(3) Gene Expression Gene Expression (A) What is Gene Expression? (E) Splicing and post-translational modification (B) Structure and Functions of RNA (D) Translation (C) Transcription

Gene Expression (E) Name the 2 process which can lead to different proteins being expressed from one gene Describe what is meant by alternative RNA splicing Describe 3 ways in which a protein can be modified State what alternative RNA splicing and post translational modification of one gene can lead to

Varying Protein Expression Different proteins can be expressed from one gene. There are 2 processes which allow for this: Alternative RNA splicing Different mRNA molecules are produced from the same primary transcript depending on which RNA segments are treated as exons and introns. Post-translational modification The post-translation protein structure can be modified by cutting and combining it with polypeptide chains or by adding phosphate or carbohydrate groups to the protein

Alternative Splicing of the SAME gene

Alternative Splicing of the SAME gene One gene can produce many different mature mRNA and therefore proteins by a process known as alternative RNA splicing TASK: Using the following primary transcript show how many different mature mRNA molecules can be produced:

Post Translational Modification Once translation is complete, further modifications may be required to enable a protein to perform its specific function. Cleavage: The process of cutting a single polypeptide (by enzymes) into smaller, active sections held together by sulphur bridges

Molecular Addition: Proteins can have additions of carbohydrates or phosphates groups Example – mucus is a glycoprotein (protein with carbohydrate). Example – some enzymes require a phosphate group to make them functional (phosphorylation)

Where does all this happen? animation: Golgi Body

Sectretion of proteins – ER, Golgi and vesicles 1. Vesicle containing freshly synthesised protein pinches off 2. Pinched vesicles join up to form Golgi apparatus 3. Protein processed in the Golgi usually sugar is added R.E.R. 4. Vesicles with finished protein pinched off 5. Vesicles move towards the cell membrane Cell membrane Secretory Cell 6. Vesicle fuses with cell membrane 7. Protein secreted

Gene Expression (E) Name the 2 process which can lead to different proteins being expressed from one gene Describe what is meant by alternative RNA splicing Describe 3 ways in which a protein can be modified State what alternative RNA splicing and post translational modification of one gene can lead to