutions A single base pair is replaced 3 types: silent nonsense missense silent: no effect on amino acids nonsense: results in a stop codon, unfinished protein missense: changes amino acid Insertions or Deletions 1 or more bases are added or removed often called frameshift mutation causing the reading frame to change (reads 3 at a time) unless THREE bases are added or deleted

Thanks! Any questions? playfactile.com/proteinsynthesismcgough

QUIZ TIME! Please describe the process of transcription in detail using the words: DNA, Nucleus, RNA polymerase Please 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?