Protein SynthesisAthena, Jen, Natalie

DNA versus RNADNA RNA

Contains a 5-C sugar Contains a 5-C sugar

5-C sugar is deoxyribose 5-C sugar is ribose

Each nucleotide has 1 of 4 nitrogenous bases

Each nucleotide has 1 of 4 nitrogenous bases

The bases are adenine, thymine, cytosine and guanine

The bases are adenine, uracil, cytosine and guanine

Double stranded molecule Single stranded molecule

TranscriptionWhen a cell needs to make specific polypeptides

Transcription factors tell a special enzyme where to bindUpstream from a gene, template strand of DNA,

This enzyme is called RNA polymeraseIt binds to a site packed with adenine and thymine

It’s not transcribed but unwinding is very easyBetween these bases are only 2 hydrogen bonds;

This promoter region’s bonds are not as strongRNA polymerase unwinds the Helix

And so the template strand gets complimentedInto a single strand of mRNA,

There’s no thymine in itBut uracil takes its place

Polymerase then adds nucleotides In the direction of mRNA’s 5 to 3 prime

Just like DNA replicationIt’s the direction of all genetic creation

The DNA strand that is read is called the templateIts bases compliment those bases in the RNA

A template strand of TACTG Will code for AUGAC

But what about the other strand of DNA?It isn’t read at the same time as the polymerase

Its coding strand and RNA are identicalExcept thymine contains the base uracil

Protein synthesis

Protein SynthesisBegins in the nucleusmRNA is synthesized

Then to the cytoplasm where it binds To a ribosome tRNA finds

Amino acids to form a polypeptideGene to polypeptide

Transcription happens ‘til a terminator sequenceWhere there’s RNA and DNA dissociation

The polymerase then is free to bindWith another promoter that it can find

Before primary transcript leaves the nucleus It’s been modified because outside of it

It would be destroyed by digestive enzymesWe wouldn’t want that cause the cell would probably die

The 5 prime cap, 7- methylguanosine Is added to the 5 prime end of our primary

Transcript, and then a poly-A tailIs added to the 3 prime end so it won’t fail

There are parts of our molecule that do not codeFor a polypeptide, and so...

For our protein not to be dysfunctionalIntrons are cut out by spliceosomes

Introns versus exons

• Introns: DNA or RNA segments that interrupt the sequence of genes

• Exons: DNA or RNA segments with important info coding for a protein or peptide sequence

Prokaryotes versus Eukaryotes

• Eukaryotes have many more genes, spread across multiple chromosomes

• Prokaryotes have fewer genes all located on one chromosome

Where do we go next?

• Then out to the cytoplasm mRNA goes• Where it meets up with its friend ribosome• 60 and 40S subunits then clamp on to the

mRNA...

Next up: Translation!• In the ribosome there are 2 special sites• A is for acceptor P is for peptide• Once the subunits have clamped on• mRNA reading frame is read in codons• Codon: a sequence of 3 nucleotides• AUG: the first codon recognized• The start codon codes for methionine• Whose tRNA enters the P-site• tRNA: single stranded nucleic acid• It’s shaped like a clover and here’s what happens

Aminoacyl tRNA synthetase Binds one amino acid to the tRNA

tRNA also has an anticodon This complements the mRNA codonIf the codon transcribed was AUG

The anticodon would be UACMethionine tRNA is in the P siteA second tRNA enters the A site

The 2 amino acids then peptide bind To begin the formation of a polypeptide

The first transfer RNA leaves the ribosome The second one moves over for elongation

To the A site another one comes alongAnd it goes on and on and on and onUntil comes the end of translation When the A site hits a stop codon

For these codons no tRNA existElongation is almost finished

A release factor protein dismantles the complexThe ribosome can bind to more mRNA next

Sugars or phosphates may be added at this time And these polypeptides make up proteins and enzymes

Roles of proteins in life

1. Proteins in the cell have a duty as enzymes, which catalyze chemical reactions

2. Proteins are necessary in animals' diets, since proteins are crucial in the formation of amino acids. Without proteins they would not have the nutrients they need to survive. They obtain essential amino acids from food.

Primary Protein Structure

The amino acid sequence, determined by the base sequence of the gene that codes for the protein

Secondary Protein StructureSecondary structures have cylindrical alpha helices and planar beta pleated sheets, which form due to H-bonds between the peptide groups of the main chain

Tertiary Protein Structure 3D conformation occurs because of protein folding, which is stabilized by H-bonds, hydrophobic interactions, ionic bonds & disulphide bridges. The bonds are intramolecular, and form between the R groups of different amino acids.

Quaternary Protein Structure• 2 or more polypeptide

chains associate to form a single protein

• Ex. Haemoglobin consists of 4 polypeptide chains. Haem group is a prosthetic group

• Conjugated proteins have a non-polypeptide structure called a prosthetic group

Gene Mutations & their impact

• Addition/deletion of nucleotides a shift in the reading frame of the codons in the mRNA. This may alter the amino acid sequence during translation. This can alter the function of the protein.

• Base Pair substitution: replacement or substitution of a single nucleotide base with another in a DNA/RNA molecule.

Impact of gene mutations

• A condition caused by mutations in one or more genes is called a genetic disorder.

• What are some examples of genetic disorders?

Credits

• Kathleen June, singer songwriter who wrote the protein synthesis song

• IB Biology textbook• Biology 12 textbook