Protein Synthesis

Learning Objectives

By the end of this class you should understand:

The purpose and mechanism of codons

The two steps of protein synthesis (transcription and translation)

The purpose and process of removing introns

The major components of transcription and translation and their functions

The terminology and function of amino acid chains

The process of protein folding and what disorders are caused by folding errors

Major pathways of gene expression and regulation

Genetic Information

So now we know how DNA bases work So far, this is just like knowing

what a book is made of and what ink it uses

Now we learn to read! Each active coding segment

of DNA (a gene) contains info for a protein But how??

The Composition of Protein Proteins are made of many

amino acids strung together like beads

Different amino acids have different properties Some bond with each other Some repel each other Some are hydrophobic like oil

Our body uses 20 different types

Peptide Bond

Each amino acid has a C end and an N end

The C and N can make a peptide bond This links them into a

chain

An H2O is removed

The side chain is what makes the amino acid special

Sample Amino Acids

The Full Set

How To Code For Amino Acids?

If your DNA alphabet is only four letters, how many different things can you code for? 1 letter: 4 possibilities 2 letters: 4*4=16 possibilities 3 letters: 4*4*4=64 possibilities

One codon is 3 DNA/RNA bases and codes for one amino acid

Complete Codon Chart

Gene Expression Each cell has the entire

genome so why only express certain proteins? Most genes are inactivated

Protein in the chromosome can be modified to deactivate the gene Chromatin remodeling

DNA can also be directly methylated block its activity Gene silencing

DNA to RNA to Protein

Permanent information is stored in DNA

DNA information is copied using RNA

The information is for protein sequences Alterations to the DNA

are faithfully copied and result in different protein sequences

This is mutation!

DNA to RNA The DNA sequence is copied onto a strand of

RNA in a process called transcription Referred to as messenger RNA or mRNA

Technically must be processed first to be mRNA Achieved with RNA Polymerase

Promoter Region The DNA

sequence “upstream” of the coding sequence is very specific and allows a promoter to attach to the DNA The promoter is a

protein that facilitates the transcription process

RNA Polymerase Remember

RNA polymerase causes RNA bases to attach that match their complement

RNA sequence must still be processed

mRNA Formation

mRNA Processing To be considered mRNA three things must

occur: The 5' (head) has a methylated cap to prevent it

being damaged The 3' (tail) has a lot of extra As attached to also

prevent damage The introns must be removed

Introns & Exons Some portions of the RNA are removed

Introns stay in the nucleus Exons form the mRNA that ultimately leaves

By removing different introns, the sequence may code for more than one protein!

Outside the Nucleus Once the mRNA is fully prepared it exits the

nucleus Ribosomes rapidly attach to it

Ribosomes are made of protein and rRNA Actually two parts that attach around the mRNA

Translation

The ribosome performs translation of the nucleic acid language to the amino acid language

Initiation is the attachment of the ribosome, followed by elongation

Key player: tRNA http://www.youtube.com/

watch?v=NJxobgkPEAo

TL;DR The ribosome has

spaces to let each tRNA match its anticodon to the mRNA one by one

It then catalyzes the chain to move forward, using energy in the process

Many ribosomes may attach to a single mRNA and all produce proteins at once!

Protein Folding

Once the chain is complete it must still fold into the correct organization

The forces between the various amino acids are complex Includes hydrogen bonds

and covalent bonds, as well as repulsion forces

Four Levels of Structure

Protein Folding Note the proteins below, one has more helix

forms but the other has more sheets The second protein is called a prion and it is an

infectious particle Smallest infectious particle known to man! Can force existing regular proteins to switch shape

to prion shape

Infectious Protein?? Was only discovered recently (Nobel prize in

1997 for the discovery) A major outbreak in England of Mad Cow's

Disease caused by these proteins

Prion Diseases

Bovine Spongiform Encephalopathy (Mad-cow disease) is caused by a misfolded protein Transmissible to humans Some humans are also

genetically at risk to develop natural prion diseases in the same protein

Most proteins fold without lethal complications!

Transcription & Translation

mRNA can also be blocked at the translational level to control gene expression Controls level

rather than presence/absence

RNA Interference

Through a complex chemical pathway, RNA can be used to block translation of mRNA These molecules are

called RNAi Very recent discovery

that may provide new pathways for medicine

Have an excellent 4th of July!