Part three…

Protein Synthesis

AS 90715 Describe the role of DNA in relation to gene expression Take me to NZQA Documents relating to this standard

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 of uses code on mRNA to make a chain 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

Protein Synthesis (so what are proteins

 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)

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

 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.

A C T A T G DNA Coding DNA Template T G A mRNA A C U

Codon tables

Each codon codes for 1 amino acid

Translation



Transfer RNA (

tRNA

) molecules move into a

ribosome

mRNA. , where they line up with the



The

codons

mRNA line up with

anticodons

from 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.

click

here

for a narrated animation of an egg denaturing .

  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.



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)

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.

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, 2007 90715 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) (iii) DNA helicase 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.