Take me to NZQA Documents relating to this standard AS Describe the role of DNA in relation to gene expression Protein Synthesis Part three…

Contents Protein Synthesis – The basics What are Amino Acids and Proteins? Transcription - in detail Translation- in detail Degenerate Code

What is Protein Synthesis We (hopefully) know that DNA contains the instructions for the cell to operate. DNA = Hard drive Sequence of nucleotides = software A section of nucleotides (gene) = one software programme Protein Synthesis = running one software programme to create an application A protein = an application PROTEIN SYNTHESIS = protein making

Protein Synthesis -The Basics A copy of the DNA is made using mRNA mRNA moves out of nucleus into cytoplasm tRNA uses code on mRNA to make a chain of amino acids This a.a chain forms a protein.

Protein Synthesis – the detail Key words: Transcription Translation Codon Anticodon RNA Polymerase Ribosome Amino acid mRNA tRNA You tube animation on Protein Synthesis

Proteins are made up of very long chains of amino acids (see next slide for more info on amino acids). A cell uses proteins for structure (eg keretin in hair) and to make enzymes. Enzymes are used to speed up biochemical reactions. There are 1000s of different enzymes (see poster on Ms Blythe’s wall) Protein Synthesis (so what are proteins

Amino Acids Amino acids are the building blocks of proteins. They band together in chains to form the stuff from which your life is born. Think of amino acids as Legos for your life. There are 20 different amino acids. The essential amino acids cannot be synthesized by the body; instead, they must be ingested through food. And yes, we normally refer to essential amino acids as______________? Amino acids link together with a peptide bonds in polymers called Polypeptide bonds

Genes A gene is a section of DNA that carries the information for one particular job. A gene may code for more than one protein. Within a gene there are both: Introns (part of the gene removed) Exons Coding part of the gene

Now that we understand the terms: Protein synthesis Protein Amino acid Gene Intron Exon Next, we can look at the detail of protein synthesis Protien Synthesis is involves 2 steps Transcription - transcribing the DNA into mRNA Translation - translating the mRNA into a amino acid chain

Transcription Transcription is the synthesis of RNA from a DNA template. Remember, in RNA, T is replaced with U. Nucleotides are added to the 3' end of the growing RNA chain by RNA polymerase. One gene is transcribed into one length of RNA.

Transcription Note the mRNA forms from the ‘template’ strand The template strand is sometimes called the ‘antisence’ strand.

Transcription Transcription Detail Animation Transcription Detail Pink Shirt man explains Transcription

Translation The mRNA moves into the cytoplasm – where the introns are removed. Then the exons connect to a ribosome. The ribosome reads the nucleotides on the RNA in sets of three – each set of three nucleotides is called a codon. DNA CodingDNA TemplatemRNA ACTACT TGATGA ACUACU ATGATG

Codon tables Each codon codes for 1 amino acid

Translation Transfer RNA (tRNA) molecules move into a ribosome, where they line up with the mRNA. The codons from mRNA line up with anticodons on the tRNA molecule.

Protein Structure The sequence of a.a makes up the primary (1°) structure. This chain rolls up on itself to form a 3 dimensional structure secondary (2°) The protein then folds back on itself to form a tertiary (3°) And finally several polypeptide chains may be brought together to make the final protein’s quarternary (4°) structure.

Denaturing of Enzymes The unique shape of an enzyme creates its specificity. An increase in temperature or a change in pH, changes the shape of the enzyme and it may not work. (revision L2 Bio) But also a change in the a.a sequence by just one a.a may also alter the active site and make the enzyme disfunctional. click here for a narrated animation of an egg denaturing.here

Splicing Splicing is a modification of an RNA after transcription, in which introns are removed and exons are joined before translation. Simple illustration of exons and introns in pre-mRNA and the formation of mature mRNA by splicing. The UTRs are non-coding parts of exons at the ends of the mRNA. Just for interest: About 2% of the DNA codes for a protein (the exons). The rest was thought to be "evolutionary junk". Now scientists are finding that much of the rest actually does have a function. 8% of the introns make mRNA chains that have a regulatory purpose.

Animations The following animations are provided by the University of Nebraska Institute of Agriculture and Natural Resources. Requires Flash 5 Player. Transcription/Translation Overview Transcription Detail Translation Detail (protein synthesis) Translation Detail

GENE EXPRESSION DIFFERENCES IN PROKARYOTES AND EUKARYOTES Bacteria don’t have a nucleus. This makes protein synthesis a bit easier as mRNA doesn’t have to travel from the nucleus to the cytoplasm as in eukaryotes. Transcription and translation happen at the same time. Also there are very few introns in Prokaryotic DNA. This makes the whole process much more simple. In your average eukaryote the mRNA must be processed in the nucleus to separate the introns and the exons, and the exons reassembled, before translation takes place in the cytoplasm. Check out this for an animation on the differences. animation

Degenerate code How many combinations of A,U, G, C is there on a 3 nucleotide codon? This is shown on the codon table But there are only 20 amino acids – so there is more than 1 codon for each a.a. This is known as the degenerate code. IT IS A GOOD THING – WHY?

Advantage of the degenerate code Mistakes happpen! On occasions either at replication or transcription the nucleotide sequence can change – this is called a mutation. With a degenerate code a change in a nucleotide will either: The new codon will code for the same a.a The new codon will code for a different a.a What effect will the different a.a have on the resulting polypeptide structure?

Summary Diagram

Review Questions Level 3 Biology, Describe the role of DNA in relation to gene expression

2007 NCEA exam – Q1 The following diagram shows part of a DNA molecule. (a)Identify the structures labelled A, B, C and D in the diagram, by writing their names in the spaces provided. (b)DNA is able to make copies of itself. This process is controlled by several enzymes. Describe the role of each of the following enzymes in DNA replication: (i)DNA polymerase (ii)DNA helicase (iii)DNA ligase The information carried by DNA controls protein synthesis. Protein synthesis includes transcription and translation. (c) Discuss the reasons why both transcription and translation are necessary for protein synthesis.